280 Dr. Playfair o?i the NiiroprussideSy 



Altered Nitroprusside of Sodium. 



23. The previous analyses of the crystallized nitroprussic 

 acid and of the nitroprussides of ammonium and barium, and 

 the composition of the silver salts prepared from them, show 

 a want of accordance between the iron in the electro-negative 

 constituent and the metal in the electro-positive one. The 

 iron in all these cases is about a half per cent, in excess, 

 therefore not sufficient to be considered as being in atomfc pro- 

 portion. It was thought, from the very distinct crystallization 

 of the sodium salt, that this excess might not accompany it if 

 prepared from the respective silver salts of the above com- 

 pounds. Accordingly the silver salt was decomposed by an 

 equivalent quantity of hydrochloric acid. The resulting solu- 

 tion was neutralized with carbonate of soda and crystallized. 

 Analyses I. and II. were made on a salt thus prepared from 

 crystallized nitroprusside of barium. Analysis III. on a salt 

 similarly made from nitroprusside of ammonium. Again, when 

 we referred to the action of caustic soda on the nitroprussides, 

 it was obvious that by using a less quantity of the alkali than 

 sufficed to effect the complete decomposition, a nitroprusside 

 with a similar impurity in solution was to be expected. 



Analysis IV. was made on a specimen thus prepared, and 

 its accuracy is confirmed by a future analysis of a silver salt. 



{I. 13*695 grs. gave 3*72 grs. peroxide of iron. 

 II. 20-93 grs. gave 5-72 Fe^O^ and 9-93 NaO, SO^. 



III. 15-35 grs. gave 4.'25 Fe^O^ and 7*10 NaO, SO^. 



IV. 11-13 grs. gave 3-07 Fe^ O^ and 5-06 NaO, SO^. 



The combustions were made with chromate of lead. 



II. 13-34 grs. gave 9-74. grs. CO^ and 1-58 gr. HO. 



III. 14.-475 grs. gave 10-68 grs. CO^ and 1-67 gr. HO. 



IV. 6-730 grs. gave 5*33 grs. CO^ and 1-01 gr. HO. 



100-00 100-00 10000 



It will be seen from these analyses that the excess of iron 

 still remains, and this is further confirmed by silver salts again 

 made from them and analysed. It will also be observed that 



