On some seleniocyanates; on the electrolytic estimation of mercury; specific gravity determinations

IN 1855 Buckton discovered and described the double sulphocyanates of platinum.* Of these, the potassium salt is perhaps the olle 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. When 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. The 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 j 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 garnet red. Specific gravity, 3'377 at lOo'2, 3'3iS at 12°'5. The weighings were made in benzoL Determinations of platinum and potassium came out as follows: