220 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



in a current of chlorine, and the same method is still in 

 general use. 



A striking contrast was observed on comparing the effect 

 of heat alone on dry and on moist chlorine. The dry gas 

 resisted all attempts to decompose it, but the introduction 

 of moisture was followed by the immediate production of 

 oxygen and muriatic acid. In this experiment chlorine 

 11 alone or mixed with the vapour of boiling water " was 

 introduced " into a porcelain tube exposed to a red heat. 

 In the first case the gas did not suffer any alteration ; but 

 as soon as the vapour of water was introduced, oxygen gas 

 and muriatic acid were obtained. It is not necessary for 

 this decomposition that the temperature should be very 

 high, as it still takes place below a red heat." When 

 hydrogen was used in place of water the formation of 

 muriatic acid took place even more readily " at a tempera- 

 ture only a little higher than that of boiling water" (A.C.R. 

 XIII. 41). 



At the conclusion of their experiments Gay-Lussac and 

 Thenard were obliged to admit that since chlorine " is not 

 decomposed by charcoal ... it might be supposed . . . 

 that this gas is a simple body," and agreed that " the pheno- 

 mena which it presents can be explained well enough on this 

 hypothesis" (A.C.R. XIII. 48). But they were not 

 prepared to abandon the view that it contained oxygen and 

 preferred to regard it still as a compound. It was therefore 

 left for Davy to adopt and to advocate the view that 

 chlorine was a simple or elementary substance, and finally 

 to win general recognition for a conception that gave the 

 death-blow to Lavoisier's oxygen theory of acids. 

 P Davy (1810) regards chlorine as an element. At the 

 time when Gay-Lussac and Thenard were making their 

 experiments on chlorine, Davy was engaged in similar 

 researches on this gas. During the early part of 1810, the 

 failure of all attempts to decompose chlorine, even by the 



