DR. A. SCOTT ON THE COMPOSITION OF WATER BY VOLUME. 
563 
sub-series. It is plain that the source of the hydrogen ought to be varied. This was 
done by passing the hydrogen over palladium, and getting the hydrogen from the 
hydride formed by heating it. 
Finally silver oxide was substituted for mercuric oxide, as it decomposes at a more 
convenient temperature. 
The fracture of the measuring vessel rendered a new apparatus necessary, and one 
or two improvements were now introduced, the chief being the use of a constant 
volume, so that pressures only required to be measured for the large volumes, and the 
use of a narrower tube for measurina: the residues. 
One interesting point about the fracture of the measuring vessel is that, while 
surrounded by water and full of mercury, it broke in exactly the same way that a ' 
spare one which was kept ready for fear of accidents broke at the same time. The 
one in use was found fractured on a Wednesday morning, and the spare one had been 
handled and put on a shelf on the Monday afternoon just preceding. On going on 
the Wednesday to take it down to replace the other which had broken, it was found 
to have broken in such a similar manner that the pieces had to be fitted to each other 
to find out to which apparatus they belonged. The spare one had never been used, 
and not even calibrated. 
In Series II. the oxygen was always got from oxide of silver, and the hydrogen 
from sodium and water or from palladium hydride, the hydrogen for which -was 
furnished by sodium and water, with the exception of the first four experiments in 
Series IIa., when the hydrogen charge in the palladium was what was left in it from 
Series If., the hydrogen for which was obtained by tlie electrolysis of dilute hydro¬ 
chloric acid. The 93 grms. of palladium absorbed usually somewhat over G litres of 
hydrogen, enabling twelve experiments to be done consecutively from one charge. 
In Series IIa. the only two experiments which perhaps ought to be rejected are 
Nos. XII. and XIII., w'hich were the first two performed after the apparatus had 
stood unused for over a year. Why these results should be so low I can ofter no 
suggestion, but they differ notably from those of the same charge both before and 
after them. 
Series Iln. 
The results in this series vary remarkably, two of the ratios being very high and 
the mean ol the whole being high, but with a large probable error. The oxygen from 
the mixture of silver oxide and barium sulphate seemed to be very pure. 
Series lie. 
The hydrogen from the palladium hydride at first behaved in a peculiar way, and 
some air seemed somehow to have got in with the oxygen, and in two of the experi- 
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