摘要:

THE ANALYST. MAY, 1889. NOTES ON LACTOSE. BY E. W. T. JONES, F.T.C. (Read at the Meeting, March 1889.) ABOUT twelve months ago I carefully purified some milk-sugar, and subsequently obtained some very nice crystals, which after draining, etc., were finally dried in vacuo over H,SO,. The following notes of the results obtained with them I have every con- fidence in publishing, and although I do not propose to give all the experiments in detail, the results may be taken as very carefully fixed by repeated experiments. 5 grms. (exactly) of the crystals (=4*75 grms. anhydrous lactose) were put into a correct 100 C.C. flask, about 80 C.C. distilled water added, and solution effected by heating82 THE ANALYST. in boiling wafer for twenty minutes to half an hour. up at 60° F, to exactly 100 C.C.divisor for sp. gr. above 1,000 to get grms. per 100 C.C. of Tbe next day the flask waa filled Thus I avoided bi-rotation. Tbe sp. gr. a t 6O9 F. of such a solution is 1018.6, hence at this concentration the CI,H,¶Oll is 3.9 1 Using a Soleil-Ventzke-Scheibler polariscope, I find at this concentration the and O1J3,,O,, + OH, is 3.72 sp. rot. pr. for - - 60*5[a], - - 6 4.6 [a] 51.9 ,, - C,2H¶3OIl+ 0% - - 57.5 ,) - ~ 1 , ~ 2 2 ~ 1 1 Cupric reducing power with Fehling solution, using not less than 30 c c. (diluted with two volumes of water) for 0.1 grm. lactose, heated in vessel surrounded by boilhag water for fifteen miiiu t es (O’Sullivan’s met hod). 012Ht*O,l - CUO X 0,5723 CUO X 0.6024 - - C,2H,,Oll+ OH, I weigh as CuO, i e., I convert the Cu,O into CuO by ignition in a porcelain crucible -the whole eecreb of sure complete oxidation being to use at first a very small flame to just char and destroy the filter paper, after which more heat may be applied and final ignition over the blow-pipe resorted to-proceeding thus the CuO does not cohere, and there is not the slightest risk about not obtaining full oxidation by ignition alone- duplicates should not, and generally do not, in my hands, differ more than a milligram.Action of citric acid.-I have corroborated that lactose is not affected optically, nor in cupric reducing power, by this acid, when proceeding as follows, whilst cane-sugar is completely inverted under such circumstances. Crystallised citric acid is added a t the rate of 1.6 grms. per 100 C.C.of solution. Generally I take 50 C.C. of sugar solution and add 0*8 grm. of citric acid, and heat in 100 C.C. flask in boiling water for thirty minutes, and then make up to within half a grm. of the original weight. During the heating a little more loss in volume occurs by evaporation than the increase caused by the citric acid. The weight of the flask, solution and acid being taken before heating, and after- wards made with distilled water to within 1 grm. for 1.6 grm. citric acid, or within half a gremme for 0.8 grm. citric acid, exactly the same volume is obtained after treatment with acid as before, and, therefore, if only lactose is present, the polariscopic readings will be the same. The proportion of citric acid recommended increases the bulk of the solution &th, viz,, 1.6 grms.citric acid to 100 C.C. makes it 101 c.c., and 0.8 grm. to 50 makes it 50.5 c.c., hence we arrive a t the proper allowance for adjusting the solution to the original volume. I have said that cane sugar is completely inverted, and may I be pardoned for mentioning here that although the real sp. rot. pr. of invert sugar is, 23.75[r~],, i.e., mleulated on the increased molecule of the original cane-sugar, if calculated on t h e cane- sugar, aa generally will be the case in practical work, 25-0 must be used. Crystals of lactose do not lose their water of crystallisation by twenty-four hours’ heating in a water oven, but if the crystals be just diasolved in water and evaporated over a water bath to dryness, and then dried in the water oven for a few hours, anhydrousTHE ANALYST. 83 lactose is obtained ; but the drying must be continued till the weight is constant, which proceeds slowly if the residue is thick. It has been stated that our residues containing lactose after drying in the water oven contain this body in the hydrated state, but this I dispute, if drying is conducted till constant weight occurs. 2.3810 grms. of the crystals aftor drying for twenty-four hours in the water oven, weighed 2.3806, practically no loss. 0.6828 grm. crystals just dissolved by addition of distilled water, then evaporated t o dryness, after drying four or five hours in the water oven, became constant at 0.6500 grm. against 0,6487, the correct amount of anhydrous lactose corresponding to the crystals taken. It is qriite needless for me to point out the practical application of these results in such analyses as those of condensed milk, etc., etc.

ISSN:0003-2654    

DOI:10.1039/AN889140081c

出版商:RSC    

年代:1889

数据来源: RSC

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THE ANALYST. 83 COLOURTNG MATTER (ARSENICAL) USED FOR COLOURING CANDLES BY W. F. LOWE, F.I.C., F.C.S., ASSOCIATE OF THE ROYAL SCHOOL OF MINES. (Read at the Meeting, March, 1889.) WHILST the use of dangerous mineral colours for colouring tinned and bottled fruits, wall papers, etc., has been pretty nearly stamped out, their use for colouring wax candles appears t o have been overlooked. The danger of using them for such a purpose has recently been brought to my notice, and a brief description may be of interest to the members of our Society. A children’s party was given by a gentleman in the district for which I am Public Analyst, and a Christmas-tree with a large number of small coloured candles was the principal attraction. On the day following the party about twenty per cent.of the children who had been present, and also several grown-up persons, suffered from symptoms of irritant poisoning. At first it was naturally supposed that something in the food had caused the mischief; but on making inquiries the gentleman found that some of those attacked had taken nothing t o eat or drink in the house, but had been present at the Christmas-tree, so that it could not possibly be the food. His suspicions then fell on the green candles which had been used for lighting the tree, and as he had had a chemical training, he examined one of the green candles himself, and found traces of arsenic in it. He then forwarded the remainder to me for examination, and I found the green ones contained both copper and arsenic, evidently having been coloured with one of the arsenical greens, which appeared to be ‘‘ emerald green.” There was not sufficient material to estimate with any accuracy the amount present, but I was able to separate a small quantity of the colouring matter itself by dissolving the wax in warm ether.It is well to note that at first it appears as if the colouring matter had also dissolved, for it is in such a finely divided state that it floats about in the ether for some time, thus giving the appearance of a green solution ; but if it is filtered or allowed to stand a, few hours it is seen that it is merely in suspension. From information I have obtained, it appears to be a common practice in the smaller candle works t o use arsenical greens for colouring candles, as they are easier t o84 THE ANALYST.use than the aniline green, and stand the action of light so much better, the candles coloured with aniline greens having a tendency to fade unless kept in a dark place. oz. to over 1 oz. of emerald green to 28 lbs. of wax, and that for the small green candles about 1 oz. to 28 lbs. would be employed. A t this rate each small candle, I find, would contain about 2 grain of colour- ing matter, and would be capable of yielding about + gr. of arsenious anhydride ; so that I should say that a dozen or two of such candles burnt in a room of moderate size would be capable of producing very serious effects. Red candles also are usually coloured with an injurious mineral colour, a t least for such a purpose, for vermilion is used, and a red candle from the same Christmas-tree, I find contains vermilion, but I believe the candles used were chiefly green ones.I intend to make a further examination of the matter, and I hope some of the other members will do the same, for I think that such a practice should, if possible be stopped. DISCUSSION. Mr. HEBNER said that about twelve years ago he was just about to publish a note on the same subject when he found that Prof. Church had already drawn attention to the matter. Mr. CASSAL said that the fact of arsenic having been found in candles was not new. Some years ago the question had been brought forward, and it was alleged that some people had been actually poisoned by arsenical candles, but if he recollected rightly they were white candles, not coloured ones. The subject was of very considerable interest and importance from a hygienic point of view.The statements that the practice was being stamped out he could not agree with. Most analysts still had a good many things to examine for the presence of arsenic. Some years ago, a t the time of the Health Exhibition, he had occasion to examine a number of articles for arsenical and other poisonous pigments, among them butterfly nets, coloured balls, and various children’s toys, arsenic in large amount being frequently found. The green gauze used for nets had been found to contain arsenic. The point was the extreme minuteness of the quantity by which the injury may come about. It would be a good case to help Mr. Dyer, as the whole chain of evidence was complete. With regard t o the use of arsenious acid in candles, he understood it was used to give the burning wick the turn; and if that were so, he was surprised some evil effect had not been discovered.As to the rash mentioned, that was quite a fact; he had heard of several instances of rash being produced by arsenical pigments, which have an irritating effect on the skin. The whole matter was very interesting to him from a medical as well as chemical point of view, with the experience he had had. Mr. ALLEN said that the paper just read showed the desirability of extending the Sale of Food and Drugs Act. Public analysts ought to have under their care all such articles as arsenical wall-papers, fabrics of candles, besides disinfecting powders, &c. The subject was not strictly a novel one, but it was only by calling attention to cases which came within their own experience that it was brought home to them, and he thought they were indebted to the author for bringing the matter forward.He might remind them of the historical case of a member of the royal family of Austria who was practised on by introducing arsenic into the candles used in his bedroom. It was not fair to judge of the poisonous effects of arsenical paper or candles from the amount of arsenic present, for the finely-divided arsenious oxide would be so distributed through the atmosphere as to affect the system far more strongly than if an equal amount had been taken into the stomach; in fact, the effects would probably be more properly The quantity employed, I am informed, is fromTHE ANALYST.85 comparable with those attending the breathing of arseniuretted hydrogen, which was known to be intensely poisonous. How any candle could contain a measurable or weighable amount of copper which did not go into the wick he could not understand; in fact, if he had had to analyse such a candle, he thonght he should have burned the candle and condensed the arsenic by some con- trivance similar to that for estimating sulphur in coal gas, and should have looked in the candle end for the whole of the copper which had been previously distributed throughout the candle. Mr. BERNARD DYER said he would be glad if Mr. Harvey would send him the medical details of the case. It might be known to members that this question of injurious colouring matters, not only applied as to papers, but to other things, had been taken up at various times by various societies, but more especially by the National Health Society.The Society of Arts had previously collected evidence and made a report, but nothing came of it. The National Health Society, in 1883, appointed a committee consisting of medical men and chemists to draft a Bill for the suppression of the sale of arsenical wall paper, on the same lines as the Acts of Parliament in operation on the Continent and, he believed, also in America, I n Germany, he believed, arsenical paper was made and exported to this country, but it could not be sold in Germany. I n Sweden there was a very stringent law on the subject. The great difficulty in drafting a Bill was in defining the word “ arsenical.” After considering the question for some time, Mr.Cam, Mr. Heisch, and Dr. Bartlett suggested a very excellent modification of the Xarsh apparatus which seemed to meet all difficulties, both as to testing and defining arsenical colours. Dr. Willoughby was a t first secretary of the committee, and was succeeded by himself (Mr. Dyer), and the Bill became finally matured during his (Mr. Dyer’s) secretaryship, in 1885; and Dr. Cameron undertook to briag the matter before the House of Commons. But the Irish question came up, and Dr. Cameron said it would be perfectly hopeless t o bring this forward then, as it would certainly be opposed by the large trade interests, and as he, moreover, was very busy; so nothing was done, and the draft Bill was still on the shelf awaiting an introducer and an opportunity of introduction. The fact remained that England is almost the only civilised country where arsenic-dyed wall papers were allowed to be sold.One of the great difficulties Dr. Cameron said they mould have to contend with was that, as large trade interests were involved, and there would be much opposition, a Select Committee would be doubtless appointed, and that Committee would ask them for their medical evidence. Now, the Society of Arts and the National Health Society had gathered a drawer full of medical evidence, but much of it related to cases where the arsenic was so abundant that, on wiping the paper with a duster, the green came off on the cloth, and much more to cases where patients being out of health, and wall paper.being found arsenical, the two facts were assumed to be cause and effect on grounds which, though very strong, did not afford strictly accurate and convincing evidence. They felt that, before the matter could be brought forward with full confidence, they should strengthen their medical evidence. Any strictly authentic cases of domestic poisoning from arsenic he should be glad to receive on behalf of the National Health Society, that he might hand them to Mr. Kenneth Millican, who had undertaken the collection and collation of medical facts on the question. Mr. CANAL said that general practitioners among medical men who had not studied hygiene were not likely to give specially valuable opinions on the points referred to- a t least, that was his experience, which was not a small one.Mr. Cassal mentioned the case of a lady who had been wearing a bonnet with bronzed leaves in it, some of these leaves having been kept in close contact with the skin. The leaves contained a large H e should like to know what became of the copper in the candles.86 THE ANALYST. quantity of arsenic, and the lady had suffered from an obstinate skin eruption and other arsenical symptoms. Another lady who had bought some coloured " Indian " muslin at a large establishment in the West End, and worked at it with her maid, had noticed that both of them were beginning to suffer from inflammation of the eyelids. The muslin was brought to him fm analysis, and 210 found large quantities of arsenic. The vendor had said that he would eat all tho arsenic that could bo found in it, and he (Mr.Cassal) was sorry he did not do so. I n another case five or six children were being kept in a room with a large fire in it, the walls being covered with a green arsenical paper. The symptoms had been mis- taken for those of a violent common cold. Dr. MUTER said he had had some similar Indian muslin sent to him, and he also found arsenic in it. Dr. HARVEY stated that he frequently met with arsenical wall papers. Only on the previous day a case was brought to his notics of serious illness traced to a drab-coloured bedroom paper, which upon analysis was found to contain a considerable amount of arsenic. He was acquainted with numerous other cases where injury appeared to have resulted from the use of such papers.Mr. ADAMS said that more than twenty times he had had patients suffering from arsenical poisoning. It was a common result that the eyelids became affected; they had a peculiar red appearance which a practical oculist a t once knew to be due to arsenic. He had a case quite lately showing what a very minute amount would do the mischief. Of course, in the case of the candles it must have been a very small quantity that each person could have breathed. The poisonous effects of arsenic depended in a measure on two things-first, the idiosyncracies of the person (some could take it with impunity whilst others are injuriously affected by the smallest amount), and secondly, if it gets into the system by the air cells of the lungs it is absorbed much more quickly and injuriously. A lady patient of his had some fur which he had mamined and found t o contain arsenic. She wrote to him about it on the previous day as follows:--"I am very pleased to tell you anything I can about the fur you found contained arsenic. Directly I began to wear it I had every symptom of a very bad cold in the head, and later on this was accompanied by sore throat and diarrhea. Naturally in hot rooms I always felt worse " When she resumed wearing it, all the symptoms recommenced. This experience was repeated again and again till she came to associate the symptoms with the wearing of the fur, which was then sent to him, and he found olit the cause. The sulphide was a t his service. The lady put the fur on one side and at once recovered.

ISSN:0003-2654    

DOI:10.1039/AN8891400083

出版商:RSC    

年代:1889

数据来源: RSC

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86 THE ANALYST. THE METHODS FOR DETERMINING FAT IN MILK. BY DR. P. VIETII, F.C.X., F.I.C. ON looking over the chemical literature of the last decade, we find that much attention has, during that period, been paid to the determination of fat in milk. So numerous are the methods brought out, and the alterations and improvements suggested, that it seems to me, that the supply far exceeds the demand, and that it becomes necessary to classify the various methods in divisions and subdivisions, when attempting to briefly review them in anything like a lucid manner. I will with your permission try to do so in the remarks which I am going to make. I. Methods which can be worked outside the chemical laboratory, and by persons having no analytical training. 1. Processes confined to the dairy.(Read at the Meeting, March, 1889.)THE ANALYST. 87 ~ ( a ) Control apparatus worked in connection with the Danish Centrifugal Cream The milk samples are simply subjected to centri- Thisvolume indicates Separator. fugal force in suitable vessels, and the volume of cream read off. the percentage of fat sufficiently near for all practical purposes. The milk is treated with strong acids, whereby the fat is, so to speak, set free, and under the in- fluence of centrifugal force unites, so that its volume can be determined. It is generally admitted that results thus obtained agree very closely indeed with those arrived at by determining the fat gravimetrically. At the same time it is rather curious that some experimenters, e.g., W. Blyth, compare it with Adams’ method, while others-among them, Soxhlet-compare it with the latter’s method ; both parties find agreeing results, and still paper and plaster method do not give results agreeing among themselves.It should be mentioned that a smaller machine has been constructed, which can be used in the laboratory of the analyst, although, I am afraid, the price will not facilitate its introduction. 2. Optical Methods.-They are based upon the assumption that the opacity of milk stands in direct relation to the amount of fat the milk contains. Not only is this supposition wrong, but the test is also influenced by a number of uncontrollable circum- stances. The results are, therefore, always doubtful, frequently quite fallacious. Feser’s Lactoscope is, relatively speaking, the best of all the optical tests.3, SoxhZet’s Areometric Process.-Milk is mixed with potash solution, and then shaken with ether. The ethereal fat solution is allowed to separate, and its specific gravity determined. The results may be considered to be identical with those arrived a t by extracting milk dried up on plaster of Paris. 4. Cronunder and Liebnzccnn shake a mixture of milk and potash solution with ether. After complete separation they allow the ether to evaporate and measure the volume of the fat left behind. I do not think these methods recommend themselves, and cannot find that they have been taken up. 5 Marchand’s Lactobutyrometer.-~lilk is shaken in a gauged tube with ether t o dissolve the fat; shaking is continued after the addition of alcohol, and the tube then placed in warm water.The mixture separates into three layers; the volume of the upper one, containing the fat, is read off. Every one-tenth C.C. indicates -2 per cent. of fat, in addition to 1.2 per cent. which is kept in solution. The results are fairly correct in the majority of cases, when dealing with milk which is not too rich. 6. Short heats milk with strong alkali in a boiling water-bath for two hours, decomposes the soap by the addition of a mixture of sulphuric and acetic acid, allows the liberated fatty acids to rise, and determines their volume, which is then enlarged in the proportion of 87 to 100. This method seems to be rather troublesome, and open to grave objections. The results are said to be lower than those obtained by Adams’ method.11. Methods which must be considered as confined to the chemical laboratory, and the hands of the analyst. No chemicals required. ( b ) Lactocrite, worked in connection with Swedish Cream Separator. A table gives the corresponding percentage of fat.88 THE ANALYST. 7. Bxtyacting the fut from the residue left when milk is evaporated without the (u) No care is taken to disintegrate the residue (Wanklyn). ( b ) Pains are taken that the residue should be in a readily exhaustible condition (Dr. Jas. Bell, Carter Bell). The diffichty of completely exhausting such milk residues, more especially if the milk is poor in fat, is now generally recognised and the methods may be looked at as abandoned. 8. Jfuter proposes to precipitate the casein which carries down the fat with it; to wash the precipitate first with water, then with alcohol, and at last with ether, which is collected and evaporated, when the fat is left behind.The substances suggested are glass powder, sea sand, plaster of Paris, asbestos, pumice stone, filter and blotting paper, wood fibre, sponge ; and these various modifications are connected with the names of Abraham, Adams, Babcock, Gantter, Johnstone, Macfarlaue, Soxhlet, Storch, and others. This group certainly contains the mosb exact methods for the deter- mination of fat in milk. 10. Morse and others suggest t o dry milk on anhydrous sulphate of copper, extract the fat by means of light petroleum, saponify, and determine the quantity of alkali required for saponification. I find only one account of experimenting with this method, in which it is said that the results fall below those arrived at by using Adams’ method.11. Roese shakes milk first with alkali, then with a mixture of ether and light petroleum, reads off the volume of the upper layer after complete separation, and determines in an aliquot part of it the fat gravimetrically. An allowance is made for fat retained in the aqueous layer. 12. JV. Schrnid first heats milk with strong hydrochloric acid, after cooling shakes with ether, notes the volume of ethereal layer, and ascertains the fat in an aliquot part. Determining the fat in an aliquot part of its solution appears to me very undesir- able, considering that one has to deal with ether, which is not only highly volatile, but the volume of which is also much influenced by temperature ; besides, experimental errors are much increased.This is a rather long list of methods for the determination of fat in milk, and still, I am convinced, it is very incomplete, containing only those methods which have come under my notice and impressed themselves on my memory. Of some of the methods enumerated there exist modifications with regard to the chemicals and apparatus employed. Very generally acknowledged as standard methods are Adams’ paper and Soxhlet’s plaster processes; the indications of other methods which do not give direct results are compared with and gauged by either of these processes. Methods like those of Roese and Schmidt can claim no other advantage but speed combined with a near approach to correctness.Speed, no doubt, is a valuable item, and approaching correctly results may sufice under certain circumstances, but certainly not with regard to the official work of addition of an inert mbstance. 9. Milk is dried up on some inert substance and then extracted.THE ANALYST. 89 a Public Analyst. Me ought to employ the most exact methods which are at his disposal. As an apology for the deficiency of new matter in the foregoing remarks I may say, that they were originally not intended to be read as a separate paper, but meant to be thrown into a discussion which, however, had to be abandoned for want of time. DISCUSSION. MR. DYER suggested that calcined gypsum might give erroneous results by causing slight saponification of the fat, for gypsum usually contained some carbonate of lime which became caustic on calcination, and might make a lime soap.DR. MUTER noticed that Dr. Vieth had referred to the method of coagulating the milk with acetic acid, collecting the curd, washing the same first with water and then with spirit, and finally percolating with ether. This was in certain cases a very good way of working as he had had occasion to before mention to the society. MR. HEHNER said i t would be very interesting to get a full catalogue of the different methods. As Dr. Vieth had gone so far perhaps he would go farther and complete it. DR. VOELCI~ER corroborated Mr. Dyer, and said that only last week he had such a sample of gypsum sent to him. Mr. Allen said that a good many years ago the late Mr. W. W. Stoddart, of Bristol, exhibited what was known as Horsley’s process and tube, a t a meeting of the British Pharmaceutical Conference, and also described a modified method by which the test was said to be applicable to butter.He, Mr. Allen, was very much interested in the description given, and consequently read a paper on the same subject a t the following meeting of the conference, in which he expressed a very unfavourable opinion respecting the method. As a matter of fact, the process did not originate with Horsley, but had been described by Marchand many years previously. The whole subject had gone so completely oiit of his mind, that when a question was asked him in the “English Mechanic,” as to the nature of the lacto-butgrometer, which was simply a Marchand’s or Horsley’s tube, he said he had never heard of the instrument.Dr. Vieth thereupon pointed out that the instrument had been advertised on the front page of the ANALYST, for a whole year previously, which he was afraid showed that advertisements were apt to be wasted on some people. DR. VIETH in reply said, that he considered plaster of Paris when employed in milk analysis, an inert substance inasmuch as its desired action was a purely mechanical one. Plaster of Paris was alkaline, but they must remember that milk was not neutral, but displayed besides alkaline, also acid reaction. A number of experiments had shown him that the acidity of milk, was in excess of the alkalinity of the plaster of Paris which he used. H e had no difficulty in getting good plaster €rom Hopkin and Williams. With regard to the method of extracting the caseine, he had followed that himself in a great many instances, extracting the precipitate aftor it ha3 been dried in the air bath; he found the results agreed very well indeed with the plaster extraction. The Marchand’s process gave very fair results in the majority of cases, of course, the results were not exact enough for the work of public analysts; but, for instance, in the hand of a farmer who wanted to pick out his best and worst cows, it gave very good results indeed. He had made thousands of determinations ; when the fat was within the limits of 3.per cent. and 3.5 per cent. the results agreed very closely. When dealing with richer milks, the results were not so reliable. He would never recommend the process for the use of public analysts, especially at the present day, when the amount of fat could be calculated with great accuracy, from the figures for specific gravity and total solids. (Conclzcsion, of the Society’s Proceedings.)

ISSN:0003-2654    

DOI:10.1039/AN8891400086

出版商:RSC    

年代:1889

数据来源: RSC

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90 THE ANALYST. Mini- mum. per ct. 1.3 0.4 0-0 i i . 7 ON SOURCES OF ERROR IN DETERMINATION OF NITROGEN BY SODA- LIME, AND MEANS FOR AVOIDING THEM. BY W. 0. ATWATER. (Continued from page 76.) Efects of long heating and of open spuce i.n tu6e upon amounts of nit?*ogen o6tuinccZ as nmmoniu from casein containing 12.43 per cent. of nitmgen. TABLE Iv. NITROGEN LOST. Aver- age. per ct. 2.8 5.2 5.5 68.5 77.0 Conditions of Experiments. No channel, long heating (26 hours) . , Channel, 8 hour . . .. .. . . Channel, long heating, long tube Channel, long heating . . .. . . Channel, long heating, high heat . . . . In per cent. of Weight of Casein, per ct. 0.47 1-92 2.95 9.88 . . Maxi- 1 mum, 1 :::: per ct. 0.16 0.05 0,OO 9.29 .. Aver- age. per ct. 0.35 0.65 0.68 8.5 1 9.58 In per cent.of Total Nitrogen. Maxi- mum. per ct. 3.8 15.4 23-7 7-95 When the tubes were closely packed so as to insure the maximum of contact between the gases produced and the heated soda-lime (water-vapour at high tempera- ture), and the combustion was conducted at a moderate heat and kept within the usual time of about three quarters of an hour, the full amount of nitrogen, 12.43 per cent. of the water-free casein, was obtained as ammonia. But when the combustion proceeded very slowly so as to occupy two and a half hours, the other conditions remaining the same, only from 12.27 to 12.08 per cent. of nitrogen were obtained as ammonia, making a loss of from 0.16 to 0.47 per cent. reckoned on the weight of the water-free casein, or from 1.3 to 3.8 per cent. of the total nitrogen. It seems reasonable to ascribe this loss to dissociation during the long time that the ammonia was exposed to the heat, though possibly some of it may have been due to incomplete ammonification of nitrogenous decomposition products. It is easy to understand how the ammonia passing rapidly through the interstices between the particles of soda-lime in the closely packed tube, in the ordinary analyses, would be so mixed with water-vapour and other gases that the nitrogenous distillation products would be completely changed to ammonia, and in the very brief exposure to heat the resultant dissociation would be too small t o be noticeable.On the other hand, when the operation extends through two and a half hours instead of three quarters of an hour, it would seem by no means improbable that the anterior layer of soda-lime might, before the end of this long period during which it is kept hot, cease to give off any considerable amount of water-vapour.But it is probably this water-vapour which yields the hydrogen to form ammonia with the nitrogen of the volatile distillation products, and it is not impossible that the same vapour may also tend by its presence to prevent dissociation of ammonia. Add the fact that, when the operation goes on slowly, the time of sojourn of the ammonia in the heated tube is ofTHE ANALYST. 91 course relatively much longer than the increased time of combustion would imply, and a large loss by dissociation and incomplete ammonification is easy to understand. When a channel was left in the tube, so that the contact between distillation pro- ducts and the soda-lime was less intimate, the loss of nitrogen was still greater.When, with the channel, the combustion occupied only three quarters of an hour, this loss varied from 0.4 per cent. to 15.4 per cent. of the total nitrogen. But when the com- bustion, with the channel, was prolonged to two and a half hours, the loss reached in one case 27 per cent. of the total nitrogen. This increased loss would seem most probably due to both incomplete ammonification and dissociation. A t any rate, the conditions provided for less perfect contact between soda-lime and substance ; for reduction of the supply of moisture which would provide hydrogen for ammonification and would also tend to prevent dissociation ; and for a very long exposure of ammonia to heat.When, with channel and long heating as before, the temperature of combustion was raised as high as the tubes would endure, the loss was very much greater, and amounted to 68.5 per cent. of the total nitrogen. The most natural explanation of this increased loss is the increased dissociation of ammonia. When the length of the anterior layer of soda-lime was increased, and with it, consequently, the amount of open space inside the tube, the loss of nitrogen was greater still, namely, from 76 to 79 per cent. of the whole. It would, of course, be foolish to attempt to say how much of the loss in these latter cases was due to dissociation and how much to incomplete ammonification. Such questions can be answered only by more detailed experiments, in which the gases produced should themselves be analysed.But it does seem reasonably safe to say that both dis- sociation and incomplete ammonification must account for a large part, if not all, of the errors here observed, and that there is great danger of loss in these ways unless due precautions are observed. To conclude : As regards loss by dissociation and oxidation, the facts above cited appear to warrant the inferences that, in combustions conducted by the method here described, in which (1) the tubes were so closely packed with soda-lime as to leave a minimum of free space inside, (2) full opportunity was provided for contact between distillation products and soda-lime (water-vapour at high temperature) by the anterior layer of soda-lime 12 em.long or thereabouts, which was well heated before applying the heat to the mixture of soda-lime and substance, and maintained a t a medium heat during the whole operation, and (3) the operation was completed in not over three quarters of an hour : 1. Provided the tube and contents are allowed to cool slightly before aspirating with air, there need be no loss by oxidation. 2. At a temperature sufficient to heat the tube only to dull redness, there need be no considerable loss by dissociation. 3. Ammonia may be dissociated and nitrogen lost by either very high heat, or by conducting the operation so slowly as to leave the ammonia exposed for a long time to heat. Very likely the danger of long exposure is heightened by lack of moisture from the anterior layer of soda-lime after the latter has been heated for some time.4. A vacant space in the tube (channel as ordinarily recommended) may involve serious loss. This loss is probably due to both incomplete ammonification of distillation products and to dissociation of ammonia. The danger of loss of ammonia from rapid flow of the gases through the acid solution in the bulb-tube is sometimes assumed to be considerable. MUSSO, for instance, lays great stress upon uniform and slow evolution of gas, and prolongs the combustion for several hours, the main purpose seeming to be to insure complete absorption of the92 THE ANALYST. ammonia.* The experiments cited by Mr. Haynes in a previous article imply that the real danger from this source is very small.All his attempts to push the combustion fast enough to force ammonia through the solution were ineffectual. For instance, in a combustion of sulphate of ammonia, completed in 12 minutes, the ammonia, which was suficient to neuteralise half or a little over haif of the acid, was entirely absorbed. The volume of the acid solution was 10 c.c.; it was contained partly in the bottom bulb and partly in the outer bulb of an ordinary Knop and Arendt bulb apparatus, in accordance with our usual practice. Bearing of t?be Results upon the Interpretation of those obtained by other Experimenters. The Dificzclti’es with the Soda-lime Method observed by fleegen and Nowack, Musso, and otfzers. OF the investigations which have been interpreted as casting doubt upon the reliability of the soda-lime method, those of Seegen and Nowack have, perhaps, been the most frequently quoted.These have carried great weight because the figures obtained were so wide of the truth despite the evident pains taken to secure accurate results, and because similarly bad results have been obtained by other chemists. The apparently unavoidable sources of serious error in the soda-lime method have been alleged as a ground for doubting the correctness of important series of researches in which the soda- lime method has been used. The question of the validity of this doubt is a very important one. I n his account of his own experiments with flesh, Nowack states that care was taken to insure uniform development of gas, and the tubes were kept glowing hot for three hours (“ die Rohre stets durch 3 Stunden gliihen ”), I n the report of their joint experiments with animal and vegetable protein compounds, albumin, casein, syntonin, flesh, gluten, legumin, Seegen and Nowack state that they employed the same analytical methods and precautions (“ die Analysen wurden in derselben Weise und midt denselben Cautelen ausgefuhrt, die .. . ausfiihrlich erortert sind”) as were employed by Nowack in his own investigations just referred to. The inference is that their combustions were likewise continued through a long time, if not at a high temperature. MUSSO, whose experiments were made with milk, whey, and cheese, says his combustions lasted hardly less than three hours, and in some cases they were prolonged for even six hours. I n the work of Nowack, of Nowack and Seegen, and of MUSSO, the figures obtained for nitrogen were very small.Taking those for nitrogen obtained by the absolute method as the standard, the loss of nitrogen in Nowack’s experiments reached 20 per cent., and even more, of the whole nitrogen ; in those of Seegen and Nowack the loss was from 1 to 20 per cent., while in those of Musso it was over 30 per cent. of the whole nitrogen. On the other hand, Gruber, who in reply to the criticism of Seegen and Nowack upon analyses by Voit and others in Munich, gives very satisfactory results obtained in Voit’s laboratory with protein in flesh, never allowed more than half an hour for the combustions. The experiments cited by Mr. Woods and myself in article No. IV. of this series seem to us to give satisfactory assurance of the reliability of soda-lime determinations of nitrogen in ordinary protein compounds when the combustions were made with proper precautions.Of the latter, the chief seem to us to be (1) sufficiently fine pulverisation and careful mixture of the substance with soda-lime; (2) close packing of the tube and sufficiently long anterior layer of soda-lime, so as to insure sufficient contact between soda-lime (heated water vapour) and distillation products, as well as to avoid too long sojourn of ammonia in the heated tube ; and (3) maintaining the anterior layer at a moderate heat during the whole time of combustion, which should not be too protracted. * Ztschr. anal, Chern. 16, 414.THE ANALYST. 93 Messrs. Seegen and Nowack do not state whether they left a channel in their tubes or not; but it is evident that the conditions of their work were such as to favour incomplete decomposition of the nitrogenous substance, imperfect ammonification of volatile decomposition products, and dissociation of ammonia.Prof. Seegen reports a nitrogenous residue in the tube after the cumbnstions, and Dr. Nowack found the acid solution in the nitrogen bulbs so highly coloured as t o interfere with titration with litmus solution. The combustion was prolonged for three hours, and during part of this time a t a very high heat. The determinations of Muss were conducted very slowly, in some cases even more so than those of Seegen and Nowack, and the results obtained were likewise very low. Mr. Ball and I found that either leaving a channel in the tube, or high heating, or prolonging the combustion to two and a half hours, involved large loss of nitrogen, the loss with these conditions combined amounting, in some cases, to two thirds or three fourths of the whole nitrogen.It would seem, therefore, that we have here cases of a kind not unfrequent i n scientific research, in which the very effort to secure correct and reliable results involves grievous error. I lay especial stress upon this matter because of the use that has been made of Seegen and Nowack’s results to discredit the soda-lime method in general, and par- ticularly to throw doubt upon the work of Voit and others in the Physiological Laboratory at Munich, in which this method has been employed in the study of the fundamental problems of nutrition.It was my fortune some time since, while working in that laboratory, to be permitted to observe very closely the ways in which deter- minations of nitrogen by soda-lime are there conducted. Although the effort to insure close packing of the tubes was perhaps less than in the experiments above detailed, and upon which the conclusions here given are based, yet on the whole the details of manipulation as I observed them were such as would, with the experience in this laboratory, lead one to expect correct results. Although the results of experiments by Gruber and others in the Munich labora- tory, and accumulated experience elsewhere, make any vindication of its work superfluous, yet I trust these statements, in connection with an explanation of the error into which Seegen and Nowack have unwittingly fallen, may, in the interests of science, not seem out of place.The experience of other chemists, as well as that in this laboratory, of which part has been described in these pages, leaves me with the decided belief that the Scylla and Charybdis of the soda-lime determination are incomplete ammonification of nitrogenous distillation products and dissociation of ammonia. The other difficulties are, in general, easy to overcome. They may all be prevented, in ordinary animal and vegetable protein compounds, by the precautions above enumerated. But in alkaloids and allied com- pounds, and in some amines, and amido and wo-compounds, loss by incomplete ammoni- fication seems very difficult to avoid.The observations I have had occasion to make, as well as printed accounts of the methods followed in different laboratories, have given me the decided impression that the most common difficulties are loose packing of the combustion tube so as to leave a channel, insufficiefit anterior layer of soda-lime, and too high or too long-continued heating. The soda-lime method is beset with dangers, and requires great care to avoid them. Indeed, after the experience in this laboratory, covering a period of several years and including some thousands of nitrogen determinations, if I were going to undertake again a series of analyses like those for which these studies were made, and the details of the work were fo be placed in the hands of an analyst, however expert, who had not been through some such experience as that above described, I should feel under the94 THE ANALYST. necessity of asking him to do a considerable amount of preliminary work, including comparison of results by the soda-lime with other methods, before I’ could feel sure of his results.After most of the above detailed experiments had been made and we had the method in such control that we were wont to say jocosely that from a given protein compound we could obtain the whole or any desired fraction of the nitrogen as ammonia, a t will, a gentleman of no little experience, and who afterwards proved himself a skilful and efficient analyst, came to our laboratory as assistant. We placed a number of sub- stances, mostly animal tissues, in his hands for nitrogen determinations by the soda-lime method, instructing him in the details of the process, and going through a number of determinations with him.He wds very confident that he could secure perfectly reliable results and at the same time make the determinations with considerable rapidity. After a list of substances had been analysed, I looked over his figures, and was somewhat surprised at the variations in the duplicate determinations, which, in some cases, as I now recall, reached nearly 0.2 per cent. Mr. Woods, by whom most of the nitrogen determinations of this investigation have been made, repeated the analyses and found in almost every case a considerably higher percentage of nitrogen, so that the whole work had to be repeated. The most plausible explanation of the errors seemed to be that the determinations in question were made rather hurriedly, and either because the nitrogenous material was not well enough mixed with the soda- lime, or from too loose packing of the tube, some of the nitrogenous distillation products were incompletely ammonified, and thus escaped detection in the titration subsequent to combustion. At the same time I must repeat what I have already said, that our experience leads me to place the greatest confidence in the soda-lime method for the determination of nitrogen in ordinary protein compounds, provided the work be conducted with the precautions here insisted upon.The perfection to which Kjeldahl’s method has lately been brought, and its accuracy, convenience, and inexpensiveness, have led t o its use in this as in many other laboratories.Our experience leads us to decidedly prefer it to the soda-lime method, though we find it advantageous to use both, making one check the other. But the danger of incomplete ammonification of some classes of compounds, e.g., alkaloids, makes us feel it necessary to control both by the absolute method for all classes of substances, except those for which they have been most thoroughly tested. SUMMARY. The experimental and other considerations presented in this and the previous articles on the determination of nitrogen by soda-lime, may be conveniently summarised, after first recalling the probable reaction by which the nitrogen is changed to ammonia, and the principal sources of error in the operation. 1.It seems decidedly probable that the change of nitrogen to ammonia is effected by union, a t high temperature, with water vapour yielded by the soda-lime (or slaked lime in case the latter is used). It is essential that the contact between nitrogenous distillation products and water vapour be sufficient, and not a t too high or too low temperature to insure conversion of all the, nitrogen to ammonia, and that the ammonia be not dissociated or oxidised. The main objects, then, are to secure complete ammonification and to avoid dissociation and oxidation. 2. The chief difficulty in the way of complete ammoniiication of protein compounds appears to be the formation of gases which do not readily yield their nitrogen to be united with the hydrogen of the water vapour. With certain other classes of nitrogenous compounds, as leiicine and its congeners, alkaloids, amines, and amido and azo-compounds, A case in point may be worth mentioning.This led me to question their accuracy.THE ANALYST. 95 this difficulty is greater, and sometimes apparently insuperable. The tendency of protein compounds to be decomposed by heat and other agencies into leucine, amines, etc., appears to explain the difticulty frequently found in getting all their nitrogen into the form of ammonia by heating with soda-lime. The evident means to secure complete ammonifica- tion must be sufficient contact with soda-lime at proper temperature. 3. The danger of dissociation of ammonia evidently increases with increase of tern- perature and time of exposure, and is probably diminished by presence of water vapour and other diluting gases.If this be so, the danger will be avoided by measurably rapid combustion a t not too high heat, and by keeping the ammonia in contact with sufficient moisture from the soda-lime until it leaves the heated tube. 4. Leaving out of account substances such as nitrates, nitro-compounds, etc., whose nitrogen is imperfectly converted into ammonia by soda-lime, even in the presence of organic matter, and assuming palpable errors of manipulation, to be avoided, such as (a) loose pack- ing of asbestos plug, which would allow particles of soda-lime to be swept into the acid bulb ; ( b ) heat at anterior end of the tube, so low as to perinit ammonia to be retained with moisture about the cork, or so high as to char the cork and give rise to acid or alkaline distillation products ; ( c ) use of soda-lime containing nitrates or nitrites, which may, ac- cording to circumstances, either furnish nitrogen to be transformed into ammonia, or oxygen to burn the ammonia formed from the nitrogen of the substance; (d) use of dis- tilled water containing ammonia for rinsing the acid bulb ; (e) imperfectly-cleaned or incorrectly-calibrated burettes ; the principal sources of error above discussed involve loss of nitrogen, and may be recapitulated thus : I. Loss from imperfect ammonification of the nitrogenous substance, due to :- a. Incomplete decomposition of the substance, part of the nitrogen being, from coarseness of the particles of the substance, imperfect mixing with the soda-lime, insuffi- cient heat, or other cause, left behind in the charred residue. b.Change of nitrogen into compounds other than ammonia, either such as may remain in the tube, e.g., cyanogen ; or volatile distillation products which escape ammo- nification and pass through the acid solution unabsorbed, or, if absorbed, are not accu- rately determined by the titration or other means used to find the amonnt of nitrogen in the solution. c. Escape of nitrogen in the free state. 11. Loss of ammonia through :- a. Dissociation at high heat in the combustion tube. b. Oxidation by air present in the tube before, or introduced in aspirating to wash c. Neutralisation by acid products, e.g., of sugar, where the latter is used in the d. Incomplete absorption by the acid solution.5. Complete decomposition of the substance has, in our experience, been readily aecured by pulverisation fine enough for it to pass through a of seive of 1 mm. aperture ; thorough mixing with soda-lime; avoiding the shaking by which the particles gather at the top of the soda-lime; and heating to low redness, 6. With sufficient soda-lime, not too dry, we have fomd no reason to fear the for- mation of cyanides, nor have we been able to obtain any indication of the escape of free nitrogen when the operation is properly conducted, although it might, perhaps, occur by oxidation of ammonia if there were nitrites or nitrates present, or if aspiration with air were done while the tube and contents are hot. Turning off the flame before aspirating has, in our experience, sufficed to avoid oxidation by air. At least, if ammonia has been oxidised, the quantity bas been too small to be detected, out ammonia after, the combustion. comb us tion.96 THE ANALYST. 7. When sugar is used, acid products may be formed in quantities large enough to impair the accuracy of the determinations. With ordinary animal and vegetable pro- tein compounds, provided enough soda-lime is employed, the use of hydrogen or sugar, or other substances for supplying gases, either to expel air, or to yield nascent hydrogen to form ammonia with the nitrogen, or to dilute the ammonia and prevent dissociation, or to wash out the ammonia, appears to be unnecessary. The danger of loss by incom- plete absorption of the ammonia by the acid solution appears to be very small indeed, even when the development of gases is very rapid, provided sufficient acid solution be used. (To be continued.)

ISSN:0003-2654    

DOI:10.1039/AN8891400090

出版商:RSC    

年代:1889

数据来源: RSC

摘要:

96 THE ANALYST. CORRESPONDEKCE. [The Eclifor i s ?Lot ill. aity ?~lng responsible for opinions czpcssed by A s cori.es~~o11‘2eiLts. ] To the Editor of the ANALYST. ABNORMAL BUTTERS: A REPLY TO MR. ESTCOURT’S PAPER I N THE ANALYST,” MARCH, 1889. SIR,-Mr. Estcourt appears to have had two objects in view in his paper on ‘( Ab- normal Butter,” viz. : (1) to show that Mr. Allen failed to prove the esistetce of genuine butter of an abnormal composition, and (2) to defend the conclusion drawn from his analysis of a sample of butter from Wigan. So many cases of abnormal butters have been found of late, that had Mr. Allen not brought the subject before the Society, some other analyst would surely have done it by this time. On the second point, I may explain why a t the time I considered the question of the Wigan butter to be one of abnormal butter, but shall at o3ce admit that-as far as Mr.Estcourt is concerned-I was mistaken. Had Mr. Estcourt been more willing to dis- cuss the matter at an earlier stage, the whole case would probably have received quite a different treatment. Some butter was sampled at Wigan last summer and pronounced to be adulterated. Mr. Estcourt, who analysed the sample for the defendant, certified it to be (‘ a sample of margarine,” “ having regard both to its specific gravity and the very low per centage of soluble fatty acids.” Some samples of butter were taken a t the dairy from which this butter No. 402 was believed to have come. These were marked G ’’ and N.” Some of these samples G and N were sent to Mr. Estcourt, who wrote of them, ‘ I The specific gravity of both is lower than that of any genuine butter I have yet analysed, The soluble fatty acids are also not present in such a per centage as to indi- cate a genuine butter.” From the figures in his paper on “Abnormal Butters,” i t appears that he found No.402, G and N, almost identical in their composition. Professor Stein found those samples, G and N, to yield about 24 C.C. by the Reichert- Wollny process, and a small sample of butter-fat sent him from the agent of the shipper of the Wigan butter, who had obtained it from Mr. Estcourt as the remainder of sample 402, yielded the same amount of volatile acid, viz., 24 c c. The two analysts were therefore agreed upon the very close similarity between these three samples.I shall not enter into any discussion as to the supposed genuine nature of sample G; it is not to the point here. I merely wish t o deny ever to have written about ‘‘ the supervision of the milking ” from which samples G and N were As to the first point, Mr. Allen has already answered. This is the sample No. 402 of Mr. Estcourt’s paper.THE ANALYST. 97 obtained. I only note that both analysts found the Wigan butter and samples G and N very similar ; of G and N samples exist still in the original packing and with un- broken seals. The genuine nature of a butter-fat yielding 2 4 O C.C. by R.-W. may well be questioned, as such butter-fat is of rare occurrence, which fact has made Professor Stein name it H e did a t first question the genuineness of the butter from the dairy in question, but having learnt the history of sample G he-rightly or wrongly- altered his opinion, and pronounced this butter genuine but abnormal, and having found the sample of butter-fat, said to be the remainder of Estcourt’s sample 402, to be very similar to sample G, he concluded that abnormal butter of this composition was not known to Mr.Estcourt.” Having a t the time no knowledge of the actual results of Mr. Estcourt’s analyses, I concurred in Professor Stein’s view, and I concluded that a demonstration of the existence of genuine butter of this composition, taken with sufficient guarantee, would suffice to show that the analysis of the Wigan butter (402) was not sufficient proof of its adulteration. I do not yet see how we could have come to a different conclusion. My first step was then to write to Mr.Estcourt (on Sept. 18th), asking him for the particulars of his analyses of the samples, mentioning that the Wigan case was ‘( likely to throw some new light on the question of the variations of volatile or soluble acids in butter.” Mr. Estcourt replied (Sept. 20th) that ha should “ b e pleased to ex- change particulars of analyses ” with me, if 1 would give him the results obtained by the chemist in Denmark. On Sept. 28th I called on Mr. Estcourt in Manchester, and gave him the figures he has published, as obtained by Professor Stein, being all that Professor Stein had at that time estimated in the three samples. I naturally under- stood that Mr. Estcourt would give me his figures in return ; but although I urged him to do so, he declined, promising, however, that he would send them on three days later. I have never since heard from 7tirn.It is somewhat surprising that he should complain that he ‘( heard no more of this matter,” for I left him with the understanding that I was first to hear something from him. My plan to discuss with Mr. Estcourt the question of the existence of genuine butter yielding 24 C.C. R.-W., had, of course, to be given up after this breach of promise. Had Mr. Estcourt, according to his promise, made both by letter and verbally, informed me that he had found about 3.5 per cent. of soluble fatty acids in these samples, I should then have seen a t once that the question was not one of “ abnormal butter,” but of u abnormal analysis,” and 1 should have proceeded accordingly. It could never enter my mind that a sample of fat containing only 3.5 per cent.of soluble acids could be genuine butter-fat ; but neither could I ever be expected to suppose that in a sample yielding about 24 C.C. by R.-W., anybody could find only 3.6 per cent. of soluble acids. the Reichart method.” H e does not mean that, however. From the way in which he uses the name ‘( Keichart,” I gather that he means the Reichert-Wollny method, which is described by Mr. Allen as the one used by him and Professor Stein, Mr. Estcourt argues against this method, that it is liable to give erroneous results, in extreme cases-according to Wollny-30 per cent. too low. B u t he does not mention, although he quotes the very paper by Wollny, that these errors are those of the original process, and that they are impossible when using the method as modified by Wollny ! But, even should Mr.Estcourt have employed the original and faulty Reichert’s method, how did he succeed in getting a result which is just 30 per cent. too high ? * As stated previously, Professor Stein had met with abnormal butter yielding even less than 24 C.C. the year before this Wigan case. abnormal.” I therefore sought and obtained the assistance of Mr. Allen. Mr. Estcourt speaks of98 THE ANALYST. B 0 402 G N B 0 ‘‘ I desire to call attention to the paper by Dr. Wollny in the January and February numbers of THE ANALYST for 1888,” and I ask, how is it possible that an analyst should find 30 per cent. too hiyh a result, even if he cares to ignore the improvements to the method 1 Wollny finds that carbonic acid in the original process may cause an error of + 10 per cent.ns a muxinizsm. After the publication of Mr. Estcourt’s paper, I asked Professor Stein to estimate the soluble fatty acids in samples G and N, and in the remainder of the small sample obtained from Mr. Estcourt as No. 402. With his permission, 1 publish the results of his analyses, obtained by the modification of the method suggested by Dr. Muter. I give (1) the per cent. of soluble acid ; (2) the result by Reichert Wollny ; (3) the per cent. of butyric acid corresponding to the number of C.C. of 2 found by R.-W. ; and finally (4) the per cent. of butyric acid found in this way by R.-W., expressed as per cent.of the total amount estimated by Muter’s method. To this I add the results of Mr, Allen’s analyses of samples B and 0, and of Mr. Estcourt’x analyses of samples 402, G, N, B, and 0, all calculated in the same manner. 10 4.44 4.68 3.40 3.53 3.57 4.51 4.70 _-_______ p. c. Soluble Acid. 402 G N 4.7 4.70 4.79 I R.-W. c.c.= I p. c. Butyric Acid= BY PROF. STEIN. 24.0 4.22 23.9 4.2 1 BY ALLEN. 22.39 3.94 24.70 1 4.35 BY ESTCOURT. 24.2 1 4.26 I . . 23.60 22.55 22-44 24.64 .. 4.15 3-97 3.95 4-34 p. c. of Total Soluble Acids. 89.8 90.6 87.9 88.7 92.9 .. 117.6 111.2 87.6 92.3 The only acid in butter-fat which is volatile, and not soluble, is capric acid, but as it amounts to less than one per cent. of the total amount of soluble acids, it is of no consequence. As only about four-fifths of the solution is distilled off in the Reichert- Wollny process, only part of the volatile acids pass over in the distillate, viz., about 90 per cent.Mr. Estcourt, however, has succeeded in distilling over considerably more than the total amount of the soluble acids! I n sample G he found 3.53 per cent. of soluble acids, 90 per cent. hereof is 3.177, which calculated to 5 gram9. of fat, and ex- pressed as C.C. of; solution of butyric acid is 18. This figure, therefore, should be the result by R.-W. of a sample of butter containing 3 53 per cent. of soluble acids. Mr. Estcourt found 23.60, or, he found either 30 per cent. too ?high a result by Reichert- Wollny (which beats the record), or he found 1 per cent. too Z0.w a result by estimating soluble acids, which means that ovev 20 pey cent.of $he soluble acid escaped his w t i c e .THE ANALYST. 99 As his opinion of the Wigan butter is based on his estimation of the soluble acid, it is therefore not surprising that he should consider it adulterated. I must however neoessarily doubt the correctness of his analysis, and thereby his right to conclude, that the Wigan butter was adulterated. Yours faithfully, HARALD FABER. - ___- To the Editor of the ANALYST. Simt,-I shall only occupy a very small space in reply to Mr. Allen’s reply. I desire to call especial attention to the statement which he boldly makes, (apparently from his own knowledge), that I for years used a Westphal balance of which the plummet was broken, and the results obtained with it which were incapable of being published.In answer to this, I can only say I am pleased to believe that the most of Mr. Allen’s statements have a better foundation on fact than this, or the scientific world would suffer, Mr, Allen does not give his authority for this incorrect statement, so he must have evolved it from his inner consciousness. Since 1876, wken I first introduced the Westphal balance to chemists in this and other countries, for ascertaining the specific gravity of liquids a t high temperatures, I have always had in my pos- sesion at least one duplicate bulb made by Westphal, for my instrument, which is also subdivided by Westphal to indicate half drgrees. In November, 1885, I suggested to Mr. Allen that he chould give up quoting specific gravities, at 100 F.and use my apparatus and bath, &c. He thanked me for my suggestion and altered the whcle of the gravities in his new volume in accordance with the method which I have been using since 1876. This much of ancient history I have given in justice to myEelf, as i t will serve probably better than anything else to show the improbability of Mr. Allen’s statement. With regard to Mr. Allen’s other statements, they are already sufficiently answered in my paper published in the March number of the ANALYST, The allusion, in the last two paragraphs, to the Reichert result of G sample serve to show what has been already stated, that the Reichert process gives erratic results.-I am, sir, yours, CHARLES ESTCOURT. To the Editor of the ANALYST. Sm,-In connection with the articles on Abnormal Butter which have appeared in recent nnmbers of the ANALYST, the following lines may be of interest.In December, 1885, both a t the beginning and the end of the month, I made in my Laboratory butter from the milk of a single cow, and this butter, both in my own hands and those of Mr. Shippen Wallace, Chemist, Philadelpbia, Pennsylvania, gave by the Reichert test figures ranging from 11.3 to 11-5 C.C. of deci-normal alkali consumed in neutralizing the first acid distillate of 50 C.C. I found the insoluble fatty acids (by Hehner’s piocess) to be 89 6 per cent. As stated by Wallace and myself (Ninth Annual Report, N.J. State Board Gf Health, ISSS), the cow was one of a herd of eight cows in Princeton, N J. She was of mixed breed, chiefly Alderney ; nearly five years old ; had a calf about eight montt s before, and was expected to have another late in the following spring ; yielded six to seven quarts of milk daily at that time ; her food was barley meal and corn-stalks (maize) ; she was appaltentiy in sound condition.The butter made separately from five other cows in the same 1 erd, within the same week or nearly so, ranged from 12.2 to 15.1 C.C. deci- normal alkali, so that neither the season of the year nor the food appeared to have any influence on the result. In consequence of this result, we recommended that the minimum for butters made from the milk of a single cow should not be above 11 C.C. of deci-normal alkali. I have no doubt that the milk was delivered to me in its normal condition, because I sent my own private messenger to obtain i t ; the owner of the herd did not know what use was to be made of it ; exactly the same result was obtained from the milk a t intervals of a month (or within very narrow limits, the same results) ; and finally, the milk from five other cows in the bame herd was normal as to the behaviour of the butter fat.While this is not intended to have any especial bearing on Mr. Estcourt’s paper on Abnormal Butters, ANALYST, March, 1889, it is presentedas evidence that pure butter fat from the milk of a single cow, under normal conditions so far as we can judge, may yield by Reichert’s method, figures decidedly below the usual standard. I would add that I place more dependence on Reichert’s than on any other process, and do not hesitate to condemn by its results butters which I can know have been made in this country and from the mixed milk of several cows ; accepting then as high a standard M 11.5 to 12 C.C.of deci-normal alkali.-Respectfully yours, H. B. CORNWALL. John C. Green School of Science, Princeton, New Jersey, U. S, A. March 20tb, 1889,100 THE ANALYST To the Editm of the ANALYST. “ON THE DETERMINATION OF CITRIC ACID IN LEMON JUICE.” SIR,-Will you kindly permit me to make a brief reply to the letter of Mr. G . H. Ogston (not Upton) on the above subject, which appeared on page 86 of the April number of the ANALYST 1 Mr. Ogston says he would have been glad to have taken part in the discussion on my paper had there been one, and complains of my not having informed him of my intention t o criticise the method which he employs for the examination of lemonjuice.This was sure@ quite unnecessaqy. Mr. Ogstonis a member of the Society of Public Analysts, and would no doubt receive due notice of the title of my paper, so he could presumably have attended the meeting if he desired. I can scarcely be held responsible for Mr. Ogston’s absence, and I can assure him that no one anticipated and wished for his presence more than myself. Mr. Ogston is quite mistaken.wben he insinuates that, some months previously, I wrote asking him for certain information with the object of making it the basis of my paper. My sole reason for communicating with Mr. Ogston was because there had been complaints from calico-printers in this district a t the discrepancies which were sometimes found to occur between my figures and Mr.Ogston’s, and I thought it would be to our mutual advantage if our results agreed more closely in future. The explanation offered by Mr. Ogston with regard to the cause of the difference between our results, viz., the presence of carbonic acid in my titrations is, though plausble enough, altogether inadequate. I am quite certain that no carbonic acid could have been present, as in all the experiments every possible precaution was taken to ensure accuracy. I followed Mr. Ogston’s own directions as carefully as possible, viz., ‘‘ Have the test paper nearly neutral and light in colour. After the addition of about two thirds of the necessary quantity of soda solution, boil for ten minutes to expel carbonic acid, and boil between each subsequent addition of the test.” There seems to be some uncertainty in Mr.Ogston’s mind as to whether I meant to suggest that the alkali in sodium carbonate has a different saturating power for citric acid than the alkali in caustic soda. What I clearly meant, and what I still contend is that, when titrating solutions of citric acid with sodium (or with caustic soda for that matter), using litmus paper as indicator, the point of saturation is reached sooner (owing to the alkaline reaction of sodium citrate to litmus paper) than when caustic soda and phenolphthalein are employed, consequently the sodium carbonate appears stronger than is theoretically possible. For instance, suppose 7 grains of pure citric acid are dissolved in water, and the solution titrated with normal caustic soda, using phenolphthalein as indicator, 100 fluid grains will be required.But if, on tjbe other band, normal carbonate of soda solution and litmus paper are employed, the addition of, say 97 grains, with subsequent thorough boiling and cooling, will in all probability be sufficient to produce a distinct blue colour ; 100 grains of the alkaline solution would, therefore, appear capable of neutralizing 7.2 grains of citric acid, owing to the unsatifactory nature of the indicator employed. For obvious reasons Mr. Ogston seems to be aggrieved because reprints of my palper have been distributed among those interested in the matter, but I may say that the majority of these persons entirely approve of my action. While writing, I have before me a letter from the chemist a t a well-known calico-printing works, confirming my statement with regard to the greater accuracy of citric acid determinations made with caustic soda and phenolphthalein. For my own part, I know of no reasons why sodium and potassium carbonates are frequently to be preferred,” as is stated by Mr. Ogston near the close of his letter. Mr. Ogston may protest as strongly as he pleases against the inferences to be drawn from my tables, but, to slightly alter the words used by Mr. Allen in the discussion which followed my paper, and which Mr. Ogston rather strangely ignores, “there can be no doubt on which side the truth lies, -1 remain, sir, yours faithfully, ROWLAND WILLIAMS. 28, Pall Mall, Manchester, April loth, 1889. CATALOGUE of Chemical and Physical Apparatus, and Chemicals Manufactured and Imported by Philip Harris and Co., Limited, Bull Ring, Birmingham. This is a very complete and exceedingly well got up catalogue, the illustrations being numerous and well executed. The list of physical apparatus is most complete, and does great credit to the firm. A TREATISE on Manures; or, the Philosophy of Mtlriuririg. A practical handbook for the London : Agriculturalist, Manufacturer and Student, by A. B. Griffiths, Ph. D., F.R.S. (Edin.), F.C.S. Whittaker and Co.

ISSN:0003-2654    

DOI:10.1039/AN8891400096

出版商:RSC    

年代:1889

数据来源: RSC

摘要:

100 THE ANALYST ERRATUM. Mr. G. H. Ogston, F.C.S,, F.I.C., 39, Lime Skeet, E.C., was the writer of the letter, which, by a printer’s unfortunate error, appeared over the signature, ‘‘ G. H. Upton,” in our last issue,

ISSN:0003-2654    

DOI:10.1039/AN8891400100

出版商:RSC    

年代:1889

数据来源: RSC