30 On decomposing the Chromate of Iron, ^c. 



lour is deep citron yellow : if the alkali on the contrary be 

 predominant, the sluide is a reddish vellow , and sometimes 

 a fine deep red ; the shades iilso vary in proportion as we 

 operate in the hot or cold manner; 



Chromate of lead made vMih a solution slightly acid is 

 that whieh is most in request by painters, and ii is m fact 

 the most solid/ .We may heignicn its colour, either by a 

 little alkali, or by precipitating it hot v\ith acetate of leadJ 

 In the latter case it should seem tliat a part of the acetic 

 acid is separated, and that the ox'de of lead which it aban- 

 dons is i.iuted to the common cliromate and heightens its 

 colour. 



We should conceive that the chromates which contain 

 an excess of oxide of lead must be more alterable by sulphu- 

 rous vapours than those in which this oxide is saturated by 

 the chromic acid. 



Cliromale of Copper* 

 The simplest way of forming chromate of copper is to 

 mix a soluhon of neutral chromate of potasii with a solu- 

 tion of sulphate of copper: a brownish-yellow precipitate 

 is formed, which, when well washed and driedj assumes a 

 bistre brown colour. 



Chromate of Silver, 



Chromate of silver is prepared by decomposing, nitrate of 

 silver by neutral chromate of potash : a reddish-brown 

 precipitate is produced when the operation is performed with 

 heat, and of a pur|)le-red when done in the cold: lastly, 

 it is of a carmine- red colour if the solution of chromate of 

 potash contains a sligiu excess of acid : in the latter case 

 the precipitate is not so quickly formed, and is less abun- 

 dant, but it is crystallized in small semitransparent grains. 



This salt becomes brown on exposure to light; it is so- 

 luble in the nitric acid, and from which the muriatic acid 

 separates the oxide of silver. 



Uses to ivliich the Preparations of Cftrome are applied. 



This oxide is now G,enerally ertiployed in the porcelain 

 manufactories throughout France. It supports better than 

 any other metal, and without undergoing any alteration, 

 the intense heat employed to prepare hard porcelain : it 

 produces an extremely beauiirul green, which has not yet 

 been obtained with any of the other metals. 



A very line enamel resembling in colour the emerald of 

 Peru is made with the oxide of chrome. Another enamel 



is 



