216 Dr. Playfair on the Niiroprussides, 



Iron . . 



Barium . 



Carbon 



Hydrogen 



Nitrogen 



Oxygen 



In the above analysis the proportion of carbon to the iron 

 is higher than obtained with the other salts, but the error is 

 usually on this side when chromate of lead, as in this instance, 

 is used in the combustion. It will also be seen in a further 

 part of the paper, that a carbonaceous impurity, probably an 

 attached cyanide, not separable by crystallization, but removed 

 when it is converted into a silver salt, is produced when a so- 

 lution of this salt is kept for some time, and it is possible that 

 a small portion may be present in the salt analysed. If we 

 could be assured of the absence of all impurity, which it will 

 be afterwards seen that it is difRcult to believe from the vari- 

 able composition of this salt, it is obvious that the above ana- 

 lyses might be much more simply expressed by the following 

 calculation : — 



On the first formula the dried salt would be Fe^Cy^23NO, 

 5Ba+15HO, on the second Fe^C/NO, Ba2 + 6HO. The 

 water lost in the water-bath would in the first case correspond 

 to 20 equivs., in the latter case to 8 equivs. 



Nitroprusside of Silver. 



14. This salt may be prepared by adding nitrate of silver 

 to any of the soluble nitroprussides. 



The colour of the salt varies according to its state of pre- 

 paration, from a fleshy white to a pale buff. When dry it 

 has a flesh colour. It is insoluble in water, alcohol and nitric 

 acid. Hydrochloric acid decomposes it with the formation of 

 nitroprussic acid and chloride of silver. The caustic alkalies 

 decompose it, as they do the soluble nitroprussides generally : 



