216 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



tains hydrogen and (2) is the sole product of the combina- 

 tion of hydrogen with chlorine was proved by the French 

 chemists Gay-Lussac and Thenard in 1809. The presence of 

 hydrogen was shown by the fact that this gas was liberated 

 freely when the muriatic gas was acted upon by metals. 1 

 Thus they write : 



" We have also examined the action of the metal of potash 

 on muriatic gas. At the ordinary temperature this action 

 is very slow ; but as soon as the metal is fused there is com- 

 bustion with disengagement of light, and there result muriate 

 of potash and hydrogen gas." 



" The quantity of hydrogen collected in this experiment is 

 precisely the same as that which the metal would give in 

 contact with water." 



"We passed a current of muriatic gas over well-cleaned 

 iron turnings at a dull red heat. Much hydrogen gas was 

 disengaged, without sensible admixture of muriatic gas ; 

 much muriate of iron was at the same time obtained ; the 

 residual turnings were not oxidised" (A.C.R. XIII. 34 and 



38). 



Hydrogen, combined with oxygen in the form of water, was 

 also collected " by passing muriatic acid gas at a moderate 

 heat over litharge which had been fused and then reduced 

 to coarse powder." 



Muriatic acid gas a compound of hydrogen and 

 chlorine. Gay-Lussac and Thenard observed further that 

 equal volumes of hydrogen and chlorine combined together 

 to form muriatic gas (a) by keeping the mixture for several 

 days, (b) by gently heating it, (c) by exposure to light. 

 They found 



" that a mixture, in equal parts, of [chlorine] gas and hydro- 

 gen gas changes, in the course of several days, into ordinary 

 muriatic gas, and that no water is deposited." 



" If a mixture of equal parts of these two gases is made 

 and a small piece of iron heated in mercury to 150 intro- 



1 These were now generally recognised as elementary substances. 



