12 Mr. E. W. Davy on some new Methods of 



The proportions usually employed were about 1 part by weight 

 of the ferrocyanide, from 2 to 3 of the chlorate, and 3^ of hydro- 

 chloric acid diluted with about twice its own bulk of water. 



The two salts, being separately reduced to powder, were care- 

 fully mixed and then treated with the acid. I generally placed 

 the mixture in a bottle leaving the stopper loose, and shook its 

 contents from time to time to promote the reaction ; when, after 

 two or three days, the presence of a nitroprusside was detected 

 in the mixture, and the quantity formed gradually increased with 

 the time it was allowed to remain. By treating the ferrocyanide 

 of lead in the same way, I found that a nitroprusside was very 

 readily formed. It is probable, therefore, that many of the 

 other ferrocyanides, particularly those the bases of which form 

 soluble salts with nitroprussic acid, would give rise to the forma- 

 tion of nitroprussides when treated in like manner. 



I may observe, that the application of heat to such mixtures as 

 I have referred to, seems, instead of promoting, to be unfavour- 

 able to the formation of the nitroprussides, as the gaseous pro- 

 ducts arising from the action of hydrochloric acid on the chlo- 

 rate principally escape without producing the desired effect ; so 

 that after gently heating such a mixture, only a mere trace of 

 nitroprusside is ever formed, and that only when the chlorate 

 and the hydrochloric acid have been in large proportions com- 

 pared with that of the ferrocyanide. But if the mixture be 

 allowed to remain at the ordinary temperature, little gaseous 

 matter is evolved, and after some days a considerable proportion 

 of nitroprusside will be formed. 



2nd. By the action of hypochlorous acid on the ferrocyanides. 

 Thus, when an aqueous solution of hypochlorous acid obtained 

 by the usual way is gently warmed with a little of the ferrocya- 

 nide of potassium, some nitroprusside is quickly produced, its 

 formation commencing at about 90° F., and being completed at 

 about 110°. It is also produced, though very slowly, when 

 those substances react on each other at ordinary temperatures, 

 so that it cannot be detected till after the lapse of a day or two. 

 I have also succeeded in forming nitroprussic acid compounds by 

 gently heating the hydroferrocyanic acid, the ferrocyanide of 

 lead, and prussian blue, with an aqueous solution of hypochlo- 

 rous acid. In any of these instances the formation of the nitro- 

 prusside may be detected by the addition of a soluble sulphuret, 

 as, for example, the sulphuret of ammonium, previously filtering 

 the solution if necessary. 



3rd. When ferrocyanide of potassium is dissolved in water 

 together with chlorate of potash, and the mixture exposed to the 

 action of light and the sun's rays, the two salts will very slowly 

 react on each other, and a series of changes occur, amongst which 



