42 
he lights, and then thrusts the iron into ajar containing vital air ■ when the 
hot extremity immediately takes fire, and burns away lapidly, exhibiting a 
dazzling light. , resembling the most brilliant fire -works/' a white filmy 
jmoke is produced, and the iron, as it consumes, becoming saturated with 
oxygen, falls to the bottom of the glass in red-hot globules, which prove 
upon examination to be an sethiops, or oxyd of iron. 
At the beginning of the combustion there is a slight augmentation in the 
volume of the air in the bell-glass, from the dilatation caused by the caloric 
or heat; but presently after a rapid diminution takes place, and the mercury 
rued in the glass, insomuch that when the quantity ofi iron id sufficient , and 
the oxygen air operated on is very pure , almost the whole air employed is ab¬ 
sorbed or should the quantity of iron be insufficient , the remaining air un¬ 
absorbed will be found perfectly pure vital air . 
The theory of this experiment is the same as the last. 
At a certain temperature iron has a stronger affinity for the oxygen than 
caloric and light have. 
It therefore attracts to itself the oxygen, and caloric and light becoming 
disengaged, are rendered active and evident to the senses. 
* The rationale of fire-works are now no longer any difficulty. As nitre contains vital air in 
great abundance, from the combustion of different bodies, especially iron-filings, in this air arises so 
astonishing and pleasing a spectacle. 
f That is, if 100 grains of iron be consumed in 70 cubic inches of oxygen air, the whole volume 
of air will disappear; and as 70 cubic inches of oxygen air weigh 35 grains, the loo grains of iron 
will weigh, in its state of cethiops, oxyd, or calx, 135 gj'ains. 
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