ON SOME CHEMICAL AGENCIES OF ELECTRICITY, 47 



electrical, and rendered the conductors brought iii coutact General pnn- 

 ... . . ciples of the 



with them positive. chemical 



I made several experiments in a similar manner on the changes pro- 

 effects of the contact of potash and soda with the metals. tr i c i t ^ 

 Potash in no instance afforded a satisfactory result; its pow- 

 erful attraction for water presents an obstacle probably un- 

 surmountable to the success of any trials made in the free 

 atmosphere. Soda, in the only case in -which electricity was 

 exhibited, affected the metal iu the same way as lime, strou- . 

 titcs, and magnesia. Upon this occasion the soda had been v 

 prepared with great care, exposed in a platina crucible for 

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

 cible inverted over mercury : when cool it was immediately 

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

 experiment was performed in the open air; the weather was 

 peculiarly dry, the thermometer stood at 28° Fahrenheit, and 

 the barometer at 30*2 inches : six contacts gave a charge to 

 the condensing electrometer in the first trial; in die 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 electri- 

 city the sulphur separates on the negative side. The expe- 

 riments of various electricians prove, that, by the friction of 

 sulphur and metals, the sulphur becomes positive and the 

 metals negative ; the same thing I lind happens from the 

 contact of an unexcited cake of sulphur and iusulated 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 be- 



* As sulphar is a nonconductor, and easily excited by slight friction, 

 tor small changes in its temperature, some caution is required in drawing 

 conclusions from the experiments in which it is employed. Sulphur, 

 examined immediately after having been heated, gives a positive charge 

 to conductors, agreeing in this respect with the alkaline substances; and 

 a slight contact with the diy hand is sufficient to render it negative. In 

 general likewise in experiments of contact care should be taken that the 

 metallic plate is free from electricity : well polished plates of copper and 

 zinc will, I find, receive a negative charge from being laid on a table of 

 ■common mahogany. 



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