VOLTAIC IGNITION. 347 



In the water without the tube, from . . 60 to 87. 

 In the water containing the tube, from . 60 to 86. 



Here the difference, slight as it was, was against what theory 

 would have led one to anticipate ; the exact equality, however, 

 of the previous experiment, and the close approximation of 

 the results in this one, afford no conclusive information as to 

 the point under consideration, though the negative result 

 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 men- 

 tioned, viz. the inverse relation of the conducting power of the 

 wire to the heat developed in it, I tried the following experi- 

 ment. A platinum wire of one foot long and -^th 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 tem- 

 perature of 60 Fahrenheit ; by this means the intensity of 

 ignition of the other half was notably increased ; the volta- 

 meter 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 im- 

 mersed 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 por- 

 tion 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, 

 I 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 



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

 f Phil. Trans., 1846, p. 573. 



