610 SALTS OF OXIDE OF CHROMIUM. 



and no longer effervesces from the escape of carbonic acid gas, 

 upon the addition of either the acid or alcohol. In this experi- 

 ment the chromic acid, liberated by the hydrochloric acid, is 

 deprived of half its oxygen by the hydrogen and carbon of the 

 alcohol, and the resulting oxide of chromium is dissolved by the 

 excess of hydrochloric acid present, and in fact converted into 

 the corresponding sesquichloride of chromium. Many other 

 organic substances may be used in place of alcohol in this expe- 

 riment, such as sugar, oxalic acid, &c. The oxide of chromium 

 is precipitated from the green solution by ammonia, and falls as 

 a pale bluish-green hydrate. The same oxide is obtained more 

 directly, when to a boiling solution of bichromate of potash, 

 a hot solution of the pentasulphuret of potassium is added, the 

 chromic acid then giving half its oxygen to the sulphur. 



Hydrated oxide of chromium is soluble in acids, and forms 

 salts. It is also dissolved by potash and soda, but not to a 

 great extent by ammonia. Its solution in acids is generally 

 green or purple by reflected, and red by transmitted light. Its 

 salts have a sweet taste, and are poisonous ; they are not affected 

 by sulphuretted hydrogen ; alkaline sulphurets precipitate from 

 them the hydrated oxide. The oxide itself becomes of a greener 

 colour when dried, and loses water. A moderate heat affects 

 its relations to acids, the sulphate of the heated (or green) oxide 

 not forming a double salt, for instance, with sulphate of potash. 

 When heated to redness, it glows, or undergoes the same change 

 as zirconia, peroxide of tin, and many other hydrated peroxides 

 when made anhydrous, becomes denser, of a pure green colour, 

 and ceases to be soluble in acids. 



A sesquisulphuret of chromium, Cr 2 S 3 , corresponding with the 

 oxide, is obtained by exposing the latter,, in a porcelain tube, to 

 the vapour of bisulphuret of carbon, at a bright red heat. It is a 

 substance of a dark grey colour, which is dissolved by nitric acid. 



Sesquichloride of chromium, Cr 2 Cl 3 ; 2031.6 or 162.79. This 

 salt is obtained as a sublimate of a peach-purple colour, when 

 chlorine is passed over a mixture of oxide of chromium and 

 charcoal, ignited in a porcelain tube : or, by evaporating the 

 solution of sesquichloride of chromium to dryness. The salt 

 obtained by the latter process is a green powder, and retains 

 3HO at 212o ; above 400o it loses water and becomes anhydrous, 

 assuming the same colour as the sublimed chloride. In the 

 anhydrous state it dissolves very slowly in water. 



