288 



CLEAN MILK 



solution and twentieth normal solutions of each, in well stoppered 

 bottles, those containing the alkali stoppered with rubber, and pro- 

 tected with soda-lime (or KOH) U-tubes. Phenolphthalein solu- 

 tion (}4% phenolphthalein (powder) in 50% alcohol, i. e., 1 gram 

 phenolphthalein, alcohol 100, water 100), and a 1 c.c. pipette. 



Fig. 69. 



Aormal 



. yioNormat 

 NaOff 



Two burettes arranged for titrating culture media. 



Process. — Set the evaporating dish on the gauze, the gauze on? 

 the tripod, and measure into the dish 5 c.c.s of the media to be di- 

 trated. Add 45 c.c.s of distilled water. Boil freely one minute to- 

 expel C0 2 ; lower the flame until the liquid merely simmers ; add 1 

 c.c. phenolphthalein solution; if no pink color develops, the media is- 



