136 MODERN METHODS OF TESTING MILK 



(2) a pipette for measuring the amount of milk, cream, 

 etc. to be tested; (3) a white cup or glass beaker for 

 holding the milk, cream, etc. during titration, that is, 

 while the alkali is running into the liquid tested; (4) 

 a glass or gutta-percha stirring-rod, with which to 

 stir the mixture during the titration; (5) a standard- 

 ized alkali solution; (6) solution of phenolphthalein 

 in alcohol to indicate when the liquid tested becomes 

 alkaline (p. 132). (7) a liter flask or graduate for 

 making up alkali solution. Some of these essentials 

 we will consider in more detail. 



The Burette should be accurately graduated and the 

 smallest divisions should be o.i cc. at least. The size 

 of the burettes in use varies. A common and conven- 

 ient size is one that holds 50 cc. When the amount 

 of solution taken for testing is small (not over 9 

 grams), a 10 cc. burette can be used. 



The Pipette most easily available is the ordinary 

 17.6 cc. pipette used in milk testing. Some of the tests 

 use a 50 cc. pipette ; others, 8.8 cc. 



Standardized alkali solution, This usually consists 

 of pure sodium hydroxide (caustic soda) dissolved in 

 pure water (distilled water should always be used if 

 possible). It must be prepared so as to be of exact, 

 known strength. We will consider this solution in re- 

 spect to (i) different strengths used, (2) methods of 

 preparation, and (3) precautions in keeping. 



(i) Different strengths used. The alkali solution 

 differs in strength in different forms of tests, usually 

 being one-tenth normal ( -^ ) or one-fiftieth normal 

 ( -^V ). A tenth-normal alkali solution is of such 

 strength that i cc. neutralizes 0.009 gram of lactic acid. 



