534 SCIENCE PROGRESS. 



escaped notice previously were, firstly, the formation of 

 sulphur dioxide when hydrogen was allowed to stand in 

 contact with strong sulphuric acid, and secondly, as carried 

 out by Erdmann and Marchand, the fact that the escaping 

 gas was only dried by fused calcium chloride, although the 

 gas supplied to the copper oxide was dried by means of 

 phosphoric anhydride and fused potash. Full details are 

 given as to the apparatus used and of each experiment, and 

 the mean of the seven best experiments gives O - 15*866 

 when H = 1 or H = 1-0085 when O = 16. Leduc (9) has 

 made some similar experiments, but only scanty details are 

 given, and his result is stated as O = 15*882. 



A very interesting modification is that of N oyes (10), 

 who used an apparatus entirely of glass, containing copper 

 oxide and having a part which could be cooled so as to con- 

 dense any water formed. The apparatus with copper oxide 

 was exhausted of air and weighed, then heated and con- 

 nected with an apparatus supplying pure hydrogen, water 

 was formed and condensed in the cold side tube. After 

 the experiment was finished the apparatus was again ex- 

 hausted with suitable precautions and the weight of hydro- 

 gen which had entered into combination with oxygen was 

 found directly. The whole apparatus was now heated and 

 the water distilled out and the apparatus again exhausted 

 and weighed. We have therefore here directly obtained the 

 weight of hydrogen and that of the oxygen which combined 

 with it, as well as that of the water produced. The value 

 for oxygen so obtained is 15*886 + '0028, or, if O = 16, then 

 H = 1*00717. 



Cooke and Richards (11) and also Reiser (12), weighed 

 the hydrogen and also the water formed from it and thus 

 escaped the most serious objection to the copper oxide 

 method. The first-named chemists weighed their hydro- 

 gen in a large glass globe, which was first weighed empty, 

 weighed again after filling with hydrogen, the hydrogen 

 was then driven first by a current of pure nitrogen and finally 

 by dry air over red hot copper oxide. The water was 

 weighed but not the copper oxide. The great objection to 

 this method is the great size of the glass globe required to 



