xi MURIATIC ACID AND CHLORINE 219 



could be accounted for by the combination of the hydrogen 

 of the acid with the oxygen of the litharge, quite independ- 

 ently of the existence of any oxygen in chlorine. 



The difficulty of decomposing chlorine. Chlorine as an 

 agent for purifying charcoal. Gay-Lussac and Thenard 

 made many attempts to separate oxygen from chlorine and 

 thus to set free its other hypothetical constituent. But all 

 their efforts were unsuccessful, since neither the metals, nor 

 phosphorus, nor any of the well-known absorbents of oxygen 

 were capable of separating oxygen from the gas. 



" Finally, as a last method, we tried to decompose 

 [chlorine] by charcoal ignited at the extreme heat of the 

 forge. To avoid the presence of the smallest quantity of 

 water, we made the gas pass slowly through a large glass 

 tube a metre and a half in length, filled with muriate of 

 lime. This tube communicated with a porcelain tube in 

 which the charcoal was exposed to a red heat. The first 

 portions of the .... gas were completely converted into 

 ordinary muriatic gas. This effect diminished gradually in 

 spite of a very great elevation of temperature, and soon the 

 gas passed without alteration, mixed only, towards the end 

 of the experiment, with one thirty-third of an inflammable 

 gas, which we believe to be carbonic oxide gas. This result 

 clearly showed us that [chlorine] is not decomposed by char- 

 coal, and that the muriatic gas which we had obtained at 

 the commencement of the operation was due to the hydro- 

 gen of the charcoal. ... In fact, on taking ordinary char- 

 coal without igniting it, muriatic gas was disengaged during 

 a lengthened period, even at a temperature only slightly 

 elevated. . . . According as the charcoal lost its hydrogen, 

 however, the quantity of muriatic acid went on diminishing, 

 and finally nothing was obtained but [chlorine]" (A.C.R. 

 XIII. 39-40). 



In this passage Gay-Lussac and Thenard disclose incident- 

 ally a very efficient method of purifying charcoal. The 

 charcoal which Stas used in determining the composition of 

 carbonic anhydride (p. 149) was purified by heating it 



