﻿584 The "Swan" Spectrum. 



rapidly deposited, so that there is only a very short time in 

 which observation of the spectrum is possible. For this 

 reason, it was arranged, in some cases to have a continuous 

 flow of fresh liquid so as to carry the separated carbon away 

 as rapidly as possible. 



We observe the " Swan" spectrum also in liquids containing 

 oxygen, such as ethyl and methyl alcohols, and glacial acetic 

 acid; and in these liquids the decomposition takes place without 

 separation of carbon (or only slight blackening) but with 

 evolution of a combustible gas. In the liquids not containing 

 oxygen there is rapid separation of carbon, so rapid in the 

 case of naphthalene, benzol, &c, that the observation of the- 

 spectrum is only possible for a few seconds. 



We describe more at length our observations with 

 chloroform. 



The chloroform employed was the purest we could obtain : 

 it was allowed to stand for some weeks in contact with freshly- 

 fused zinc chloride and then redistilled. The distillate was 

 allowed to stand in contact with bright sodium and again 

 distilled, and the process repeated several times. Pure 

 chloroform does not appear to act upon bright sodium. 



When subjected to the action of the spark in the liquid, 

 chloroform is rapidly decomposed with separation of much 

 carbon and evolution of torrents of' hydrochloric acid. It 

 gives the " Swan " spectrum superposed upon a continuous 

 spectrum, due, no doubt, to the solid carbon deposited. A 

 rough quantitative determination was made in order to obtain 

 some light upon the nature of the decomposition of chloro- 

 form by the spark. For this purpose the chloroform was 

 sparked in a bent piece of combustion-tube, and the gas 

 evolved passed through water in absorption-bulbs. The 

 deposited carbon was filtered off, in the same tube, through 

 asbestos, and burnt in a current of oxygen : the weight of 

 carbon dioxide obtained was 0*2196. The hydrochloric acid — 

 precipitated and weighed as silver chloride — amounted to 

 0*5472. The chloroform filtered from the carbon gave white 

 crystals on standing which seemed to be carbon sesquichloride, 

 and the decomposition thus appears to take place according 

 to the equation 3CHC1 3 =C 2 C1 G + C + 3HCJ, which would 

 require 0'5449 of HC1 for 0*2196 carbon dioxide. 



Carbon tetrachloride also gives the Swan spectrum and 

 evolves chlorine with very rapid separation of carbon. The 

 liquid employed had been repeatedly redistilled from bright 

 sodium. 



Ethyl bromide gave the Swan spectrum brightly,* the 

 groups y, 8, and e were observed. 



