34 
Mr. Davy's Lecture on some 
electrometer of Mr. Cuthbertson’s construction, Mr. Ca- 
vallo's multiplier, and a very sensible electrical balance, on the 
principle of torsion, adopted by M. Coulomb ; but the effects 
were unsatisfactory, the circumstances of evaporation, and of 
chemical action, and the adherence of the solutions to the 
surfaces of the metals employed, in most cases, prevented 
any distinct result, or rendered the source of the electricity 
doubtful. I shall not enter into any details of these processes, 
or attempt to draw conclusions from capricious and uncertain 
appearances, which, as we shall immediately see, may be fully 
deduced from clear and distinct ones. 
The alkaline and acid substances capable of existing in the 
dry and solid form, give by contact with the metals exceed- 
ingly sensible electricities, which require for their exhibition 
the gold leaf electrometer only with the small condensing 
plate. 
When oxalic, succinic, benzoic or boracic acid, perfectly dry, 
either in powder or crystals, were touched upon an extended 
surface with a plate of copper insulated by a glass handle, the 
copper was found positive, the acid negative. In favourable 
weather, and when the electrometer was in perfect condition, 
one contact of the metal was sufficient to produce a sensible 
charge; but seldom more than five or six were required. 
Other metals, zinc, and tin for instance were tried with the 
same effect. And the metal received the positive charge, appa- 
rently to the same extent, whether the acid was insulated 
upon glass, or connected with the ground. 
The solid acid of phosphorus, which had been strongly 
ignited, and most carefully excluded from the contact of air, 
rendered the insulated plate of zinc positive by four contacts ; 
