Chemistry. — ''Determination of the Vapour Pressure of Metallic 

 Arsenic". By Shinkichi Horiba. (Coinmiinicated by Prof. 

 P. Zeeman). 



(Communicated at the meeting of October 28, 1922). 



Arsenic is one of the most interesting elements, which should be 

 studied fi-om the view-point of the theory of allotropy. It is a well 

 known fact that arsenic can exist in three kinds of modilication, i. e. 

 gray, black, and yellow ; the gray modification is quite stable in a 

 wide range of temperature, while the others are rather metastable. 

 Although many investigations have been carried out about this 

 important element, yet it has never been tried to define the exact 

 lines of demarcation between these three modifications. Recently 

 some observations of its melting point have been reported by Goubeau^), 

 Heike '), Rassow '), and some measurements of the vapour pressure of 

 its solid phase by Heike, but in the oase of the latter, an indirect 

 method was used, so that the results were not very accurate. The 

 vapour pressure of the liquid phase of this element has never been 

 deteimined. On the suggestion of Professor Smits, the author has 

 undertaken the measurements of the vapour pressure of this element 

 in the laboratory of the University of Amsterdam ; the object of 

 the present study is, of course, to investigate the whole system of 

 this element, but the author is not yet in the position to complete 

 this study, owing to the difficulties of the technics of the measure- 

 ments. The present communication will only represent the results 

 of the measurements of the vapour pressure of the gray modification 

 and give some thermal data which can be calculated from these 

 vapour pressure data. 



The Method of Investigation. 



The same method of investigation, used by Prof. Smits and Bokhorst") 

 for the study of phosphorus, was applied ; a small modification, 

 which was made in the present investigation, was that a quartz 

 indicator of pressure was used instead of the hard glass, in view 



1) Compt. rend., 152, 1767, (1911). 



2) Z. anorg. chem., 117, 147 (1921): the literature of the melting point was 

 given in this paper. 



3) Z. anorg. chem., 114, 131 (1920). 



4) Z. physik. chem., 91, 249 (1916). 



