gio Mr. Chenevix's Enquiries concerning the Nature 
that similar fixations of volatile substances are not uncommon. 
If an ore containing sulphur, or arsenic, or antimony, be gently 
roasted, a great part of those volatile bodies is driven off; but, 
if a fusing heat be suddenly applied, the mass unites in such a 
manner that a very small share of them escapes. Mr. Hatchett 
has instanced an artificial combination of gold and arsenic, from 
which he could not expel the latter metal, by any degree of heat. 
Yet arsenic, though less fusible, is not much less volatile than 
mercury. I will also add a case still more in point ; viz. the 
combination of arsenic and platina, which is not to be broken by 
a fusing heat. 
An example of this fact, occurs again in water. The lique- 
faction or solidification of two gases to produce water, by a 
loss of caloric, never shocks our mind, because it is familiar to 
us. We cannot say what loss of caloric may be sustained by 
mercury, in order to unite with platina ; or how far the presence 
of the latter may contribute to expel caloric from the former. 
We know too, that at any temperature, without the aid of a 
combustible body, to act as a reductive, we have not been able to 
disunite the last portions of oxygen, from the oxides of iron or 
of manganese. Yet, in the usual method of reducing a metallic 
oxide, the oxygen is surrounded by a much greater quantity of 
caloric than is necessary to convert it into gas. Every fixation 
of a volatile substance is analogous to the present question; 
and they whose minds have taken alarm from the novelty 
of the fact, may thus be familiarized with the necessity of ad- 
mitting it. 
But, it may be objected, in the instances of iron or manganese, 
oxygen is combined with a combustible body, and retained in it 
by a decided and powerful affinity. There is no reason to suppose 
