NEGATIVE ELECTRICITY FROM HOT CALCIUM AND FROM LIME. 168 



shown that the constant A is proportional to the number of free corpuscles in a cubic 

 centimetre of the conductor in question. 



From experiments on the negative leak from hot platinum in air and in hydrogen 

 H. A. WILSON* has come to the conclusion that the phenomenon cannot be completely 

 explained by such a simple theory, and, moreover, he has shown that in order to 

 obtain the above formula it is not necessary to make any assumption as to the 

 manner of formation of the ions, but only to assume that they are produced in some 

 way at the surface of the hot platinum. In WILSON'S view, the constant Q is a 

 measure of the work required to produce a gramme molecular weight of ions at the 

 surface of the hot platinum, but experiments on the negative leak in hydrogen at 

 different pressures have led to the conclusion that the constant A cannot be regarded 

 as proportional to the number of corpuscles in a cubic centimetre of the cathode, and 

 WILSON shows that the number so deduced does not agree with the value found by 

 PATTERSONt from experiments on the variation of the resistance of platinum in a 

 magnetic field. A comparison of the values of A found for lime and for calcium in 

 the present research appears to support this view of WILSON'S, for it does not seem 

 possible that there can be 10 7 times as many free corpuscles in a cubic centimetre 

 of lime as in a cubic centimetre of calcium. Further, it is well known that the 

 electric conductivity of lime increases rapidly with rise of temperature. The author 

 has shown that this conductivity is mainly, if not entirely, metallic in nature, and, on 

 the ionic theory of metallic conduction, due to a large increase in the number of free 

 corpuscles contained in the substance, for it is improbable that the velocity of the 

 corpuscles increases to this extent. If, then, A is proportional to the number of 

 corpuscles per cubic centimetre, its value should increase with the temperature. 

 In the present experiments with lime, although there were considerable variations in 

 the value of A calculated from the negative leaks at different temperatures, there was 

 no sign of a progressive increase with increasing temperature. 



From WEHNELT'S work on the discharge of negative ions from glowing lime and 

 other metallic oxides, RICHARDSON has drawn the conclusion that the corpuscles 

 proceed not from the glowing oxide, but from the platinum, and that the oxide 

 merely has the effect of lessening the amount of energy required to set them free. 

 This conclusion is arrived at from the fact that the number of corpuscles per cubic 

 centimetre calculated from the value of the constant A, as found from WEHNELT'S 

 numbers, is about the same as for platinum. The value of A for lime obtained in the 

 present experiments is much greater than the value obtained for platinum, the former 

 being 6'42xlO u and the latter 1 '55x10*. Other experiments with lime-covered 

 cathodes gave values ranging from A = l'23x 10 l to A = 7'12x 10 13 , the value given 

 by the observations recorded in Table VI., taken after the cathode had been heated 

 for a long time to a high temperature. The values of A, calculated from observations 



H. A. WILSON, ' Phil. Trans.,' A, vol. 202, p. 243. 

 t PATTERSON, 'Phil. Mag.,' 6, HI., 655. 

 Y 2 



