OF ARTS AND SCIENCES. 291 



out. The usual " wire form " of cupric oxide is not subject to this 

 cause of inaccuracy, however. 



In the uear future other oxides will be investigated at this laboratory 

 with regard to their possible occlusion of gases. 



IV. Upon Typical Copper. 



It has been noticed that most of the calculations described in the 

 present paper have been referred to electrolytic copper. Whether 

 such copper represents the typical element or not is a most impor- 

 tant question, but is one which unfortunately cannot be conclusively 

 answered here. 



Many authorities have discussed the subject,* and both sulphur and 

 occluded gases have been found in metal prepared in this way. Hampe 

 has shown that the occasional presence of sulphur is probably due to 

 minute drops of solution imprisoned between the electrode and the 

 deposit. When pure copper was to be prepared in the present inves- 

 tigation, the metal was invariably detached from the dish in order to 

 prevent such imprisonment. In the determination of copper already 

 in solution, the current was always made as weak as possible in order 

 to avoid the chance of error. Besides, it will be remembered that 

 there was a slight loss rather than a gain daring electrolysis. 



The occlusion of gases is at worst very slight. In order to reduce 

 the error from this cause to a minimum, the crucible which formed the 

 negative electrode was usually coated beforehand with copper, that the 

 initial and the final surface might be subject to the same error. To 

 determine the amount of volatile material absorbed by electrolytic 

 copper, very thin strips were ignited in a stream of hydrogen, with the 



This correction is too small to be applied, even supposing that the 

 method of precipitation just mentioned did not render the application 



* Soret, Compt. Rend., CVIT. 733, CVIII. 1298; Hampe, loc. cit.; also 

 Macintosh, Classen, Foote, Smith, and many others. 



