138 On the Combinations of Chromium. 



a pneumatic apparatus, oxygen is given off at a tempera* 

 ture below 400° Fahrenheit. " The oxide obtained by ex- 

 posing nitrate of chromium to heat, until vapor of nitrous 

 gas ceases," — yields nitric acid, when treated with lime and 

 water. An unknown weight of the moist oxide, yielded chro- 

 mic acid 8.17 grains, protoxide of chromium 4.07 grains : 

 — it probably contains one prime of each. 



Peroxide of Chromium, or Chromic Acid. — When dry, 

 its color is yellowish brown ; its solution when somewhat di- 

 luted is yellow with a shade of brown ; the solution has an 

 acid and astringent taste ; — it bleaches litmus and blue pa- 

 per ; — it does not afford crystals by evaporation, but is reduc- 

 ed to a yellowish brown crust, which is slightly deliquescent. 

 It unites to alkalies and oxides, and forms salts. At a tem- . 

 perature below the boiling point of mercury, it fuses with 

 bubbling, and is partially decomposed ; at a red heat, it be- 

 comes the protoxide. It may be obtained by dropping mu- 

 riatic acid into a mixture of chromate of silver and distilled 

 water, until the red brown color of the chromate is reduced 

 to white with a tinge of red ; filtering, and cautiously add- 

 ing a few drops of muriatic acid, till a white precipitate 

 ceases to be formed. When large quantities are required, 

 the bichromate of lead may be added to strong muriatic 

 acid, and the mixture placed on a warm sand bath for a few 

 hours, occasionally stirring the mass. Water may then be 

 added and filtered from the chloride of lead, and the filter- 

 ed fluid used instead of the muriatic acid, in decomposing 

 the chromate of silver ; — in either process a solution of pure 

 chromic acid is obtained. This acid possesses the property 

 of coloring salts which crystalize in its solution. 



Protoxide of Chromium and Acids. — Nitrate of Chromi- 

 um. — Nitric acid dissolves protoxide of chromium, and affords 

 a solution, which, when concentrated, is of a dark green col- 

 or when viewed by reflected light, but by transmitted light, 

 thick portions of the fluid appear of a dark red ; by lamp 

 light, the solution transmits red light. By evaporation it does 

 not afford crystals, either when neutral or acid ; but is redu- 

 ced to a syrup, and ultimately, to a dry and brilliant gum like 

 mass, which often splits into long prismatic masses ; its col- 

 or is dark green both by reflected and transmitted light. Its 

 solution has a sweet and astringent taste, resembling the 



