Contamination of Milk. 53 



ing them in clean soft water, one tablet for each ounce of 

 water; thus eight tablets to an eight-ounce bottle of water. 

 In determining the acidity, a number of common white cups 

 are used, one for each patron. Two measures full ' of the 

 alkali solution are placed in each cup, and then as the milk 

 is received at the weigh-can, one measure of milk is added 

 to the alkali solution in the cup, 2 and the whole gently, but 

 thoroughly shaken. If the pink color of the alkali solution 

 persists even fainth r , it shows that there is not enough acid 

 in the milk to neutralize the the same; if it disappears alto- 

 gether, leaving the milk white in color, it indicates that 

 there is more acid in the milk than can be neutralized by 

 the alkali of the tablet solution. When these proportions 

 of milk and alkali solution (2:1) are employed, it indicates 

 an acidity of 0.2 per cent, figured as lactic acid. Milk 

 should not contain more than this amount of acid, and 

 under good methods of handling, the acidity should be 

 brought down to 0.15 per cent if possible. 



Circumstances may arise that might lead to an error if 

 this method is blindly followed. It has been pointed out * 

 that if milk is allowed to stand in rusty cans for some 

 time its acid content is diminished materially. The aver- 

 age acidity of nine samples of milk brought to a factory in 

 clean cans was .228 per cent acidity, while that of nine 

 other patrons brought in rusty cans was only .134 per cent. 

 Milk kept in rusty cans is sure to contain large quantities 

 of bacteria, even though its acid content may be low. 



Kinds Of bacteria in milk. The number of bacteria in 

 milk is not of so much consequence as the kind present. 



1 A brass cartridge shell provided with a handle serves admirably for a meas- 

 ure. 



2 Farrington, Bull. 52, Wis. Expt. Stat. 

 8 Biddick, Hoard's Dairyman, July 30, 1897. 



