METHODS FOR QUANTITATIVE DETERMINATIONS. 405 



between two watch-glasses held together by means of a brass or nickel 

 clamp, as shown in Fig. 61. 



The above-described methods may be employed for the determina- 

 tion of those substances which can be precipitated from their solu- 

 tions in the form of some stable compound. Aluminum, zinc, iron, 

 bismuth, copper, etc., may, for instance, be precipitated as hydroxides 

 and weighed as oxides, into which the precipitated compound is con- 

 verted by ignition. Sulphuric acid may be precipitated and weighed 

 as barium sulphate, phosphoric acid may be precipitated by magnesia 

 mixture and weighed as magnesium pyrophosphate, etc. Some sub- 

 stances, like nitric acid, chloric acid, etc., cannot be precipitated from 

 their solutions, for which reason other methods have to be employed 



for their determination. 



FIG. 63. 



FIG. 62. 



10 CO 



Liter flask. 



Pipettes. 



