CHROMATES. 325 



jewellers paste, which is used in producing imitations 

 of precious stones. 



CHROMATES. 

 828. CHROME YELLOW. To prepare this 



How is chrome . ., . , 



yellow pre- pigment, a solution of the commercial 

 pared? bichromate of potassa is added to a solution 



of sugar of lead. A double decomposition ensues ; the 

 result of which is the production of a beautiful 

 yellow precipitate, known as chrome yellow. 

 The precipitate is a chromate of lead. The 

 bichromate of potassa used in the experiment, is 

 made from the mineral chrome iron, which has 

 been mentioned in a previous chapter. The acid itself, 

 which is without practical applications, may be made 

 from the salt. It contains, like sulphuric acid, three 

 atoms of oxygen. 



How is chrome ^^' CHROME ORANGE. Chrome yellow 



yellow con- ma y be converted into chrome orange, by 



verted into . . , , . 



chrome digestion with carbonate of potassa. Cloth 



dyed yellow by dipping it alternately into 

 a solution of bichromate of potassa and sugar of lead, is 

 instantaneously changed to orange by immersion in 

 boiling milk of lime. This action of the lime, as well 

 as that of carbonate of potassa, depends upon its ab- 

 stracting a. certain portion of the chromic acid, leav- 

 ing thereby a chromate of lead of different composi- 

 tion and color. 



