508 
DR. PLAYFAIR ON THE NITROPRUSSIDES, 
Theory of nitroprusside of silver. 
Iron .... 
. 12-92 
13-01 
Silver . . . 
. 49-81 
50-18 
Carbon . . . 
. 13-28 
13-38 
Hydrogen . . 
Nitrogen ") 
Oxygen J 
0-097 
. 23-02 
0-18 
23-25 
100-00 
100-00 
In the previous calculation the cyanide supposed to be present is Fe Cy 2 ; this 
only denotes the proportion of iron to the cyanogen ; it is possible though less pro- 
bable that it might be 2(Fe Cy-fHCy). In this case we might suppose the analysed 
silver salts to contain this cyanide somewhat in the following proportion : 7 equivs. 
nitroprusside to 1 equiv. of the supposed cyanide. On this supposition the calcu- 
lated and actual numbers would be as follows : — 
Iron .... 
Calculated. 
. 13-*50 
Mean. 
13-36 
Silver . . . 
. 49-26 
48-78 
Carbon . . . 
. 13-76 
13-64 
Hydrogen . . 
. 0-20 
0-09 
It is not however to be supposed that this cyanide is present as a chemical com- 
pound in the above proportion, as the differences in the analyses show that it occurs 
in varying and not very definite proportions. 
It would indeed appear that the barium and sodium nitroprusside contained a 
body in which the iron and cyanogen are in the same proportion as in ferrocyanogen 
(FeCy 3 ). But as the silver salt precipitated from them does not contain an excess 
of carbon, it can scarcely be supposed that this would not be precipitated. But in 
fact there are no data further than the mere ultimate analyses upon which reasoning 
can be founded with regard to this dissolved and combined foreign substance in the 
partially decomposed nitroprussides. As however all their essential characters and 
their crystalline form remain altogether unaltered, we cannot view the foreign sub- 
stances as more than accidental. 
Section IV. — Action of Caustic Alkalies on the Nitroprussides. 
25. When a dissolved caustic alkali, such as potash or soda, is added to a solution 
of a nitroprusside, the dark red colour of the solution changes to an orange-yellow. 
If both solutions have been moderately dilute, no oxide of iron is precipitated, nor is 
ammonia evolved. The addition of alcohol to the orange-yellow liquid causes the pre- 
cipitation of an aqueous solution of a new salt. This salt may be procured in a solid 
state as follows. Nitroprusside of potassium is dissolved in water and double its volume 
of alcohol is added. Caustic potash is now added to this solution, and a yellow curdy 
precipitate is obtained. This precipitate is washed with alcohol to free it from an 
excess of either of the reagents, but it is almost impossible to remove the last traces. 
