544 
DR. A. SCOTT ON THE COMPOSITION OF WATER BY VOLUME. 
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 shoidd 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 tyj^e described in my former paper in which 
both pressure and volume had to be measured, in the later form the pressure onlv 
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 ;— 
1 . 
3. 
4. 
Electrolysis of dilute sulphuric acid 
Using in both cases a platinum elec¬ 
trode for the hydrogen to be 
hydrochloric acid j evolved from, and amalgamated zinc 
[ for the absorption of the oxygen. 
Action of steam on sodium. 
Palladium hydride, formed by passing hydrogen from sources 2 and 3 over 
palladium at the ordinary temperature. 
The oxygen was prepared from— 
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. 
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 srases, and then added to the o’eneratino' vessel while hot. 
The sodium used was such as had never been at any time in contact with paraffin 
or naphtha, and was obtained direct from the manufiicturers. 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 scimi. 
