摘要:

MAY, 1915. Vol. XL., No. 470. THE ANALYST. PROCEEDINGS OF THE SOCIETY OF PUBLIC ANALYSTS AND OTHER ANALYTICAL CHEMISTS. AN ordinary meeting of the Society was held on Wednesday evening, March 31, in the Chemical Society’s Rooms, Burlington House. The President, Mr. A. Chaston Chapman, F.I.C., occupied the chair. The minutes of the previous ordinary meeting were read and confirmed. Certificates of proposal for election to membership in favour of Messrs.P. ti. Amp, B.Sc., A.C.G.I., A.I.C., F. H. Carr, F.I.C., A. S. Dodd, B.Sc., F.I.C., and H. Heap, M.Sc., F.I.C., were read for the second time; and certificates in favour of Messrs. Edward Theodore Brewis, F.I.C., 31, Belgrave Road, Leyton, chemist to Messrs. Stafford Allen and Sons, Ltd. ; Percival John Fryer, ‘‘ Ravenscar,” Pembury Road, Tonbridge, Kent, chief chemist to the Yalding Manufacturing Company, Yalding, Kent, Lecturer on Oils’and Fats at the Regent Street Polytechnic, London; and William McDonnell Mackey, F.I.C., Victoria Chambers, Lkeds, analytical and consulting chemist, were read for the first time.Messrs. C. W. McHugo, A.I.C., C. J. H. Stock, B.Sc., F.I.C., G. Tate, Ph.D., F.I.C., and T. E.Wallis, B.Sc., F.I.C., were elected members of the Society. The following papers were read : A Method for the Determination of Chlorides in Cheese,” by Miss E. C. V. Cornish, M.Sc., and John Golding, F.I.C. ; Estimation of Methyl Alcohol in Presence of Ethyl Alcohol,’’ by G. Cecil Jones, A.C.G.I., F.I.C. ; “Note on the Determination of Niobium in Presence of Tantalum, and Some Reactions of Tantalum Compounds,” by Arthur G. Levy, B.Sc., F.I. C. ; “ Estimation of Carbon Dioxide in Self-Raising Flour and Baking-Powder,” by Thomas Macara, F.I.C. ; ‘( Bromine Method of Determining Phenol,” by W. Versfield, B.A., D.Sc. ; and “ The Estimation of Sulphide and Sulphate Sulphur, and the Action of Solvents on Vulcanised Rubber,” by H. P. Stevens, M.A., Ph.D., F.I.C. Dr. E. K. Rideal exhibited a specimen of the new chemical hygrometer described by himself and Mr. A. Hannah (ANALYST, 1915, 48-54).

ISSN:0003-2654    

DOI:10.1039/AN9154000187

出版商:RSC    

年代:1915

数据来源: RSC

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188 S. JUDD LEWIS : APPLICATIONS OF SPECTROGRAPHY TO APPLICATIONS OF SPECTROGRAPHY TO ANALYTICAL AND INDUSTRIAL CHEMISTRY. BY S. JUDD LEWIS, D.Sc. (Tubingen), B.Sc. (London), F.I.C. (Read at the Meeting, December 2, 1914.) MANY discoveries of fundamental significance have been made by means of spectro- graphy, and yet the spectrograph is seldom applied to the ordinary purposes of analysis and industry.No doubt this is to be explained by the expensive character of the equipment, and the somewhat extensive practice which is necessary to obtain results which are useful and reliable; also by the limited applicability of any individual outfit. The most generally useful and convenient apparatus is a spectrograph constructed with quartz prisms and lenses. The dispersion is not great, so that it is not to be preferred for visual work; but the quartz refracts, and allows to pass the whole of the ultra-violet rays from those having a wave-length of about 2,000 Angstrom units, as well as those of the visible spectrum.Inasmuch as the more refrangible portion is invisible, its study is of necessity conducted through the medium of photography. There are four important advantages in this arrangement : First, the photograph is a true and permanent record of the experiment.Secondly, the ultra-violet region is included, where lines are exhibited by several elements which show no lines, or only a few, in the visible region-for example, boron, phosphorus, silicon, antimony, iron, magnesium. Thirdly, most of the absorption spectra studied with reference to chemical constitution have been produced in the ultra-violet.Fourthly, most of the purposes to be serted with a visual glass apparatus can be equally well attained with this. Spectra may be classified primarily into (a) emission spectra, produced from the light emitted by the incandescence of the body under examination, consequently they are usually possible with inorganic matter only; and (b) absorption spectra, obtained by analysing the light which has passed through the substance, usually in solution, which is being investigated. The light in selected parts of the spectrum is absorbed wholly or partially in a manner peculiar to the substance effecting it.The method is available for both organic and inorganic compounds. Of emission spectra, the Jlame spectrum is of very limited value.The arc spectrum is the most generally useful, and is available for all metallic and certain non-meballk elements ; with this the spark spectrum is an equal rival for utility, and for solutions almost indispensable. I t is usual for spectra, either ‘‘ arc ” or ‘‘ spark,” to be composed of the spectrum of the substance composing the electrodes and the spectrum of the substance under examination.Whatever may be done in academic research, where there are few restrictions as to time and expense, it may be accepted as a general rule, though not a universal one, that in the practical applications of spectrography only compurison spectra, or spectra photographed on similar principles, call for consideration.The spectra to beANALYTICAL AND INDUSTRIAL CHEMISTRY 189 compared are photographed in juxtaposition, an arrangement which enables the strictest comparison to be made. A very important application of the method is the study of those mineral constituents of water which occur in traces only, for they must have marked influence on the life-history of both animals and vegetables.For example, the wide dis- tribution of boron in these originates, no doubt, in the natural water-supplies (gee (‘ Year-Book of Pharmacy,” 1914,362, where the application of spectrography to drcg analysis is also referred to). Minerals, ores, clays, building materials, alloys, impure metalg, and the like, are equally ready to reveal their constituent elements. To summarise, emission spectra can find application in analytical and industrial practice as follows : 1.There is certainty as to the identification of the elements. There can be no doubt as to the presence of a given element, even if only one characteristic group of lines is evident, or even a single line in some circumstances. 2. Substances, the composition of which is entirely unknown, which are difficult to resolve by reason of complexity, insolubility, or otherwise, are analysed com- pletely and without difficulty.3. Unsuspected elements are readily discovered, for such elepents register their spectra on the plate. 4. Very small quantities, whether absolute or relative, are sufficient for dis- closing the presence of the various elements composing the material. 5.Those impurities which are difficult of detection by chemical means often reveal themselves at once in the spectrum, as in the case of a trace of barium in a strontium salt (‘ guaranteed free from baryta.” 6. Differences in qualitative composition between two similar specimens can be found readily, and identified without the necessity of ascertaining the general com- position of either. 7. The qualitative analysis of an inorganic substance with reference to its metallic and certain non-metallic elements is complete. 8. I t is rarely necessary to prepare the material in any way for the analysis. I t is apparent that many useful purposes may be served by the more extensive study of spectroscopy, and that the spectrograph can no longer be regarded merely as a means to the ends of academic science, but also as an instrument for investi- gating and solving many of the practical problems of everyday life. My thanks are due to Messrs. Adam Hilger, Ltd., for exhibiting a spectrograph with its accessories at the meeting.

ISSN:0003-2654    

DOI:10.1039/AN9154000188

出版商:RSC    

年代:1915

数据来源: RSC

摘要:

190 T. E. WALLIS : THE STRUCTURE OF PEPPER: SOME NEW FEATURES. BY T. E. WALLIS. (Read at the Meeting, March 3, 1915.) DURING the microscopical examination of the crude fibre from some trade samples of white pepper, I noticed several pieces of tissue showing strongly marked characters which are not included among those described and figured in the available textbooks and atlases. This led one to suppose that the samples might contain some added material other than pepper.Having noted that all the specimens examined con- 1 2 3 4 FIG. I.-BEERIES OF WHITE PEPPER ( x 7). 1, Berry seen from the side, showing depression above and conical projection below. 2, Base of berry, showing conical projection. 3, Base of berry, showing pigment layer exposed by removal of the parenchyma forming the cone-shaped projection.4, Apex of berry, showing depression. tained these tissues, it seemed possible that they were actually structures properly belonging to pepper, but which had been overlooked and omitted from the published descriptions. An examination of the crude fibre prepared from a sample of pepper obtained by powdering white pepper berries revealed the presence in authentic material of the same tissues, and so demonstrated the genuineness of the original samples.Some white pepper berries (Piper nigrum, L.) were next examined, with a view to finding portions which might be expected to show structures of a special type, and it was then noticed that peculiarities might be sought at the apex and a tTHE STRUCTURE OF PEPPER: SOME NEW FEATURES 191 the base of the fruit, which are marked respectively by a slight circular depression and a small bluntly conical projection (Fig.I., 1, 2, and 4). In many berries the parenchyma forming the conical part is rubbed off, and a brown circular patch-the pigment layer-becomes exposed, as shown in Fig. I,, 3. Scale 4J microns. 1 ' * _ - * ' * - - ' * ' s f 0 50 I00 150 FIG.II.-PREPARATIONS FROM THE APEX OF THE WHITE PEPPEK BERRY. 1, Diagram showing general disposition of the tissues present ( x 18). 2, Transverse section of the seed coats and inner portion of the pericarp from just above the embryo ( x 400). 3, Surface view of the tissues shown in the transverse section. a, Innermost layer of the pericarp. e, Embryo. end, Endo- sperm. hy, The hyaline layer.par, Parenchyma. per, Perisperm. pig, Pigment layer. scE, Inner sclerenchyma of the pericarp ( x 400). The diameter of a white pepper berry is about 4 mm., giving an area of about 50 sq. mm. ; the diameter of the slightly conical area at the base is about 2 mm. and of the depression over the embryo at the apex is 0.75 to 1.0 mm., giving areas192 T. E. WALLIS: of 3.1 and 0.8 sq.mm. respectively, so that the total area of these two regions is about one-twelfth of the whole area of the fruit, and the tissues of which they are composed must form a considerable part of the fibre obtained from samples of white pepper. Berries were soaked in water until sufficiently softened and the apex and Scale of mic~ons. 0 60 I00 160 FIG. I I I . 1, Transverse section of seed coats and inner part of the pericarp from the equator of the fruit.2, Surface view of the same tissues. a, Innermost layer of the pericarp. hy, Hyaline layer. o.g, Oil gland. par, Parenchyma. per, Perisperm. pig, Pigment layer. scE, Inner sclerenchpa of the pericarp. All x 400. base cut off. The sections which were made of these portions revealed modifications such as were being sought.In a, transverse eection of the apex of the berry the hemispherical hollow, containing the endosperm, appears as a, semicircular area just below the pigment Iayer, and the embryo itself occupies a similar smaller area in the upper part ofTHE STRUCTURE OF PEPPER: SOME NEW FEATURES 193 the endosperm. The general arrangement of the tissues is shown disgrammatically in Fig.II., 1. The inner sclerenchyma of the pericarp is more lightly built in this region than in other parts of the fruit, as may be seen by a comparison of Figs. 11. FIG. Iv. 1, Innermost layer of the pericarp from over the embryo ( x 106). 2, A portion of the same as found in powdered pepper, and more highly magnified ( x 200). 3, Hyaline layer, showing transition from straight-walled cells to those with wavy walls ( x 200).and 111. ; otherwise it is very similar. The narrow layer of the pericarp within the sclerenchyma appears in sections from the middle of the fruit as ti narrow, nearly194 T. E. WALLIS structureless band (Fig. III., 1, a), having a slight brown colour and showing in the form of short lines the compressed lumina of the cells of which it is composed.In surface view (Fig. II., 2, a) it is seen to consist of thin-walled, irregularly polygonal cells, measuring 15 to 40 p in either direction. In a section from the apex of the fruit the same layer appears as a single row of cells, with very thick sparsely pitted walls and rectangular lumina. They have a height of about 20 p and are from 15 to 40 p wide.In surface view the cells are seen to converge upon the centre of the small circular area covering the endosperm, their long axes being directed towards the centre (Fig. III., 2, a ; and Fig. IV., 2). Their length varies from 40 to 130 p ; the walls are thick and show pits, particularly in the angles. At the centre of this area is a small opening (Fig. IV., I), which marks the end of the canal through which the pollen-tube passes to the ovary.The pigment layer, which comes next, is also modified. Ordinarily it consists of flattened rectangular cells (40 to 80 p long and 12 to 18 p wide), filled with dark brown contents, as shown in Fig. III., 2, pig. At the apex of the fruit above the embryo, the cells, as seen in a vertical section of the fruit, gradually increase in height from 5 to 40 p and decrease in width from 50 to 10 or 20 p (see Figs.II., 2 ; and III., 1). In surface view the same cells are Been to be polygonal in shape and have thickened walls. They are from 10 to 25 p in either direction (Fig. II., 3, pig.). The hyaline layer shows a peculiar structure in this region. The cell walls, which in other parts of the fruit are straight (Fig.III., 2, hy.), are here thrown into folds, giving rise in transverse section to the appearance shown in Fig. II., 2, hy., and in surface view to a tissue consisting of cells with much waved walls and measuring from 30 to 50 p in either direction, as represented in Fig. II., 3, hy. The transition from straight-walled cells to those with wavy walls is shown in Fig.JV., 3. These three tissues are so strongly built and have such characteristic features that, although they only form a small proportion-about one-fiftieth-of the whole area, of their respective layers, they are found in every preparation of fibre from pepper, and unless known to belong properly to the fruit of Piper nagrum would lead one to the erroneous conclusion that some admixture was present. A section through the conical portion at the base of the fruit reveals the fact that the pigment layer is here again much altered, while the inner sclerenchyma of the pericarp, with the layer next to it, and also the hyaline layer outside the perisperm, disappear entirely (see Fig.V., 2). The formation of this prominence is due to the entrance of the fibro-vascular bundles into the pericarp at this point, whence they spread in all directions, to travel from the base to the apex of the fruit (Fig.I., 1 and 3), so that the parenchyma is specially supported in this region and is raised in the shape of a slight cone. The pigment layer increases in thickness from one cell to three or four, and finally to eight or ten cells, and continues at this thickness across the base of the conical prominence referred to above.Fig. V., 1, shows the general arrangement diagrammatically. The cells of the pigment layer are here less compressed and are of rather smaller dimensions, being 15 to 35 p in either direction, as seen in surface view. The superposition of several similar layers of cells produces a tissue of characteristic appearance when seen from aboveTHE STRUCTURE OF PEPPER: SOME NEW FEATURES 195 Scale C f r n t - C T O I L S . 1 * a; 1 ' * * I * J 0 so 100 CEO FIG.V. 1, Diagram of a transverse section through the conical projection a t the base of a white pepper berry ( x 27). 2, A ,ortion showing in detail the transition of the pigment layer from a narrow band to a wider one, and! the abrupt ending of the other tissues.3, Pigment layer in surface view. 4, Scler- enchymatous cells from periphery of the conical projection. a, Innermost layer of the pericarp. d, Pigment cells, showing delicate pitting of walls. f.v.b, Fibro-vascular bundle. hy, H aline layer. o.g, Oil gland. par, Parenchyma. per, Perisperm. pig, Pigment layer. sc2, Sclerenc&ma. sp, Spiral from a vessel.(2, 3, and 4 all x 400.)196 THE STRUCTURE OF PEPPER: SOME NEW FEATURES (Fig. V., 3). Some large sclerenchymatous cells are found on the outside of the conical projection of the base, and are shown in Fig. V., 4. Although no complete description of these tissues appears to have previously been given, reference is made to the occurrence of some of them in powdered pepper by Eugene Collin (Annales des FaZsiJications, 1910, 3, 272, et seq.).He says (p. 274) : ‘( Comme elements accessoires ou pourra retrouver dans quelques prises d’echantillon des cellules tr&s sinueuses, fortement colorees en brun, et d’autres aussi fortement colorees, assez regulihrement polygonales, ou cylindriques, qu’on serait tent6 d’attri- buer A la presence de matieres etrangeres ; il faut bien s’en garder ; car ces elements assez rares d’ailleurs sont normaux et representent des debris du tegument s6mina1, pris aux deux p6les opposes du fruit du poivre.” In the description attached to the figure of the anatomical elements of powdered pepper the cells having sinuous walls are erroneously referred to the base of the fruit, and are stated to be the modified pigment layer, whereas my preparations indicate that they belong to the hyaline layer, and come from the apex just over the embryo.The modified pigment layer from the base is also figured, but is stated in the description to come from the apex of the fruit. The pigment layer from the apex of the fruit, as seen in surface view, is also figured by M.Collin, and is correctly referred to the summit of the fruit. I have also been unable to confirm the presence of such numerous pits as to give a beaded appearance to the walls of the cells of the pigment layer covering the greater part of the fruit. In all preparations which I have examined they appear as shown in Fig. III., 2,pig. The cells from the portion o this tissue where it becomes several layers thick across the base of the conical end of the fruit do, however, show a delicate pitting which gives the walls a finely beaded appearance.Reference to modifications at the apex of the fruit is made by Tschirch and Oesterle in their (( Anatomischer Atlas der Pharmacognosie,” p. 105, where the appearance of the innermost layer of the pericarp and of the epidermis of the seed (the pigment layer), as seen in a transverse section, is noted, and a, drawing of s.uch a section is shown on Plate 25, Fig.13, of their Atlas. No description of these modified tissues in surface view is given, nor is their occurrence in powdered pepper referred to. DISCUSSION. Professor H. G, GREENISH said that he imagined that Mr. Wallis’s mode of procedure had been to concentrate the cellular elements in a comparatively small space, the starch being got rid of, while the delicate parenchymatous tissue of the perisperm became transparent and nearly invisible in chloral hydrate.Each particle would then have to be minutely examined in order to ascertain, if possible, from what part of the berry it came. He (the speaker) had carried out that very tedious process with 8ome other articles, and he sympathised with Mr.Wallis in his task. He should like to see some of the more common drugs taken in hand in the same way and examined as thoroughly. Mr. E. T. BREWIS asked whether there was any possibility that these new structures which Mr. Wallis had described might be confused with any part of the outer coats of black pepper.A METHOD FOR THE ESTIMATION OF CHLORIDES IN CHEESE 197 Mr.E. R. BOLTON said that extravagant claims were sometimes made as to the possibility of making quantitative estimations of the amounts of shell or husk by microscopical examination, and he thought it would be useful if Mr. Wallis would indicate what he considered to be the limitations of the microscope in this respect. Mr. WALLIS said that the tissues to which he had drawn special attention were so entirely different from those of the outer part of the pericarp that he did not think there was the least likelihood that any confusion would arise. The quantita- tive use of the microscope was a matter calling for very considerable caution. It was impossible to form any opinion as to quantity except by making up samples containing the genuine substances and the suspected admixtures in known pro- portions, and then, by microscopical comparison, getting an idea as to whether the foreign particles were present to a similar extent in the samples of known composition and in the suspected sample. This, of course, was necessarily very tedious, and in the end the results obtained were only roughly approximate.

ISSN:0003-2654    

DOI:10.1039/AN9154000190

出版商:RSC    

年代:1915

数据来源: RSC

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A METHOD FOR THE ESTIMATION OF CHLORIDES IN CHEESE 197 A METHOD FOR THE ESTIMATION OF CHLORIDES IN CHEESE. BY ELFREIDA C. V. CORNISH, M.Sc., AND JOHN GOLDING, F.I.C. (Rend at the ~Weeting, March 31, 1915.) THE usual method for the estimation of chlorine in cheese, by water extraction from the incinerated solid and subsequent titration with silver nitrate, using potassium chromate as indicator, was found to give unsatisfactory results unless the incineration was performed at a very low temperature.Carried out in this manner the experi- ments are very tedious, and attempts to hasten the process by raising the temperature were attended by considerable loss of chlorine, due to volatilisation of the chlorides present. The well-known method of incineradhg with lime gives satisfactory results, but is equally tedious.O’Sullivan in a paper (ANALYST, 1914, 39, 425) pointed out that chlorides are decomposed and chlorine lost on incinerating organic substances, especially in the presence of magnesium sulphate. The quantity of this latter compound present in a substance containing chlorides may be sufficient to cause the. total loss of the chlorides on incineration. We therefore determined to devise a method which should, if possible, be both more rapid and more accurate than those just mentioned.The method as first adopted was as follows : About 1 grm. of cheese was weighed on a chlorine-free filter-paper and placed in a Kjeldahl flask, and about 20 C.C. of strong, nitrogen-free sulphuric acid and a few small pieces of pumice added.These quantities were used because it was hoped that th6 ordinary Kjeldahl nitrogen determination might subsequently be carried out on the residue from the chlorine determination. A nitrogen bulb, containing a known volume of & silver nitrate and198 CORNISH AND GOLDING : some strong nitric acid, was inserted into the neck of the flask by means of a tightly fitting cork.The flask was clamped in an almost horizontal position and heated over an Argand burner. The hydrochloric acid formed by the action of strong sulphuric acid on the chlorides present in the cheese was driven over into the acid silver nitrate solution and precipitated as silver chloride. When the reaction was completed (determined by inserting another bulb with fresh solution) the silver chloride was filtered off, the precipitate washed till free from nitrate, and the washings added to the filtrate.Volhard's method of titration was used for the determination of the residue of the silver &rate, the result was subtracted from the original quantity, and the chlorine calculated as sodium chloride from the results so obtained. In this method the precipitated silver chloride must first be filtered off; the solution of silver nitrate is then titrated with potassium thiocyanate, using saturated iron alum as indicator.White silver thiocyanate is precipitated, and as soon as the reaction is oomplete brown iron thiocyanate is formed. The end-point is not readily determined in the presence of silver chloride, as a counter-reaction may take place, resulting in the formation of silver thiocyanate and ferric chloride, thus : Fe( CN S), + 3AgCl= FeCl, + 3AgCN S.For this reason it is necessary to filter off the silver chloride as already stated (Landw. V'rsuchsstat., 1914, 83, 309-316). About 1 C.C. of saturated iron alum is used as indicator, Preliminary experiments to determine the amount of nitric acid necessary to retain in solution all the salts other than silver chloride were made.Various solutions were made up containing 5, 20, 40, about 60 and 80 per cent. nitric acid and 10 per cent. water and the remainder & silver nitrate. I t was found that solu- tions containing 5 and 20 per cent. nitric acid gave results which were much too high, owing to the precipitation of carbonate and probably sulphate, while thoae containing 40 per cent. and above gave concordant results.It was decided that the solutions should always contain about 50 per cent. strong nitric acid. The apparatus first used, and already described, was not always satisfactory, as occasionally the silver nitrate solution sucked back into the Kjeldahl flask. I t was therefore decided to aspirate.This having been done, the next difficulty experienced was that of corks. It was necessary that the corks should fit perfectly, but their corrosion was rapid by reason of the oonstant exposure to strongly acid fumes. It was decided, therefore, to eliminate them altogether from the distillation flasks. This was done by inserting into the necks of the flasks the tubular end of a large soda-lime tube of such a size that the bulb just blocked the mouth of the flask.An extension of the narrow end of the tube dipped into the silver nitrate and nitric acid solution in a flask fitted with a rubber stopper with a second tube leading to the aspirator pump. It was decided later to add a second control wash-bottle between the first flask and the pump. Even with aspiration, however, it was found that the hydrochloric acid condensed in the bulb of the soda-lime tube.This was readily prevented by passingA METHOD FOR THE ESTIMATION OF CHLORIDES IN CHEESE 199 a Bunsen flame rapidly up and down the neck of the flask while the reaction was taking place. The hydrochloric acid was thus kept vaporised and its rate of absorption accelerated.Some difficulty was experienced in obtaining an absorption flask which was efficient and did not require an unnecessarily large quantity of silver nitrate and nitric aoid. The form finally adopted was that shown in the diagram. FIG. 1. Experiments using pure NaCl gave the following results : Amount taken. 0.246 0.1128 0.2362 0.184 0.1005 0.0879 0.0937 0.1174 0.1026 Amount found.0.2469 0.1139 0.2364 0-1865 0.0993 0-0886 0.0936 0.1170 0.1036 Control experiments were carried out with sulphuric acid and pumice, and also with pure casein, but no precipitation of silver chloride resulted in either case.200 CORNISH AND GOLDING : Further experiments with cheese were then carried out. The cheese used was a Stilton, showing brown discoloration, and it was thought that interesting results might be obtained by determining the chlorine in the brown as distinct from the white part.Chlorine, expressed as Sodium Chloride. Brown Part. White Part. (1) 2.519 per cent. (2) 2.468 ,, (2) 2.750 ,, (3) 2.432 ,, (3) 2.536 ,, (4) 2.584 ,, (1) 2.617 per cent. -- Maximum Error. Maximum Error. Average 2.473 ... k 1.6 per cent. Average 2-622 ... k 4.9 per cent.These results show no marked difference in the chlorine content of the discoloured and the white parts of the cheese, but the degree of accuracy which may be expected from this method may be seen from them. In order to save time in the duplicating of results, a battery of four flasks in series was fitted up, so that the aspiration of all four could be carried out simul- taneously from one pump.To prevent the condensation of hydrochloric acid in the necks of the flasks, a rectangular water-tank, provided with a cover and heated by a special burner, was used. Four round openings were made in each of the two long sides, those on the one side being lower than those on the other. These openings were joined up by slanting metallic cylinders soldered into the sides of the tank.The Kjeldahl flasks rested on a metal platform, and were heated by separate Argand burners. The neck of each flask passed through one of the slanting cylinders, and from the other side of the tank the soda-lime tubes were inserted into the necks of the flasks. The flasks were thus kept constantly heated by steam from the wate? in the tank. The absorption flasks and control wash-bottles were placed on adjustable wooden platforms.After the sulphuric acid (about 20 to 30 C.C. nitrogen-free) had been added to the Kjeldahl flask, and the neck inserted into the cylinder, connection was made with the absorption flask and control wash-bottle, and aspiration begun. The neck of the flask was gently rotated round the soda-lime tube until the contents of the flask were well mixed.I t was found advisable to add a little distilled water as well as the sulphuric acid, or to grind up the cheese, after weighing, with warm distilled water, and then wash into the flask before adding the sulphuric acid. The contents of the flasks having been well mixed by rotating, the flasks were heated, at first gently, then more strongly, until the contents boiled briskly.The length of time necessary to insure complete volatilisation of the hydrochloric acid depends naturally upon the amount of Eiubstance originally taken and the quantity of chlorides present. In no case was the time required found to exceed one and a half hours. After the removal of the first absorption flask, a second one was always connected with the Kjeldahl flask in order to make quite sure that all the hydrochloric acid had passed into the first.The Kjeldahl flasks were then removed to the fume chamber, the sulphuric acid reaction continued with subsequent addition of potassium sulphate and potassium permangenate, and the nitrogen determination completed by the ordinary Kjeldahl method.A METHOD FOR THE ESTIMATION OF CHLORIDES IN CHEESE 201 The following results were obtained, using the battery : STILTON CHEESE NO.c 50 (1ST SAMPLE), SHOWING BROWN DISCOLORATION. GI expressed as NaCI. White Part. Brown Part. (1) 1-821 per cent. (2) 1.825 ,, (2) 2.138 ,, (3) 1.802 ,, (3) 2.037 ,, (4) 1-814 ,, (4) 2.191 ,, (1) 2.209 per cent. -- Mrtximnm Error. -- Maximum Error. Average 1.815 ... +, 0.7 per cent. Average 2,144 ...+, 5 per cent. STILTON CHEESE NO. C 50 (2ND SAMPLE). CE expressed as NaCE. Brown Part. (1) 2.071 per cent. (2) 2.046 ,, (3) 2-053 ,, -- Maximnm Error. Average 2.057 ... +, 0.7 per cent. STILTON CHEESE No. 89, SHOWING BROWN DISCOLORATION. CE expressed as NaCE. Brown Part. (1) 2.610 per cent. (2) 2.771 ,, (3) 2.738 ,, (4) 2.732 ,, .., Maximnm Error. Average 2.713 ... * 3.8 per cent.CHEDDAR CHEESE. CI expressed as NaCE. (1) 1.574 per cent. (2) 1.553 ,, (3) 1.613 ,, Maximum Error. Average 1.580 ... & 2.1 per cent. In each case the cheese was prepared by passing through a mincer, and was then very carefully and thoroughly ground with a, pestle and mortar. Some experiments on butter gave the following results : CE expressed as NaCE.(1) 0.746 per cent. (2) 0,726 ,, (3) 0.759 ,, (4) 0.787 ,, Maximum Error. Average 0.7545 ... f 4.3 per cent.202 CORNISH AND GOLDING : The butter was heated by placing it in a flask in hot water till it melted, and was then well shaken until cool to insure thorough mixing. From the results obtained, the advantages of this method over that of incinerating and water extraction seem to be : (1) Greater accuracy and rapidity.There is no danger of loss of chlorides, and no necessity for lengthy and careful heating. (2) The same cheese residue, in the same flask and with the same sulphuric acid, may be used for the nitrogen estimation in the solid cheese by Kjeldahl’s method, part of the necessary heating having been carried out in the chlorine estimation.DAIRY RESEARCH LABORATORIES, UNIVERSITY COLLEGE, READING. DISCUSSION. The PRESIDENT, in inviting discussion, remarked that the method of ignition with alkali was perhaps not entirely free from error, particularly in the case of sub- stances-of which cheese was a notable example-which it was difficult to mix intimately with the lime or other alkali employed. I t was, moreover, a lengthy process, as the ignition must be effected at a low temperature, and this had to be followed by extraction with water, and possibly further ignition of the residue.The authors’ method, which evidently gave concordant results, appeared to have the advantage of being more speedy, and also of enabling the chlorine and the nitrogen to be estimated in one and the same operation.Possibly the authors might extend their experiments in the direction of meat extracts, in the case of which it would be a convenience to be able to determine the chlorine and the nitrogen together. The quantity of chlorine, however, was in that case much larger than in the case of cheese or butter. He should like to ask whether in the case of butter any trouble was experienced through bumping; and also-although this had no bearing on the actual subject of the paper-whether the authors could say what was the exact nature of the difference between the brown and the white portions of the cheese.Dr. VOELCKER remarked that, while it was undoubtedly valuable to have a reliable method for the estimation of chlorides in organic substances, this did not carry one much farther as regards the significance of chlorides in the case of such materials as cheese and butter.If, as the President had hinted, the presence of salt had some bearing upon the quality of cheese, and could indicate why some portions of a cheese were good and others inferior, the accurate estimation of the chlorides would be of importance. As it was, everyone who had to do with the making of cheese and butter knew that the use of salt in these was quite arbitrary, nor, unless where brine and not solid salt had been employed in butter-making, was there any likelihood of the salt being evenly distributed throughout a sample.Mr. E. M. HAWKINS, referring to the addition of water to the cheese, asked whether the quantity of water added was such that it might possibly affect the nitrogen determination.It was well known that in the Kjeldahl process the presence of an excessive quantity of water was liable to cause the results to be low. Mr. GOLDING, in reply, said that in the case of butter a little pumice was used,A METHOD FOR THE ESTIMATION OF CHLORIDES IN CHEESE 203 and no bumping had occurred. He desired to lay particular stress on the necessity for keeping the neck of the flask sufliciently warm. In reply to Dr.Voelcker, it was in the course of an endeavour to ascertain the cause of the discoloration referred to that this investigation was undertaken. The matter was an important one, for the occurrence of this ‘( yellow discoloration ” caused an annual loss of many thousands of pounds to Stilton cheese makers, since, when cheeses were so affected, their market value was greatly reduced, and they quickly deteriorated in quality and would not keep.It seemed that the discoloration was due to an organism producing tyrosinase, or some similar enzyme, which acted on the decomposition products of the casein. In his early work on the subject he had isolated such an organism, which blackened tyrosine media,.and many more had been isolated by Dr. R. Sten- house Williams, who has not yet published his results. While visiting the cheese factories he (Mr. Golding) had noticed that the cheeses were freer from this dis- coloration when but little salt was used than when the quantity of salt was large; but, as he had not been able to visit more than twenty-five or thirty factories, this evidence was not very weighty from a statistical point of view, although it appeared to have some scientific support, as was shown in a recent article in the Journal of the Board of Agricultum.It was thought that possibly accurate determination of the salt present in the cheese might throw some light on the matter. Uneven salting was, of course, very common ; the quantity of salt varied from about 7 to 13 ounces per cheese, and this was liable to be unevenly distributed; but if it appeared that the discoloration was regularly accompanied by the presence of an excessive quantity of salt, he thought that a step would have been made in the direction of providing a practical means for checking the fault. Now that the method of analysis had proved satisfactory, they proposed to make further estima- tions in the discoloured parts and in the white parts respectively. With regard to the addition of water, the quantity of water necessary to soften the cheese was very small, and was not enough to upset the nitrogen estimation. He had, however, made a good many estimations in which rather large quantities of water were used, and had never found this to cause any difficulty.

ISSN:0003-2654    

DOI:10.1039/AN9154000197

出版商:RSC    

年代:1915

数据来源: RSC

摘要:

204 LEVY: ESTIMATION OF NIOBIUM IN PRESENCE OF TANTALUM, THE ESTIMATION OF NIOBIUM IN PRESENCE OF TANTALUM, AND SOME REACTIONS OF TANTALUM COMPOUNDS. BY ARTHUR G. LEVY, B.Sc., F.I.C. INVESTIGATION CARRIED OUT UNDER THE SOCIETY’S ANALYTICAL INVESTIGATION SCHEME. (Read at the Meeting, Hamh 31, 1915.) INTRODUCTION. THE most generally trusted method for the separation of niobium and tantalum at the present time still appears to be Marignac’s old method of fractionally crystallis- ing the double potassium fluorides.The drawbacks of this method, its inaccuracy and tediousness, are familiar to every chemist who has worked with it, and quite a number of attempts have been made to find a method to supplant it. As far back as 1885 Osborne (Amer. J . Sci., 1885 [3], 30, 328), basing his work on some earlier experiments of Marignac, described a method for the volumetric estimation of niobium in presence of tantalum, and extended it to include the presence of titanium.His work may be summarised as follows: Dissolving potassium niobium oxyfluoride (K,NbOF,) in hydrochloric acid, and reduc- ing with amalgamated zinc and a piece of platinum foil at a temperature of about 80° C., he found (apparently ~ E I the result of one experiment only) that reduction went as far as a hypothetical oxide (Nb,O,,), which is fairly close to another oxide, (Nb,06), mentioned by Marignac.This degree of reduction was only reached, however, if concentrated hydrochloric acid was used. If even a small quantity of water was present, reduction stopped short at a point depending on the concen- tration of the acid.This result seems to me not very probable. When the acid has reached a temperature of 80’ C., its composition should be much the same, whether concentrated acid or concentrated acid plus a little water was used in the first place. The quantity of acid left would indeed be different, but Osborne states that (within limits) the quantity of acid used is immaterial.Osborne next applied his method to the analysis of a sample of mixed oxides of niobium and tantalum of known oomposition, obtained by precipitation with ammonia and drying at looo C. Five estimations on this sample gave 46.64 to 47.45 (average 46-95) per cent. Nb,O, as against a theoretical 47.36. Osborne then added 0.0900 and 0.3728 grm.respectively of potassium fluoride to two portions of a little over 6.5 grms. each of mixed oxides supposed to contain 45-99 per cent. of Nb,O,. He found 43-83 and 43.87 per cent. respectively, and concluded that potassium salts inhibited reduction to an extent independent of their amount. This, however, appears to be in conflict with his earlier experiment, in which he worked with potassium niobium oxyfluoride.Osborne finally showed that titanium solutions are completely reduced to Ti@, by his method, both when the titanium is alone and when it is mixed with niobiumAND SOME REACTIONS OF TANTALUM COMPOUNDS 205 and tantalum. When both titanium and niobium are present together, they are estimated together by his reduction method, and then titanium is determined colori- metrically by Weller’s method (Ber., 1882, 15, 2592).Since, however, hydrofluoric acid prevents the colour, and hydrochloric acid deepens it, it is necessary to precipi- tate the oxides by ammonia, and then to redissolve (without filtering) in the smallest possible amount of sulphuric acid. Piecing together Osborne’s method as given in various parts of his paper, to estimate niobium in a mineral containing tantalum as well, the mixed oxides are obtained as usual and ignited.They are then fused with potassium bisulphate, digested with water, filtered, washed, and dissolved in hydrofluoric acid ; the excess of acid is evaporated off (in one place he says “nearly dry”) on the water-bath, 50 C.C. concentrated hydrochloric acid, some amalgamated zinc and a piece of platinum foil are added, and reduction carried out for about three-quarters of an hour at 80” C.in an atmosphere of carbon dioxide. After cooling, the reduced solution is poured into a beaker, diluted to about 350 c.c., and titrated with potassium permanganate. I have described Osborne’s work at some length, as it forms the basis of my own experiments ; moreover, the details of his work are but little known.Warren (Amer. J. Sci., 1906 [4], 22, No. 132; Chem. News, 1906, 94, 298) carried out six experiments by Osborne’s methods on mixtures containing in five cases about as much titanium oxide as niobium oxide; in four cases smaller quan- tities of tantalum oxide were also present, The quantity of permanganate used was always less than that calculated by B large and irregular amount, and Warren concluded that the method was hopeless.It should be said, however, that he misread Osborne’s paper and based his calculations on a supposed reduction to Nb,O, instead of to the Nb,O,,, as stated by Osborne. Correcting for this, in five cases the minus errors become very considerably smaller, although even so the results are far from good.It seems obvious that there is grave danger of reoxidation of both niobium and titanium during the transfer of the solution from the reduction flask to the beaker in which the titration is made. Metzger and Taylor (School of Nines QzLart., 1909, 33, No. 4; Zeitsch. Anorg. Chem., 1909, 62, 383) have described a method in which succinic acid is used to prevent precipitation of the mixed oxides on diluting a sulphuric acid solution of a potassium bisulphate melt ; the dilute solution is passed through a Jones reductor containing amalgamated zinc and the reduced solution titreted with permanganate. Niobium is reduced to an oxide of the formula Nb,0,.,,7, 1 C.C.of & solution corresponding to 0.007052 grm. Nb,O,. The degree of amalgamation, and probably the acidity of the solution, are of great importance, and the details given by the authors must be closely followed.The test results given by Metzger and Taylor for pure niobium solutions are excellent, but for mixtures of niobium and tantalum of known composition they are not nearly so good, the error of the niobium oxide taken (0.05 to 0.22 grm.) ranging from +0*0007 to - 0.0079 (average -0.0032) grm.in the eleven estimations given. Duplicate analyses on the same mineral sometimes differ by as much as 1.2 per cent. reckoned on the mineral. None of the newer gravimetric methods-all modifications of Marignac’s method, or Webs and Landecker’s process, which depends on an entirely different principle-206 have come into general use.Foote and Langley’s specific gravity method will be mentioned in an appendix. The standard textbooks are mostly silent as to the volumetric methods for deter- mining niobium. Moissan, however, in his (( Trait6 de Chimie Minkrale,” Paris, 1905, vol. ii., states that reduction of potassium niobium oxyfluorides with zinc in hydro- chloric acid solution goes as far as Nb,O,( = NbzO,.NbO), but gives no details except to state that alkali fluorides prevent the reduction.Beckurts’ Massanalyse,” Braunschweig, 1913, p. 595, gives both Osborne’s method” and Metzger and Taylor’s, and states that the last-named is at present the best. LEVY: ESTIMATION OF NIOBIUM IN PRESENCE OF TANTALUM, EXPERIMENTAL. Contrary to the usual textbook statements, both niobium and tantalum oxide are readily soluble in hydrofluoric acid, even after strong ignition.The simplicity with which a fluoride solution of the mixed oxides, as they are ordinarily obtained in the analysis of tantalum minerals, can be produced in this way, led me to determine whether, in spite of Warren’s adverse criticism, Osborne’s method or a modification could not be made to work. The experiments described below are the outcome.The method followed at first was to dissolve weighed portions of pure niobium pentoxide in about 3 to 5 C.C. of hydrofluoric acid in a 25 C.C. platinum crucible, and then to evaporate to dryness. Both solution and evaporation were occasionally carried out on a water-bath, but in the great majority of cases on a hot plate, at a temperature below the boiling-point.The residue was taken up in concentrated hydrochloric acid, the solution transferred to a glass flask, using a glass rod, the crucible being rinsed out with successive portions of hydrochloric acid, and finally with water. The solution so obtained was generally slightly cloudy. Ten grms. of zinc were then added, and when the reaction slackened, usually at the end of ten minutes, the flask was gently warmed on a hot plate.As soon as all the zinc was dissolved, generally in about thirty minutes from the start, the contents of the flask were diluted, and the fitration was carried out at once with an approximately pv potassium permanganate solution. The first few experiments were made in flasks provided with a rubber stopper carrying a Bunsen valve.On account of the presence of so much chloride, how- ever, the reduced solution must be considerably diluted before titrating, and ordinary flasks of sufficient size will not often stand the pressure created when the solution cools. Transfer from a smaller flask to a larger vessel is to be avoided on account of the risk of reoxidation. Consequently, reduction was later carried out in a 500-C.C.conical flask provided with a double-bored rubber stopper carrying an inlet tube for hydrogen and an ordinary thistle funnel, the stem of which terminated at such a height that it was still above the liquid at the end of the titration, at which stage the flask holds nearly 400 C.C. This thistle funnel serves as the exit tube for * ,Beckurts states that Osborne removed the last traces of hydrogen fluoride “ by heating in a glass Osborne merely mentioned that most of the fluorine left appears to go off as SiF, during the vessel.reduction.AND SOME REACTIONS OF TANTALUN COMPOUNDS 207 the hydrogen during the reduction, and to add the diluting solution before the titra- tion. By filling the funnel with the solution and simultaneously loosening the rubber stopper slightly, the solution can be added easily without introducing any air.The permanganate solution is also run in through this thistle funnel." Hydrogen, washed with copper sulphate solution, was used to give an inert atmosphere during reduction and titration. Carbon dioxide would probably do as well, but coal-gas cannot be used, as it rapidly reduces permanganate. To keep the method as simple as possible, unamalgamated zinc was used throughout. I n order to lessen the briskness of the reaction somewhat, a certain amount of water was usually added to the hydrochloric acid, the standard quantities finally adopted being 40 C.C.of concentrated hydrochloric acid to 20 C.C. of water and 10 grms. of zinc. The zinc was in fairly massive form, the thicker pieces only from a sample of granulated zinc being used for the earlier experiments, Nos.1 to 22, and zinc '' shot," 23 of which usually weighed 10 grms., being used for the later ones. In Experiments 1 to 5 and 11 to 13 the reduced solution was diluted simply with from 150 to 300 C.C. of water. The end-point so obtained was fairly sharp, but very transient ; hence in Nos.6, 14, and 15, 10 C.C. of concentrated sulphuric acid were also added. Whilst this improved matters somewhat, it was found that a very much sharper end-point could be obtained by adding sodium phosphate solution as well, and after two trials with larger quantities of phosphate, Experiments 7 to 10 and from 18 (inclusive) on were made by diluting the reduced solution with a mixture of 270 C.C.of water, 10 C.C. of concentrated sulphuric acid, and 20 C.C. of a cold saturated solution of sodium phosphate. This diluting solution should be cold and free from air. The permanganate solution was run in at such a rate that single drops could just be distinguished until the originally dark brown solution became almost colourless. From this point on the permanganate was added a few drops, and finally one drop at a time, each successive addition being washed down the funnel with a little water.The pink colour so obtained persists for at least two minutes, With very little practice, it is easy to ascertain when the end-point is near, the solution becoming perfectly colourless a little before this point. A complete control was run whenever a new chemical was employed.It generally amounted to 0.25 C.C. of Fa solution. Two slightly different, but nearly cG solutions of potassium permanganate were used during the course of the work. To facilitate comparison of results, all figures have been calculated to & strength, and the figures so obtained are given. The actual burette readings were only to 0.05 C.C.It may also be stated that the order in which the experiments are given in the tables is not quite that in which they were made, some of the experiments in Table 11. being made before the later ones of Table I. Note.-In the fourth column of Tables I., II., and IV., and the fifth column of Table II., after the first result, all zeros are omitted, significant figures only being given.* Alternatively, the flask may be closed by a three-holed stopper. Two of the holes serve for inlet and exit of the gas. The diluting liquid, and afterwards the tip of a long-stemmed burette, are introduced through the third. The reduced and diluted solution need not be further cooled.208 LEVY : ESTIMATION OF NIOBIUM IN PRESENCE OF TANTALUM, TABLE I. Evaporation carried to Dryness.No. 1 2 3 4 5 6 7 8 9 10 ' Nb20, & ICMnO, taken. required. - Gm. C.C. 0.0590 5-85 0.0508 I 6-14 0.0592 ' 5.56 0.1139 0.0794 0-1292 0.0626 0-0582 0.0711 0.1023 11 12 13 14 15 16 17 18 19 20 21 22 23 24 13.56 9.36 13-95 5.90 4.63 7.66 11.60 Grm. 0-0954 0.0584 0.0996 0.1202 0.1394 0.1186 0-1243 0.1134 0.1168 0.0712 0-1041 0.1699 0*1111 0.1026 Nb205 per C.C.Grm . 0.01009 0*00827 0.1065 0-0840 0.0848 0.0925 0-1061 0.1257 0.0928 0.0882 Hydrochloric 1 Water Acid present. , present. i C.C. Nil A little 30 9 1 $b 20 9 9 9 9 9, TABLE XI. Evaworation carried nearly to Dryness. L & KMn04 required. C.C. 11.12 7.02 12-14 14.53 17.07 14.19 15-12 13.60 13.80 8.53 12.48 20-38 13.36 12.26 Nb20, I Deviation from per C.C. 1 mean, 0'00833. I Grm.0.00858 0.00832 0.00820 0.00827 0.00817 0.00836 0.00822 0*00834 0.00846 0.00835 0.00834 0.00833 0.00832 0.00837 Grm. + 0*00025 - 0~00001 - 0.00013 - 0*00006 - 0.00016 + 0*00003 - 0~00011 + 0~00001 + 0.00013 + 0~00002 + 0~00001 f 0~00000 - 0~00001 + 0.00004 Hydrochloric Acid present. C.C. 50 Water Present. C.C. 20 30 30 20 5 20 9 7 9 9 9 9 9 9 9 9 I 9 9 9 1 9 The results obtained in this way are given in detail in Table I., the first two experiments being made in a flask with Bunsen valve and the others in the flask fitted with the thistle funnel described above.It will be seen that the results are very irregular, reduction usually stopping far short of the oxide Nb,O,,. The pro- cedure just mentioned near the end of Osborne's paper of evaporating near@ to dryness was next tried. For this purpose the final evaporation was carefully carried out on a moderately warm " hot " plate until only a few drops of solution remained,AND SOME REACTIONS OF TANTALUM COMPOUNDS 209 and crystals separated out when the crucible was lifted off the hot plate and cooled a little.The residue so obtained, which gave a perfectly clear solution in hydro- chloric acid, was reduced, diluted, and titrated exactly as before, with the results given in Table 11. These results may fairly be said to be good for a titration which appears to be as delicate as the one under consideration.The average of all the results in Table 11. is 0*00833 grm. of Nb,O, for the equivalent of 1 C.C. & permanganate solution. Excluding Nos. 11, 13, 15, 17, and 19, all of which differ from the mean by more than 0.00010, the almost identical figure 0-00834 is obtained, which has been adopted in the subsequent work.This happens to be the equivalent of a hypothetical oxide NblOOl7, which may be written 4Nb,O,.Nb,O,. The degree of reduction obtained by different observers is summed up in Table 111. I t will be seen that in the present method reduction does not go as far as in any of the others, which may be an advantage, in that the less one aims at the more likely one is to obtain that little.The higher permanganate equivalent is, of course, a slight disadvantage. TABLE 111. Degrees of Reduction found by Diferent Observers. Reduced Oxide. I I I Observer. Marignac ... ... 1 Nb.305=Nb1200200 Author .. . * 1 b10017 = b1200204 Osborne ... . . . Nb,O,, = N b1100195 Metzger and Taylor Nb,0,.,07 = Nb1200,86.42 Acid present. NbzO5 per C.C. of -N 1V Solution. Grni . 0.00763 0~00801 0.00834 0.00705 A higher permanganate equivalent might, of course, be due to impurity in the niobium pentoxide used. This had been repeatedly ignited ; finally at a temperature of l,OOOo C. (measured) for one hour, and may be taken as free from SO, and water.I t seemed possible that it might contain some tantalum. Part of it was therefore fractionated by Marignac's method, nearly equal quantities of soluble and insoluble double potassium fluorides being obtained. Experiments 23 and 24 were made on portions of the more soluble oxides, and are in good agreement with the others made on unfractionated material.Some possible sources of error were next examined, with results collected in Table IV. In Experiments 25, 26, and 27, evaporation was not carried nearly as far as before, with the result that a little more hydrofluoric acid remained in the liquid, and reduction stopped shorb of the point reached before. Hence some little care is needed in the final stage of the evaporation.On one hand, enough hydrofluoric acid must be present to give a perfectly clear solution in hydrochloric acid; on the other, the quantity must be so small as not to interfere with the reduction. The Hence tantalum was not present.210 LEVY : ESTIMATION OF NIOBIUM IN PRESENCE OF TANTALUM, operation is quite similar to the corresponding stage in the separation of bismuth as oxychloride from copper.::: I t wag found that whenever the correct degree of evapo- ration was reached, a bulky white precipitate separated out from the solution shortly after the end of the titration, usually within fifteen to thirty minutes, or even less.If this precipitation does not take place, the result obtained should be treated with suspicion, probably being too low.Unfortunately, this indication is only given at the end of the whole determination. TABLE IV. Variozts Sources of Error. - NO. __ 25 26 27 28 29 30 31 * 32 33 34 NbzO, taken. Grm. 0.0972 0.1168 0.1334 0.0930 0.1116 0.0916 0.0584 0.0462 0.0362 0.0842 A KMn04 required. c. c. 10-78 13.70 15-21 10.73 12.92 10.29 5-90 2-93 2.69 8.97 Nb20, per C.C. Grm . 0*00902 0.00853 0.008 7 7 0.00866 0.00864 0.00890 0.00990 0-01 5 76 0.01345 0,00939 Conditions.Too much HF left. 9 , 7 7 ?, 9 , 9 7 9 ) 0*13grm.Ta205 present. Concentrated HCI ; no water. 7 7 2, Y ? Too finely divided Zn. 9 9 Y 7 Y, No hydrogen. Poor supply of hydrogen. 9 7 ¶, 32 Two experiments, Nos. 28 and 29, were made to see whether in concentrated hydrochloric acid reduction will go further than in the 2 : 1 mixture used.I n Experiment 28 the reduction flask was cooled in water during the first part of the reduction, whilst in No. 29 it stood on the bench as usual. I n both cases reduction did not go as far as when a little water is present. Experiments 30 and 31 were made using very small pieces of granulated zinc. Dissolution only took a short time, end reduction was not complete.In Experiment 32 no hydrogen was passed into the reduction flask ; in Nos. 33 and 34 the hydrogen- supply was purposely interrupted for short periods during reduction. As was expected, these experiments gave poor results. I t is advisable to insert the stopper and to start a good current of hydrogen as soon as the zinc has been placed in the flask. By doing this one is sure of having swept all air out of leading tubes, etc., by the time the evolution of hydrogen in the reduction flask itself slackens.Mixtures of niobium pentoxide with tantalum pentoxide were next analysed by this method, using the factor 0.00834 found above. The results are given in Table V. They are nearly as good as those found with pure niobium oxide, with the exception * An easier, if less simple, alternative is possible: The original solution may be evaporated to dryness, and the residue taken up by heating with 10 C.C.of very dilute (1 : 30) hydrofluoric acid. Solution is complete in less than ten minutes. I have used this variation in a few cases with good results.AND SOME REACTIONS OF TANTALUM COMPOUNDS 211 of the last three, in which the proportion of niobium oxide to tantalum oxide is small.I believe that this represents the difficulty of driving off enough of the hydrofluoric acid in presence of much tantalum fluoride. If much tantalum is present, it appears to be best to conduct the final evaporation at as high a tem- perature as possible without boiling, as otherwise tantalum is apt to separate out in a gelatinous form before the proper degree of concentration is reached.TABLE V. Mixtures of Nb20, and Ta20,. NO. 35 36 37 38 39 40 41 42 43 Nb20, taken. - Grm. 0.0946 0.1215 0.1329 0.0442 0.1516 0.1073 0.0314 0.0146 0.0070 TaaO, taken. GITl. 0.0803 0.1272 0.0798 0-1000 0.1766 0.0750 0.1400 0.1704 0.0750 & KMnO, required. - c. c. 11.17 14.48 15.85 5-27 18.19 12.92 3.54 1 -37 0.39 NbzOj found.~ _ _ _ _ Grm. 0.0932 0-1208 0,1322 0.0440 0.1517 0.1077 0.0295 0.0114 04033 Error. Grm. - 0.0014 - 0*0007 - 0*0007 - 0.0002 + 0~0001 + 0.0004 - oooo19 - 0.0032 - 0.0037 Finally, some experiments were made on a sample of mixed oxides of niobium and tantalum, the results being given in Table VI. Experiments 44 to 47 were made using the method given above. I n Experiments 48 and 49 the effect of having alkali present was studied.For this purpose the mixed oxides, together with 1 grm. of potassium fluoride, were dissolved in 5 to 7 C.C. of hydrofluoric acid, and the solution carefully evaporated almost to dryness on the hot plate. The residue was then further heated over a Bunsen burner, very cautiously at first, more strongly as the melt solidifies, and finally to redness, when a clear melt is obtained.The melt was broken up by warming with a little water in the crucible, transferred to the reduction flask, the remainder of the 20 C.C. water and 40 C.C. of concentrated hydro- chloric acid was added, solution completed, and the estimation finished as before. It will be seen that the results obtained in this way agree well with those obtained in the absence of alkali.This is at variance with Osborne's results, though, as noted above, these are mutually contradictory.* Experiment 50, though not made on the mixed oxides, but on nearly pure niobium oxide, may be cited here. The procedure was the same as for Experiments 48 and 49, except that the residue obtained by evaporation was not fused but only heated very gently-ie., much of the acid potassium fluoride was left undecomposed.Only 85-86 per cent. of the Nb,O, * In Marignac's well-known test (Zeitsch. anal. Chem., 1868, 7, 112) for titanium in presence of niobium, which depends on the non-reduction by zinc of niobium in presence of potassium fluoride, the conditions are very different, very dilute hydrochloric acid (sp.gr. 1 '015, or even less) being used, and the solution being perfectly cold.212 LEVY : ESTIMATION OF NIOBIUM IN PRESENCE OF TANTALUM, present was found, showing the need for fusing and expelling as much hydrogen fluoride as possible. To test the influence of more dilute acid in presence of alkali, Experiments 51 and 52 were made, proceeding as in Experiments 48 and 49, except that in Experiment 51, 45 C.C.hydrochloric acid and 45 C.C. water were used, and in Experiment 52, 40 C.C. hydrochloric acid and 40 C.C. water. The results obtained are considerably lower than those gi'ven by the stronger acid. Experiments 53 and 54 were next made on mixtures of these mixed oxides with more tantalum oxide, proceeding as in Nos. 48 and 49, but using 2 grms.potassium fluoride. The results obtained are much too low. Experiment 55, in which twice the usual quantity of all the reagents was used in order to diminish the concentration of the alkali fluoride, gave a higher result, but still much below the truth, TABLE VI. Experiments on a Sample of Nixed Oxides of Nb and Ta. No. - 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 - Nh05 taken.Mixed Oxides taken. G m . 0.2002 0.2012 0.2212 0'1978 0.2217 0.2076 0.2084 0.2040 0.1170 0-0966 0.1092 0*2030 0.2108 0.2317 - N m KMn04 *equired C.C. 14-30 14.35 15.72 14-05 15.87 14.74 10.95 14.50 14.06 5.90 4-13 6.53 17-34 17.78 19-65 NbO5 found. arm. 0.1192 0.1197 0'1311 0.1172 0.1324 0.1229 0'0914 0.1210 0'1172 0.0492 0,0345 0.0545 0.1223 0.1254 0.1386 NW5 found. -. . - 'er Cent 59.54 59.50 59.27 59 -24 85-86 58-03 57.48 42-07* 35*67* 49W* 60.24 59'50 59.81 I z:> E22.Average 'er Cent 59.39 59-44 - - - - - - 59-85 Remarks. Standard fluoride method. Fusion with 1 ,qm. KF. 1 grm. KF ; not fused. 45 C.C. HCI, 45 C.C. H20 40 l l 40 } fusion. 1 grm. KF 40 1' 2o ' 1 40 20 B 9 80 40 l l fusion. Metzger and Taylor's method, One-half grrn. of the same mixed oxides was next analysed by Marignac's method, only one crystallisation being made : 45-36 per cent.of tantalum oxide and 54.33 of niobium oxide were obtained. Instead of carrying out a second fractiona- tion as usual, each oxide was analysed by the volumetric method. The niobium portion gave 54-10 per cent. of niobium oxide-that is, it was nearly pure; the tantalum fraction gave 4.67 per cent, of niobium oxide, or a, total of 58-77 per cent. of niobium oxide.The fact that this is 0-62 per cent. below the value 59.39 per cent. found volumetrically I ascribe to the tendency previously noticed of the volumetric method to give low results in mixtures containing much tantalum oxide. The tantalum portion probably contained more niobium oxide than that here found.The same sample of mixed oxides was finally analysed by Metzger and Taylor's method, Experiments 56, 57 and 58 of Table VI, The procedure given by these * These percentages are calculated on the "mixed oxides " taken, and are directly comparable with all others in the same column, except No. 50, which relates to the Nb20, taken.AND SOME REACTIONS OF TANTALUM COMPOUNDS 213 authors was closely followed, with the exception of three unimportant details : (1) As a matter of convenience, hydrogen was used as inert gas instead of carbon dioxide.(2) An ordinary burette tube of 4-inch bore was used as reductor instead of the Q-inch bore tube recommended. The succinic acid solution froths slightly, however, and probably the wider tube permits easier working, (3) Instead of adding the 20 C.C.succinic acid solution in a fine stream from a wash bottle, it was poured in a little at a time along a stirring rod. There was no trace of turbidity at this point. A blank of 0.3 C.C. was found. The method works well, and the results obtained do not differ more from each other than those found by Metzger and Taylor on similar samples. The average result is 0.46 per cent.higher than the average of the fluoride method, which seems fair agreement. One point may be mentioned here : Metzger and Taylor state that succinic acid is not affected by permanganate in acid solution. This seems to be true only if the temperature is kept low. To test this point, 3 grms. of succinic acid were dissolved in 390 C.C. water and 45 C.C. sulphuric acid, this being the approximate concentration of the reduced solution in Metzger and Taylor’s method, 10 grms.of zinc dissolved in the solution, and its action on potassium permanganate solution noted. At 48O C. it required several C.C. to produce a red colour ; by the time the liquid had cooled to 3 6 O C., several C.C. more could be run in before a red colour appeared.In another experiment 0*1101 grm. of succinic acid was dissolved in 50 C.C. of water and 5 C.C. of snlphuric acid. After heating, the solution required 3-25 C.C. & per- manganate solution before a permanent red colour was obtained, the temperature at the end of the titration being 67O C. Although the end-point in Metzger and Taylor’s method seems perfectly sharp, I am inclined to attribute an occasional high result to this oxidation of succinic acid, and would advise that the receiving flask be cooled whilst the solution runs through the reductor.Comparing Metzger and Taylor’s with the fluoride method, the first can be carried out in about one to one and a half hours, and works smoothly, but demands nearly continuous attention. The second takes about one and a quarter to two hours, and requires little attention except for a short time during the final evapora- tion, but this operation demands a small amount of judgment.The fluoride method has a tendency to give low results with low percentages of niobium oxide, but, even so, the results are at least as concordant as those given by the succinic acid method. Both volumetric methods give results which appear to be more accurate than those given by Marignac’s method in a very much shorter time and with less labour.THE SOLUBILITY OF TANTALUM AND NIOBIUM OXIDES IN HYDROFLUORIC ACID, AND THE VOLATILITY OF TANTALUM FLUORIDE. In 1900, in the course of experiments made in the laboratory of Mr. B. Blount, I noticed that tantalum and niobium oxides, both separately and when mixed together, are readily soluble in hydrofluoric acid of ordinary strength (48 per cent.), even after strong ignition (ANALYST, 1901,26,64).The solubility is a little irregular ; at moderate temperatures considerable quantities of acid can be evaporated in con- tact with the oxides without much solution taking place. At temperatures near but214 LEVY: ESTIMATION OF NIOBIUM IN PEESENCE OF TANTALUM, well below the boiling-point, however, solution is quite rapid, especially if the liquid is brought to this temperature quickly.Thus, in one experiment 0.14 grm. of tantalum oxide which had been ignited for three-quarters of an hour in a covered crucible at the hottest temperature of a coal-gas air blowpipe flame dissolved com- pletely in less than ten minutes in about 5 C.C.hydrofluoric acid heated to about 90” C. Niobium oxide is still more easily soluble. Thus, Roscoe and Schorlemmer (vol. ii., p. 935, 1907 edition) state that “the ignited (tantalum) oxide does not dissolve in any acid, but volatilises completely when ignited with ammonium fluoride.” Even Moissan’s ‘( Trait6 de Chimie Minerale ” (vol. ii., p.158, 1905) states that (‘ strongly ignited niobium oxide is insoluble in sulphuric, hydro- chloric, nitric, and hydrojuoric acids, and on p. 151 that “tantalum oxide is not soluble in acids even on boiling.” Ruff and Schiller (Zoitsch. anorg. Chm., 1911, 72, 349), on the other hand, have more recently found that even quite dilute hydrofluoric acid dissolves the ignited oxides on prolonged boiling under a reflux condenser, and that stronger acid effects solution readily at a boiling temperature.In the same paper (p. 334) Ruff and Schiller give four experiments, in two of which tantal’um oxide was dissolved in hydrofluoric acid, the solution evaporated to dryness, the residue dried and ignited. In the other two the procedure was similar, but sulphuric acid w a ~ added to the fluoride solution, The authors state that there was no loss in any of these experiments.(As a matter of fact, in three experiments there were losses of 0.30, 0.62, and 0.27 per cent. ; in the fourth there was a gain of 0.15 per cent., probably due to SO,.) They conclude that tantalum fluoride solutions can be evaporated to dryness and the residue ignited without any loss, both when sulphuric acid is present and when it is not.They also state that tantalum oxide can be repeatedly ignited with ammonium fluoride without any loss, and that the double fluoride of potassium and tantalum can be ignited without loss of tantalum. Some of these conclusions are in direct opposition to results found by me in the paper cited above. I there stated that ‘‘ it was found that neither niobic nor tantalic oxide volatilises when treated with HF and H,SO,, and that niobic oxide does not form volatile compounds even when treated with HF alone, but that tantalic oxide by the action of HF loses in weight each time the operation is repeated,” and on fusing a mixture of about two-thirds niobium oxide and one-third tantalum oxide with acid potassium fluoride a loss of over 7 per cent.was noticed. My results were largely in accord with Rose’s (Pogg. AnnaE., 1856, 99, 481), who found very large losses of tantalum on igniting (a) residues from fluoride solutions, ( b ) mixtures of tantalum oxide with ammonium fluoride, and (c) the double potassium tantalum fluoride. Rose also found, however, small losses (about 1 per cent.) when sulphuric acid was present in the tantalum fluoride solutions, and the incorrectness of this result, familiar to every analyst, has thrown doubt on the rest of his work.Ruff and Schiller’s statements led me to repeat some of my work of fourteen years ago, as follows : 0.1530 grm. of pure tantalum oxide was ignited for twenty minutes over a blowpipe; it then weighed 0.1529 grm.I t was next dissolved in about 5 C.C. of Most of the standard textbooks continue to state the contrary.AND SOME REACTIONS IN TANTALUM COMPOUNDS 215 hydrofluoric acid, the solution evaporated to dryness on a hot plate as quickly as possible without boiling, and the residue ignited first very gently over a Bunsen burner, then more strongly, and finally for twenty minutes over the blowpipe.Dense white fumes came off during the early stage of the ignition, which in small part settled on the upper portion of the crucible. The weight at the end of the operation was 0.1182 grrn., a loss of 22-7 per cent. The operation was repeated, but this time the residue was baked for about ten minutes on the hot plate before igniting; the weight obtained was 0.0988 grrn., a loss of 16.2 per cent., appreciably less than in the first experiment.This 0.0988 grm. of tantalum oxide was next dissolved in 5 C.C. of hydrofluoric acid together with 1 grm. of potassium fluoride, the whole evaporated nearly to dryness on the hot plate, and then heated over a Bunsen burner, at first very cautiously, then more strongly, and finally at a red heat until a clear fusion was obtained.I t was kept at this temperature for about five minutes, allowed to cool, heated with sulphuric acid for about twenty minutes, and boiled with water. The oxide was filtered off and ignited as before. It weighed 0-0790 grm., showing a loss of 20.0 per cent. The operation was repeated, but this time the potassium fluoride melt was only just melted ah a red heat and allowed to cool at once.The weight obtained was 0,0744 grm., or a loss of only 5.8 per cent. The hydrofluoric acid used in all these experiments was taken from a freshly opened bottle. The experiments were made in a room free from all fumes. Finally, a single experiment was made in which 0.0828 grm. of well-ignited tantalum oxide was heated with 1 grm. of ammonium fluoride, at first very gently, aad finally to redness.The melt behaved much like the double potassium fluoride, but near a red heat copious and dense white fumes were evolved, which I have not observed with the potassium salt. The ignited oxide obtained weighed 0.0442 grm., a loss of 46.6 per cent. Whilst Ruff and Schiller’s experiments show that there are special conditions which minimise the loss on igniting residues from tantalum fluoride solutions, potassium tantalum fluoride, and mixtures of tantalum oxide with ammonium fluoride, I think that the experiments just cited, together with my earlier work, show that in general the loss to be expected in these operations is very considerable. SUMMARY.A volumetric method for the estimation of niobium in presence of tantalum is described.The method is based on the fluoride method of Osborne, but reduction only goes as far as an oxide, Nb,,-,Ol7, with an +$ permanganate equivalent of 0-00834 grm. per C.C. It is shown that large losses of tantalum are caused by (a) dissolving tantalum oxide in hydrofluoric acid and igniting the residue obtained on evaporation to dryness ; ( b ) igniting potassium tantalum fluoride with excess of potassium fluoride at a red heat ; and ( c ) igniting mixtures of tantalum oxide and ammonium fluoride.216 LEVY : ESTIMATION OF NIOBIUM IN PRESENCE OF TANTALUM, Ta2O, per cent.... Sp. gr. ... ... Nb20, ,, ,, ... APPENDIX. ddetxger and Lamme on the Specifi Gravities of Niobizcm and Tantalum Oxides. Foote and Langley (Chem. News, 1911, 103, 52; in ANALYST, 1911, 36, 239) have determined the specific gravities of mixtures of niobium and tantalum oxides precipitated and ignited together, and show that the results do not fall on a straight- line curve.Their somewhat irregular curve is reproduced and apparently adopted by Mellor (‘( Quantitative Inorganic Chemistry,” 1913, p. 423). I t was my intention, if time permitted, to make some experiments by this method, but I find that the field has been pretty well covered by M.A. Lamme working under Dr. Metzger (Ic Columbia University Dissertation,” 1909). By the latter’s kindness I am permitted to refer here to these results, which have never been published. Lamme found that the specific gravity of both oxides varied with the degree of ignition, and to a much smaller extent with the method of preparation.He obtained his oxides by decomposition of the fluorides with sulphuric acid, using a small amount of ammonia in the final washing. Ignition of from thirty to ninety minutes in a coal-gas air blowpipe flame was necessary to give constant results. The specific gravity of niobium oxide decreases, whilst that of tantalum oxide increases, with prolonged ignition. On account of many difficultiee with water, the specific gravities were finally compared with that of chloroform at its boiling-point.Quantities of a little over 1 grm. were generally used. The results obtained are given in Table VII. 0 3.265 100 TABLE VII. Zetzger and Lamme’s Results for Specijc Gravities of Mixtures of Nb205 and Ta205 referred to that of Boiling Chloroform.89.80 10 -20 5.843 100 0 6.201 On plotting these, it is seen that up to 40 per cent. of Nb20, the results lie on a straight line a little below and parallel to that connecting the specific gravity of the pure oxides. From 50 to 90 per cent. of Nb20,, the results lie on a, second straight line considerably below and inclined to the pure oxide line.Between 40 and 50 per cent. there is a very sharp break in the curve. A mineral which by Metzger and Taylor’s volumetric method showed on an average 54.21 per cent. of Nb20, and 22.75 per cent. of T%Os, was analysed in triplicate by this method. The specific gravities found were 3.612, 3.616, and 3.577, which, allowing for the slightly different amounts of total oxides obtained, gave values 57.43, 57.47, and 58-75 per cent.of Nb205 and 19.82, 19.68, and 18.16 per cent. of Ta20, respectively, differing by 2.93, 2.87, and 4-59 per cent. of Ta205 respectively from the results of the volumetric method.AND SOME REACTIONS IN TANTALUM COMPOUNDS 217 Lamme concludes that the method can only be relied on to an accuracy of about 5 per cent. (on the mineral).Incidentally, Lamme mentions a fact which I have often noticed-namely, that crystallised potassium bisulphate decomposes the mixed oxides (and some minerals) more rapidly than does the fused pyrosulphate. My experience is that the bisulphate should be fused at a low temperature just before the oxides are added. If pyrosulphate only is available, it may be made much more active by adding a little concentrated sulphuric acid.I n conclusion, I have great pleasure in thanking Professor F. J. Metzger for the generous gift of some of his carefully purified tantalum and niobium oxides. To the authorities of the Department of Uetallurgg, more especially to Emeritus Professor Henry M. Howe, I am greatly indebted for permission to carry out this work at the School of Mines, Columbia University, in the City of New Pork.DISCUSSION. The PRESIDENT, in inviting discussion, remarked that the increase which had taken place during recent years in the commercial value of minerals containing niobium and tantalum made the estimation of these elements a matter of the greatest importance, while its difficulty was illustrated by a case which had recently been brought to his notice, in which the results obtained by three expert analysts had varied in an extraordinary manner.The method dealt with by Mr. Levy depended on the reduction of the higher oxides, not to some definite, well-defined oxide, but to an intermediate stage of oxidation. Under such circumsbances it was necessmy that the conditions of reduction should be very clearly defined, and he thought that perhaps the chief merit of Mr.Levy’s paper was that he had done more than any of his predecessors in laying down those conditions clearly. The necessity for such clear definition was illustrated by the case of the closely related element vanadium, V20, being reduced to V20, by sulphur dioxide, to V20, by magnesium, and to V202 by zinc.About ten years ago, in a paper read before the Society relating to molybdenum and vanadium, he had called attention to the very different results that one obtained, not merely when using different reducing reagents, but when using different qualities of zinc. Thus, he had shown that different results were obtained with an alloy of zinc and platinum on the one hand, in which case the potential of the hydrogen was low, and an alloy of zinc and cadmium on the other, when the potential of the hydrogen was higher.I n another paper com- municated to the Society he had detailed some experiments on the reduction of molybdenum and vanadium oxides with palladium-hydrogen, and it might be inter- esting to know to what extent the reduction would go in the case of tantalum and niobium. His impression had hitherto been that tantalum oxide was not easily volatilised on heating with ammonium fluoride, and he had quite recently repeated the experiment. On heating 0.244 grm. of pure ignited tantalum pentoxide with 3 grms. of ammonium fluoride, the ultimate loss of weight was found to be only OaOO9 grm., or 3.7 per cent.-a result which seemed to indicate that tantalum oxide was not as volatile under these conditions as was usually stated in the textbooks. He218 J. CECIL JONES: ESTIMATION OF METHYL ALCOHOL thought the Society was to be distinctly congratulated on this admirable communica- tion, and it was a further source of gratification that the work had been carried out under the Society’s Investigation Scheme. Dr. W. R. SCHOELLER agreed that the solution of the problem of estimating niobium in presence of tantalum lay in a volumetric method, the conditions of the reduction being very carefully laid down. The method of fractional crystallisation and precipitation of the niobium-potassium oxyfluoride would only be successful in the hands of a highly experienced chemist, and would not be of much use for the purposes of a commercial laboratory. The determination of the specific gravity, after Foot and Langley’s method, had the disadvantage of requiring rather a large quantity of the chemically pure mixed oxides, such as it was difficult to obtain by decomposition of the ore. He had found that in the presence of succinic acid the pink colour produced by permanganate vanished very quickly, and if this modifica- tion could be adopted it would be a distinct advantage. I t was much more difficult, in the presence of tantalum, to estimate small quantities of niobium than large quantities. In Marignac’s process the quantity of potassium fluoride added was rather important. If too much were used, the separation was much more imperfect than with the exact quantity prescribed. Mr. BLOUNT agreed that the conditions must be very carefully defined, because it was not to be supposed that the oxide obtained was a definite oxide, nor that the extent of oxidation would not vary if the conditions were altered. I t was obvious that the process of Marignac was out of the question for ordinary commercial work, but there was no doubt that for really crucial work Marignac’s process was the best.

ISSN:0003-2654    

DOI:10.1039/AN9154000204

出版商:RSC    

年代:1915

数据来源: RSC

摘要:

218 J. CECIL JONES: ESTIMATION OF METHYL ALCOHOL ESTIMATION OF METHYL ALCOHOL IN PRESENCE OF ETHYL ALCOHOL. BY G. CECIL JONES, A.C.G.I., F.I.C. MANY methods for the detection and approximate estimation of methyl alcohol in presence of ethyl alcohol have been based on the oxidation of the former to formal- dehyde, for the detection of which many delicate reagents are available. So delicate are these reagents for formaldehyde that most extravagant claims have been made for the corresponding methods for the detection of methyl alcohol, regardless of the fact that it is impossible to oxidise methyl alcohol to formaldehyde without simul- taneously oxidising ethyl alcohol to acetaldehyde, which reacts with many of the reagents, and difficult to avoid some oxidation of ethyl alcohol to formaldehyde itself.These facts should have been generally known at least since Scudder published his review (J. Amer. Chem. Soc., 1905, 27, 892) of the methods available for the estimation of methyl alcohol in presence of ethyl alcohol, but scarcely a year elapses without the appearance of one or more methods of this type, novel-if at all-only in the choice of reagent for formaldehyde, and generally accompanied by claims to delicacy which cannot be substantiated. Until the appearance of Denigds’ method in 1910, it is doubtful if any of these methods could be depended on to detect lessIN PRESENCE OF ETHYL ALCOHOL 219 than 2 per cent.of methyl alcohol in strong spirit. Hinkel (ANALYST, 1908, 33, 417) put the limit of such methods at 5 per cent.Clearly a method which could only just differentiate between ethyl alcohol and industrial spirit, and could not detect adulteration of the former with 50 per cent. of the latter, was of little practical use. Denigds’ method (Compt. rend., 1910, 150, 832), framed with due regard to the facts mentioned above, constituted a very notable advance. The conditions of oxidation are so chosen that ethyl alcohol never gives rise to enough formaldehyde to affect the reagent used for the detection of that substance, and the final test- with Schifs solution-is made in so strongly acid a medium that acetaldehyde develops no coloration.A much more convenient practice is to dilute the liquid to be examined until it contains 10 per cent, of total alcohols, and to operate on 5 C.C.of this solution, as direcbed by Simmonds (ANALYST, 1912,37,16). This author’s directions for carrying out DenigBs’ method need only trifling amendment, but the writer, who had some difficulty before he discovered the limitations of the method and could confirm the claims made for it, thinks the following notes may prove useful : Simmonds’ directions are very brief, and it will be convenient to reproduce them here.He writes : The alcoholic liquid is first purified, where necessary, either by the method of Thorpe and Holmes or by other suitable means. I t is then diluted with water or mixed with ethyl alcohol until it contains 10 per cent. of total alcohol by volume. “To 6 C.C. of this prepared liquid, contained in a wide test-tube, are added 2-5 C.C.of potassium permanganate solution (2 per cent.), and then 0-2 C.C. of strong sulphuric acid. When the reaction has proceeded about three minutes, 0.5 C.C. of oxalic acid solution (9.6 grm. crystals per 100 c.c.) is added. On shaking, the liquid becomes clear or nearly colourless. One C.C. of strong sulphuric acid is now run in and well mixed with the solution, which is finally treated with 5 C.C.of Schiffs reagent. A violet colour is developed in the course of a few minutes, unless mere traces of methyl alcohol were present, when twenty or thirty minutes may be required. “ A preliminary experiment carried out as described serves to detect the presence of methyl alcohol and to give some idea of the quantity. According to the indications thus obtained, another part of the prepared liquid is further diluted, if necessary, with ethyl alcohol of 10 per cent.strength, until it contains from 0.001 to 0.004 grm. methyl alcohol in 5 c.c., and the experiment is repeated side by side with two or more standards for comparison. These contain 0.001, 0.002, 0-003, etc.: grm. methyl alcohol in 5 C.C. of 10 per cent. ethyl alcohol.” In his original paper (Com,t.rend., 1867, 64, 182), Schiff gave no formula for his reagent beyond that it was a solution of rosaniline sulphite in sulphurous acid. The many different formulae in the textbooks are due to Gayon, Mohler, and others, and usually prescribe the use of fuchsine with varying quantities of sodium bisulphite and mineral acid. Two such solutions, selected a t random from modern textbooks, failed to give any colour when applied to ethyl alcohol containing 5 per cent.of Deniges worked on 0.1 C.C. of strong spirit. In the first place, “Schiffs reagent” is an ambiguous term.220 J. CECIL JONES: ESTIMATION OF METHYL ALCOHOL methyl alcohol that had been oxidised as directed by Simmonds. By reducing the amount of acid directed by Simmonds to be added immediately before the Schiffs reagent, they might have been made to work, but this was not followed up, as the stock Schiff solution of the writer’s laboratory was found to serve well.It is important, however, to note that the formula of the Schiffs reagent used has a marked influence on the sensitiveness of the test. In the writer’s laboratory Schiffs solution is prepared by dissolving 0.2 grm.of magenta base in 10 C.C. of a freshly prepared, cold, saturated aqueous solution of sulphur dioxide, and after twenty-four hours diluting the solution to 200 C.C. with water. Such a solution is very sensitive, and will develop a distinct colour within a minute or so, even with such substances as vanillin or salicylic aldehyde. I n the notes that follow the use of Schiff’s solution of this composition is assumed.The amount of permanganate used must be rigidly adhered to in quantitative work, since it determines the amount of formaldehyde formed and the final colour intensity. The use of 2 C.C. in place of 2.5 C.C. reduces the final colour intensity about 30 per cent., whilst the use of 5 C.C. more than doubles the sensitiveness of the test, when all other conditions are kept the same, except that the use of 5 C.C. of permanganate necessitates the subsequent use of nearly 1 C.C.instead of 0.5 C.C. of oxalic acid solution. Provided all the other standard conditions are rigidly adhered to, this is the simplest and safest way of increasing the sensitiveness of the test, as ethyl alcohol under these conditions yields no formaldehyde and no colour, but the permissible latitude in some of the other measurements then becomes narrower.The amount of sulphuric acid added with the permanganate is less important. The amount of formaldehyde formed is greater with more acid, but, within the limits 0.1 to 0.3 c.c., the final results are indistinguishable, owing to the compensating effect’of the higher final concentration of acid reducing the intensity of colour due to a definite quantity of formaldehyde. Larger quantities, however, might lead to the formation of formaldehyde from ethyl alcohol itself.The exact concentration of acid necessary to bring this about was not determined, but Denighs’ original paper shows that if 0.7 C.C. of sulphuric acid were present in a total volume of 8 c.c., formaldehyde would certainly be produced from ethyl alcohol.The time allowed for oxidation, provided it be not less than three minutes, appears to be without effect. The influence of temperature may not be negligible, but the point was not investigated, as the temperature might be expected to be constant in any one set of experiments, and duplicate experiments run simul- taneously without any special precautions to insure uniformity of temperature invariably gave identical results.Of all the reagents used, oxalic acid is the one of which the exact concentration is least important. For some reason, not plainly evident, ‘Simmonds gives the concentration of this reagent with exceptional precision-namely, 9.6 per cent. As a, matter of fact, solutions of oxalic acid of this strength deposit crystals at ordinary temperatures.The writer uses 0.5 (3.0. of a cold, saturated solution. Not much less will reduce the excess of permanganate in the cold, faintly acid solution, but larger quantities, up to 1 c.c., appear to have no measurable influence on the results.IN PRESENCE OF ETHYL ALCOHOL 221 The subsequent addition of sulphuric acid must be as nearly as possible the same in any one set of experiments, and is most conveniently made 1 c.c., as directed by Simmonds.With only 0.6 C.C. added, the acetaldehyde derived from the ethyl alcohol will give a distinct coloration with Schiffs solution of the character described. With 0.75 C.C. or more, pure ethyl alcohol gives no purple or even blue colour, provided all the other standard conditions are rigidly adhered to, but it is unwise to reduce the amount below 1 C.C.except in very special circumstances, where it, is necessary to make the test as sensitive as possible. In such cases the sensitiveness of the test can be increased 40 per cent. by using only 0.75 C.C. of acid, but very careful control experiments become necessary.On the other hand, not more than 1 C.C. of acid should be used, as the use of so much as 1-25 C.C. reduces the sensitiveness of the test about 30 per cent., whilst 1.5 C.C. reduces it 50 per cent., and 2 C.C. nearly 90 per cent. If 10 C.C. be taken instead of 5 c.c., the acid concentration is so much reduced that even the acetaldehyde from ethyl alcohol develops a colour; On the other hand, the use of only 2 C.C.in place of 5 C.C. reduces the amount of colour developed by a fixed quantity of formaldehyde about 90 per cent. The method is thus eeen to be very sensitive to small variations in the experi- mental conditions, a fact that cannot have escaped Simmonds, but which is not emphasised in his paper. I t is, however, quite easy to secure sufficient uniformity in the preparation of the assay and comparison liquids, and it is quite worth while, for the method is incomparably quicker than any other with any pretence to accuracy, and, if conducted with care, is at least as accurate as any.As described above, it will not detect much less than 0.2 per cent, of methyl alcohol expressed as a per- centage of the.tota1 alcohols.This is sensitive enough for almost any purpose, but if greater sensitiveness be needed, the foregoing notes indicate the directions in which the test should be modified so as to show 0.1 per cent., or even less. They also show that it is scarcely advisable to strive after the utmost sensitiveness unless some substantial reason exists for doing so. Proportions of the order of 1 per cent.can be estimated with an error not exceeding 1 part in 20. Finally, the amount of Schiff’s solution taken is not without influence. DISCUSSION. The PRESIDENT, in inviting discussion, remarked that, particularly when the quantities of methyl alcohol were small, processes depending on oxidation under strictly defined conditions were liable either to under-estimate or to over-estimate the quantity of methyl alcohol to a considerable extent, and for that reason he felt that Mr.Jones had done good service in investigating what was perhaps one of the best of such methods, and in emphasising the need for close adherence to the condi- tions laid down by the original author. Mr. A. E. PARKES said that in his experience even small quantities of perman- ganate would oxidise ordinary ethyl alcohol, and he asked whether, under the condi- tions of this process, it was possible to oxidise methyl alcohol without oxidising the222 ESTIMATION OF METHYL ALCOHOL IN PRESENCE OF ETHYL ALCOHOL ethyl alcohol.Any acetaldehyde that might be formed would, of course, give a strong reaction with Schiff’s reagent, just as formaldehyde would.Mr. F. H. LEES said that it seemed difficult to understand why the sensitiveness should be increased by the use of a larger quantity of permanganate. One explana- tion that suggested itself was that more acetaldehyde wag produced when more permanganate was used, and that the final acidity of the solution to which Schiff’s reagent was added was then not suffioient to prevent the acetaldehyde from producing a coloration.Mr. W. T. BURGESS asked what precautions were taken in the measurement of the small quantities in whioh some of the reagents were added. In measuring accurately a liquid like strong sulphuric acid, he should expect Bome difficulty to be experienced when the quantity was as small as 1 C.C. Mr. JONES, in reply, said that permanganate under these conditions certainly did oxidise ethyl alcohol to acetaldehyde, but it would be found that, in presence of the quantity of sulphuric acid which was added at the end, the acetaldehyde would give no coloration with the Schiffs reagent described in the paper or with that described in the British Pharmacopoeia.No formaldehyde was formed from ethyl alcohol under these conditions.He thought that the increased sensitiveness when more permanganate was used was due to the production of more formaldehyde. Although this method of estimating methyl alcohol was more or less quantitative, the oxidation of methyl alcohol to formaldehyde was by no means quantitative. With regard to the question of measuring, since, in the case of the permanganate solution, the use of 5 c.c., instead of 24 c.c., would result in an over-estimate of 100 per cent., if 2.6 C.C. were used the error would be 4 per cent., and it should certainly be possible to measure such a quantity with a smaller error than 1 in 25. For the sulphuric acid he used a 1 C.C. graduated pipette with a very fine orifice, giving about 5 drope to 0-1 C.C. I t was only necessary to add the same number of drops in the control experiment as in the other, and that could certainly be done with all the accuracy that the test required. If 12 C.C. of sulphuric acid were used, the sensitiveness would be increased by 30 per cent. It was quite easy to measure the 1 C.C. so closely that the method was accurate within 5 per cent., and more than this he did not expect from it.

ISSN:0003-2654    

DOI:10.1039/AN9154000218

出版商:RSC    

年代:1915

数据来源: RSC

摘要:

THE ANALYSIS AND EVALUATION OF RUBBER AND RUBBER GOODS 223 RECENT ADVANCES IN THE ANALYSIS AND EVALUATION OF RUBBER AND RUBBER GOODS.* BY PHILIP SCHIDROWITZ, PH.D. I. CRUDE RUBBER. THE examination of crude rubber may involve : (a) Chemical Analysis, with a view to determining the quantity of pure rubber and of various “impurities,” and, to a certain extent in some instances, the nature of the latter.(b) Physical or Mechanical Tests, carried out either on the crude material or on the latter modified by the vulcanisation process, with a view to determining the physical or mechanical qualities of the rubber substance. Hitherto chemical analysis has played a somewhat subordinate part in the commercial evaluation of crude rubber, partly on account of our lack of exact know- ledge regarding the nature of the secondary products (resins, nitrogenous substances, etc.), partly owing to the absence of specific information on the influence exercised by them on the vulcanisation process on the one hand, and on the more important attributes (strength, elasticity, etc.) on the other hand. If the difficulties associated with the chemical investigation of the nature and influence of the “impurities ” neceesarily make progress in this direction slow, it is not surprising that work having as its object the identification and evaluation by chemical means of different rubber substances or caoutchoucs, is still in a more or less embryonic state.I n this connection, however, may be mentioned the work of Gottlob (Gummi-Zeit., 1907, 22, 305; of Harrieg, Annalen, loc.cit., infra) on the fission products of caoutchouc ozonides obtained from rubber of different sources, and of Harrieg on the rate of decomposition of these substances (Annalen, 1913,395,211 ; Zeitsch. angew. Chem., 1912, 25, 1457; Ber., 1908, 41, 3552). Some comparatively recent work by Caspari (J. Soc. Chem. Ind., 1913, 32, 1041) suggests the possibility of discriminating, up to a point, by physico-chemical methods, between caoutchoucs of different commercial quality.According to Caspari, rubber is of a composite character, and consists (1) of aoluble ” rubber-a weak but elastic colloid, soluble in light petroleum-and (2) of “insoluble ” or ‘‘ pectous ” rubber-an elastio colloid of considerable mechanical strength. The latter, which in some respects resembles a slightly vulcanised material, preserves its structure on contact with solvents. It is, however, gradually dissolved by benzene and carbon tetrachloride, but whereas, for instance, the viscosities of the soluble ” in Brazilian and Plantation Para, respectively are very similar, the “pectous” in the latter is far more readily attacked by benzene or carbon-tetra- chloride than the ‘‘ pectous ” of the former.According to Caspari, fine Brazilian * This is the second of a series of articles dealing with recent advances in certain branches of analytical work. Others will follow a t intervals.-EDITOR.224 SCHIDROWITZ : RECENT ADVANCES IN THE grades contain 35 per cent. to 80 per cent. of pectous, whereas plantation rubbers examined by him showed no more than 10 per cent.to 25 per cent. Caspari appears to believe that ‘‘ nerve ” or strength is mainly due to the ‘‘ pectous ” variety. While the work of Caspari will require confirmation and much amplification before it can be applied to practical rubber evaluation, the writer has referred to it at some length, inasmuch as it suggests a new field of research, and one which at least indicates the possibility of estimating quality by a direct physico-chemical method.Investigations on Secondary Products--(a) Rubber Resins.-Hinrichsen and Marcusson (Zeitsch. angew. Chem., 1910, 23, 49; ibid., 1911, 24, 725) have examined the resins from a number of commercial grades in regard to optical activity, saponifi- cation, and iodine absorption values.The outstanding feature in this work is that all resins, excepting that from Para (Hevea), are optically active. In certain cases, therefore, the absence of optical activity in the extracted resin may be taken as evidence that no rubber other than Hevea is present. Para resin contains roughly 15 per cent., other rubber resins up to 100 per cent., of unsaponifiable matter.The optical activity appears to be mainly due to the latter. Iodine values varying from 30.6 (Hubl) for Jelutong resin to 118 for Para resin were found. So far &S the investigation has been carried, it appears that the resins from vulcanised rubber exhibit the same characteristics as those extracted from the crude material. D. Bloom (Chem. Zeit., 1912, 36, 815), as the result of the examination of about 150 samples of resin from different species, came to the conclusion that the “ acid value” of the resin from the same species is a constant.M. Klassert (Xeitsch. uzgew. Chem., 1913, 26, 471; ANALYST, 1913, 38, 465) examined the resins obtained from a number of species, and found melting-points 110 to 119” C. (not sharp); ash, 0.8 to 2.5 per cent. ; iodine value (Hubl), 28.3 to 36.3 ; saponification value, 62.3 to 90.5 ; acid value, 0-9 to 1.2; ester value, 61.4 to 89.2.Hinrichsen (ANALYST, 1913, 38, 336) recommends that the extraction of resin should be carried out in an apparatus of brown glass, to avoid the effect of light. The effect of rubber resin on vulcanisirtg capacity has been the subject of some controversy.Lothar E. Weber (Eighth Int. Congress Appl. Chem., 1912 ; J. Xoc. Chem. Ind., 1912, 31, SSS), using a mixture containing inter alz‘a litharge, concluded that the extraction of resin renders the rubber practically uncursble ; D. Porritt ( 4 ‘ Chemistry of Rubber,” London, Gurney and Jackson, p. 46) finds that the absence of resin renders litharge almost inoperative as a catalyst. On the other hand, Beadle and Stevens (India Rubber J., 1913, 45, 313 ; also Koll.Zeitsch., 1914, 14, 91 ; ibid., 1913, 12,46 ; ibid., 1912, 11, 61) did not find that resin exercised any marked effect on curing capacity, but these workers employed a mixture containing no litharge or other catalyst. ‘( IwolzLble ” Matter : Nitrogenous Substances, - In a general way the term insoluble matter” is not applied to accidental mechanical impurities (such as sand, bark, soil, etc.), but to the natural and normal substances always present to some extent in crude rubbers. Nechanical Impurities.-Beadle and Stevens (ANALYST, 1912, 37, 13) have devised a method aiming a t the determination of mechanical impurities only.This consists, substantially, in “ depolyrnerising ” the rubber by heating with a solvent of high boiling-point, thinning still further with a, solvent of low viscosity, filtering, and weighing.Under these conditions it is claimed that theANALYSfS AND EVALUATION OF RUBBER AND RUBBER GOODS 225 “ insoluble ” (protein, etc.) is broken up, the mechanical impurities alone remaining. Nitrogenous Substances.-While there is no rigid proof that normal ‘‘ insoluble ” is essentially a nitrogen product (a part of the same frequently, without serious doubt, consists of oxidation products), it is now fairly certain that it normally contains a high proportion of nitrogen.There is some controversy as to the general nature of the nitrogen-bearing substance. Spence (J. Inst. Commercial Research in Tropics, No. 13 ; J.SOC. C‘hom. Ind., 1907, 26, 1287), to whom we are indebted for the dis- covery of the nitrogenous character of the insoluble,” in the course of earlier work (Zoc. cit.) found that it contained at the most 5.4 per cent. of nitrogen, and came to the conclusion that it was probably a glyco-protein. Subsequently, A. Tschirch and W. Schmitz (Gummi-Zeit., 1912, 26, 2079; ANALYST, 1913, 38, 272), and the latter in a further paper (Gummi-Zeit., 1913, 27, 1085), found that by the method of separation referred to below, a product could be obtained containing from 14 to 16 per cent.of nitrogen-i.e., a figure agreeing with that found in simple proteins. The authors mentioned admit, however, that the qualitative reactions are not those characteristic of proteins.Spence (KoZZ. Zeitsch., 1914, 14, 262), also adopting 8 new method of separation (cf. below), obtained a product containing at most 10 per cent. of nitrogen, and showing reactions characteristic of the glyco-proteins. Spence argues that Schmitz’ results are unreliable, as the latter based his statements regarding nitrogen-content on the results of analyses made by the Kjeldahl method ; but as Schmitz’ results were higher than those of Spence, the latter’s argument is not very illuminating.Methods of Separation and Estimation.-W. Schmitz (Zoc. cit.) found that by treating 2.5 grms. of rubber with 50 C.C. of pentachlorethane for five to seven hours at 85” to 90” C., a very fluid solution, readily filterable, particularly if somewhat diluted with chloroform, could be obtained.The residue may be further purified by dissolving in 5 per cent, sodium hydroxide and reprecipitating with hydrochloric acid. D. Spence and G, D. Kratz (Zoc. cit., supra) found that if crude rubber is heated with a solvent such as benzene, and a small quantity of a strong acid is added, the “depolymerising” effect* of the latter is so great that, for example, the liquid obtained by the action of 0.3 to 0.5 per cent.of trichloracetic acid on 100 grms. of rubber suspended in 1 litre of benzene (after standing for forty- eight hours in sunlight) may be separated from the bulk of the insoluble matter by simple decantation. The 8‘ insoluble ” may be further purified by repeated treatment with acidified solvent, and finally with pure solvent.Spence considers that the g L depolymerising ” effect of the solvent used by Schmitz (pentachlorethane) is really due to the hydrochloric acid split off from the latter. G. Bernstein (KoZZ. Zeitsch., 1914, 15, 49) states that the viscosity of rubber solutions may be readily reduced to approximately that of the solvent, by the action of ultra-violet rays generated in a quartz-lamp.Practical Considerations.-There is considerable evidence to warrant the assumption that the 6‘ insoluble ” matter in crude rubber has an important bearing on vulcanising capacity, but hitherto no quantitative relationship has been discovered. * D. Spence (KoZZ. Zeitsch., 1909, 4, 70) had reviously noted thc remarkable reduction in viscosity produced in rubber solutions by traces of a miner8 acid.226 SCHIDROWITZ : RECENT ADVANCES IN THE While, on the one hand, Beadle and Stevens’ work (Zoc.cit.) shows that the removal of “ insoluble ” markedly decreases curing capacity, the writer’s practical experience so far is that rubbers with a low proportion of (‘insoluble ” do not necessarily cure badly, nor, conversely, do samples containing a high proportion necessarily vulcanise rapidly. It is highly probable that the “insoluble” varies considerably in com- position,” and, if this is so, further methods of separation will have to be devised before the ‘( insoluble ” can be taken as a criterion of quality.While Spence’s and Schmitz’ (Zoc. cit.) methods of separation are obviously convenient, it will be desirable, before adopting them for analytical or research purposes, to obtain satis- factory evidence that the strong acids employed are without action on the insoluble substances.i Meanwhile the writer prefers for analytical purposes the indirect method (Schidrowitz, I‘ Rubber ” [Methuen], p.252), which consists in evaporating a convenient volume of clear solution-obtained by treating 0.5 to 1 grm. of rubber with 100 to 200 C.C.of benzene in a tall cylinder, whirling gently at intervals, and then allowing to settle-pipetted from above the settled (‘ insoluble ” and weighing the residue. Estimation of Rw,bber.-The fundamental difficulty of differentiating with certainty between soluble and 6Linsoluble’’ matter, not to speak of the cognate problem of accurate separation, has an important bearing on the estimation of caoutchouc in the raw material.This applies to the indirect or difference methods as well as to the direct methods (determination as bromide, nitrosite, or nitrosate). With regard to the former set of methods this is obvious ; with regard to the latter, it may be indicated that separation is either an essential preliminary, or, if not, the 66 insoluble ” matters are likely to form halogen or nitrosite compounds on their own account.Fortunately, the problem, regarded from a purely technical or practical point of view, is not of any great moment. The great bulk of the rubber now coming to market (plantation rubber and fine Brazilian grades) shows very little variation for the same commercial grades in regard to resin, ash, and nitrogen content respectively.Within reasonable limits, therefore, the figures for resin, ash, and nitrogen are of very little value as a criterion of commercial quality. Assuming a satisfactory method of separating the ‘( insoluble ” matter, the most satisfactory indirect method of estimating caoutchouc or rubber is by deducting the sum of moisture +resin + insoluble matter from 100.This method involves the assumption that the whole of the ash and nitrogen are present in an insoluble form. At the present time the writer considers that the most suitable way of returning the results of a, technical orude rubber analysis is as follows : * Beadle and Stevens (Im$ia-Bzibber J., 1913, 46, 313) show that there is no apparent connection between the amount of L‘ insoluble ” and the nitrogen content in a rubber.t A recent paper by J. G. Pol (International Xubber Coizyress, Batavia, 1914, published by 3. H. de Bussey, Amsterdam, p. 446) clearly indicates the importance of adopting a standard method of some kind for the determination of “ insoluble. ” Shaking, heating, previous mechanical working, and other influences, have an enormous influence on the quantitative results obtained (extreme variations for the same sample, 0.65 per cent.-20.0 per cent.). Similar observations have been made by Beadle and Stevens aud by Caspari. The explanation of these apparently anomalous results is, no doubt, that shaking, maceration, etc., break up a part of the “insoluble ” matter, and, conversely, of the rubber proper, into very fino particles, which are either so transparent or so fine as not to be noticeable.ANALYSIS AND EVALUATION OF RUBBER AND RUBBER GOODS 227 Per Cent.- Moisture ... ... .-. ... Insoluble matter ... ... - Resin (acetone extract) . . . ... - - Rubber (by differencej" . . . ... The above contains- - Ash (mineral matter) ... ... Nitrogen ... ... ... ... 9 , =protein ... ...... - - These notes, it must be understood, apply only to routine technical analysis, of which the chief object is to ascertain-mainly from the point of view of controlling methods of production or of gauging suitability for specific manufacturing purposes- whether or not any distinct abnormality is disclosed. For research purposes the direct methods should be kept in view. In this respect the original work of Budde, Harries, and Alexander respectively, on bromination and nitrosation methods may be supplemented by the following brief references to papers of recent date: W.Vaubel (Gummi-Zeit., 1912, 26, 1879) employs a bromination method which consists in treating a solution of rubber in carbon-tetrachloride with potassium bromate, and titrating the excess of the latter in the usual way. The reaction is stated to be- C,,H,, + 6Br = C,,H,,Br, + 2HBr.F. Kirchof (ibid., 1912, 27, 9) was unable to confirm Vaubel's results. According to the former, the amount of HBr split oft' largely depends on the purity of the reagents, temperature, and concentration. The presence of hydrobromic acid is due to decomposition of the tetrabromide. Returning to the attack, Vaubel (ibid., 1913, 28, 92) in a joint paper with E.Weinerth states that his method gives results con- cordant with those obtained with the bromination processes of Budde and Axelrod, but admits that it requires further development before it can be regarded as generally applicable. K. Ute (ibid., 1912, 26, 968), in a review of the bromide methods, suggests that a French process, in which the tetrabromide is oxidised with chromic acid mixture, possesses advantages.Pontio (Ann. Chim. anatyt., 1914, 19, 60 ; ANALYST, 1914, 39, 179) condemns all methods depending on the use of a solvent of low boiling-point. He prefers the indirect method, but of the direct methods described he regards Budde's tetrabromide process as the most promising.E s t i m t ~ n of Moistwe.-A recent paper by J. G. Fol (Zoc. cit., 439) confirms the practical experience of the writer, which is to the effect that drying in the air-oven at 100' C. does not involve any serious error owing to oxidation. An examination of six samples showed that the results obtained at looo C. in air and in a stream of carbonic acid respectively are substantially the same.Drying over sulphuric acid in a vacuum at room temperature gave Zower results than drying either in air or in carbonic acid. These results and further direct experiments lead Fol to the con- clusion that the effect of oxidation during a two hours' heating in the air-oven may be neglected. In the opinion of the writer, moisture is best determined (1) by drying in the water-oven at approximately 913" C.until an increase of weight becomes apparent, or for a standard time of two hours; or (2) by taking the difference228 SCHIDROWITZ RECENT ADVANCES IN THE between the original weight of the sample and the weight after the acetone extrac- tion plus the extract. Washing Loss.-It is generally agreed that if the sample is sufficiently large, and if it requires washing, that the analytical determinations generally should be carried out on the washed, air-dry material.Physical and Mechanical Tests-Viscosity .-The work of Axelrod (Gummi-Zeit., 1905, 19, 1053 ; ibid., 20, 105) and of Schidrowitz and Goldsbrough (J. SOC. Chem. Ind., 1909, 28, 3 ; LL The Rubber Industry,” 1911, 260) indicated that the determina- tion of viscosity was likely to afford a valxable criterion as to quality; or that, at least, it would prove of practical utility as a L6 sorting out ’’ test where vulcanisation tests could not be applied.Further experience of the writer and others suggests that while a decidedly low viscosity figure is almost invariably a sign of poor quality, the converse does not always hold good. This may be due (cf. Caspari, loc.cit.) to the difficulty of satisfactorily separating suspended (minute or trans- parent) particles. In view of the relationship between viscosity, swelling capacity, and solvate formation (E. Hatschek, KoZZ. Zeitsch., 1913,12, 213 ; E. Posnyak, KoZZ. Chem. Beiheft., 1912, 3, 417 ; F. Kirchof, KoZZ. Zeitsch., 1914, 15, 30) it seems possible that 8 determination of imbibition or swelling capacity (cf.Caspari, Zoc. cit.) may give more satisfactory results. J. Fol (KoZZ. Zeitsch., 1913, 12, 131) suggests that the viscosity curve should be calculated in terms of the subtended area, and that this method is preferable to the tangent method of Schidromitz and Goldsbrough (Zoc. czt.). R. Gaunt (J. SOC. Chem. Ind., 1914, 33, 446) finds that by plotting the logarithms of the viscosity (efflux time) numbers against concentration, a straight line is obtained, and advocates that the inclination of this line to the abscissa shall be taken as a measure of ’viscosity.Adhesion Tests.-Clayton Beadle and Stevens ((‘ The Rubber Industry,” 1911, 274) determine the load required to separate pieces of paper evenly coated with a solution of the rubber.The paper is coated by drawing it over the surface of the (5 per cent. or less) solution. MechanicaZ Tests.- The writer is of opinion, as the result of published (cf. India-Rubber J., 1912, 44, 1147, 1198) and unpublished work, that mechanical (tensile) tests carried out on raw (unvulcanised) rubber are of no practical value. Considering that manufacturers and experts generally appear to agree that, regarded as criteria of quality, appear- ance (colour, etc.), and strength of crude rubber are of very little value, it is remark- able that the bulk of the rubber produced is still sold on rule-of-thumb, “sight- and-pull ” tests. Vulcaizisatzon Tests.-With insignificant exceptions rubber is employed in the arts and commerce in the vulcanised state.In the process known as hot curing,* which is used for the bulk of the goods (tyres, hose, buffers, valves, shoes, etc.) manufactured, the following factors, so far as we are aware, have an influence either on the course of the process or on the quality or durability of the wares: (a) Material.-State of aggregation (degree of 6 L polymerisation ”) or physical con- dition of the rubber substance; quantity and nature of resin and of Lcinsoluble” matter ; acidity (?).(b) Process.-Temperature, duration of heating ; method of heating ; quantity of sulphur ; if fillers are used, the nature and quantity thereof. So long as our knowlsdge of the physical and chemical nature of the impurities and * This consists, substantially, of the interaction of masticated rubber (with or without fillers, pigments, etc.) with elementary sulphur a t a temperature above 130” C.ANALYSIS AND EVALUATION OF RUBBER AND RUBBER GOODS 229 of the rubber substance in crude rubber is incomplete, it is naturally impossible to devise any method of analysis or physicall tests which will enable us to determine, quantitatively, the effect of the various factors on vulcanisation.Direct vulcanisation tests me therefore, for the present, essential for the purpose of practical evaluation. Very broadly it may be stated that such tests may comprise ( a ) observations regarding the behaviour of the material during, or rather towards, the process ; ( b ) observations on the nature of the vulcanised product. With regard to (a) the writer considers the most important point to be rate of cure (cf.Schidrowitz, The Rubber Industry, Conference Book, Rubber Exhibition, 1914, p. 215). In this connection the writer relies entirely on an examination of the mechanical properties of the vulcanisate ; there appears to be no direct connection between the “ coefficient of vulcanisation ” (i.e., combined sulphur) and the technical properties of the material (author’s unpublished work.Cf. also Spence, Koll. Zeitsch., 1912, 10, 299 ; ibid., 1912, 11, 274; ibid., 1913, 13, 41 and 265). Various types of tests have been proposed and &re applied to vulcanised rubber - namely, tensile tests (Schidrowita, Rubber [London, Methuen, 19111; also Rubber Industry, 1914, loc. cit. ; J. Fol., Batavia Congress, 1914, 456 ; Clayton Beadle and Stevens, Rubber Industry, 1911, 265; Memmler and Schob, Arbeit.des. Kgl. Materialpriifunpamt, 1909, 4. Also Memmler, Rubber Industry, 1911, 351 ; Stratton, Bureau of Standards, U.S.A. Circular, 38, 1912, such as breaking-strain, elongation, stress, strain, curves to the break) ; hysteresis tests (Schwartz, J. Inst. Elect. Engin., 1910, 701; Shedd and Ingersoll, Phys. Review, 1904, 19 121, 107 ; Clayton’ Beadle and Stevens, Eoc.cit., sup., and I , d h - Rubber J., 1912, 44, 603 ; 1913, 46, 161) ; elasticity tests (P. Breuil, L e Caout. et la Gutta., 1908; Memmler, loc. cit., 365) ; hardness tests (Breuil, Zoc. cit. ; Memmler, loc. cit.) ; abrasion tests (Memmler, loc. cit. ; ibid., Gummi-Zeit., 1912, 27, 2 ; Clayton Beadle and Stevens, ibid., 1912, 27, 167; Schidrowita, Zoc.cit.), etc., but it is neces- sary to bear clearly in mind the essential difference between tests designed for the comparative evaluation of crude rubber and tests applied with a view to examining the specific properties of any given- (vulcanised) rubber article. With regard to the former it is desirable to use methods calculated to measure certain intrinsic and typical properties of the raw material, such as curing capacity, strength, distensi- bility, capacity for recovery (Schidrowita, Batavia Congress, 1914, 371 ; ibid., Rubber Industry, 1914 ; also Standardisation Report, Indict-Rubber J., 1913, 46, 1215).In view of the factors which are of influence on the vulcanisation process, it is obvious that any system of evaluation based thereon must be carried out under strictly stsndardised conditions of mixing, curing and testing.The writer considers a (‘ pure ” rubber and sulphur mixing the most suitable for the purpose, partly for the reason that the introduction of a filler * renders the reaction less delicate, partly because a “ pure ” mixing is less likely to be heterogeneous t than one containing minerals.* The reference is to inert fillers. The use of fillers having a specific action would obviously still more complicate matters. .I. Skellon (KoZZ. Zeitsih., 1904, 14, 96) has shown that if doughs (i.e., uncured mixes) containing widely different quantities of sulphur are vulcanised in contact with one another, a wandering of the sulphur to an equilibrium throughout the mass takes place.It seems (although no work on the sub’ect has been published) highly improbable that a similar phenomenon would occur in the case of filfers, particularly of such as do not melt at the teniperatures employed.230 SCHIDROWITZ : RECENT ADVANCES IN TBE 11. VULCANISED RUBBER. Analysis. Preparation for Amlysis,-L. Archbutt (ANALYST, 1913, 38, 550) recommends, for purposes of comminution, a pair of grooved rollers, working either in gear (3 : 2) or with one roller fixed.The machine has partly a cutting, partly a grinding action, which varies according to the adjustment of the rolls. It is stated that all com- mercial grades can be readily reduced to a good sample by the machine without further treatment . General Scheme of Analysis.-The Henriquez-Weber scheme (C.0. Weber, “ The Chemistry of India-Rubber,” London, Griffin, 1902), details of which may be found in every textbook on the subject, is still the basis of quantitative rubber analysis. In one respect, however, it requires serious modification. The work of Britland and Potts (J. Soc. Chem. Ind., 1910,29, 1142) and others has shown that pyridine frequently attacks rubber, and this solvent, therefore, can no longer be recommended for the separation and estimation of the pitch, asphalt, and bitumert group of $fillers.Caspari (“ Technical Methods of Chemical Analysis,” Lunge-Keane. London, Gurney and Jackson, 1914, Vol. III., Part I., 426) states that ethyl acetate following acetone sometimes gives good results. R.Becker (Gummi-Zeit., 1911, 25, 598) recommends carbon bisulphide, and Potts (“ The Chemistry of the Rubber Industry,” London, Constable, 1912, 132) confirms Becker’s view that extraction for one hour in the Zuntz type of apparatus with carbon bisulphide swells but does not appreciably dissolve rubber. It is not clear, however, whether this refers to all types of mixings. The writer prefers to make a, preliminary qualitative test with cold benzene or, preferably, nitro-benzene.If the solvent does not become appreciably (yellow to brown) caloured or fluorescent, it may be assumed that no appreciable quantity of bitumen, ‘‘ mineral-rubber,” or similar material has been used. I t should be borne in mind, however, that substances of thiq class vulcanise to a certain extent, and may be modified as regards solubility in consequence.If qualitative tests give a positive indication, the analyst must be guided by the general character of the mixing as to choice of methods. If indirect methods are not available, an extraction with cold nitro-benzene (as originally proposed by Henriquez) or with carbon bisul- phide (cj. above) may be resorted to.Separation of Minerals, Starch, Fibres, etc.-In Weber’s scheme nitro-naphthalene was recommended for this purpose. The writer, in common probably with the majority of other workers on rubber, has abandoned this inconvenient solvent, using as a rule high boiling petroleum (Axelrod, Gummi-Zeit., 1907, 21, 1229 ; Hinrichsen, Chern. Zed., 1909, 33, 184, and ibid., 735). Frank and Marckwald (Gummi-Zeit., 1908,22,134) recommend xylene under pressure.Anisol at a, moderate temperature has also been suggested by Hinrichsen (“Der Kautschuk und seine Prufung,” Leipzig, Hirzel, 1910, 126) and collaborators. F. Jacobsohn (emmi-Zeit. , 1913, 27, 1906) prefers a mixture of petroleum and camphor oil. Estimation of Sulphur.--D. Spence and J. Young ( J . Id. and Eng. Chem., 1912, 4, 413; J.Soc. Chem. Ind., 1912, 31, 651) have devised an electrolytic methodANALYSIS AND EVALUATION OF RUBBER AND RUBBER GOODS 231 which is stated to give accurate and rapid results ; 0.5 grm. material is treated first with nitric acid (sp. gr. 1*4), then with fuming nitric acid. A current of 3 amps. at 8 volts is suitable for the process, which in the case of high-grade soft rubber takes two to three hours as against three-quarters of an hour for low-grade hard rubber.After electrolysis the solution, to which 1 grm. of sodium carbonate is added, is evaporated to dryness, then evaporated with hydrochloric acid, and finally precipi- tated with barium chloride in the usual way. For soft rubbers the barium chromate volumetric process (J. SOC.Chem. Ind., 1904, 23, 31) may be used for the final deter- mination, provided the sulphur content is within certain limits. Kaye and Sharp (Indict-Rubber J., 1912, 44, 1189) have described a rapid method (two to three hours), which consists in heating 0.25 grm. to 0.5 grm. of the sample with zinc oxide and potassium nitrate, The melt is taken up with hydrochloric acid and precipitated with barium chloride in the usual way.Utz (Gkmmi-Zeit., 1914, 28, 631; ANALYST, 1914, 39, 368) finds that this method gives sufficiently accurate results for technical purposes, and suggests some minor modifications. H. P. Stevens (ANALYST, 1914, 39, 74) states that oxidation with nitric acid in an open vessel may lead to serious losses, owing to the formation of volatile sulphur-containing bodies.This may be avoided either by working in a vessel connected with a condenser, or by passing the gases evolved through potash or nitric acid. R. Gaunt (ANALYST, 1915, 9) heats the rubber in a stream of oxygen in a combustion tube and collects the sulphur dioxide formed in a solution of hydrogen peroxide. The sulphuric acid formed is determined in the usual way, after boiling with hydrochloric acid to decompose the excess of peroxide.I n rubber containing mineral matter the sulphates in the residual ash must also be estimated. Estimation of Rubber-Direct Methods.-It cannot be stated that any of the direct methods can be relied upon to give even approximately correct results in regard to all grades of vulcanised rubber. Nevertheless, in the absence of sub- stances (other than rubber) likely to form nitrosites, bromides, etc., or if the non- rubber nitrous acid or bromine derivative is not capable of interfering or can be allowed for, one or other of the direct methods may frequently be employed as a useful check on or confirmation of the indirect method.I t may happen, also, in the case of simple mixings, or of mixings the general nature of which is well known, that a direct method may be of convenience in regard to control or rapidity of work.Alexander’s (Gummi-Zeit., 1907, 21, 653) nitrosite method and Axelrod’s (ibid., 1907, 21, 1229) tetrabromide method have been described in practically every modern textbook, and need not, therefore, be referred to at length. The writer has no experience of the nitrosite method, but it is certainly (cf.Potts, op. cit., 141) long and tedious. Axelrod’s method has, in the case of soft rubbers, frequently given useful results in the writer’s laboratory. Hubner’s Method (Chm. Zeit., 1909, 33, 11; ANALYST, 1909, 34, 170 and 365), although modified by him with a view to preventing loss of bromine (Gummi-Zeit., 1912, 26, 1711), has been the object of much criticism and suggestion (cf.Potts, op. cit., 141; Hinrichsen and Kindscher, Chem. Zeit., 1912, 26, 217 and 230 ; Hubner, Gummi-Zeit., 1912, 26, 1281 ; R. Becker, ibid., 1503 ; P. Alexander, Chem. Zeit., 1912, 36, 554). The impression of the writer is that for certain types of mixings the method and its principles are worth keeping232 SCHTDROWITZ : RECENT ADVAXCES IN THE in mind, and that it might well repay further investigation.C. R. Bogg’s (Int. Con- gress Appl. Chem., 1912 ; Koll. Zeitsch., 1913, 12,SS) proposes a modified Axelrod-Budde method in which toluene is used as a solvent and the bromine is finally titrated. In the opinion of the writer toluene is not likely to be effective except in the case of very soft mixings.W. A. Ducca (zbid.), who has investigated a number of direct methods, concludes that the nitrosate methods are useless both for crude and vulcan- ised rubbers ; that Budde’s method is good for crude but not for vulcanised goods, and that Hiibner’s method is unreliable. P. Goldberg (Chem. Zeit., 1913, 37, 85 ; ANALYST, 1913, 38, 111) distils off the caoutchouc (in a combustion tube) at a tempera- ture not exceeding 400” C.in a current of nitrogen, and weighs the residue. The differ- ence represents vulcanised rubber, from which 3 per cent. is deductedfor combined sul- phur. Special methods have to be applied where readily decomposable carbonates, antimony sulphides, or mercury salts, are present. The process should in many cases be useful as a check on the difference method.Another combustion method has been sug- gested by L. G. Wesson ( J . Ind. and Eng. Chem., 1914,6, 459; ANALYST, 1914,39,568). I t consists in preparing a nitrosite and subjecting the latter to combustion. The caoutchouc is calculated from the carbonic acid obtained. The method, originally devised for the analysis of crude rubber, is scarcely likely to be of practical value in the analysis of the vulcanised material.Indirect (Diference) Methods.-Consider- able attention (cj. above) has been paid to the separation of the caoutchouc from fillers by means of solvents. In the absence of the asphalt-bitumen-pitch class of fillers, treatment with a suitable solvent-after extraction with acetone, followed by saponification-mush, in most cases, neceasarily give a fairly accurate result. The distribution of sulphur may, however, cause some difficulty.Moreover, it should not be forgotten that no process yet devised can distinguish with any certainty between new rubber on the one hand and waste, or reclaimed, rubber on the other hand, The estimation of (I rubber ” or ‘( caoutchouc ” is, consequently, a somewhat illusory problem.By carefully estimating the various non-rubber constituents the experienced analyst will in the majority of cases be able to form a very fair opinion as to the quantity of rubber actually employed in a mixing. If mechanical tests are applicable as well, one can in many cases conclude that not less than a certain proportion of waste or reclaim has been employed.Special Problems-Examination of Cable Insulations.--Rubber mixings are used to a very large extent for the protection or insulation of electric light and power cables. Hitherto no standards of composition or of analysis have been published in this country, but in the United States and in Germany attempts in this direction have been made. In both these countries leading manufacturers, in conjunction with public authorities and experts, appear to have accepted the principle that a rubber mixing for insulation purposes shall contain no ingredients beyond rubber, mineral matter, sulphur, and hydrocarbons of the paraffin series (such as ceresin wax).In the United States a conference of manufacturers, experts, and users (J. Ind. and Eng. Chem., 1914, 6, 75 ; ANALYST, 1914,39, 137), have adopted as a basis a mixing containing not less than 30 per cent.hwea (Para, or Plantation (( first latex ”) rubber. Limits are suggested for the waxy hydrocarbons, free and combined sulphur, etc., and detailed methods of analysis have been described. AANALYSIS AND EVALUATION OF RUBBER AND RUBBER GOODS 233 German Government institution, in conjunction with a number of cable factories (cf.F. W. Hinrichsen, ANALYST, 1913, 38, 336), have proposed a mixing contain- ing 33.3 per cent. of rubber (containing not more than 6 per cent. of resin) and 66.7 per cent. of fillers, including sulphur. No organic filler excepting ceresin or parafin wax-to a maximum amount of 3 per cent.-is to be used. Definite methods of analysis, including the separation of fillers by means of a solvent (paraffin oil or camphor oil) have been laid down, Some criticisms of the methods of analysis proposed have appeared.Thus, Britland and Potts (India-Rubber J., 1912, 42, 333) point out that the method of estimating ceresin proposed gives results which are too low. Moreover, they cannot confirm the work of Hinrichsen and Kindscher (Chem. Zeit., 1910, 34, 230) in regard to the alleged raising of the acetone extract due to the presence of the waxy filler. F. Jacobsohn (Gummi-hit., 1913, 27, 1906 ; ANALYST, 1914, 39, 91) criticises, in particular, the suggestion regarding the solvent to be used for the separation of the fillers. Proofed or “Rubberised ” Goods.-A number of interesting suggestions on the testing of proofed goods are made in a paper by M. B. Setlik and J. Zofka (Eighth International Congress of Applied Chemistry; ANALYST, 1912, 37, 575). A method for estimating lead szdphate in rubber goods is described by J. A. Schaeffer (J. Ind. and Eng. Chem., 1912, 4, 836; ANALYST, 1913,38, 44). This substance appears to be used in America in the form of subZimed white lead, a material containing about 78.5 per cent. PbSO,, 16.0per cent. PbO, and 5.5 per cent. ZnO. Direct Determiitation of Antimony and Mercury SuZphides. - These sulphides, particularly the former, are very widely used as pigments, end their direct estimation is frequently desirable. Methods for accom- plishing this (both based on the principle of destroying the rubber and other organic matter by strong reagents) have been worked out by F. Frank and K. Birkner (Chem. Zeit., 1910,34, 49 ; ANALYST, 1910,35,131) and by W. Schmitz (Gummi-Zeit., 1911, 25, 1928; ANALYST, 1912, 37, 64). The former destroy organic matter by means of fuming nitric acid and ammonium persulphate. The metals are finally weighed as sulphides. If both mercury and antimony are present, separation is effected by dissolving the antimony sulphide by means of carbon bisulphide. Schmitz (loc. cit.) uses a modification of the Kjeldahl method for the destruction of organic matter.

ISSN:0003-2654    

DOI:10.1039/AN9154000223

出版商:RSC    

年代:1915

数据来源: RSC

摘要:

234 ABSTRACTS OF CHEMICAL PAPERS ABSTRACTS OF PAPERS PUBLISHED IN OTHER JOURNALS. FOOD AND DRUGS ANALYSIS. Faced Pearl Barley. J. F. Liverseege and H. Hawley. ( J . SOC. Chem. Ind., 1915, 34, 203.)-Of 73 samples of pearl barley examined, 50 contained less than 0.05 per cent. of ash insoluble in dilute hydrochloric acid ; 6 of the samples yielded more than 0.1 per cent. of ash, the amounts ranging from 0.22 to 0.82 per cent.Other samples were found to be faced with rice, and 2 samples were faced with a mixture of rice and talc. w. P. s. Beans from British West Africa. (Bull. Imp- Iqzst., 1914, 12, 547-552.)- Beans. origin. I Mois- 1 ture. I _~ ____ I I 1 Per 1 Cent. Yigna C'atjang (" Kroo $ierra Leone1 11 *3 beans ") PhaseoZm Zunatzu (" Towe ltJierra Leone 11-3 1 13.4 beans 'I) Ditto ...Sword beans (G&aca~~~ j Gold'boast 1 8.2 e?zsiformis) I Ditto . . . . . . . . . I Honduras ' 14'4 Cm~avnlic6 obtus@lia ... Gold Coast . 10-9 Ditto . . . . . . . . . Nigeria 8.7 Ditto . . . . . ... 1 Hong-Kongl 11.7 I Crude Pro- teins. Per Cent. 24-3 22.0 22.9 23-4 27-4 25.0 22.0 22.5 True Pro- teins. Per Cent. 22'3 20.4 21.0 21 -0 17.5 14.8 21 -0 - Fat.Per Cent. 1'1 1'2 0.8 0.8 1.3 2 *7 1.9 0 -7 Starch etc. Per Cent. 55 -2 58-0 55 *7 55 -8 45.7 48-4 54'5 61.6 Fibre. Per Cent. 4 *9 3.8 4 -8 3 '8 14.7 6 -8 8 -1 2.9 Ash. Per Cent. 3.2 3.2 2.7 2 'a .a*7 2.7 2 -6 3-6 Nutri- ent Ratio. 1 : 2.4 1 : 2.7 1 : 2.5 1 : 2.5 1 : 1.8 1 : 2.2 1 : 2.6 1 : 2.8 Food Units. 118.7 116.2 115.0 116.0 117.4 117.0 114.0 120.0 The two samples of Tow6 beans yielded, on hydrolysis, 0-025 and 0.03 per cent.of hydrocyanic acid respectively. The other species of beans were free from cyano- genetic glucosides or alkaloids. C. A. M. Estimation of Bolted Flour in Bread. C. J. Koning and W. C. Mooij. (Chem. Weekblad, 1914,11,1064-1066.)--Estimation of the pentosans in bread affords a means of calculating the amount of bolted flour in bread.This is illustrated by the following results, in which the pentosans were estimated by distillation with dilute hydrochloric acid and precipitation with phloroglucinol : I Pentosans calcnlated ' on the Dry Material. Per Cent. Water* I I - -- ~ ~ ~- Unbolted flour ... ... ... I 14.2 Bread containing 25 per cent. bolted Bread containing 35 per cent. bolted I Bolted flour ...... ... ~ 12.1 Bread baked from unbolted'flour ... I 50.22 flour ... ... ... ... ! 49.42 flour ... ... ... ... I 49.33 I. 6.12 2.41 6.23 5.36 4-93 11. 6.39 2.55 6 -23 5.50 5.13 Pentosans calculated. Per Cent. - j - - i - 4.82 i 5.05 C. A. M.FOOD AND DRUGS ANALYSIS 235 Microseopieal Detection of Potato Starch in Bread. G. Schutz and L. Wein. (Chem. Zeit., 1915, 39, 143.)-The large gelatinised granules of wheat and rye, though somewhat irregular, preserve their spherical type, while those of gelatinised potato starch are irregularly oval, with brain-like convolutions and one or more forks; they are also larger and more highly refractive.The potato-starch granules, even when gelatinised, possess a greater affinity towards certain dyestuffs than the granules of the cereal starches, and are easily detected by the use of micro- chemical stains.A few crumbs of bread are steeped in water in a watch-glass, well kneaded, and a portion is placed between two cover-slips, which are then forced apart. The preparation is dried in the air, fixed by passing three times quickly through a flame, and then treated with a drop of the stain. Suitable stains are neutral red used fairly strong, and methylene blue well diluted.The best differen- tiation, however, is obtained with concentrated thionine solution, diluted with twice its volume of water. The stain is allowed to act for two and a half to three minutes, and the excess removed by washing. In the case of thionine the cereal starches remain unstained, while the potato-starch granules are stained a lilac colour.The cellular tissue of the potato is coloured deep reddish-violet, also the endosperm tissue of the cereals. The tissues of the fruit and seed husks of the cereals, the cortical tissue, reticulated vessels, and sclerenchyma cells, of the potato rind, are all stained blue; but since the potato rinds are mostly removed, it may be assumed for practical purposes that all blue-stained elements are derived from the cereals.By comparison with typical mixtures of known composition approximate quantitative results may be obtained, and, owing to the strong contrast of the tigsue colorations, the degree of grinding of the flour may be estimated. When boiled or steamed potatoes have been used in making the bread, some of the highly gelatinised starch granules might be destroyed by the above method of mounting.In such cases a well-mixed sample of the crumbs is moistened on a, glass slide, and broken down by simple pressure with a scalpel without any rubbing action. The preparation is drained with blotting-paper, and stained and washed on the slide in the same manner by irrigation, the cover-slip being then pressed very gently on.The gelatinised paste-granules of the potato, very large and mostly well preserved, are distinguished by a red stain. J. F. B. Estimation of Total Fatty Acids and Other Ether-Soiuble Consti- tuents of Feeding Stuffs. (J. Ind. and Elzg. Chem., 1915, 7, 218-220.)-1t is shown that extraction with ether, no matter how prolonged, fails to extract the whole of the fat from many materials.From hay and from the excrement of herbivorous animals, less than one-third can be extracted. On the other hand, ether extracts are not necessarily all fat or fatty acids, the ether extracts of the above-mentioned materials containing on a average nearly 70 per cent. of material which is either unsaponifiable, or saponifiable but still not common fat or fatty acid, since the acids set free by acidifying a solution of the soap are largely insoluble in petroleum ether.If anything more than approximation of the fat content of such material is desired, some such method as the author’s Precipitation Method (Texas Exp. Sta. BUZZ. 169) or the method now described must be employed. J. B. Rather.236 ABSTRACTS OF CHEMICAL PAPERS The Precipitation Method consists in extracting the material with ether and frac- tionating it as described below.In the new method, instead of being extracted with ether, the material (10 grms.) is saponified with 50 C.C. of 8 per cent. alcoholic soda for an hour under a reflux condenser. The extract is filtered through asbestos in a carbon funnel, and the residue washed with hot alcohol.The filtrate and washings are evaporated to about 10 c.c., washed into a separator with warm water, acidified with 10 C.C. acetic acid, and the warm solution extracted five times with 50 C.C. of ether. The ethereal liquid is washed once with water in a pear-shaped separator, which makes it easier to run off suspended solids with the water. About 10 C.C. of warm aqueous sodium hydroxide solution(1: 2)is shaken gently with the ethereal solution.About 25c.c. warm water is added, a rotatory motion given to the separator, and the aqueous layer drawn off, leaving any emulsion in the separator. This treatment is repeated, and followed by five washings with cold water, after which the ethereal solution is evaporated and the residue weighed. The extreme error involved by assuming this to be wholly unsaponifiable matter appears to be about 0.2 per cent.on the sample. The error ,may be eliminated by shaking the ethereal extract with about 20 C.C. of hydro- chloric acid before evaporation, running off the aqueous layer, evaporating the ethereal layer, and weighing the residue, and then proceeding as follows : The residue is dissolved in 20 C.C.of hot alcohol, the solution titrated with TG sodium hydroxide, and the consumption of the latter in C.C. multiplied by 0.28 is subtracted from the apparent percentage of unsaponifiable matter as previously determined, and added to the percentage of fatty acids found in the next operation. The soap solution is deprived of ether, cooled nearly to room temperature, acidified with 8 C.C.acetic acid, and extracted with 40 C.C. of petroleum ether, shaking violently. The aqueous layer and any suspended solids are drawn off and washed three times in a similar manner. The combined ethereal extracts are washed twice with 50 C.C. of water, allowing any emulsion to run out with the aqueous layer. This is washed once more with petroleum ether, which is washed twice with water and added to the main extract, which is then evaporated and the fatty acids weighed.The aqueous residue, after exhaustion with petroleum ether, is made more acid by adding hydrochloric acid, and is extracted warm with five portions of ether, each of about 40 C.C. The ether extract is washed twice with water, evaporated, and the (' saponified residue " weighed.The term '' saponified residue " is used to cover ether-soluble, saponifiable material difficultly soluble in petroleum ether, Practically all the chlorophyll, when present, is found in this fraction. The other constituents are acids of approximately the 8ame mean molecular weight as the acids derived from the commoner fats. G. C. J. Estimation of Crude Fibre. R. Fanto and W.Nikolitsch. (Zeitsch. anal. Chem., 1915, 54, 73-76.)-The following procedure is recommended for accelerating the rate of filtration of the acid and alkaline digestion liquids in the estimation of crude fibre : The substance is boiled for thirty minutes with 100 C.C. of 1-25 per cent. sulphuric acid, and the mixture is then poured into an ordinary extraction thimbleFOOD AND DRUGS ANALYSIS 237 of such capacity that it will hold the whole of the liquid and residue : when the liquid portion has filtered through, the thimble is suspended in a beaker of water so that the level of the water is just below the edge of the thimble.The water passes rapidly inwards, and when the thimble is full it is raised and allowed to empty. These operations are repeated until the residue is washed ; the residue remaining after the alkali treatment is washed in the same way, and is then rinsed into a platinum basin, dried, and weighed. This method of filtration and washing prevents the pores of the filter being clogged by the finely divided substance.w. P. s. Estimation of Formaldehyde and Methyl Alcohol in Aqueous Solution (Analysis of Formalin).G. Lockemann and F. Croner. (Zeitsch. anal. Chem., 1915,54, ll-26.)-1n an aqueous solution containing both formaldehyde and methyl alcohol, the former may be estimated by adding hydroxylamine hydrochloride and titrating the liberated hydrochloric acid, or by adding sodium sulphite and titrating the free alkali formed; the methyl alcohol is estimated by oxidising the solution with permanganate and calculating the quantity of alcohol present from the amount of permanganate reduced, allowance being made for the permanganate reduced by the formaldehyde.In the hydroxylamine method the reaction proceeds according to the equation and methyl-orange is used as the indicator in titrating the acid produced. The reaction with sodium sulphite is shown by the equation CH20 + NH20H.HCl = CH2NOH + H20 + HCI, CH,O + Na2S03 + H20 = CH,(OH)SO,Na + NaOH ; rosolic acid is used as the indicator in the titration, since it gives a sharper end- reaction than does phenolphthalein (cf.ANALYBT, 1903, 28, 363). For the oxidation with permanganate, the formalin (40 per cent. formaldehyde solution) is diluted with 100 times its volume of water, and 5 C.C.of this solution are mixed in a flask with 75 C.C. of water and 25 C.C. of alkaline permanganate solution (15-82 grms. of potassium permanganate and 40 grms. of sodium hydroxide per litre) ; the mixture heated for twenty minutes on a water-bath, then treated with an excess of oxalic acid solution (31.51 grms. of crystallised oxalic acid and 75 C.C. of concentrated sulphuric acid per litre), and the excess of oxalic acid is titrated with acid per- manganate solution (containing 40 grms.of crystallised phosphoric acid per litre). One C.C. of permanganate solution is equivalent to 0,00375 grm. of formaldehyde or 0.00267 grm. of methyl alcohol. The authors found that it was impossible to separate the aldehyde from the alcohol by distillation even after the addition of substances such as ammonia, alkali bisulphite, the sodium salt of sulphanilic acid, etc.; traces of formaldehyde were always found in the distillate.Attempts were also made to bring about the separa- tion by converting the formaldehyde into an insoluble compound by treatment with aniline or p-nitrophenylhydrazine and subsequent filtration, but it was not possible, by distillation, to separate the methyl alcohol from the excess of precipitant in the filtrate.w. P. s.238 ABSTRACTS OF CHEMICAL PAPERS Detection and Estimation of Free or Combined Glycerol. Analysis of Glycerophosphates. M. Franeois and E. Boismenu. ( A m . FaZs$., 1915,8,3-16.) -Free glycerol, after having been heated to expel aldehydes, alcohol, and other volatile substances which may be present, can be identified by heating it with potassium hydrogen sulphate ; acraldehyde (acrolein) is formed, and if the vapours containing this substance are conducted into magenta-sulphurous acid reagent, a red coloration is produced which changes to blue when the mixture is heated.The glycerol in glycerophosphates may be identified by this test. For the estimation of glycerol in glycerophosphates the bichromate method is recommended ; the authors find that the oxidation is complete only when a large excess of bichromate is employed, and the mixture boiled for two hours under a reflux apparatus. The phosphorus in glycerophosphates may be estimated by boiling the substance for two hours under a reflux apparatus with a mixture of 10 grms.of water, 10 grms.of concentrated sulphuric acid, and 4 grms. of potassium bichromate. The mixture, while still hot, is diluted with 30 C.C. of water, 10 grms. of sodium sulphite are added, followed by 20 grms. of sodium acetate; after the solution has been heated for fifteen minutes on a water-bath, the phosphoric acid is precipitated by the addition of molybdic acid reagent, the precipitate is converted into ammonium magnesium phosphate, and weighed as magnesium pyrophosphate (cj.ANALYST, 1915, 152). w. P. s. Colouring Matter of Raw and Cooked Salted Meats. R. Hoagland. (J. Agric. Research, 1914, 3, 211-225.)-1n uncooked salted meats the colour was soluble as a rule in alcohol, and in some cases in water. All samples gave extracts showing an absorption band just at the right of the D line.In general, treatment with hydrazine hydrate or sodium nitrite did not affect the colour or spectrum of the extract. Potassium ferricyanide and hydrazine chloride generally destroyed the red colour of the extract, and caused the absorption band to disappear. The NO-hemo- globin (nitric oxide), to which the red colour is due, is readily soluble in water, but insoluble in alcohol and ether.There is ample evidence to show that the action of potassium nitrate in the curing of meats is primarily to cause the formation of NO-haemoglobin, but it is probable that under some conditions of manufacture this oompound may undergo changes, and in such cases may yield a colouring matter soluble in alcohol but not in water. Haldane (J.Hygiene, 1901, 1, 115-122) has shown that the red colour of cooked salted meats is due to the presence of NO-haemo- chromogen, a, reduction product of NO-hmmoglobin. NO-haemochromogen is soluble in alcohol, and is characterised by its resistance to the action of reducing agents and by a spectrum showing a distinct band just to the right of the D line and a faint band a trifle to the left of the E line.I t is concluded that the colour of uncooked salted meats cured with potassium nitrate is generally due in large part at least to the presence of NO-haemoglobin, although in some cases part of the colour may be due to NO-haemochromogen. The NO-hemoglobin is produced by the action of the nitric oxide resulting from the reduction of the potassium nitrate used in salting upon the haemoglobin of the meat. The colour of cooked salted meats cured withFOOD AND DRUGS ANALYSIS 239 2.9 13*5 3.9 1 16.4 4.2 1 15.9 saltpetre is due to the presence of NO-haemochromogen resulting from the reduction of the colour of the raw salted meat on cooking. H.F. E. H. 12.9 15.5 15.3 Studies in the Expansion of Milk and Cream. H. W. Bearce. (J. Agric.Research, 1914, 3, 251-268.)-Certain variations exist in the coefficient of expansion of different samples of market milk, single cream, and double cream. The principal object of the author was to determine the change in volume which occurs when the temperature of a given volume of milk or cream is changed, and thus to construct a table of relative volumes of milk and cream at various temperatures.Thus, when milk is pasteurised and put into vessels at a high temperature, it is often desirable to know what volume of milk must be measured out at that temperature so that it may occupy the required volume a t some other temperature. It was found that by the method adopted the density determinations of individual samples may be depended upon to about 1 unit in the fourth decimal place.The rate of expansion of any given sample appears to depend upon something more than the density or the percentage of fat present, and is undoubtedly dependent upon the physical and chemical condition of the sample at the time the observations are made. This condition is probably much affected by the time that has elapsed since the preparation of the sample and upon the temperature at which it has been kept.The density deter- minations were made by the method of hydrostatic weighing, a sinker of known mass and volume being suspended in tbe liquid and weighed, Elaborate precautions were taken to correct for all probable sources of error, and a very large number of results are appended in the form of tables and graphs, for which the original paper should be consulted.H. F. E. H. 72.3 70.5 64.6 Seeds of Carnardurn Species. (Bull. Imp. Inst., 1914, 12, 545-547.)-The kernels of Canarium commune and C . rufum from the Straits Settlements, and of C. Colophania from Mauritius, gave the following results on analysis. I n the case of the two first, the seed-coats were removed before the analysis. 7.4 trace 3.9 1 : 12.5 j221-9 4.2 trace 5.0 1 : 10-1 i231-4 9.0 2.1 4.2 1 : 10.0 210.5 ! I Species.C. commune C, rufum C. Colop han"& I I --I I- I -I /-I-- I I .. The seeds of C. Zuzonicum, from the Philippine Islands, are used in United States for dessert under the name of (( pili nuts." C. A. M. * The ratio between the percenta.ge of crude proteius and the sum of the percentages of starch and t The total obtained by adding the percentage of starch to 2.5 times the sum of the percentages of fat, the latter being first converted into its starch equivalent.fat and crude proteins.240 ABSTRACTS OF CHEMICAL PAPERS Organic Phosphoric Acid of Rice. A, R. Thompson. (J. Agric. Research, 1915, 3, 425-429.)-Phosphoric aoid occurs in organic combinations with inosite as phytin or phytic acid in the seeds of many plants.Phytin is probably a hem- phosphoric acid ester of inosite, and is completely hydrolysed into phosphoric acid and inosite with difficulty, even when boiled for several hours with concentrated nitric acid. The total phosphorus in rice bran is 2.29 per cent., in unpolished rice 0.32 per cent., and in polished rice 0.14 per cent. Phytin was determined in the bran by extracting with 0.2 per cent.hydrochloric acid and precipitating with alcohol, after which it is washed with 50 per cent. alcohol, then with ether, and dried. Phytin so prepared formed 8.2 per cent. of the bran, and as phytin contains a considerable amount of organio phosphorus, it is evident that rice bran contains much of its phosphorus in the organic form.Phytin could not be obtained from polished rice ; that obtained from unpolished rice was doubtless contained in the outer layer removed by polishing. Preparations of barium phytate were made, having the following composition, calculated on the anhydrous substance : Unpolished rice, 1 ... 6-63 1.75 16.43 36.93 Rice bran, 1 ... ... 6-62 1.82 16-06 37.79 9 , 9 9 2 a * * ... 6.51 1-87 16.05 37.84 C. H. P. Ba. , 9 ,, 2 ... 6.97 1-84 16.38 36.84 (Cj. also ANALYST, 1913, 38, 279.) H. F. E. H. Tea from New Sources. (BUZZ. Imp. Inst., 1914, 12, 540-545.)-Samples of tea from Uganda, East African Protectorate, and Fiji gave the following analytical results : Moisture , per Cent. Uganda, 1913 ... ... 8-05 Uganda, 1914, " Golden Tip " 8-8 Y7 ,, '' Broken Leaf '' 8.8 East African Protectorate .. . 8.6 Fiji, 1909 ... ... ... 10.6 Caffeine, Tannin, Ash, Extract, per Cent. per Cent. per Cent. per Cent. 3.67 9.5 4.76 36.0 4-90 12.6 4.2 35.2 3-85 15.5 4.8 35.0 5.0 9.6 4.8 33.9 2 *8 7.9 4.6 26-2 C. A. M. Reactions of Vanillin. E. P. Haussler. (Zeitsch. anal. Chem., 1914, 53, 691-695, 1915,54,104.)-Albumin, casein, peptone, and fibrin yield violet colorations when evaporated with an alcoholic solution of vanillin and the residue warmed after the addition of a drop of dilute hydrochloric acid (see ANALYST, 1914, 39,315).Urea, under these conditions, yields a yellow coloration, whilst gelatin gives a red colour which changes to brown and then black. A sample of pepsin when tested in this way yielded a brown-violet coloration which changed to brown-red. By using con- centrated hydrochloric acid in place of the dilute acid, a violet coloration was produced. In the absence of vanillin, the pepsin gave a brown coloration with con- centrated hydrochloric acid, but no trace of violet. The pepsin gave a, slight biuret reaction, but it was not ascertained whether the violet coloration obtained in the treatment with vanillin and hydrochloric acid was due to the pepsin itself or to the presence of traces of proteins in the same. w. P. s.BACTERIOLOGICAL, PHYSIOLOGICAL, ETC. 241 Composition of Date Wine. D. Bachilli. (Annali Chim. AppZic., 1915, 3, 101-110.)--The fruits of different varieties of Phmix dactylifera are used by the Arabs in the preparation of a light wine called Zdghtbi. Three samQles of the musts and of the wines made from them in Tripoli had the following corn osition in parts per litre : 1-0542 ' 1'0153 1-0679 19285 1.0718 1'0220 1. Must .. Wine .. 2. Must .. Wine .. 3. Muet .. Wine .. -- -- 143'89 57'16 1S6'19 97'24 182'43 80.15 I l'S1 1-55 1-51 2-04 2-17 2-57 0'31 4.4 2 0.36 5'89 0'06 6.20 0'35 0'33 0-45 -- 12.82 l(i'12 8'3% - - - - - - lOO%'i 113'06 116'70 - - - 11'86 37'6G - 30.07 - i 3 13 d - 10'40 12-36 10'96 - - C. A. M.

ISSN:0003-2654    

DOI:10.1039/AN9154000234

出版商:RSC    

年代:1915

数据来源: RSC

摘要:

BACTERIOLOGICAL, PHYSIOLOGICAL, ETC. PEEL : PULP : Green bananas ... Ripe ? ? ... Green bananaR ... Ripe 9 9 ... 241 41-72 36-51 5-21 0.55 0.34 0.26 0.37 0.29 ' 0.10 2.02 3.75 1 038 36'38 31.50 4.88 0'56 0'38 0.23 0.39 1'35 0.04 0'71 2-27 I 0.32 58.28 41'35 16'93 0'51 0'29 0.70 0'14 0'37 0'48 13'15 1;:;: i 0.40 59-73 42.99 16'74 0'51 0.28 0.74 0'14 10'34 1'52 2'40 0'18 BACTERIOLOGICAL, PHYSIOLOGICAL, ETC.Changes in Composition of Ripening Bananas. H. C. Gore. (J. Agric. Besewch, 1914, 3, 187-203.)-West Indian bananas were used for the experiments, two of which were conducted by placing bunches of green bananas to ripen in a large respiration calorimeter designed for experiments with man, while in the other two R specially designed ripening chamber was employed in order to investigate the rate of starch hydrolysis during ripening in relation to changes in the rate of respiration.The following figures were obtained, showing the composition of bananas before and after ripening in the respiration calorimeter : COMPOSITION EXPRESSED IN TERMS OF PERCENTAGE OF PEEL OR PULP WHEN ANALYSED. PULP : Ripe 9 9 ... 1 62-15 , 71-98 28'02 0.85 0'47 1-24 0'24 17-31 2.54 4.84 1'94 1 ff 1 :::: 22'66 26'28 0.69 4'02 0-30 COMPOSITIOlS EXPRESSED IX TERMS O F THE WHOLE GREEN BANANAS.*242 ABSTRACTS OF CHEMICAL PAPERS The principal change during ripening is the conversion of starch into sugars, which proceeds most rapidly while the fruits are turning from green to yellow.During this period the respiration-rate increases manyfold, becoming greatest at the time when tho rate of starch hydrolysis is most rapid.Starch hydrolysis then gradually slackens, later ceasing altogether. The respiration-rate, too, becomes slower, but still remains far more active than in the green fruit. The peel loses, while the pulp gains weter'steadily; the increase in water in the pulp during ripening being all derived from the peel except when bananas become over-ripe, when the water formed in respiration may more than balance the water absorbed in starch hydrolysis.The quantities of ash, protein, and ether extract undergo but slight changes during ripening, while pentosans decrease markedly in the pulp but remain little changed in the peel. Carbohydrates were determined by extracting weighed samples with 80 per cent.alcohol, the residues being dried and weighed and the weighed portions used in the estimation of starch and pentosans. The extracts were evaporated nearly to dryness with a little calcium carbonate, and after treatment with lead acetate were used for the estimation of reducing sugar and cane sugar. Starch was determined in the alcohol-insoluble portion by hydrolysis with hydrochloric acid.H. F. E. H. Ability of B. cold to survive Pasteurisation. S. H. Ayers and W. T. Johnson, (J. Agric. Research, 1915, 3, 401-409.)-The thermal death-point of 174 cultures of B. coli isolated from cow faxes, milk and cream, human faeces, flies and cheese, showed considerable variation when the cultures were heated in milk for thirty minutes under conditions similar to pasteurisation.At 60' C., the lowest pasteurising temperature employed, 95 cultures, or 54.6 per cent., survived ; at 62.8' C., the usual pasteurising temperature, 12 cultures, or 6.9 per cent., survived. One culture was not entirely destroyed at 65.6' C., but in repeated experiments this temperature always proved fatal. There is a, marked difference in the effect of heating at 60" C.and 62.8' C. Although the difference in temperature is only 2.8" C., yet it was found that 87 per cent. of the cultures that survived at 60' C. were destroyed at 62.8' C. Considerable variation was found in the thermal death-point of the colon bacilli which survived at 62.8" C. When the 12 cultures that survived were heated again at the same temperature, it was found that many did not survive, and in each repeated heating different results were obtained.It would appear that 62.8" C. maintained for thirty minutes is a critical temperature for colon bacilli. Among the 174 cultures examined, all were found to have a low majority thermal death-point, but were able to survive pasteurising temperatures in virtue of the survival of a few cells. An attempt to make the colon bacillus test an index of the efficiency of the pasteurisation process is thus complicated by the ability of certain strains to survive a temperature of 62.8' C.for thirty minutes and to develop rapidly when the milk is then held under temperature conditions which might be met with during storage and delivery, Experiments so far made indicate that no cdon bacilli will survive thirty minutes heating to 65.6' C., though such heat-resisting strains may yet be encountered.H. F. E. H.BACTERIOLOGICAL, PHYSIOLOGICAL, ETC. 243 Studies on Enzyme Action. XIII. : The Lipase of Soya Beans. K. G. Falk. (J. Amer. Chem. SOC., 1915,37,649-653.)-The lypolytic properties of soya beans were studied by the methods used in the similar studies of castor beans and of duodenal contents.Soya beans contain a lipase active towards triacetin (and therefore pre- sumably towards fats), somewhat soluble in water, with a maximum solubility in 1.5 N-sodium chloride solution. Castor beans contain an esterase soluble in water, and a lipase insoluble in water and soluble in sodium chloride solution, with maximum solubility at a concentration of 1.5 N.Duodenal contents contain an esterase and a lipase, the former predominating in the intestinal juice and the latter in the pancreatic juice and bile. Marked similarities in the action of neutral salts and alcohols are shown by the lipases from different sources. The action of heat and of drying on the soya bean lipase was found to be similar to their action on castor bean lipase and esterase.The analyses of the soya bean lipase preparations showed no marked differences in comparison with the analyses of the castor bean preparations. J. F. B. Mouldiness in Butter. C. Thorn. (J. Agric. Research, 1915, 3, 301-309.)- The following three forms of mould are most usually met with in butter : (1) Orange- yellow areas with a submerged growth of mycelium produced by Oidium lactis.(2) Smudged or dirty-green areas either entirely submerged or with some surface growth produced by species of Alternuria and Cladosporium. (3) Green surface colonies produced by species of PemkiZlium, or more rarely Aspergillus, either upon the butter, causing decomposition, or upon the container or wrappings, injuring the appearance of the sample in the markst.The occurrence of any of these forms in a sample of butter indicates low salting, since species of Oidium alternaria and CZadosporium cannot develop in butter containing 2.5 per cent. of salt. Excess of curd is found to favour mould growth, while well-washed butter is less subject to mould. Leaky butter-butter from which water of buttermilk exudes and collects in the wrappings or in the container-furnishes the best conditions for the beginning of mould growth, while from these'wet area8 colonies may spread to the butter itself.Mould will not grow upon the surface of a piece of butter exposed to humidities of 70 per cent. or lower. The water in the butter is thus not suficiently available to the mould to support the development of the colony unless evaporation be reduced by high humidities; Wet surfaces and wet wrappings must therefore be strictly avoided, A salt content of from 2.5 to 3 per cent.in butter is sufficient to eliminate mould or reduce it to a negligible amount, This is equivalent to the use of a 12 to 15 per cent. brine. H. F. E. H. Estimation of Sulphur in the Culture Medium for the Detection of the Bacteria producing Hydrogen Sulphide.H. W. Redfield and C. Huekle. (J. Amer. Chem. SOC., 1915, 37, 612-623.bThe methods standarised in the paper (see p. 250) were applied for the study of the changes brought about by the activity of sewage bacteria in culture media composed of peptone and potassium chloride. The following facts were established : The portion of the peptone medium which is insoluble in water contains the same percentage of sulphur as the soluble244 ABSTRACTS OF CHEMICAL PAPEES peptone ; filtration of the medium is therefore not essential.In cultures inoculated with artificial sewage and incubated at 38O C. for forty-eight hours, the ratio of total solids (excluding potassium chloride) to total sulphur is very nearly the same in the soluble and insoluble portions; hence the insoluble matter may be regarded as consisting mainly of peptone.The production of hydrogen sulphide by the bacteria present in the sewage employed was 50 per cent. greater when a current of air was passed over the surface of the culture than in the quiescent state, and 100 per cent. more than when a current of carbon dioxide was passed through the flask.In tt current of air 25 to 30 per cent. of the total sulphur was converted into hydrogen sulphide in forty-eight hours; 50 to 60 per cent. in seventy-two hours. For the estimation of the hydrogen sulphide evolved, the volumetric iodine method is inaccurate, probably because of the presence of unsaturated volatile organic com- pounds. The best method consists in absorbing the volatile sulphides in potassium hydroxide and determining the sulphur by the Liebig-Koch method.In order to expel all the volatile sulphides at the end of the period of observation, the cultures were heated on the water-bath for thirty minutes while a current of air was passed through. The sulphur retained in the cultures as non-volatile sulphides was determined by adding 25 C.C. of concentrated hydrochloric acid to 300 C.C. of the culture and distilling under reduced pressure for thirty minutes into a wash-bottle containing sodium peroxide solution, then estimating the sulphur by the Liebig-Koch method. The total sulphur-easily oxidisable sulphur and loosely bound sulphur- remaining unattacked in the culture media were then estimated by the methods already eatablished (see p. 250). Somewhat higher proportions of the loosely bound and the easily oxidisable sulphur were converted by the bacteria into hydrogen sulphide than of the total sulphur. J. F. B.

ISSN:0003-2654    

DOI:10.1039/AN9154000241

出版商:RSC    

年代:1915

数据来源: RSC

摘要:

244 ABSTRACTS OF CHEMICAL PAPEES ORGANIC ANALYSIS. Estimation of Carbon Monoxide by the Iodine Pentoxide Method. V. Froboese. (Zeitsch. anal Chem., 1915, 54, 1-11.)-In this method the U-tube containing the iodine pentoxide should be heated to 100' C. in a beaker of boiling water ; there is no need, to make the temperature higher by means of a paraffin bath (cf. ANALYST, 1914,39, 445). The amounts of iodine liberated or of carbon dioxide formed are both measures of the quantity of carbon monoxide present, but the more trustworthy results are obtained by estimating the carbon dioxide ; the latter may be estimated gasometrically, or it may be absorbed in barium hydroxide solution and the excess of this titrated, or the resulting barium carbonate may be collected, converted into barium sulphrtte, and weighed.I n this way carbon monoxide can be estimated in the presence of hydrogen or coal-gas, but the gas under examination must be freed previously from carbon dioxide, acetylene, and ethylene. Hydrogen liberates iodine from iodine pentoxide; at 70" C. the action is but slight, but at 160' C. a consider- able quantity of free iodine is formed, 80 that the amount of carbon monoxide cannot be calculated from the quantity of iodine set free.The iodine titration method may, however, be used for the estimation of small quantities of carbon monoxide in air, provided that a current of air free from carbon monoxide and carbon dioxide isORGANIC ANALYSIS 245 passed through the heated iodine pentoxide tube for one hour before and after the air under examination is conducted through the tube.The quantity of carbon monoxide in a gas is without influence on the results obtained by the iodine pentoxide method if the gas be passed through the apparatus at a rate not exceeding 1 litre per hour. w. P. s. Detection and Estimation of Small Quantities of Carbon Oxysulphide in Carbon Dioxide [Mineral Waters] and Well-Gases.L. Dede. (Chem. Zeit., 1914, 38, 1073-1075; through J. SOC. Chm. Ind., 1915, 34, 298.)-Certain mineral waters containing much carbon dioxide, although originally failing to respond to the usual tests for hydrogen sulphide, developed appreciable amounts of that substance upon keeping ; the gases from these waters, including one particular specimen of carbon dioxide used commercially for aerating purposes, behaved similarly.The presence of sulphur was established and its amount det'ermined in the original gases by fixation as lead sulphate, according to Dennstedt's combustion method. No sulphide was produced from dissolved sulphate either in the presence of ferrous bicarbonate or of cork fragments, even after keeping for long periods; its formation is ascribed to the presence of small amounts of carbon oxysulphide in the waters.The decomposition of this substance by water, being a reversible process, oocurs very slowly. in the presence of carbon dioxide : COS + H , 0 Q H 2 S + GO,. When water containing 0-05 per cent. of sodium bicarbonate was saturated with carbon dioxide containing 0.02 per cent. of carbon oxysulphide and preserved in stoppered bottles, the odour of hydrogen sulphide became perceptible after about four days.Carbon oxysulphide was most conveniently detected and determined by aspirating a slow stream of the gas through a Lunge bulbtube containing a dilute (1 : 1,000) solution of palladious chloride acidified with hydrochloric acid and kept at 50' C. : COS + P d Q + 4 0 = PdS.+ 2HCl+ GO,.In the presence of fairly large amounts of hydrocarbons and other reducing gases which cause the separation of metallic palladium, stronger solutions of palladium chloride (up to 4 : 1,000) were necessary. The precipitate was collected, washed, and dissolved in hot 10 to 15 per cent. hydrochloric acid containing a little potassium chlorate, the bulbs being washed out with the same reagent.The amount of sulphate in the diluted solution was estimated by precipitation with baxium chloride. Three successive quantities of 25 litres of the commercial carbon dioxide mentioned above yielded, respectively, 0.0057, 0.0059, and 0-0048 grm. BaSO,, corresponding to 0-0029 per cent. COS by weight. The gas obtained directly from a well by means of a partially immersed bell-jar and a 25-litre aspirator gave, similarly, 0.0037, 0.0031, 0.0038, 0.0035, and 0.0039 grm.BaSO, per 25 litres, corresponding to 0-0019 per cent. COS by weight. I t is suggested that the change in the physiological action of certain mineral waters upon storing may probably be connected with the gradual decomposition of small amounts of carbon oxysulphide. Estimation of Formic and Acetic Acids and the Separation of these Acids in very Dilute Solutions.E. Heuser. (Chem. Zeit,, 1915, 39, 57-59; through J. SOC. and Chem. Id., 1915, 34, 286.)-The estimation of formic and acetic246 AESTRA CTS OF CHEMICAL PAPERS acids by acidifying with sulphuric acid and distilling with steam requires too much time for ordinary use, and if the sulphuric acid be replaced by phosphoric acid, the results are vitiated hy the latter passing over into the distillate.Good results are obtained if the vapours are passed through a flask filled with glass beads and heated by a water-bath on their way to the condenser (cj. Wenzel, Monats. Chem., 1897, 659). The sample is mixed with 50 C.C. of water and 50 C.C. of phosphoric acid of sp. gr.1.2 and distilled at 44" C. (56 mtn. pressure) until the volume is reduced to 50 C.C. A further 50 C.C. of water is then added, and the mixture again distilled to a volume of 50 C.C. A current of air free from carbon dioxide is drawn through the apparatus during distillation. The use of a flask filled with glass beads is also necessary in determining acetic acid by distillation in a mixture of formic and acetic acids after destroying the former by oxidation with bichromate and sulphuric acid.Separation of Gases by Fraotional Distillation in a Vaeuum at Low Temperatures. G. A. Burrell and I. W. Robertson. (J. Ind. and Eng. Chem., 1915, 7,209-210.)-The authors summarise their previous work (ANALYST, 1914, 39, 414; 1915, 162, 163), and give particulars of further separations that they have effected by similar methods.From a mixture of gaseous olefines, ethylene can be separated by cooling to -140' C., and then exhausting the containing vessel by means of the vacuum-pump. From the residual liquid propylene can be removed by allowing the temperature to rise to - 120" C. and again exhausting. Mixtures of gaseous paraffins and olefines can be analysed as follows: The methane is removed by cooling to the temperature of liquid air and exhausting. Ethane and ethylene are removed at -140" C., and propane and propylene at -120" C., leaving the butanes and butylene as a residue.The pairs of constituents are then analysed by combustion with oxygen, Like fractional distillation of liquids at temperatures above room temperature, the above methods do not give sharp separations at one operation; but methane can be sharply separated in two operations, three or four being necessary to recover in a pure state the whole of the ethane or propane from a, mixture of gaseous paraffins.I t is even possible to separate ethane from ethylene, but the process is so tedious that it is not reoommended. G. C.J. Rapid Method of Fractionating Gases at Low Temperatures. G. A. Burrell and I. W. Robertson. (J. Ind. and Eng. Chem., 1915, 7, 210-211.)-The method is essentially identical with that already described (see preceding abstract), the novelty consisting in detailed instructions for securing sharp separations with a minimum expenditure of trouble and time. The following details show the best means of making a complete analysis of illuminating gas similar to that supplied to New York City, the composition of which is given below.About 1,000 C.C. is taken for analysis, freed from carbon dioxide by means of potash, and liquefied by means of liquid air. At the temperature of liquid air as much gas as possible is pumped off, constituting fraction A, which is preserved in a separate container.The residual liquid is next allowed to attain a temperature approximating, but not higher thanORGANIC ANALYSIS 247 Per Cent. Carbon dioxide ... ... 4.7 Carbon monoxide ... ... 29.8 Hydrogen ... ... ... 32.0 Methane ... ... ... 13.1 Ethane ... ... ... 2.8 Propane ... ... ... 0.3 Per Cent. ... Ethylene ... ... 9.8 Propylene ... ... ... 2.7 Butylenes ...... ... 1.6 Nitrogen ... ... ... 1.7 Benzene ... ... ... 1.5 Estimation of Unsaponiflable Matter in Greases. E. Twitchell. (J. Ind. and Eng. Chem., 1915, 7, 217-218.)-Five grms. of the sample (or, preferably, of the fatty acid prepared for 6 L titer " test, as this is cleaner) is saponified with alcoholic potash in a dish and evaporated nearly to dryness. A little alcohol is added, and the water and the solution obtained is washed into a separator. The alcohol-water ratio should be about 1 : 4, and the total volume 150 to 200 C.C.The soap solution is shaken twice with ether, using 50 C.C. each time. A third treatment with ether extracts so little that for ordinary analytical work it may be omitted. Owing to the comparatively high concentration of alcohol, the separation of the liquid into clear and sharply defined layers is almost instantaneous.More soap passes into the ethereal layer than is the case when less alcohol is used, but this is readily corrected for. The ethereal solution is washed once with water, then with hydrochloric acid, again with water, transferred to a weighed dish, and evaporated. The residue is dried at 110" C., weighed, dissolved in neutral alcohol, and the solution titrated with standard alkali.The fatty acids thus found, derived from soap dissolved by the ether and subsequently decomposed by hydrochloric acid, are calculated as oleic acid and deducted from the weight before obtained. The method, which has been in use five years, never gives lower results than other methods.Occasionally the results248 ABSTRACTS OF CHEMICAL PAPERS are higher, but are believed to be more exact, examination proving absence of neutral fats and of ethyl esters, which might conceivably be formed when the alcoholic ethereal extract is shaken with hydrochloric acid. G. C. J. Estimation of Small Quantities of Hydrocyanic Acid. A. Viehoever and C. 0. Johns. (J. Amer.Chem. Soc., 1915, 37, 601-607.)-1n the colorimetric estimation of cyanides by the Prussian blue reaction, the maximum formation of blue is only obtained when the volume of the solution tested is sufficiently small. The solution of hydrocyanic acid must therefore be concentrated, which may be done without appreciable loss by evaporating under reduced pressure in presence of a small excess (0.02 to 0.1 grm.) of sodium hydroxide.The evapora- tion is performed in a distillation flask, which is heated in a water-bath at 70" C., and loss of cyanide by entrainment is avoided by interposing an adapter, like that employed in distillations of ammonia by the Kjeldahl method, between the flask and the condenser. With quantities of about 0.5 mgrm. of hydrocyanic acid or 1 mgrm.of potassium cyanide, it is essential that the solution be evaporated to a volume not exceeding 1 C.C. ; 0-2 to 0.5 C.C. of a freshly prepared 3 per cent. solution of ferrous sulphate and 0.05 grrn. of potassium fluoride are then added, the flask is again connected with the vacuum pump, and the contents are mixed by agitation, Quick exhaustion of the air is necessary, because it ie desirable that the reaction take place without the formation of any considerable quantity of ferric salt by oxidation.After five to ten minutes a t the ordinary temperature the flask is detached from the pump, and the mixture acidified with 30 per cent. nitric acid. Sulphuric acid may be used, but hydrochloric acid in excess tends to produce a green colour. When only traces of hydrocyanic acid are present, it is sometimes necessary to warm to about 50" C.before the colour appears. It is noted that the presence of the potassium fluoride has a most favourable effect on the formation and clearness of shade of the blue, The results are obtained by colorimetric comparison with a standard solution of potassium cyanide similarly treated. When less than 1 mgrm.of potassium cyanide is present, the quantities of the reagents should be reduced, as an excess is to be avoided. As a qualitative test, the reaction is sensitive to 0-00002 grm. of potassium cyanide. J. F. B. Analysis of Vegetable Parchments. R. W. Sindall and W. Bacon. (Chem. Engineer, 1915, 21, 75.) - The preparation of slides for the microscopic analysis of vegetable parchments is difficult on account of the resistance of the paper to disintegration into its constituent fibres.Chemical methods of disintegration- e.g., by the use of cuprammonium solution (Vidal) or of moderately diluted sul- phuric acid (Bartach)-are open to the objection that some of the fibres are more profoundly attacked than the others, so that in papers composed of a mixture of rag and wood cellulose fibres, a portion of the latter may be lost.The authors therefore prefer a mechanical method of disintegration, such as is readily performed by a small vertical coffee-mill. About 0% grm. of the sample is crumpled up with hot water, then torn into small piecee, and passed through the mill several times with a little water. The friction of the particles of paper upon each other andORGANIC ANALYSIS 249 between the closely set surfaces of the mill separates the fibres fairly completely, and the resulting pulp can then be mounted for microscopic examination in the usual.manner. In staining with the iodine-zinc chloride reagent, the solution should be diluted before applying it to the preparation, as the chemically modified fibres of vegeta.ble parchment react so strongly with the ordinary stain that all distinguishing tints are obscured.J. F. B. Analytical Distillation of Petroleum. W. F. Rittmann and E. W. Dean. (J. Ind. and Eng. Chem., 1915, 7, 185-195.)-A comparative study of three types of apparatus-(1) Those designed to effect fractionation in a high degree, such as that of Hempel; (2) those designed to prevent any cooling of vapour between the surface of the boiling liquid and the outlet to the condenser, of which Allen and Jacobs’ apparatus (U.S.Bweau of Mines, BzlZZ. 19) was selected as example ; and (3) those in general use in the petroleum industry, which come midway between these types, and of which Ubbelohde’s was selected as example. As might be expected, the gradation in specific gravity of successive fractions showed that Hempel’s method effected the highest degree of separation, Allen and Jacobs’ the least.On redistillation of the separate fractions in the apparatus with a Hempel column, it was found that on the average only 14 per cent. of each of the fractions from Allen and Jacobs’ apparatus distilled between the original temperature limits, whilst the percentage in the case of fractions obtained by Ubbelohde’s method was about 25, and in the case of fractions originally distilled from Hempel’s appa- ratus it was 55.The comparative extent of fractionation effected by the three methods is brought out in several tables and curves, but most strikingly by a table obtained from one of the curves. The curve was constructed by plotting the specific gravities of each small fraction obtained by redistillation, in the Hempel apparatus, against the percentage of distillate collected when that small fraction was half collected.By interpolation, the specific gravity of the distillate at any stage of the redistillation could be obtained. I t was found that when crude petroleum was distilled in a Hempel apparatus, the receiver change! at each 25’ C.rise of tem- perature, and any one of the fractions redistilled in the same apparatus, the differ- ence in specific gravity of the liquid coming over when only 5 per cent. had distilled and that coming over when only 15 per cent. remained in the still was only 0.010 when the fraction submitted to redistillation was a high fraction, increasing to 0.024 for the lowest fraction.When a fraction obtained by Ubbelohde’s method was similarly distilled in the Hempel apparatus, the corresponding rise in specific gravity between 5 per cent. and 85 per cent. distillate (chosen to eliminate irregularities at the beginning and end of a, distillation) was from 0.025 for fractions boiling above 275’ C. to 0.047 for the lowest fraction.The corresponding range, starting with Allen and Jacobs’ method, was as great as 0.043 to 0.075. I t is sometimes assumed that any method of distillation will give useful information, provided it is somewhat rigidly defined. In support of this it might be alleged that when temperatures are plotted against percentage of distillate below that temperature, nearly straight lines are traced in the case of petroleum, and that these lines, though not identical if varying methods be adopted, are substantially250 ABSTRACTS OF CHEMICAL PAPERS parallel.This is approximately, but only approximately, true, and the divergence is most marked at the bottom of the curve-that is to say, the most important part of its range, having regard to the present high price of motor spirit compared with other petroleum distillates.No method is yet recommended; but the work now described is part of an attempt by the United States Bureau of Mines to improve on existing methods. The ideal method must minimise, or, if possible, eliminate ( ‘ cracking ”; the apparatus must be standard and easily obtainable; and the results must meet the needs of both the scientist and the oil technologist.They need not be identical with those obtained in the refinery-in fact, they cannot be, having regard to the variations in works procedure. G, C. J. Comparative Study of Methods for the Quantitative Estimation of Sulphur in Peptone. H. W. Redfield and C. Huckle. (J. Amer. Chem. SOL, 1915, 37, 607-611.)-0f the various methods tested, the Liebig-Koch method (diges- tion with nitric acid and fusion with potassium nitrate and hydroxide) gave the highest and most consistent results. A slight modification was introduced : the solution of 2 grms.of peptone, after digestion with nitric acid (sp. gr. 1-4) on the water-bath for two hours, was introduced into a nickel crucible containing 8 grms. of potassium hydroxide and 0.5 grm.of potassium nitrate and evaporated over an alcohol lamp, a jet of air being directed over the surface of the liquid ; in this way a perfectly homogeneous mixture for fusion was insured. I n transferring the liquid from the beaker to the crucible, the particles adhering to the sides of the beaker were wiped off with a piece of filter-paper wrapped round the end of a glass rod, the paper being added to the solution in the crucible.Tests were made which proved that no sulphur was lost in the form of volatile compounds during the preliminary digestion with nitric acid in open vessels. The time of the digestion beyond two hours had no influence on the results. The following results for total sulphur in Witte peptone, corrected for moisture and for sulphur introduced by the reagents, are recorded : Liebig method, 0.9902 ; Osborne method, 0,9479 ; A.O.A.C. method, 0.9664 ; Liebig-Koch method, 1.0061 per cent. For the determimtion of loosely bound sulphur, the Schulte method was approved, and for that of the easily oxidis- able sulphur, the method of digesting 2 grms. of peptone with 20 C.C. of a saturated solution of potassium chlorate in nitric acid for two hours on .the water-bath, evaporating to dryness, adding 5 C.C. of hydrochloric acid and 20 C.C. of water, evaporating to dryness, dehydrating and determining the sulphate, gave the most consistent and valuable results. The numbers recorded are-for loosely bound sulphur by the Schulte method, 0.3813 per cent.; for easily oxidisable sulphur, 0.5194 per cent. The portion of peptone soluble in alcohol showed total sulphur 0.7950 per cent. by the Liebig-Koch method, the residue insoluble in alcohol, 1.0743 per cent. J. F. B.

ISSN:0003-2654    

DOI:10.1039/AN9154000244

出版商:RSC    

年代:1915

数据来源: RSC