﻿192 Dr. J. N. Pring and Mr. A. Parker on the 



orangite may be undergoing some molecular or chemical 

 change. The mineral is subject to alteration, and perhaps 

 the warming and loss of water during exhaustion started 

 some change which was still proceeding at only a slightly 

 decreased rate a year later. As the total heat evolved during 

 that time only amounts to about 2 calories per gram of 

 orangite it might possibly be produced in this way, though 

 the smallness of the diminution observed in the rate of evo- 

 lution indicates that the action will proceed for several years 

 to come, and by the time it is over the quantity of heat 

 generated by each gram may amount to a much larger 

 figure. 



Jt is hoped to make a fresh determination on an entirely 

 fresh sample of orangite which will not be heated beforehand, 

 and also to employ the method used with pitchblende as a 

 check on the values obtained above. 



In conclusion I wish to express my gratitude to Dr. Joly 

 for his kind assistance and advice throughout the work, and 

 for the loan of the orangite employed, 



Physical Laboratory, 



Trinity College, Dublin, 



October 5, 1911. 



XVI. The Ionization -produced by Carbon at High Tempe- 

 ratures. By J. N. Pring, D.Sc, and A. Parker, 

 University of Manchester *. 



THE escape of negative electricity from heated carbon 

 was noticed by Edison f when making experiments 

 with lamp filaments. This leak of current from a heated 

 filament to an adjacent electrode which is at a positive 

 potential relative to the filament can, in some cases, become 

 of the same order as that conducted through the filament. 

 Edison found that when xhese filaments have been used for 

 some time the ionization effect diminishes, but increases 

 again if the carbon is allowed to stand. 



0. W. Richardson % made systematic measurements of the 

 ionization produced by carbon. Use was made of a carbon 

 filament and a surrounding met;«l cylinder, and between 

 these a potential difference varying from 30 to 300 volts 

 was maintained, the heated carbon being made negative. 

 The current produced by ionization was conducted across to 

 the surrounding metal. By exhausting to very low pressures, 



* Communicated by Prof. E. Rutherford, F,R,S, 



t Engineering (1884), p. 553. 



\ 1'hil. Trims. (1903) A.cci. p. 497. 



