OF THE ELEMENTARY BODIES. 245 
white, of a high metallic lustre, has a greater specific gravity 
than the preceding, and is not changed by the air, when in the 
finest powder, even at a temperature of 158° to 176° F., and 
sometimes even considerably above 212°. 
Arsenious acid assumes both the corresponding isomeric mo- 
difications, and what is remarkable, they are formed by sublima- 
tion under exactly the same circumstances as the allotropic states 
of the metal. The radical of the vitreous acid is then Asg, and 
that of the white, or that which crystallizes in octahedrons, Asa. 
The higher specific gravity of Asg occurs likewise in the vitreous 
acid. 
One isomeric modification only of arsenic acid is known to us ; 
as far as we can conclude, from analogy with phosphoric acid, 
Asa is the radical in it. 
Tellurium is also as yet known in but one allotropic modifica- 
tion, and even in that it has been but little examined. However, 
both tellurous as well as telluric acid possess two distinct iso- 
meric modifications, and these are of such kind as lead us to 
presuppose allotropic modifications similar to those of silicium. 
Exactly the same holds good with respect to antimony. 
Chromium however affords a particularly instructive example. 
When oxide of chromium is reduced by charcoal at a very high 
temperature, it yields a pale gray metal, which cannot be oxi- 
_ dized either by a red heat or boiling with nitromuriatic acid. 
The action of fluoric acid, or combustion with potash or soda 
with access of air, or with nitre, are the only means whereby it 
can be brought to its original condition, which may be expressed 
by Crg. 
When, on the contrary, chloride of chromium, free from water 
and oxide, is reduced by potassium, a gray pulverulent metal is 
likewise formed, which cannot be oxidized by boiling water, but 
when heated to between 392° and 572° F., inflames and burns 
vividly into the green oxide of chromium, and dissolves in hy- 
drochloric acid with copious evolution of gas. This then is Cre. 
We have here then the same behaviour as in the case of sili- 
cium, and the behaviour of oxide of chromium exactly agrees with 
that of silicic acid. We havea green oxide of chromium, which is 
soluble in acids, and, like the soluble silicic acid, at a higher 
temperature passes into the insoluble modification, resembling 
silicic acid which has been heated to redness ; but in this trans- 
formation a viyid evolution of light occurs, which has never been 
