Dr. Beetz on the Electromotive Force of Gases. 91 



touch the liquid, no current was set up, as we should expect; 

 when it was entirely covered by the liquid, the current was 

 very feeble. Five oxyhydrogen pairs were not capable of 

 decomposing iodide of potassium; but when the angles of the 

 platinum were in contact with the gas, this decomposition was 

 effected by only one pair of plates. This law does not, how- 

 ever, appear to me generally established. In the case of gases 

 which are copiously absorbed by water, as chlorine, it is cer- 

 tainly incorrect* ; in fact, I found with the circuit of hydrogen 

 and chlorine that the electromotive force was always greatest 

 when the chlorine contained in the tube was perfectly ab- 

 sorbed (free from air). It certainly holds good in the case of 

 other gases, but in a less degree, especially when in ascer- 

 taining the intensity of the current, the circuit is closed for 

 longer than a moment. The small quantities of gas dissolved 

 by the conducting liquid are very rapidly consumed by the 

 gas evolved electrolytically, and the liquid may not be able to 

 absorb gas throughout its entire mass with sufficient quickness 

 to bring the current again to a moderate intensity. The expe- 

 riments of Jacobi and Poggendorfff tend to show that platinum 

 also exerts an action upon the gas when covered by the liquid ; 

 they found that in a voltameter with platinized electrodes, the 

 quantity of gas evolved entirely disappears again, even after 

 the water has risen above it. I however avoided the use of a 

 voltameter, at the poles of which the gases were evolved, be- 

 cause the electromotive force produced by the polarization is 

 always greater than that of an ordinary gas battery. The plates 

 of platinum were cemented into the tubes in the ordinary way, 

 after the upper parts of them had been thickly coated with 

 shell-lac. Only that part of the plates thus isolated was sur- 

 rounded by the gases ; those parts with a metallic surface re- 

 mained completely immersed in the conducting liquid. In a 

 circuit arranged thus, I obtained an electromotive force of 

 15*64<, which is much too small. The principal cause of this 

 was, that the conducting liquid, which at that heat would have 

 absorbed too little gas, on cooling not only absorbed hydrogen 

 from above, but also air from below, from contact with which 

 it was not protected. 



If the platinization of the plates of platinum only increases 

 the electromotive force of gas batteries because the counter 



* Mr. Grove did not^tnean to assert that there was no action when the 

 electrodes were immersed in the solution and the gas soluble, as he treats 

 of this action in other parts of his paper; but that even under these circum- 

 stances the points of electric action were those at which the platinum, liquid 

 and gas met — Ed. Phil. Mag. 



f PoggendorfF's Annalen^ vol. Ixx. p. 201 . 



