xi MURIATIC ACID AND CHLORINE 223 



to be a binary compound of two simple gases, hydrogen and 

 chlorine, succeeded also in establishing its composition by 

 volume. Davy states that Cruikshank had shown th^ 

 chlorine and hydrogen, when mixed in equal proportions, 

 gave a product almost entirely condensible by water ; Gay- 

 Lussac and Thenard showed that the product was muriatic 

 acid, but did not make any measurements of volume. 

 These could not be made in the ordinary way either over 

 water (which dissolved the acid gas) or over mercury (which 

 was acted on by chlorine). In Davy's experiments the two 

 gases " were mixed in equal volumes over water, and intro- 

 duced into an exhausted vessel and fired by the electric 

 spark." As the gases were moist, "there was always a 

 deposition of a slight vapour, and a condensation of from 

 one-tenth to one-twentieth of the volume ; but the gas 

 remaining was muriatic acid gas." The contraction was 

 reduced when the gases were dried, " by introducing them 

 into vessels containing muriate of lime, and by suffering 

 them to combine at common temperatures." Although 

 Davy was never " able to avoid a slight condensation," he 

 found that " in proportion as the gases were free from 

 oxygen or water, this condensation diminished." It was 

 therefore reasonable to suppose that the pure gases would 

 unite in equal volumes without contraction (A.C.R. IX. 26). 



Davy also mixed together equal volumes of chlorine and 

 sulphuretted hydrogen, both dried : " in this instance the 

 contraction was not ^ ; sulphur .... was formed on the 

 side of the vessel, but no vapour was deposited. The 

 residual gas contained about i of muriatic acid gas, and 

 the remainder was inflammable " (A.C.R. IX. 26) 



These experiments proved that hydrogen and chlorine 

 combine together in equal volumes and without any marked 

 contraction, as shown by the equation : 



Hydrogen + chlorine -> hydrogen chloride, 

 i vol. i vol. 2 vols. 



