of
air, in the same manner as I had before treated the charcoal; and
throwing the focus of a burning mirror or lens upon them, so as to make
them fume copiously. I presently perceived a diminution of the air. In
the first trial that I made, I reduced four ounce measures of air to
three, which is the greatest diminution of common air that I had ever
observed before, and which I account for, by supposing that, in other
cases, there was not only a cause of diminution, but causes of addition
also, either of fixed or inflammable air, or some other permanently
elastic matter, but that the effect of the calcination of metals being
simply the escape of phlogiston, the cause of diminution was alone and
uncontrouled.

The air, which I had thus diminished by calcination of lead, I
transferred into another clean phial, but found that the calcination of
more lead in it (or at least the attempt to make a farther calcination)
had no farther effect upon it. This air also, like that which had been
infected with the fumes of charcoal, was in the highest degree noxious,
made no effervescence with nitrous air, was no farther diminished by the
mixture of iron filings and brimstone, and was not only rendered
innoxious, but also recovered, in a great measure, the other properties
of common air, by washing in water.

It might be suspected that the noxious quality of air in which _lead_
was calcined, might be owing to some fumes peculiar to that metal; but
I found no sensible difference between the properties of this air, and
that in which _tin_ was calcined.

The _water_ over which metals are calcined acquires a yellowish tinge,
and an exceedingly pungent smell and taste, pretty much (as near as I
can recollect, for I did not compare them together) like that over which
brimstone has been frequently burned. Also a thin and whitish pellicle
covered both the surface of the water, and likewise the sides of the
phial in which the calcination was made; insomuch that, without
frequently agitating the water, it grew so opaque by this constantly
accumulating incrustation, that the sun-beams could not be transmitted
through it in a quantity sufficient to produce the calcination.

I imagined, however, that, even when this air was transferred into a
clean phial, the metals were not so easily melted or calcined as they
were in fresh air; for the air being once fully saturated with
phlogiston, may not so readily admit any more, though it be only to
tr