140 MR J. Y. BUCHANAN ON THE 



The first point has been adequately dealt with in the immediately preceding section, 

 and the two remaining ones will now be considered. The diagram on next page 

 clearly shows the relations pointed out above, and the following are the more 

 distinctive features which are illustrated. 



All the halide salts, with the possible exception of KI, have the property of causing 

 expansion with dilution of their respective solutions, this expansion, in the case of the 

 chlorides, being nearly proportional to the rise in the atomic weights of the base, as 

 shown by the almost parallel march of the curves. In the case of the bromides the 

 march is not so regular, the solutions of the rubidium and caesium salts inducing a 

 greater relative expansion on dilution than is the case with the potassium salt, the 

 change being greatest in the case of the rubidium salt. 



With the iodides, this increased effect of expansion which occurs on dilu- 

 tion of solutions of the salts of rubidium and csesium over that of potassium is 

 considerably enhanced, the solutions of potassium iodide showing practically no 

 expansion. 



Thus, summarising the effects, the mutual relations of halogen and base in the cases 

 of halide salts of potassium and the chlorine compounds of rubidium and csesium produce 

 normal effects, as shown by only slight changes in the values of vjm as the solutions 

 decrease in concentration, while the remaining salts show expansion on dilution of 

 solutions of them, which increases in magnitude with increase in molecular weight, 

 reaching a maximum with csesium iodide. This is interesting when it is considered 

 that csesium is the most electro-positive element, and seems to point to the expansive 

 effect produced by both csesium and iodine independently, while mutual interference 

 occurs in the other cases. 



The oxyhalides are not comparable in any sense with their respective halide 

 compounds, which have been treated above. 



The most obvious feature of the incorporation of the oxygen atoms is, that the 

 values for vjm decrease with the increase in molecular weight when triads of the salts 

 having common base and the same concentration are compared, the only exception 

 being the case of potassium bromate ; and this feature is the reverse of that in the case 

 of the halide salts. Also in the case of KCIO3 and KIO3 contraction occurs on dilution 

 of their respective solutions ; and where expansion occurs on dilution, the general order 

 is that of proceeding from the iodates to the chlorates, where the greatest expansive 

 effect is seen in the case of csesium chlorate. This is the reverse of the order which is 

 seen in the case of the halides. The chlorates show the greatest variations in the 

 values of vjin with dilution of solutions of the salts, and least with the bromates, the 

 iodates beit)g intermediate. 



Thus the effect of the inclusion of the oxygen in the molecule of the halides is to 

 greatly increase the expansion effect when solutions of the chlorates of rubidium and 

 csesium are diluted, to exert very little if any effect in the case of the bromides, and to 

 diminish the effect of expansion in the case of the iodides, the general effect in the 



