416 Dr. Svante Arrhenius on the Electric 



Now it seems to me that the following explanation of 

 Prof. Thomson's experiments is much more plausible. In the 

 cases under discussion he was always able to prove the presence 

 of free halogen — in the above example, of free chlorine 

 (Cl 2 ) — by the reaction of the heated gases with potassium 

 iodide and starch. It must be expressly stated that this 

 reaction is for the molecules Cl 2 , Br 2 , and I 2 , and not for the 



ions 01, Br, and I, which in aqueous solution do not exhibit 

 the reaction. If Prof. Thomson, then, is of opinion that he 



has proved the presence of 01 in the heated hydrochloric-acid 

 gas, his conclusion cannot be accepted. On the contrary, it 

 may easily be shown that the two charged ions of an electro- 

 lyte cannot be separated from each other in appreciable 

 quantity (about 10~ 5 milligram-equivalents) by mechanical 



means ; for the separation of 10~ 10 milligram- equivalents of 01 

 would be sufficient to charge a sphere of 10 centimetres radius 



to 900 volts — an electromotive force which would certainly 



+ 

 suffice to bring the 01 back to the H. 



Prof. Thomson has only thus proved the presence of free 

 chlorine (Cl 3 ) in the heated hydrochloric acid of his experi- 

 ments. This may be accounted for in two ways. Either 

 HC1 decomposes at a high temperature so as to produce a 

 state of equilibrium between H 2 , Cl 2 *, and 2H01 ; or — and 

 this alternative seems to me much more probable — oxygen 

 (air) may have been present in the hydrochloric-acid gas, and 

 have liberated chlorine with formation of water. We are 

 informed that the experiments with sulphur and hydrogen 

 sulphide were conducted in an atmosphere of nitrogen ; but 

 no such indication is given with respect to the other gases 

 (HOI, NaCl, KC1, NH 4 C1, KI, and HI). In either case the 

 quantity of free chlorine (Cl 2 ) would be diminished by the 

 presence of hydrogen. Now it is quite likely that the free 

 halogen would favour convective conduction, if such is 

 assumed in Prof. Thomson's experiments. Crafts tells us 

 (loc. cit. p. 186) that his chlorine attacked platinum with 

 violence, and the same is probably true of the other halogens, 

 although perhaps in their case the action is less intense. 

 It is therefore easily conceivable that platinum would be dis- 

 persed as fine particles more readily in an atmosphere con- 

 taining Cl 2 , than in an atmosphere where chlorine gas is 

 absent ; and it is owing to the transport of electricity by 



* Cl 2 does not decompose perceptibly into 2Clatll00° — Crafts. 



