(If ■ Galvanic Potoifs of different Metals. . 



hietalllc pieces, which were ufed, being circular, and about 1.3 inch diameter, refted 

 upon the edges of this groove, and which, with a fmall block of wood at each extremity ot 

 bafe, ferved to keep them in their places. The board being inclined to the horizon, tht 

 channel carried off the water that oozed from the wetted difcs. 



In thofe experiments in which mercury was combined with other metals, it became 

 neceflary, on account of the fluidity of the mercury, to adopt fome other contrivance fof 

 the ajiparatus, by which the flowing of the mercury might be prevented. To efi"e£l this, 

 I procured 20 flat pieces of mahogany of two inches fquare, and of 0.3 inch in thick- 

 nefs : in the middle of each of thefe pieces was made a circular hole, of one inch 

 diameter on the lower fide, and of 1.5 inch diameter on the upper fide, forming a rabbet 

 at about two-thirds of the thicknefs of the wood from the upper furface. The lower 

 fide was then covered with a piece of leather attached to it with a cement, which was not 

 cafily a<^ed upon by the water ufed in the experiment ; and the leather was turned up 

 the fides of the wood to make it more fecure. The cement I ufed is made of melted wax, 

 rofin, and red ochre. 



When this apparatus was to be ufed, the pieces of wood were put into pure watef for 

 a fufficient time to foak the leather ; and when taken from the water, the mercury was 

 poured into the fmall cifterns, filling them to the edge of the rabbet; the folid metal was 

 then laid upon the rabbet, having its lower furface in contact with the mercury. If this, 

 folid metal was not of fufficient thicknefs to be level with the furface of the wood, a wetted 

 difc was laid upon it to fill up the vacant fpace. Thefe fmall blocks of wood, thus pre- 

 pared, being piled upon each other, the metallic fubftances they contaiRed became capable 

 of afting as a galvanic apparatus. 



The order in which thefe experiments are arranged is according to the degrees of in- 

 fluence, the difierent metals fecmed to poflefs, in forming the oxydating bafes or poles of 

 the apparatus, when any oxydable metallic wires, placed in tubes of water, were fub- 

 mltted to examination ; the other metal conftituting the oppofite or gafeous bafe or pole. 

 The difcs, that were ufed, were fometimes of card, and fometimes of leather, and were 

 foaked in pure water. Though the epidermis of an animal is obvioufly an infulating 

 fubftance, with refpeft to the galvanic influence (but lofes a part of that property by being 

 wetted) yet I have not difcovered any difference in the efl^eft, whether wetted card, or 

 wetted leather, was employed ; the leather has the advantage of retaining the moifture, 

 which is fo abfolutely requifite in the whole operation of a galvanic apparatus, a longer 

 time than the card ; but it difcolours very much the adjoining furfaces of the metallic 

 plates. It feems to be only neceflary th^t each pair of plates fliould be feparated from 

 the adjacent pairs by fome fubftance that is not a perfcfi: condu£lor of the galvanic in- 

 fluence, a property which feems to be confined to metalline fubftances ; and that the 

 feparating fubftance or difc fliould be conftantly wet. The wire ufed in thefe experiments 

 was of copper, and the glafs tubes were filled with pure water. 



3 Experiment 



