OXYGEN. 19 



The mean of all the twenty-four determinations, taken as one series, 

 with the correction to the third series included, is = 15.8966, .0017. 

 In sum, there were consumed 18.5983 grammes of hydrogen and 147.8145 

 of oxygen ; whence = 15.8955. 



Dittmar and Henderson,* who effected the synthesis of water over 

 copper oxide by what was essentially the old method, begin their memoir 

 with an exhaustive criticism of the work done by Dumas and by Erd- 

 mann and Marchand. They show, as I have already mentioned, that 

 hydrogen dried by sulphuric acid becomes contaminated with sulphur 

 dioxide, and also that a gas passed over calcium chloride may still retain 

 as much as one milligramme of water per litre. Fused caustic potash 

 they found to dry a gas quite completely. 



In their first series of syntheses, Dittmar and Henderson generated 

 their hydrogen from zinc and acid, sometimes hydrochloric and some- 

 times sulphuric, and dried it by passage, first through cotton wool, then 

 through vitrioled pumice, then over red-hot metallic copper to remove 

 oxygen. In later experiments it first traversed a column of fragments 

 of caustic soda to remove antimony derived from the zinc. The oxide 

 of copper used was prepared by heating chemically pure copper clip- 

 pings in a muffle, and was practically free from .sulphur. In weighing 

 the several portions of apparatus it was tared with somewhat lighter 

 similar pieces of as nearly as possible the same displacement. The re- 

 sults of this series of experiments, which are vitiated by the presence, 

 unsuspected at first, of sulphur dioxide in the hydrogen, are stated in 

 values of H when = 16, but in the following table .have been recalcu- 

 lated to the usual unit : 



Wt. of Water. Wt. of O. At. Wt. O. 



4.7980 4.26195 I5-9 01 



7.55025 6.71315 16.039 



6.2372 5-53935 15.875 



11.29325 10.03585 J 5-963 



11.6728 10.3715 I5-940 



11.8433 10.5256 15.976 



11.7317 10.4243 15-947 



19.2404 17.0926 15.916 



20.83435 18.5234 16.031 



17.40235 15.4598 I5-9I7 



19.2631 i7."485 x 5-934 



Mean, 15.949, =b .0103. 



Reducing to a vacuum, this becomes 15.843, while a correction for the 

 sulphur dioxide estimated to be present in the hydrogen brings the value 



* Proc. Roy. Soc. Glasgow, 22, 33. Communicated Dec. 17, 1890. 



