858 Dr. Playftiir on the NiiropriissideSf 



have prevented the completion of this study in time for the 

 presentation of this paper. 



On the Constitution of the Nitroprussides. 



31. In the preceding part of the paper the analyses of the 

 nitroprussides led to the extremely complicated formula Fe^ 

 Q24 j^i3 Q3 j^5^ This formula was a 2>rio7-i very improbable, 

 and naturally led to the belief that an error in the estimation 

 of the carbon forced its adoption. In fact, if 25 instead of 

 24< equivs. of carbon were present, the formula would resolve 

 itself into the much simpler expression Fe'^ C^° N^ O R^. It 

 is therefore important to review the evidence, in order to 

 see whether the simple proportion of iron to carbon, 1 : 5, 



might be derived from it. 



The following table exhibits the 



proportion of iron and carbon found in the analyses of the 

 respective salts : — 



Name of salt. 



Number of 

 analyses fur- 

 nishing the 

 mean. 



Quantity of 

 iron. Mean. 



Quantity of 

 carbon. 

 Mean. 



Atomic rela 



tion of iron to 



carbon. 



Nitroprusside of sodium . . 

 Nitroprusside of potassium 

 Nitroprusside of ammonium 



Nitroprusside of silver 



Nitroprusside of copper 



Nitroprusside of iron 



Nitroprusside of zinc 



Nitroprusside of calcium .. 



Nitroprusside of barium 



Nitroprussic acid 



Mean of the whole , 



19-54 

 19-05 

 22-08 

 13-03 

 20-45 

 19-09 

 20-07 

 21-09 

 14-10 

 23-80 



2003 

 19-63 

 22-69 

 13-29 

 21-25 

 19-96 

 20-53 

 21-47 

 14-98 

 24-80 



28 : 28-7 

 28 : 28-8 

 28 : 28-7 

 28 : 28-5 

 28 : 29-0 

 28 : 29-2 

 28 : 28-6 

 28 : 28-5 

 28 : 29-7 

 28 : 29-1 



35 



192-30 



198-63 



28 : 28-9 



Now the proportion of 1 equiv. of iron to 5 equivs. of carbon 

 would require the proportion 28 : 30. This difference is too 

 great to be due to any errors of observation, especially when 

 it is remembered that these, in the case of a body containing 

 much nitrogen, tend to increase and not to diminish the ap- 

 parent quantity of carbon. The actual proportion found, 

 28 : 28'9, indicates, in equivalents, 5 equivs. iron to 24 

 equivs. carbon ; this proportion would require 28 : 28*8 ; the 

 slight excess found is in the direction of the known errors of 

 observation. 



These considerations forced the adoption of the complex 

 formula given above. It will also be seen, from an examina- 

 tion of the analytical details, that the quantity of nitrogen 

 corresponds to 6 equivs, for every 10 equivs. of carbon, or 15 

 equivs. for the 24 equivs, of carbon required by the formula. 



