1888.] 



Densities of Hydrogen and Oxygen. 



361 



The second column shows that globe (14) and certain platinum 

 weights were suspended from the left end of the beam, and the third 

 column that (in this series) only the counterpoising globe (11) was 

 hung from the right end. The fourth column gives the mean balance 

 reading in divisions of the scale, each of which (at the time of the 

 above experiments) represented 0*000187 gram. The degree of agree- 

 ment of these numbers in the first part of the table gives an idea of 

 the errors due to the balance, and to uncertainties in the condition of 

 the exteriors of the globes. A minute and unsystematic correction 

 depending upon imperfect compensation of volumes (to the extent of 

 about 2 c.c.) need not here be regarded. 



The weight of the hydrogen at each filling is deduced, whenever 

 possible, by comparison of the " full " reading with the mean of the 

 immediately preceding and following "empty" readings. The 

 difference, interpreted in grams, is taken provisionally as the weight 

 of the gas. Thus for the filling of Nov. 5 — 



H = 0-154-2-25 x 0-000187 = 0-15358. 



The weights thus obtained depend of course upon the temperature 

 and pressure at the time of filling. Reduced to correspond with a 

 temperature of 12°, and to a barometric height of 30 inches (but 

 without a minute correction for varying temperature of the mercury) 

 they stand thus — 



November 5 0-15811 



8 0-15807 



10 0-15798 



12 0-15792 



Mean...... 0' 15802 



The hydrogen obtained hitherto with similar apparatus and puri- 

 fying tubes from hydrochloric acid is not quite so light, the mean of 

 two accordant series being 0'15812. 



The weighing of oxygen is of course a much easier operation than 

 in the case of hydrogen. The gas was prepared from chlorate of 

 potash, and from a mixture of the chlorates of potash and soda. 

 The discrepancies between the individual weighings were no more 

 than might fairly be attributed to thermometric and manometric 

 errors. The result reduced so as to correspond in all respects with 

 the numbers for hydrogen is 2 5186.* 



But before these numbers can be compared with the object of 

 obtaining the relative densities, a correction of some importance is 

 required, which appears to have been overlooked by Professor Cooke, 



* An examination of the weights revealed no error worth taking into account at 

 present. 



