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./ On Electricity in Plants^ and onVegetO'terrestrial Currents. 93 



these are sometimes positive; and sometimes negative. What are 

 the causes which operate in the production of the electric effects 

 of the earth and atmosphere? We cannot give a reply wholly 

 satisfactory to this question, although we know that chemical 



changes going on upon the earth's surface must be powerful 

 causes. 



De Saussure and several other physicists have endeavored to find 

 evidence of the disengagement of electricity daring the evaporation 

 of water. But as they hav^e not taken into account the alteration 

 which the vessels experience in the process, the results were evi- 

 dently unsatisfactory. M. Ponillet undertook the experiments 

 anew, endeavoring to get rid of the causes which complicate the 

 problem. He sought to prove that evaporation and chemical ac- 

 tion in vegetables were the two great sources of atmospheric 

 electricity, I will mention his results, that they may be com- 

 pared with the facts presented in this memoir. 



If a little water is thrown into a platinum crucible heated to a 

 white heat it takes the spheroidal state and evaporates slowly, 

 and on cooling to a certain temperature suddenly passes to a state 

 of vapor. By means of the condenser no disturbance of electric 

 forces was perceived, either during the slow evaporation; or the 

 rapid dispersion of the water. 



With acetic acid, sulphuric acid, very pure nitric acid, in place 

 of water, there was no disengagement of electricity perceived; 



but the result was different when the water held in solution a 

 salt or some substance that is a conductor of electricity. Accord- 

 ^^ig to M. Pouillet, electricity was produced with a solution of 

 strontian during slow evaporation ; and whe^ the water was put 

 in vibration, the amount was quite considerable. The vessel be- 

 came positively electric and the vapor negative. Hence, at the 

 instant when a separation takes place between the molecules 

 of water and those of strontian, electricity is given out; the 

 strontian retains the positive, whilst the water on evaporating 

 carries with it the negative. The earths and alkalies act in the 

 same manner as strontian. 



On experimenting with water containing ammonia, there was 

 an abundant discharge of electricity, but with reverse electric 

 products; the vessel becomes negative, and the water which va- 

 porizes with the ammonia positive,— indicating that the latter, in 

 pfissing off, carries with it an excess of positive electricity. 



If the water holds in solution J-iOO of sulphuric acid or even 

 ^^^' ^here is a discharge of electricity and the vessel is negative. 



^^Uh saline solutions, electricity was equally given out; the 

 vessel was always negative whether the salts were neutral, sub- 

 ^ns, or acid. The vapor of water was constantly positive. 



1 should here state that several physicists who have repeated 

 ine experiments of M. Pouillet with saline solutions, a solution 



