Gooch and Peirce — Separation of Selenium, etc. 181 



Aet. XYIII. — A method for the Separation of Selenium from 

 Tellurium based upon the difference in volatility of the 

 Bromides ; by F. A. Gooch and A. W. Peirce. 



[Contributions from the Kent Chemical Laboratory of Yale College — XLTX.] 



It has been shown in previous articles from this laboratory* 

 upon the reducibility of selenic acid by the action of the halo- 

 gen acids, that when small amounts of selenic acid are boiled 

 in aqueous solution with potassium iodide and hydrochloric 

 acid, selenium is precipitated, while the iodine set free simul- 

 taneously may be collected in the distillate, estimated, and 

 taken as the measure of the selenic acid originally present ; 

 that if the iodide is omitted from the mixture, so that the 

 hydrochloric acid alone shall be the reducer, the reduction 

 proceeds only to the point of formation of selenious acid, pro- 

 vided the boiling is not continued after the hydrochloric acid 

 has reached the condition of half-strength at which it boils 

 unchanged under normal atmospheric pressure ; and that a 

 solution of selenic acid, potassium bromide, and sulphuric acid 

 of regulated dilution and proportions also yields under defined 

 conditions selenious acid as the product of reduction. When, 

 however, the ebullition of a solution of selenious acid in hydro- 

 chloric acid is continued after the acid has reached the condi- 

 tion of half-strength, traces of selenium appear in the receiver 

 and connecting tubes, the distillate sets free iodine from potas- 

 sium iodide, and it is evident that the selenious acid is under- 

 going further reduction. So also when the boiling of the 

 mixture of sulphuric acid, potassium bromide, and selenious 

 acid is pressed beyond the point at which the solution begins 

 to be colored, selenium appears in traces in the tube leading to 

 the receiver and the distillate liberates iodine from an iodide. 

 Obviously the conditions have been at this time reached in the 

 processes of concentration when selenium tetrachloride and 

 selenium tetrabromide, respectively, are forming from the acid, 

 and that the appearance of the elementary selenium is due 

 to partial decomposition of the halogen salts. We have 

 observed more recently phenomena of a similar nature (as 

 would naturally be expected under the conditions), when aque- 

 ous solutions of selenious acid, phosphoric acid, and sodium 

 chloride are submitted to distillation : that is to say, there 

 comes a time in the process of boiling such mixtures when the 

 appearance of elementary selenium and the action of the dis- 

 tillate upon potassium iodide make evident the volatilization 

 and partial decomposition of the selenium compounds of the 



*This Journal, 1, 254, 400, 402. 



