摘要:

PROCEEDINGS OF THE SOCIETY OF PUBLIC ANALYSTS. AN ordina,ry meeting was held at Burlington House on Wednesday, the 9th ult., the President, Mr. A. H. Allen, in the chair. The minutes of the country meeting were read and confirmed. On examining the ballot papers the scrutineers reported that the following gentle- men were elected :-As members, Mr.,H. Smith, M.D., F.I.C., F.C.S., etc., Public Analyst for Woolwich and Plumstead; J. M. Vargas, analyticztl chemist, Bogota. As associates, G. W. Gray, assistant to Mr. Norman Tate; W. Chattaway, assistant to Mr. Allen. The following papers were read and discussed :- “ Allowances for Decomposed Milk.” By A. W. Stokes. <‘ On the Preservation of Milk Samples.” ‘‘ The Substitution of Asbestos Cloth for Blotting Paper, in Mr. Adams’ process “ Doe8 Neutral or Sub-Acetate of Lead precipitate Hop Bitters ? ” By W ‘‘ On Filtration.” By Otto Hehner and Henry D. Richmond, who exhibited “ Alumina as a Natural Constituent of Wheat Flour. By Otto Hehner, of Milk Analy&.” Johnstone, the filter and apparatus empIoyed. Mr, HEHNER read the correspondence from Mr. Estcourt and Dr. Bell, which has recently appeared in THE ANALYST, on the subject of milk analysis, and also the further communication from Mr. Estcourt which appears on another page. By W. C. Young. 2% three lmt-lzamed papers, by Mesars. Johnstow, Hehmr, and Young, will appear in the next hue of THE ANALYST.

ISSN:0003-2654    

DOI:10.1039/AN887120223b

出版商:RSC    

年代:1887

数据来源: RSC

摘要:

224 THE ANALYST. ANALYSIS OF DECOMPOSED MILK. C. ESTCOUBT, F.I.C., F.C.S. THE communication made by me upon the above subject, which appeared in the September number of the ANALYST (page 168), xems to have caused considerable trouble to Dr. Bell, the gentleman who represents the Somerset House Laboratory. Dr. Bell, in face of such a series of analyses as I presented, feeling himself upon the horns of a dilemma, is compelled, apparently, to take one of two courses : he must either admit (what is already recognised by the majority of public analysts) that the analysis of curdled, partially decomposed milk is unreliable, or he must take the unusual and extraordinary course adopted by him in his communication of October 11th (vide ANALYST, page 221). Dr. Bell says, (‘ Mr. Estcourt has tried hard,” etc., when, in fact, I confined myself to a bare statement. Dr, Bell thinks it right to suggest that ‘‘ the sample had been seriously tampered with,” rather than disbelieve in the unreliability of a necessarily fallible method.The fact is, his figures are only explicable upon the supposition that no complete mix- ture is p i b e of fat, curd, and whey after long standing. I f the case I have given stood alone, it might be deemed impossible that such a result could be obtained as was obtained by the Somerset House analysts. It is, how- ever, not unusual for these gentlemen to differ both as to results and inferences with pllblic analysts. The Somewt House chemists reported upon the analysis of a milk contained in a bottle which had been broken in transit, and from which some of the liquid portion had escaped.This was in connection with a certificate of adulteration given by Mr. E. W. T. Jones, the result being that the case was dismissed, together with another which depended upon the Somerset House certifimte (see ANALYST, vol. i., 1877, page 74). It is interesting to observe in the second case alluded to, that Somerset House found 0.14 per cent. ash more than Mr. Jones had done, and advanced the ash result as afford- ing the main proof of the genuine character of the milk, (see also difference of 0.10 per cent, between Somerset House and Dr. Hill, ANALYST, vol, i., lS77, page 40). hgarding my own case, and assuming that the ash given by Somerset House is correct, I will compare it with milks analysed by Mr. E.W. T. Jones and Mr. Percy Smith (see ANALYST, vol. i., page 76, and vol. v., page 149). I n these communications may be found several examples of very low ash, thus :- Solids not Fat. Ash. E. W. T. Jones’ sample 8.97 0-56 1, 7, 7-96 0.53 9 , 99 7.67 0049 C. Estcourt’s ,, 7.70 0.47 Percy Smith’s ,, 9-10 0.49 I n these analyses, unfortunately for this reference, the chlorine is not estimated, but I do not doubt that, if estimated, the results would have borne out the views of the authorities upon the subject. Mr. John Pattinson (ANALYST, vol. i., page 98) says, “ Usually the amount of chlorine is from 006 to -08 per cent.” Nr. Otto Hehner (ANALYST, vol. vii., pages 6 and 6) says, “The percentage of ash found by Somerset House (in a referred milk case of his) cannot be correct.” He a180 (same communication) shows solids not fat reduced by decomposition in 74 weeks from 8.37 to 4.22 per cent.Dr. P. Vieth (ANALYST, vol. vii., page 215) gives loss of solids not fat ranging from 2.0 t o 2.66 per cent in four days.THE ANALYST. 225 There is also a case in which Dr. Wynter Blyth analysed a milk, a portion of which, when sour, being analysed by the Somerset House chemists, gave the following results :- Wynter Bly t h 8-81 2.09 Somerset House 7.84 3.35 Solids not Fat. Fat. (See ANALYST, vol. ii., page 202.) Dr. Blyth reported it skimmed; Somerset House certified to added water. Here is an error in fat almost equal to their error in solids not fat in my w e . In face of these facts and a large number which have never been publisbed, it will be a matter of regret to all public analysts that Dr.Bell should prefer to consider many of them incompetent and some officials dishonest, rather than admit that the inferences from the analysis of decomposed milks are sometimes unreliable. NaTE.-The sample to which Dr. Bell’s letter refers was obtained from a farmer’s can at a railway-station in town, and was therefore not divided into three parts, I divided it myself, sealing and returning one part, with the certificate, to the inspector. The magistrates themselves forwarded it to Somerset House at the farmer’s request. The farmer had been supplied by our Inspector with a duplicate of my original sample. It appears from Dr. Bell’s letter he had never before seen a sample sealed with the analyst’s own seal, as provided by the Act when a sample has been procured in transit.It is also rather late in the day to put forward figures of ash and chlorine which, if of any value (which is, I submit, doubtful in the c ~ e of decomposed milk), ought to have figured upon the Somerset House certificate. The sample was sent to Somerset House on the 25th March, but the certificate was not received until three weeks later, a total period of nearly eight weeks from the date when it was first procured. The PRESIDENT said in reference to the division of the sample that Mr. Estcourt had further explained that it was divided at the station into two parts, one part being given to the farmer, and the other taken to Mr. Estcourt, who again divided his part into two, sealed up one portion, and used the other for the analysis.On finding it adulterated he returned the sealed-up portion to the inspector, who produced it in Court in the usual way. The part given t o the farmer was analysed on behalf of the defendant by a local chemist. The only point of importance was that Dr. Bell suggested as the ash of his sample was so very low it could not have been the same milk as was analysed by Mr. Estcourt. But it did not appear that Dr. Bell gave the ash and chlorine in his certificate, although he states in his letter that he always makes those determinations ; it would be interesting to know why he suppressed the figures. Of course he could understand that observations might sometimes be made for the sake of learning, and not for reporting, but that would not account for Dr. Bell reporting the chlorine and ash in certain cases, and not in all. I n Dr. Bell’s book there was an ash of genuine milk given as low as -65 per cent., and with 14 per cent. of water it would be reduced to -56 per cent. Mr. Estcourt had shown by a number of examples that the error of analysis in the determination of the ash at Somerset House sometimes amounted to fully -10 per cent,, and therefore the difference was perfectly capable of explanation without the insinuation made in Dr. Bell’s letter. Mr. J. Pattinson had shown that the amount of chlorine in milk was usually between -06 and -08 per cent., so that there was nothing in Dr. Bell’s figures to show that the milk analysed by Somervet House was not the same milk as that analysed by Mr, Estcourt, With r-espect to the ash, it was curiously low.

ISSN:0003-2654    

DOI:10.1039/AN8871200224

出版商:RSC    

年代:1887

数据来源: RSC

摘要:

226 THE ANALYST. ALLOWANCES FOR DECOMPOSED MILK. BY A. W. STOKES, F.C.S., F.I.C. (Red at Meeting, November 9th, 1887.) VARIOUS isolated analyses of the same samples of milk, before and after the commence- ment of decomposition, have been published, though, so far as I: know, no series of such analyses haa hitherto been printed. Even such analyses as have been recorded have usually been by different analysts, the one doing the analysis of the fresh sample, the other when decomposed. In such cases the method of analysis has not been necessarily, or even probably, identical, so that the results are not strictly comparable. During the last few months I have made a series of analyses, using the same method for the fresb and the stale samples; this I now bring before you. The method used was as follows :-A careful mixture of the sample was made ; 5 grms. of this were weighed into flat-bottomed dishes of 3 inches diameter.After com- plete drying in the water-bath the total solids were weighed. The dishes were now repeatedly filled with light benzoline, boiled, dried, and re-weighed. The fat was thus taken by difference. In the case of the same milks when decomposed the 5 grms. taken for analysis were carefully neutralised by decinormal soda solution before drying ; in mi- culating the results *0022 grm. for each C.C. of NaHO was subtracted from the total solids, as recommended by Mr. James Bell, of Somerset House, in his book on (‘ Analysis and Adulteration of Foods.” All were done in duplicate. This method was not adopted as baing the very best for milk analysis, but because of its simplicity, and of its near resemblance to the method quoted in the above book.Whatever error there may be in the method from the abstraction of fat possibly not being absolute, etc., runs through the series both of fresh and stale milks, but does not vitiate the comparison of these with one another. Almost all of the samples are adulterated; they are, therefore, such as usually appear in reference cases. They are actual samples sent to me by various Vestries for analysis. The times of keeping of the samples varied from 8 to 117 days, and the season from July 6th to November 3rd, 1887 ; hence a fairly wide range of changes of temperature has been tried. In the following list are recorded the total solids, fat, and solids not fat; then under the heading of “ s.n.f.+ allowance” is placed the s.n.f. of the previous column, with the addition for keeping suggested by Mr. J. Bell in above book: that iss for 7 days, -24 ; for 14 days, -34; 21 = *41, 25 =*48, 35 := 055, and -01 more for every day after is to be added to the 9.n.f. found. In the next column is placed the difference between this last figure and the s.n.f. obtained from the fresh milk. If, in,spite of the allowance, the weight is less than at first, the letter ‘ I L ” for ‘‘ loss ” is placed before the difference shown ; if it is greater, the letter I‘ Q ” for gain” is prefixed, and the time during which the sample has been kept follows. I n the next column I have placed the total acidity, calculated as lactic acid.In the last column, at the suggestion of our President, Mr. A. H. Allen, I have placed the difference between the original total solids and the total solids of the stale milk p l m the Somerset House addition for decomposition. All figures are percentages. There are 26 samples; all were analgsed at two periods, and three of them at three periods. They are generally arranged according to the length of keeping, beginning at the shortest time. In most cases the vendors were fined €or adulteration.THE ANALYST. 227 Sept. 27 11.26 Oct. 12 11.26 Nov. 3 10.72 Sept. 27 10.92 Sept. 22 10.54 Oct. 11 10.02 Nov. 2 8.40 5 Sept. 22 11.13 Heated 60 hrs. { Oct. 11 10.14 Aug. 18 1023 Sept. 14 8.54 Aug. 18 10.30 1 Sept. 16 7.82 2 3 8 { Sept 30 29 :&; Aug. 29 10.67 / Oct.1 1032 Aug. 5 1096 lo { Sept. 10 9.30 Sept. 10 7.54 Aug. 12 10.45 Sept. 20 1012 Aug. 10 9.93 { Sept. 20 9.24 15 { &!f 89::; Sept. 20 12.76 Oct. 31 12.02 Sept. 12 1202 Oct. 31 11.76 July 13 9-74 1 Sept. 13 9.50 19 812 Smell very bad. { ;:$. ;i 3.68 21 12.74 20 Sept. 28 12.36 1 July 20 1013 23 { Sept. 28 8.80 July 6 1021 Nov. 1 9-40 Sept. 20 1079 26 i Oct, 19 1054 Fat. 2.06 2-02 3 06 3-28 3.10 2-88 3.10 3.14 2-34 2.38 1.74 2.44 2.06 2.83 2-90 2.74 2.66 2.14 2.20 2.65 2.70 2.82 3.32 2.1 3 2.12 014 0.52 2.70 254 1-92 1.42 2.54 2 62 3.28 3.62 314 446 2.44 2.72 1.92 1.44 4.22 4.42 1.81 2-00 2.32 2.14 2.01 2.10 2.09 236 2.25 1.98 3.07 3.39 S.n.f. 4.84 4.90 8.20 7.98 7.62 8.04 7.80 7.26 8.20 7.64 6.66 8.69 808 7.40 5.64 7.56 5.16 7.68 6.52 8.02 7.62 8.14 5.98 7.50 5.42 10.31 9.60 6.39 5.88 8.01 7.82 6.48 5.74 9.48 840 888 7.30 7.30 6.78 6.20 2.24 8.52 7.94 6.59 5.52 7.37 4.08 8.12 6.70 6.16 488 7.96 7.42 7.72 7.15 S.n.f.+ Tot. sols. allow- S.n.f. difference. Lactic differ- ance. acid* ence. 5.15 G. 0.31 in 8 days 0.52 G. 0.27 8.39 G. 0.12 in 14 days 0.52 G. 0.24 8.18 L. 0.02 in 36 days 0.99 G. 0.02 8.14 G. 010 in 14 days 055 G. 0-32 7.82 L. 022 in 36 days 1.78 G. 0.04 8.02 L. 0.18 in 18 days 0.61 L. 0-16 7.26 L. 0.94 in 40 days 1.09 L. 1.54 846 L, 0.23 in 18 days 036 L. 0.61 6.10 L. 1.30 in 26 days 1.76 L. 1.23 $64 L. 1.92 in 28 days 0.97 L. 2.00 7.03 L. 055 in 31 days 072 I;. 049 8-14 G. 0.12 in 32 days 0 77 G. 0.17 6.53 L. 1.61 in 35 days 1.18 L. 1.11 5.97 L. 1.53 in 35 days 2.07 L. 1.54 10.18 L. 0-13 in 38 days 1.08 G.0.25 6-46 G. 0.07 in 38 days 082 L. 0.09 8.41 G. 040 in 39 days 1.02 L. 0.10 6.33 L. 015 in 39 days 1.18 L. 017 9.00 L. 048 in 40 days 082 L. 0.14 7'98 L. 0.90 in 48 days 2.12 G. 042 7.59 G. 0.29 in 61 days 2.10 G. 0.57 3.07 L. 3*13 in 63 days 010 L. 3.61 8.82 G. 0.30 in 68 days 1.24 G. 0.50 6.40 L. 019 in 68days 1-15 000 4.96 L. 2.41 in 68 days 052 L. 2-69 7-69 L. 053 in 69 days 1.35 L. 0.54 5-78 L. 038 in 70 days 2.01 L. 0.11 8.79 G. 0.83in 117 days 234 G. 056 7.63 L. 0.09 in 28 days G. 0.23228 THE ANALYST. Examining the more noteworthy of these we find that in Sample 1 there has been practically no change during the 8 days of its keeping. This is the only case where the analysis shows (by error of experiment) a very slightly higher s.n.f. after keeping than when fresh.Here, therefore, the addition of an allowance must result in a gain, as shown. Samples 2 and 3 are milks of the same date, and of very similar constitution, They were analysed when fresh, after 14, and after 36 days. Sample 2 was left all the time at the average temperature of the laboratory (about 58O F.), but sample 3, during the latter part of the first 14 days, was kept at a temperature of 70" F. for 66 hours. During the 14 days both samples altered so little, that making the allowance for keeping, we get s.n.f. greater than in the original samples. The heating of sample 3 for 66 hours has apparently not made any appreciable difference. Both samples, after keeping 36 days, show a loss of s.n.f. after the addition of the allowance. But No. 3 received also an additional heating to 70° F.for 102 more hours; adding the allowance to this, its s.n.f, show a greater loss than in the unheated sample. The lactic acid is about twice aa great in this. In these two cases it is evident that for a short period the allowance is too great, but for a longer time it becomes too small, and that heating the sample increaljes the deficit-that is, hurries on the decomposition. In samples 4 and 5 the same effect of heating is seen, though at no period is there a gain. The alternations of the allowance being either too little or not enough are shown in the following samples, till we come to No. 19. This sample after 63 days' keeping developed an unusually disgusting odour, quite unlike that of every other sample (except one) kept either for longer or shorter periods.I n it we find, after making the allow- ance, a loss of s.n.f.=3*13. With this is a lactic acid the lowest of the whole series. That the mere period of keeping has notbing to do with this anomalous result is seen by reference to the samples adjoining it, Nos. 18 and 20. These, kept through about the same period and at the same temperature, actually show a gain instead of this enormous loss when the allowance is made. No. 22 is another sample possessing after 68 days the same dreadful smell, com- bined also in this case with a strong yellow colour. Here, when the allowance is made a loss of s.n.f. = 2-41 is shown, and yet it has an acidity as small as that of a sample kept only for 8 days. Each side of it are milks of the same date that show but a trifling loss after making the allowance. So remarkable are samples Nos.19 and 22 that they were repeated 3 times with concordant results. Sample 7 shows the great loss of 1.92 s.n.f. (after making the allowance) in only 28 days, yet it has a very low acidity, and gave no very bad smell'. In No, 25 is seen a sample kept for 117 days, in which, if the allowance is made there is actually a gain of s.n.f. = 0.83, while the acidity has run up very high. For the original analysis of No. 26 I am indebted to Dr. Thomas Stevenson, this being the only sample in which I did not make the analysis while fresh. The method of our analyses being, I believe, the same I have inserted this example in the series. It shows, except in one other m e , the closest approximation between the analyses of the fresh and stale samples, after making the allowance.THE ANALYST.229 Reviewing the entire series by comparison of s.n.f., we find that after making the Somerset House allowance, there are 9 cases in which the allowance is too great, and 20 in which it is too small. The average gain of s.n.f.+allowance being 0.28, and the average loss 0.84. According to Mr. J. Bell, the s.n.f. after making the aliowance ought not to differ from the original s.n.f. more than 0.10 per cent. Only 4 of these cases fell within or upon this limit, Considering the series from the point of view of total solids only, there are 12 cases in which, after making the allowance, there is a gain shown, and 16 in which the allow- ance is not great enough.The average gain of total solids is 0.29, the average loss 1.00 when the allowance is made. I n 8 C&SBS the loss or gain shown by the s,n.f. is inverted by the total solids when the allowance is applied to each ; these inversions, however, do not happen in any of the very large differences. These inversions are just what one would expect if the constituents of a milk do not decompose in an invariable manner. The allowance is founded upon the decomposition producing principally lactic acid ; and SO far as this is normally produced the allowance somewhat follows with it. But the series shows that lactic acid is not by any means always the chief product of decom- position, the very worst decomposed milks (e.g., Nos. 19 and 22) having but little acidity ; hence the allowance breaks down.Nor does the time of keeping produce either the same difference of s.n,f., or the same amount of lactic acid even when the tempera- ture and the quality of the milks are about the same. Increase of temperature usually increases the loss of s.n.f., and adds to the lactic acid, but not invariably. What seems t o me is at the foundation of the different changes that undoubtedly take place in milks similarly treated is the nature of the initial fermentation set up. It entirely depends upon what germs reach the sample as to the change that will ensue. Two samples, under like conditions, but differently impregnated with fungus-spores, will produce different results, and no possible allowance can be made for this, seeing that we do not know the nature of the original fertilisation.This is complicated, too, by our ignorance of the temperature at which the sample was kept before it reached us in the ordinary reference cases. I have examined these samples microscopically, and have been surprised to find how differently they have become infected with fungus. There are mainly two classes :- those (the ropy samples) containing largecelled spores, and a thick, branching mycelium ; and the ordinary samples, in which only excessively minute bacteria are seen, and no mycelium is visible. That milks do not decompose in any regular manner is obvious to the senses. Some retain their fresh appearance for a long time, while others of the same date separate rapidly into layers of serum and casein; a few burst their bottles, while others do not.I f the decomposition be the same in all these cases why are the physical results so varied ? I have looked through the records of other examples of milk samples analysed at d.Xerent periods by other analysts, and I find it impossible to make any allowance to account for decomposition. They range from a gain of 0-83 to a loss of 3.13. They range from a gain of 0.57 to a loss of 3.61. Others show both of these.230 THE ANALYST. A few by Dr. W. Blyth will be found in the ANALYST, vol. iu., p. 230, and others are scattered through the vols. of the ANALYST, A notable example is shown in the September, 1887, number of the ANALYST, where, through applying an allowance, the Somerset House chemists find 40 per cent, of added water, after 27 days, while the sample when fresh contained only 14 per cent.of added water. Had any of the above samples found their way to Somerset House, it is not pleasant to contemplate the results that might have issued. I have not worked out the serious differences of added water ” that would be indicated in the series given, but any one can easily do that. The only conclusion I can come to is that-no allowance for decomposition can possibly be made in our present state. of kmwZedge. I might perhaps be allowed to suggest that in cases where stale milk is analysed some such report as follows might be made if the sample fall below the standard : (( The sample was too far decomposed to enable me to form an accurate judgment of its original state, but I am of opinion that it contains about . .. per cent. of added water.” Of course, if the sample come above the standard (without making any allowance) it may certainly be returned as genuine. To Mr. E. Michael I owe thanks for assistance and care in carrying out much of the work here recorded. DISCUSSION. The PRESIDENT said they would agree with him that the subject brought before the Society by Mr. Stokes was one of the highest interest to them as public analysts. It was unfortunately one of the great drawbacks to the proper performance of their duties that, after having effectually and thoroughly satisfied themselves of the character of a milk, they should be liable to see justice annulled, and have their reputations slurred by reports made by the Somerset House chemists on the results of analyses of milk, some- times four, six, and seven weeks old at least, and in which the opinion is based upon the unwarrantable amumption that milk changed on keeping at a practically uniform rate, no matter at what temperature it was kept, or whether a preservative had been added.Common-sense sufficed to discredit such an extraordinary theory, and most public analysts had within their personal knowledge cases which absolutely disproved the assumption, but Xr, Stokes was the first to bring an extensive and systematic series of observations before tbe Society. By the courtesy of Mr. Stokes, he (the President) had had an opportunity of seeing the paper previously, and had suggested that it was undesirable to base the proof of the rate of change on the solids not fat, as such a course left a loophole for Dr.Bell to urge that the variations were due to imperfect and unequal extraction of the fat. As Dr. Bell alleged that no change in the proportion of fat was produced by keeping the milk, it was clear that any diminution of the total solids was caused by change in the solids not fat, and hence the determination of the total solids gave at once a memure of the change which had occurred in the milk, and enabled one to avoid any but the very simplest manipulation-namely, that involved in drying the total milk-solids to a constant weight. The determinationsof totai solids were all made by Mr. Stokes in duplicate, and some in triplicate, so that the accuracy of his figures was beyond question, and it was not possible to evade the conclusions deducible from them by suggesting manipulative error.From the column in Mr. Stokes’table showing the departure from the truth resulting from the analysis of the decomposed milk, and the use of the Somerset House ‘( allowance for change,” it appeared that only in five instances out of twenty-nine did the total solids thus corrected come as near as 0.1 per cent. to the actual amount foundTHE ANALYST. 231 ~~~ ~ in the fresh milk. Hence the odds were nearly six to one against Somerset House arriving at a reasonably correct result by the analysis of a decomposed milk. It was true that the figures showed they were twice as likely to find too high a result as too low, but such variations proved that the method of allowance was intrinsically worth- less and false in principle, and could not be amended by a revision of the figures alleged to represent the daily variations. He, the President, had been so much struck with the deductions to be made from Mr.Stokes’ figures that he had been at the trouble of comparing the rate of change observed in cases in which the figures had been published, and the results might be worth recording in a tabular form. Analyst concerned. Wynter Blyth $9 1 ) $9 2) 99 99 E. W. T. Jones 0. Hehner A. Hill C. Estcourt J. Baynw A. H. Allen and M. A. \ M. A. Adams Adams i Reference. ANALYST, iii., 231 99 9, 2 9 99 99 Y 9 ANALYST, i., 74 ANALYST, vii., 5 ANALYST, i., 40 ANALYST, xiii., 168 Communicated Communicated Communicated 29 99 9, 99 ANALYST, vii., 215 4ge of decomposer milk.21 14 34 18 153 153 80 80 { (3) ;; :: 21 15 33 42 47 47 47 47 Error in total So- lids after applying S. H. allowance. Per cent. + 0.23 + 0.66 + 0.49 - 2.20 - 1.46 + 0.48 - 2-25 - 0.01 - 0’19 - 3.08 +0*31 + 0.37 + 0-55 - 4.07 - 0.53 - 2-05 - 5.05 +0*79 + 0.53 + 0.79 + 037 + 0.35 - 0.88 - 1.80 With reference to the case in the table in which Mr. Adams and the President were jointly concerned, they both analysed the milk when fresh with closely concordant result. After an interval of a fortnight tho speaker analysed his portion again, and found a loss which, even after making the Somerset House correction, amounted to - 2-05 per cent., while Mr. Adams’ portion had undergone comparatively little change. The President’s portion was transferred to another bottle during the fortnight, and when analysed the second time had a pleasant beer-like odour, having evidently undergone alcoholic fermentation.This fact would account for the great loss in the solids, and if a fall of 2.05 per cent. can occur in a fortnight, why not a loss of 4.07 per cent. in a month, as in Mr. Estcourt’s case ? * Where results in the table were bracketed together, they were obtained by analysis of the same milk at different ages, except in the w e of Dr. Vieth’s samples, where * Since the meeting the sample in question has been again analysed, and at an age of 33 days has sustained a loss of 558 per cent. of total solids, which leayes a Somerset House error of - 6.03 !232 THE ANALYST. ~~~ ~ the difference in the rate of decomposition, which was unusually rapid, was apparently due simply to the difference in temperature, one portion of the milk being kept at 10-15’ c.and the other at 19-21“ C. In the case of Mr. Adams’ samples, the solids in the fresh milk were determined in duplicate. After 34 days the samples were sent to Somerset House, where the referees kept them another three weeks before reporting. Hence the age given (47 days) was the mean between 34 and 60, at which latter age the certificates were issued by Dr. Be11 and his colleagues. In two cases the Somerset House error was more than twice aa great as in two others, but in all cases the error was too large to be tolerated. It was quite possible that in some cases the errors in the analyses of Dr. Bell were increased by the difficulty of taking a fair sample of the curdled milk, and the same objection applied to all such analyses of decomposed milk, as usually made.He was, therefore, instituting a series of experiments in the following manner :-5 C.C. quantities of milk of known specific gravity were placed in a series of test tubes, which were then duly closed and preserved. One of these was every week opened, the contents com- pletely removed to a dish, evaporated, and the residue weighed. A series of twelve tubes would enable him to examine the rate of decomposition of a sample during three months, with a minimum of labour. Doubtless one of the great difficulties in interpreting the results yielded by decom- posed milk was the various kinds of fermentation which could occur, and the im- possibility of predicting which of these would occur or predominate.As a rule, the h t i c fermentation proceeded most actively, but it was almost always complicated with alcoholic and butyric fermentations. These latter formed volatile products, and hence a great diminution of the total solids, but such facts did not prevent the Somerset House chemists from applying their constant allowance to a milk which they analysed when eighty days old, and which was stated in their certificate to be in “an advanced state of decomposition, having gone beyond the lactic fermentation ” (ANALYST, i., 75). Notwithstanding this, however, by a happy coincidence the solids thus corrected differed only by 0.01 per cent. from the determination made by Nr. Jones on the fresh milk- an agreement which, under the circumstances, !peaks as eloquently against the value of the allowance as do the enormous discrepancies in other cases.Mr. ADAMS said one of the greatest dirsculties in dealing with sour milk was the sampling. He would like to ask Mr. Stokes whether he accounted for the monstrous difference between 2.38 per cent. of fat and 1.74 per cent. in the sour milk by that dsculty. He himself had had much trouble in dealing with sour samples; do what he might, he found that the fat would adhere to the vessel or else distribute itself unequally --in lumps- through the sample. Referring to the preservation by ammonia which he formerly brought before the Society, he had had some results which led him to infer that the ammonia caused fat to separate from the solids not fat. After further experiments he had found that the temperature of an ammoniated milk should be raised to about looo F., and the sample then vigorously shaken, when the fat should become equally distributed, so that he was now more in favour of preserving samples by ammonia than he had been some time since.Referring to a case mentioned by the President, he had analysed the same milk on the same day, and found the loss to be only -69. He thought that was an important point, as it showed that the same milk kept in two laboratories might change in a per- fectly different manner. His original analysis was 11 *82 ; Mr. Allen’s, 11 -75 After 15 days 11-13 77 11.51 Loss -69 27 024THE ANALYST. 233 He had some other samples of exactly the same age, and kept under the same con- ditions, the loss in these being -45 and -96.Dr. VIETH said the question of allowance ought to be disposed of without much dis- cussion. There was no possibility of calculating the decomposition which might occur in a sample of milk. The question had, however, been raised in a quarter which public analysts could not ignore, and even if they could kill the question, ways and means would be found to bring it back again. As Dr. Bell stated in his book that he had based his allowance on practical experiments, he thought it was very well that Mr. Stokes’ experiments should be brought before the Society, to show the fallacy of Dr. Bell’s assumption. He made some experiments four or five years ago, but thought they would scarcely bear on the question, as he worked them in a different way.He divided a sample of milk on platinum capsules, put 5 C.C. on 10 capsules, kept 5 of them in the laboratory, and five others in an ice safe, and weighed them at intervals, and found a reduction took place. However, he did not think those experiments bore on the keeping of milks in the hands of analysts. He did not believe in the President’s suggestion of taking the total solids only, because he thought it was impossible to redistribute the fat after it had been standing for any length of time; the only way would be, to warm the milk, which again would curdle it and make it impossible to redistribute the casein. According to the advertisements at shows of glacialine and other similar things, he must take it that they are very largely used, and in London it was rather difficult to buy a milk from a dealer which did not contain any preservative, and, of course, those milks did not decompose so quickly.Decomposition was due to the milk-sugar, which, very curiously to note, might de- compose in two Werent mays, either by splitting up into lactic acid, or into alcohol. Dr. VIETH gave some instances of each. Mr. LLOYD, Chemist to the Dairy Farmers’ Association, said he wati glad to be able to say a few words on the paper, which was not only of much interest to him, but was of double importance to him because he had a large number of samples sent him from farmers which are turned, and they wanted to know if they were genuine, and, on the other hand, he had a number of samples which were still sweet when reported upon.He thought Mr. Stokes had opened up a subject which could not be allowed to rest until something more definite had been obtained. R e would like to know whether the samples had been preserved in absolutely tight bottles, because if not there might be entirely different changes taking place and resulting in the enormous loss and forming butyric acid, but if the milk is preserved in a tight bottle and butyric acid is formed, then the bottle must be broken. Dr. Vieth had said that alcoholic fermentation did not take place in milk except under certain circumstances. Subsequently the lactic acid might be split up into butyric acid, and then the bottle would burst. I f the bottle were not tight then there would be such losses as Mr.Stokes gave in No. 19. They had to remember that the samples sent to Somerset House ought to be in tight bottles, and therefore they must put aside this butyric acid and the possibility of its having taken place. As regards artificial heating, he had tried all temperatures up to boiling point, and he had found that there was a material difference in the change which took place. If they could only settle tohe question of preservation in a manner which could be carried out by inspectors, it would put aside thig question of allowance. One result he had obtained might throw some light on the matter. In all his experiments where the bottles had corks his results were all right, but when they were not well corked he obtained very different results. One other important consideration he would mention, vie., as to the opening of the234 THE ANALYST.bottles once or twice. They all knew how important the opening of bottles was, causing changes which would never have taken place had the bottle not been opened. It had bean laid down experimentally that the milk-sugar split up into two molecules of lactic acid, consequently, there should theoretically be no loss. After a large number of experiments he had found in only two cases the milk had not undergone any material loss although lactic acid had been formed; the loss in total solids was -02 and 007. Other samples he had kept One for '7 days, on which the loss was *38; lactic acid, 1.11. Another for 14 ,, 99 9, -42 ,, ,, 1-19. He had taken a large number of samples from 14 days to 40 weeks, and he found, whatever the loss might be (and he had obtained losses from 057 up to 1.20 per cent. on the total solids), the lactic acid was 1.17 and 2.14. Taking these figures, they represented approximately that the loss is almost exactly half of the total amount of lactic acid present in the milk. If fermentation has taken place, that did not hold good for a moment. He had not been able to explain the chemical changes which produced this loss, but if they considered that the ferment was living upon the nitrogenous organic matter in the milk, they should assume that the amount of nitrogen consumed should be in proportion, and consequently if nitrogenous gases were formed during that fermentation the loss would be in proportion to the amount of lactic acid. He trusted the idea might lead other members who are interested in the subject to make experiments in a similar way. Mr. CASSAL said he should like to point out that, as a practical Society, they had almost written enough, and they ought now to take some practical action similar to that the President wa8 taking. The results obtained by Mr. Stokes were, no doubt, valuable, but we ought to demonstrate to the public that the Somerset House analysts had assumed a position which they had no right to assume. Mr. ALLEN, in concluding the discussion, said that one of the samples he referred to smelt like butter, which would probably account for the low results. Dr. Bell made two extraordinary admissions in his letter, and if they could only induce him to write a few more letters they would have nothing to answer.

ISSN:0003-2654    

DOI:10.1039/AN8871200226

出版商:RSC    

年代:1887

数据来源: RSC

摘要:

234 THE ANALYST. THE SUBSTITUTION OF ASBESTOS CLOTH FOR BLOTTING PAPER I N MR. ADAMS’ MODIFICATION OF MR. ABRAHAM’S PROCESS OF MILK ANALYSIS. BY DR. W. JOHNSTONE. ( R e d at tlte Meeting, November 9th, 1887.) MR. PRESIDENT AND GENTLEMEN,-In appearing before you this evening 1 must at once apologise for having practically, so to speak, no paper to bring before you, as the subject of milk analysis has been so often before the Society. However, I am sure you will accept my apology, when I tell you that the information I intended to communicate to you this evening is already in your hands, viz., 6‘ The Substitution of Asbestos Cloth for Blotting paper in Mr. Adams’ modification of Mr. Abrahams’ process of Milk Analysis.” The following figures represent the results obtained from samples of milk analysed in my laboratory in the ordinary course, and therefore not selected for the occasion.THE ANALYST.235 Specific Gravity. Total Solids. Fat Found. Fat Calculated. 1029.4 11*810 11.821 3.244 3.143 3.465 1030.3 12.417 12.411 3.433 3.402 3.780 1031.2 12.350 12.324 3950 3.270 3.508 1031.7 18-870 12-820 3.598 3.632 3.810 1029.4 11.97 11.94 3.260 3.248 3.408 1033.8 11.60 11.65 1.630 1.627 1036.2 10.81 10.82 0.740 0.752 The specific gravity was carefully taken at 60° F. and the total solids obtained in duplicate from about 5 grms. of milk. The fat was extracted from the residue of about 10 grms. of milk by ether in an ordinary Soxhlst’s tube, the milk taken having been absorbed by a coil of asbestos cloth 12 inches long by 2& wide and thoroughly dried previous to commencing the extraction. (Here is one of the coils.) The advantage to be obtained in the use of asbestos cloth, is that, after having been thoroughly ignited, the operator has a material of great porosity, which is absolutely insoluble in ether, and therefore can yield no ethereal extract what- ever. It is therefore a very suitable material t o use in extracting the fat from a milk residue, as the size of coil mentioned easily and rapidly absorbs 10 grms. of milk, and when dry the fat is readily extracted from the thin film of the milk residue distributed on the asbestos. Another advantage is that the coils can be used an indefinite number of times ; all that is required to be done, is simply to burn off the milk residue, allow them to cool, when they are again ready for use. Conclzcgion of the Societds Proceedings.

ISSN:0003-2654    

DOI:10.1039/AN8871200234

出版商:RSC    

年代:1887

数据来源: RSC

摘要:

THE ANALYST. 235 ON REICHERT-MEISSL'S METHOD OF BUTTER ANALYSIS, AND ITS APPLICATION FOR THE EXAMINATION OF BUTTER AND BUTTER SUBSTITUTES. BY DR. RUDOLF WOLLNY. (Continued fvom page 210.) The following arrangement was devised to take the requisite volume of alkali from the bottle without risk of absorption of carbonic acid. One aperture of a WoulfF's bottle carries through a cork a glass tube, 2 c.m. in width and 5 c.m. in length, filled with soda- lime. Through the other aperture of the bottle (capacity about 1 litre) goes a glaw tube through a cork to the bottom of the bottle. The upper end of this tube is joined by means of a narrow india-rubber tube, which carries a pinchcock, with the lower end of an ordinary burette, into which, near its lower end, a side tube has been blown, carrying a pinch-cock, india-rubber tube, and a glass nozzle.The upper end of the burette carries a soda-lime tube. The whole arrangement is firmly joined together by means of a board. The burette is filled by sucking at the upper soda-lime tube, whilst the pinohcock at the pipe which communicates with the bottle is opened. Soda solution, which is made and kept as described, furnishes from 3 c.c., no more volatile acid than will neutralise -2 to 03 C.C. deci-normal solution. It was next necessary to prevent absorption of carbonic acid during saponification. This could have been readily managed by saponifying in a corked flask carrying a suffi-236 THE ANALYST. ciently long glass tube, the upper end of which is bent downward; through this, the alcohol vapours could escape, whilst carbonic acid could not enter.The strong odoun of butyric ether which is always observed when butter is saponified, however, proves that she Reichert-Meissl method has a second source of error, butyric acid being lost when alcoholic potash is used. (Note by Translator.-This has long been pointed out by Hehner, Allen, Wanklyn and others.) As butyric ether is decomposed by heating with alcoholic potash, it seemed advisable to heat the mixture for some time under a reflux condenser. The following experiments will show that in this manner the ether is completely decomposed, and the butyric acid retained. Experiment 102.-5 grms. butter were saponified with 3 C.C. NaHO and 6 C.C. alcohol in a flask connected with an ordinary condenser, the alcohol being distilled into a second flask.The soap dissolved in 100 C.C. water, and distilled with 40 C.C. H,SO, (1 : lo), required for 110 C.C. distillate 27.86 C.C. deci-normal solution. was heated with 3 C.C. NaHO under reaux condenser for half an hour. then distilled off, the residue diluted with water, and distilled with H,SO, as above. 100 C.C. distillate required -69 C.C. deci solution. Experiment 104.-5 grms. of the same butter were heated with NaHO, and alcohol in the same proportions as in 103 for half an hour under reflux condenser. 110 C.C. of the soap distillate required 28.52 C.C. deci-solution, that is, the sum of the quantities used in 102 and 103. In other similar experiments, a quantity of butyric ether was obtained which neutralised respectively -2, '2, -4, '9, 1.5, and 1.7 C.C.deci-solution, the amount of ether being the larger the greater the volume of NaHO and alcohol. The two chief sources of error of the Reichert-Meissl method are therefore a loss of butyric ether, and a gain by absorption of carbonic acid, and from what has been said, it follows that the saponification must be carried out under a reflux condenser, that the alcohol must be distilled off from the closed flask, and that the soap must be dissolved in water, also in a closed flask. I have devised the following arrangement in order to combine these various operations in a convenient manner. A condenser slanting upward at an angle of 45O is fixed near the water-bath upon which the saponification is to take place. The flask is connected with the condenser by means of a T-piece and india-rubber tubes, so that the leg of the T-piece can be directed upward or downward as desired.During saponifi- cation, which should take half an hour on the boiling water-bath, the leg of the T-piece is directed upward, being closed with a short piece of india-rubber and glass-rod. The alcohol in this manner runs back into the flask. After that time the T-piece is turned downward and opened : the alcohol can thus be collected in a flask standing beneath. After twenty minutes, when distillation is complete, the T-piece is again turned up- wards, and through it 100 C.C. of boiling water are run into the flask by means of a pipette being tightly joined to the short piece of india-rubber. The T-piece is closed again until the soap is completely dissolved in the water, solution being assisted by gently Experiment 103.-The distillate obtained in 102 smelling strongly of butyric ethei The alcohol waTHE ANALYST; 237 shaking the flask.The flask is then taken off the water-bath, its contents cooled under the water-tap to 5O-6OQ (not lower), 40 C.C. HzSO,, and a few pieces of pumice are added, 110 C.C. distilled off, filtered, and 100 C.C. titrated with deci-normal baryta water, phenol-phthaleine being the indicator. I prefer baryta to alkali solution, because with it the change of colour is somewhat sharper, although the colouration produced is rather pink than purple. Baryta has also the advantage that it at once indicates if accident- ally some sulphuric acid has been mechanically carried over into the distillate. The baryta solution should be kept in a Woulff’s bottle precisely as the 50 per cent. soda solution previously referred to. A few blank experiments should be made, and the small quantity of volatile acid obtained subtracted from the figures yielded by fats. The nozzle of the soda burette must, previous to each experiment, be wiped clean from any carbonate, and the first few drops which issue must be rejected. The alcohol must not be blown into the flask by means of the pipette; no respired air must be allowed to enter ; all vessels used must be absolutely clean and neutral. (To be continued.)

ISSN:0003-2654    

DOI:10.1039/AN8871200235

出版商:RSC    

年代:1887

数据来源: RSC

摘要:

THE ANALYST; 237 E8TIMATION OF POTASSIC BITARTRATE I N WINE-YEAST AND CRUDE CREAM OF TARTAR. BY ARTHUR BORNTRAGER.* Two processes are m x t commonly used : The direct titration with standard soda and Riihrig’s process a la Camerole. THE DIRECT ESTIMATION. This process has been often objected to because the tartar often contains other bodies of an acid nature, which are even sometimes fraudulently added, to deceivo the analyst. Warington, who has thoroughly investigated the process, often obtained results in excem of what was expected from the amount of potash. THE METHOD t3 la Casserok. I was not able to get the original paper, and therefore had to be content with consulting some abstracts, which did not, however, well agree with one another. According to one abstract 50 grammes of the coarsely powdered tartar must be boiled for ten minutes with one litre of water, The fluid must then be at once poured off, and after standing for twelve hours at normal temperature, the crystals must be washed with cold water, then dried and weighed.According to another abstract, 50 p m m e s of the crude tartar are boiled for ten minutes with 1250 C.C. of water, the fluid allowed to stand for two minutes, and then carefully decanted from any insoluble matter. After standing for six hours the crystals are collected, and then three times washed with cold water, using altogether one litre of washwater. In analysing yeast, the hot liquid should be poured through a fine sieve. As by this process the crystallisable matter is simply weighed and considered to be pure potassic bitartrate, it must in many cases only be a crude approximation. An allowance is made for solubility of the bitartrate They are then dried and weighed.~~~~ ~~~ ~ * Hepert. Anal, Chemie, 37,87,238 THE ANALYST. in the mother liquor, but the amount varies considerably with the temperature. To practically ascertain the amount dissolved, the easiest plan is to make an experiment side by side with pure cream of tartar. Boil a sufficiency of pure potassic bitartrate with about 100 parts of water for ten minutes, let crystallise, and by means of standard soda estimate the amount of the salt retained in one litre. We then know how much to allow in our analysis of the crude sample. The following example will show the necessity of making a proper allowance. Suppose the crystallisation took place at a temperature of 28.29 deg.C., the amount of potassic bitartrate contained in the 1000 C.C. mother liquor will be no less than 8-54 grammes; whilst if the temperature had gone down to 11-5-13.5 degs. C., only 4.1 grammes will be retained. It therefore is not fair to simply make an allowance of 10 per cent., as some analysts are in the habit of doing. An improvement in the process consists in washing the crystals with a cold saturated solution of pure cream of tartar instead of plain water. But a great source of error is caused by calcic tartrate. According to various authorities, neutral calcic tartrate is soluble in 300-400 parts of boiling water ; but it is much more freely soluble in solution of cream of tartar.The greater part of the calcic tartrate must, therefore, crystallise out with the cream of tartar and make the rendemnt too high, unless the crystals are subjected to further analysis. The potassic bitartrate I used consisted of a once recrystallised cream of tartar, which contained but unweighable traces of lime, sulphates, and chlorides. To make perfectly sure 2.5 grammes were titrated with normal soda, and took 13.5 c.c., whilst the ash of another 2.5 grammes, when titrated with semi-normal sulphuric acid, also took 13.5 c.c., which proved the perfect purity of the salt. I now made fhe following ezperiments :- I now prepared pure calcic tartrate as follows :- A clear solution of pure Rochelle salts was precipitated with a perfectly pure and carefully neutralised solution of calcic chloride.The precipitate which soon became crystalline was first washed with water until free from chlorine, then with alcohol, finally with ether, and dried at 50-60 deg. C. To test the purity of the salt, two grammes were ignited (once with addition of a little pure sugar) before the blowpipe, and I obtained 15.56 and 15-55 per cent. calcium. The percentage calculated from the formula CaC4H40,4H,0 is 15.38. By my oxalic acid process (Zeitschr f. Anal. Chemie, 1887) I got 57.59 per cent. tartaric acid, theory requiring 57.69 per cent. 50 grammes of the pure cream of tartar were boiled, with and without addition of 5 grammes of the pure calcic tartrate, in a porcelain dish with 1100 C.C. hot water, for ten minutes. After standing at rest for two minutes, the liquid was decanted, and the residue was three times boiled with 50 C.C.of water, which liquids were added to the chief mother liquor. Ths liquid a s allowed to stand over night, was then filtered off (filter and basin were weighed together), and the deposit dried, and weighed. The crystals in the experiment with the mixed tartrates were slightly washed with some of the mother liquor of the other. The amount of potassic bitartrate in the mother liquor was now estimated with normal soda. The crystals obtained from the mixed tartrates were analysed as follows :-THE ANALYEIT. 239 Ualcic tartrate used, The acid tartrate was estimated by dissolving 2.5 grammes and titrating with normal soda, To estimate the calcium, 5 grammes were incinerated, and the char exhausted with water.The residue was then burnt to white ash anddissolved in hydro- chloric acid. The acid was mixed with the watery solution and, after boiling the calcium, was estimated by precipitation with ammonia and ammonic oxalate, and finally weighed as oxide. In every experiment with pure potassic bitartrate the sum of the weight of the crystals plus the allowance came very close to the quantity originally taken, but when 5 grammes of calcic tartrate had been added the results were far too high. Accurate results were of course obtained by titrating the actual amount of potassic bitartrate in the crystals with normal soda. If to the quantity so obtained is added the weight of the calcic tartrate calculated from the calcium, the weight exceeds the original weight taken.Calcic tartrate readily parts with a considerable amount of its water of crystallisation at a temperature of 100 deg. C. TABLE I. This is caused by the drying. Weight of Crystals. None. 5 None. 5 None. 99 9 , 9 , 5 None. 5 45.3 44.3 48.5 44.5 49.2 44.4 44.4 45.3 49.1 45.0 48.7 Pure bitartrate therein contained. 45-3 44.3 44.2 44.5 45.4 44.4 44.4 45.3 45.4 48.0 44.5 Calcium found. -6997 06612 *6039 -6925 Crystallised Jalcic tartrate 4.5481 4.29’78 3.926 45013 Allowance bitartrate. 4.7 1 5.61 5-66 5.3 3 4-78 5*31 8-43 4.69 4.50 5-01 5.44 From this table it is plain the results obtained by the camerole are much too high. It has been argued this does not matter much, as the calcic tartrate is also a valuable pro- duct; but still, it contains only 67-69 per cent.of tartaric acid, whilst the bitartrate contains 79.79 per cent., and for many purposes we want to know the percentage of real potassic bitartrate. I now felt anxious to know how a mixture of cream of tartar and gypsum would behave in the crystallisation process. I therefore made a similar experiment as before, using 50 grammes of the pure bitartrate, and also 50 grammes of the same, mixed with 6-5 grammes of gypsum. In the blank experiment I obtained 42.85 grammes of crystals, and the mother liquor had retained 6.93 grammes. In the mixture I got 41.80 grammes of crystals, which were analysed as follows :-- They required 12 C.C. equivalent to 2.2541 potassic bitartrate. The total rtmount was) there- fore, 37-69 gramrnes=30.08 gramrnes tartaric wid, 2-5 grammes were dissolved in hot water, and titrated with normal soda,240 THE ANALYST.2.5 grammes were boiled under upright condenser with 30 C.C. water and 10 C.C. of a 20 per cent. solution of potassic carbonate for one hour. After cooling, the liquid was made up to 100.5 C.C. 50 C.C. of this were evaporated to 10 c.c., mixed first with 2 C.C. of glacial acetic acid, and after five minutes, with 100 C.C. of 98 per cent. alcohol. After standing over night, the deposit was filtered off, washed with alcohol, then redissolved in hot water, and titrated with normal soda. Used 6.48 C.C. =*9705 gramme tartaric acid in 1.25 of the salt, a total 32-45 grammes tartaric acid. 5 grammes of the salt were carefully charred, the mass extracted with water, and the residue burnt to ash.The ash was treated with hydrochloric acid, which was now added to the watery extract. After filtering, the sulphuric acid was, as usual, precipitated with baric chloride. I obtained -0200 gramme BaSO,= -0148 CaSO$H,O or *1237 in the crystals. As the crystals contained 32.45 grammes of tartaric acid, of which 30.08 grammes existed as potassic bitartrate, 2.37 grammes must be present as lime compound. The composition of the crystals was, therefore-- 37.69 potassic bitartrate 4.1 1 calcic tartrate crystallised -1 2 calcic sulphate crystallised -- 41.92 The residue insoluble in boiling water was nicely crystalline, and looked like pure calcic tartrate, which it nearly proved to be on analysis. The mother liquor had a much stronger acid reaction than the one got in the experiment without the gypsum. The total acidity was equal to 8.38 grammee tartaric acid, showing the presence of free acid.This was tartaric, and not sulphuric, acid; then it gave no blue colour with dimethylaniline violet. The reaction between the cream of tartar and the gypsum seems to be- 2 KC4H406 + CaSO,= K2S04 + CaC,H,06 + C4H606. The presence of plaster, therefore, considerably affects the rendement of the crystals, and renders the process inaccurate. INDIRECT PROCESSES. Several processes have come to my notice, which were originally recommended for tartars only, but have also been applied to wine yeast. Ten grms. of the substance are incinerated, and the char extracted with water. The solution is evaporated to dryness, and the salts (potwic carbonate) calculated to potawic bitartrate ; or, instead of merely weighing, the alkalinity of the ash may be taken with normal acid and then calculated to cream of tartar ; or the potash may be determined with platinic chloride.None of these methods will be always successful when the yeast is in a decomposed state, or when the tartar contains much gypsum, or when fraudulent additions have been made. The potassic carbonate formed during the incineration of the sample will act on the gypsum and form calcic carbonate and potassic sulphate. The result obtained by the titration with acid must, therefore, be too low, but this may be remedied by estimating the sdphate of potash and calculating this also to the bitartmte, but the process then becomes rather tedious.According to Warington a certain portion of the sulphate is, during theTHE ANALYST. 241 charring, reduced to sulphide. This may be remedied by first treating the char with a little hydrogen peroxide, but this is no longer practicable when the tartars or yeast con- tain free sulphur, which is sometimes sprinkled on the grapes. As, however, calcic sulphide, on heating with potassic carbonate, yields calcic carbonate and potassic sulphide (which is as alkaline as the carbonate) I cannot see how the reduction of the sulphate can influence the result of the titration. On applying the titration process to materials in a state of decomposition, it is as well to make an estimation of the carbonic acid in the original sample, but it is difficult to decide how this acid is distributed.between the potash and the lime. Oliveri estimates the cream of tartar in yeasts as follows:- 10 grms. of the sample are digested with 40 C.C. of water and 5 C.C. fuming hydrochloric acid for 24 hours, then filtered off, and titrated with standard baric chloride. The sul- phuric acid thus found is calculated to calcic sulphate. The liquid is now filtered from the baric sulphate and divided into two equal parts. Part a is made alkaline with am- monia, and precipitated with ammonic oxalate, to get the lime; part b is first nearly neutralised with caustic soda, then mixed with slight excess of ammonia, and then pre- cipitated with calcic chloride. The calcic tartrate is not weighed as such, but ignited, and then converted into sulphate.Any lime not existing as sulphate is supposed to exist as tartrate, and the balance of tartaric acid is calculated to potassic bitartrate. The process is fairly good, but it is perfectly useless if salts of sorrel, Epsom salts, potassic sulphate, or calcic carbonate have been added. DIRECT PROCESSES OF RECENT DATE. Kammer neutralises 2 pms. of yeast, or tartar, with caustic soda. To prevent the tartar dissolving any calcic carbonate, the neutralisation must be done in the cold. The whole is now made up to 101 C.C. (1 C.C. being occupied by the insoluble matter) and filtered. I n 50 C.C. the total tartaric acid is now estimated as follows :-The fluid is evaporated to a low bulk, and then mixed with acetic acid and alcohol. The precipitate is washed with a 5 per cent.solution of potassic chloride saturated with pure cream of tartar. After washing the precipitate is dissolved in hot water and titrated with semi- normal soda. About this process I want to make the following remarks : The neutrali- sation of the acid tartrate in the cold is a very slow operation. It took me half an hour to dissolve 2 grms. of finely powdered tartrate in 30 C.C. of water by means of normal alkali. The choice of potassic chloride as washing fluid seems to me to be an unfortunate one, and the washing may just as well be done with alcohol. Then, again, the cold neutralisation will not altogether prevent the acid tartrate from acting on any calcic carbonate which may be present. The makers of cream of tartar, however, only care to know how much pure acid tartrate may be obtained by re-crystallisation of the crude product, and cannot prevent the acid tartrate acting on any calcic carbonate.To them the process must be in many cases useless. As calcic tartrate is soluble in solution of neutral alkaline tartrates I thought it advisable to ascertain whether in Kammer’s process any calcic tartrate passes in solution and may interfere with the result. I therefore neutralised a very finely powdered mixture of 2 grms. of chemically pure cream of tartar and half a grm. of2#2 THE ANALYST. cryshllised calcic tartmte suspended in 30 C.C. of water with normal potash. This took half an hour in the cold. I now made up to 100.5 c.c., filtered off and evaporated SO C.O. of the filtrate down to 10 C.C.; 2 C.C. of glacial acetic acid were now added, and after five minutes vigorous stirring, 100 C.C. of 98 per cent. alcohol. After standing over night the precipitate was filtered off, washed with the said alcohol, dissolved in boiling water, and at once titrated with normal soda. I used 5.33 C.C. instead of 5.32 = 100.18 per cent. acid tartrate. The presenue of even 20 per cent. crystallised caloic tartrate does not therefore interfere with the estimation, notwithstanding a little calcic tartrate pasms in solution. I now tried the process with a mixture of cream of tartar and gypsum. Two pins. of pure bitartrate and *3 grm. of gypsum mixed with 30 C.C. of water were neutralised in the cold with normal soda, which operation took about 40 minutes. The liquid was made up to 100.6 c.c., and filtered off, when 50 C.C.of the filtrate was treated as described. Used 4-67-4069 C.C. normal soda = 87.98 per cent. potassio bitar- trate. The presence of 13 per cent. of gypsum (yeasts often contain as much), there- fore, seriously affects the accuracy of the process. F. KLEIN’S PROCESS. This process, which is a great improvement on the others, is based on the slight solubility of cream of tartar in solution of potassic chloride. It has the advantage of being the best process from a manufacturer’s point of view. 1.8-2-2 grms. of the sample are boiled 5 times with distilled water, and the residue washed on a filter with boiling water, until every trace of acidity is removed. The filtrate is evaporated down to 40 c.c., when 5 ems. of potassic chloride are intro- duced. After vigorous stirring for 15 minutes, the precipitate is filtered off, washed with a 10 per cent. solution of potassic chloride (saturated with cream of tartar) and then titrated with normal soda. (To be continued.) 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ISSN:0003-2654    

DOI:10.1039/AN8871200237

出版商:RSC    

年代:1887

数据来源: RSC