EXPERIMENT STATION". 79 



MILK. 



By Dr. E. H. Jenkins. 



During the last two years the Station has been called upon to 

 make a large number of milk-e"xaminations, partly for retail buy- 

 ers and sellers, and partly in the interest of the creameries in the 

 State. Between 200 and 300 complete or partial analyses have 

 been made, but only those are referred to here which are believed 

 to be of general interest.* 



Before entering into the details of the Station work on the 

 subject of milk, we give a brief outline of the composition of 

 that liquid and of the two methods which serve as tests of its 

 quality. 



Chemical Composition of Milk. 



An " average" analysis of milk is as follows : — 



"Water, 87.5 



Fat, - -. 3.5 



Casein and albumin, 4.1 



Milk sugar, - 4.3 



Ash, 0.6 



Solids, 12.5 



100.0 



* Method of Analysis. — As the methods of milk analysis used by chemists, dif- 

 fer somewhat, a brief description of the process employed at this Station is given. 

 Specific gravity is determined in all cases by the Jolly spring balance. Water is 

 determined by drying a weighed quantity of milk, about 1.8 grams, in a weighed 

 •capsule containing 10 or 15 grams of washed and ignited sand, till the weight is 

 constant. The contents of the capsule remaining from this determination are 

 transferred to an extractor and the fat extracted with absolute ether. The fat is 

 finally dried in a steam bath at 100° C. and weighed. Another weighed portion 

 of milk is dried over the water bath in a capsule of thin glass, capsule and milk 

 residue are pulverized and mixed with soda lime and the nitrogen determined in 

 the usual way. " Casein" is reckoned from the amount of nitrogen found, by 

 multiplying by the factor 6.25. This of course includes the albumin and all other 

 nitrogenous matters of the milk. It is only approximately correct, but the results 

 serve for comparing difEerent samples of milk and the method is in general use. 

 The factor 6.4 would no doubt give a closer approximation to the actual amount of 

 nitrogenous matter. 



Milk sugar is determined in 8-10 grams of milk, after removing fat and nitro- 

 genous matters by means of copper sulphate and sodium hydrate — (Fresenius' 

 Zeitschrift, 1878, p. 242) by Tollens' method— (Fres. Zeitschrift, 1879, p. 605.) 

 Ash is estimated by difference only in those cases where all the other ingredients 

 have beeu determined. 



