484 



Prof. W. A. Douglas Rudge on the 

 Table I. 



Element. 



Charge. 



Re marks. 



Sulphur 



+ 

 + 



+ 



4- 



i 

 T 



Magnitude of charge varied with the 



.kind of carbon. 

 Very strong charge. 

 Amorphous and carefully dried. 

 Strong* charge. 



;> )) 

 5) ;) 



)5 )) 



>> )> 



Fairly strong. 



Phosphorus 



Silicon „„ 



Boron 



Selenium 



Tellurium 



Iodine 



Arsenic 





* By strong, one means that a few centigrammes of the substance would 

 produce sufficient electricity to send the gold-leaf out to a right angle. 



Particular note should be taken that the so-called metallic 

 arsenic is included in the above list. Carbon occurs in 

 several modifications, and o£ these wood and sugar charcoal 

 and diamond dust were strongly positive, graphite not very 

 definite and sometimes strongly negative, whilst " animal '* 

 charcoal, a mixture of various substances, gave practically 

 no electrification. Sulphur in all its modifications was 

 always strongly positive. Amorphous phosphorus was, of 

 course, the only kind which could be used. 



Law II. Metallic elements give negatively charged clouds when 

 the finely divided material is Mown into a cloud by a current 

 of air. 



As a positive charge seemed to be associated with a 

 non-metallic dust-cloud, it seemed likely that a metallic 

 dust should give a negatively charged cloud, and this was 

 borne out by the experiments ; but, as is seen from Table II., 

 some important exceptions occur. 



The list of metals is far from being complete, but it is 

 very remarkable that those which are so definitely "metallic" 

 in their character should acquire a negative charge ; whilst 

 tungsten and vanadium, which form strongly acid oxides, 

 i. e. approximating to the nature of a non-metal, should, 

 under the same circumstances, give positive charges. 

 Uranium and titanium should probably be included in the 

 same category, but the charges obtained were indefinite, and 

 only a small quantity of the material was available. One 

 would expect zirconium to behave similarly to calcium or 

 aluminium, but the material was probably impure. Only 

 those metals could be used which were obtainable in a finely 



