Electric Discharge on Gases and Vapours. 527 



are subjected to the electric discharge is so rapid and striking 

 that it can readily be demonstrated to a large audience in 

 lecture. 



The carbon separated out from each of these gases is the 

 same in kind and form. Filaments 6 to 8 millim. long can 

 be readily obtained in a few minutes, and on continuing the 

 discharge they finally connect the two poles, when the spark 

 ceases. The growth of the filament is entirely avoided by 

 frequently reversing the current. 



By the action of the electric discharge on vapour of chloro- 

 form no carbon filaments are formed, and chemically the 

 decomposition is not simple in character. There is a large 

 amount of gas formed consisting of chlorine (iodized starch- 

 paper is blued) and hydrochloric acid (the gas is rapidly 

 absorbed in part by water and the aqueous solution is strongly 

 acid), while a dark red liquid is observed on the mercury of 

 the eudiometer due to the solution of one of the products of 

 decomposition in excess of the chloroform. A further exami- 

 nation of this was not attempted. 



An exact measurement of the increment in volume of 

 vapour was out of the question, owing to the action of the 

 chlorine formed on the mercury of the eudiometer. 



Carbon tetrachloride is decomposed very slowly indeed by 

 the discharge. As in case of chloroform, so here also no 

 carbon filament is formed, while the rate of decomposition is 

 entirely different from that of chloroform. A voluminous 

 yellow deposit is observed on the walls of the eudiometer 

 around the negative pole and chlorine is set free, as appears 

 by the starch test. The gaseous products of decomposition 

 are not rapidly absorbed by water, as was the case with 

 chloroform. A black deposit is observed on the surface of 

 the mercury. Unquestionably, therefore, it follows from all 

 this that the decomposition of carbon tetrachloride by the 

 electric discharge is by no means simple in character. 



When the electric discharge acts upon the vapour of carbon 

 disulphide the volume diminishes rapidly. The vapour of 

 this substance offers an enormous resistance to the passage of 

 the discharge. When the poles are only 1 millim. apart only 

 very few sparks pass through, the discharge taking its course 

 outside round the eudiometer through the air, a distance 

 twenty to thirty times as great, a proof that the vapour of 

 carbon disulphide is an almost perfect insulator. In the 

 course of the discharge a grey-blue smoke is observed which 

 gradually pervades the entire volume of the vapour. Here, 

 then, we have no noticeable evidence of electrolysis taking 



2N2 



