the Chromate of Iron, ^c* 99 



pearl-like laminse. To conclude, this salt is easily decom- 

 posed by heat; even when it is dissolved, brown flakes are 

 •eparated, which are oxide of chrome, and which become 

 green by calcination. 



Chromate of Lime. 

 Chromic acid forms a very soluble salt with lime ; its so* 

 lution furnishes by evaporation silky flakes of a yellowish 

 brown, which are easily dissolved in water r this salt is de* 

 composed by the fixed alkalis. 



Chromate of Magnesia, 



Magnesia easily combines with chromic acid : the sail 

 which results from it is very soluble in water; the solution 

 crystallizes in prisms with six faces perfectly tran>parent, 

 and of a fine topaz yellow : when they are in considerable 

 quantity the colour is orange yellow. 



Magnesia is separated from the chromic acid by the fixed 

 caustic alkalis and the alkaline earths. 



Metallic Chromaies, 



If into a solution of sulphcrttj of iron at the mim?num 

 we pour chromate of potash, we obtain a fawn-coloured 

 precipitate, which, when treated with caustic alkali, gives 

 no trace of chromic acid : this precipitate is dissolved with 

 'great facility in muriatic acid, from which the alkali sepa- 

 rates it completely without the least trace of alkaline chro- 

 mate remaining. The nitric acid dissolves a part of the 

 precipitate, and assumes a fine green colour : this precipi- 

 tate therefore is not a chromate of iron, but a mixture or 

 combination of oxide of iron and oxide of chrome, which 

 seems to resemble strongly what is presented to us by na- 

 ture. 



It is evident from the result of this experiment, that the 

 chromic acid has been decomposed by the oxide of iron, 

 which, in passing to the maximum^ has reduced the rather 

 to the minimum, or to the state of green oxide. If we 

 wished therefore to form chromate of iron, it vi'ould be 

 necessary to employ this last metal saturated with oxvgen, 

 in order that it may not be able to act upon that of the 

 chrome. 



Chromate of Lead, 



This combination assumes different shades, accordins; to 

 the manner in which it has been prepared. 



• If the chromate of potash be neutral, we obtain an 

 ^range-^yellow colour; if it has an excess of acid, the co- 

 lour 



