274 



Prof. H. E. Armstrong. Electrolytic [Mar. 25, 



The noteworthy point is the large excess of water required to initiate 

 this change: when v=16 the solution contains less than 1 per cent. 

 H 2 SiF 6 , and at this point, according to Ostwald, decomposition 

 probably begins, but that it is far from complete even when a very 

 much larger excess is present is evident from the fact that the 

 maximum when v = 32,768 is 282 and not above 400. 



Now it is well known that hydrogen chloride, bromide and iodide 

 are, practically speaking, perfect gases under ordinary circumstances: 

 in other words, masses of these gases would "mainly consist of mole- 

 cules such as are represented by the formulas HC1, HBr and HI. It 

 has been proved, however, by Mallet that hydrogen fluoride at tem- 

 peratures near to its boiling point mainly consists of molecules of the 

 formula H 2 F 2 . In the aqueous solution the molecules would be 

 brought more closely together, and therefore it is probable that, even 

 in the case of hydrogen chloride, bromide and iodide, a certain pro- 

 portion of more complex molecules would result ; the relatively high 

 boiling point of hydrogen fluoride (19 "4°) renders it probable that in 

 the liquid state this compound would at least partially consist of 

 molecules more complex even than is represented by the formula 

 H 2 F 2 . On the hypothesis put forward in this paper, the influence 

 exercised by the one member of the composite electrolyte upon the 

 other member during electrolysis is at all events mainly exercised by 

 their respective negative radicles, and the extent of the influence 

 thus mutually exerted by these radicles would depend on the extent to 

 which they are still possessed of "residual affinity." If the hydrogen 

 chloride, bromide and iodide are present chiefly as simple molecules, 

 they should exert, ab initio, almost the full effect which they are 

 capable of exerting ; and the chief effect of dilution being to decom- 

 pose the more complex molecules, conductivity should increase to but 

 a slight extent if the extent to which simplification can take place be 

 but small. On the other hand, if owing to the formation of molecular 

 aggregates the residual affinity be more or less exhausted, the initial 

 conductivity will be low, and it will increase on dilution only in pro- 

 portion as these aggregates become broken up. 



It appears to me that the behaviour of the four hydrides under 

 discussion is absolutely in accordance with these requirements of the 

 hypothesis. Even the difference between hydrogen chloride and 

 hydrogen bromide and iodide is not without its bearing. The determi- 

 nations of the density of chlorine at various temperatures by Ludwig, 

 and of the density of bromine by Jahn (" Monatshefte fur Chemie," 

 1882, p. 176), have shown that it is necessary to raise the temperature 

 considerably higher above the boiling point in order to reduce the 

 density to the theoretical value in the case of chlorine than in the 

 case of bromine : in other words, there is a greater tendency in 

 chlorine to form aggregates more complex than those of the formula 



