THE; ANALYST. 89 THE COMPOSITION OF MILK AND MILK PRODUCTS. BY H. DROOP RICHMOPU'D. (Read at the Jfeeti?zy, Mamh 16, 1598.) OF the 35,007 samples analysed during 1897 in the hylesbury Dairy Company's laboratory, 25,762 were samples of milk. The average composition of 12,907 of these, taken on arrival of the inilk from the farms at the depots, is given in Table I. TABLE I.-AVERAGE COMPOSITION OF MILK DURING 1897. January ... February ... March ... April ... June ... August . . . September . . . October ... November ... December ... May ... July ... Average ... Solids- Specific Total Gravity. Solids. Fat. not- Fat. 1-0327 1,0326 1.0325 1.0325 1.0328 1.0325 1.0318 1.0315 1.0321 1.0324 1.0324 1.0325 12-75 3-69 9.06 12.65 3-63 9-02 12.59 3-60 8.99 12.54 3.58 8.96 12.38 3.38 9.00 12-29 3.37 8-92 12.32 3.53 8.79 12.42 3.67 8.75 12.59 3.68 8.91 12.59 3-62 8.97 12.68 3.70 8.98 12-75 3-74 9.01 1-0324 12.54 3-60 8-94 EVENISG MILK.Solids- Specific Total Gravity. Solids. not- Fat. 1.0326 1.0325 1.0324 1.0323 1.0324 1.031.9 1.0314 1.0311 1.0316 1.0321 1.0320 1.0324 1.0320 13.16 1304 12.96 12 93 12-92 12.81 12.68 12.81 13-05 13.04 13.20 13-17 4.07 9.09 3-99 9.05 3-95 9-01 3.93 9.00 3-91 9.01 3.91 8-90 3-92 8-76 4.07 8-74 4.17 8.88 4.06 8-98 4.22 8-98 4.15 9-02 12-98 4.03 8.95 AVERAGE. Specific Gravity. 1.0327 1.0325, 1.0324 1.0324 1-0325 1.0322 1.0316 1.0313 1,0319 1.0323 1-0822 1-0323 Total Solids. 12-95 12.85 12-78 12-73 12-65 12-55 12.50 12.61 12-82 12-81 12.94 12.96 Solids- Fat. not- Fat. 3.88 9'07 3-82 9.03 3-78 9-00 3-75 8.98 3.65 9-00 3-64 8-91 3.73 8-75' 3-87 8.74 3.93 8.89 3.84 8.97 3.96 8.98 3.95 9.01 1.0322 12.76 3.82 8.9490 THE ANALYST.It is seen that the composition differs but very slightly from that found in 1896. As usual, the lowest fat was found in June, and the highest during the latter months of the year, and a marked depression of solids-not-fat was noticed in July and August. The methods used in 1896 have been employed without any modification ; in the few cases where the solids-not-fat fell below 8.5 per cent., milk-sugar, protaids, and ash have been determined. The following samples are the only ones showing any abnormality, and were passed as genuine, though not authenticated : I. 11. 111. Specific gravity ... 1.0294 ... 1.0288 ... 1:0355 Total solids ... 12-63 ... 12.34 .._ 13-63 Fat ...... ... 4.35 ... 4.20 ... 3.80 Sugar ... ... 4.14 ... 4-13 ... 4-67 Proteids ... ... 3-38 ... 3-29 ... 4-35 Ash ... ... 0.76 ... 0-71 ... 0.77 Solids-not-fat 8-28 8.14 ... 9.83 ... ... I have looked through the results of analyses for many years past, and have compiled the following table of the probable number of samples which will be found per 100, having solids-not-fat between the limits named. These figures only refer to the mixed milk of herds : Percentage of Solid s-not-Fat. 8-4 .to 8.5 8.3 ,, 8.4 8.2 ,, 8-3 8.1 ,, 8.2 8.0 f , 8.1 Below 8.0 ... ... ... ... ... Probable Number per 100. ... 1.092 ... 0.242 *.. 0.02'7 ... 0.022 ... 0.008 0.002 I t is seen that the proportion of samples appreciably below 8.5 per cent. i.4 excessively small ; the bulk of these occur during the months of July and August.I am not in possession of sufficient data to say definitely that the few genuine samples with solids-not-fat below 8 5 per cent. can be distinguished from adulterated milks ; but the whole of the samples low in solids-not-fat that I have examined, with whose genuineness I am satisfied (forty-six in all), have had an ash above 0.70 per cent., and nitrogen above 0.50 per cent. On the other hand, all samples to which I have added water have been below those limits, as well as below 895 per cent. of solids- not-f at. I would urge on public analysts the importance of determining the ash and proteids (or nitrogen) on every saniple which, from their preliminary results, they consider suspicious. The preparation of ether for milk analysis has received some attention; the occurrence in commercial ether of an acrid substance, which appears to be obstinately retained by fat, has probably been noticed by all.My first attempts at removing this were by distillation from oil, with a fair amount of success; I have, however, found that by distillation of the ether on a water-bath not exceeding 40" in temperature, from a flask fitted with Glynsky's bulbs, a product is obtained which is eminently satisfactory ; the last fraction (B.P. 34.6" to 34.8") can be used for thermo-regulatorsTHE ANALYST. 91 for incubators, as at 37" to 38" it has a vapour tension of about 24- inches of mercury above atmospheric pressure. I n the analysia of cream and clotted cream amyl alcohol has been substituted for ether to dissolve the f a t ; in this menstruum fat is easily soluble while hot, though it largely deposits on cooling; the other constituents of milk are almost insoluble. A series of comparative experiments showed that no appreciable difference was found between ether and amyl alcohol.Amyl alcohol is readily volatile at 100" in a current of air. The method used is as follows : 4 grammes of cream are weighed into a large platinum dish and evaporated in the water-oven ; after about one hour the solids-not- fat become adherent to the basin, and by inclining it the fat runs away to the lower portion, and the solids-not-fat are left comparatively free from fat. Under these circumstances drying is complete in about five to six hours. To extract the fat 25 C.C.of amyl alcohol are poured on, and the basin placed for a short time in the water- oven ; the amyl alcohol is then carefully decanted ; the solution of fat can be separated without loss of solids-not-fat if attention be paid to the slow decantation. This process is repeated about eight or nine times, the basin being usually allowed to stand overnight between the fourth and fifth treatments. The following experiment will show the results obtained with ether and amyl alcohol : Weight Weight after Four at 100". Hours' Drying. Weight Taken, after Drying Washings and Three Ether 3.9985 ... 2.898 ... 0.246 Amyl alcohol 3.998 ... 2.894 ... 0,2405 Amyl alcohoi ,.. 0.239 . . Weight after Four more Washings and Three Hours' Drying. ... 0.2385 Ether 0.240 ...Weight after Four more Washings and Three Hours' Drying. 0.238 The solids-not-fat are then dried for about three hours at 100" C. and weighed, the fat being found by difference. Determination of the fat by the Werner-Schmid or Leffmann-Beam methods gives results agreeing within the limits of experimental error : Fat bv Difference. 30.60 57-16 51.78 56.73 The solids-not-fat centage df ash. Werner - Schmid. Leff mann-Beam. ... 50.58 ... 50.14 ... 57.20 .. left in the basin on incineration at dull redness give the per- Clotted cream analysed by the method given above yielded the following results : Maximum. Minimum. Average. Total solids ... ... 75.50 ... 55.16 ... 66.64 Fat ... ... ... 67.69 ... 44-29 ... 58-22 Ash ... ... ... 1.11 ... 044 ... 0.70 Solids-not-fat .. ... 11-51 ... 5.68 ... 8.4292 THE ANALYST. The following percentages of water in butter have been found : Maximum. Minimum. Average. English fresh butter . .. 14.64 . . . 11.59 . . . 13.05 ,, salt ,, ... 15.44 ... . 11.50 .. 13.23 French fresh ,, (X) 1'7.82 ... 14-30 ... 15-73 ,, salt ,, . .. 14.84 . . . 9.09 ... 12.73 Danish ,, ,, ... 17.10 ... 8.90 ... 12.58 3 , Y 9 ,, (Y) 16.31 ... 13.08 ... 14.33 Tho English butters were examined within twenty-four hours of churning ; it is seen that there is no appreciable difference between fresh and salt butter. The most notable point is the high percentage of water in French fresh butters; these have been divided into two classes according to the district of origin. Of the X samples no less than 40 per cent.contained above 16 per cent. of water, which has been proposed as a limit, the maximum reaching 17.82, while the average is only just below 16 per cent. Only one sample of series Y contained above 16 per cent. of water, Two samples of Danish salt butter contained above 16 per cent. of water ; on microscopic examination the appearance described by Storch (ANALYST, vol. xxii., p. 197) as '( thick"-ie., the presence of enormous numbers of small water-globules- was noticed. They did not appear at all watery on casual examination, but seemed to be slightly (' overworked "; salt butters containing a lower percentage of water almost invariably look '' wet " if a short period after churning has elapsed. The French fresh butters did not appear '' thick," but had a tendency to break off short, or, in other words, had a low tensile strength. The manufacturers of the X butters have evidently worked out a method for retaining a somewhat large percentage of water, without in any way deteriorating the flavour or keeping qualities; seeing that the same thing occurred in 1895, and to a lesser extent in 1896, I believe I am justified in regarding the extra average per- centage of water (2 per cent.) as an addition.An interesting and difficult question is raised : Is this addition (which may be safely assumed to be commercially successful) to be regarded as an adulteration, seeing that the essential qualities of the butter (flavour, texture, etc.) are not only retained, but manifest themselves in a high degree? I may add that there was no suspicion of adulteration by margarine; the butyro-refractometer results usually fell between 45" and 46" at 35" C., and never appreciably exceeded 46". DISCUSSION. Mr. BEVAN inquired what was regarded as the particular advantage of amyl alcohol over ether in the determination of fat. Unless absolutely pure, it would contain substances boiling at a high temperature, which he doubted very much would be volatile at 100" C., even in a current of air. Mr. L. K. BOSELEY said that it was never suggested that amyl alcohol should be used in a Soxhlet, but merely for extracting the fat from quantities of, say, 100 grammes of butter, the advantage being that it could be boiled in a water-bath without loss. Amy1 alcohol would extract fat much better at a high temperature than ether would at a low one ; and any residual non-volatile substances could be afterwards washed out with ether,