32 THE ATOMIC WEIGHTS. 



If we reject all of Morley's data for the density of hydrogen except his 

 third, fourth, and fifth series, the mean becomes 



O = 15.8991, .00048. 



In either case Morley's data vastly outweigh all others. 



If oxygen and hydrogen were perfect gases, uniting by volume to form 

 water exactly in the ratio of one to two, then the density of the first in 

 terms of the second would also express its atomic weight. But in fact, 

 the two gases vary from Boyle's law in opposite directions, and the true 

 composition of water by volume diverges from the theoretical ratio to a 

 measurable extent. Hence, in order to deduce the atomic weight of 

 oxygen from its density, a small correction must be applied to the latter? 

 dependent upon the amount of this divergence. Until recently, our 

 knowledge of the volumetric composition of water rested entirely upon 

 the determinations made by Humboldt and Gay-Lussac* early in this 

 century, which gave a ratio between H and of a little less than 2:1, 

 but their data need no farther consideration here. 



In 1887 Scott t published his first series of experiments, 21 in number, 

 finding as the most probable result a value for the ratio of 1.994 : 1. In 

 March, 1888, J he gave four more determinations, ranging from 1.9962 to 

 1.998:1; and later in the same year another four, with values from 

 1.995 to 2.001. In 1893, || however, by the use of improved apparatus, 

 he was able to show that his previous work was vitiated by errors, and to 

 give a series of measurements of far greater value. Of these, twelve were 

 especially good, being made with hydrogen from palladium hydride, 

 and with oxygen from silver oxide. In mean the value found is 

 2.00245, .00007, with a range from 2.0017 to 2.0030. 



In 1891 an elaborate paper by Morley^fl appeared, in which twenty 

 concordant determinations of the volumetric ratio gave a mean value of 

 2.00023, .000015. These measurements were made in eudiometer 

 tubes, and were afterwards practically discarded by the author. In his 

 later and larger paper,** however, he redetermined the ratio from the 

 density of the mixed electrolytic gases, and found it to be, after applying 

 all corrections, 2.00274. The probable error, roughly estimated, is .00005. 

 Morley also reduces Scott's determinations, which were made at the tem- 

 perature of the laboratory, to 0, when the value becomes 2.00285. The 

 mean value of both series may therefore be put at 2.0028, .00004, with 

 sufficient accuracy for present purposes. Leduc's ft single determination, 



* Journ. de Phys., 60, 129. 



tProc. Roy. Soc., 42, 396. 



I Nature, 37, 439. 



g British Assoc. Report, 1888, 631. 



I! Proc. Roy. Soc., 53, 130. In full in Philosophical Transactions, 184, 543. 1893. 



^ Amer. Journ. Sci. (3), 46, 220, and 276. 



** Already cited with reference to syntheses of water. 



ft Compt. Rend., 115, 311. 1892. 



