ON BICHROMATE OF LIME, ETC. 
71 
2. The mixture is now calcined for nine or ten hours at 
a bright red heat upon the sole of a reverberatory furnace, 
taking care to spread it equally in a layer from 5 to 6 cen- 
tim. in thickness, and to renew the surface tenor twelve 
times with the rake. At the end of this time, if the fiame 
was sufficiently oxidizing, the conversion of the oxide of 
chromium into chromate of lime is effected. This is easily 
ascertained ; in the first place from the appearance of the 
substance, which exhibits a yellowish-green colour,* and 
then because it has the property of dissolving entirely in 
hydrochloric acid with the exception of particles of sand. 
3. The very friable and porous mass is now crushed 
under a mill, mixed with hot water, and the liquid mass 
constantly kept in agitation, and sulphuric acid added until 
the liquid slightly reddens blue litmus-paper. This charac- 
ter indicates the complete change of the chromate of lime 
into bichromate, and the formation of a little sesquisulphate 
of iron. 
4. Some triturated chalk is now gradually added to the 
liquor until the whole of the peroxide of iron is removed. 
The bichromate of lime does not by this treatment experi- 
ence any change as regards its state of saturation. 
5. After being allowed to stand quiet for a short time, 
the clear supernatant liquid, which contains only bichro- 
mate of lime and a little sulphate, is drawn otf ; it may now 
be used immediately to prepare the bichromate of potash, 
the neutral and basic chromates of lead, and even the chro- 
mates of zinc, which will probably ere long be consumed 
to a great extent in the arts, since the oxide of zinc has 
already taken the place of carbonate of lead in white paint 
with drying oil. 
*This singular peculiarity of the chromate of lime with an excess 
of base, of retaining the green tint of the oxide of chromium, must 
have led to the beUef that no chromate of lime was produced, espe- 
cially as the latter is scarcely soluble in water. 
