Negative Ions by Glowing Metallic Oxides. 83 



The number of corpuscles emitted by glowing platinum 

 was investigated in detail by Messrs. O.W.Richardson* and 

 fl. A. Wilson t, according to whom — as had already been 

 found by J. J. Thomson — the relation between the number 

 of negative ions and the absolute temperature may be repre- 

 sented by an exponential formula, into which the number of 

 corpuscles contained in unit volume enters as a constant. 

 This number, according to Richardson's researches, amounts 

 in the case of platinum to about 10 21 . 



Now I have investigated the emission of negative ions by 

 platinum wires coated with the oxides of calcium, barium, 

 and strontium, and found that, for equal temperatures, the 

 oxide-coated wires emit far more corpuscles than the pure 

 platinum wires. 



The experimental arrangements were essentially the same as 

 in the previous investigations, only in this case various leading 

 wires to the electrodes were melted into the glass, and the tube 

 was fused on to a mercury pump having no greased joints %. 



At pressures less than 0*1 mm. of mercury, well-marked 

 saturation-currents were observed which were independent of 

 the pressure. At pressures exceeding # 1 mm., ionization 

 already occurred by ionic impact, the saturation currents 

 were not well marked, and were in addition dependent on the 

 pressure. Hence, in order to find the relation connecting 

 the saturation current with temperature, pressures less than 

 0*1 mm. were invariably used. 



In what follows, the results will be given for BaO alone, 

 as those obtained with CaO and SrO were very similar, both 

 qualitatively and quantitatively. The results cannot, of 

 course, be expected to be perfectly concordant, as a perfectly 

 uniform coating of the wires with the oxides is unattainable. 



Table II. contains the results obtained with BaO ; instead 

 of the saturation-current, the saturation current-densities are 

 given — i. e., the currents per unit of area [zcm. -2 ]. 



Table II. — Relation connecting Saturation Current-Density 



(z'cm. -2 ) with Temperature (T). Wire coated with BaO. 



p = 0'04: mm. of mercury. 



1050°. 1140°. 1220°. i 1300°. 



3-8.10-* 314. 10-5 | 2-18.10-4 1-6.10-3 



1380°. 1460°. 



8-1.10-3 2-4.10-2 



i 



* Loc. cit. f Loc. cit. 



X Sealing-wax joints and joints rendered air-tight by means of grease 



were avoided, as the vapours of organic compounds are decomposed by 



the glowing wire, whereby the coating of oxide on the wire is destroyed. 



The carbides formed cause a black deposit on the walls of the glass tube. 



- G2 



