932 Pi of. 0. W. Richardson on the Positive 



The method adopted consists in measuring the deflexion 

 o£ the path or! the ions, between two parallel plates at 

 different potentials, produced by a known transverse magnetic 

 field. It was, in fact, the same as that used in the investi- 

 gation of the specific charge of the ions emitted by hot bodies. 

 So that, for the description of the apparatus and the method 

 of using it, it will be sufficient to refer to the first of the two 

 ] tapers mentioned, which contains a very full account of the 

 matter. 



The experiments were carried out in the following manner : 

 a strip of platinum 0'5 cm. long, '002 cm. thick, and about 

 •05 cm. wide, was mounted in the apparatus. The distri- 

 bution of the ionization over a parallel plate about *5 cm. 

 away was then determined in the usual manner, with 

 oppositely directed magnetic fields of about 4700 lines 

 per cm. From the displacement of the maximum the value 

 of e/m for the positive ions from platinum could be calculated. 



After the measurement had been made, the platinum was 

 strongly heated for several hours until it gave only a 

 negligible leak at the temperature at which the test was 

 made. The apparatus was then taken down, and a layer of 

 the pure alkali salt to be tested was melted over the front 

 surface of the strip. The apparatus was again set up and 

 exhausted. It was now found that a large positive ionization 

 could be obtained at a temperature below that at which the 

 tesl on the platinum had been made, showing that the 

 ionization was due to the alkali salt and not to the platinum. 

 The distribution of the ionization on the opposite plate was 

 now determined with the magnetic field in opposite directions, 

 and the displacement of the maximum measured. 



From this displacement together with the distance and 

 difference of potential between the plates and the strength of 

 the field the values of e/m and of m could be calculated from 



9 Y.v 2 

 the formula : e/m = s.TjTV In calculating the value of m 



the ions were assumed to carry the same charge as an 

 atom of hydrogen in electrolysis, and the value of e/m 

 for the hydrogen ions in electrolysis was taken to be 

 9*66 x 10 3 E.M. units. In the present case we have a 

 valuable check on the results thus obtained, on account 

 of the simultaneous measurements which were made of the 

 displacement in the case of the ions from platinum. Previous 

 work has shown that the value of e/m for the positive ions 

 emitted by this metal * does not vary much for different 



* Richardson & Hulbirt, loc. cit. 



