35$ Dr. Playfair o?i the Nitroprussides, 



And probably the ferroso-ferric oxide is transformed at the 

 expense of the oxygen of water into ferric oxide, the hydrogen 

 forming ammonia with nitrogen, 



6FeO + 3HO + N=3Fe2 03 + NH3. 



29. In giving the above equation, the blue sulphur com- 

 pound was supposed to consist of nitroprusside of sodium with 

 3 equivs. of sulphuret of sodium attached. The following 

 calculation shows that this is an expression of the analysis : — 



Calculated. Mean experiment. 



806 100-00 100-00 



The approximation is sufficiently near when the difficulty 

 of getting the substance in at all a stable state is considered. 

 Two views might be taken of the constitution of this singular 

 compound (1), that it is nitroprusside of sodium with 3 equivs. 

 of sulphuret of sodium attached — 



Fe^ Cyi2 3NO, 5Na+3NaS + 6HO; 



but this would scarcely account for its extreme facility of de- 

 composition ; it may therefore be supposed that caustic soda 

 is attached to the salt, as we have seen that it can be, in stu- 

 dying the action of alkalies on the nitroprussides, and that the 

 sulphur has taken the place of the oxygen, thus: — 

 Fe^ Cyi2 3NS, 5Na4- 3NaO + 6HO. 



Either of these formulae would suit the analysis ; in support 

 of the latter may be adduced the fact observed by Gregory, 

 that sulphuret of nitrogen in the presence of caustic alkalies 

 acquires a deep transitory amethyst colour, which, on disap- 

 pearing, evolved ammonia, a description exactly accordant 

 with the present case. 



Action of Sulphuretted Hydrogen on the Nitroprussides. 



30. Sulphuretted hydrogen decomposes the soluble nitro- 

 prussides. The products of transformation are most conve- 

 niently obtained in the following way : — Nitroprusside of 

 sodium is dissolved in the smallest possible quantity of cold 

 water, and three or four times its volume of alcohol is added 

 to the solution. Sulphuretted hydrogen is now passed through 



