Milk Supfly 45 



of butter floating on the surface of the milk, the inspector can 

 readily tell if the milk has or has not been properly cooled. A correct 

 thermometer should always be on the platform for guidance. 



Inspection of Milk by 'rnii; UsE of Acid Tests. — Since the 

 degree of acidity, or the sweetness of the milk, is one of the chief 

 factors that determines its fitness for condensing purposes, tests 

 that rapidly and accurately determine the per cent of lactic acid in 

 the fresh milk, are of great service. 



Some concerns have adopted a definite acid standard of milk, 

 rejecting all milk containing more than the maximum per cent of acid 

 of their standard, and they test every can of milk received with an 

 acid test. This method insures sweet milk in the factory, provided 

 that the alkaline solutions used are correct. This work involves 

 considerable expense, however, and unless the solution is carefully 

 prepared and made up fresh often, its use may yield misleading 

 results. Again, when the acid test is performed on the milk of each 

 can, the acceptance or rejection of the milk depends altogether on 

 the per cent of acid it contains. Although milk may be otherwise 

 unfit for use, it will pass, as long as it is low in acidity. Experience 

 has shown that, while it is necessary for the condensery to decide 

 on a maximum acidity of milk above which all milk be rejected, 

 the nose and the palate of the experienced inspector are better 

 criterions than the acid test alone, as to the fitness of milk for con- 

 densing. Acid tests are valuable in the case of uncertainty and 

 suspicion as to the quality of any given can of milk. All milk con- 

 taining .2 per cent lactic acid or more is dangerous for condensing 

 purposes and should be rejected. 



Acid Test for Daily Use, Where Bach Can of Milk is Tested. — 

 Stock Solution. — Weigh out two hundred grams of sodium hydrate 

 C. P. and add distilled water to make up one liter. Keep tightly 

 stoppered. 



Solution for Daily Use. — Mix 4 c.c. of stock solution with 991 

 c.c. of distilled water, and add 5 c.c. of phenolphthalein indicator. 

 The indicator is prepared as follows : dissolve one gram of dry 

 phenolphthalein in 100 c.c. of 50 per cent alcohol. Each cubic 

 centimeter of the prepared alkaline solution neutralizes .01 per cent 

 lactic acid, 20 c.c. of the prepared solution, therefore, neutralize .2 

 per cent lactic acid, when a 17.6 c.c. pipette is used for measuring 

 out the milk. 



