Blue Pnijiate of Iron, .r. 



of the air on a filter. It becomes blue by abforbing oxygene ; and the colour does not ac- 

 quire its greateft intenfity until the oxide of iron has obtained ^\% of that principle. 



Of all the faline combinations of iron, there is none of which the bafis becomes faturated 

 with oxygene fo rapidly as the pruffiate. The carbonate of iron is not to be compared 

 with it. 



The fulphuric and muriatic acids poured on the white pruffiate of iron occafion no 

 change. The oxygenated muriatic acid, on the contrary, enlivens the pruffiate in an inftant, 

 and lofes its odour. The nitric acid likewife converts it to blue, but more flowly, becaufe 

 it does not abandon its oxygene with the fame facility as the oxygenated muriatic acid. 



The folution of fulphurated hydrogene, which does not alter the green fulphate, as has 

 already been remarked, has likewife no adion on the white pruffiate. It merely reduces to 

 white the fmall quantity of pruffiate which had become blue by the accefs of air ; or in 

 other words, it deprives it of that portion of oxygene which, it may already be feen, con- 

 ftitutes the difference between the white and the blue pruffiates. 



It may perhaps be an anticipation of the facls, to diftinguiflt that pruffiate by the name 

 of white, which in flrifliiefs is fuch only at the moment of its formation, and afterwards 

 becomes covered with a greenilli white ; but it is very probable tliat it acquires this fhadc 

 merely from the air contained in the veffiel, and in the liquids made ufe of. There exifts like- 

 wife another caufe in the fmall portion of red oxide, from which the alkaline and even the 

 calcareous pruffiates derive their yellow colour. This oxide becomes converted into blue 

 pruffiate, and mixes with the white pruffiate at the moment wherein the pruffic acid being 

 difengaged from the alkalis, is at liberty to unite with the diffi;rent oxides it meets with. 

 Thefe oxides are, as we have feen, a great quantity of the black oxide mixed with the red 

 oxide of the alkaline pruffiate. It mud therefore neceflarily follow, that a fmall portion of 

 the blue pruffiate will be mixed with a great quantity of the white pruffiate ; whence thislaft 

 acquires its greeniffi tinge. 



From the whole of thefe fafts, it is evident that the oxide, which conftitutes the bafe of 

 the white pruffiate, polTefles the fame degree of oxidation as when it formed the bafis 

 of the green fulphate. This oxide in efteft paffies from the fulphate to the white pruf- 

 fiate, without the interference of any caufe which can either increafe or diminifli the pro- 

 portion of oxygene. Hence it follows, that fince the alkalis feparate the oxide of the green 

 fulphate of a grafs-green colour, they ought alfo to feparate it from the white pruffiate 

 under the fame tinge. 



This in facl happens at the inftant when the cauftic alkali, or ammoniac, is poured ort 

 the white pruffiate. But in order to judge better of the fhades, it is advifable to ufe thefe 

 folutions diluted with water. The green oxide is not completely deprived of pruffic acid 

 till after the repeated application of alkalis. This may be ffiewn by taking up the green 

 oxide, by an acid which does not diffijlve the white undecompofed pruffiate. 



The Blue Prujpate. 

 AFTER what has been faid, it is eafy to forctcl the habitudes of the nitrate, and alF the 

 folutions of wiiich the oxide is at its maximum of oxidation, when alkaline pruffiates ar6 

 applied. No interval is perceived between the precipitation and the mofl lively blue. The 



colour 



