44 METHODS OF QUANTITATIVE ANALYSIS. 



A piece of litmus paper may be thrown in for an in- 

 dicator. When the strong alkali is being added the flask 

 should be immersed in cold water to prevent the solution 

 from becoming hot and consequent loss of ammonia. 

 The distilling flask is now connected with a Liebig con- 

 denser and a 150 c. c. to 200 c. c. distilled off. The dis- 

 tillate which contains all of the ammonia, is collected in 

 a flask containing a measured quantity of standard acid. 

 In order to prevent any of the boiling fluid from being 

 carried over mechanically, a Stutzer-Rietmeyer or Koe- 

 nig safety tube should be used for connecting with the 

 condenser. 



Instead of distilling, the ammonia may be driven out 

 by forcing steam through the solution. For this pur- 

 pose the flask is fitted with a two-hole stopper. Through 

 one hole is put a short safety connecting tube and 

 through the Other, a long tube which reaches nearly to 

 the bottom of the flask. This latter tube is connected 

 with a steam generator. 



For collecting the distillate and for absorbing the am- 

 monia, a so-called Pelligot tube or a simpler and cheaper 

 Erlenmeyer flask of 500 c. c. capacity may be used. Into 

 the absorption tube or flask 25 c. c. of a fifth normal solu- 

 tion of sulphuric acid are carefully measured and treated 

 with a few drops of Congo-red, rosolic acid or cochineal 

 splution, for an indicator. Twenty-five c. c. of acid is 

 sufficient for 10 c. c. of milk. The ammonia in the distil- 

 late is conducted through a condenser and then into the 

 acid. 



Sulphuric acid is most satisfactory as an absorption 

 fluid for the ammonia. It is easily titrated and has the 

 advantage that it does not change in strength by long 

 standing. For an indicator any of the following solu- 

 tions may be employed: Congo-red, one gram in 

 one liter of water : with ammonia produces a red-brown 



