ON CHEMISTRY. 
147 
were suffocated in a few seconds, and when a taper was plunged in¬ 
to it, it was extinguished as if it had been immersed in water.” 
This is no fanciful experiment, it is not one of mere science, per¬ 
formed by a gentleman in his private laboratory. With some modi¬ 
fications it is, and has long been, repeated by the operative chemist, 
for the production of one of the most energetic preparations of mer¬ 
cury, add (the red oxide, or Mercurius calcinatus.) The late Sir 
H. Davy states in few words that follow the converse of the experi¬ 
ment just adduced. 
“ To procure pure oxygen from air, quicksilver may be kept 
heated in it, at about 600 degrees till it becomes a red powder: this 
powder when ignited, will be restored to the state of quicksilver by 
giving off oxygen.”— Agricul. Sects, p. 194. Edit. 4. 
That the reader may acquire some idea of the chemical changes 
effected by these processes, I add the mercury in the vessel, sub¬ 
jected for many days to a high temperature, is acted upon by a por¬ 
tion of the atmospheric air within the vessel. It gradually loses its 
metallic appearance, and certain portions of it acquire a red colour 
and crystalline figure. These red particles are heavier than the por¬ 
tion of mercury which has disappeared; for if the remaining metal, 
and the red particles be weighed, they will be found to exceed in 
weight that of the mercury originally employed; and if the air re¬ 
maining in the vessels be also correctly weighed, it will be found to 
have lost in weight exactly as much as the red particles of the pre¬ 
paration have acquired. 
These red particles (as Davy asserted, and Lavoisier’s experiment 
had in its completion clearly demonstrated,) will give forth by the 
agency of heat, that portion of the air, which they had attracted. 
The air of the atmosphere is thus proved to be composed of two aeri- 
riform fluids or gases at the least; and by a variety of well conduc¬ 
ted experiments, chemists have arrived at the'conclusion that, the 
non-respirable part exists in the proportion of about 79 in every 
100 parts of air. The remaining 21 parts consist of a gas which is 
not only respirable, but capable of supporting combustion in a very 
eminent degree. In my first paper, page 436-7, I alluded to both 
these gases; to the former under the terms of Azot or Nitrogen, and 
to the latter, under that of oxygen. 
How the agency of fire may be exerted so as to cause, first, the 
attraction and fixation of the oxygen, or vital principle of the air; 
and second, its separation and expulsion from the red oxide, the for¬ 
mation of which it had previously induced, is one of those mighty 
secrets, which the human mind may, perhaps, never be permitted to 
l 3 
