96 Blumenthal — Preparation of Selenic Aeid. 



The residue, consisting chiefly of sodium selenate and sodium 

 carbonate, could not be crystallized from water. It was found 

 necessary to convert the carbonate to sulphate in order to 

 obtain crystallizable material, and after careful neutralization 

 with sulphuric acid, the mixture of sulphate and selenate was 

 crystallized by repeated evaporations. The sulphate tends to 

 crystallize first, and a partial separation may be accomplished 

 in this manner. The mixed crystals of sodium selenate and 

 sulphate first obtained were quite efflorescent, but on warming 

 and evaporating to greater concentration, crystals of a lower 

 order of hydration were obtained. The selenate and sulphate 

 can also be thrown out by alcohol, but this method was not 

 satisfactory and was discarded. 



The several crops of crystals were combined, filtered on a 

 Buchner funnel with suction, well drained, and finally the 

 mass was heated to 108° C. for some hours, whereby most of 

 the water was driven out, and a mixture of nearly anhydrous 

 sodium salts was obtained. Analysis of the mixed product 

 showed it to average about 65 per cent of selenate and the 

 total yield of sodium selenate was about 58 per cent of the 

 theoretical amount. Considerable material was lost in the 

 preliminary attempts at purification, in the tests made from 

 time to time and in the mother liquor from the crystallizations. 



This material thus prepared is serviceable for immediate use 

 with sulphuric acid in the method proposed for the separation 

 of bromine and chlorine, and no attempts were made to sepa- 

 rate the sulphate and selenate completely. In vie^v of expe- 

 rience obtained in this work, it seems probable that by rapidly 

 evaporating the filtered solution of selenate and hydroxide 

 over a free flame, and rapidly extracting the residue with abso- 

 lute alcohol, the carbonate formation may be, to a large degree, 

 inhibited. This, of course, reduces the amount of sulphate 

 ultimately formed, since the greater part of the alkali, except- 

 ing the carbonate, is removed by the alcohol treatment. The 

 resulting aqueous solution, containing a small amount of sul- 

 phate, but no selenite, can be purified fairly well by fractional 

 crystallization, as the selenate is more soluble in water than the 

 sulphate. 



It is to be noted that sodium selenate may also be pre- 

 pared by fusing with sodium carbonate the barium selenate 

 obtained in the process previously described for making selenic 

 acid, the amount of carbonate taken being less than that 

 required to decompose the barium salt completely. Upon 

 extracting the product with water the sodium selenate dis- 

 solves and may be crystallized from the filtered solution. 



The processes described afford easy means for preparing 

 selenic acid and sodium selenate in such condition that, though 

 these products are not pure, they are suitable for use in the 

 quantitative elimination of bromine from haloid salts accord- 

 ing to the methods to which reference has been made. 



