1 24. Mr. Grove on the Effect of 



rather tends against the view which would assimilate the effects 

 of voltaic to those of ordinary ignition. 



As another method of attaining the object before mentioned, 

 viz. the inverse relation of the conducting power of the wire 

 to the heat developed in it, 1 tried the following experiment. 

 A platinum wire of one foot long and one-eightieth of an inch 

 diameter was ignited in air by ten cells of the battery, a volta- 

 meter being included in the circuit; the amount of hydrogen 

 given off by the voltameter was one cubic inch in forty-four 

 seconds : half the wire was now immersed in water of the 

 temperature of 60° F. ; by this means the intensity of ignition 

 of the other half was notably increased ; the voltameter now 

 yielded one cubic inch in forty seconds : two-thirds of the 

 wire immersed, gave one cubic inch in thirty-seven seconds; 

 and five-sixths immersed, gave one cubic inch in thirty-five 

 seconds. The heat of the portion of wire not immersed in 

 water had in the last experiment nearly reached the point of 

 fusion of the platinum. By this result it appears that the 

 increased resistance to conduction of the ignited portion is not 

 equal to the increased conducting power of the cooled portion 

 of the same wire. 



With a view of seeing how far the cooling effect upon the 

 ignited wire might be due to the greater or less fluency or 

 mobility of the particles of the different media surrounding it, 

 1 have looked into the papers of Faraday* and of Graham f. 

 In the experiments of the former, it appears that the escape 

 of different gases at a certain pressure through capillary tubes, 

 or the velocities of revolution of vanes or floats surrounded by 

 different gases, was in some inverse ratio to the density of 

 such gases ; and the experiments of the latter show that the 

 effusion or escape of gases through a minute aperture in a 

 plate, takes place with velocities inversely as the square root 

 of their specific gravities. In Graham's experiments, how- 

 ever, when the escape took place through capillary tubes, the 

 results seemed subject to no ascertained law, though the com- 

 pounds of carbon with hydrogen passed through with greater 

 facility than other gases. 



The cooling effects of gases on the ignited wire are decidedly 

 not in any ratio with their specific gravities ; thus, carbonic 

 acid on the one hand, and hydrogen on the other, produce 

 greater cooling effects than atmospheric air ; and olefiant gas, 

 which closely approximates air, and is far removed from hy- 

 drogen in specific gravity, much more nearly approximates 

 hydrogen, and is far removed from air in its cooling effect. 



* Quarterly Journal of Science, vol. iii. p. 354. 

 t Philosophical Transactions, 1846, p. 673. 



