448 Count he Muistres Memoir on [Dec. 



colour of the earth ; but when it is formed, it is perfectly similar 

 to the finest prussian blue of commerce. 



Observations. 



When we review the facts contained in this memoir, we may 

 observe, that when the combinations of prussic acid with 

 cai oonate of lime, sulphates of lime, barytes, and strontian, pass 

 from green to blue by the slow absorption of oxygen from the 

 atmosphere, it is not, in all probability, the bases of these prus- 

 siates which are oxidized ; for the carbonate and the sulphate of 

 the earths are not capable of uniting with an additional dose of 

 oxy°'en. It. is probable then that it is the prussic acid itself 

 which unites with the oxygen in this case. 



We find a proof of the oxidation of this acid in its combina- 

 tion with indigo. The boiling sulphate of indigo precipitated 

 by pvussiale of potash is all at once disoxygenized, and assumes 

 a green colour, as when it is treated by sulphate of iron in the 

 dyer's vat. 



It is likewise very probable that in all the blue metallic prus- 

 siates the prussic acid is oxidated ; while the bases are at a 

 minimum of oxidation, and this is evident for the blue prussiate 

 of copper. We see in fact that the protoxide and peroxide of 

 copper in all their solutions form red prussiates ; while in the 

 blue prussiate (experiment 10), the copper dissolved in contact 

 with the prussic acid is seized upon in a nascent state at a degree 

 of oxidation which is doubtless less than that of all the known 

 oxides of copper, which give red prussiates. 



If the peroxide of iron gives a blue prussiate at the instant of 

 its formation, the reason is that it contains enough of oxygen to 

 saturate the acid while it passes into the state of protoxide, 

 while the peroxide of mercury which contains only OlO or 015 

 of oxygen forms a green prussiate. Now as it is known that 

 mercury is incapable of combining with a greater quantity of 

 oxygen, it follows that when the green prussiate passes into blue, 

 it is not the base which absorbs oxygen, but the prussic acid 

 itself. 



Sulphur, phosphorus, and carbon, form green prussiates, 

 because they cannot furnish the requisite quantity of oxygen to 

 the prussic acid. It is obvious that these radicals cannot pass 

 to a maximum of oxidation, when their prussiates change from 

 green to bine, because, when saturated witn oxygen, they become 

 acids. This is the case also with those substances which con- 

 tain much oxygen in such a degree of union that the prussic acid 

 is unable to abstract it. These substances combine green, a* 

 the earthy sulphates, and the oxides of aluminum and silicon. 



By means of this theory, which explains all the facts, the 

 phenomena of the two prussiates of mercury, one soluble and 

 colourless, the other blue and insoluble, are easily understood. 



