394 

 Q 336 X 10' 



= 37.8. 



T 889 



This is a very high abnormal value, just as in the case ofphosphoi'iis. 



2Vte Black Modification of Arsenic. 



It was tried to measure the vapour pressure of the black modi- 

 fication by means of the same indicator as was used in the above 

 experiments. But when the vapour pressure was high enough to 

 measure bj this indicator, ail the sample in it was transformed 

 into the gray modification ^), so that it was necessary to find a 

 suitable negative catalyser for this transformation, which would not 

 disturb the pressure measurement. The author hopes to continue this 

 study on a future occasion. 



SUMMARY. 



The vapour pressure of the gray modification of arsenic and its 

 liquid state were measured. From these data, the molecular heat 

 of sublimation, of vaporization and of fusion were calculated. 



In conclusion, the author expresses his cordial thanks to Professor 

 A. Smits for his kind suggestion and for the excellent advice he 

 has given during the work. 



Amsterdam, July 15, 1922. 



1) Laschtschenko, (J. chem. Soc, 121. 972 (1922)) gave some remarks 

 on polymorphism of arsenic from the measurement of heat evolved on cooling. 



