On some Chemical Agencies of FAectncity. 229 



placed upon a -surface of mercury, and separated by an insu- 

 lating body, is found positive, the mercury is negative : the 

 effects are exalted by heating tlie metals ; but let them be 

 kept in contact sufficiently long to amalgamate, and the 

 compound gives no signs of electricity. I could mention a 

 great number of other instances of pure chemical action in 

 which I have used all the means in my power to ascertain 

 the fact, and the result has been constantly the same. In 

 cases of effervcr;cence, indeed, particularly when accompa-' 

 nied bv much heat, the metallic vessels employed become 

 negative, but this is a ph^Euomenon connected with evapo- 

 ration, the change of state of a body independent of che- 

 mical change, and is to be referred to a diflerent law*. 



I mentioned the glass plates of Beccaria as affording a 

 parallel to the case of combination in consequence of the 

 different electrical slates of bodies. In Guyton dc Morvcau's 

 experiments on cohesion, the diff"ererent metals are said to 

 have adhered to mercurv with a force proportional to their 

 chemical affinities. But the other metals have different elec- 

 trical energies, or different degrees of the same electrical 

 cnert!;v with regard to this body ; and in all cases of contact 

 of mercurv with another metal, upon a large surface, they 

 ousiht to adhere in consequence of the difference of their 

 clt-ctrical states, and that with a force proportional to the 

 exaltation of those stales. Iron, which M. Guyton found 

 slightly adhesive, I find exhibits little positive eleptricity. 



• The cl<aiij;e of the canncities of hodies in consequence of the alteration 

 in their vohunes or states of cTistence by heat, is n continually operating source 

 of electrical effects; and, as I have hinted page 117, it often interferes with the 

 results of experiments ou tlie electrical energies of hodies as exhiliited by con- 

 tact. It is likev/ise prohably one of the sources of tlic capricious results of 

 eipciimcnts of friction, i.i which t!ie same body, acco ding as its texture is 

 akered, or its temperature changed, assumes dilFerent states ^vith rcijStrd' to 

 another body. Friction m.iy be considered as a succession of contacts, and 

 flic natural energies of bodies would probably be v^'ii'st'^'y exhibited by it, 

 if the uncqu J excitation of heat or its unequal aomn'.unicatio;j to the different 

 •utfaces did not interfere by alterinj; unequally their electrical cap?.c!ties. Of 

 ||^ ctbincntsof flint i;;la-i«, si'ex isslij^htly negative with regard to the tnet.nls, 

 ike soda ii positive ; and in contacts of ffla-s with metals 1 find it exhibits the 

 cxpcMof the energy of the alkali : the case, as is well known, is the same in 

 ■friction, the amal;j'am of the common machine ii essential to its pyv/crfulcn- 

 ciutiori. 



P 3 after 



