the Thermo-Electric Properties of Liquids. 



543 



positive electricity by contact with acids, and with negative by contact 

 with alkalies ; and its electrical condition in acids to be the opposite of 

 that which would have been produced by chemical corrosion. All these 

 results agree with mine. The statical electric effects which Pfaff 

 obtained with other liquids, such as solutions of argentic nitrate, cupric 

 sulphate, ferrous and ferric sulphates, and other salts, also agree in the 

 main with the dynamic ones obtained with my apparatus. Rise of 

 temperature, therefore, usually only increased and sustained the differ- 

 ence of electric condition between metals and liquids which contact 

 produced ; and this effect was the same in acid and alkaline solutions. 

 As also the direction of the current agreed usually with that of electric 

 polarity produced by contact, if we know that of the one at a particular 

 temperature, that of the other may be predicted from it. These con- 

 siderations also indicate the existence of a zero of temperature for each 

 pair of substances, below which contact would not develop electricity 

 in them. 



(Added March 25, 1878.) 



Since writing the above, I have met with a paper by M. Pouillet on 

 " New Phenomena of the Production of Heat,"* in which the author 

 stated, that at the instant a liquid wets a solid, or is absorbed by it, 

 there is a disengagement of heat, and proved this statement by nu- 

 merous experiments, made with a variety of substances, in such a 

 manner as was likely to secure trustworthy results. The liquids 

 employed were confined to water, oil, alcohol, and acetic ether only ; 

 but the solids were very various, chiefly organic substances, but in- 

 cluding also (in a state of fine division) porcelain, glass, clay, carbon, 

 sulphur, silica, alumina, magnesia, oxides of chromium, the peroxides 

 of iron and of manganese ; also finely-powdered metals, viz., iron, zinc, 

 tin, antimony, and copper. The rise of temperature found with in- 

 organic bodies varied from '2 to *5 of a C. degree, and lasted from two 

 to four minutes, and then the temperature returned to its former state. 

 Regnault has confirmed the general result. f 



As the mere contact of metals and liquids develops heat, and as 

 (without the aid of chemical action) heat excites an electric current, 

 and the direction of the current produced by heating platinum in con- 

 tact with either acid or alkaline solutions, agrees with the signs of 

 static electric polarity excited by the contact of that metal with those 

 liquids, we may reasonably conclude that the heat and free electricity, 

 excited by such contact, are related to each other, either as cause and 

 effect, or as coincident effects of some other cause contained in the act 

 of contact. 



* " Annales de Chimie et de Physique," 1822, vol. xx, pp. 141-162. 

 f " Annales de Chimie et de Physique," 1841, vol. i, p. 133. G-melin's " Hand- 

 book of Chemistry," vol. i, p. 300. 



VOL. XXVII. 2 



