SUPPLY 



tory, 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 per- 

 formed 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 acid- 

 ity of milk above which all milk be rejected, the nose and the 

 palate of the experienced inspector are better criterions tnan 

 the acid test alone, as to the fitness of milk for condensing. Acid 

 tests are valuable in the case of uncertainty and suspicion as 

 to the quality of any given can of milk. All milk containing .18 

 per cent lactic acid or more is dangerous for condensing pur- 

 poses. 



Acid Test for Daily Use, Where Each 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 indi- 

 cator. 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, 18 c.c. of the prepared solution, there- 

 fore, neutralize .18 per cent lactic acid, when a 17.6 c.c. pipette 

 is used for measuring out the milk. 



Making the Test. With the Babcock pipette, measure 17.6 

 c.c. into a white cup. With a small dipper, holding exactly 18 

 c.c., pour 18 c.c. of the prepared solution into the cup; stir or 

 shake. If the mixture remains faintly pink, it contains less than 

 .18 per cent acid and will pass; if it turns white, it contains more 

 than .18 per cent acid and should be rejected or subjected to addi- 

 tional tests. 



The stock solution should be standardized by a chemist. 

 The prepared solution should be made up daily. Both solutions 



