F. W. Clarke—Seleniocyanates. 199 
Art. XIX.—On some Seleniocyanates ; on the Electrolytic Esti- 
mation of Mercury; some Specific Gravity Determinations. 
Being Parts VII, VIII and IX of Laboratory Notes from the 
University of Cincinnati; by F. W. CLarKkE, S.B., Professor 
of Chemistry. 
VIL On some Seleniocyanates. 
In 1855 Buckton discovered and described the double sul- 
phocyanates of platinum.* Of these, the potassium salt is 
perhaps the one best known, partly because of its beauty, and 
partly because of the ease with which it may be prepared. 
Recently, my attention having been called to this compound, 
it occurred to me that it might be interesting to prepare the 
corresponding seleniocyanate. Accordingly I assigned the task 
to Mr. W. L. Dudley, a student in the University of Cincinnati, 
who had little difficulty in attaining to success. 
hen an alcoholic solution of potassium seleniocyanate is 
added to a similar solution of platinic chloride, a heavy reddish 
brown precipitate is immediately formed. This, upon boiling, 
becomes darker in color, and apparently in part dissolves. e 
filtered liquid deposits crystals of the new salt, mixed with a 
reddish sediment of selenium; and these, although they are 
slightly unstable, may be purified by recrystallization from 
alcohol. The crystals are usually very small; mere scales in 
fact; although on one occasion they separated out as regular 
six-sided tables, several millimeters in diameter. By reflected 
light they are nearly black; but by transmitted light, deep 
eee red. Specific gravity, 3°377 at 10°-2, 3:378 at 12°. 
he weighings were made in benzol. Determinations of plati- 
num and potassium came out as follows: Z 
Theory. 
Potassium 8°57 8°61 
Platinum 21°64 21°73 
There is, therefore, no reasonable doubt that the new salt is 
represented by the formula K, Pt(CSeN),, and that it is strictly 
analogous to Buckton’s sulphocyanate. 
An attempt to prepare gold salts resembling the sulphocyan- 
ates described by Clevet was only partially successful. hen 
alcoholic solutions of potassium seleniocyanate and neutral gold 
chloride are mixed, a red precipitate falls, which consists in 
large part of free selenium. The pale orange-yellow filtrate 
from this precipitate yields by spontaneous evaporation a crys- 
talline crust, which under the microscope is seen to be made 
up chiefly of minute, deep red prisms. These crystals are so 
* Chem. Soc. Quart. Journ., vii, 22. + Jahresbericht, 1865, p. 295. 
