SURROUNDING MEDIA ON VOLTAIC IGNITION. 
57 
any glass tube at all. The circuit having been completed as before, the thermometer 
rose in five minutes — 
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 mentioned, viz. the inverse rela- 
tion of the conducting power of the wire to the heat developed in it, I tried the 
following experiment. A platinum wire of one foot long and ^th of an inch dia- 
meter was ignited in air by ten cells of the battery, a voltameter 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° Fahr. ; by this means the intensity of ignition of the other half was notably in- 
creased ; 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 im- 
mersed, 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 reaehed 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, 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 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, however, when the escape took 
place through capillary tubes, the results seemed subject to no ascertained law, 
though the eompounds 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 hydrogen 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. f Philosophical Transactions, 1846, p. 573. 
MDCCCXLIX. 
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