1904.] on Development of the Theory of Electrolytic Dissociation. 553 



multiple proportions has frequently been assumed, when a closer in- 

 vestigation has found nothing of the sort. 



The law of multiple proportions is the one fundamental conception 

 upon which modern chemistry is built up. Another is the law of 

 Avogadro, which asserts that equal volumes of diflferent gases under 

 like conditions of temperature and pressure contain the same number 

 of molecules. This conception, dating from the beginning of the 

 nineteenth century, was at first strongly combated, and it was its 

 great value in explaining the new discoveries in the rapidly growing 

 domain of organic chemistry which led to its general acceptance in 

 the middle of the past century, 

 after Cannizzaro had argued 

 strongly in its favour. 



There were^ however, some 

 difficulties to be removed before 

 Avogadro's law could be accepted. 

 For instance, it was found that 

 the molecular volume of sal- 

 ammoniac, NH4CI, in the gaseous 

 state was greater than might be 

 expected from its chemical com- 

 position. This led to the sup- 

 position that the molecules of 

 sal-ammoniac when in the gaseous 



N^ 





I 



Pmk 



3luz 



Fig. 1. 



state are partially decomposed into 

 ammonia, NH3, and hydrochloric 

 acid, HCl. Indeed v. Pebal and 

 v. Than succeeded in showing that _, 



this really happens. They used "~*~ 

 an apparatus that is shown in the 

 annexed figure (Fig. 1). Two co- 

 axial tubes are placed the one 

 inside the other by means of a cork. 

 The outer tube was closed at its 

 upper end, the inner one was 

 open, and contained at C a 

 diaphragm of asbestos and above that a piece of sal-ammoniac. The 

 upper end was heated by an air-bath, so that the piece of sal-ammoniac 

 was volatilised. After this a current of hydrogen was led through 

 both glass-tubes D and E. Now ammonia diffuses more rapidly 

 than hydrochloric acid ; if, therefore, the vapour of sal-ammoniac 

 is partially decomposed into ammonia and hydrochloric acid, we 

 should expect that above the asbestos diaphragm there would be an 

 excess of hydrochloric acid and beneath it an excess of ammonia. 

 This V. Pebal showed to be the case. The hydrogen-current from D 

 showed an acid reaction on a piece of litmus-paper in A, and that 

 from E showed an alkaline reaction on a similar piece of litmus - 

 paper placed in B. It was objected that the decomposition might 



