摘要:

THE ANALYST. JULY, 1891. PROCEEDINGS OF THE SOCIETY OF PUBLIC ANALYSTS. A GENERAL meeting of the S,ociety was held on the 3rd ult., at Burlington House, the President, Mr. Hehner, in the chair. The minutes of the previous meeting were read and confirmed. A ballot was taken for new members, and the following were declared elected : As member, J. Rymer Paterson, B,Sc., Analyst, Edinburgh. As associate, B. H. Gerrans, assistant to Mr. Cassal. “On the Action of Milk Preservatives,” by A. W. Stokes. (‘ Experiments on the influence of Boric Acid on Peptic Digestion,” by the ‘‘ Experiments on the Estimation of Boric Acid,” by the President. ‘ Note on the Composition of Butter-fat,” by A. 11. Allen. ‘‘ Fat-free Paper for use in Milk Analysis,” by Dr. P. Vieth. The following papers were read and discussed : - President.The President said that those gentlemen who had received THE ANALYST that That journal, day would have seen that a new era had commenced with the Society.122 THE ANALYST. . which for many years had been in private hands, had now become tho property of the Society, and would in future be carried on by the Council. That such a change was not only desirable, but necessary, must have been evident to all those who had wakched THE ANALYST during the last few years. They, as a Society, owed a debt of gratitudeto Dr. Muter, who had carried them over a time of difficulty. As mentioned in the manifesto he had published, Dr. Muter took over TEE ANALYST, and carried it on at a time when, had he not done so, it was possible that both the Journal and the Society might have come to grief. The Society stood now in z1 different position, and they could look upon their future with con6dence. It was determined to take THE ANALYST over on the first opportunity, and they had done so that, day. They firmly relied upon every member of the Society, perhaps even more than in the past, to assist in filling the pages of their journal with matter which would be, not only worthy of the Society, but would also be honoured and quoted by men of science all over the world. The summer meeting of the Society, with which it is proposed to combine an ex- cursion into the adjacent country, will be held this year in London. Full particulars will be announced in due course.

ISSN:0003-2654    

DOI:10.1039/AN891160121b

出版商:RSC    

年代:1891

数据来源: RSC

摘要:

122 THE ANALYST. . THE INFLUENCE OF MILK PRESERVATIVES. BY MR. A. W. STOKES. (Read at Meeting, June 3 4 1891.) DURING about a year I have been interested in determining the acidity of milk as in- fluenced by temperature and by the addition of preservatives. Between four and five hundred determinations of acidity have been made for that purpose under various con- ditions, Though there is much more remaining that might be done t o complete the enquiry the results so far obtained may be of interest. Milk as delivered to the London trade is always acid, this acidity on an average is equal to 0.2 per cent, of lactic acid. Such an amount of acidity usually develops in the milk within eight hours of its coming from the cow. I n England, according to the temperature, in from 30 to 40 hours after it has reached an acidity of 0.2 per cent., its acidity rises to 0.35 or 0.4 per cent., at which point it has acquired an acid taste, and is said to be sour.Usually a t an acidity of 0.6 to 0.7 per cent. it separates or coagulates. If kept for a long period milk rarely develops a greater quantity of lactic acid than 2 per cent. In some milk, the acidity of which I determined (see ANALYST, xii., 226), the highest acidity found was 2.34 per cent. after i i 7 days of keeping. The reason of this is, that when this amount of acidity is reached the acid formed is destructive t o the fungus forming it. Milk that has not yet developed an acidity of 0.3 per cent,, but is near it, will coagulate on boiling j it is therefore customary in the trade to test the freshness of a milk, if it is suspected to be stale, by boiling it.To find how long a milk, not sealed up, will keep fresh, without becoming at all sour to the taste, I took a large quantity of the same milk and divided it into 11 parts ; one part was kept in its original state, another part was boiled, and to the others various preservatives were added. All these were placed in separate bottles, which were kept open j at intervals of about four hours their acidity was determined.123 - THE ANALYST. They were shaken each time that tho acidity was determined. The time was noted when each became sour. Taking the moment when the unpreserved milk became sour as the starting point I find that the others kept fresh to the following extent longer :- Samples containg one part per 1,000 of a mixture of equal parts of (dry) carbonates of soda and potash kept fresh five hours longer and became sour to the taste at an average acidity oE 0.32 per cent.lactic acid. Samples containing two parts per 1,000 of the above mixture kept fresh for twenty hours longer and tasted sour at an average acidity of 0.45 per cent. Samples boiled kept fresh twenty hours longer than the ordinay milk and tasted sour at 0.32 per cent. acid. Samples containing 10 per cent. of a saturated aqueous solution of salicylic acid kept fresh twenty hours longer, tasting sour at about 0.44 per cent. acid. Samples containing one part per 1,000 of borax (crystal) kept fresh for seventeen hours longer, tasting sour at about 0.4 per cent. of acid. Samples containing two parts per 1,000 of borax, kept fresh for twenty-five hours longer, tasting sour at about 0.42 per cent.of acid. Samples containing one part per 1,000 of boracic acid kept fresh for twenty-four hours longer, tasting sour at about 0.44 per cent. of acid, Samples containing two parts per 1,000 of boracic acid kept fresh for forty-two hours longer, tasting sour at about 0'46 per cent. of acid. Samples containing one part per 1,000 of a mixture of equal parts of borax and boracic acid kept fresh for twenty hours longer, tasting sour at about 0.42 per cent of acid. Samples containing two parts per 1,000 of above mixture kept fresh twenty-seven hours longer, tasting sour a t about 0.49 per cent. of acid. The average temperature was 6 5 O F. The usual proportion recommended by the vendors of of which are, in my experience, composed of borax or boracic two)is about one part to 1,000 of the milk, Salicylic acid is too insoluble to make it possible to use I have never found it in milk.preservatives (almost all acid, or mixtures of the much of i t ; personally, From thesa experiments I find that boracic acid is the best preservative. What- ever the preservative, the milk tastes sour when it reaches about the same acidity 0.4 per cent. to 0.49 per cent. Though the addition of carbonates of soda and potash or borax reduces the original acidity of the milk, and should therefore apparently give it a longer range and time before it reaches the acidity at which it must turn sour, and while on the other hand boracic acid adds to the original acidity and so apparently lessens the range and time, yet the action ia reversed and boracic acid is the best preservative.How great the apparent difference is may be noted from an instance : a sample of milk had an acidity of 0.15 per cent. On adding two parts per 1,000 of borax its acidity sank to 0.11 per Cent.124 THE ANALYST. While that to which two parts per 1,000 of boracic acid was added had an acidity of 0.33 per cent. Boiling the milk seems as efficacious as the use of one part per 1,000 of any the preservatives. Four years ago I endeavoured to find the limit at which borax could be detected by the turmeric reaction in milk. I found that a drop of milk containing the thousandth of a grain of borax would give the reaction if treated thus :-On a porcelain slab place one drop of the milk with two drops of strong HCI and two drops of a saturated turmeric tincture.Dry this on the water bath, take it off directly it is dry. Add a drop of ammonia by means of a glass rod. A slatey-blue colour changing to green is produced, Even less than this will give the green tint, but not the blue. The turmeric tincture must be fresh, other- wise it is better to use the powdered turmeric. Even half this quantity of boracic acid can thus be detected j in such case the HCl should be omitted from the test. Though unpreserved milk usually turns sour to the taste when its acidity reaches 0.3 per cent. there are yet exceptions. I found three samples which, when they reached me they were quite fresh to the taste, though having an acidity of 0.5 per cent.In forty-seven hours later they were of an acidity of 0.54 per cent. At this stage I took parts of each and boiled them without their coaguIating at all. Only a t the 71st hour, when their acidity was 0.65 per cent., did they become at all sour to the taste. Such exceptions show that milk does not always decompose at the same rate as is asserted in some quarters. To Mr. W. N. Yarrow I am greatly indebted for care and attention in carrying out much of this tedious enquiry. The acidity in the above cases was determined by means of decinormal soda solu- tion, using phenol-phthalein as an indicator. Being asked some time ago to devise some method simpler than the burette for rapidly determining the acidity of milk for use in the milk trade, I had made som0 compressed pellets containing carbonate of soda and phenol-phthalein, By modern automatic machinery it is possible to weigh out successive quantities of as little as two tenths of a grain with great accuracy.So that, compressed into little pellets of & inch diameter and weighing only one grain each, we have accurate quantities of the alkali and theindicator. Into a narrow tube milk is poured up to a 10 C.C. mark, a pellet is dropped into this milk and crushed by a glass rod. If a permanent pink colour is not produced other pellets are dropped in until the pink colour is permanent. The number of pellets used gives in tenths of a per cent. of lactic acid, the acidity of the milk. The accuracy of the method within the range of acidity in milk and within the limits of one- tenth of a per cent. have been vouched for by several analysts.The principle of these pellets, that is, the use of accurate quantities of dry com- pressed reagents, may be useful in other branches of’ science-hence I may be excused for mentioning the subject. DISCUSSION. MR. CASSAL said that the use of boric acid and of other antiseptic agents for the preservation of food was a subjeot which required immediate and full discussion by Cool.THE ANALYST. 125 public analysts. Inasmuch as refrigeration when properly applied was a legitimate method of preserving milk, it would be interesting to know how long decomposition could b3 retarded by it under normal conditions. He did not gather that Mr. Stokes had made any experiments in this direction.He had reason to believe that refrigera- tion was found to be amply sufficient for all practical purposes, when it was deemed necessary to adopt precautions against premature decomposition. With regard to the tumeric test, evaporation on porcelain had already been mentioned at the Society as a useful modification of the application of this test. He understood that Mr. Stokes approved of this modification for the detection of minute quantities of boric acid. With regard to the acidity pellets, he (Mr. Cassal) was bound to say that he regarded with strong disfavour the introduction of all devices, which were calculated to make untrained persons of various degrees of ignorance imagine that they could act as their own analysts or consulting chemists.It was highly undesirable to put these “tests” into the hands of dairymen and others. They were edge tools likely to wound unskilled hands; while, from a professional point of view, it was objectionable also. As it was, the public, in their ignorance, were far too ready to believe that the whole of the work of analytical chemists cocsisted in the application of ‘( tests” of this kind. He submitted that, in any case, such a step should only be taken after consultation, and with the general approval of the profession. DR. VIETH said he supposed Mr. Stokes had make his experiments during the winter months, and he was quite sure that if they were repeated during the summer or autumn the results would be very different. The temperature of the room in which they were made was not the only factor to be taken into account.There was on doubt milk went sour mush more quickly in summer and autumn, October and November being the most troublesome months. Farmers attributed this to the decaying lesves, and this was per- haps not far from the truth. He was rather surprised to see that the milk kept for about 170 days had contained 2.3 per cent. of lactic acid ; his own experience was, that as soon as 1 to 1.5 per cent. was reached, fermentation practically ceased, or at any rat0 proceeded with extreme slowness. With reference to the retarding action of boracic acid on lactic fermentation, other experimenters had not got such good results as Mr. Stokes. His impression was that Mr. Stokes had made his experiments at a time most favourable for showing the best action of the preservative.As far as the milk trade of London was concerned, he most emphatically repeated what he had said on former occasions, viz , that in his opinion there was no reason whatever for using any preserva- tive. Dr. Vieth added, that in cheese making it was a necessity that the milk should have a certain degree of acidity. During the last four yearsa number of tests had been introduced for determining the acidity of milk, and he thought that Mr. Stokes’ was the most simple, handy and reliable that could be placed in the hands of the practical cheese maker, The PRESIDENT said, that if allowance was made for the content of inert matter in borax, its activity was as near as possible the same as that of boric acid ; this was shown by Mr. Stokes’ experiments. As to hydrofluoric acid, his experience was that it kept milk samples perfectly for a great length of time. I n reply, Mr. Stokes said that the mass of milks referred to were analysed from January to May last. I n reference to Mr. Cassal’s objection to his supplying the milk trade with an apparatus that could be readily and cheaply used for stopping the sale of stale milk, he really thought such an apparatus would be an advantage to all parties. Acidity must be determined at the moment the milk is suspected. It would be impossibla to send such samples to professional analysts, since, in the majority of cases, the milk would have so far changed in its passage to the analyst as to make an acidity determina-126 THE ANALYST. ~ ~~ tion then of very little value. He thanked Dr. Vieth for his generous testimony to the accuracy and simplicity of the pallet method referred to. If it only prevented, to some extent, stale samples being sent for analysis, it would save much trouble and not a few ambiguous results. Mr. Stokes certainly objected to milk being ‘; preserved ” by any other means than refrigeration or scalding.

ISSN:0003-2654    

DOI:10.1039/AN8911600122

出版商:RSC    

年代:1891

数据来源: RSC

摘要:

126 THE ANALYST. ON THE INFLUENCE OF BORIC ACID ON PEPTIC DIGESTION. BY OTTO HEHNER. (Read at Jfeetiny, June 3rd, 1891.) IN view of the extending us9 of boric acid and several of its compounds for the preservation of food, precise information as to its action upon the animal body is exceedingly desirable. While Leffman and Beam (ANALYST, Vol. xiii., p. 103) have found that boric acid has practically no influence on the diastatic action of malt extract, and, pre- sumably, also upon that of the saliva, Gorup-Besanez (Lehrbuch Physi02 ; Chernie, p. 45), a high authority, states that a solution of borax, whilst without influence upon organised ferments, renders non-organised ones inactive. I n order to put these conflicting statements to the test, as regards pepsine, I charged twelve bottles each with 50 grms.of hard-boiled white of egg, which had been rubbed through a very fine sieve, added 250 C.C. of water, containing 0.15 per cent. of hydrochloric acid and 0.34 grms. of pepsine, which had been previously ascertained to be capable of completely dissolving 2,500 times its weight of albumen, in about five hours, at a temperature of 40° C. j 0.033 grms. of pepsine were, there- fore, capable of dissolving completely 82.5 grins. of albumen. To bottle No. 1 no further addition was made ; to the other eleven the following quan- tities of pure boric acid were added : 0.1, 0.2, 0-3, 0.4, 0.5, 0.6, 0.8, 1.0, 1.5, 2.0, 2.5, and 3.0 grrns. The whole of the bottles were then plunged into a water bath and kept at a temperature of 40° C., with frequent shaking.The albumen dissolved equally well in the whole of the bottles, and after about five hours, solution was complete in all the samples. There was no difference whatever between the action of pure pepsine and that charged with as much as 3 grms. of boric acid, I conclude that boric acid, even in the amounts used, has no retarding influence upon peptic digestion. DISCUSSION. Mr. CASSAL said that Mr. Hehner’s experiments were of great interest and import- ance, They certainly seemed to show that boric acid had no influence on peptic diges- tion-at any rate outside the body. But it could not, of course, be assumed that boric acid, even in very minute amount, would not injuriously affect the processes of digestion and assimilation in the body. I n the experiments with pepsin and albumen, they were not dealing with living tissue or vital processes; and Mr.Hehner had obviously no intention of drawing any other conclusions from his experiments than that the dissolving of egg-albumen by pepsin in a glass vessel, under the usual conditions, was not interfered with by the presence of boric acid. The actual effects of small doses of boric acid required further study j the results hitherto recorded, such as those of JFGrster, went to show that injurious effects were produced, as indeed on a priori ground it would be reasonable to expect. But apart from this question of injuriousnessTHE ANALYST. 127 it was necessary that public analysts should arrive a t a clear understanding and agree- ment as to how the presence of boric acid in articles of food was to be regarded by them.Was it an adulterant wit'hin the meaning of the Act? For his own part, he was unable to see how any public analyst could conscientiously arrive a t the conclusion that it was not. Mr. HEHNER, in reply, said that he had not in any way altered the opinion which he had expressed on a previous occasion. He objected to the indiscriminate use of chemical food preservatives, as they were bound to have some physiological action. The experiments which he had brought forward that night showed that boric acid, a t least, had no influence upon gastric digestion; but they did not in any way show that boric acid was a desirable ingredient in food. He had lately had to analyse some hams, which had been alleged to have produced injurious effects, and he had found them to be strongly impregnated with boric acid. He had since ascertained that bacon was very largely borated. He was convinced that the dealers in food, who were responsible for the employment of antiseptics, would not knowingly use anything injurious; but it was the duty of public analysts to probe this matter to the bottom, the more so as, sooner or later, it would have to be decided either in a court of law or subjected to legislation.

ISSN:0003-2654    

DOI:10.1039/AN8911600126

出版商:RSC    

年代:1891

数据来源: RSC

摘要:

THE ANALYST. 127 FAT-FREE PAPER FOR USE I N MILK ANALYSIS. BY DR. P. VIETH. (Read at Meeting, Jwne 3 4 1891.) IN a paper read before this society in May, 1889 (THE ANALYST, 1889, Vol. XIV., p. 121), Mr. Richmond stated that Messrs. Schleicher and Schull were placing on the market a fat-free paper suitable for fat determinations in milk. For this paper we have had to wait a long time; but it has made its appearance at last, and I thought members might like to know that the paper can now be had of the well-known firm of Townson and Mercer. After consider- able trouble and many disappointments, we have been successful in manufacturing a fat-free paper by systematically treating it with absolute alcohol. The new article thus produced contains such a slight trace of fat that it has no influence whatever on the ana1ysis.d’ As soon as I had heard of the existence of the paper, I procured some for the purpose of experimenting with it, and with a view of adopting it for future work, in case the experiments should turn out satisfactory.The paper is thicker than that originally recommended by Mr. Adams, and the strips are consequently heavier; as to matter soluble in ether: this is certainly not totally absent. I n three lots of filter paper, such as I was in the habit of using for plaster cartridges, I had found some years ago *232, 0161, and 0181 per cent, ether extract, and in two lots of blotting paper of the kind recornmended by Mr. Adams 0297 and 0314 per cent. The new paper gave in one experiment *0278 per cent, ether extract, and in another, in which I experimented on strips which had been previously wetted with dilute acetic acid and dried again, *0250 per cent, The latter figure proves that there was nothing of a soapy nature present.The average amount of matter soluble in ether for one strip, weighing six grammes, is *U016, and this quantity would increase the result of a fat determination by *03, provided the same amount, which is extracted in a blank experiment, is also got out after five grammes of milk have been dried on the paper. I n a circular the manufacturers state that, I am not at all sure that the latter is the case.128 THE ANALYST, No. of Siphonings, Time Min. I Sample No. Mr. Richmond, in the paper already mentioned, recommends to continue the extraction for three to four hours, My own experiments lead me to believe that extraction is practically completed in a much shorter time.Two samples, one of whole and one of skim milk, when extracted for different lengths of time, gave the folIowiag results :- Time of Extraction, Whole Milk. Skim Milk. 1 hour .. .. . * 3 048 -28 2 hours ,. . * .. 3.50 -30 * * I . * . 3.54 -28 * . .. .. - *28 3 99 4 99 Experimenting upon six other samples-three of whole and three of skim milk- The experiments were The I noted not only the time, but also the number of siphonings. made with a view to find out the shortest time required for extracting the fat. following results were obtained :- Fat-Per cent. I. 3 17 *28 -24 6 37 9 52 I 11. 19 41 59 111. -2 2 *24 024 3 5 9 13 47 41 - I *24 -2 4 02 6 24 33 51 I 4.1 8 4.14 4.24 3 6 9 6 3-68 3.68 3 6 9 3 6 9 15 2.84 41 2188 50 2 90 VI. OF these results, those referring to samples 111. and VI. are particularly note- worthy, where with three siphonings, and in the short time 02 thirteen and fifteen minutes respectively, practically the whole of the fat had been extracted. AlthoughTHE UALYST. 129 * perhaps of little practical value, this observation is not without some interest, Con- tinuing the extraction for an hour appears to be more than suffioient for all practical purposes*

ISSN:0003-2654    

DOI:10.1039/AN8911600127

出版商:RSC    

年代:1891

数据来源: RSC

摘要:

THE UALYST. 129 THE SEPARATION OF TITANIUM, CHROMIUM, ALUMINIUM, IRON, BARIUM AND PHOSPHORIC ACID IN ROCK ANALYSIS. BY THOMAS M, CHATARD.* HAVING to examine some magnesian silicate rocks containing, in addition to iron and aluminum, small quantities of titanium, chromium, barium and phosphoric acid, the methods for the decomposition of such rocks and the separation of their constituents were studied and compared so as to determine the most advisable manner of procedure. After repeated trials the following course, combining a number of well-known methods, has been found to be the most satisfactory. The silica and bases are determined by the ordinary sodium carbonate fusion method, in which the hydrates of titanium, chromium, iron and aluminum, together with the phosphoric acid, are precipitated together, and, after weighing, fused with sodium bisulphate, dissolved, the small amount of silica separated, and the solution, after reduction of the ferric oxide, titrated for total iron.To separate these oxides and at the same time to determine the barium, two grams. of the finely pulverised mineral are put into a platinum crucible or dish, moistened with water, dilute sulphuric acid (1:l) and pure strong hydrofluoric acid added in considerable excess, the vessel put on a radiator to evaporate, and stirred from time to time. When the solution is so far evaporated that fumes of sulphuric acid begin to come 06 there should still be so much acid present as to form a solution or emulsion and not a paste, since the paste is liable to bake on the bottom of the vessel and form the difficulty-soluble anhydrous sulphates produced by overheating, especially when magnesia is present in quantity.At this point it is well to add a few drops of nitric acid to oxi- dise the ferrous oxide, and a little more hydrofluoric acid to insure the complete expul- sion of the silica. The evaporation is then continued until the sulphuric acid fumes strongly and no odour of hydrofluoric acid can be detected when the solution is cooled below the point at which the sulphuric acid fumes. About 25 C.C. of dilute hydrochloric acid (1:5) is now added, the stirring being continued, and the material is then evaporated on the water-bath until most of the hydrochloric acid has been driven off. The material is then washed into a beaker, and any residue adhering to the vessel can be removed by a few drops of hot, strong hydro- chloric acid, the vessel being rubbed with a bit of paper if necessary. If the solu- tion be very turbid it can bedigested on the water-bath for some time, but ultimately it is diluted with hot water to 250-300 c.c , allowed to stand for several hours, and then filtered.The residue contains the barium as sulphate, and sometimes small amounts of chro- mite or other minerals of the same class. It is washed, ignited and thoroughly fused with sodium carbonate in a small crucible, the fused mass being then digested with hot water. The well-washed residue is dissolved on the filter with dilute * Journ. Am, Chew, Socy. Vol. XIII. No. 2.130 THE ANALYST. hydrochloric acid, and this solution filtered through the same filter, which, after washing, is burned, the ash fused with a little sodium carbonate, the mass dissolved in dilute hydrochloric acid and added to the washings, which are now acidified and added to the main solution, after reduction of the chromic acid.The hydrochloric acid solution con- taining the barium is evaporated to a few drops to get rid of the excess of acid, diluted, the barium precipitated, and the filtrate from the barium sulphate added to the main soh tion, This main solution, which should be perfectly clear and contain the iron and chro- mium as sesquioxides, is now made alkaline by ammonia, and the precipitate redissolved by dilute hydrochloric acid. A few drops of acetic acid are added, the liquid brought to a boil, ammonia added in very light excess, the boiling continued for a, few minutes and the precipitate filtered and washed, As the sole reason for this precipitation is to get rid of the magnesia and the accumulation of other salts, the washing need not be thorough, but the filtrate must be tested and the precipitation proved complete.The precipitate is dissolved in hot dilute hydrochloric acid. The filter after washing is burned in a large platinum crucible, into which the solution, concentrated to a small bulk, is put and evaporated on the water-bath till it becomes pasty. Just enough water is added to dissolve the salts, and then dry sodium carbonate is added in small portions, with continual stirring, till a comparatively dry mass results. This must be carefully done, for if too much soda is added at a time, and each addition is not thoroughly stirred into the maes, the after fusion is apt to be ‘‘ lumpy ” and unsatisfactory.When a good excess of carbonate has thus been added, the mass is dried and gradu- ally brought t o clear fusion, which should be continued for half an hour. If lumps form, which is, however, rarely the case if lime and magnesia are absont and the fore- going directions are followed, they can be broken up by shaking the crucible with a circular motion to detatch them from its walls. When the fusion is complete, the mass is spread around the walls of the crucible and slightly cooled. A small quantity of sodium nitrate is now added, the whole rapidly fused and carefully boiled for not more than five minutes; it is then again spread over the crucible and rapidly cooled with a blast of air.The mass is boiled with water till completely disintegrated, and then filtered and washed ; repeated tests have shown that the residue which contains the titanium is, when well washed, free from chromium and phosphoric acid. The washed residue is dissolved in hot dilute hydrochloric acid, the filter burned, the ash fused with sodium bisulphate, dissolved in water and added to the solution. The titanium in this solution is separated by the excellent method of Dr. Gooch,* all the details a9 laid down by him being followed. I have, however, found it convenient, after the destruction of the tartaric acid by potassium permanganate, and the clearing of the solution by sulphurous acid, to add ammonia in slight excess, then at once acetic acid in excess, and boil with addition of sulphurous acid, The precipitate of titanium hydrate, mixed with some alumina, is filtered and washed with water containing sul- phurous acid and a little acetic acid. It is thus freed from manganese and brought into a small compass, rendering the after work easier, Before the final precipitation of the titanium the platinum generally in the solution should be removed by hydrogen sulphide.* Proc. Am. Acad, 12, 435 seq. (Bull. No. 27, U.S.G.S., p. 16 seq.).THE ANALYST. 131 The filtrate containing the chromic and phosphoric acids is heated, and ammonium nitrate cautiously added till no further precipitation of alumina occurs. The precipita- tion of the alumina phosphate seems to be complete, but some alumina always remains in solution.The precipitate is allowed to settle, the supernatant liquid decanted and the precipitate wanhed with a solution of ammonium nitrate until the yellow tinge dis- appears; it is then dissolved in dilute nitric acid, and the phosphoric acid precipitated by moly bdat e solution. The filtrate containing the chromic acid is acidified, boiled, neutralised with ammonia, and the chromium precipitated by freshly prepared ammonic sulphide. The precipitate, after some washing, is dissolved in hot dilute nitric acid, and, after concentration, potassium chlorate is added, the solution boiled, and finally evaporated nearly to dryness t o expel the excess of acid. It is then diluted with cold water, and a saturated solution of sodium bicarbonate added in small excess, separating the last traces of alumina.After standing about three hours, the alumina is filtered and washed with moderately dilute solution of bicarbonate. The filtrate is acidified and the chromic acid reduced and precipitated by ammonium sulphide in a platinum dish, filtered, washed, redissolved to get rid of traces of alkali, reprecipitated, and finally weighed as chromic oxide. This method, due to Baubigny, for the separation of aluminum from chromium is very good and cmvenient if the solution be free from iron and contain but little alumina. Careful tests have shown that if iron be present some of it always remains in solution, while if there be much alumina it is almost impossible to wash out all the chromate from the buIky precipitate with the cold solution of bicarbonate which must be used.It must also be noted in this connection that a solution of iron and chromium prepared by the Baubigny method was made ammoniacal, and it was proved that while all of the iron was precipitated, this precipitate, even after the most careful washing with hot water, contained chromium, Although the number of details in this process may seem very great, experience has shown that none of them can be safely neglected for the purpose of shortening the work ; if the whole process be carefully followed out, the results are very satisfactory, as shown by the following tests on a typical magnesian rock :- Percentage Crz03. TiOz. BaO. PSOS. No. 1, ,270 -46 -040 *375 No. 2, -285 *39 *060 -385 No. 3, a317 *46 *055 e . No. 4, *280 .. .. .. - -- -- -- Average, ~288 -44 0052 -380 The use of sodium nitrate for the fusions is not absolutely necessary, though one is more sure of complete oxidation if it be employed. In the analysis of chrome ores the best results have been obtained by fusing the flnely-pulverised ore with sodium carbonate alone, but keeping it in clear fusion for an hour. The fused mass is treated like an or- dinary silicate fusion, the silica after weighing being volatilised by hydrofluoric acid, and the refiidue, usually small, again fused with sodium carbonate, giving a clear solution in hydrochloric acid.

ISSN:0003-2654    

DOI:10.1039/AN8911600129

出版商:RSC    

年代:1891

数据来源: RSC

摘要:

132 THE ANALYST. ON THE ANALYSIS OF OLD FLOURS. BY M. M. BALLAND AND V. PLANCHOW.* OLD flour, which has reached the extreme limit of its possible preservation, and has there- fore lost its commercial value, has lately been employed in a new traffic which constitutes an actual fraud. By re-passing such an article through the mill with fresh flour, the mixture escapes detection by trade experts, and passes current as genuine new flour. The apparent goodness, when fresh from the mill, rapidly passes off, however, and, in a very short time, the whole becomes stale. M, Balland has recently had occasion to examine several samples of such flour, with the following results : the proportions both of water and ash were normal ; while that of the €at was much less, and the acidity much greater, than the usual amount.The first sample, although really the most ancient, had only issued from the mill within three months, while samples Nos. 2 and 3 were also of the same nature, although not quite so bad. Water per cent. Samde No. 1 . , .. 13.70 - 1. 79 9) 2 ' ' .. 13.82 I, 9 ) 3 ' 2 . 13.92 New Flour A . . .. 13.16 9 , j , B ' .. 13.20 9 , sb c .. 13.96 Ash per cent, 1.10 0 38 0.34 0.36 0-76 0.38 - Acidity per cent. 0.147 0.069 0-074 0.039 0.049 0.049 - Fat. per cent, 0.78 0.94 0.84 1.22 1 a 7 4 0.76 - The estimation of the gluten gives excellent indications, being less cohesive than the gluten of fresh flours, If it be extracted in the usual manner, and then left under water for twenty- four hours, and if, at the expiration of that time, the washing and squeezing between the fingers be resumed, it froths and loses much of its weight.The following table will show the difference in this respect between genuine young flours and the mixtures now under consideration ;-- Original gluten Gluten, after twenty-four hours in water, per cent. per cent, Sample No. 1 . . .. . . 29.6 9 , ?) 2 ' .. , , 36.4 99 19 3 - ' .. , , 36-0 New Flour A . . .. , , 38-8 9 , 9 , €3 9 . , . 36.0 9 , 99 c .. . , 36.0 18-0 27-2 2 6.4 34.8 3 2 4 31.2 It is therefore evident that the amounts of acidity and of fat and the behaviour of the gluten permits us to pronvuce upon the age of the flour, and also enables us to differentiate between a stale and a good flour even when the former is comparatively freshly made. M. Planchon has made the following experiments :-After quoting the researches of M.Balland to the effect that the normal acidity of good flour represented in mono- hydrated sulphuric acid can vary between *015 and ,040 per cent., he says '' One can well conceive that the precise estimation of such small quantities of acid presents consider- * Rev. Internal.THE ANALYST. 133 ~~ able difficulties, especially when we consider that the titration is performed in an alcoholic liquor, resulting from the prolonged maceration of several grams only oE flour, and with turmeric paper as an indicator. It is true that in following exactly the method of operation described, I have always obtained, when working with good flours, figures com- prised within the indicated limits ; nevertheless, I believe that these figures, although comparable amongst themselves, do not represent the real acidity, because I have obtained very different results by operating in the following manner :- 6' Five grams of flour are gradually mixed with 50 C.C.of cold distilled water ; when the mixture is perfectly homogeneous two or three drops of alcoholic solution of phenol- phtlein are added, and the whole is titrated with normal soda solution, such solution being delivered from a delicate burette, and the whole being kept in constant agitation during the titration. The number of C.C. of soda used is multiplied by the co- efficient *0245, and the figure so obtained gives, in my opinion, the actual acidity of the flour. To obtain the exact point of neutrality it is necessary to compare the colour with that of a mixture of five grams.of the same flour with 50 C.C. of water, and the same number of drops of the indicator. The operation is so short that the action oE the water and the ferments do not cause the formation of any notable quantity of acid. I: have proved that when a mixture of flour and water is allowed to stand the amount of the total acidity does not increase during the first two hours. Here, for example, is the result of the titration of the same flour maintained in contact with water for different periods :- Total Acidity per Cent. (H,SO,). Titrated immediately . , .. .. . , 0.110 ,, after 1 hour .-. .. . I . , 0.110 .. .. . , 0.110 9 9 9 9 4 9 9 ' ' .. .. , . 0.113 7, 9 9 7 ?? * .. * . . , 0.115 ? ? 9 7 24 ?, * ' .... , , 0,126 ? ? J Y 48 9 7 .. .. , . 0.145 (manifest decom- 9 9 7 7 2 ?, poei tion). If the total acidity remains the same for two hours, it is still much larger than the amount of acid that enters into solution, because in measuring the acidity of the liquid separated by filtration from the same mixtures I obtained the following results :- Soluble Acidity per Cent. (H,SW. Immediately , , * * .. .. . 0.0107 After 1 hour . , .. * . * . .. 0.0225 9 , 2 9 , ' 9 .. .. .. .. 00230 9 ) 4 9 9 ' ' .. .. .. . . 0.025 7 , 7 9 9 ' .. .. .. , . 0.0275 ? 7 24 ?, * ' .. .. .. , . 0.0425 ? ? 48 ?, 9 ' * . * . .. , , 0.083 Maceration in rectified spirit of the same flour during twenty-four hours showed after filtration the presence of -03 per cent. of acidity soluble therein.We thus see that flour does not give up its total acidityimmediately either to water or alcohol,134 THE ANALYST. and that the only true method is to directly apply the alkali to the flour itself, in presence of water. I have tested this method of analysis on eleven samples of fresh flour, and from nine of them which were cylinder ground I bave obt,ained a total acidity varying between 0105 and ~122. The remaining two flours, which were from ordinary stone mills, showed respectively ,119 and ,133 per cent. of total acidity. I have also had occasion to analyse two samples of flour manifestly damaged and unfit for use in the bakery. I n the one case I obtained -16 and in the other -565 of total acidity. I n both of these cases the estimation of the total acidity furnished exceedingly characteristic results, and I consider this simple operation ought never to be neglected in the examina- tion of flour intended for bread-making.ON THE ESTIMATION OF NITRIC ACID BY CONVERSION INTO AMMONIA, AND OBSERVATION OF THE DEFICIT OF HYDROGEN. BY K. ULSCII (Zeitsch. f. Anal. Chem. Vol. 30, p. 175).-The use of zinc for the reduction of nitric acid brings about a loss of nitrogen, owing to the production of nitrous acid. If, however, metallic iron is taken for the reduction, no nitrites are produced. When the reaction is carried out at a temperature ol about 7O0 C. it is completed in less than half an hour. The author operates as follows :-A small flask, provided with a triple-bored rubber cork, through one hole of which passes a tapped funnel tube, through the second and third two glass tubes bent at right angles, one reaching to the bottom of the flask, is connected with a nitrometer.Into the flask are placed 3 grammes of iron powder (ferrum redactum), and 20 C.C. of a copper solution containing 100 grammes CuSO, per litre. The contents of the flask are heated gently, until the fluid is no longer blue. The precipitate is then washed with several quantities of warm water. The flask is now closed and connected with the nitrometer; 10 C.C. of normal sulphuric acid are then added through the funnel tube and the flask warmed in the water-bath to 754 C. until there is no more evolution of hydrogen. Once more 10 C.C. of standard acid are added, and the hydrogen produced is measured after it has cooled down t o the ordinary temperature, corrections being of course applied for temperature and pressure.The flask is then emptied by means of the tube going to the bottom of the flask, and the nitrate solution to be examined introduced with 10 C.C. of normal acid. The deficit of hydrogen obtained gives the measure of the quantity of nitrate present. 1-106 C.C. hydrogen corresponds to one milligramme of potassium nitrate. The test experiments given are in every way satisfactory. A single charge of 3 grammes. of iron suffices for 25 determinations, if the amount of nitrate does not exceed 10 milligrammes in each Case. 0. H. The apparatus is now free from air. A NEW METHOD FOR THE QUANTITATIVE SEPARATION OF MANGANESE AND ZINC. P. JANNASCH AND J. F. MACGREGORY (J0ur.f.prakt Chem. [Z] 43, 402-406).-Manganese can be completely precipitated as dioxide in an ammoniacal solution by hydrogen dioxide. To ensure the freedom of the precipitate from zinc, when that metal is present, excess of ammonium chloride and ammonia must be employ&. The authors experimented with 0.5 grm. of re-crystallised manganese and zinc sulphates respectively, dissolved in 15--100 C.C. of water, following the method here set forth :-The solution is acidifiedTHE ANALYST. 135 with hydrochloric acid, and transferred to a 600 C.C. Berlin porcelain dish ; there are then added successively at least 100 c c. of a 15-20 per cent. solution of ammonium chloride, 60-100 C.C. of strong ammonia, and an excess (50-60 c.c.) of hydrogen dioxide, the dish being covered with a clock glass to avaid loss by the spurting which occurs from escape of oxygen when the hydrogen dioxide is in excess.The dish is then heated for 10-15 minutes on the water-bath, the precipitate collected on a filter and washed, first with hot ammonia water, and finally with hot pure water, until the washings leave no residue or evaporation. The precipitate can be burnt in a platinum or porcelain cru- cible while still wet, and must finally be heated over the blowpipe until constant in weight. To determine the zinc, the mixed filtrate and washings may be precipitated with ammonium sulphide, the zinc sulphide being re-dissolved and precipitated as carbonate in the usual way. A more rapid method, however, is to evaporate the filtrate and washings, dry the residue at 125-150' for one hour, and ignite ii; over a piece of asbestos mill-board to expel ammonium salts ; the asbestos is to prevent the temperature from rising high enough to volatilize zinc salts, its presence renders it necessary to push the salts down from the sides of the dish into the centre.The ignited residue is dis- solved in water containing a little hydrochloric acid, and the zinc precipitated from the hot solution with sodium carbonate in the usual manner. A. G. B. L. F. WILSON, Chew. Zeit., 1891, 15, 649-656).-The growing importance of dairy products and their production as a definite industrial undertaking, requiring the aid of some means of readily checking the quality of the raw material, milk, both to ascertain its commercial value and to determine in what degree the yield from cows and other milk-giving animals can be improved by breeding, have led to the device of numerous methods for the esti- mation of the constituent with which the butter-maker is most concerned, viz., the fat.The most expeditious method hitherto proposed is that of De Laval, who in applying the principle of the separators in use on a large scale, to the analytical problem stated above, has given us an instrument, the lactocrite, which appears to attain the desired end more perfectly than any other known means. The construction and mode of use of the lactocrite are well known to our readers (for a description see the ANALYST, 1887, 130). Its accuracy and ease of working have been testified to by many chemists, and it is now made so that it can be driven by hand instead of power, The chief objection that can be urged against the lactocrite,is that it fails to indicate the presence of any fat whatever in skim milk containing less than about 0.5 per cent.of fat, and that its readings up to 1.5 per cent. require the application of a considerable and varying correction (cf. Faber, THE ANALYST, 1887, 130). The cause for this seems to lie not in the construction of the apparatus itself, but in the fact that the mixture of sulphuric acid and glacial acetic acid, which is used to dissolve the casein and allow the separation of the fat, attacks the latter to some extent. By sub- stituting for this a mixture of hydrochloric acid and lactic acid in proportions similar to those of the acids they replace, this difficulty is entirely overcome.The modified process has3 been patented by the Separator Company of Stockholm. The chemist to this corn- THE ESTINATION OF FAT IN MILK BY MEANS OF THE LACTOCRITE.136 THE ANALYST. pany, M. Ekenberg, has devised a process for preparing lactic acid, by which it will be so much cheapened that the cost of using the lactocrite under the new conditions will be scarcely greater that it was formsrly (for another new process for the preparation of lactic acid see &xrnaZ of $he Society of ChemicaZ Industry, 1891, 312). The author has compared the indications of the instrument used with the altered acid mixture, with the results given by various anslytical processes of repute. A brief description of each method as carried out by him is first given, I.LAVAL'S LACTOCRITE METHOD. The instrument used was supplied by the Separator Co., and was of the size known as '' baby," having places for twelve tubes and driven by hand. The milk and acid were measured by the same pipette, it being, of course, previously rinsed with the liquid about to be measured. I n testing whole milk the mixture was kept in the water-bath for eight to ten minutes, while for skim milk six to eight minutes sufficed. The lactocrite was heated to 50-60' C., by means of steam, and the rotation continued for about five minutes at the usual speed of 6,000-7,000 revolutions per minute. Each sample was tested either aix or twelve times, the results baing usually identically or, in any case, very closely concordant for the same sample.I n a few instances a bubble made its appearance in the cdumn of fat in the capillary portion of the lactocrite tube, in which cage the experiment was rejected. If an apparatus of somewhat larger size, e.g., one with twenty-four tubes be used and the operator have assistance in washing up, etc., some two dozen tests per hour can be made, so that with two persons familiar with the instrument, and workingalternately, 300-400 tests can be carried out in an ordinary working day. It is thus remarkable not only as the first analytical apparatus dependent upon mechanical power, but also results are obtained by it more speedily than by any known analytical process whatever. 11. SOXHLET'S AREOMETBIC &lETHOD. (Zeit. Lmadwirtii. T'eer. Bay.Miinchen, 1880). The apparatus used by the author was obtained from J. Greiner, of Munich, and was accompanied by two cartificates by the inventor stating that the two hydrometers sent therewith wera accurate. When tested against ordinary gravimetric methods for the analysis of whole milk the process was found perfectly satisfactory. The ethereal fat solution was always brought, in the test experiments, to the nor- mal temperature of 17.5'' C.? by means of a stream of water of that temperature supplied from a vessel holding about 15 litres kept continuously running through the water-jacket, and thus all correction for temperature was avoided. The ether was purified before use by treatment with calcium chloride and caustic lime, distilled and saturated with water at the ordinary temperature.No difficulty in separating the ethereal from the aqueous layer was experienced either with whole or skim milks, a circumstance that may have been due to the fact that the samples were fresh, 111. GI.BA-JIMETRIC METHODS, Of the methods that depend on the absorption of the milk by some porous substance, such as sand, pumice-stone, asbestos, cotton, wool, and the like, and the extraction of the fat from the total solida thus finely divided, the author bag used the following :-TXE ANALYST. 13’7 (a) Pumice-stone, broken and aifted, so as t o produce a material of which the particles were Os5-1*0 m.m. in diameter, is washed with water, ignited, and about twelve grms. placed in a porcelain basin. About 12 grms. of milk are then allowed to drop upon it so as to be thoroughly absorbed, dried at 9 7 - 9 8 O C., the operation being coapleted in a vacuous water oven, kept exhausted by a water-pump.The residue is transferred to a paper cartridge and extracted with ether in a Soxhlut appwatus in the ordinary way, any particles adhering to the dish being removed by a little more pumice and a plug of pure cotton-wool. The paper cartridge is made of best Swedish filter- paper used double, which has been extracted for at lea3t twelve hours with ether, and thoroughly dried, and is supported on a layer of cotton-wool similarly purified, to retain any fine particles of pumice that may find their way through. The ether used in extraction is freed from water and alcohol by the method described under (2), supplemented by treatment with sodium until hydrogen ceases to escape, and final distillation.Good as pumice-stone is, its pores are too large for perFect division of the particles of milk solids, the fat globules remaining encased in casein to some extent, a fact evidenced by the perceptible extra yield of fat obtained by pulverising the pumice, and re-extraction after previous thorough exhaustion. (6) In pursuance of the principle of J. Lahmann’s method, which consists in the use of clay plates as an absorbent, the author has employed powdered, lightly burnt clay vessels, freed from dust by washing with water on a sieve, so as to leave particles about 0.5 to 1.5 mm. in diameter. The proces3 is carried out in the same way as with pumice-stone, save that 2.2 grms.of the absorbent material are taken instead of 12. The extraction apparatus used by the author consisted of a battery of four Soxhlet tubes, with flasks and condensers ground in, thus avoiding the use of corks. Each flask was supported by a small porcelain dish containing a little sand, heated by means of a jet of gas from the small inner gas tube of a bunsen burner, the flame being so placed that one side of the basin was heated and bumping thus avoided. By this arrangement the rate of extraction could be easily regulated, and the syphon of the Soxhlet discharged about every five minutes. In order t o prevent the formation of bubbles in the ether collected in the extraction tube, a paper shield was placed round the extractor just above the flask. As the flow of ether out of the double paper cartridge, and through the underlying plug of cotton-wool, is somewhat slow, a little piece of cotton-wool is inserted into the mouth of the syphon, so that the rate at which the extraction tube is emptied is also decreased.The use of a sand-bath instead of a water-bath for the extractor flasks is advantageous, as their weights remain practicalIy cmstant and they last much better . Test anaIgses were made of whoIe and skim-milk, to ascertain how long the extraction should be continued in order t o be complete. It was found that three hours generally sufficed for the extraction of fat from whole milk, but that twelve hours were necessary for skim milk containing about 0.8 per cent. of fat. (c) The author also examined Adanus’ process, and quotes the opinicns of Klein, Richmond, and others as to its accilracy, mentioning that it tends to yield higher results than the other methods.In his investigations he used Schleicher and Schull’s (‘ fat-138 THE ANALYST. free paper,” having first ascertained what quantity of matter soluble in ether was present in it. The amount found was just over 1 m.grm. for each strip, that being the form in which the paper is sold. Extraction of the paper with ether for two hours removes this impurity. Experiments made to determine the length of time for which extraction had t o be continued to dissolve the fat from the milk solids showed that three hours were ample, thus confirming Adams’ statement. Nevertheless, the author adopted the period of five hours for whole milk, and twelve hours for skim milk, to avoid possibility of error.He records the fact that of all the methods tried, the Adams’ process showed the closest concordances in successive experiments, The following table shows the mean results of the different methods with various samples of milk :- Powdered earthenware 3.66 3.63 3-09 3.08 2.67 2.55 2.38 2.19 1 *35 0.85 0.76 - - 0.3 1 I Lactomite. 3.71 3-62 3.1 3 3.10 2.72 2.52 2.43 2.23 1.41 0.90 0.82 0.69 0.42 0-28 - Areometer. 3-71 3.68 3.18 2.77 2-56 2-49 2-34 1.47 1 -0.2 0.94 - - - 0.50 - Blotting paper. 3.74 3.73 3.18 2.76 2.60 2-49 2.28 1.43 0.94 0.86 0.74 0.48 0.40 0.33 - Remarks. Morning milk from cow No. 7. Morning milk from cow No. 3, Morning milk from several cows. Morning milk from cow No. 13. Morning milk from cow No. 14.Mixtura of two parts of hand-skimmed milk, 24 hours old, with one part of morning milk from cow No. 14. Milk, 24 hours old, from several cows. Milk, 48 hours old, from several cows. Milk (‘ separated ” by hand ‘ I separator.” (‘ separated ” by ‘‘ separator ” I riven by power. The differences between the three methods that give the best and most concordant results, viz., the Adams process, the powdered earthenware method, and the lactocrite, are as follows :-- Maximum. Minimum, Mean. Between Adams and earthenware ” . . . + O * l l +0*05 3-0.088 Between Adams and lactocrite , , , . + O * l l 3-0.02 +0*052 It therefore appears that the lactocrite used with the new solvent mentioned a t ths beginning of this paper gives thoroughly reliable results with the most diverse kinds of milk, Soxhlet’s areometric method is less accurate than the lactocrite, particularly with skim milks.The reason for the constant tendency of the Adams process to give higher results than any method in which an absorbent ohher than blotting-paper is used, appears to be due to the interstices of the blotting-paper being so fine that the fat globules fail Between lactocrite and earthenware . . 3.0.06 -0.03 +0*035THE ANALYST. 139 to penetrate into them, and remain, therefore, on the surface already largely freed from the milk serum, and consequently are easily dissolved by the ether. The porous earthenware method gives lower results, because the sample used by the author was not sufficiently close in texture, but this disadvantage he considers in some measure counterbalanced by the facts that no special care is needed to free it previously from matter soluble in ether, and that it can be used repeatedly after mere ignition, the presence of the ash from the milk increasing its powers as an absorbent.The author supplements the foregoing work with a description of some experiments made by him on the use of kaolin as an absorbent as proposed by Dr. Norblad. Kaolin is elutriated, and the finest portions cast into plates in plaster of Paris moulds, burnt at a sintering temperature, broken up and washed on a sieve until uniform particles about 0.5-105 mm. in diameter are obtained. The material thus prepared and used in the proportion of 25 grammes to 10 grammes of milk gave results closely approximating to those obtained by the Adams process, and is in every way equal to it Eave in the greater care needed to transfer it to the extractor.The conclusions arrived at in this exhaustive and important paper are as follows :- 1. The lactocrite used with a mixture of hydrochloric and lactic acids gives results quite comparable with those obtained by the best gravimetric processes. 2. Kaolin prepared and used as described, and when dry extracted directly with ether, gives figures agreeing with those arrived at by the Adams process. 3. The Adams process leaves nothing to be desired if the strips of paper be first thoroughly extracted with ether. 4. The aerometric method, though giving very small errors for milks containing more than 2.5 per cent. of fat, is unreliable for poor and skim milks, and is altogether of more limited applicability than the foregoing processes.B. B. ANALYSIS OF BUTTER AND OTHER FATS. BY J. KONIG AND F. HART. ( z e d s f , Anal. Chm., Vol. 30, p. 292.)-Theauthors add one more to the numerousmodifications of older methods. Following the proposal of J. West-Knights (ANALYST, VOl. 5), they convert the fatty acids into the baryta salts, and estimate the amount of combined baryta. They operate as follows:-About five grammes of the fat are placed in a graduated 300 C.C. flask, 50 C.C. of alcohol are added, heated on the water-bath until all fat is dissolved; 40 C.C. hot baryta solution, containing 17.5 barium hydrate in 100 c.c., are then added, and the mixture boiled under a reflux condenser, with addition of a few pieces of pumice, for three to four hours.The solution is then allowed to cool, water is added to the mark, and filtered. Through 200 C.C. of the filtrate carbonic acid is passed until the reaction is no longer alkaline, the whole is then boiled in a porcelain basin nearly to dryness, allow to cool, make up to 250 c.c., and 200 C.C. filtered off; to the clear filtrate dilute sulphuric acid is added (the original says hydrochloric acid and barium chloride), and the BaSO, weighed, The quantity found is multiplied by 0.657 to obtain the amount of caustic baryta, combined with the soluble fatty acids, this is then multiplied by $. The authors call the figure SO obtained the baryta value of the soluble fatty acids. They also makea blank experiment, by the140 THE ANALYST.results of which the original figure is corrected. The following baryta values have been obtained :- LinPeed 18.7, poppy 7.0, olive 9.4, colza 17.6, sesame 6.9, earthnut 22.9, cotton 29.1, liver oils from 25.2 to 52.8, palm-kernel oil 86.3, coco-nut oil 118.5, coco-butter 195,1, six samples of butter-fat 238.5, 216.9, 231.5, 216.4, 236.0, 199.6 ; beef-fat 35.8, mutton fat 4.9, lard 17.1, three samples of margarine 21.6, 21.7, 22.8. The baryta value of fats therefore runs, in general, parallel with the Reichert- Wollny figure. In the six samples of butter just quoted the Wollny figure was 30.7, 29.0, 28.7, 28-2, 27.5, 26.3. The variations of the baryta values are, therefore, much wider than those of the volatile fatty acids. It is difficult, therefore, to understand the reasoning by which the authors come to the conclusion that their method surpasses the Reichert- Wollny, as regards simplicity, and equals it as to sharpness of distinction, 0.H. VOLUMETRIC ESTIMATION OF MANGANESE. BY L. BLUM (Zeits.f, And. Chem. Vol. 30, p. 284).-This is a modification of Donath and Hattensaur's method (Chem. Zeit. 1890, p. 323). It depends upon the fact that in a manganese solution, which contains tartaric acid, ammonium chloride, and a ferric salt, and rendered ammoniacal, potassium ferrocyanide precipitates the whole of the manganese as mangan-ammonium-ferrocyanide. The iron is not precipitated under these conditions. A standard solution is made of 10 grammes cryst. MnC'1,4HzO in 500 C.C. water ; 50 c c.of this are pipetted into a beaker, B few drops of ferric chloride, 20 C.C. of cold saturated ammonium chloride and 30 C.C. tartaric acid solution and ammonia are added, the fluid heated to boiling, and titrated with a ferrocyanide solution containing 38.487 grammes. pure crystallised potassium ferrocyanide per litre, each c c. of this being equal to -005 gramme manganese. Theend-reaction is obtained by taking out from time to time a drop of the solution and bringing it together upon a white plate with a drop of dilute acetic acid, which, when the ferrocyanide is in excess, produces the blue colour of prussian blue. The author compare6 his method with Tolhard's permnnganate method, with which it agrees very well. He adds the warning, not to rely implicitly upon the purity of the ferrocyanide, as this salt sometimes contains much sodium in place of potassium. 0. H. DETECTION OF SESAME OIL IN OLIVE OIL. J. Ts TOCHER~ A.1.C. (Pharrn. JouT~., Jan. 24, 1891).-PPrepare a solution of pyrogallol in pure hydrochloric acid. Measure $ oz. of this solution into a wide-mouthed test tube provided with a cork, and add $ oz. (1 oz- if the adulteration be small) of the oil to be tested. Shake well, and allow the oil and acid to separate. Draw off supernatant liquid with pipette, and boil the hydrochloric acid solution for about five minutes, when, if sesame oil be present, the colour of the solution will have changed to pnrple. The purple develops slowly on boiling. The colour by transmitted light is wine-red to purple, and, by reflected light, blue. Of oils of known composition treated in this way, pure olive gave a faint yellow; sesame, deep purple; 20 per cent. sesame, purple; 5 per cent. sesame, faint purple ; 1 per cent. sesame, very faint purple ; almond, colourless ; ground nut, colourless ; cotton-seed, very faint red j sun flower, faint olive ; rape, colourless,

ISSN:0003-2654    

DOI:10.1039/AN8911600132

出版商:RSC    

年代:1891

数据来源: RSC