144 Remarks on Priestley’s Analysis 
tal is a compound substance, consisting of a calx 
and phlogiston (p. 39); that a metal becomes a calx 
by losing its phlogiston (p. 43);* and that a calx is 
reduced by acquiring phlogiston. They afterwards 
tell us, that a metal may become a calx, and at the 
same time retain its phlogiston (p. 40); and that a 
calx, in becoming a metal, may part with phlogis- 
ton ;f and when a metal, in becoming a calx, is al- 
lowed to have lost phlogiston, they contend, that 
that phlogiston was not necessary to the constitution 
of the metal, provided the calx can be revived by 
mere heat (p. 41 and 42); and, finally, that a metal 
has the same properties whether it have a deficiency 
or an excess of phlogiston! (p. 42). 
It must, however, be confessed, that these gra~ 
tuitous assertions, so fatal to the cause they are in- 
tended to defend, are peculiar to Dr. Priestley; at 
least I have not seen them in the writings of other 
chemists. It is on the contrary generally allowed, 
that the red oxyds of mercury, whether obtained by 
* “ Precipitate per se (says Dr. Priestley) is much more 
easily procured in dephlogisticated than in common air, and 
probably not at all in phlogisticated air; this air not being 
capable of taking any phlogiston from mercury, without 
which the calx cannot be formed.’”? Experiments on Air, 
vol. 11, p. 185. 
‘+ The azotic gas, which is mixed with the oxygenous 
gas, obtained from precipitate per se, is ascribed by Dr. 
Priestley (p. 41) to phlogiston retained by the calx, with 
which it parts when it becomes a metal. 
