﻿32 



INDIANA UNIVERSITY 



Preparation of Materials. Sodium perchlorate was used as the 

 starting' material for the preparation^- of the perchloric acid. The 

 solid, dry sodium perchlorate was treated with an excess of concen- 

 ti*ated hj^drochloric acid. After thorough stirring to break up 

 lumps, the mixture was filtered through asbestos and the residue of 

 sodium chloride was washed with successive small portions of con- 

 centrated hydrochloric acid. The filtrate, consisting of a mixture 

 of aqueous perchloric acid, hydrochloric acid and small amounts of 

 sodium perchlorate, was heated on the hot plate until the tempera- 

 ture reached 135°. This completely volatilized the hydrochloric 

 acid with only an insignificant loss of perchloric acid. This aqueous 

 perchloric acid is stable, and is no more dangerous to handle than 

 nitric acid. Impurities, such as sodium chloride and sodium chlo- 

 rate in the commercial sodium perchlorate, are entirely eliminated 

 by this method, and are objectionable only since they act as filling 

 agents, reducing the quantity of perchloric acid that may be ob- 

 tained. The lead perchlorate was made by neutralizing this aque- 

 ous perchloric acid ^\'ith litharge. There is no need of using white 

 lead for this reaction, except perhaps for the sake of speed in the 

 neutralization of the last small amounts of the perchloric acid. In 

 the preparation of lead fluo-silicate, the fluo-silicic acid must be 

 neutralized with white lead, because litharge is strongly enough 

 alkaline to decompose the fiuo-silicic acid into silica and lead fluo- 

 ride. Perchloric acid is a stable acid that is not decomposed by an 

 alkali. Perchloric acid may also be made by treating barium per- 

 chlorate with sulphuric acid. It is necessary to heat the perchloric 

 acid thus obtained until the temperature reaches 135° in order to 

 volatilize the hydrochloric acid, since chlorides are generally present 

 in the commercial material. It is best to use an excess of sulphuric 

 acid, which is precipitated later by the addition of the litharge. 



The free perchloric acid in the lead perchlorate baths was deter- 

 mined by direct titration with standard sodium hydroxide using 

 methyl orange as an indicator. Th-e results obtained by this method 

 are approximately correct. The lead was then determined as lead 

 peroxide by deposition from a nitric acid solution. 



Beakers were used as electrolyzing vessels. 



The lead anodes were cast in graphite molds. They were sus- 

 pended in the bath by means of copper wires passing through holes. 

 Two anodes were placed in each beaker. The cathode of copper foil 

 was suspended between them. The volume of the bath was 400 cc. 

 in most of the experiments, although baths containing 2,000 ec. 



11 Mathers, Journal American Chemical Society, XXXII, 60 (1910). 



