On some Chemical Agencies of Electricity. i 1 7 



strontites, and magnesia. Upon this o'ccasion the soda had 

 been prepared with great care, exposed in a platina crucible 

 for nearly an hour in a red heat, and suffered to cool in the 

 crucible inverted over mercury ; wher> cool it was immedi- 

 ately removed, and the contact made with a plate of zinc : 

 the experiment was perfornied in tiie open air; the weather 

 was peculiarly dry, the thermometer stood at 2S° Fahren- 

 heit, and the barometer at 30"2 inches; six contacts gave a 

 charge to the condensing electrometer in the lirst trial ; in 

 the second ten were required to produce a similar effect ; 

 and after this, though two minutes only had elapsed, no 

 further result could be obtained. 



In the decomposition of sulphuric acid by Voltaic elec- 

 tricity the sulphur separates on the negative side. The ex- 

 periments of various electricians prove, that by the friction 

 of sulphur and metals the sulphur becomes positive and the 

 metals negative ; the same thing I find happens from the 

 contact of an unexcited cake of sulphur and insulated me- 

 tallic plates. Mr. Wilke has stated an exception to lead, 

 as rendering sulphur negative by its friction. The results 

 that I have obtained with lead, in trials very carefully made, 

 are the same as those with other metals *. Sulphur, by 

 being rubbed or struck against newly-polishsd lead, always 

 became positive, lyir. Wilke, perhaps, was misled by usiug 

 tarnished lead : sulphur, I find, rubbed against litharge, or 

 lead the surface of which has been long exposed to air, be- 

 comes negative ; and this exception being removed, all the 

 facts on the subject arc confirmations of the general prin- 

 ciple f' 



On 



* A^ sulphur is a nonconductor, and eaf.ily excited by slip;Iit friciion, or 

 *mall chani.^cs in its temptratiii-e, some caution in rc;i]uired in drawinp con- 

 chiiions from the experiments in which it is employed. Sulpluir, examined 

 immediately after havinjj been heated, gives a positive charge to conductors, 

 agrteinfj in this respect with the alkaline substances; and a slijfht contact 

 with the dry hand is suflicicnt to render it ncjfative. In general, likewise, 

 in experiments of contact care should betaken that the metallic plate is free 

 from tltctricity : well polished plates of copper and zinc will, I find, receive 

 a ncjjativc char;^e fn-ni beinj; laid on a table of common mahogany. 



f Concentrated solution of phosphoric acid, I find, is decomposed by Vol- 

 taic tltrtricily : the phosphorus combines with the negatively elcctrifiid 

 H 3 metal 



