THE ANALYSIS OF MILK. 81 



percentage. Chiefly for the purpose of satisfying this desire, a short 

 description is given in what follows of how an analysis of milk is 

 made. 



Before proceeding to the analysis, the milk is tested in respect of its 

 appearance, smell, taste, and reaction. Its specific gravity is taken at 

 15 C., and it is tested by boiling. The action of rennet on it is also 

 tested and its percentage of cream estimated by allowing it to stand for 

 24 hours at from 12 to 18 C. in a Chevalier cremometer. Further, it is 

 desirable, where possible, to obtain information as to whether the milk is 

 from one cow or from several, whether milking is carried on in the byre 

 from which it has come, twice a day or oftener, and from which milking 

 the milk comes. Particulars with regard to breed, treatment, feeding, 

 age, length of time after calving, general health of the cow, and the method 

 in which the sample has been taken, so as to decide whether the analysis 

 represents correctly the composition of a milk such as should have been 

 obtained under these conditions, should also be obtained. 



When a sample of milk is drawn for analysis, the milk should not 

 only be thoroughly mixed, but should also be brought always to the same 

 temperature, for example, 15 C. 



Determination of the Percentage of Water, or of Total Solids. Into a thin 

 porcelain basin is placed 15 grams of washed, ignited sea-sand which has 

 been treated with hydrochloric acid. The basin with the sand is dried at 

 100 C. till the weight is constant. It is then removed to a desiccator, 

 and, after being cooled, is weighed. About 30 c.c. of milk are then poured 

 into a clean small beaker of about 40 c.c. capacity, and a small glass stirrer 

 which does not reach above the lip of the beaker is added. The beaker is 

 covered with a watch-glass and v/eighed. After removing the watch-glass 

 and stirring the milk with the stirrer about 10 c.c. of the milk are poured 

 over the weighed sand in the porcelain vessel, the watch-glass is again 

 replaced and the beaker weighed. The difference between the two weigh- 

 ings gives the weight of the milk used. This is added to the weight of 

 the vessel containing the sand. Drying is first carried on in the water- 

 bath; the porcelain basin with its contents is then introduced into the 

 drying-bath and dried for 45 minutes at 100 C., and then for 15 minutes 

 at 105 C., cooled in the desiccator and weighed. It is then introduced 

 into the drying-oven for 30 minutes at 100 C., again cooled in the desic- 

 cator, and again weighed. This is repeated until two successive weighings 

 show no greater difference than 1 '5 mg. The loss in weight, subtracted 

 from the original weight, represents the weight of the water driven off, 

 and by subtracting this from the weight of the milk used, the weight of 

 the total solids is obtained. 



( M 175 ) F 



