414 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



rule (ibid. 33, 301), and had an obvious motive in append- 

 ing to Dumas's paper a still more remarkable illustration of 

 the possibilities of substitution without change of type. 



Wohler (1840) on substitution without change of type. 

 The substance selected was manganous acetate, and the 

 action of chlorine upon it was described as follows : 



" I passed a current of chlorine through a solution of 

 manganous acetate, under the direct influence of sunlight. 

 After 24 hours I found in the liquid a superb crystallisation 

 of a violet-yellow salt." This was manganous chloroacetate, 

 the whole of the hydrogen of the acetic acid having been 

 displaced by chlorine. 



"This salt, heated at 110 in a current of chlorine, was 

 converted with liberation of oxygen gas into a new golden- 

 yellow compound." In this compound, the oxygen of the 

 base, as well as the hydrogen of the acid, had been dis- 

 placed by chlorine. 



"The new substance was dissolved with the aid of heat in 

 pure chloral, and this liquid, which is not attacked by chlorine, 

 was used to continue the treatment by this agent. I passed 

 dry chlorine into it, during 4 days, keeping the liquid 

 always very near its boiling-point. During this time a white 

 substance was constantly deposited, which on careful exami- 

 nation was recognised as manganous chloride. I cooled the 

 liquid some time after, when there was no longer any more 

 precipitate and I obtained a third substance in small, green- 

 ish-yellow, silky needles." It contained no manganese, as 

 this in its turn had now been displaced by chlorine. 



" On acting again with chlorine on an aqueous solution of 

 this substance, carbonic acid was set free and on cooling the 

 liquid to + 2 it deposited a yellow mass formed of small 

 plates, closely resembling chlorine hydrate. The carbon 

 had, in fact, been replaced by chlorine, which was now 

 the only element present in the compound. The mangan- 

 ous acetate had been converted by substitution into pure 

 chlorine, which, however, had a vapour-density which indi- 

 cated the presence in the molecule of not fewer than twenty- 

 four atoms of chlorine, MnO,C 4 H 6 O 3 , having been converted 

 into C1 2 C1 2 ,C1 8 C1 6 C1 6 ." 



