16 Mr. Colquftoun on the Life and Writings [Jan. 



when Berthollet, nine years after this, again resumed the subject, 

 again investigated the nature of sulphuretted hydrogen, and 

 again confirmed every former statement he had made, 

 though he had long been confessedly one of the first French 

 chemists, again found the same ill success in attempting to 

 establish an important truth which has only commanded 

 general assent since the recent era to which we have already 

 alluded. 



But the year 1787 is further remarkable as the date of the 

 publication of some of Berthollet's most important researches 

 into the nature of chlorine. He had already given to the world 

 his first memoir on this subject in 1785 : it was one which came 

 repeatedly under his notice, and on each occasion his investiga- 

 tions were attended by results the most important ; at one time 

 to the interests of science, at another to the advancement of the 

 arts. His experiments on this substance may be divided into 

 three branches. The first regards the nature of simple chlo- 

 rine ; the second, its combination with oxygen ; and the third, 

 its property of destroying vegetable colour. 



The history of M. Berthollet's researches into the constitution 

 of chlorine is one of the greatest interest and instruction. The 

 views which he adopted have been proved by subsequent expe- 

 riments to be erroneous ; but the process of reasoning by which 

 he arrived at his results appeared so plain, his conclusions 

 seemed so inevitable, and all the phenomena were by its means 

 so satisfactorily accounted for, that during a period of twenty- 

 five years, his theory was universally received. Its overturn has 

 been the consequence only of the discovery of facts unknown 

 at the time of its formation, the metallic basis of the alkalies, 

 the new substance iodine, and several others, all of which are 

 closely analogous in their properties with chlorine. 



Scheele, who discovered chlorine in 1774, had also the great 

 merit of takino- a correct view of its constitution. He called it 

 dephlogisticated muriatic acid, or, in modern tetvas,, muriatic acid 

 deprived of its hydrogen. Berthollet, on the contrary, considered 

 muriatic acid to be the simple (or at least the till then undecom- 

 pounded) body, and he regarded chlorine as a compound of this 

 simple substance and oxygen. And his reasoning on the subject 

 seemed then to be close and irrefragable. 



If muriatic acid be digested over the black oxide of manga- 

 nese, a portion of it is decomposed, and separates in the state 

 of chlorine gas ; the remaining portion is found to hold in solu- 

 tion the oxide of manganese at an inferior degree of oxidation. 

 Of course, the black oxide has also undergone decomposition, 

 and given up a portion of its oxygen ; bat not a trace ot this gas 

 remains in the liquid. From this, Berthollet concluded, that it 

 hadgowe off tvith the chlorine, and formed part oj' that substance: 



