130 ELECTRIC LIGHTING. 



electrodes for the electric light, made of a mixture of pounded 

 coke and sugar, which, after having been moulded and 

 powerfully compressed, was baked, then steeped in a con- 

 centrated solution of sugar, and heated again to whiteness. 

 Three years afterwards, in 1849, Leonolt patented carbons 

 for the same purpose, made of two parts of retort-coke, two 

 parts of wood charcoal, and one part of liquid tar. These 

 substances were mixed into a paste, then subjected to power- 

 ful compression, afterwards covered with a coating of sugar- 

 syrup, and left for 20 to 30 hours at a high temperature. 

 They were afterwards purified by successive immersions in 

 acids. Lacassagne and Thiers conceived the idea of purify- 

 ing sticks of carbon by steeping them in fused caustic, 

 potash, or soda. The object of this operation was, accord- 

 ing to the author, to change the silica contained in the carbon 

 into soluble silicates. They were then steeped a few moments 

 in boiling water, and afterwards exposed to a current of 

 chlorine in a porcelain tube heated to redness, in order to 

 convert the earths left unattacked by the potash or soda into 

 volatile chlorides of silicium, calcium, potassium, iron, &c. 

 A short time after these experiments Curmer proposed to 

 form carbons by the calcination of a mixture of lamp black, 

 benzine, and turpentine, the whole moulded into a cylindrical 

 form. The decomposition of these substances left a porous 

 coke, which was saturated with resin or syrup, and again 

 calcined. These had little density and a low conducting 

 power, but they were very uniform and free from all im- 

 purities. 



The greatest success was, at the period we are speaking of, 

 obtained by Jacquelain, formerly the chemist of the Ecole 

 Centrale. Experiments on the electric light made with his 

 carbons for the French lighthouse authorities were so con- 

 clusive that the problem was supposed to be solved. In 

 connection with these experiments I cannot refrain from 

 giving here a letter written to me in 1858 by Berlioz, at that 

 time manager of the Alliance Company, a man of intelli- 



