44 MODERN METHODS OF TESTING MILK 



dilution depends upon the strength of the acid used. 

 One should start with a small dilution and increase 

 gradually until the s])ecific gravity of the acid becomes 

 1.82 to 1.83. After diluting the acid with water, the 

 mixture becomes hot, and it is necessary to allow it 

 to cool to 60° F. before testing with the acidometer. 



Useful indications regarding strength of acid. — 

 After one has acquired some skill in making the Bab- 

 cock test, one can readily tell whether the acid is too 

 strong or too weak from its action when mixed with 

 milk in the test-bottle. One bases his judgment on 

 the rapidity with which the milk-casein is coagulated 

 and redissolved, and also upon the quickness with 

 w'hich, and the degree to which, the mixture of acid 

 and milk turns dark. 



Keeping acid from air. — The acid should be kept 

 in tightly stoppered bottles, because, if exposed to air, 

 it absorbs moisture and becomes too w^eak. The stop- 

 per should be glass, since a common cork stopper is 

 soon destroyed by the acid, and even rubber is not 

 long satisfactory. 



Care in handling sulphuric acid. — Strong sulphuric 

 acid is extremely corrosive and is dangerous to han- 

 dle except with care. In contact with articles like 

 clothing or leather, it quickly ruins them, while on 

 the skin it causes serious burns in a short time. If 

 sulphuric acid gets upon one's skin, it should be imme- 

 diately and thoroughly washed with an abundance of 

 water, and this may be followed by washing with di- 

 lute ammonia or sodium carbonate. In case acid gets 

 on the clothing, treat it first with abundance of water 

 and then with ammonia. Red discoloration on cloth- 



