5 o 
Mr. Davy’s Lecture on some 
mumcation with the same instrument do not by their agencies 
in the slightest degree affect the gold leaves. Solid pure 
potash and sulphuric acid made to combine in an insulated 
platina crucible produce no electrical appearances. A solid 
amalgam of bismuth and a solid amalgam of lead become 
fluid when mixed together : the experiment, I find, is con- 
nected with a diminution of temperature, but with no exhi- 
bition of electrical effects. A thin plate of zinc, after being 
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 the 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 effervescence, in- 
deed, particularly when accompanied by much heat, the metallic 
vessels employed become negative, but this is a phenomenon 
connected with evaporation, the change of state of a body inde- 
pendent of chemical change, and is to be referred to a different 
law.* 
* The change of the capacities of bodies in consequence of the alteration in their 
volumes, or states of existence by heat, is a continually operating source of electrical 
effects: and as I have hinted, page 36, it often interferes with the results of ex- 
periments on the electrical energies of bodies as exhibited by contact. It is like- 
wise probably one of the sources of the capricious results of experiments of friction, 
in which the same body, according as its texture is altered, or its temperature 
changed, assumes different states with regard to another body. Friction may be 
considered as a succession of contacts, and the natural energies of bodies would pro- 
bably be accurately exhibited by it, if the unequal excitation of heat or its unequal 
communication to the different surfaces did not interfere by altering unequally their 
electrical capacities. Of the elements of flint glass, silex is slightly negative with 
