490 
DR. PLAYFAIR ON THE NITROPRUSSIDES, 
It is obvious that if the analyses would authorise 25 equivs. of carbon instead of 24, 
a very much more simple formula might be given. The mean proportion of iron 
to carbon is 19*54 : 20*03, while the proportion, 5 equivs. ; 25 equivs. or 1 : 5, would 
require 19*54 : 20*93 of carbon. Throughout all the salts, this less quantity of car- 
bon refuses to enrol itself in the simple proportion of 1 : 5, and necessitates the use 
of the much more complex one of 5 : 24. The above formula may be expressed as 
Fcj Cyi 2 3NO, 5Na-l-10 HO. 
Nitroprusside of Potassium. 
12. This salt may be obtained in several ways. 
1. By acting upon prusside of potassium with nitric acid, exactly as described under 
nitroprusside of sodium, but the neutralization of the acid is effected by carbonate of 
potash, instead of carbonate of soda as therein described. The nitrate of potash is 
crystallized out and the mother-liquor is put in the hot chamber to crystallize. 
2. It may be prepared from the nitroprusside of iron, or better from the copper 
salt, by decomposing it with caustic potash, care being taken to keep the nitroprusside 
in excess. 
Properties . — This salt, from its great solubility, is somewhat difficult to crystallize. 
It is apt to deposit in an amorphous form ; but this may be avoided by a little prac- 
tice, and fine large crystals may be obtained. These crystals belong to the oblique 
system, and have been measured by Prof. Miller. 
Symbols : — ^010, m 1 10, 5 012, e 101, rill. 
Angles between normals to the faces : — 
ah 30 0 
rb 54 5 
mb 49 46 
sh 68 52 
em 113 55 
57 7 
sm 69 3 
The axis of the zone mb, makes an angle of 57° 56' with that of the zone rb, and an 
angle of 71° O' with the axis of the zone sb. 
This salt dissolves in its own weight of water at 60°; 60*06 grs. of a saturated 
solution of this salt evaporated in the water-bath left 30*40 grs. of the salt. It is 
not precipitated from its solution by alcohol. With caustic potash it unites and forms 
a salt which is described in a further part of the paper. Nascent hydrogen does not 
decompose it. Hydrogen, chlorine and sulphurous acid were passed through both 
cold and hot solutions of the salt without effecting any change. It is slightly deli- 
quescent, and acquires a greenish shade when exposed to light ; its solutions on long 
keeping deposit prussian blue and become partially decomposed. 
The crystals of this salt are of a dark red colour. 
