846 



The author expresses his hope to lay before the Society a con- 

 tinuation, containing some original mathematical investigations on 

 magnetic distributions, and a theory of induction, in ferromagnetic 

 or diamagnetic substances. 



8. " On the Nitroprussides, a new Class of Salts." Bv Dr. Lyon 

 Playfair, F.R.S., F.C.S. 



When nitric acid is made to act on yellow prusside of potassium, 

 in the proportion of one equivalent of acid for every equivalent of 

 potassium present in the salt, the following reactions are observed. 

 The salt dissolves in the acid with a dark red, almost black colour, 

 a very little nitric oxide is evolved, which soon ceases, and is fol- 

 lowed by a copious evolution of cyanogen mixed with nitrogen. 

 The continued action of the acid causes the liquid to cease the usual 

 reactions of red prusside of potassium ; the addition of sulphate of 

 iron now produces a slate-coloured instead of blue precipitate. On 

 allowing the solution to cool, abundance of nitrate of potash cry- 

 stallizes out, mixed with a little prussian blue, and about 5 per cent, 

 of the original weight of the salt, of a white granular substance, 

 which is scarcely soluble in cold, and only very slightly so in boil- 

 ing water. This white substance, on examination, proves to be the 

 remarkable body oxamide, the production of which in an oxidising 

 medium is highly singular. 



The dark red supernatant liquor, being neutralized with an alka- 

 line carbonate, and boiled, deposits a green precipitate and yields a 

 clear ruby-red solution. This solution furnishes the new class of 

 salts, which is the subject of this paper. It may be evaporated to 

 crystallization, and yields the nitroprusside of the base used in the 

 neutralization. 



The characters of the nitroprussides thus obtained are very 

 marked, and cannot be confounded with those of any known class 

 of salts. 



With soluble sulphurets, the nitroprussides produce the most 

 magnificent purple-coloured solution, and of such intensity, that 

 they form by far the best test for the presence of a sulphuret, and 

 betray its presence when the usual tests for a sulphuret are insuffi- 

 cient to expose it. 



With a protosulphate of iron, the nitroprussides produce a salmon- 

 coloured precipitate ; with salts of silver, zinc and cobalt, a preci- 

 pitate of a flesh colour ; and with nickel, a dirty white precipitate. 

 With a salt of copper, the precipitate is of a light green, and with 

 salts of lead, no precipitate is occasioned. 



Nitroprussic acid is obtained by adding muriatic acid to the silver 

 salt, and forms a dark red solution, which yields on evaporation in 

 vacuo, large and well-defined crystals. 



The nitroprussides of sodium, potassium, ammonium, barium and 

 calcium, are all soluble and crystallize readily, forming fine large 

 red crystals, which have been measured by Prof. Miller of Cam- 

 bridge, and are described in the paper. The salts of barium and 

 calcium decompose on evaporation, and can after that no longer be 



