122 Notice of some Recent 



Rhodium, Platinum, Palladium, Gold, Tellurium, Cobalt, and 

 Nickel. Silver, Copper, Brass, and Tin, are also almost al- 

 ways negative, but sometimes positive. Antimony has once 

 or twice given positive signs. The nature of the electricity 

 developed in Iron and Zinc was variable, although in iron, 

 the tendency was to a negative state. Lead and Bismuth 

 were constantly positive, the latter highly so. 



The circumstances under which the two electricities are 

 developed, in respect to the uncertain metals as they may 

 be termed, are as follow : — in very dry air, and with the 

 fingers or wood well dried,, these metals are always nega- 

 tive, as the surface may be well polished or more or less 

 oxidated. When the surface rubbed is very great, and 

 when the rubbing body is drawn along all its extent, the 

 metal becomes positive. It becomes more readily positive, 

 when rubbed with cork than with wood, in the same cir- 

 cumstances. The electric effect is increased by an elevation 

 of temperature. Iron, Zinc, and Tin, exposed for some 

 moments to a high temperature, and rubbed immediately 

 after upon a very smooth face, gave most frequently positive 

 electricity, while, if in the same circumstances, the friction 

 is performed over an angle the indications are negative. 



De la Rive considers, that all the metals when polished 

 and rubbed take negative electricity, but that the more 

 oxidizable metals, in consequence of their possessing a thin 

 imperceptible layer of oxide on their surfaces, develope 

 under these circumstances, positive electricity. 



This source of electricity should be carefully attended to 

 in experimenting with the metals. De La Rive states his 

 conviction, that an electrical effect has often been ascribed 

 to contact, which was in reality to be attributed to friction. 

 Thus, he considers it probable, that the electrical signs 

 obtained in the experiment, when two insulated disks of 

 copper and zinc are alternately brought in contact and 

 separated, are owing to the friction of one metal upon the 

 other. He has produced, by friction in the method de- 

 scribed, an electrical current, but has not obtained any in- 

 dications of tension, because the two substances rubbed are 

 such good conductors, that the two electricities re-unite im- 

 mediately after their separation.* 



* Mem. de la Soc. de Phys. et d'Histoire Nat de Geneve, vi. 1? 1. 



