1818.] Prof. Berzelius on Selenium and Lit h ion. 447 



MY DEAR FRIKND, Plough-court, Lombard-street, Oct. 7 , 1817. 



I consider that the plan for producing a vacuum, or even a 

 partial vacuum, in the vessels destined to receive the products of 

 distillation, is a very great improvement ; for in proportion as 

 the vacuum is rendered more perfect, the spirit will be drawn 

 over at a lower temperature, and will be more fragrant and 

 better in every respect ; and the still being surrounded with 

 water, the heat can never rise beyond 212° ; and consequently 

 that unpleasant smell which the spirit always has when the 

 matter in the still is over heated, or burned to the bottom, is 

 entirely avoided. It is further obvious, that upon this plan 

 distillation may be carried on with a smaller expenditure of fuel 

 than upon the old system. 



I remain, thine sincerely, 



To Henri/ Tritton. WlLLIAM ALLEN. 



Article XIII. 

 On Selenium mid Litkion. By Professor Berzelius.* 



My experiments on this very singular and interesting body 

 have been now for some time completed, and the memoir printed 

 in Swedish contains no less than six sheets. The combinations 

 of selenium with the alkalies and the alkaline hydroselenurets 

 (hydroseleniates according to the nomenclature of Gay-Lussac) 

 elucidate many points of theory. Selenium may be combined 

 with potash without a seleniate and a seleniated hydroselenuret 

 being produced from it when it is dissolved in water. Yet this 

 combination possesses similar properties to the alkaline sulphur- 

 ets ; from which it seems to follow, that the opinion of the dry 

 sulphuret of potash being a mixture of sulphate or hydrosulphate 

 of potash with the sulphuret of potassium, is erroneous. 



Fhe hydroselenurets have the same taste and the same gene- 

 ral properties with the hydrosulphurets and the hydrotellurets : 

 it appears, therefore, that the hepatic taste, the spontaneous 

 decomposition from the contact of the air, &c. characterize the 

 compounds of those acids into which hydrogen enters in place of 

 oxygen. These characters differ essentially from those of the 

 muriates, the rluates, and the iodates ; in my memoir upon 

 selenium, 1 have endeavoured to give a lull explanation of these 

 points. 



You have expressed your doubts respecting the metallic nature 

 of selenium ; what will you say then when I inform you that 

 this body is a non-conductor of electricity and of caloric. 



* Extracted from a letter of Prof. Berzelius to Dr. Marcet. 



