M. Martius on the Platinum Metals. 5038 
- Osmiocyanide of Potassium, Os Cy, 2 KCy -+-3HO.—This salt 
was prepared byadding cyanideof potassium to a solution of osmie 
‘acid, evaporating to dryness, and heating to redness in a covered 
crucible. On dissolving out the mass in a small quantity of 
water and crystallizing, the salt was obtained in fine yellow 
laminz, which belong to the dimetric system, like the ferrocya- 
nide of potassium: the osmiocyanide of potassium, besides being 
analogous in composition and crystalline form to this salt, has 
the still closer resemblance that it exhibits (as a special investi- 
gation by Kobell showed) the same abnormities in its optical 
relations which have lately been found characteristic of ferro- 
cyanide of potassium. 
_ By the action of nitric acid on osmiocyanide of potassium a 
nitro-compound appeared to be formed. Experiments made to pre- 
pare a series of compounds analogous to the ferricyanides were 
unsuccessful. Chlorine passed into a solution of osmiocyanide 
of potassium, produced a red colour, but on evaporation only 
erystals of the double salt of chloride of osmium and chloride of 
potassium were obtained. 
Osmiocyanide of Hydrogen: Osmiocyanic Acid, Os Cy, 2HCy.— 
This substance was obtained in a way analogous to the ferrocyanic 
acid: by treating a cold saturated solution of osmiocyanide of 
potassium with fuming hydrochloric acid, 
_ Os Cy, 2KCy+2HCl = Os Cy, 2HCy + 2KCl, 
—a reaction which distinguishes osmium and ruthenium from 
other platinum metals—a precipitate was obtamed, which was 
filered, washed with strong hydrochloric acid, dissolved in alcohol, 
and ether added. In this way the body was obtained in trans- 
parent columnar crystals of strongly acid properties. 
Perfectly stable in the dry state, osmiocyanic acid decomposes, 
when exposed to the air in a moist state, ito cyanide of osmium 
and hydrocyanie acid. 
When any osmiocyanide is boiled with strong hydrochloric 
acid, hydrocyanic acid is disengaged, and a dark-violet precipitate 
is formed, which is cyanide of osmium, Os Cy. 
When osmiocyanide of potassium is mixed with a persalt of 
iron, a splendid violet precipitate is formed, which is as delicate 
a test for iron as the ferrocyanide. This precipitate could not be 
analysed, on account of its retaining a quantity of water, which 
eould not be expelled without decomposition ; but it 1s doubtless 
formed according to the equation 
2¥e? CB + 30s Cy, 6(KCy = 30s Cy, 2 Fe? Cy? + 6KCL. 
When this precipitate was treated with baryta water, sesqui- 
oxide of iron was formed, and osmiocyanide of barium passed into 
solution and was afterwards obtained in reddish-brown crystals 
