OXYGEN. 17 



this purpose consisted essentially of a glass bulb of 30 to 50 cc. capacity, 

 with a stopcock tube on one side and a sealed condensing tube on the 

 other. In weighing, it was counterpoised by another apparatus of nearly 

 the same volume but somewhat less weight, in order to obviate reduc- 

 tions to a vacuum. After filling the bulb with commercial copper oxide 

 (90 to 150 grammes), the apparatus was heated in an airbath, exhausted 

 by means of a Sprengel pump, cooled, and weighed. It was next re- 

 placed in the airbath, again heated, and connected with an apparatus 

 delivering purified hydrogen. When a suitable amount of the latter had 

 been admitted, the stopcock was closed, and the heating continued long 

 enough to convert all gaseous hydrogen within it into water. The appa- 

 ratus was then cooled and weighed, after which it was connected with* a 

 Sprengel pump, in order to extract the small quantity of nitrogen which 

 was always present. The latter was pumped out into a eudiometer, 

 where it was measured and examined. The gain in weight of the appa- 

 ratus, less the weight of this very slight impurity, gave the weight of 

 hydrogen oxidized. 



The next step in the process consisted in heating the apparatus to expel 

 water, and weighing again. After this, pure oxygen was admitted and 

 the heating was resumed, so as to oxidize the traces of hydrogen which 

 had been retained by the copper. Again the apparatus was cooled and 

 weighed, and then reheated, when the water formed was received in a 

 bulb filled with phosphorus pentoxide, and the gaseous contents were 

 collected in a eudiometer. On cooling and weighing the apparatus, the 

 loss of weight, less the weight of gases pumped out, gave the amount of 

 water produced by the traces of residual hydrogen under consideration. 

 This weight, added to the loss of weight when the original water was 

 expelled, gives the weight of oxygen taken away from the copper oxide. 

 Having thus the weight of hydrogen and the weight of oxygen, the 

 atomic weight sought for follows. Six results are given, but as they are 

 repeated, with corrections, in Noyes' second paper, they need not be 

 considered now. 



Noyes' methods were almost immediately criticised by Johnson,* who 

 suggested several sources of error. This chemist had already shown in 

 an earlier paper f that copper reduced in hydrogen persistently retains 

 traces of the latter, and also that when the reduction is effected below 

 700, water is retained too. The possible presence of sulphur in the 

 copper oxide was furthermore mentioned. Errors from these sources 

 would tend to make the apparent atomic weight of oxygen too low. 



In his second paper J Noyes replies to the foregoing criticisms, and 

 shows that they carry no weight, at least so far as his work is concerned. 

 He also describes a number of experiments in which oxides other than 

 copper oxide were tried, but without distinct success, and he gives fuller 



*Chem. News, 59, 272. 



f Journ. Chem. Soc., May, 1879. 



jAmer. Chem. Journ., 12, 441. 1890. 



