240 THE ANALYST. T H E C O M P O S I T I O N O F M I L K . BY H. DROOP RICHMOND, F.I.C. (Read at the iWeetiizg, May 7, 1902.) -.?Wean Composition during 1901. -Of the 37,662 samples examined in the Aylesbury Dairy Company's Laboratory during 1901,32,635 were analyses of milk. The com- position of 13,936 received from the farms is given in Table I. TABLE I. Average Composition of Milk during 1901. 1 Morning Milk. -- January .., February.. . March ... April ... May ... June ... July ... August . . , September October ... November December -- A v e r a g e Gravity. 1 *0328 1.0328 1.0326 1.0323 1.0326 1.0326 1.0319 1.0319 1.0321 1.0321 1.0321 1.0322 1.0323 Total Solids. 12-58 12.58 12'49 12.38 12.25 12.25 12.17 12-27 12-47 12-58 12'74 12-75 Fat. 3-52 3.54 3'50 3-46 3-29 3-31 3 41 3-47 3.59 3.69 3'82 3.80 Jolids.not- Fat. 9.06 9-04 8.99 8 -92 8-96 8.94 8-76 8.80 8.88 8-89 8-92 8-95 - - Evening Milk. / I Specific Gravity. --- 1-0327 1.0326 1.0325 1.0320 1.0323 1.0320 1.0313 1.0313 1*0317 1.0316 1.0317 1-0319 Total Solids. 12.90 12-94 12.85 12-73 12-70 12-58 12.37 1259 12-59 13.02 13.03 13-13 12.81 Fat. 3.83 3-88 3-85 3-85 3-76 3.70 3.69 3-85 4-03 4.15 4.14 4.18 - Solids- not- Fat. 9.07 9-06 9.00 8.88 8 -94 8-88 8-68 8 '74 8.86 8.87 8 '89 8.95 Average. T- A \ Specific Gravity. 1.0328 1.0327 1,0325 1 -0321 1 -0324 1'0323 1.0316 1-0316 1-0319 1.0318 1 -031 9 1.0320 Total Solids. 12-73 12-74 12-65 12-55 12-47 12'42 12-27 12.43 12-68 12-80 12-89 12.94 Fat. 3.67 3-70 3.66 3'66 352 3 5 1 3'55 3-66 3 '81 3'92 3 '9s 3 '99 Solids- not- Fat. -- 9 '06 9-04 8'99 8-89 8.95 8.91 8 '72 8-77 8.87 8 *88 8-91 8 -95 3-91 I 8.90 I 1.0321 112.631 3-72 I 8.91 The morning and evening milks have been kept separate, and show the usual average difference of 0.3 to 0.4, which has been always previously observed.I n previous years the average percentage of fat has usually shown a slight fall from that found in the previous year; in 1901 there is a distinct rise, the percentage being 3.72 as against 3.64 in 1900. This rise is chiefly due to higher figures in the last four months, which average 0.16 per 'cent. higher than the corresponding months of 1900, the rise in the previous eight months averaging only 0.03 per cent.TRE ANALYST. 241 The cause of this is uncertain, but the fact that the rise in fat percentage is coincident with the establishment of an official standard may indicate that milk- producers are paying more attention to the quality of the milk yielded than formerly. The former experience that the lowest fat occurs in May and June and the highest in the winter months, and that the solids-not-fat are low in July and August, is again repeated.Accuracy of Methods Used.-As in the bulk of the analyses the fat is determined by the Gerber method, I have compared the results with those obtained by the Adams method for fat. In 52 analyses the difference between Adams and Gerber was : In 40 cases, or 76.9 per cent., 0.1 or less ; In 11 cases, or 21.2 per cent., 0.1 to 0.15; and In 1 case, or 1.9 per cent., above 0.15. The mean Gerbar figure was 0.006 per cent. higher than the mean Adams figure.The Proteids of Millc.-In a paper read last year (ANALYST, xxvi., 310) I showed that when the minimum quantity of a mineral acid was added to milk the quantity necessary to just curdle the milk on boiling was practically equal to the amount necessary to replace the sodium by hydrogen in the formula, : As a further confirmation of the view that this is the action that takes place, I determined the casein, ash, lime, and phosphoric acid in a sample of milk, and in the serum obtained by curdling with a minimum quantity of hydrochloric acid at the boiling temperature the figures were : Milk. Serum. Difference. Casein . . . ... ... 3.05 - - Ash ... ... ... 0.79 0.56 0.23 CaO ... ... ... 0.176 0.056 0.120 P,O, ... ... ... 0.232 0.112 0.120 The figures calculated for the removal of Ca and t(Ca,PO,) with each molecule of casein are : Ash ...... ... 0.234 CaO ... ... ... 0.116 P,O, ... ... ... 0.118 The difference between the solids-not-fat after allowance for the ash was 2.91 per cent., and I have constantly found that the quantity of casein removed does not quite coincide with the estimate of the quantity of casein present. I do not propose at present to discuss the significance of this fact. I n the same paper I also mentioned that on filtration through porcelain the casein and albumin were both removed. There is a, possibility that both albuminoids may exist in milk in combination, and the compound may only be split up under the influence of reagents. I t appeared to me that filtration through filter-paper would settle the question. I filtered half a litre of milk kept at 0" C .; three fractions were collected, and it was found that the last fraction, which contained a trace of casein, contained sensibly the same amount of albumin as the portion left on the filter, which was very rich in casein. As it does not appear probable that filtration through242 THE ANALYST. paper would break up a compound, it may be concluded that casein and albumin are not decomposition-products of one albuminoid existing in milk. Attempts were made to ascertain whether any change in the acidity of milk took place when the albumin was coagulated by boiling; a quantity of acid sufficient to curdle the milk at temperatures below the coagulating point of albumin was added to milk, the serum removed, and the acidity estimated before and after boiling.The results showed considerable variation, the reduction of acidity varying from 3.6" to 5.3" in the same milk ; it was, however, found impossible to completely remove the casein, which probably existed in euspension, and was removed on boiling. The casein was estimated as organic phosphoric acid by the method given in '' Dairy Chemistry " (p. 113),':: and the greatest reduction was found where the greatest amount of casein was present, and vice versd. The amounts of casein found would account for the greater portion of the reduction of acidity, and that due to the coagulation of the albumin must be extremely small; as experimental error would bear a large proportion to the absolute amount, it appeared hopeless to attempt quantitative determinations in this way.A series of experiments was carried out to ascertain the strength of casein as an acid. It was oertainly stronger than carbonic acid, as & N. solutions of sodium and potassium carbonate dissolved 1.86 and 1.83 per cent. of casein respectively, the quantity calculated for the replacement of 2H by the alkali in C,,,H,,,N,,SPO,, being 1.84. Boric acid produced in concentrated solution a partial coagulation on boiling, and casein is probably a somewhat stronger acid than boric under these conditions. Organic acids, such as acetic and lactic acids, were distinctly stronger than casein, as nearly the s&me amounts (9 to 10 C.C. normal acid per litre) were re- quired to curdle milk as those of mineral acids (8.6 c.c.).Phosphoric acid was quite anomalous in its behaviour, as about 34 to 35 C.C. were required to curdle milk on boiling. This behaviour of phosphoric acid incidentally shows that milk is neutral to the casein compound which exists in milk, as, were it not so, a mineral acid should liberate phosphoric acid from the phosphates present, and a larger quantity of acid than that required to replace one atom of base for each molecule of casein should be necessary. This, I think, indicates that casein is an acid of the same strength as the second hydroxyl of phosphoric acid, as I have previously shown (Zoc. cit.) that the phosphates of milk are mono- and diphosphates. Composition of Human Milk.-Four samples of human milk were examined. The composition was : Specific gravity ... ... ... ... Sugar (by difference) ... ... Total solids ... ... ... ... Fat ... ... ... ... ... ... Proteids ... ... ... ... ... Ash ... ... ... ... ... ... Zeiss refraction of fat at 35" C. ... ... ... ... ... Sugar (gravimetric as lactose) ... ... ,, (polarized as lactose) ... ... ,, (polarized as sugar, having [.ID 48.7') I. I -0329 11 -45 2.53 6 87 1.77 0.28 51.5" 6-42 11. I1 J. IV. 1.0294 1.0285 - 10.48 i i . 9 0 13.77 2.63 4.00 5-60 6.34 6.06 6.74 1-25 1.62 1.24 0.26 0.22 0.19 - - 53-2" 5.62 - 6-39 - - - - - - * I now find that it is unnecessary to add alkali to the filtra.te from the mercuric nitrate solution before evaporation aiid ignition ; the ash is always strongly alkaline without this.THE ANALYST. 243 The only figures calling for any remark are the sugar estimations. In conjunc- tion with Professor Carter (British Medical Journal, 1898, No. 1) I have shown hhat the sugar of human milk appeared to differ from lactose, and had an [.ID for the anhydrous sugar of 48.7' ; the cupric reducing power is also slightly less than that of lactose. The present figures bear this out.