1892.] Relative Densities of Hydrogen and Oxygen. 449 



hydrogen was prepared from zinc and sulphuric, or from zinc and 

 hydrochloric, acid, and was liberated upon a platinum plate, the 

 generator being in fact a Smee cell, enclosed in a vessel capable of 

 sustaining a vacuum, and set in action by closing the electric circuit 

 at an external contact. The hydrogen thus prepared was purified by 

 corrosive sublimate and potash, and desiccated by passage through 

 a long tube packed with phosphoric anhydride. The oxygen was 

 from chlorate of potash, or from mixed chlorates of potash and soda. 



In a subsequent paper on the Composition of Water,* I attacked 

 the problem by a direct synthesis of water from weighed quantities of 

 the two component gases. The ratio of atomic weights thus obtained 

 was 15-89. 



At the time when these researches were commenced, the latest 

 work bearing upon the subject dated from 1845, and the number then 

 accepted was 15'96. There was, however, nothing to show that the 

 true ratio really deviated from the 16 : 1 of Prout's law, and the 

 main object of my work was to ascertain whether or not such devia- 

 tion existed. About the year 1888, however, a revival of interest in 

 this question manifested itself, especially in the United States, and 

 several results of importance have been published. Thus, Professor 

 Cooke and Mr. T. W. Richards found a number which, when cor- 

 rected for an error of weighing that had at first been overlooked, 

 became 15'869. 



The substantial agreement of this number with those obtained by 

 myself seemed at first to settle the question, but almost immediately 

 afterwards there appeared an account of a research by Mr. Keiser, 

 who used a method presenting some excellent features, and whose 

 result was as high as 15'949. The discrepancy has not been fully 

 explained, but subsequent numbers agree more nearly with the lower 

 value. Thus, Noyes obtains 15'896, and Dittruar and Henderson give 

 15-866. 



1 had intended further to elaborate and extend my observations 

 on the synthesis of water from weighed quantities of oxygen and 

 hydrogen, but the publication of Professor E. W. Morley's masterly 

 researches upon the " Volumetric Composition of Water "t led me to 

 the conclusion that the best contribution that I could now make to 

 the subject would be by the further determination of the relative 

 densities of the two gases. The combination of this with the number 

 2'0002,J obtained by Morley as the mean of astonishingly concordant 



* ' Roy. Soc. Proc.,' vol. 45, p. 425, February, 1889. 



f ' Amer. Journ. Sci.,' March, 1891. 



J It should not be overlooked that this number is difficult to reconcile with 

 views generally held as to the applicability of Avogadro's law to very rare gases. 

 From what we know of the behaviour of oxygen and hydrogen gases under com- 

 pression, it seems improbable that volumes which are as 2-0002 : 1 under atmo- 



