be promoted by that small quantity of
oil of vitriol, which I am informed is contained in chalk, if not in
lime-stone also.

But it is an objection to this hypothesis, that the inflammable air
produced in this manner burns blue, and not at all like that which is
produced from iron, or any other metal, by means of an acid. It also has
not the smell of that kind of inflammable air which is produced from
mineral substances. Besides, oil of vitriol without water, will not
dissolve iron; nor can inflammable air be got from it, unless the acid
be considerably diluted; and when I mixed brimstone with the chalk,
neither the quality nor the quantity of the air was changed by it.
Indeed no air, or permanently elastic vapour, can be got from brimstone,
or any oil.

Perhaps this inflammable principle may come from some remains of the
animals, from which it is thought that all calcareous matter proceeds.

In the method in which I generally made the fixed air (and indeed
always, unless the contrary be particularly mentioned, viz. by diluted
oil of vitriol and chalk) I found by experiment that it was as pure as
Mr. Cavendish made it. For after it had patted through a large body of
water in small bubbles, still 1/50 or 1/60 part only was not absorbed by
water. In order to try this as expeditiously as possible, I kept pouring
the air from one glass vessel into another, immersed in a quantity of
cold water, in which manner I found by experience, that almost any
quantity may be reduced as far as possible in a very short time. But the
most expeditious method of making water imbibe any kind of air, is to
confine it in a jar; and agitate it strongly, in the manner described in
my pamphlet on the impregnation of water with fixed air, and represented
fig. 10.

At the same time that I was trying the purity of my fixed air, I had the
curiosity to endeavour to ascertain whether that part of it which is not
miscible in water, be equally diffused through the whole mass; and, for
this purpose, I divided a quantity of about a gallon into three parts,
the first consisting of that which was uppermost, and the last of that
which was the lowest, contiguous to the water; but all these parts were
reduced in about an equal proportion, by passing through the water, so
that the whole mass had been of an uniform composition. This I have also
found to be the case with several kinds of air, which will, not properly
incorporate.

A mouse will live very wel