434 Experiments and Observations upon the State of the Air 
at the sides, near the floor and at different heights from it, and 
close to the beds of the patients. In every instance, the air was 
obtained by emptyitig on the spot bottles that had been pre~ 
viously filled with distilled water, and immediately closing them. 
The bottles were perfectly air-tight, being all furnished with well 
ground glass stoppers. The air was examined soon after it had 
been collected. 
The first and most important object of my inquiry was to as- 
certain the quantity of oxygen gas in the several bottles of air. 
For this purpose | employed hydrogen gas, and the electric 
spark, ‘a method that seems to unite more simplicity and ele- 
gance than any other, and with due precaution is susceptible of 
great accuracy. As the purity of the hydrogen used in experi- 
ments of this kind is of consequence to the aceuracy of the re- 
sults, it may be proper to notice the mode by which it was ob- 
tained, especially as'it has, I think, some little novelty, and 
seems to be quite unexceptionable. I put some small pieces of 
zine into a glass, and nearly filled it with water that had been 
boiling for some time; then filled a tube with the boiling water, 
and inverted it in the glass; and after adding sulphuric acid, I 
shortly after collected the gas. 
I made a great number of experiments, using in every in- 
stance an excess of hydrogen gas. In every trial I mixed 0.30 
of a cubic inch of the air under examination, with 0.80 of pure 
hydrogen gas; and after agitating the mixture in a thick deto- 
nating tube: furnished with wires, the charge of a Leyden phial 
was passed through the tube, and the residual air, on being trans- 
ferred to the cubic inch measure, oecupied about 0.40 of it. I 
venture to state this as a general result ; for though in a few cases 
there was a difference of about 1 per cent. more or less, yet this 
difference was rather apparent than real, owing to the difficulty 
of measuring uniform quantities of air, and it was corrected by a 
careful repetition of the experiments. Now, as two volumes of 
hydroger: and one of oxygen gas enter into the composition of 
water ; if the foregoing results are made the basis of calculation, 
the apparent quantity of the oxygen gas in the air from the dif- 
ferent fever wards will amount to abovt 22.22 per cent.—but 
this is not the real quantity. A slight allowance must be made 
for'a ininute portion of air disengaged from the water, after the 
detonation of the mixed gases; and when this is taken into ac- 
count, the oxygen may be fairly estimated at about 21 per cent. 
And according to the statements of Sir Humphry Davy, and other 
able chemists, 21 per cent. is the actual quantity of oxygen gas 
i the external atmosphere in different parts of the globe. It 
may be remarked that the variations in the temperature and pres- 
sure of the atmosphere, during the precediug experiments, were 
