646 
MR, H. B. DIXON OX CONDITIONS OF CHEMICAL CHANGE 
current of cold water from the main, running into the cylinder near the bottom and 
being siphoned off at the top. In the experiments made at ordinary temperatures a 
drop of water was drawn into the top of the barometer and the space thus saturated 
with aqueous vapour, while the eudiometer remained dry. On lowering the mercury 
in the two tubes, the level stood lower in the barometer than in the eudiometer by the 
difference of aqueous tension in the two tubes. By comparing this difference with the 
values given in PtEGNAULTS table for the aqueous tension at the particular temperature 
observed, the dryness of the eudiometer was verified. 
The carbonic oxide was prepared from magnesium formate by the action of sulphuric 
acid. It was passed through a small wash-bottle containing a strong solution of potash, 
thence through a U-tube containing fragments of caustic potash, and collected over 
hot mercury in cylinders of glass containing phosphoric oxide. As I found that a 
trace of air was always introduced with the sticks of compressed oxide, I allowed the 
gas to stand some time in each cylinder with the oxide, and then poured it away hv 
inclining the tube under the surface of mercury, leaving the stick of oxide hi the tube. 
The tubes were then filled with the gas used in the experiments, and were used over 
and over again for collecting the gas without being recharged with phosphoric oxide. 
The hydrogen was prepared by the electrolysis of dilute sulphuric acid, an amalgam of 
zinc and mercury being employed for the positive electrode. The gas was collected 
and dried in the same way as the carbonic oxide. The oxygen was prepared by 
heating re-crystallised and well-dried potassic chlorate in a bent tube dipping under 
mercury. The oxygen and the electrolytic gas were collected over mercury and dried 
in the same way. 
After the explosion of the gases and the absorption of carbonic acid formed, the 
residue was exploded with an excess of oxygen, and the contraction on explosion and 
subsequent treatment with potash observed. The two portions of the experiment 
together made a complete analysis of the original mixture, which served to control the 
result of each part of the experiment. In calculating the results, the measurement of 
the gases originally taken and the analysis of the residual mixture were taken to give 
an independent determination of the quantity of each gas burnt in the first explosion, 
and the mean of these two determinations was taken as the correct number. 
The following table contains the results of the experiments made to test the effect 
of varying the length of the column of gases exploded:— 
Composition of Mixture. 
Carbonic oxide 
Hydrogen 
Oxygen 
100-00 
67-10 
21-91 
11-09 
