210 Dr. Play fair on the Nitroprussides, 



filtering from the oxides of these metals and evaporating the 

 solution by a gentle heat. When prepared from the iron salt, 

 it is apt to contain a little iron in excess. 



Nitroprusside of sodium is however most easily prepared 

 in the following manner: — 1 equiv. of yellow prusside of 

 potassium is digested with 5 equivs. nitric acid, as described in 

 page 202, until the solution precipitates salts of protoxide of 

 iron of a slate colour. It is now neutralized with carbonate 

 of soda, both solutions being employed cold. The neutralized 

 liquid is now boiled, and the green precipitate is separated by 

 filtration from the dark red-coloured solution. This is then 

 evaporated down and again filtered from a brown precipitate 

 which falls during evaporation. The nitrates of soda and 

 potash are allowed to crystallize out. 



The dark red solution is now evaporated on the sand-bath, 

 and during evaporation prismatic crystals separate from the 

 hot solution. These are removed, dissolved in water, and 

 again crystallized by allowing the solution to cool. The reason 

 of taking the crystals from the hot solution in the first instance 

 is to obtain them uncontaminated with the nitrates, which are 

 more soluble in hot water than this nitroprusside. By this 

 process any quantity of the nitroprusside of sodium may be 

 obtained in fine large ruby-coloured crystals. 



Properties. — This salt crystallizes in fine ruby-coloured 

 prisms, which have been measured by Prof. Miller. 



Symbols: — a 100, bO\0, e 101, r Oil, w 110, <r 211. x \& 

 common to the zones eniy ra. The angles between the nor- 

 mals to the faces are, — 



Nitroprusside of sodium resembles very much in appearance 

 the ordinary red prusside of potassium when the latter salt is 

 crystallized from alkaline solutions*. 



Nitroprusside of sodium is not at all deliquescent, but is 



* Red prussiate of potash crystallizes more easily and with much greater 

 beauty from alkaline than from neutral or acid solutions ; the reason being 

 that the excess of alkali decomposes a small quantity of a green precipitate, 

 which crystallizes along with it. 



