Page:Philosophical Transactions of the Royal Society A - Volume 184.djvu/557

544 Throughout I have endeavoured to use the simplest apparatus possible and to prepare the gases themselves from only the purest materials, and those of the simplest composition that I could find, so that no purification should be required and all unnecessary contact with other chemical substances avoided, to work with an apparatus of glass throughout, so that no diffusion could take place, and, finally, so to work, that with a given amount of materials, I might compare the gas given off in the first fractions continuously to the last fractions, and thus endeavour to detect any possible impurity, either by variation of the ratio, or by actual observation from the residual gas.

My new experiments are divided primarily into two series, as two different forms of measuring vessel were used, one of the type described in my former paper in which both pressure and volume had to be measured, in the later form the pressure only required measurement, the volume being kept constant. This tended greatly to increase the accuracy of measurements, both because it lessened the number required, and, also, even if the total volume were as much as one cubic centimetre wrong, it would make no appreciable error in the ratio found, as all were measured in the same vessel. This will be obvious on slight consideration of the conditions.

The hydrogen required was obtained from the following sources:—

The oxygen was prepared from— Before using either the sulphuric or hydrochloric acid, after the necessary dilution it was boiled with some zinc amalgam for an hour or an hour and a half to get rid of all dissolved gases, and then added to the generating vessel while hot.
 * 1) Re-crystallized potassium chlorate, sometimes with the addition of a little pure sodium hydrate (from sodium).
 * 2) Mercuric oxide.
 * 3) Silver oxide.
 * 4) Silver oxide and barium sulphate.

The sodium used was such as had never been at any time in contact with paraffin or naphtha, and was obtained direct from the manufacturers. It was, before use, fused in a clean iron ladle and cast in an iron mould. It was always heated up till the anhydrous oxide fused so that the metal could be poured quite free from all scum.