摘要:

THE ANALYST. APRIL, 1889. AN IMPROVED METHOD FOR THE ANALYSIS OF FATS AND OILS. BY JOHN MUTER, PH,D., F.R.S.E., F.I.C., & L. DE KONINGH, F.I.C. (Red at the Meetirtg, Pebruary, 1889.) INTRODUCTORY. JN the year 1878 the senior author of this paper contributed to the Society of Public Analysts a method for the estimation of oleic acid in fats and oils. This process was based upon the formation of an absolutely neutral oleate of lead, solution of the salt in ether, and decomposition of the same in a special apparatus by means of hydrochloric62 THE ANALYST. acid. in the various price lists as ‘‘ Muter’s Olein Tube.” The apparatus then described has since been rather extensively used, and is figured It has since undergone considerable alterations, and, as it plays a prominent part in the method now about to we give, to commence with, a fresh description of the tube as now employed.From the illustration in the margin (which is not to scale, and is too wide in proportion to the length) it will be seen that it is essentially a burette with a bulb a t the top, and provided with a well-ground stopper. The graduated part is of such a width as to distinctly show 1 C.C. in the graduations, and it has a stop cock a t a height of 50 C.C. from the bottom. The graduations commence a t 40 C.C. from the lower end, and continue up to 250 c.c., ending just below the bulb. I n winter the tube can be used in a clamp attached to an ordinary retort sta2d, but when the temperature of the laboratory exceeds 60 F., it may be arranged in an outer jacket, which can be kept filled by running water, or some other means may bo taken for keeping the temperature low and fairly equal during the whole progress of an operation.This jacket is not shown in the drawing, but any chemist will easily see how it should be fitted. We are not aware that the improved tube can be got anywhere but from Cetti’s, of Brooke St., Holborn (who make them for us) ; but no doubt, they will shortly become as general in the price-lists as the former pattern. In the remarks that follow, this apparatus will be henceforth referred to as the ‘‘ olein tube,” and having thus got quit of any further necessity for referring t o it proceed to our main subject. be described, in detail, we The remarkable advance renderad possible in fat analysis by Hubl’s discovery of the iodine absorption method has opened up a large field of research, which is now being actively worked by many experimenters.It will be readily admitted by all analysts that in dealing with the power of fats to absorb iodine, three factors come into play, viz. .-- (1) The difference in the iodine absorbing power of oleic and linoleic acids. (2) The joint amount of these acids actually present in the fat. (3) The ability to always perform the process in the presence of an exces~ of iodine that shall be as nearly constant as possible. If, therefore, we can first isolate the fluid acids of any fat, and having found the actual amount of such acids present in the sample, submit them to the action of the iodine under fixed conditions and, without having risked any chance of an alteration in their nature during the process of isolation, it is evident that we have attained a distinct step in advance of our present methods. Up till now we have been unable to find any published process for the estimation of the fluid acids of a fat without their having been exposed to the air, dried by heat, or a ohange in their nature otherwise rendered possible by the method of isolation employed.Before such a process could be devised, it was necessary to prove two points. (1) Can the amount of the acids be found directly from their ethereal solution with fair accuracy ? (2) Can the iodine be applied to the acids without any previous exposure to the air, and consequently to oxygen 8 It is Experiments have proved that both these points are quite attainable.THE ANALYST.63 not our purpose to overload our paper with a tedious account of such experiments, because it is a matter that any analyst can easily verify for himself. We will therefore content ourselves by saying that a comparison of the results af our process, with those obtained by the gravimetric method in the case of fats so widely different in their nature as tallow and linseed oil, has proved the sufficient accuracy of the volumetric process hereafter detailed, for the purpose for which it is intended. There is little doubt but that the prolonged use of the process, side by side with gravimetric methods, will ulti- mately throw light on the respective combining weights of oleic and linoleic acids when we venture to think that it will be found that there is not so great a difference as is at present supposed to exist by many authorities.All such speculations are, however, foreign to the purpose of our present preliminary paper, and must be reserved for a future occasion. At the moment, our intention is simply to give our method of working, and to leave the consideration of its various possible applications to future papers. The subject of the analysis of lard and butter being very pressing matters at present for public analysts, we are dealing with them first, and will give the results of such investi- gation after describing the details of the main process. THE PROCESS. A flask of suitable capacity is counterbalanced, and about 3 grms. of the oil or fat having been introduced, the weight is ascertained.To this are added 50 C.C. of alcohol and a fragment of solid potassium hydroxide sufficiently large to saponify the fab. The mouth of the flask having been closed by a cork, through which passes a long tube drawn out t o a fine point, the whole is heated on the water bath until the fat is thoroughly saponified. A drop of alcoholic solution of phenol-phthalein having been added, acetic acid is dropped in until the solution becomes faintly acid, and then alcoholic potash is carefully stirred in until the very faintest pink tinge is restored. With certain oils the solution will be too dark for the use of the indicator in this manner, and in such cases it must be applied in the form of phenol-phthnlein paper. 200 C.C. of boiling distilled water are then placed in a 500 C.C.basin, 30 C.C. of a 10 per cent. solution of plumbic acetate are added, and the whole brought to the boil. Into this the soap solution from the flask is slowly poured, with constant stirring, and the whole is allowed to cool slowly, stirring well so as to cause the precipitate to agglomerate, and the clear liquor is poured off. Boiling water is immediately poured on, and the precipitate is rapidly washed by decantation. When the washing is complete, the precipitate is scraped from the basin into a stoppered bottle, and SO C.C. of redistilled ether having been poured upon it, the remaining particles of the precipitate are washed from the basin into the bottle with ether, and the bulk of ether in the bottle is finally made up t o 120 C.C.The bottle is securely closed and allowed to stand for twelve hours (with occasional shaking), during which time the plumbic oleate will entirely dissolve. A funnel with a ground edge is then arranged over the ‘6 olein tube,” a filter is placed therein and the contents of the bottle having been filtered into the tube, the insoluble plumbic stearate, etc., remaining on the filter, is washed with ether until ths washings pass free from lead. This will usually be attained by the use of 100 c.c. of ether, and during the filtration and wash- ing the funnel must be kept covered by a ground glass plate. The funnel having been removed, dilute hydrochloric acid is poured into tho tube up to the first mark (thus using64 THE ANALYST. about 40 C.C.of acid, 1 in 4), and the tube having been closed by the stopper and taken from the clamp, is thoroughly shaken until the decomposition is complete, which is indicated by the ethereal solution clearing up. The tube having been put back in its support, the liquids are allowed to separate and the aqueous layer is run off by the bottom pinch cock. Water is then poured in up to the same mark, the whole is again shaken and separated as before, and this is repeated until the washings are drawn off free from acidity. Water is then once more run in until the ether is forced up to the zero mark, and ether is added (if necessary) so as t o bring its upper layer t o a definite point (say 200 c.c.), and the total volume is read off and noted. 50 C.C. of the ethereal solution of the fluid acids are runinto an Erlenmeyer’s flask, and the flask having been attached to a condenser, the ether is distilled off by a bath of warm water until only a little remains.It is important that the whole of the ethor should not be distilled off, so a3 to avoid contact of the acids with the air. 50 C.C. of pure alcohol (or methylated spirit that has been rectified over potassium hydroxide) are added to this residue, and the solution is titrated with deci-normal soda, using phenol-phthalein as indicator. Each C.C. of soda used represents -0382 of oleic acid, and the amount found is calculated up to the total bulk of the ethereal solution, so as to obtain the total fluid acids in the weight of fat started with. Having thus ascertained the total acids, and also the strength of the remaining ethereal solution of the same in the ‘‘ olein tube,” the next step is to run off as many C.C.OF that liquid as will contain 05 grm. of oleic acid (or as nearly that quantity as can be conveniently measured by means of the instrument, of course carefully noting the amount taken) into a stoppered bottle of at least 350 C.C. capacity, and to immediately close the mouth of the same by a cork through which passes two tubes, the one going down nearly to the surface of the liquid, while the other just passes through the cork. The long tube is then connected with a gas apparatus, in which carbonic anhydride” is bsing generated from marble and hydrochloric acid, and the gas washed by passing it through a solution of sodium bicarbonate, and then dried by passing it over fused calcium chloride.The bottle is placed in water a t about 120° F., and a rapid stream of gas is passed through until every truce of the ether has evaporated. To the residue 50 C.C. of Hiibl’s reagent is instantly added, and the stopper having been a t once inserted, the bottle is put aside in an absolutely dark cupboard for twelve hours. A blank experiment is, as usual, started in another similar bottle with the same amount of Hiibl’s reagent, and set to stand side by side with the other bottle. At the expiration of the proper time, 35 C.C. of 10 per cent. solution of potassium iodine are added to each of the bottles, and the contents having been made up to 250 C.C. with water, 15 C.C. of chloroform added, and the whole shaken, both are titrated in the usual manner with a deci-normal solution of sodium thiosulphate (hypo) that has been just previously standardised with an accu- rate deci-normal iodine solution.The difference between the amount of ‘‘ hypo ” con- sumed by the check and the experiment respectively, gives the amount of iodine * NOTE.-When tbe paper was read it was stated that ordinary gas had been succeesfully employed, but since that we have preferred the arrangement now detailed. It is very imporiant that the volume of the ether should not alter between the running off of the first 50 c.c., and the taking of the amount representing the *5 grm. of acid. If i t cannot be maintained by regulating the temperature. the volume remaining after taking the 50 C.C. must be noted, and then again renoted before taking off the second quantity, and corrected by calculation.THE ANALYST. 65 absorbed by the weight of oleic acid taken, which is then calculated to the amount required by 100 grms. and put down as the ‘‘ iodine absorbing power ” of the fluid acids of the fat under examination. Such therefore is the process, and by it we not only obtain the amount of fluid acids present in the fat with a fair amount of accuracy, but w0 also believe that a reasonably constant iodine number for the acids from each fat can be determined when in 9 reasonably fresh condition, thus enabling us to calculate the amount of any admixture with a very much more tolerable amount of certainty than has hitherto been attainable. We invite our colleagues to t r y the method, and to assist 3s in establishing reliable iodine numbers for the acids from every oil and fat. Meantime we are going on with such an investigation, and will continue to submit the results, as rapidly as possible, in the pages of the ANALYST. As being at the moment the most interesting to public analysts, we have commenced with some solid fats used for food. (To 6e continued.)

ISSN:0003-2654    

DOI:10.1039/AN889140061c

出版商:RSC    

年代:1889

数据来源: RSC

摘要:

THE ANALYST. 65 DENSITY. BY H. DROOP RICHMOYD. ( X e d at Jlr,eti.lzg, Febncaiy, 1 SS9 .) WHEN we talk of the density of a body we mean the mass of a imit of volume of that body, or, as the unit of mass has been fixed at 1 grm., and the unit of volume a t 1 cubic centimetre, the number of grms. in 1 cubic centimetre; thence it follows that density is not a relative, but an absolute property. Notwithstanding that the cubic centimetre has been fixed as the volume of 1 grni. of water a t 4 O C. (the point of maximum density), acustom has sprung up of assuming that an instrument for taking density graduated to hold x grm. of water a t 15", 1 5 . 5 O , or 16@ C. (as the case may be) holds s cubic ceiitimetres; this arbitrary creation of units of volume, besides being clearly wrong, is liable to create confusion, and renders the expression of results uncer- tain, which uncertainty is not removed entirely by the use of such an illogical expression as " the density a t 15" compared with water at the same temperature." To compare an absolute quantity is absurd ; this uncertainty is much less, however, than that caused by errors of observation, many of which are not even noticed, much less corrected.I do not propose to discuss either the taking of densities of either gases or solids, on account of tho special methods and precautions against errors, which are so well known in the case of gases, and of the comparative unimportance attaching to the determination of the densities of solids ; my remarks must therefore be taken as applying t o liquids only.We use practically three methods for determining the densities of liquid :-1. By hydrometers. 2 . By the measurement of the loss OF weight of a solid in a liquid, e.g., the Westphal balance and the torsion balance. 3. By the determination of the mass of known volume, e.g., the pyknometer. 1. .Hydrometers.-The faults of these instruments consist in errors introduced by the cohesion of the liquid to the material of which the instrument is made, which render it dif3icult to read off the exact point which is at the love1 of the surface of the liquid ; as also the volume of the portion immersed is determined in part by the cohesion, i b follows that hydrometers do not give the same reading in different liquids, whose density may be the same, i f the viscosity is different. Another error is caused by expansion by heat if the hydrometer is used at a different temperature than that for which it was graduated.Their merits consists in speed, and if they are graduated for66 THE ANALYST. use in one particular liquid, and at a pretty constant temperature, fairly exact results are obtainable (within *0005). 2. Instruments which measure loss of weight in a liquid.-Of these the Westphal balance is the most important and widely used, and is extremely quick and convenient, where great accuracy is not required, though open to grave errors. I t s faults are the errors due to cohesion (very slight); to the difference between true weight and apparent weight in air ; to the condensed film of air on the plummet, which is, however, removed on immersion in most liquids; to the unequal expansion of plummet and liquid of which the density is to be taken a t any other temperature than that for which the instrument is set, and of the arms of the balance ; to the wire or thread used to suspend the plummet (usually reduced to a minimum by the use of a very fine thread) ; and t o the imperfec- tions in the balance (often large in those commonly in use).Many of these errors may be neglected in ordinary work, for instance, those due to cohesion, unless the fluid is very viscous ; to difference between true weight and apparent weight in air, if the substance has a density near 1 ; to the condensed film of air ; to the use of a wire or thread ; and to the expansion of the arms, It is in the construction that the Westphal balance chiefly errs, one error having been pointed out by Allen (-ANALYST, 1889, p.11) in the length of the intervals between tho divisions. The beam of the Westphal balance is usually made 10 centimetres in length, so that t o insure absolute accuracy the intervals should be 1 centimetre apart, within &, of a millimetre, an amount of accuracy which it is not easy to attain in practice, and which may easily be diminished by wear. Another error is introduced in the hook riding on a knife edge, from which the plummet hangs ; if the position of this is changed, as it must necessarily often be, a difference in the read- ing may be observed, amounting sometimes to *001. Another error may occur from one of the riders not sitting absolutely exactly in its place, but inclined to one end of the beam or the othar ; this error may amount to as much as *0005.The error intro- duced by the expansion of the plummet is of course obvious, and should be allowed for by noticing the difference between the actual density of water at various temperatures and the indicated density. Unless this is done, determinations made a t higher tempera- tures are only relative, and cannot even be compared with those obtained by another instrument, unless the coefficient of expansion of the material of which the two plum- mets are made is the same. An inconvenience is felt if the density of a liquid is to be taken at a temperature differing from the temperature a t which it is a comparatively large bulk of liquid having to be warmed or cooled as the case may be.I should fix the limit of accuracy of the Westphal balance at not much less than *0005, although closer duplicate readings are often obtained. The torsion balance is open to all the faults of the Westphal balance, except those due to construction, and besides has the tendency to acquire a slight permanent set, and is not to be recommended except for rough density determinations. 3. Instruments in which the mass of known volume is taken, or pykn0meters.- These are practically two in number, the specific gravity bottle and the Sprengel tube and its modifications, neither of which presents any real advantage over the other. It is perhaps rather easier t o adjust the temperature of the liquid in the Sprengel tube, but, on the other hand, the Sprengel tube is more liable to lose weight than the bottle, when in constant use.The errors, all of which can be readily allowed for, are the following : those introduced by the condensed film of air, both inside and outside ; by the difference between true weight and apparent weight in air ; and by the expansion of the glass or other material of which the instrument is made. The most difficult to allow for is the condensed film of air, which I consequently try to eliminate as far as possible by the following plan : dry the bottle or tube by heating it and passing aTHE ANALYST. 67 current of dry air through it (of course removing the thermometer if the temperature is higher than the highest it will bear), coo1, by pouring a current of cold water on the outside, wipe dry and weigh a t once; duplicate weighings very rarely differ by as much as -0005 grm.I then fill with distilled water freshly boiled in a platinum vessel, adjust the temperature accurately to 4 O C., wipe dry and weigh a t once. The increase of weight in grams., corrected for the volume of displaced air, will give the number of cubic centimetres the bottle or tube will hold. The ciifference between duplicate weighings should not exceed -0005 grm.; the difference between the capacity a t 4* and the weight (corrected) of water in grms. held by the bottle or tube a t any other temperature, divided by the density of water at that temperature, will give the increase of capacity due to expansion of the glass or other material of which the bottle or tube is made.A table of capacities at various temperatures, and a formula for the expansion, may easily be made of it for each instrument. TABLE OP DENSITIES OF WATER. (CompiIed from the results of Pierre, Despretz, and Kopp.) Temp. C. O0 .. .. 40 .. * . 10" . . 30° .. . . 30@ I . .. i5.50 (600 i j . . 37.8" (looo F.) . . Density. -99988 1~00000 -99975 *99910 ~99826 .99575 *99313 ~~ Temp. C. 40" . . .. 50° . . . . 6 0 O . . . . 700 .. . . 80" . . .. 90Q . . . . 100" .. .. Densit,y. 99237 *98Sl'i -98342 *97791 -97193 -96561 95865 Should the capacity of the instrument be required at 100" C., some rather special precautions must be taken; the tube should be filled hot, and while the water is absolutely boiling, and the liquid should be adjusted to the proper level, while under slight pressure.I accomplish this as follows (with a Sprengel tube) : To the end of the tube from which the liquid is drawn, a tube, about 1.2 c.m. in diameter, having its other end narrowed, and to which a side tube is attached, is fixed by means of a cork ; a rod, on the end of which a bundle of filter paper or other absorbent material is fixed, is passed through the narrowed end in such a way that the joint is air-tight (Le. either through a cork or india-rubber); the side tube, and the other end of the Sprengel tube are attached to a bottle, by means of a T-piece, in which a pressure of about ten inches of mercury is kept up by suitable means; the Sprengel tube is, after being filled, im- mersed in steam, and when the water ceases to expand the rod supporting the filter- paper, is brought to the end of the tube and by its means the water is accurately adjusted to the mark ; the tube is then taken out and weighed in the usual manner.The determination of densities at higher temperatures than 15.5'' is usually only required for body that are solid at that temperature, such as butter, and other fats ; Muter proposed to do this at 1 O O O F . (37.8" C.) and graduated his instruments with water at the same temperature, and gave to these determinations the name of '' actual density," an unfortunate name, as they were really the actual densities divided by the density of water at that temperature. These, however, were good determinations, as there could be no mistake as to what they really were. Three years ago Estcourt proposed to take density of fats at 100° C.by the Westphal balance, a plan which has become rather general among English analysts, but is a distinct falling off from Muter's method, because the expansion, which is not usually allowed for, is enormously increased68 THE ANALYST'. a t that temperature ; and moreover the temperature is exceedingly difficult to obtain, as the boiling point of water depends on the pressure of the air. I do not consider that the results obtained by two analysts taking their densities t h w are comparable within ,002 ; t,he only advantage which this method has over the other, is that beeswax and carnauba-wax are liquid a t 100O C. while solid a t 100') F. I n the regulations for analysis for the State of Colorado, it is laid down the densities of fats shall be taken a t 40@ C., which seems to me the most convenient temperature, now that the Centigrade scale is in general use, and I think that w0 may expect, if the precautions I have drawn atten- tion to are taken, that two analysts should not differ by more than a0002 or *0003. There are two minor precautions I should wish to draw the attention of analysts to, first, to allow a sufficient time (when using the bottle or tube), for the liquid to con- tract to its full amount ; alcohol contracts very quickly, glycerol very much more slowly, while as an extreme case Perkin has recorded a mixture of aldehyde and water C,H,O+B,O which took several hours (J.Chem. SOC. 1887, p. 517) ; the other precau- tion is to use an accurate thermometer, the great majority of low-priced thermometers being sensibly wrong. In conclusion, I would recommend that all densities should be the weight (mass) of the substance in the cubic centimetre, that the density of liquids should be taken at 1 5 O , and of fats at 40'). A symbol, such as DI;" meaning density a t 15') arid Diu at 40" might be advmntngeously adopted. Some results actually obtained are appended. I. Experiments showing the unequal expansion of specific gravity bottles arid tubes :- VOl. Between 15.5 and 37 8 Kxpansion pcr C.C. of capacity. 25. C.C. *00042 12-1 C.C. .00055 7.9 C.C. *00044 5.5 C.C. *00081 11. Results obtained in graduating a Sprengel tube :- Wt. of Sprengel after beating and rnpici cooling Difference due to condensed :tir film . . . . 7 8.G30S gr. 1 , ,, after standing 15 mic. . . 18-6328 gib. .0020 gr. Wt. of Sprengel filled with water at 4*0° . . i 9 7 , 15.5" . . 9 , 7 9 1, ,, 37.8" . . Capacity of Sprenge1:- Fixnd. .?O 12.1445 c.c. 1 0" J2*1454 C.C. 15.3" 13 1462 C . C . 203 12.14iG C.C. 3 0 O 13.1505 C.C. 37'SQ 12.1535 C.C. 4 0 O - Calc. 12.1~164 !2*14G2 12.1475 12.1506 12.1533 12,1541 - . Formula for capacity a t t@ : - v- 12.1448 1- *0001(t - 1)" + 4ooooi5(t-4)2

ISSN:0003-2654    

DOI:10.1039/AN8891400065

出版商:RSC    

年代:1889

数据来源: RSC

摘要:

THE ANALYST. 69 ~~ ~~ ON THE COMPOSITION OF MILK -4ND MILK PRODUCTS. BY DR. P. VIETH. (Read at Xeeting Febrztayy, 1889.) W H ~ T I have to bring before you to-night is my annual report on tho work done during the year lS8S in the laboratory, which is under my charge. Particulars with regard to the purpose for, and the way in which the work is carried out may be found in my former papers of a similar nature (see the ANALYST, VII., p. 53 ; VIII., 13. 33 ; IX., p. 56 ; X., p. G7; XI., p. 66 ; XII., p. 39; and XIII., p. 46), and need not be repeated on the present occasion. The total number of samples submitted to analysis during the year 1888 is 20,218, com pi-ising- 15,354 eampIes of milk. 1,144 ,) ,, cream. 553 ,, ,, skim milk. 36 ,, ,, buttermilk. 44 ,, ,, butter and butter-fat. 6 ) ? ,, cheese.35 ,, ,, milk preparations fw infants and invalids. 59 ,, ,, water. Yi I ) ,, sundry articles. I n addition to these analyses, the specific gravity of about 75,000 samples of whole and skim milk was determined. Of the milk samples 12,652 were taken from the railway chums on their arrival in the dairy, and 2,545 by the inspectors employed by the business, from the men while the latter were serving the customers. The following table contains the monthly averages of the results referring to these samples :- AVERAGE COMPOSITION OF MILK. 1888. January February Ma& . . April . . May . . June .. July . . August September October November December . . . . . . .. . . .. .. .. .. . . . . .. Yearly average Samples Taken Specific Gravitj 1.0325 1.0325 1.0325 1.0384 1.0324 1.0324 1.0320 1.0319 1.0322 1-0325 1.0322 1,0321 I On Arrival. Total Solicls.12.97 13.00 12.90 12*si 12.82 12.83 12.82 12.54 13.06 13.09 13.15 13.01 1-0323 I 12.94 Fat . 3.79 3.s 1 3.715 3-68 3*G9 3.69 3.76 3.80 3-94 3.89 4.03 3-91 ~ 3.81 Solids not Pat !)*l s 9-19 ‘3.17 (3.1:; 9.13 9.14 9.06 9.04 9.1 2 9.30 9.15 9-10 9.13 On Delivery. Total Solids. 12.9 1: may safely leave it to you to draw your own conclusion from these figures. A further number of 1,806 milk samples was analysed in connection with a very extonded investigation into the composition of milk yielded by individual cows kept a t70 THE ANALYST. the Aylesbury Dairy Company’s estate, near Horsham. The results of this interesting investigation, which was commenced in the year 1887, will form very valuable material, which I hope to be able to lay before you on some future occasion.As in the case of milk, so in the case of cream, supplied to customers, two series of samples were examined, viz., 412 samples taken before the cream was sent out, and 304 samples taken by the inspectors from the men when working thsir rounds. The results were as follows :- AVERAGE Aarovm OF FAT IN CREAM. - Samples Taken 1888. Before Sent out. January February March April . . May . . June . . July . . August Septombor October November December .. .. .. . . I . . . . . . . . . . . .. .. * . .. .. . . . . .. . . .. . . . . . . . . . . . . . . .. .. .. . . . . . . * . . . . . . . . . .. . I .. . . . . . . . . . . . . . . .. .. . . . . .. . . .. .. . .* . . . . . -----I ---_A- Yearly average . . I 3n Deiivery. 44.7 43.5 44.4 45.1 46.5 45*!) 45.7 46.0 45.5 46O7 48.0 46.6 45.7 The agreement between the two series of samples is satisfactory, considering the difficulty of drawing a fair average-sample of cream of such richness, and further con- sidering that cream sent out with the morning delivery was sampled before sent out, but not on delivery, being handed to the men, and by the latter to the customers, in sealed cans. Water . . . . . . 31.57 to 44-11 average 35.54 per cent. Fat . . . . . . 45.78 ,, 61.49 ,, 57-09 ,, Solids-not-fat , . . . 5.S3 ,, 10.14 ), 7-37 ,, The composition of 55 samples of clotted cream was as follows :- Bsh . . . . . . .‘14 ,7 *so ,, *57 ,, Skim milk produced by abstracting cream from milk by means of the centrifugal cream separator was exceedingly poor in fat, containing generally less than -3, and only in exceptional cases more than -4 per cent.of fat. The butter samples were derived from three different sources ; six referred to butter churned in the Aylesbury Dairy Company’s dairy, fourteen to French, and fifteen to Danish and Swedish butter. I. think it will be more instructive to give the results of the analyses of the three kinds separate. BUTTER CHURXED IN LONDON. Water .. . . . . 10.94 to 18-61 average 11.72 per cent. Fat . . . . . . . . 85.66 ,, 87.59 ,, 86.53 ,, Ash . . * . . . . . -79 ,, 2-51 J 7 1-34 :, Insoluble fattyacide, Hehner 88-27 ,, 88-39 ,, 88-32 , Deci-normal alkali, Reichert 12.9 ,, 13.3 ,, 13-1 C.C. Proteids, etc. .. . . -14 ,) *73 ,, -41 7, Chlorides, as NaCl . . .GS ,, 2.30 ,? 1-20 > 9THE ANALYST. 71 FRENCH BUTTER, FRESH. Water .. . . . . 13.40 to 14.41 average 13.79 per cent. Pat . . .. . . . . 53.98 ), 85.58 ,, 84.86 ,, Proteidc, etc. i . a . *S9 ,, 1.56 ,, 1-16 ,, Ash . . . . . . .. -14 ,, a 2 5 1, *I9 > 7 Chlorides, as NaCl .. *05 ), -12 ,, 9 ) Insoluble fatty acids, Hehner 87.15 ,, 87.55 ), 87.38 ,, Deci-normal alkali, Wollny 26.1 ,) 27.6 ,) 26.9 C.C. DARISH AND Water . . . . .. Fat . . . . . . . . Proteids, etc. . . . . Ash . . * . . . . . Chlorides, as NaCl . . Insoluble fatty acids, ITchner Deci-normal alkali, Reichert ¶ I ,, Wollny SWEDISH BUTTER, SALT. 11.78 to 15.65 average 13.72 per cent. 81.72 ,, 85-49 ,, 83.11 ,, *71 ,, 1.71 ,, 1.09 ,, 1.32 ,) 2.71 7, ,”m 1 , 1.12 ,, 2.44 ,, 1.85 ), S7.30 ,) 88.43 ), 57-78 ), 13.0 ,, 14.3 ,, 13.6 C.C.27.6 ,, 29-3 ,, 28.3 ,, Two samples of butter-fat, which had become bleached by three years’ exposure to the action of air and light, contained 83.79 and 84.18 per cent. of insoluble fatty acids respectively. The examination of two preparations, sold as preservatives for milk and cream under the names of ‘‘ Preservitas ” and ‘& Neigeine ” respectively, revealed the old story, viz., that the preparations contained boracic acid as active principle. I n addition to bringing under your notice the above analytical results, I should like to make a few observations on specific gravity determinations. Although the specific gravity offers such a ready means for the detection of that wholesale adulteration which consists in the addition of large quantities of water, and which has so frequently been, and still too often is, heard of through the police courts’ proceedings, it is only of comparatively recent date that attention is paid in this country t o the determination of the specific gravity of milk.Of late, however, this determina- tion has become of particular importanco, forming, as it does, in conjunction with the determination of the total solids, the basis for calculating the fat, thereby avoiding, or at any rate checking, the determination of the latter constituent. To ascertain the specific gravity quite correctly becomes under these circumstances of great importance. I am convinced that specific gravity bottle, Sprengel tube, or lactometer give, if carefully used, equally satisfactory results, the last-named instrument undoubtedly with the least amount of trouble.That due regard must be paid to the temperature is a matter of course, but another precaution may be mentioned in this place, which, although it has been long, is still less widely known. I refer to the rise of the specific gravity which takes place and continues for a considerable time in milk, after the latter has been drawn from the udder, and which is quite independent from the escape of gases the milk might have contained. 1: availed myself of an opportunity which presented itself to make some obser- vations on this point. The experiments referred to milk yielded by cows kept in a London shed. The cows were milked between 4 and 5 o’clock in the afternoon, a sample drawn from the mixed yield, and its specific gravity determined at about 5.30 o’clock. The determination was repeated on the following morning, a t 9.30. Fifteen samples showed an average specific gravity of 1.0296 directly after milking, and of 1.0309 after sixteen hours, or an average rise equal to m0013. I n two instances the rise amounted to -0020, in six to -0015, and in seven to -0010. According to investigations made by Recknagel, the specific gravity becomes station- ary, &?., normal, after five hours or less, provided the milk is cooled don below 15 C.;THE ANALYST. at temperatures above 15" C . the apparent oontraction proceeds much more slowly, and goes on for twenty-four hours, and even longer. If milk, after its specific gravity had become stationary, is warmed up to 40" C. the specific gravity will be found to have decreased, and it will take some time before it baomes normal again. Itecknqpl believes that molecular changes in the state of the casein account for the remarkable phenomenon. (Conclusion of ths Society's poceedirup .I

ISSN:0003-2654    

DOI:10.1039/AN8891400069

出版商:RSC    

年代:1889

数据来源: RSC

摘要:

THE ANALYST. ABNORBIAL DANISI-I BUTTERS: A REPLY TO NR. ESTCOURT. BY ALFRED 13. ALLEN. THE article by Mr. Estcourt on Abnormal Butters, published in the last number of the Ar*.aIAnsrr requires no detailed reply from me, but there are some points which it may be well to explain, lest other readers should have drawn as erroneous deductions as those of MY. Estcourt. It is to be regretted that Mr. Estcourt did not make his criticism the subject of a paper before the Society of Public Analysts, as the misconcep- tions into which he has fallen could then have been a t once met and explained, and time, space, and trouble saved thereby. Nr. Estcourt writes of my ‘‘ apparent wish to show that the specific gravity of I3 and 0 are normal.” I n my paper I distinctly make the statement that the average density of hitter fat a t 100“ C.is -8658 (corrected). The abnormal Danish butters B and 0 are described (page 10) as having specific gravities of sS639 and *8G41 respectively. How, in the face of these figures, Mr. Estcourt can have supposed that I regarded or “wished to show ” the specific gravity of these samples to be normal I am unable to understand. The very object of my paper was to show that genuine butter might be physically and chemically abnormal to an eut.ent not generally recognised. Everyone knows that there is a marked difference between the density of beef-fat and that of butter-fat, and this difference will be just as great whether the observations are taken with a faulty instrument or an accurately divided one. Mr. Estcourt himself for years used a Westphal balance the piunimet of which was broken, and hence was only capable of yielding arbitrary results, strictly comparable among themselves no doubt, but which were incapable of being published or communicated to other chemists.IVhatever Nr. Xstcourt may “ fear,” I am quite lwepared, if need be, to maintain, iiricler cross-examination in the witnesh-box, that no foreign oily matter coz(Zd possibly have been introduced into either of the Danish milks during the manufacture of tho abnormal butters C and 0. The produce of each of the 31 cows a t I; farm was brought as obtained by the milkers, who were fully within view, to a, weighing machine, where the yield of each separate cow was observed, and the milk then poured through a fine hair-sieve into a tub.The smallest yield from any one cow a t B farm was 1 Danish pound*, and the largest 10 pounds ; the total weight of the milk, 119 pounds, which for 31 cows gives an average of 3.8 pounds of milk per con-. My.. Estcourt, suggests that we should have run this quantity of 13 gallons of milk through a centrifugal separator, and apparently assumes the existence of a separator in every dairy. There was no separator at B farm, and Mr. Estcourt, with his exceptional experience, should be aware that some of the finest buttel., both in England and Den- mark, is mado without a separator Tho leaving of the milk or cream for ‘‘ ripening ’’ is an essential of the Danish system of butter-making. 1511.. Estcourt considers that it was ‘‘ dangerous ” to leave the milk all night, even All this was done under my eye.* 1 Danidi pound = 500 granirrics = l . 1 111s. English.THE ANALYST. 7 3 though it was sealed up. As a public analyst, I have had some experience of sealing, and knowing how the milk was sealed in the case in question, I am able to state posi- tively that it was not tampered with. The seals placed on it by the British Vice-Consul [ Mr. McGregor) and myself toget her rendered such a malpractice absolutely iinpossible. Mr. Estcourt concedes that the supervision of the milking at the Danish farms “ was performed by gentlemen whose honour, intelligence, and high ability in the special professions to which they are devoted cannot be questioned,” but on the ground of their entire lack of experience of the new calling they undertook, Mr.Estcourt thinks L‘ grave objection might well be taken.” Mr. Estcourt is evidently unaware that two of the gentlemen referred to, Nr. Faber and Mr. Biiggild, have gone through a course of training in dairy-farming amounting to a practical apprenticeship, and Mr. Biiggild, in his capacity of consulting Dairy Chemist t:, the Royal Agricultural Society of Denmark, actually epends his li€e in visiting the Danish farms, and giving assistance and advice in the manufacture of dairy-products ! It is quite corrcct that the whole of the dairy operations were conducted under the unremitting supervision of the whole party, and I added the words, “especially air. RlcGregor and myself,” bacauss we checked the weighing, set our seals on the milk and the finished products, and took other precautions with the express purpose of preventing any imaginable fraud, and of meeting such criticisms as those o€ Mr.Estcourt. It is a curious fact that while Mr. Iktcourt suggests that the Danish farmers EUC- ceeded in surreptitiously introducing foreign fat under the very noses of the party, regardless of the consequences of their detection in the act, from various other sources 1 am hearing of samples of butter fully as abnormal in character as €3 and 0. In fact, the more general cry is that our experience was not novel. I sent Mr. Estcourt somewhat more than 30 grammes of the fat rendered from B butter, and am surprised to learn from his paper (page 56) that this quantity was found by him insuficient for the determination of the specific gravity by the Westphal balance. It is a fact generally recognised that the result of the distillation of butter fat by Eeichert’s process, expressed as butyric acid, gives a somewhat lower figure than the soluble acids, expressed as butyric acid. But Mr. Estcourt found his G sample to require, when examined by Eeichert’s process, an amount of alkali corresponding to 4.1 6 of butyric acid, while the soluble acids in the same sample are stated as equivalent to 3.53 of butyric acid ! I will not ask Mr. Estcourt to state which of these two figures is erroneous, as f write this chieily as a personal explanation, and do not intend to discuss the matter f urthor.

ISSN:0003-2654    

DOI:10.1039/AN8891400072

出版商:RSC    

年代:1889

数据来源: RSC

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THE ANALYST. 7 3 QUANTITATIVE ESTI&TATION OF ADULTN1:ANTS IN LAED. BY H. W. WILEP. THE progress of qualitative analysis has rendered it possible for the skilled analyst a t the present time to detect with certainty every commercial adulteration OF lard. It is probably true that laboratory adulterations amounting to only 2 or 3 per cent. may escape the quest of the skilled chemiat ; but when adulterations are made for commercial purposes the amount of adulterant added is n!ways in suEcient quantities to render its qualitative detection easy. For quantitative purposes, however, the matter is not so readily determined. For practical purposes the two adulterants which are used in making compound lards are cotton oil and the stearines derived by pressing partially crystallised lard or tallow.The first of these stearines is usually called prime lard stearine, and the second oleo-stearine. The following methods have been proposed for the quantitative detoction of these aclultemnts.74 THE ANALYST 1. WLe amount of insoluble gsesiclue obtuined upon treating the samples with a mixtuw of ether and alcohol.-This method, as was shown in the celebrated trial of McGeoch, Everingham S; Co., against Fowler Bros., in Chicago, was wholly unreliable, and it may be dismissed from the category of useful methods. 2. The spec$% gravity.-This method has great value, and may be relied upon to give approximate results. 3. Absorption of iodine.-This method would be an excellent one for determining the amount of cotton oil added to a lard, provided that no stearine was present ; but the careful addition of cotton oil and stearine will enable the mixer to make a lard whose iodine number is almost identical with that of the pure article.4. The rise of temperature zohicli samples undeygo when mixed with sdphuric mid.- This process, devised by Maurnem&, may give valuable information in regard to the quantity of adulterants added. Unfortunately, however, it is open to the same objec- tion as lies against the iodine method, viz., the rise of temperature with the stearine is much less than that with lard, so that by the addition of stearine and cotton oil a mixture can be made in which the rise of temperature is not very much greater than that produced by lard itself. 5. Melting point qjJ the samples.-This method is of but little practical benefit when taken alone.Mixtures of lard and cotton oil do not show a mean melting point as in- dicated by theory. Cotton oil melts one or two degrees below zero, while pure lard melts a t about 40°. A mixture of equal quantities of these two substances shows a theoretical melting point of 20". Such a mixture, however, mill melt only a few degrees below the fusing point of pure lard. 6. Refractive index.-I am not aware that the refractive index has been used as a method of quantitatively approximating the amounts of cotton oil and stearine added, and I propose to say a few words in regard to its value in this respect. Fourteen samples of lard, known to be pure hog-grease, examined in my laboratory, gave the following mean data :- Refractive index * .. . * . * . . . 1.4620 Percentage of iodine absolbecl . . . . . . . . 62.48 Specific gravity at 3.5" . . . . . . * . . . *9053 Rise of temperature with sul1)huric acid . . . . 41.5" Melting point . . . . . . . . * . . . 40.7" Eloven samples of steam lards passed by tlie Chicago Board of Trade gave as t mean the following data :- Refractive index . . .. . . . . . . 1.4623 Percentage of iodine absorbed . . . . . * . . 63-86 Specific gravity a t 3 5 O . . . . . .. . . -9055 Thirteen samples of Armour's mixed lards gave the following data :- Rise of temperature with sulphuric acid . . . . 39.9" Melting point . . . . . . . . . . . . 3 7 O Refractive index . . . . .. , . . . 1.4634 Percentage of iodine absorbed . . . . . . . . 63-58 Rise of temperature with sulphuric acid .. . . 46-5O Specific gravity at 35" . . . . . . . . . . -9060 Melting point . . . . . . . . . . . . 40.6"THE ANALYST. 75 Sixteen samples of Fairbank's mixed lards gave the following data :- Refractive index . . . . . . . . . . 1.4651 Percentage of iodine absorbed . . . . .. . . 55-31 Specific gravity at 35" . . . . . . .. .. ~9095 Melting point , . . . . . .. . . . . 38*1@ Eefractive index . . .. . . . . . . 1*4G'ic5 Percentage of iodine absorbed . . . . . . . . 106.54 Rise of temperature with sulphuric acid . . . , 57*9@ Sixteen samples of purified cotton oil gave the following data :- Rise of temperature with sulphur'ic acid . . . . 83.7" Specific gravity at 35? . . . . . . . . . . -9145 Making use of these data, we reach the following results :- Determined by the rise of temperature with sulphuric acid, Fairbank's lards con- tained 32-80 per cent.of cotton oil, and Armour's 11-59 per cent. Calculating from their respective specific gravities, Fairbank's lard contained 45.65 per cent. of cotton oil, and Armour's 7-60 per cent. Determined by the iodine absorption alone, Fairbank's lard contained 53-29 per cent. cotton oil, and Armour's 3.6 per cent. As determined by the refractive index, Fairbank's lard contained 56.36 per cent. cotton oil, and Armour's 25.45 per cent." The unknown quantity, however, is the effect which the stearines employed had upon the data given. An oleo-stearine examined in my laboratory had an iodine absorption of 18 per cent.; a prime lard stearine an iodine absorption of 44 per cent.Thusmore than twice as much of the oleo-stearine could be used as of the lard stearine without perceptibly influencing the percentage of iodine absorption. The specific gravity of the lard stearine used was about the same as that of the lard, viz., 0905; although a larger number of determinations might show a lower specific gravity. The refractive index of one sample of oleo-stearine calculated at 25O was 1.4646. Before formulating any rule in regard to the matter 1 readily admit that a much larger number of samples of stearine should be examined, and their refractive indices deter- mined. I think, however, it will appear finally that both the speci6c gravities of the stearines employed, and the refractive indices will be found not to vary greatly from the numbers for pure lard; the specific gravities being somewhat lower.It is seen by the above result that the approximate quantity of cotton oil in lard, as indicated by the refractive index, is much nearer the true proportion for the Fairbank and Armour samples than that given by any of the other methods employed. For instance, let us suppose that the Fairbank samples were composed of 60 per cent. cotton oil, 20 per cent. pure lard, and 20 per cent. lard stearine; the quantity of iodine absorbed by such a lard would be as follows :- 60 x 107 = 6420 30 x 62 = 1240 20 X 44 = 880 100 parts - 5540 Iodine absorption theoretical . . . a 85.40 per cent. Actual iodine number obtained by analysis 85.31 ,, Thus from the above theoretical calculation the amount of cotton oil added was 60 per cent., which as indicated by the refractive index was 56.36 per cent., by the specific gravity 45.65 per cent., and by the rise of temperature with sulphuric acid 32*SO per cent.* The above numbers are calculated from the mean data for the fourteen samples of pure lard and t.he sixteen samples of purified cotton oil,76 THE ANALYST. I n the case of Armour’s lard take the following :- Ingredients, Iodine Per Cent. Number. Total Pure lard . . . . * . $0 x 62 = 4340 Cotton oil . . . . . . 20 x 107 = 2140 Oleo-stearine . . . . . . 10 x 18 = 1so 100 = 6GC;O Theoretical iodine numbjr . . . . 66 60 per cent. Actual iodine number . . . . . . 63.55 ,, --- - Let 11s suppose again that the compound was made with prime lard stearine, in which case me have the following cornpntation :--- Ingredients, Iodine Per Cent.Number. Total. Pure lard , . . . . . . 70 x 62 = 4340 Cotton oil . . . . . . 15 x 107 =- 1605 Lard stearine . . . . . . 15 x 44 = 6G0 -- -- I 100 - 6605 Theoretical iodine number . . , . 66-05 per cent. Actual iodine number . . . . . . 63.58 ,, From the abme computations the vnl110 of the relractive index in determining approximately the respective quantities of cotton oil and steariue in mixed lards is apparent. It is true that in individual cases the variation might be very much greater than indicated above, but as an expression of the mean result it appears to me that the refractive index is fully as valuable if not more so than the specific gravity in the quantitative determination of mixed lards. I propose to push this investigation somewhat further by more extensive exami- nations of the specific gravities and refractive indices of lard, oleo-stearine, prime steam lard, and mixed lards, The refractive index of pure water at 2 5 O as indicated by the instrument employed (Abbe’s large model) was 1.3300. When the index of water a t the above temperature is taken a t 1.3330, -0030 should be added to the numb3rs given in the above paper.

ISSN:0003-2654    

DOI:10.1039/AN8891400073

出版商:RSC    

年代:1889

数据来源: RSC

摘要:

76 THE ANALYST. ON SOURCES OF EEROR I N DETERMINATION OF NI‘l?ROGEX EY SODA- LIME, AND MEANS FOR AVOIDING THEN. BY W. 0. ATRATER. (Cont inzcec-l from page 5 9 .) From these results, as well as from consideration of what is known of dissociation in general, it is evidently impossible to predicate anything definite regarding the amount of decomposition that would take place a t a given temperature in a glass tube contain- ing soda-lime and such a complex mixture of gases as occur in an ordinary combustion. I regret the lack of facilities which prevented determinations of the temperature at which the combustions in these experiments were made ; but 80 far as one can judge from obaervation, I should say that what I have here designated as “medium heat ’’ or 6‘ usual heat,” namely, that in which the combustion tube is dull red and the soda-lime yellowish, is about that a t which combustions are very commonly made in the laboratories where I am acquainted.THE ANALYST.77 Prehn and Hornberger have reported observations which imply large losses of nitrogen by oxidation in soda-lime combustions. When sugar was burned in the tube to expel the air before the combustion and to sweep out the ammonia afterwards, con.. siderably more ammonia was obtained than where this precaution was omitted, and the apparent oxidation by the air present in the tube at the beginning was greater than that from the air used in the aspiration at the end. But the experiments were made with ammonium salts, and where no sugar was used there was apparently no gas to drive out the air and prevent its oxygen from acting on the ammonia.In ordinary combustion of nitrogenous materials large quantities of gases are produced, and in the experiments I have just described oxalic acid was used, which naturally drove out the air. On the other hand, numerous analysts find that with proper precautions there iw noloss from oxidation. I n our work we have taken pains to have the tubes well filled with soda-lime and substance so as to leave only very little open space for air, and to heat the anterior layer of soda-lime before applying the heat to the mixture of soda- lime and substance, thus expelling a large part of the air in advance, and have been careful not to aspirate with air until after putting out the flames, so that the contents of the tube have become somewhat cooled before the air has been admitted.I n how far omission of these precautions may explain the apparent oxidation elsewhere observed, I, of course, cannot say. Naturally there would be the less danger of loss the more the air is removed by diluting gases before heating. But considerable experience has left me with the very strong impression that with the precautions I have suggested there need be very little fear of oxidation. This must be especially true where, as in ordinary combustions, large amounts of hydrocarbons are present to combine with the oxygen. Makris has shown that Oxidation may take place, but his experiments were made under conditions especially arranged to insure admixture of air with ammonia at a high temperature.* Prehn and Hornberger have also experimented upon the effect of diEirent degrees of heat on the ammonia in determinations with ammonium salts and potassium ferro- cyanide, They find, at what they call ordinary heat or dull redness, no considerable indications of dissociation, but on heating to bright redness they found with tubes 35-40 cm.and the anterior layer of soda-lime 15 cm. long, considerable, and with tubes 65-65 cm. and the anterior layer 30-40 cm. still more indication of the dissociation of ammonia. Their results thus agree with those above given, except that they get more dissociation with the high heat in the long than in the short tubes. This they very reasonably explain by the fact that the ammonia in the long tubes had more time t o dissociate, from which I infer that the gases were caused to pass more slowly than was the case in our work.Makris also tested the dissociation of ammonia by passing a slow current of gas through a tube 70 cm. long filled with pieces of soda-lime and heated to bright redness. Analysis of the gases coming from the tube showed a very considerable amount of disso- ciation. But, as Gruber has observed, the case here mas different from that in an ordinary combustion, in that a large amount of ammonia was exposed for a long time to * Ann. Chem. (Liebeg) 184, 376.78 THE ANALYST. a high heat and without any considerable amount of diluting gas, whereas in ordinary combustion there is less free space in the tube, and that largely filled with other gases, so that the ammonia is rapidly swept away, ancl furthermore the diluting gases aro largely hydrocarbons which would naturally furnish nascent hydrogen to regenerate dis- sociated ammonia.My results above detailed accord very exactly with those of Gruber and of Johnson and Jenkins above cited, who found no indications of loss by dissociation. But it is evident that both the complete transformation of nitrogen into ammonia, and the loss of ammonia, depend largely upon the manipulation. Thus Kissling gets very good results with an anterior layer 35 cm. long, ancl evident loss of nitrogen when the anterior layer is only from 7 to 10 cm. long, the combustion being carried on slowly.* The experiments described by Mr. Ball and myself in a previous article bear upon the questions of dissociation of ammonia and of incomplete ammonification of nitrogen of distillation products. They were made with casein, the conditions being varied so as to allow in some cases very little, and in others considerable opportunity for the ammonia formed to be dissociated. The results, given in detail in the article referred to, are more concisely set forth in Table I V . (To be continued.) * Ztschr. anal. Chem. 24, 1885, 441.

ISSN:0003-2654    

DOI:10.1039/AN8891400076

出版商:RSC    

年代:1889

数据来源: RSC

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78 THE ANALYST. REPORT OF RECENT RESEARCHES AND IMPROVEMENTS I N ANALYTICAL PROCESSES. F. FILSINGER. Zeitschr f. Angew Chenzie, No. I, 1S89.-The acetin process recommended by Benedict and Cantor (see ANALYST, ISSS) givcs good results with the purer kinds of glycerin, but is unreliable for the titration of samples got from soap leys, as these retain impurities which affect the process. Better results would no doubt be obtained if the impurities were first got rid of, but this would involve dilution, and the process only works with fairly concen- ESTIMATION OF GLYCERIN IN THE COMMERCIAL ARTICLE, trated samples. L. DE K. TEST FOR ANTIFEBRIN IN PHENACETIN. M. J. SCHRGDER. Nederl. Tydschr. v Pharmacie, etc. January, lSS9. - Phenacetin, when taken internally, yields phenetidin and para amido phenol, both harmless bodies, whilst antifebrin yields aniline, which is decidedly poisonous.It is therefore of importance to test for the presence of antifebrin in phenacetin. The author found the best test to be Plugge’s reagent, which consists of a solution of mercurous nitrate with a little nitrous acid. -5 grm. of the sample is boiled in a test-tube with S C.C. of water, allowed to cool, and filtered off from the re-crystallized phenacetin. The filtrate is boiled with a little potassium nitrite and dilute nitric acid, then mixed with some of Plugge’s reagent, and again boiled. If no red colour is got, the sample may be considered its practically pure; at all events, there cannot be more than 2 per cent. of antifebrin. L. DE K.THE ANALYST.79 ~ ~~~~ ~~~~ ~ ZINC SALICYLATE. L. VAN ITALLIE. Nederl. Tydschr. v. Phamnacie, etc February, 1889 .-The author tests the salt by incinerating the compound, moistening the ash with nitric acid, and finally igniting the residue, which should be not less than 21 per cent. A commercial sample only yielded 18 per cent. The author estimated the degree of solubility of this salt in various fluids. One part dissolves in 25.2 parts of water at 16Q C. One part of the anhydrous salt dissolves in 36 parts of ether of 725 sp. gr. at 1 6 O C., and in 450 parts of chloroform of 1.495 sp. gr. at 1 5 O C. One part of the salt dissolves in 3.5 parts of spirits of wine, sp. gr. 819.4 a t 15O C. I n petroleum spirit it is quite insoluble. L DE K. MODIFICATION OF KJELDAHL’S NITROGEN PROCESS. J.W. GUNNING. IVederZ. Tydschr. v. Phccrmrcie, etc., February, 1889.-The author operates as follows : One part of potassium sulphate is fused with two parts of sulphuric acid. This mixture gets semi- solid in the cold, but it readily melts: and may then be treated like a fluid. About one gramme of the substance to be analysed is put into a 300 C.C. flask with round bottom and short neck. If liquids such as milk or beer have to be tested, a suitable quantity must first be evaporated to dryness in the flask itself. About 30 C.C. of the acid mixture are now added, and the whole heated with a Bunsen burner. At first strong frothing occurs and white fumes escape, consisting chiefly of water vapour. To prevent loss of strong acid, the neck of the flask is now fitted with a funnel, which is then covered with a watch-glass.This simple arrangement will now cause the acid to condense and run back into the flask. The operation is finished when the acid looks colourless, which will be generally the case after about an hour. After cooling, the ammonia is now estimated as usual. The author prefers the standardising of the volumetric acid by the iodine and sodium hyposulphite method. The test analyses are very satisfactory. Uric acid yielded 33.3 per cent. of nitrogen, theory requiring 33.33 per cent. Aniline oxalate yielded 10 per cent., theory requiring 10.1 per cent. L. DE K. ASSAY OF CARBOLIC ACID. L. DE KONINGH. Zeitschrf. angew Chemie, No. 5.- The author, in reply to Mr. Williams, still believes the salt test to be a good one, both for the liquefied acid of the B.P.and hydrated cresylic acid. If the acid contains much tar oil, it cannot be in the hydrated state, but a little uncombined water may be shown by the benzol test, which, however, is not meant to be used for the purer forms of the acid. The percentage of tar oils is best estimated by agitating the sample with four times its volume of 10 per cent. soda ley if necessary, with addition of a fixed quantity of benzol. Williams’ process for the estimation of free acid in carbolic powders is no doubt a most excellent one, but the author fails to see in what essential particulas it differs from the one published in the ANALYST, vol. xii., by Dr. Muter and himself. To all intents and purposes it is just the same, though perhaps not quite so accurate, because not performed in specially constructed apparatus. W. H. D. STANDARDISING PERMANGANATE. R. JAHODE. Zeitschr f. angew Chernie, No. 4, 89. --Many analysts still prefer to standardise their permanganate with pianoforte wire, but the trouble always is to exclude the air after the iron has dissolved. The author operates as follows: The iron is dissolved in boiIing acid in a flask, which is closed by a cork,80 THE ANALYST. through which goes a doubly-bent tube, the end of which is made to dip into a beaker containing a solution of sodium bicarbonate. When solution is complete and the liquid allowed to cool, the soda solution finds its way into the flask, but no sooner have a few drops got in, than an evolution of carbonic acid gas setting in drives the fluid back. L. DE K.

ISSN:0003-2654    

DOI:10.1039/AN8891400078

出版商:RSC    

年代:1889

数据来源: RSC

摘要:

80 THE ANALYST. CORRESPONDENCE. [The Editor is not in any way ve.yonsible for oyirtions exyressed by his cowespondents.] To the Editor ofthe ANALYST. SIR,-In the number of the ANALYST for February last, there is a report of a paper by Mr. Rowland Williams on the Determination o€ Citric Acid in Lemon Juice,” brought before the Society of Public Analysts, I‘ to promote,” as Mr. Williams said, ‘‘ a discussion among the members.” I should have been glad to have taken part in such a discussion, had there been one, if Mr. Williams had, in pursuance of his object, kindly informed me that his paper was to be read, and that the greater part of it had reference to what he interpreted as being my method of Estimating Citric Acid in Concen- trated Lemon Juice,” and in condemning the use of a solution of an alkaline carbonate for the titration.If Mr. Williams had informed me some months ago, when he asked for some information,.that my verv general reply was to form the foundation of a paper to be read before the Society, I might haye described to him the precautions necessary to be observed in sufficient detail to have saved him from being misled into the belief that there is any objection to the use of alkaline carbonate for the Purpose, or of running the risk of misleading others, beyond a little more time being required for the experiment than is necessary when caustic alkali is employed. There is absolutely no inaccuracy involved in use of alkaline carbonate, with litmus as an indicator, when the proper conditions are appreciated and observed. I have no kind of intention of taking up the space of the journal with a criticism of Mr.Williams’ paper as a whole, but I cannot help expressing my surprise at the figures given in the two tables which accompany it. I n the first of these are given comparative results of the analyses of six samples by the caustic method and by alkaline carbonate, showing, according to Mr. Williams, that the carbonate gives uniformly and exactly one ounce of citric acid more in a gallon than the caustic solution. The only possible explanation of there being difference a t all, is that there was interference by carbonic acid retained in the solution ; but if Mr. Williams allowed carbonic acid to remain during the final testing, how is it there is anything like .agreement in the results and that the differences are almost constant 1 I n the second table the results of the analyses of seven samples of pure citric acid by the two solutions are given, and the same astonishingly uniform differences are shown.I cannot think Mr. Wiliiams means to suggest that the alkali in an alkaline carbonate has less saturating power for citric acid than it has as it exists in the caustic condition, and yet this seems to be the only possible inference to be drawn from the tables themselves. My explanation, of course, is that these differences are really errors of manipulation. I do not think I should have taken up the space of the journal with this letter if I not lately found that Mr. Williams’ paper has been distributed widely in pamphlet form amongst manufacturers and dealers commercially interested in the sale of lemon juice, of whom some, a t all events, are not in a position to estimate correctly the value of Mr.Williams’ criticism of what he believes to be my method of analysis, but which, in fact, is only his mode of employing it. At the meeting a t which the paper was read, there seems to have been no discussion, Mr. Allen only expressing what appears to me, to say the least of it, a very hasty “ regret” that chemists of repute ” should adopt an alkaline car- bonate with litmus as an indicator for the purpose under discussion. Now, in reply to Mr. Williams and to Mr. Allen, I should have thought it might have been assumed by the Society of Public Analysts that chemists of repute, who had been engaged in a special analysis for five-and-twenty years, had carefully examined and tested every process that had been suggested, and under their sense of responsibility, and as the result of their long experience, had adopted the process, which in their hands gave the most reliable returns under all circumstances.Many hundreds of analyses have been made in my laboratory with caustic and with alkaline carbonate solution side by side, and observ- ing the precautions necessary in each case, I, unlike Mr. Williams, obtain identical results, and I protest as strongly as possible against the inferences to be drawn from Mr. Williams’ tables, as being opposed to all my experience. There are reasons why sodium or potassium carbonates are frequently to be preferred. After removal of the carbonic acid with properly prepared litmus paper of the proper tint, there is absolutely no objection to their use. As a matter of fact, I do not think Mr. Williams flnds it easy to obtain caustic alkali free from carbonate.-I am, sir, yours truly, 39, Lime Street, London, E.C., 26th BIarch, 1889. 0. H. UPTON.

ISSN:0003-2654    

DOI:10.1039/AN8891400080

出版商:RSC    

年代:1889

数据来源: RSC