摘要:

THE ANALYST. APRIL, 1891. ON THE COMPOSITION OF MILE AND MILK PRODUCTS. (Read at Meethg, Pdruary, 189 1 .) FOR a number of years I have been in the habit of laying before you annual re- ports on the work done in the laboratory which is under my charge ; the report for the yeax 1890 forms the subject matter of my present paper. (For former reports see TEE ANALYST, vii. pb 53; viii. p. 33; ix. p. 56; x, p. 67; xi. p. 66; x5. p. 39; a. p. 46 ; xiv. p, 69 j and xvb p. 44). BY DR. P. VIETH.62 THE ANALYST. The total number of samples analysed in 1890 is 22,670, viz. :- 20,6 3 5 samples of milk, 1,188 ,, cream, 586 ,, skim milk, 40 ,7 butter milk, 3 7, whey, 165 ,, butter and butter-fat, 29 ,, water, 24 ), sundry articles, Of the milk sample 11,816 were taken from the railway churns in which the milk arrived from thecountry.While part of this milk is kept back for the production of cream, the bulk of it is distributed with the least possible delay. In order to keep a constant control over the men entrusted with delivering the milk to the customers, 7,104 further samples were taken before, during, and after delivery, and submitted to analysis. The following table contains the monthly averages of the results referring to all these samples :- 1890. January, . .. February .. March . . . . April . . ... May . . .. June .. . . July .. ~ . . August . . .. September . . October . . .. November . . December . . Yearly Average AVERAGE COMPOSITION OF MJLK. Samples taken Zpec.Gravit 1.0323 1.0324 1.0323 1.0322 1.0324 1.0323 1.0320 1.0319 1.0319 1.0322 1.0321 1.0322 On arrival.Tot, Sol. 12.95 12.84 12-76 12.66 12.63 12.64 12.81 12.86 12.81 13.04 13.07 ' 13.02 1.0322 1 12.84 I Fat. 3-80 3.70 3.63 3.57 3.53 3.55 3.75 3.81 3-7 7 3.89 3.94 3.89 3-74 Soh. Fct, 9 15 9.14 9-13 9.09 9-10 9.09 9.06 9.05 9-04 9.15 9.13 9.13 Before 1 During 1 After sent out. delivery. return. Tot. Sol. 12.88 12.75 12-69 12-57 12-58 12.54 12-75 12.83 12.86 12-94 12.92 12.86 Tot Sol. 12-96 12-90 12.84 12.70 12.74 12.68 12.82 12.87 12.83 13.03 13.08 13.07 9*10, 1 12-16 I 12.88 I I Tot. Sol. 13.02 12.86 12.93 12-74 12.74 12-77 12.84 12.90 12-90 13.13 13.18 13.10 18-92 The results obtained in the year 1890 are in close concordance with those of former years, not only with regard to the yearly average composition, but also with regard to the variations which the quality of milk undergoes in the course of the year.The lowest percentages of total solids and fat was found, as usual, in the second, the highest in the fourth quarter of the year. Considering that the circumstances under which the samples are taken can by no means be called very favourable, the agreement between the results referring to the severalseries of samples will, I think, be found satisfactory. Such differences as doTHE ANALYST. 63 exist might be easily explained, but to do so on this occasion seems to me to be rather beyond the limit of this paper. Cream samples were taken for analyais before the cream was sent out, and also while it was delivered to the customers. The total number of such samples was 1,010 and the average results of their analysis were as follows :- AVERAGE PERCENTAGE OF FAT IN CREAM.1890. ~~ January February March April June July August September October November December May * . .. . . .. .. .. .. .. . . .. ... .. .. .. . . .. . . . . . . * . .. . . .. Samples taken I Before sent out. 1 During delivery. I 46.0 4716 48.7 49.9 49.6 48.3 47.7 49.0 49 5 50.5 46.5 46.8 45.3 47.5 48.6 50.0 49 *3 48.6 47.3 49.2 50.3 50.4 47.0 46.9 Pearly average . . I 48.3 1 48.4 I I Clotted cream, of which 51 samples were analysed, was of the following average composition :- Water . . L 1 L . b . 35.16 per cent. Fat .. .. .. . . 58.35 ,, Ash .. .. .. Proteids and Milk Sugar . . * * 5.97 ,, .. -52 7, Skim milk, resulting when cream was separated from milk by means of centrifugal cream separators, contained, as a rule, from *2 to 04 per cent.of fat. I do not think it necessary to give the flgures relating to the analysis of 103 samples of butter, as these results, with the excsption of those obtained in December, were included in a paper which .I read before this Society two months ago (THE ANALYST, xvi. p. 1). On that occasion, however, I did not refer to the examination of the clarified butter-fat. The volatile acids- Wollny figures-found in the several classes of butter in 1890 mere as follows :-- English butter 25.3 - 30.0 average 27.6 C.C. French ,, 25.6 - 3 0 8 ,, 28 7 ,, Kid ,, 21.3 - 30.7 ,, 27.7 ,, Danish ,, 27.3 - 29.9 9, 28.8 ,, The figures fall below what is considered the limit in four cases of Eiel butter derived from two large well-known and managed dairies in Holstein-I will call them A and B-the tmme which turned out butter with low volatile acids in 1889.There were64 THE ANALYST. three abnormal samples from dairy A, the results being 24.2, 22.0, and 21.3, and one abnormal sample from dairy B, the result being 23.7. The low results were found during the time from July to October, i e . , at the same period of the year at which low volatile acids were observed in 1889. When speaking on this matter last year a good ileal of incredulity or, at any rate, suspicion was displayed with regard to the genuineness of the butter in question. Among others the question was asked, whether it was not a fact, that the volatile acids were found to be low at a time when butter prices were high.This was not the case either in 1889, or in 1890. In the former year butter prices were below the average for the year, from beginning of April to end of September, and in the latter again from beginning of April to end of August, while in both years the highest prices mere paid in March and in December. There is, then, no coincidence whatever between low volatile acids and high butter prices, and vice versa, and even if there had been, I should never have held that tho latter stood in any connection with, or explained the former in the cases in question. The matter seemed to me of sufficient interest and importance to cause my friend, Dr. Schrodt, principal of the Dairy Experimental Station at Kid, to follow it up. The proprietor of dairy A willingly agreed to send a sample of butter to Kiel for examina- tion once a week, and he has done so since beginning of May.Dr. Schrodt informs me, that with the progress of the period of lactation the volatile acids decreased reaching their lowest point in October, and that with the beginning of calving season in November they at once increased and quickly rose above 25. I will here put together all my results referring to butter from this particular dairy and add, with Dr. Schrodt’s permission, those of his results which he has com- municated to me in corroboration of my own. Results obtained in London :- 1889. *June, 27.6 ; July, 25.9, 24.7 ; August, 24.2 ; Octobsr, 22.8 ; November, 1890. July, 24.2 ; October, 22’0, 21.3 ; Nov., 2 6 9 1890. July, 24.6, 24.7, 24-0, 24.0 ; October, 23.0, 21.6, 22.2, 23.1 ; November, I may remark that results obtained in London ought to be compared with those obtained in Kiel about a fortnight previous.I once more express my firm conviction that in this instance we have to deal with a decrease in volatile acids below the usual limit, which has to be put down entirely to natural causes. I have mentioned on several previous occasions another case of naturally low volatile acids ; I refer to butter-fat derived from the milk of cows kept at the Aylesbury Dairy Company’s farm near Horsham. Of such butter-fat thirty-two samples were examined during the past year with the result, that the Wollny figures were found to be below 25 from January to middle of April, and again from August t o November. During the remaining parts of the year they varied from 25 to 26. The observed extremes were 22.1 and 26.2.In butter-fat which had been exposed to the action of air and light for eighteen 21.1; Dee., 29-2, 29.3. Results obtained in IGe1:- 2602,26*6, 27.0, 27.1 ; December, 27.3.THE ANALYST. 65 months and become bleached, the volatile acid figures had increased from 29.2 in the original to 30.4 in the bleached sample. A decrease of volatile acids was observed in butter which had been kept for more than ten years. A glass and a stoneware jar filled with such butter were accidentally found and their contents examined. In both jars the bottom layers of butter appeared fairly well preserved. I n the glass jar the top layer was extremely rancid, but contained no visible fungi; in the stoneware jar the butter had no particular smell, but was covered with a thick green fungous growth, and red fungi had penetrated the upper layer to a depth of about two inches.The results of the examination were as follows :- Glass jar, bottom layer .. . . 26.2 C.C. fi alkali. 9 ) 9 , t'?P j, .. . . 35.6 ,, Stoneware jar, bottom layer . . . . 25.7 ,, N 9 , 9 , top 9 , - - . . 21-2 ,) These results fully agree with similar ones which I submitted to you five years ago (THE ANALYST, xi. p. 70). Turning once more to the subject of milk, I wish t o relate some experiments which I have made with regard t o freezing milk. Two gallons of milk were put into an oblong tin vessel, ten inches in height, a tight-fitting lid screwed on, the vessel put in tl refrigerated salt solution, and kept therein at a temperature of 14OF.for three hours. Preliminary experiments had shown that after that length of time the mas9 of ice formed did, apparently, not further increase. On examination it was found that ice was formed at the bottom and sides of the vessel, and that a funnel-shaped cave in the centre was filled with liquid. This liquid was poured 06 and a sample of it analysed, as mere also samples of ice taken from the top and bottom layer. The results were as follows :- Ice. Liquid Cream. Skim milk, Part. Total solids ... 25.30 7-86 19.58 per cent. Fat ,.. ... 18.94 *68 5.44 ,, Ash ... ... -53 *62 1.11 ,, Sol. n. fat . ... 6.36 7-18 14.14 ,, The experiment was repeated, care being taken to drain off the part which remained liquid as completely as possible, and to carefully separate the frozen cream from the frozen skim milk.The following were the results of the examination :- Proportion . . . Spec. Gravity ... Composition : Water ... Fat ... Proteids ... Milk Sugar . . . Ash ... Ice. Cream. 8.8 1-0100 74.44 19.23 2.64 3.33 -52 Skim milk, 64.7 1.0275 92.10 *68 %SO 3.95 *60 Liquid Pait. 26.5 per cent. 1.0525 80.54 per cent. 5.17 ,, 5.3s ,, 7.77 ,, 1.18 ,, --- --- -- 100.16 100.13 100.04 These figures prove what has been shown on previous occasions, that frozen milk contains a much higher proportion of water than the original milk in which the ice wm formed, and that the part remaining liquid is a concentrated milk.66 THE ANALYST. The ice is by no means a solid mass, but a conglomerate of crystalline plate$ The fact that the latter, when examined singly, are found to be quite clear, proves tha fat globules do not enter into the crystals. The component parts of the ‘‘ Solids no fat ” seem t o participate in the formation of the crystals in about the same relativ proportion in which they. are present in the milk.This was so, at least, in the case t which my remarks refer, the relative proportions of proteids, sugar, and ash being foun as follows :- Ice. Liquid Cream. Skim milk. Part. Proteide ... 40.68 38-10 37.55 sugar ... 51.31 53-74 54.23 Ash .. ... 8-01 8.16 8.22 The behaviour of milk, when exposed to low temperatures, is not without interes in itself, but apart from this it is also of some practical importance. People who ar ignorant of what is actually taking place when milk freezes would naturally see no harr in melting milk ice and using the liquid obtained as milk.I f a milk vendor woul proceed in this way he might easily get into trouble. DISCUSSION. The PRESIDENT said that Dr. Vieth had added to the debt they already owed hin: His papers were not only welcome to this Society, but were looked forward to wit interest by all interested in dairy matters in England and abroad. Dr. MUTER said he quite confirmed Dr. Vieth’s results about frozen milk. During th long frost in January he had occasion to examine the contents of a frozen churn a delivered at the railway station. The following were the results :- (1) Milk passing through strainer :- Total solids . . . . . . . . 12.80 Fat ... . .. .. 3-80 Solids-not-fat . . .. .. . . 9-00 _I - (2) Contents of strainer :- Total solids . . .. 6 . . . 9.28 Fat .. .. . . .. .. 2-63 Solids-not-fat . . ,. .. .. 6 6 5 (3) Ice off churn lid :- Total solids . . .. . . , . 4.94 Fat . . * . .. . . . . 1-70 Solids-not-fat . . .. .. ,. 3.24 - It was evident, therefore, that unless very carefully thawed and mixed frozen mil might present moat anomalous results. Mr. FABER inquired if Dr. Vieth had any information about the way the COWS hr been kept,and whether the feeding of them had anything to do with the analysis of tl butter-fat, and as to the cows having recently calved or otherwise. Dr. DUPRE asked if Dr. Vieth had ever compared the volatile acid with the tot soluble acids; whether there was anything in the shape of compensation going o whether when the one increased the other diminished, or vice veraa.THE ANALYST.67 -~ Mr. YOUNQ said he had always taken the estimation of the ash, which he considered of great importance, and a large number of ash estimations would make Dr. Vieth’s figures very valuable indeed. Mr. Young also mentioned that large quantities of milk were frozen into blocks for the large shipping companies who used them as required for their passengers. It was evident from Dr. Vieth’s experiments that if these blocks were used in portions the milk supply on board ship must vary much in quality. The PRESIDENT remarked that presumably Dr. Vieth’s fat determinations were made by the plaster mathod ; he asked what number of cows had yielded the abnormal samples of milk referred to 1 I n his experince there was a direct connection between the price of butter and the proportion of volatile acids.He found that when butter prices went up the number of samples that yielded an abnormally low proportion of volatile acid at once went up, that is to say, that the practice of adulteration was closely connected with the market price. It was a most striking circumstance that when butter was dear whole series of samples analysed by him fell either just upon or slightly below the Reichert limit, and he could not but conclide that foreign shippers sometimes let their produce down ~ t 8 low as they could without much risk of prosecution. Of course, there could not be any connection between price and the proportion of volatile acids in undoubtedly genuine samples. DR.VEITH, in reply, said the butter showing the low results was made at a large farm where about 200 cows were kept. At the time when the abnormal results were observed the cows were fed on pasture land which was reclaimed from the sea. Dr. Schroot was under the impression that the abnormal results had nothing to do with the feed. With regard to the connection between low volatile acids and butter prices hinted at by Mr. Hehner last year, he did not think it was meant seriously, but he now saw it was as Mr. Hehner said he found it so. His (Dr. Vieth’s) experience went the other way. He had during the last three years analysed a great number of samples chiefly from France, Holstein, Denmark, and Sweden, and had never found any definite connection between the prices of butter and the quantity of volatile acids. The compo- sition of frozen milk was certainly of considerable interest. As to frozen milk being used on board ship, he knew of that long ago, but he could not understand how milk could be frozen in blocks. He had never seen milk entirely frozen ; there was always a certain quantity of liquid left which would not freeze, just a5 it was the mse with sugar and salt solutions. With regard to the ash, he must say that it was not determined in the samples referred to in the paper in which sp. gr. and solids were determined and the fat calculated. He made, of course, a great number of ash determinations, but could not see much use in bring them forward because they simply proved what he had Rtated on previous cccasions, viz., that the ash of normal milk was as near as possible 8 per cent. of the solids-not-fat.

ISSN:0003-2654    

DOI:10.1039/AN891160061c

出版商:RSC    

年代:1891

数据来源: RSC

摘要:

THE ANALYST. 67 THE WERNER-SCHMID METHOD OF MILK ANALYSIS BY T. EUSTACE HILL, M.B., B.Sc., A.I.C., Medical Officer of Health, South Shields. (Red at the Meeting, March, 1891.) IN the ANALYST of 1889, and again in the Chemical News of November of the same pear, there appeared some very interesting remarks and facts by Mr. Stokes concerning a new process for the rapid estimation of fat in milk, f i s t mentioned by Dr. Werncr- Schmid in the Zeitschrift f u r Analytische Chemie, vol. xxvii., part iv. Mr. Stokee, after detailing the process as originally carried out by Dr. Schmid, pointed out how it could be improved, and gave a very favourable experience of itei working as carried out with his modifications. The process appeared SO simple and68 THE ANALYST. ~ ~ short, and the results published by Mr.Stokes so good when compared with calculated results, that I determined to give it an extended trial, and during the last eighteen months have determined the fat in over 200 different milks by this method, with the result of being able to corroborate Mr. Stokes as to its accuracy, simplicity, and rapidity, as regards all of which it compares favourably with, and, I think, even excels any other process for the estimation of fat in milk. Apart from its rapidity, the process has the great advantage of being equally applicable t o fresh or sour milks, however advanced in decomposition, and it is quite possible to complete the determination of the fat of many samples in the time required for estimating tho total solids. I have frequently made complete analysis of six samples of milk in one morning, and however convenient and useful it may be in most cases to estimate the fat; by calculation by means of the sp.gr. and total solids, I think it will be agreed that it is more satisfactory and safe in every way to know the percentage of fat by actual analysis. For myself I should be very unwilling to take a milk case into court with only a knowledge of the fat from calculation tables. This process, however, requires no more time and but little more trouble than has to be given in the determi- nation of the sp. gr. and total solids. Dr. Schmid’s method is as follows :-lo C.C. milk is pipetted into a test tube holding rather more than 50 c.c., and graduated in tenths of a c.c., 10 c.c. of strong HC1 are then added, the mixture is shaken and boiled till it turns dark brown, and then it is cooled by placing the tube in cold water.30 C.C. of ether is then added, and the whole shaken and allowed to stand, when in a short time the ether rjeparates clear, and is measured. 10 c.‘c. is then pipetted off into a dish and evaporated, and the residual fat weighed and calculated for the original quantity of the ethereal solution. Mr. Stokes in the ANALYST, February, 1889, points out how the above process can be improved, and in the Chemical News, November, 1889, gives a full account of it as finally modified and worked in his own laboratory. Into special tubes he pipettes 10 C.C. of the milk, or if sour weighs 10 grams. and with 10 C.C. strong HCl from a wash bottle detaches any particles of milk that may adhere to the side of the tube.He boils, with frequent shaking, till the mixture of milk and HCl turns brown, and then lets it stand for three minutes before cooling by plung- ing the tube into cold water. He then fills up with ether roughly to 50 C.C. mark, shakes well for half a minute, and allows to settle for five minutes, after which he pipettes off 20 C.C. of ethereal solution into a weighed dish, evaporates, dries in air bath, and weighs residual fat. The number of c.c.’s of ether remaining in the tube is then read together with three-fourths of a fluffy-looking stratum immediately beneath the ether, and these added to the 20 C.C. ether evaporated give the total number c.c of ether to be considered in calculating the percentage of fat.A correction for sp. gr. has, of course, to be made in each case. When I first practised this process according to Werner-Schmid’s directions, I was inclined to be dissatisfied, as the results were anything but accurate, owing chiefly to the fluffy layer below the ether being disregarded, which consists chiefly of ether mixed with a little HCl and altered casein. The ether I used also was unwashed, which influences the results considerably.THE ANALYST. 69 When Mr. Stokes’ paper on the process, however, appeared in the Chemical News I gave the process another trial with much more satisfactory resultg. I determined the fat of every milk I subjected to the Werner-Schmid method by Adams’ paper coil method, using fat free coils, as that method has been approved by the Society of Public Analysts, and the fat obtained by it can be taken as a standard.All my results are, therefore, compared with the results obtained by Adams’ method, and not with calculated results, as I consider the former a better plan. At first my results were constantly about 15 per cent. below those obtained from the same milk by Adams’ method, which I ultimately found was partly owing to the different way milks drained from the pipette, as compared with each other, and also with water. For instance, 10 c,c. of a milk with a sp. gr. 1.030 would weigh not 10.3 grams., but perhaps 10.10 grams,, and this in a pipette which was correctly graduated for delivering 10 C.C. of water. This difficulty I obviated by weighing the milk into the tubes, which, though more tedious, is certainly more accurate than by delivering from a pipette.I also found, contrary to Mr. Stokes’ experience, that it was necessary to wash the ether, otherwise the results came out at least -05 per cent. too low. By weighing the milk before adding the HCl, and also using washed ether, I can constantly obtain results which differ from those obtained from the same milk by Adams’ method, only within the limits of experimental error, say (+ - 04). I obtained the same results whether the mixture of acid and milk be boiled, as is deemed necessary by Mr. Stokes, or the tube is immersed in boiling water for five minutes, shaking every now and then. I prefer the latter operation, as the tubes supplied by Messrs. Townson and Mercer are too thick to stand heating by the naked flame without danger of cracking.These tubes, which should be made of thinner glass, are graduated to half a C.C. from 20 - 50 c.c., and it is important that the accuracy of the graduation be proved. I find it to be much easier and equally accurate to pipette off 15 C.C. of ether instead of 20 c.c., as recommended by Mr. Stokes, especially in warm weather, when it is extremely difficult to pipette off 20 C.C. without getting some of the liquid beneath the ether layer into the pipette. Five minutes’ drying of the fat in the water oven is quite sufficient after the ether has evaporated. The calculation is very easy; for instance, if the total ethereal solution +$ of fluffy-looking stratum measure 26 c.c., and 15 C.C. produce 025 gram.fat, the percentage of fat in the milk will be x 26 x 10 =4*33 per cent. fat if 10 grams, of milk be taken. 15 Below are some of the results obtained by this process and by Adams’. The samples were mostly taken under the Food and Drugs Act, and comprise milk from widely different sources, and are fairly representative of the agreement between the two processes. Werner- Schmid. Adams. Difference. 1. 3.55 3.60 - -05 2. 3 58 3.53 + -03 3. 3.21 3.21 0.00 4 . 3.53 3-57 - -04 5. 3.96 3.97 - -01 6. 3 57 3.60 - -03 7. 3.3 1 3-38 - *07 8. 3.09 3.08 + .01 9. 3.16 3-14 + *02 10. 3-18 3.15 + -03 11. 3.24 3.23 + -01 12. 3.54 3.49 + *0570 THE ANALYST. ~ ~~ ~ - These are not results that are picked out on account of their agreement, but repre- sent twelve consecutive analyses of different milks, and with care the difference between the results should not be greater than is seen here.With sour milks the results obtained cannot be compared with Adams’ process, which is not applicable to milks that have curdled, but from *30 to $40 per cent. more fat is obtained by Werner-Schmid’s method than by the one recommended by Bell for sour milks. I determined the fat in one milk, which contained 3.53 per cent. of fat when fresh, after standing for three weeks, and obtained 3156 per cent. of fat ; while from another sample I obtained 3-29 per cent of fat after standing a month, the milk when fresh containing 3-24 per cent. of fat. With condensed milks (unsweetened) the process is apparently satisfactory, for two separate determinations of the same milk (taking 2 grams.of the milk and making up to 10 C.C. with water) gave 11.57 and 11.60 per cent. of fat as compared with 11.46 by the Gerber-Ritthausen method, but the process is certainly not adapted for estimating the fat in the sweetened condensed milk owing apparently to the HCl acting on the sugar and producing a dark caramel-like substance, which is soluble in ether, and there- fore gives too high results. I analysed several varieties of sweetened condensed milks, but in every w e the results came out too high, as will be seen by the following figures :- Werner-Schmid. Adams. 1. 11-95 11-49 2. 10.02 8.78 3. 3.31 2.76 4. 2.99 2.54 5. 2.34 1.90 The fat obtained by the Werner-Schmid process in all the above samples had a dark brown appearance, showing the presence of some substance connected with the decomposition of the cane-sugar.In order to get over the difficulty I tried petroleum ether as the solvent instead of ether, but without succest3, for on shaking (and the same applies to the analysis of fresh milk) the contents of the tube unite into a gelatinous mass, which is more or less permanent. I quite agree with Mr. Stokes, that the personal equation does not at all influence the result, for on many occasions Mr. Liverseege, assistanb to the public analyst for Birmingham, and to whom am much indebted for assistance, has obtained results agreeing with my own from the same sample of milk, and in the majority of cases he was responsible for the analysis by the Adams’ method, with which the results by Werner-Schmid’s method so well agree; but it is a process that requires some little practice before accurate results can always be obtained.It is so accurate, and the saving of time so great, that it is to be hoped in the future it will receive a better trial than has hitherto been given to it. I may say that the ether apparently dissolves out the whole of the fat from the acid mixture, for after well shaking I have been unable to detect any fat except in solution in the ether. The fat when dry, previous t o weighing, is quite pure and free from acid if the process is properly carried out. The last three samples are skimmed condensed milks.THE ANALYST. 71 DISCUSSION. Mr. STOKES stated that he was very pleased to find Dr. Hill’s results confirm the statements he (Mr.Stokes) first made in the ANALYST, XIV., 29, and more fully and accurately in the Chemical News of November lst, 1889. Theoretically, a process that dealt with milkas a liquid was the best; since of any substance a gas was that which offered the largest surface, a liquid came next, and the very worst of all for extrac- tion was a solid. Usually analysts reduced the milk from its natural second-best form, a liquid, and made i t into the worst form, a solid, and then tried to extract fat from it. Theory, however, is not enough. Mr. Stokes, after trying practically every method of fat-extraction he had ever read of, had now for the last two and a half years used this method in preference to every other. He had dcne some thousands of fat-extractions thereby, with an almost invariable agreement between these and the calculated fat as determined by total solids and specific gravity, shown in the admirable tables of Messrs. Hehner and Richmond (ANALYST, XIII., 26.) Other methods that he had found ta give equally good results were the Lactocrite, the Adams paper-coil, and the plaster process; only the labour involved and the time taken was greater with these.These processes, too, were quite inapplicable for stale milks or for sweetened condensed milks, while the Werner-Schmid method worked perfectly with these. Dr. Hill was mistaken in thinking his results were too high in working on sweetened condensed milks. It is true, a little caramel, sufficient to colour the ether, is taken up, but this does not appre- ciably add t o the weight of the fat.Dr. Hill uses only the old form of tube, and so works to a disadvantage. I n the new form of tuba that Mr. Stokes introduced, the tube is narrowed for six inches. in the middle of its length; this enables ether to be drawn off almost entirely, and gives very accurate readings of the small quantity of ether left in the tube. At present he knew of eight public analysts who habitually used this method. To secure accurate agreement between fat so determined and the calculated-fat, it is necessary to be sure that the total solids are quite dry, and to take the sp. gr. by the Westphal balance, or by the bottle. I n the latter case the milk should be left for a t least ten minutes after shaking, else air-bubbles will be weighed as milk.The lactometers generally used are not finely enough graduated for such critical sp. gr. Mr. ALLEN said he was happy to be able to endorse almost every word that had fallen from the writer of the paper and Mr. Stokes-in fact, he was indebted to Mr. Stokes for instructing himself and Mr. Chattaway as to his way of working the Werner- Schmidt process of fat determination. He had the highest opinion of the method. He had checked it against the coil process, and was satisfied with the results. On the other hand, there were one or two disadvantages in the practical method of working adopted by Mr. Stokes, which he had done his best t o improve, and, he thought, with some success. In the first place, Mr. Stokes had an objection to the wide tube, and had drawn on the board a sketch of the tube he preferred. Working as Mr.Stokes did, that un- doubtedly was a desirable improvement. Working as he (Mr. Allen) did, he had gone back to the old tube. He did not like the practice of drawing off a fractional part of the ethereal layer, and the subsequent calculation it involved. He proposed to draw off the whole of the ether, and then evaporate it in a flask or beaker. He objected to the72 THE ANALYST. use of R dish for the evaporation of ethereal solutions of fats, for there was always a tendency to creep up the sides. I n practice, the Adams process was liked in his labo- ratory quite as well as the Werner-Schmidt method, as it looked after itself ; but the latter had the advantage of rapidity, and was better adapted for use with sour milk.He had also used it quite successfully for the estimation of fat in condensed milk, but bad not tried it on sweetened condensed milk, and had not therefore met with the difficulty mentioned by Dr. Hill. Mr. Allen said he commended to the notice of the Society the little arrangement he exhibited. It was devised by Mr. Chattaway, and was exceedingly useful for separating an ethereal layer from an aqueous liquid. Dr. VIETH said that the author of the paper under discussion did not like to use 10 C.C. of milk, but preferred to weigh 10 grams. He himself thought it quite as well to measure the milk; it was certainly more convenient, and by using specially-gauged pipettes, he had never any difficulty in doing it sufficiently accurate. One thing struck him, and that was that, in the hands of those gentlemen who had taken up the procew, the latter did really more than the inventor of the process professed it would do.Dr. Werner-Schmid said ‘‘ the results compared favourably with the gravimetric process.” That was years ago, when he (Dr. Vieth) believed the Adams process had not been taken up generally. What he thought it was compared with was something like the Sohxlet process, and as the Adams process professed to extract more fat than the Sohxlet process, the gentlemen working the process at the present time must get about *25 per cent. fat more than Mr: Schmid got himself. With regard to taking the specific gravity, he really thought using the lactometer was the most convenient way. If the milk were properly handled, and a correct instrument, with sufficiently large divi- sions, used, he did not see why the sp.gr. determination by means of the lactometer should not be quite sufficient, at any rate for a process like the one described in the paper. As to fat calculated and determined, he was not astonished to see the figures agree at this time of year, but he did not gee how they could agree so well during the warmer time of the year, and when working on samples which were not quite fresh. Long before milk curdles it contains an appreciable quantity of lactic acid. I n such samples the total solids are found considerably lower, and a calculation of the fat must necessaxily lead to wrong results. Dr. Vieth exhibited a new form of lacto-butyrometer, brought out by Dr.Gerber, of Zurich, last year, and described the way of using it. Mr. DAVIES said that for a considerable time this process had been in use in his laboratory, and he had examined a large number of milks by it; he had entirely satis- fied himself as to the reliance that could be placed on the process. It was an extremely rapid one, and compared favourably with the Adams process, and with the resultsof the calculations. The specific gravity was invariably taken usually by the bottle, but latterly by the Westphai balance, and whether this process or the Adams process was used, the results in his opinion were concordant, He did not agree with Dr. Vieth that it was always near enough to use a pipette. He had found that the weight of milk delivered from a 10 C.C.pipette was not always such as would be expected from the sp. gr., and sometimes was less than 10 grams. This was, no doubt, due to presence of air-bubbles remaining from the shaking that was necessary before pipetting off the milk. His practice was to weigh 10 grams. in one of the Werner-Schmid tubes, and with tubes of the original form the results obtained were extremely satisfactory. Mr. CASSAL said he certainly thought that when one process was being compared with another weighed quantities ought to bs operated on. Everyone would agreeTHE ANALYST. 73 with Dr. Hill that it was improper to base prosecution cases upon analyses in which the fats had been calculated. When the fat was determined by the Adams process, worked in such a way as to eliminate all chances of error, he had always found that the results agreed very closely with those obtained by calculation, but for obvious reasons all prosecution cases should be based on actual determinations.He was in no way disposed to disparage the Werner-Schmid method. It was, no doubt, a very valuable process; but he was inclined to think that the Adam process when properly carried out was upon the whole more reliable and more satisfactory. He admitted that a longer time might be required-that is, that a greater length of time might elapse before the fat could be obtained and weighed-but the process was more automatic. The Werner- Schmid process required more personal attention. There mere several sources of error in it of such a nature as to require very special precautions.In reference to the analysis of condensed milk, Mr. Cassal contended that when these contained large percentages of cane sugar, an accurate estimation of the fat could only be effected after removal of the sugar, which was best carried out by diluting a weighed portion of the sample, precipi- tating and filtering and determining the fat in the precipitated solids. The PRESIDENT ( M i . Hehner) in summing up the discussion, said the subject of milk analysis was one of which every member thought he knew something more than anyone else did. We were now in a position to estimate fat with fairly quantitative accuracy, and counted the differences between the best methods only by hundreths of percentages. He thought that as regards the agreement between an actual result and a calculated quantity ideas of exaggerated accuracy should be avoided, as the specific gravity of solids-not-fat was, as a matter of neceesity, subject t o slight fluctuations.The Adams process had in the hands of most analysts proved everything that could be desired in point of accuracy and expeditiousness, and for his part he could not imagine any cases in which a saving of ten minutes, or even of half an hour, was of any conse- quence. The contraction of paper coils was an automatic operation, requiring the least possible amount of attention. As regards sour, or even decayed milk, he mould raise a protest, as he had done on previous occasions, against their analysis. It was demon- strated to be impossible to estimate the amount of solids-not-fat in a sour or fermenting milk, and this being so, the cases in which the exact estimation of fat was of any conse- quence in old samples could occur but most rarely.Public analysts should invariably refuse to analyse old and decomposing milk samples, and leave them to tliose who pretended to be able to deal with them. A pipette nominally delivering five cubic centimbtres of water never delivered five grams. of milk, and he preferred in every case to weigh the quantity of milk discharged. The estimation of the specific gravity, being of the utmost importance, should be treated with the same care as was bestowed upon other quantitative operations. A well-constructed lactometer was capable of giving accurate remits, but pubiic anaiysts never had a sur7icienii quantity of milk to employ such an instrument, as had already been pointed out by Mr. Stokes. Referring to the deter- mination of fat in condensed milk, he did ncjt f a d sure that'the higher results cbtsined by the Schmid method were really due to caramel-like products, for in the case of eugared milks it was necessary to dilute largely before spreading the solution on a paper coil, and in consequence but very minute quantities of condensed milk could be taken for each experiment, thus increasing the sources of error as far as the Adams process was concerned. He preferred to precipitate the casein and fat with sulphate of copper and alkali, and to extract the fat from the precipitate, as larger quantities of condensed milk could thus be dealt with. The discussion had been an instructive and profitable one, and the Society owed their thanks to Dr. Hill and to those who bad assisted in the discussion. (Conclusion of the Society's Proceedings.)

ISSN:0003-2654    

DOI:10.1039/AN8911600067

出版商:RSC    

年代:1891

数据来源: RSC

摘要:

74 THE ANALYST. REPORT OF RECENT RESEARCHES AND IMPROVEMENTS IN ANALYTICAL PROCESS. DETECTION OF ROSIN m BEES-WAX. H. ROTTQER (Chm. Zed. No. 4, 91)- Donath’s process : If a sample containing 5-10 per cent. of rosin is heated up to l l O o C, a strong smell of turpentine will be noticed. But pure wax collected in the neighbour- hood of pine woods also emits this odour. If large quantities of rosin are present, any dealer will at once notice this from the very appearance, but small percentages are best detected as follows : if rosin is boiled for some time with strong nitric acid it is gradu- ally dissolved with evolution of nitric vapours. Water being added, a yellowish floculent precipitate is obtained, which is not altered by fixed alkalies, but dissolved in ammonia with a blood-red colour.A nut-sized piece of the wax is therefore boiled in a test-tube with strong nitric acid for fifteen minutes. A little cold water is carefully added t o solidify the layer of wax, so as t o enable t o pour off the acid fluid. On cooling, or better still, an addition of more water, a precipitate is obtained which gives the charac- teristic reaction with ammonia. E. Schmidt’s process: 5 grams. oE the sample are boiled in a flask with 25 grams. of common nitric acid of 1-33 sp. gravity for one minute. An equal volume of cold water is then added, and then ammonia in slight excess. I f now the fluid is poured off from the wax into a cylindric glass, the colour will be yellowish if the wax were pure; but if adulterated with rosin, even with only 1 per cent., the colour will be reddish-brown.It is as well to test a pure sample side by side. Hager’s process : The sample is boiled with 15 times its weight of dilute alcohol (two alcohol and one water). After cooling, the liquid ie poured, or, if necessary, filtered 0% and then diluted with an equal bulk of water. I f rosin is present the liquid turns milky. Stearic acid does not interfere with this test. The German Pharmaceutical Committee recommends to boil the suspected wax with 10 parts of water and three parts of carbonate of soda for 15 minutes. If rosin i d present a per- sistent emulsion is obtained. Sedra proposes the, following process : 3 grams. of the sample are dissolved in a test-glass in 30 C.C. of chloroform, and then shaken with 200 C.C. of lime-water.Pure wax will cause an emulsion, but if rosin is present a turbid yellowish-brown liquid separates out. The author, after trying these processes, utterly condemns the last process, as he failed to dibcover an admixture of even 20 per cent. of rosin. Hager’s process gives satisfactory results, but the author finds that this chemist makes a mistake in supposing the weak alcohol not to affect the wax or any stearic acid which may be present. Traces of these bodies are dissolved, but are dis- tinguished from rosin by quickly collecting on the surface of the diluted fluid. If, how- ever, proof spirit is used, the stearic acid is practically left undissolved, and even 3 per cent. of rosin may be detected. The best plan is, however, to first thoroughly boil the sample with strong alcohol, to evaporate the alcoholic solution, and then to apply Donath’s nitric acid and ammonia test.L. DE K. THE ASSAY OF INDIGO. Dr. FRITZ VOELLER. (Zeitschr. J. Angew, Chemie. No. 4, 91).-The process most commonly employed is the one with permanganate, proposed by Fr. Mohr. The results are, however, often very inaccurate, especially with the inferior kinds of indigo, as these mostly contain other organic compounds, which are alsoTHE ANALYST. 75 oxidised by permanganate. The traders, knowing this, do not scruple to even employ oxalic acid as an adulterant. Another drawback to the process is the difficulty of pro- perly noticing the end reaction on titrating. The same may be said of other processes based on oxidation, such as Bolley’s process with hydrochloric acid and chloride of lime or chlorate of potash, Penny’s process with sulphuric acid and chromate of potash, or Ullgreen’s method with red prussiate of potash. Chevreuil’s process and other similar colour-methods are not criticised, although they do occaeionally good service, they c m scarcely be classed among the anaZyticaZ methods.The reduction processes of Pugh, with sulphate of iron and soda-ley, and hitsche, with glucose, alkalies, and alcohol, whose objects are to reduce the indigo to indigo- white, which may then be re-oxidised and finally weighed, are also likely to give too favourable results, as there is always a chance of the co-precipitation of foreign organic bodies, unless these have been first removed by suitable means.Berzelius found that, besides indigo-blue and some mineral matter, the commercial product contains three other bodies, which he called indigo-gluten, indigo-red, and indigo-brown. The first, which may be extracted with dilute acids, is closely related to vegetable albumen, and precipitated from its solution by alcohol and tannic acid. The indigo-brown, which is soluble in alkalies, is chiefly found in samples in the preparing of which lime has been employed. Berzelius’s plan is to first wash the sample to be analysed with hydro- chloric or acetic acid, then with alkali, and finally with alcohol and hot water, which will remove the three mentioned bodies, and leave a fairly pure indigo-blue; This con- tains, however, a certain quantity of silica or other mineral matter, which the acids and alkali have failed to remove.Although the amount of this mineral matter may be estimated by incineration, the author thought better results still might be obtained by estimating the nitrogen in the purified product by Kjeldahl’s process and calculating from this the percentage of indigo-blue. Por his experiment he used a sample of common Bengalese indigo. The washings with acid, soda, alcohol, and hot water were quickly performed in a perforated crucible, closed with asbestos and connected with a filter-pump. The asbestos containing the indigo-blue was then dried, and finally treated with sulphuric acid and a drop of mercury. The nitrogen multiplied by 9.36 equals the indigo-blue. Pure sublimed indigo-blue showed 99.85 per cent. The common Bengalese sample gave 75.76 per cent.1;. DE. x. VOLUMETRIC ESTIMATION OF PHENOL, THPMOL, NAPHTHOL, AND SALICYLIC AcfD. -J. MESSINGER AND a. VORTMANN have found that the principles of the process by which aristol and similar compounds are obtained-&, treatment with iodim of a strongly alkaline solution of thymol, etc.- .may be applied to the quantitative estimation of the above-named substances, and no doubt also of others chemically allied t o them. The requisite volumetric reagents are, a 23 normal solution of iodine and a & so- lution of sodium hyposulphite. In the estimation phenol. or carbolic acid, the later must be in alkaline soldtion. For each molecule of phenol there will be consumed B atoms of iodine. The mode of pfo- ceeding is as follows : 2 to 3 grams.of the phenol to be estimated are dissolved in soda so that there are at least 3 moleoules of sods present for every molecule of phenol. The76 THE ANALYST. solution is then diluted to 250 or 500 C.C. Of this an exactly measured quantity of 5 or 10 C.C. is put into a small flask, the contents heated to about 60? C., and enough of the -& iodine solution added to render the liquid strongly yellow by excessof iodine. Upon agitation a bright-red precipitate will fall. After the liquid has cooled, it is aciddated with dilute sulphuric acid, diluted to 250 or 500 c.c., and a definite portion (say 100 c.c.) titrated with .i-17; hyposulphite in order to ascertain the excess of iodine. The actual amount of iodine consumed (in grams.), multiplied by the factor 0.123518, gives the quantity of pure phenol.The factor is derived thus : -~ 93'78 = 0.123518 1 mol. phenol - 6 at. iodine 759.24 The analytical data furnished by the authors show that this method of estimation is very satisfactory, differences not exceeding 1.2 per cent. Thymol can be similarly determined, but no heat is required. The precipitate caused by iodine has a brownish-red colour. Each molecule of thymol requires 4 atoms of iodine. The amount of iodine actually consumed, multiplied by 0.2956772 indicates the quantity of thymol. From 0-1 to 0.3 gram. of thymol is dissolved in soda, so that there are at least 4 molecules of soda for 1 of thymol. The solution Is then made up to 250 or 500 c.c , and, except that no heat is applied, treated as in the cme of phenol.Naphthol (6eta).--This yields, under the same conditions, a dirty-green precipitate. Here also 4 molecules of soda must be taken for every 1 molecule of naphthol. The amount of iodine actually consumed must be multiplied by the factor 0.37843106. In the case of naphthol, the solution must be heated to 50° to 60" C. Otherwise the method is the same. Salicylic Acid.-This may be estimated either alone or when mixed with benzoic acid, the later not entering into reaction. In this case, also, 4 molecules of soda must be taken for every molecule of the acid. On adding Ghe & iodine solution to the solution of the acid warmed to 50" to 60° C., a precipitate should not be formed a t once. Only after iodine is present in excess, and the liquid has been again slightly warmed, is there pro- duced a bright-red precipitate, which increases in quantity after acidulation.If too small a quantity of alkali was present, a yellowish-white precipitate is formed before iodine is present in excess. Should this happen, more alkali is added until this precipitate disappears, after which the addition of the iodine solution is continued. The factor with which the quantity of iodine actually consumed must be multiplied is Oi181326O6. If not, the latter must be determined separately by means of the & iodine solution, and the proper correction made when the alkali is employed. Calculations of the results obtained by the above processes may be saved by the following consideration : Letf denote the factor with which the quantity of iodine must be multiplied in each case, and t the titer-that is, quantity of iodine in 1 c.c.-of the iodine solution ; then the product f x t at once shows the quantity of phenol, etc., in grams,, which corresponds to 1 C.C.of the iodine solution.-Berichte, 1890, 2753, and Am. Drug. xx. 56. The alkali which is used in these processes must be free from nitrite.THE ANALYST. 77 MICRO-CHEMICAL INVESTIGATION OF EXPECTORATION. PROF. FERDINAND HUEPPE (Chemiker-Zeitufig, 17th Dec., 1890). The author uses the following apparatus :-(1) A microsoope, which need not as a rule be provided with the strongest powers, then, owing to the staining proceBs, even isolated bacteria are readily recognised. However, it is as well to have a Gz inch power at command. (2) Some salt-cellars and a few crystalisa- tion basins of about 5-6 C.M.diameter, and a depth of 1 C.M. (3) A small pair of bellows connected with a finely drawn-out glass tube. (4) A pair of pincers and a few platinum needles. These are made by fusing into a glass rod of about 20 C.M. length a 5 C.M. long platinum wire. Either before or after use the points must be ignited, and then just allowed to cool. (5) A spirit lamp or a Bunsen-burner. (6) Test-mixers, burettes or pipettes, and a balance. (7) To get a fair sample of the expectoration the author uses a cylindric glass holding about 100 C.C. provided with a ground stopper. To measure off the fluid a pipette is used, capable of accurately delivering *01 C.C. In using the pipette the top must be closed with a piece of sterilised cotton wool, or what is still better, it should be connected with an aspirator. Reagents.-( 1) Recently boiled distilled water, which must be of course perfectly sterilised.(2). Absolute alcohol or 90 per cent. spirit. These are used for dissolving the colours, also to prepare a 60 per cent, spirit. (3). A 5 per cent. solution of phenylic acid. (4). Sulphuric, hydrochloric or nitric acids, diluted with ten times their bulk of water. cent. of alcohol, and 90 per cent. of the carbolic acid solution. first dissolved in the spirit before the carbolic acid is added. many months. They are used for the purpose of decolourising. ( 5 ) To stain the bacilli, a solution is used containing 1 per cent. The The (6). For the purpose of staining are wanted :- of fuchsine, 10 per fuchsine must be solution keeps for (a).Watery methylene blue, which means the solution of the dye in water (which must, however, often be filtered or even renewed), or an alcoholic solution is added to water in sufficient quantity immediately before use. (6). Yellow fluorescine in a saturated alcoholic solution of methylene blue. (c), Picrate of aniline. Aniline oil is saturated with powdered picric acid. A few drops of this solution are added to a small cup full of aniline. The collecting and sending out of the expectoration must be done in thoroughly cleansed glass bottles, provided with ground glass stoppers. The morning product is the best fitted for the experiments, particularly if the patient is improving. For quantitative estimation it often becomes necessary or desirable to specially pi-e- pare the expectoration.A saturated solution of borax is mixed with three parts of water. According to the consistency of the expectoration it is thoroughly shaken in a test-mixer, with an equal or even a, treble volume of the borax solution for about a minute, until all coarse lumps have disappeared. The liquid is then put into a conical glass, and after this is covered over, allowed to settle for 24-48 hours. The clear fluid is then poured off, and the deposit used for the experiment. This complicated process78 THE ANALYST. need only be resorted to when the direct testing of the expectoration has given no satis- factory result. Preparation of the slides. When the expectoration is fresh, a little is taken out by means of the platinum needle ; not the watery fluid but the pus-like part.If prepared a drop is taken by means of the pipette. The material is spread over the covering glass by means of the platinum needle with the utmost care. The layer need not be particularly thin, but must be as much as possible uniform, This may be assisted by the application of a gentle blast of air from the bellows, which will also get rid of the moisture, The cover is got hold of with the pincers and passed three times (the material upwards) through the Bunsen flame. The objects are then ready for staining. A drop of the fuchsia solution is spread over the cover and allowed to act for five minutes ; or the cover is made to Boat on this fluid, contained in a little dish for the same length of time.The time may be shortened to about one minute if the solution is applied boiling hot. After the staining, we must decide whether other bacilli besides tuberculi- bacilli are t o be looked for. Ordinary phthisis is no longer considered to be pure tuber- culose, but a mixed infection. The methods which enable us to detect the other bacteria as well are not, however, so accurate for the detection of the tuberculi-bacilli as the special methods. The excess of colouring matter is carefully removed irom the cover by means of blotting-paper, and the glass is then dipped for a few seconds in the dilute mineral acid, until the colour seems all gone. I f , however, the layer is somewhat thickish, it is as well not to immerse it too long. The covering glass must now be well washed with water and then quickly dried by means or" the bellows.A drop of the picrate of aniline is now put on a slide and the covering glass put on downwards. The excess of aniline is removed by means of blotting-paper, and the outside of the cover is then moistened with a drop of a suitable oil. The objective is now lowered until it touohes the globule of oil, and any exprienced microscopist will soon recognise the tuberculi-bacilli, appearing as they do like red rods on a yellowish field. There is little chance of mistaking them for bacteria. B, Testing for tuberculi-bacilli in presence of other bacteria. The colouring by means of fuchsine and the bleaching by acids is just as in A, The acid must, however, only act for a few seconds, when the slide is immediately immersed into 60 p.c.alcohol, contained in two separate basins, After draining off the spirit a drop of the saturated watery solution of methylene blue is put on, but washed off again after one minute. Its outer surface, after being dried with blotting-paper, is moisteaed with a drop of oil and the microscopical examination is conducted as usual. The tuberculi-bacilli appear red on a blue field, but their number seem to have somewhat diminished. The other bacteria will all be colonred blue, The fixing. Staining, The specimens look most beautiful when stained whilst cold. It is therefore as well to apply them both in succession. A. The operator wants to test for the tuberculi-bacillionly. The cover is now put on a slide wikh a drop of water.THE ANALYST.79 I f one likes to avoid the use of mineral acids (to prevent accidents to the micro- scope) the following process may be recommended : The staining with fuchsine is done as usual, and the cover is then dipped six or ten times in succession into the fluorescin methylene blue then about ten times in a strong alcoholic solution of methylene blue, and finally washed with water. This will also communicate a red d o u r to the tuberculi-bacilli, while other bacteria will look blue. L. DE K. ELDERBERRY JUICE AS AN INDICATOR, BY CLAUDE C. HAMILTON, M.D., Pa. a,- The expressed juice of the fruit of Sambzcscus canadensis, or elder, has a garnet-red colour when neutral or acid, but turns green when alkaline. This property led to some experiments by the author as to its value as an indicator in volumetric analysis. These experiments show the elderberry juice to be not only superior to litmus for any titra- tions, but equal in efficiency to rosolic acid as an indicator in the estimation of ammonia or phosphoric acid.When the indicator is first added to ammonia the colour is a (‘ muddy ” blue, becoming clearer and of a pea-green colour as the acid is added from the burette. This green is brighter and more distinct as the final end to alkalinity approaches, and, when a drop of acid is added in excess, instantly becomes a garnet-red colour. The turn of the indicator was exactly at the number of cubic centimeters required to turn rosolic acid yellow, while phenolphthaleingradually faded out at a few tenths cubic centimeters more.In titrating the precipitate of MgNH,PO, by Stolba’s method, the red colour appears at just twice the cubic centimeters of HCI required to turn rosolic acid yellow. I f the precipitate is dissolved in HCl and the excess measured back by NaHO, the green appears at just twice the cubic centimeters required to turn resolic acid red. At the point where rosolic acid just turns, elderberry juice has a violet colour. Then when the formula is Na,HPO, the elderberry juice is green, and is not restored to acid till the formula is H PO,. The fmal point is more distinct when the MgNH4P04 is dissolved in excess of HCl and the acid measured back by NaHO. The author is engaged on further experiments in regard to the action of this substance with phosphates to deter- mine its practical value.I n titrating carbonates a bluish-violet appears at the point when phenolphthalein is just decolourised (without heating), and changes to red at the same point that methyl orange is turned red. The change of colour is not very distinct, depending on keeping the solution a t a constant temperature. These experiments were made with elderberry wine carefully neutralised with with NaHO. The fresh juice may be pre- served by addition of one-fifth its volume of alcohol. The author finds it quite efficient in all titrations, unlem it be wetic acid, when the colours seem 80 pale ag to be rather hdisfinct.-Am~. Drug, XX., 50. A NEW METHOD OF TESTING HONEY. By Da. OSCAR IJiAENLI.--It is only about five years back that every expert would have condemned as adulterated any honey which was found to turn the ray of polarised light to the right instead of the left.About that time Dr. Haenle succeeded in finding, while travelling, some natural (wild) honey which polarised to the right. This was subsequently ascertained to be due to the fact80 THE ANALYST. that the bees fed upon coniferous products, while those feeding upon flowers produced laevogyre honey. While the polariscope had, before this discovery, been generally used as a certain criterion to distinguish between genuine and adulterated honey, t~ instru- ment could no longer be employed for the purpose without some restriction. The author has now ascertained that if the honey be dialysed before the polarisation test is applied, the result is a certain indication of the character of the honey.I. EXPERINENTS WITH HONEY COLLECTED FROM FLOWERS.-~. A pure Alsatian honey was dissolved in twice its weight of water. The solution polarised 2 8 O to the left (-288). It was then subjected to dialysis during sixteen hours, after which the residue remaining in the dialyser was optically inactive (00). 2. Thirty grams. of a pure honey were dissolved in 150 grams. of water, the solution decolourised and then dialysed. After eighteen hours the residue was inactive. 3. Fifty grams. of a similar honey were dissolved in 250 grams. of water. The solution polarised at-1 l o . After sixteen hours’ dialysis the residue was optically in- active. On further evaporating the latter and again dialysing, its inactivity remained unalterd.11. EXPERIMENTS WITH GLUCOSE SYRUP.-A 10 per cent. solution of glucose syrup which polarised + looo, was decolourised and then dialysed. After sixteen hours it still polarised -I- 58. The residue was then concentrated, aud in proportion as this pro- gressed so rose the angle of polarisation. 111. EXPERIMENTS WITH HONEY PUBPOSELY ADULTERATED.-~. Forty grams, of a pure honey, polarised in a 1 in 2 solution at--35O, were mixed with 10 grams. of gIucose syrup. A 10 per cent. solution of this mixture was subjected to dialysis, and the residue was found to remain dextrogyrate at + 48. 2. Thirty grams. of a pure honey were mixed with 20 grams. of glucose syrup, dissolved in 250 parts of water, and the solution decolourised by charcoal. It polarised a t + 658. After twenty-four hours’ dialysis the residue retained a permanent polari- zation of + 148, After concentrating this residue to half its weight its polarizing angle had increased to + 60°. The solution polarised at + 95’. It was then dialysed and the liquid on the dialyser examined a t intervals of two hours, The following is the rate at which polarisation decreased until it remained constant : 3. Fifty grams, of a glucose honey were dissolved in 250 grams. of water. After 2 hours . . .. , . +45”. ?> 4 9 ) .. .. . . + 3 3 O . > 9 6 > 7 . . . . .. -I-18O. Y 9 8 >) . . .. .. +15? > ? 9 >> . . .. . . +12*. >? 10 >> . . ,. . . +11*. *> 11 > > 1 . . . . . +loo. 79 12 9 ) .. .. . . +loo. Further dialysation did not change the angle (+ 10’). General cocnch8&n~.-Any honey which, after having been dialysed, does not turn the ray of polarised light to the right, is free from glucose. Any honey which, after dialysis, retains a permanent dextrogyre polarisation, contains glucose.-Arner. Drug and Ph. Ztg.

ISSN:0003-2654    

DOI:10.1039/AN8911600074

出版商:RSC    

年代:1891

数据来源: RSC