144 On the Combinations of Chromium, 



mercury and muriate of chromium. Chromic acid converts 

 it into the bichromate. It is obtained, by boiling a solution 

 of ammonia, on bichromate of mercury ; decanting, wash- 

 ing the black powder, consisting of chromate, and oxide of 

 mercury, and heating it on a vapor bath for twelve hours ; 

 the oxide is reduced, and the mercury may be separated by 

 washing ; — or acetic acid may be employed to remove the 

 oxide, from the black powder while moist. 



Bichromate of Mercury. — This salt may be obtained in 

 small scales ; it usually exists in the form of a powder ; its 

 color is a beautiful scarlet. It is slightly soluble in nitric 

 acid ; muriatic acid converts it into chloride, and bichloride 

 of mercury, and chromic acid. Ammonia, instantly con- 

 verts it into chromate and oxide of mercury. 56 parts of 

 this salt, were heated with a solution of ammonia ; the black 

 powder which resulted, was washed, and exposed to a tem- 

 perature sufficiently high to volatilize the mercury ; — the ox- 

 ide of chromium which remained, weighed 4.864 parts. The 

 fluid which was decanted from the powder, was evapora- 

 ted, and the salt which remained was heated ; 4.927 parts 

 of the oxide of chromium were obtained. It may be ob- 

 tained in the form of scales, by adding mercury to chromic 

 acid ; or by heating mercury, in an acid solution of chromate 

 and nitrate of potash. By adding chromate of potash, to 

 acid proto-nitrate of mercury, and washing the resulting pre- 

 cipitate in hot water, it is obtained in powder. 



Chromate of Chromium. — Chromic acid, dissolves moist 

 oxide of chromium, and forms with it a neutral solution, of a 

 yellowish brown color ; it does not afford crystals, but it 

 sometimes affords small prismatic fragments. Its powder is 

 brownish black, and shining. It may be repeatedly evapo- 

 rated to dryness, and redissolved in water, — if not exposed 

 to a temperature above 212° F. — without decomposition. 

 With nitrate of lead, it gives a yellow precipitate. With 

 ammonia, a dark green precipitate. When exposed to a 

 temperature equal to 212° F. for a long time, it is rendered 

 insoluble in water. 



Windsor, Vt. 9th Januartj, 1828. 



