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.)