﻿PREPARATION OF AMMONIUM SELENATE. 



51 



In a method^ similar to the one described in this research, 

 barium selenate is treated Avith a slight excess of a solution of 

 potassium carbonate. The filtrate from this mixture contains potas- 

 sium selenate and the excess of potassium carbonate. The disad- 

 vantage of this process is that there is no good way of eliminating 

 the excess of potassium carbonate and potassium selenate can not 

 be used for the preparation of other salts by the method indicated 

 above. 



General Methods for the Preparation of Selenic Acid. Briefly, 

 the processes which are used the most widely for the preparation of 

 selenic acid and the selenates, are as follows : 



(1) Treat silver selenite with bromine, which forms selenic 

 acid with the precipitation of silver bromide. This does not give 

 an absolutely pure acid, as it contains traces of bromine.'^ 



(2) Decompose lead selenate Avith sulphuric acid or hydrogen 

 sulphide.^ 



(3) Decompose barium selenate AAdth sulphuric acid.*' 



(i) Electrolytic method: Pass chlorine through pure sele- 

 nium dioxide suspended in cold water, AA^hich forms selenic acid and 

 hydrochloric acid. Neutralize Avith copper carbonate^ and, near the 

 end of the reaction. Avith freshly precipitated copper hydroxide. 

 This forms copper selenate and copper chloride. Evaporate the so- 

 lution; the copper selenate being the less soluble, crystallizes out. 

 The copper selenate crj^stals, AA^hich are recrystallized until free from 

 chlorides, are dissolved in water and the solution electrolyzed^ be- 

 tAveen platinum electrodes until all of the copper is deposited. This 

 method giA^es a pure acid, but is more or less inconvenient. 



The folloAAdng research work Avas undertaken in order to ascer- 

 tain, if possible, a cheap, convenient and quick method for the 

 preparation of ammonium selenate. Flue dust, obtained from the 

 roasting of anode slimes from a copper refineiy, Avas used as a 

 source of selenium. The selenates of barium and lead were pre- 

 pared and gram portions treated with varying quantities of "am- 

 monium carbonate," for different periods of time. 



* Gerichten, Liehig-s Annalen, CLXATIi, 214. 



^ Thomsen, Berichte der DeutscPen Cliemischen Gesellschaft, II, 598. 

 sAVohlwill, Liehig's Annalen, CXIV, 169. 

 sWohlwill, I. c. 

 ^Wohlwill, ]. c. 



^ R. Metzer, Comptes rendu s hehdomadaires des seances de Vacademie des 

 sciences, CXXA^I, 54 (189S). 



