444 Professor Berzelius on [June, 



yielded carbonic acid and azote which indicated almost precisely 

 the same quantity of cyanogen as in the former experiment. By 

 adding together the weight of the water, iron, and cyanosjen, it 

 almost precisely equalled that of the prussian blue employed. 

 No one of these experiments indicated such a relation of the 

 iron to the cyanogen as ought to have been obtained according 

 to the experiments made in the humid way, and already described; 

 they leave, therefore, some uncertainty as to the true nature of 

 this substance. 



I treated some prussian blue recently prepared, with muriatic 

 acid to separate the excess of base, and after having well washed 

 it, I mixed it with pure water, and passed a current of sulphur- 

 etted hydrogen gas through it, until the water was saturated 

 with the gas. I then corked the bottle, and left these two sub- 

 stances to react upon each other for several days. The prussian 

 blue became of a lighter blue colour, and eventually became of 

 a dirty white. 



The fluid became whitish with the sulphur precipitated ; I after- 

 wards separated the white mass, and I evaporated the excess of 

 sulphuretted hydrogen gas by exposure to the air. This fluid 

 now reddened tournsol, and precipitated of a blue colour those 

 salts of iron which contained deutoxide. The sulphuretted 

 hydrogen gas on reducing the deutoxide of iron of the prussian 

 blue to the state of protoxide, and then separated from it that 

 portion of hydrocyanic acid by which the deutoxide had been 

 neutralized in the same way as occurs with every other neutral 

 salt, whose base is a deutoxide, when the sulphuretted hydrogen 

 reduces it to the state of protoxide. It must also be observed 

 that the acid liquid in question contains no pure hydrocyanic 

 acid ; it still contained iron : it was the ferruginous prussic acid, 

 which I shall hereafter consider. 



The mass which was rendered white by the action of the 

 sulphuretted hydrogen regained its blue colour by exposure to 

 the air, and became at the same time partly soluble in pure 

 water. The blue solution again treated with sulphuretted hydro- 

 gen deposited a black substance, did not again become acid, 

 nor did it again acquire the property of precipitating the solu- 

 tions of deutoxide of iron of a blue colour. |n the same manner, 

 the insoluble portion of the regenerated blue became black by 

 sulphuretted hydrogen. These experiments prove then that there 

 are actually two blue compounds, one of which is neutral, and 

 composed of three atoms of hydrocyanate of protoxide and four 

 atoms of deutoxide of iron ; that is to say, the last contains 

 twice as much oxygen and acid as the first. The other appears 

 to be composed of an atom of hydrocyanate of protoxide and 

 of two atoms of subhydrocyanate of deutoxide of iron, analogous 

 to the blue phosphate of iron and the green arseniate of the same 

 metal. 



