.s/A' WILLIAM SIEMENS, F.R.S. 



263 



solution of acetate of lead, they were then redried and heated to a 

 dull redness, and again immersed in the lead solution. After 

 repeating this process several times, they were placed in position, 

 and a strong battery current was passed through them, by which 

 the lead was converted into peroxide. The increase of current 

 resulting from this mode of treatment was so remarkable that I 

 was able to effect the decomposition of water by means of one 

 such carbon-lead gas battery by connecting it to a voltameter. 

 No reliable methods of ascertaining the potential of the current 

 were available at that time, but, judging by the results, the power 

 of two volts must have been reached. 



It was, however, found difficult to obtain a supply of carbon 

 tubes of the right degree of porosity, and I therefore fell back on 

 a simpler form of battery, consisting of two bars or rods of dense 

 carbon, upon each of which a long series of thin laminae of porous 

 carbon, pierced laterally by holes to admit the carbon rod, were 

 strung, a certain distance between the laminae being ensured by 

 washers of the same material. Two such bars of carbon with 

 their laminae were placed side by side in a cylinder of gutta-percha 

 with a dividing diaphragm of porous clay, and constituted, when 

 impregnated with peroxide of lead, a powerful galvanic cell, Fig. 8, 

 Plate -22. The power of the cell depended more, however, on the 

 power and time of application of the exciting current than upon 

 the gases admitted into the cylinder, showing that it was chiefly 

 due to the presence of the peroxide of lead formed by the exciting 

 current. 



These exciting currents produced by a Grove nitric-acid battery 

 were, however, too expensive to render the secondary battery 

 available for practical purposes, whereas by the use of dynamo 

 currents, results might have been obtained comparable to those 

 obtained by means of the Faure battery. By the substitution of 

 porous carbon for sheet lead in the secondary battery of the 

 present day, the intervening layers of felt might be dispensed 

 with, and a large amount of active surface be aggregated in a 

 comparatively small space. 



