128 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



comparing their volumes at atmospheric temperature and 

 pressure. 



The hydrogen was prepared by the action of metallic 

 sodium on steam, with or without absorption by palladium 

 (see footnote, p. 130). The oxygen was prepared by heating 

 silver oxide. Both gases were of the highest degree of purity, 

 the residue of impurity left after explosion being usually less 

 than one part in 100,000. The ratio of the combining 

 volumes was found to be 2'00245 at 14 to 18 C. Lord 

 Rayleigh's determination of the densities of the gases had 

 given the ratio 15 '88 2 : i, the combining weights of the 

 two gases were therefore in the ratio, 



oxygen : hydrogen = 7*931 : 1. 



Morley's experiments on the composition of water. 



The redetermination of the composition of water by 

 E. W. Morley in the year 1895 (Smithsonian Contributions 

 to Knowledge, tr. Zeit. physikal. Chem.> 1895, 20, 68, 242, 

 417) was carried out with extraordinary care and accuracy, 

 and has already become one of the classics of scientific 

 literature. 



In these experiments the use of copper oxide was again 

 discarded ; the hydrogen and oxygen were weighed directly, 

 as in the earliest experiments, but with all the added 

 resources which had accrued from the experimental work 

 of the intervening century. 



The density of gxygen (prepared by heating potassium 

 chlorate or by electrolysing dilute sulphuric acid) was 

 determined by weighing it directly in globes of 20 litres 

 capacity, suspended in pairs x in a large desiccator-cupboard 

 from the pans of a balance (Fig. 29). In a typical experiment 

 the data were : 



1 The method of weighing a glass globe against a counterpoise of 

 similar form was introduced by Regnault : it serves to eliminate most of 

 the errors caused by variations of barometric pressure and of the amount 

 of moisture in the atmosphere. 



