108 Dr Turner's Experiments on the Application of 
The large quantity of oxygen indicated by these experiments 
surprised me much, and I was at a loss to conjecture whether 
this arose from the quantity of oxygen in the atmosphere being 
actually greater than was generally supposed, or whether there 
was not some source of error common to all the three experi- 
ments. It occurred to me, that the oxygen of the air contained 
in the hydrogen, as impurity, might perhaps be made to com- 
bine with a portion of hydrogen during the experiment, and 
thus occasion a greater diminution than there really ought to 
have been. It will be readily inferred from some preceding ex- 
periments that this did occur. I was not, however, aware of the 
circumstance on the present occasion, for this analysis was made 
prior to the experiments to which I allude*. Acting upon this 
supposition, I left an active ball during the night in contact 
with the hydrogen which I intended to use on the following 
day. I now made six experiments with great care, allowing the 
action to go on at one time in the graduated tube, at another 
in a capacious jar. In the latter case the diminution had at- 
tained its maximum in five or ten minutes, while half an hour 
was necessary in the former. The residue was dried by fused 
potash before being measured, and due correction made fop 
change of temperature. 
Exp. 1. 
indicated 20.3 per cent, of Oxygen. 
Exp. 2. 
20.3 
Exp. 3. 
20.7 
Exp. 4. 
21.0 
Exp. 5. 
21.3 
Exp. 6. 
21.7 
The mean of these six experiments is 20.88, so that we'rnay 
safely assume 21 to be the correct number, which agrees very 
accurately with our best analyses upon this subject. 
The action of platinum affords a neat and expeditious method 
of ascertaining the purity of hydrogen or oxygen. It is easy, 
too, to prepare nitrogen of great purity, by adding just sufficient 
hydrogen to combine with all the oxvgen of a known quantity 
of air, and putting a platinum-ball into the mixture. 
* To put this beyond a doubt, a platinum-ball v w as put into a known quantity 
of hydrogen. It did at first occasion a slight diminution of volume, proportionate 
to the quantity of air present, but afterwards had no farther action on the gas. 
