MILK 



343 



sides of the bottle should carefully be washed down by the fresh ether. 

 Finally, the pipette is rinsed with a little ether. The evaporating dish with 

 contents is now placed on a safety water-bath and the ether evaporated. 

 The drying is continued in a hot-air oven at a temperature below iooC. and 

 finally completed in a desiccator to constant weight 



CrolTs modification consists of subsequent repeated extraction of the end- 

 product of evaporation with absolute ether. The combined extracts are filtered 

 and the small filter paper is washed repeatedly 

 with absolute ether. The combined extracts 

 and washings are evaporated and dried as 

 before and then weighed. 



The piece of apparatus shown hi Fig. 112, 

 above was also devised by Croll to do away 

 with the use of the pipette. 1 On closing the 

 top with a finger and blowing into the mouth- 

 piece, the upper stratum is forced out into the 

 dish. The bottle is washed by simply pouring 

 the ether into the tube. This lessens the 

 possibility of accidental loss. 



The accuracy of the method compared with 

 that of the Soxhlet method, using the paper- 

 coil modification and extracting until fresh 

 portions of absolute ether gave no further 

 trace of extr active material, is shown by the 

 average diffe rence on twelvesamples of human 

 milk being only 0.017 per cent less than by the 

 Soxhlet and on seven samples cow's milk being 

 only 0.019 per cent less. The extreme differ- 

 ences in case of the human milk were 0.004 

 per cent and 0.044 P er cen t ^d m case f 

 the cow's milk 0.006 per cent and 0.068 

 per cent. 



(c) Adams' Paper-coil Method. Introduce 

 about 5 c.c. of milk into a small beaker, quickly 

 ascertain the weight to centigrams, stand a 

 fat-free coil 2 in the beaker and incline the vessel 

 and rotate the coil in order to hasten the absorp- 

 tion of the milk. Immediately upon the com- 

 plete absorption of the milk remove the coil and again quickly ascertain the 

 weight of the beaker. The difference in the weights of the beaker at the two 

 weighings represents the quantity of milk absorbed by the coil. Dry the coil 

 carefully at a temperature below iooC. and extract it with ether for 3-5 hours 

 in a Soxhlet apparatus (Fig. 113). Using a safety water-bath, heat the flask 

 containing the fat to constant weight at a temperature below iooC. 



Calculation. Divide the weight of fat, in grams, by the weight of milk, in 

 grams. The quotient multiplied by 100 is the percentage of fat contained in the 

 milk examined. 



1 If desired a cork with two tubes may be substituted for this somewhat complicated 

 apparatus. 



2 Very satisfactory coils are manufactured by Schleicher and Schull. 



FIG. 112. CROLL'S FAT 

 APPARATUS 



