Mr. Davy’s Lecture on some 
36 
though two minutes only had elapsed, no farther result could 
be obtained. 
In the decomposition of sulphuric acid by Voltaic elec- 
tricity 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 find happens from the con- 
tact of an unexited cake of sulphur and insulated metallic 
plates. Mr. Wilke has stated an exception to lead, as rendering 
sulphur negative by its friction. The results that I have ob- 
tained with lead, in trials very carefully made, are the same 
as those with other metals.* Sulphur, by being rubbed or 
struck against newly-polished lead, always became positive. 
Mr. Wilke perhaps was misled by using tarnished lead : sul- 
phur, I find, rubbed against litharge, or lead the surface of 
which has been long exposed to air, becomes negative ; and 
this exception being removed, all the facts on the subject are 
confirmations of the general principle. -f 
* As sulphur is a nonconductor, and easily excited by slight friction, or 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 dry 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. 
f Concentrated solution of phosphoric acid, I find, is decomposed by Voltaic 
electricity : the phosphorus combines with the negatively electrified metal, and forms 
a phosphuret ; at least this happened in the two cases that I tried with platina and 
copper. From all analogy it may be inferred, that the electrical energy of this 
^flammable substance with regard to metals is the same as that of sulphur. I tried 
some experiments of contact upon it, but without success. Its slow combustion in the 
atmosphere it is most likely was the cause of the failure: but even in gases not con- 
taining free or loosely combined oxygene, its evaporation would probably interfere. 
