in the same state with the air,
which had issued spontaneously from the same water.

I also found, that common air, confined in a glass vessel, in _contact_
only with this water, and without any agitation, would not admit a
candle to burn in it after two days.

These facts certainly demonstrate, that air which either arises from
stagnant and putrid water, or which has been for some time in contact
with it, must be very unfit for respiration; and yet Dr. Alexander's
opinion is rendered so plausible by his experiments, that it is very
possible that many persons may be rendered secure, and thoughtless of
danger, in a situation in which they must necessarily breathe it. On
this account, I have thought it right to make this communication as
early as I conveniently could; and as Dr. Alexander appears to be an
ingenuous and benevolent man, I doubt not but he will thank me for it.

That air issuing from water, or rather from the soft earth, or mud, at
the bottom of pits containing water, is not always unwholesome, I have
also had an opportunity of ascertaining. Taking a walk, about two years
ago, in the neighbourhood of Wakefield, in Yorkshire, I observed bubbles
of air to arise, in remarkably great plenty, from a small pool of water,
which, upon inquiry, I was informed had been the place, where some
persons had been boring the ground, in order to find coal. These
bubbles of air having excited my curiosity, I presently returned, with a
bason, and other vessels proper for my purpose, and having stirred the
mud with a long stick, I soon got about a pint of this air; and,
examining it, found it to be good, common air; at least a candle burned
in it very well. I had not then discovered the method of ascertaining
the goodness of common air, by a mixture of nitrous air. Previous to the
trial, I had suspected that this air would have been found to be
inflammable.

I shall conclude this letter with observing, that I have found a
remarkable difference in different kinds of water, with respect to their
effect on common air agitated in them, and which I am not yet able to
account for. If I agitate common air in the water of a deep well, near
my house in Calne, which is hard, but clear and sweet, a candle will not
burn in it after three minutes. The same is the case with the
rain-water, which I get from the roof of my house. But in distilled
water, or the water of a spring-well near the house, I must agitate the
air about twenty minute