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IX. On the Composition of Water by Volume.
By Alexander Scott, M.A., D.Sc., Jacksonian Demonstrator in the University of Cambridge.
Communicated by 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 measurements 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 be 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. Morley 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 1500th of a millimetre, and that they actually were made to 1200th 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.
