32 ANALYTICAL PROCESSES. 



and tin tube is made by a short close-fitting rubber 

 tube, and the tubes are so bent as to slope towards the 

 distilling flask. The lower end of the tin tube is con- 

 nected by a short rubber tube with a glass bulb tube 

 which dips into an Erlenmeyer flask of about 300 c. c 

 capacity. 



5 c. c. of the milk are weighed or measured into the 

 flask and evaporated to dryness over the water-bath. 

 30 c.c. of the acid potassium sulfate mixture are added 

 and heated over the Bunsen burner. At first, frothing 

 occurs and white fumes escape, consisting chiefly of 

 water vapor. To prevent loss of acid, the neck of the 

 flask is now fitted with a funnel which is covered with 

 a watch glass. This will cause the acid to condense 

 and run back into the flask. The operation is finished 

 when the liquid is colorless, which will generally be the 

 case in about an hour. After cooling, the contents of 

 the flask are transferred to the distilling flask by the 

 aid of about 200 c. c. of water, and several pieces of ig- 

 nited pumice dropped in. Sufficient of the sodium hy- 

 droxid solution (about 50 c. c.) is now added to make 

 the mixture strongly alkaline. It should be poured 

 down the side of the flask so that it does not mix at once 

 with the acid. The flask is now connected with the con- 

 denser and the contents mixed by shaking. The 

 Erlenmeyer flask into which the distillate is to be re- 

 ceived, is charged with 20 c. c. of the standard sulfuric 

 acid. The end of the delivery tube should dip below 

 the level of this liquid. The liquid is now distilled 

 until the whole of the ammonia is driven over. 



