3)5j2 Dr. Playfair on the Nitroprussidesi 



Or expressed in another way, — 



4 equivs. ferrocj'anide of sodium Fe^ Cy^'^Na^^ 

 3 equivs. nitrite of soda . . , Na^ N^ O^^ 



1 equiv. peroxide of iron . . Fe^ O^ 



3. equivs. nitrogen N^ 



2 equivs. nitroprusside+ 9 of soda=Fe^° Cy^"* Na'^ N^ O'^ 



The first change is obviously to form ferrocyanide of sodium, 

 6 equivs. of oxygen passing over to the nitrous oxide; this, 

 witli the oxygen in the latter, would make 4< equivs. nitrous 

 acid; but the 2 equivs. of iron liberated require 3 of oxygen 

 to form peroxide, which it receives at the expense of the ni- 

 trous acid, leaving therefore 3 equivs. of that acid to unite 

 with soda, the remaining 3 equivs. of nitrogen escaping as a 

 gas. During the ebullition no ammonia can be detected, 

 either by smell or by turmeric paper. 



Section V. — Aclioji of' an Alkaline Sulphide on a Nitro- 

 prusside. 



27. It has been repeatedly mentioned, that when solutions 

 of nitroprusside of potassium or sodium and of the corre- 

 sponding sulphides are mixed together, the most magnificent 

 purple colour is produced. This colour however is very trans- 

 itory and cannot be preserved in an aqueous solution. The 

 purple or blue compound may however be obtained in a solid 

 state when alcoholic solutions of the two salts are employed. 

 In order to obtain it in this state, nitroprusside of sodium is 

 dissolved in the smallest possible quantity of water, and to this 

 solution is added four or five times its bulk of alcohol. An 

 alcoholic solution of neutral sulphide of sodium (the sulphide 

 obtained by reducing the sulphate with hydrogen) is now 

 added to the alcoholic solution of nitroprusside, the addition 

 being stopped before the supernatant liquid gives a decidedly 

 black reaction on lead paper. The mixed solutions acquire a 

 magnificent purple blue colour. On stirring the mixture, an 

 aqueous solution of the purple compound falls down in oily 

 drops. After this has settled, the alcohol is decanted, and 

 the blue solution is washed repeatedly and quickly with alcohol 

 by decantation. It is now, as rapidly as posssible, put in 

 vacuo over sulphuric acid, when it soon parts with its water 

 and becomes solid. It usually dries to a dirty green powder, 

 which is a mixture of the purple compound with the products 

 of its decomposition. It may however, though this is rare, 

 dry quite unchanged in its character, being still of a fine blue 

 colour and dissolving entirely in water with all its magnificent 



