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VIII. The Combining Volumes of Hydrogen and Oxygen. 
By F. P. Burt, D.Sc., and E. C. Edgar, D.Sc., 
Senior Lecturers in Chemistry in the University of Manchester. 
Communicated by Prof. H. B. Dixon, F.R.S. 
Received December 2, 1915,—Read February 24, 1916. 
The measurement of the combining weights of hydrogen and oxygen has been the 
subject of so many researches of a high order of excellence that any fresh investigation 
of this fundamental constant must be submitted with considerable diffidence. 
Nevertheless, it must be noted that the results obtained by various observers differ 
appreciably. According to Clarke ( 1 ), the values obtained by Morley and Noyes, 
by reason of the accuracy of their methods and the close concordance of the individual 
determinations, outweigh the results of all other investigators. The atomic weight 
of oxygen being 16, that of hydrogen, according to Morley ( 2 ), is 1'00762, and 
according to Noyes( 3 ), 1'00787. (Clarke, on Noyes’ data, prefers the value 
1'00783.) It is, further, a significant fact that the arithmetic mean of all determina¬ 
tions discussed by Clarke, lies between these two values, which differ by 1 part in 
4000. Both values are based on the gravimetric synthesis of water and are indepen¬ 
dent of a knowledge of the densities of the gases. 
A physico-chemical method of determining the relative molecular weights depends 
on the knowledge of the ratio of the densities, together with that of the combining 
volumes. 
The present uncertainty in the values of these two constants is probably greater 
in the case of the combining volumes. The classical researches of Morley have 
established the densities of hydrogen and oxygen within very narrow limits, and, 
according to Clarke, writing in 1910, Morley’s value for the ratio is to be preferred 
to any other. There are now, however, good reasons for believing the density of 
oxygen to be slightly greater than Morley’s value, perhaps by 1 part in 28,000, 
though no subsequent work has advanced a more probable alternative to his value for 
hydrogen. Comparatively few investigations on the combining volumes have been 
made; of these, the two most important are due to Scott and Morley respectively. 
The historic researches of Scott ( 4 ) led to a value of 2'00245—this value being 
increased by him to 2'00285, when the necessary corrections (in calculating from room 
temperature to 0°C.) were made for the difference in the temperature coefficients of 
VOL. CCXYI. - A 545. 3 H [Published June 5, 1916. 
