1889.] 



A new Form of Gas Battery. 



301 



These figures show that in the case of the battery experimented 

 with the maximum of work was obtained with an external resistance 

 of about double the internal resistance. 



This result is probably due, as pointed out by Dr. C. A. Wright,* 

 to the fact established by Favref and Berthelot,^ that the gases 

 occluded or condensed by platinum black evolve less and less heat 

 per unit weight of gas the more gas the platinum black had pre- 

 viously condensed. 



The heat evolved by the condensation of the gases by the platinum 

 black, or a certain portion of this heat, is in all probability lost for 

 the production of the current; it follows that the more the^platinum 

 black is saturated the less energy will be lost by the condensation of 

 the gases, and vice versa. Now, probably the rate of absorption of 

 gas by the platinum black will rapidly diminish as it is more and 

 more saturated with gas, so that in order to maintain it saturated or 

 nearly saturated only a moderate amount of current can be obtained 

 from a given surface, while if it is kept far below the saturating 

 point it will condense the gases very rapidly, and a very large current 

 can consequently be obtained. 



As a practical limit we prefer to work the battery with an E.M.F. 

 with closed circuit of about 0"73 volt. This allows us to take from 

 2 to 2 \ amperes (1*45 — 1*82 watt) out of an element with an active 

 surface of 700 sq. cm., covered with 0'35 gr. of Pt leaf and 1 gr. of 

 Pt black, which gives a useful effect of very nearly 50 per cent, of 

 the total energy contained in the hydrogen absorbed in the battery. 



We have found practically no difference in these results, whether we 

 were using and H or air and gases containing 30 per cent, to 

 40 per cent, of H, such as can be obtained by the action of steam or 

 air and steam on anthracite, coke, or coal. 



With a useful effect of 50 per cent., one-half of the heat produced 

 by the combination of the H with the O is set free in the battery, 

 and raises its temperature. By passing through the battery a 

 sufficient excess of air, we can keep the temperature of the battery 

 constant at about 40° C, and at the same time carry off the whole of 

 the water formed in the battery by means of the gases issuing from 

 it, so that the platinum black is kept sufficiently dry, and the 

 porous plate in nearly the same state of humidity. 



The E.M.F. of the open battery is very considerably below what it 

 should be according to Thomson's theorem. The combustion of H and 

 O should produce an E.M.F. of 1*47 volts, while we only obtain 0*97. 

 It does not seem to us probable that this difference can be explained 

 in the same way as the deviations from this theorem in a number of 



* ' Phil. Mag.,' vol. 9, 1881, p. 169. 



f ' Comptes Kendus,' vol. 77, 1873, p. 649. 



% ' Annales de Chimie,' vol. 30, 1883, p. 519. 



