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IX, On the Composition of Water hy Volume. 
By Alexander Scott, M.A., D.Sc., Jaxksonian Demonstrator in the University 
of Cambridge. 
Communicated hy Lord Rayleigh, Sec. R.S. 
Received March 4,—Read March 23, 1893. 
In a preliminary note, “ On the Composition of Water by Volume," presented to the 
Society in June, 1887, I remarked that up to that time we had no direct measure¬ 
ments of this important constant, except those of Gay-Lussac and Humboldt. The 
value they deduced from their experiments corresponded so far with the number I 
then gave as the most probable one, in that it required rather less than two volumes 
of hydrogen to one volume of oxygen. The results of my experiments, in spite of 
this coincidence, astonished me, for it was to he expected that as oxygen is more 
compressible than hydrogen (to say nothing of its coefficient of expansion), it 
would contain more molecules per unit volume than hydrogen, and, therefore, 
necessarily require more than two volumes of hydrogen for one volume of oxygen. 
In a short note, published in “ Nature,” of March 8th, 1888, I announced that I 
had detected a most important, and hitherto unsuspected, source of error which had 
led to the consumption of oxygen, and this naturally accounted for the relatively 
small number for the hydrogen. This source of error lay in the use of a lubricant of 
a combustible nature, not because of its volatility, but because of its tending to form 
a greasy layer on the surface of the eudiometer, and which was, to a certain extent, 
burnt with each explosion in the eudiometer. 
In the ‘American Journal of Science,’ for March and April, 1891, E. W. Mobley 
gives an account of twenty experiments made with a very elaborate apparatus for 
preparing his gases, and with a measuring apparatus practically the same as I 
described in my former paper, except that he explodes his gases in his measuring 
vessel, which is a wide cylindrical tube, thus necessitating microscopical readings of 
levels and heights, which he claims he can make with accuracy to ^ milli¬ 
metre, and that they actually were made to g-^th in his experiments. How this can 
be done satisfactorily after the explosion and the accumulation of water as the result 
of it, must astonish all who have tried to measure heights of mercury in glass tubes 
with accuracy. No mention is made as to where the water was expelled to, or how 
it could be got rid of 
28.8.93 
