210 



Journal of Applied Microscopy. 



43oth on account of its own high nutritive 

 value and because a milk rich 

 in fat will generally be rich in 

 other solid constituents as well. The 

 ■determination of fat in milk was until 

 recent years always done gravimetrically, 

 .and therefore required the facilities of 

 •chemical apparatus and expert knowl- 

 edge. During late years a number of dif- 

 ferent practical methods for the estima- 

 tion of fat in milk have, however, been 

 published, most of which give accurate 

 results when properly manipulated. These 

 methods are in general based on the same 

 principle, viz., the addition of one or more 

 reagents which dissolve the non-fatty 

 solid components of the milk and set 

 free the milk fat, which is then separated 

 by centrifugal force, and its volume or 

 weight determined by special devices. 



In this country the so-called Babcock 

 Milk Test,* invented by Dr. S. M. Bab- 

 cock, professor of Agricultural Chemistry 

 <of this University, has been adopted in 

 •preference to other practical milk tests, 

 in creameries and cheese factories as well 

 as in milk laboratories. The cause of the 

 general adoption of this test is doubtless 

 to be found in its simplicity, cheapness, 

 and ease of manipulation. Briefly stated, 

 the test is operated as follows: 17.6 

 cubic centimeters of milk is measured 

 into a special milk-test bottle, an equal 

 -quantity of commercial H^SO^ (specific 

 gravity, about 1.83) is added, and after 

 mixing the two liquids, the test bottle is 

 placed in a centrifugal miachine and 

 whirled for four minutes; hot water is 

 then added to the bottle to bring the fat 

 into graduated narrow neck of the bottle, 

 and after a second whirling of one 

 minute, the per cent, of fat in the milk is 

 read off from the scale of the test bottle. 



A determination of fat in milk by this 

 method takes less than fifteen minutes, 

 and when care is taken in sampling the 

 milk and reading of the result, is accu- 

 rate to within one-tenth of one per cent. 

 Babcock testers are now placed on the 

 market by many manufacturers of dairy 

 supplies and at a remarkably low price, 

 thanks to sharp competition among the 

 manufacturers. The testers are either 

 hand or power (steam or motor) 

 machines and built to hold from two to 

 thirty or more test bottles at a time. The 

 number of revolutions at which they 

 must be run ranges from 800 to 1,200 per 

 minute, according to the diameter of the 

 testers. A very satisfactory six-bottle 

 hand tester, substantially built and with 

 complete outfit, may be bought for $9.00. 



Where milk analyses are made regu- 

 larly and in a considerable number, a 

 special machine like those just described 

 is to be recommended. In many physio- 



•Bul. No. 24, Wisconsin Experiment 

 Station. 



logical laboratories or in case of practic- 

 ing physicians, the number of samples 

 of milk analyzed is, however, small and 

 these come only, occasionally, so as not 

 to warrant the purchase of a new appa- 

 ratus for this special purpose. It 

 occurred to the writer that the small cen- 

 trifuge in use by physicians for the ex- 

 amination of urine, sputum, blood cor- 

 puscles, etc., might also be adapted for 

 milk anlysis by the Babcock method, 

 with proper changes in glassware and 

 quantities of milk and acid measured out. 

 On further examination it was found 

 that the spiral-gear "urinary centri- 

 fuge" manufactured by Bausch & Lomb 

 Optical Co. had already been adapted for 

 milk analysis by the so-called LefCmann 

 & Beam method;** this method is similar 

 to the Babcock test, with the difference 

 that the separation of the fat in the for- 

 mer method is effected by a mixture of 

 acids, a small quantity of amyl and 

 methyl alcohol being added to facilitate 

 the separation.! The apparatus recom- 

 mended for use by this method was found 

 to give correct results also in case of the 

 Babcock method, after some slight modi- 

 fications were introduced. The centri- 

 fuge with pipette and milk-test bottle are 

 shown in the accompanying illustrations. 



Milk Tube. 



Filling Pipette. 



Centnluge. 



The method as worked out by the 

 writer is as follows: Two cubic centi- 

 meters of milk is measured into the test 

 bottles and enough of concentrated sul- 

 phuric acid (specific gravity, 1.84) is 



♦♦Centrifugal Analysis, special catalogue, 

 32 pp. 



tBul. 21, Vermont Experiment Station; 

 Leffmann & Beam, Analysis of Milk and 

 Milk Products, p. 26. 



