44^ Professor Berzelius on [June, 



the contrary, the potash combinino; with their acids leaves a 

 substance as black as charcoal, which contains no combined 

 water, and which suffers much less change during washing than 

 the protoxide : it is this compound of deutoxide with protoxide 

 which I have named oxidum ferroso-ferricum ; and it is to be 

 presumed that the composition of these salts may be expressed by 



Fe P« + 2 Fe P« et par Fe As- + Fe As^ 



ji It appeared to me extremely probable that prussianblue might 

 be a completely analogous compound. Its formation by means 

 of double decomposition ought then to destroy the neutrality of 

 the two salts formed, and free acid ought to be liberated. 



I prepared a solution of neutral muriate of deutoxide of iron, 

 and after having determined by a correct analysis the relation 

 of the acid to the oxide of iron, in order to satisfy myself of its 

 being neutral, I added it drop by drop to a solution of cyanuret 

 of iron and potassium, which did not change the colour of 

 tournsol. When the greater part of the cyanuret was decom- 

 posed, I suffered the precipitate to remain. The clear liquid was 

 found to be as neutral as at first, so that the precipitate was as 

 neutral a compound as the substances employed to prepare it. 

 I continued to add the muriate of deutoxide of iron until it was 

 in excess. The liquid had then acquired the property of slightly 

 reddening the tincture of turnsol, as must happen from the excess 

 of muriate employed. The prussian blue produced in this expe- 

 riment can, therefore, only be a double hydrocyanate in which 

 the oxygen of the deutoxide is double that of the protoxide. 



I afterwards analyzed some prussian blue thus prepared, by 

 digesting it with excess of caustic potash. The undissolved 

 oxide of iron was separated and washed,* and the alkaline liquid 

 (which with the protoxide of the decomposed blue had formed 

 cyanuret of iron and potassium) was decomposed by the addition 

 of corrosive sublimate, the digestion being continued for some 

 hours. The oxide of iron precipitated by this process was 

 washed and strongly heated to separate the oxide of mercury 

 which was precipitated with it. The oxide of iron, separated 

 from the prussian blue by potash, was to that separated by cor- 

 rosive sublimate as 30 to 22. 



If the prussian blue were analogous to the phosphate and arse- 

 niate alluded to, the two weights of the oxide of iron ought to 

 have been in the proportion of 2 to 1. I, therefore, repeated 

 the experiment with the prussian blue, washed, but not dried, in 

 order that it might not be changed by the drying, and the two 

 weights thus obtained were 70*5 parts of oxide of iron, separated 

 by the potash, and 52 parts precipitated by digestion with the 



♦ I satisfied myself by an experiment previously mjide, that the oxide of iron thus 

 «btained contained no hydrocyanic acid. 



