VOL. LXXII.] PHILOSOPHICAL TRANSACTIONS. 275 



the large insulated plate. The combustion of the coals was helped by a gentle 

 wind. Some minutes after, the iron wire, by which the large insulated plate 

 was connected with the metal plate of the condenser, was taken off; then the 

 metal plate being removed from the marble by its insulated handle, and presented 

 to Mr. Cavallo's electrometer, it made the balls of it diverge with negative elec- 

 tricity. The experiment was repeated by placing on the large insulated plate 4 

 vessels, containing iron filings and water, instead of the chafing dishes: then 

 some vitriolic acid was poured into those 4 vessels, sufficient to cause a vigorous 

 effervescence, and when the strongest ebullition was going to subside, the metal 

 plate of the condenser was removed from over the marble; and being examined, 

 not only electrified the electrometer with negative electricity, but gave a sensible 

 spark. At this time having tried to obtain electricity from the evaporation of 

 water, the effects were equivocal or hardly sensible, the same thing happened a 

 few days after, when however we obtained clear signs of electricity from those 

 effervescences, which produce fixed and nitrous air. One day the electricity 

 arising from the evaporation of water seemed to be positive; but subsequent ex- 

 periments, and other circumstances, indicate that such a phenomenon must be 

 attributed to a mistake. 



The experiment on the evaporation of water, which did not answer so well at 

 Paris, succeeded much better in London, where I bethought me of throwing 

 water on the lighted coals, which were kept in an insulated chafing dish. In 

 this manner the electricity of the evaporation never fails to electrify the chafing 

 dish negatively, and strongly enough for the electricity to be discovered by the 

 simple electrometer; it will even afford a spark, if the condenser be used. 

 Another time this experiment was repeated with success at Mr. Cavallo's, in the 

 following manner. A small crucible, containing 3 or 4 small coals lighted, was 

 insulated; then a spoonful of water was thrown on the coals, and immediately 

 after an electrometer, which communicated with the coals by means of a wire, 

 diverged with negative electricity. 



The experiments hitherto made, though not numerous, yet concur to show, 

 that the vapours of water, and in general the parts of all bodies, that are separated 

 by volatilization, carry away an additional quantity of electric fluid as well as of 

 elementary heat, and consequently that those bodies, from the contact of which 

 the volatile particles have been separated, remain both cooled and electrified ne- 

 gatively; from which it may be deduced, that whenever bodies are resolved into 

 a volatile elastic fluid, their capacity for holding electric fluid is augmented, as 

 well as their capacity for holding common fire, or the calorific fluid. This is a 

 striking analogy by which the science of electricity throws some light on the theory 

 of heat, and alternately derives light from it; I mean on the doctrine of latent 

 or specific heat, the first notions of which were suggested by the admirable ex- 



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