i MILK 35 



sand, pumice, &c. ; Janke l has shown that without any such 

 material the same results are obtained. 



Fleischmann has worked out a formula with the help of 

 which, if the specific gravity and the fat contents are known, 

 the total solids can easily be calculated. The results which are 

 obtained in this way are very exact, and so this method can 

 also be used to check the direct determination of the total 

 solids. Mention will be again made of this formula in the 

 section dealing with the adulteration of milk. 



In general, the amount of total solids in milk varies between 

 11 and 14 per cent., the average may be taken as 12'25 per 

 cent., as mentioned in the Introduction. 



III. DETERMINATION OF THE FAT. 



The fat of milk, regarded economically, is without question 

 the most valuable constituent of milk. It is from this fat that 

 butter is made, which, as is well known, is an expensive article 

 of diet. In recent years it has become the practice for large 

 dairies and butter factories to buy milk on the percentage of 

 fat which it contains. This is done either by paying for the 

 amount of fat found in the milk, or a price is agreed upon for 

 milk with a certain percentage of fat, say 3 3'4 per cent., 

 and a deduction made for each 01 per cent, below 3 per cent., 

 and a supplement given for each O'l per cent, above 3*4 per 

 cent. The latter method is the more usual. 



A determination of the percentage of fat in milk is also of 

 importance in judging of the productiveness of individual cows, 

 for the value of a cow as a productive animal must depend 

 both upon the quantity of milk and the amount of fat it 

 contains when a certain ration is being fed. 



Further, an exact knowledge of the proportion of fat is im- 

 portant, because in most countries there is a legal minimum 

 standard for the percentage of fat which milk sold to the public 

 must contain. It is therefore easy to see that the determina- 

 tion of the amount of fat in a milk is looked upon as the most 

 important branch of the examination of the constituents of 

 milk. Not only in laboratories, but also in dairies and by 



1 Repert. fur analyt. Chemie, 1882, p. 33. 



D 2 



