24 



L. F. Nilson, 



analyses seem to prove that ammonium and selenious acid have very little 

 tendency to combine, the tetraselenite not being sufficiently permanent to 

 retain its ammonia, when kept for a long time over sulphuric acid. I have 

 not had the opportunity of ascertaining whether it be possible to obtain a 

 final product of free selenious acid in this manner, the ammonia totally 

 disappearing. 



SELENITES OF THALLIUM. 



Kuhlmann has examined the neutral salt and the diselenite of this 

 metal, without, however, adjoining any numbers. What here follows will, 

 for the chief part, confirm his statements. 



l. Neutral: TT.0 2 .SeO. 



This salt was prepared by saturating the diselenite described below 

 with an appropriate quantity of carbonate of thallium. The solution, as well 

 at the ordinary temperature as when warmed, yielded the salt in extremely 

 thin, yellow, shining, oblique, four-sided laraels, with one or, more generally, 

 all the summits cut off; they probably belong to the rhombic system. The 

 salt is so little soluble in cold water, that a somewhat dilute solution in 

 warm water, on cooling easily deposits part of it J ). 



An aly se s: 



1) 0.487 gr. salt gave 0.067 gr. selenium or 0.0941 gr. selenious acid and 

 0.4585 gr. sulphate of thallium or 0.3858 gr. thallious oxide. 



2) 0.539 gr. salt gave 0.0745 gr- selenium or 0.1047 gr. selenious acid 

 and 0.5065 gr. sulphate of thallium or 0.4261 gr. thallious oxide. 



') I avail myself of the opportunity of correcting a mistake that has heen in- 

 serted in Otto's Lehrbuch der Cliemie, 2:ter Th. S. 1388, where it is stated that 

 Werther (Journ. f. prakt. Ch. XCI S. 385, XCII S. 128, 351) has examined a thal- 

 lium-zinc-selenite, isomorphous and composed analogically to the corresponding 

 sulphate. Werther has never stated to have operated with such a salt, but the 

 statement will be correct, if selenite be replaced by selenate, or if it be placed un- 

 der the rubric "selensaures Thalliumoxidul". To the double salts of thallium I shall 

 have occasion to return in connexion with the other compounds of this kind. 



