of Solid Substances. 



341 



The total volume of the oxygen in chlorate of potash, on the 

 supposition that the chloride of potassium retains its original 

 volume in combination, is 15 ; whereas it is only 7 in bromate of 

 potash, if we allow that the bromide of potassium retains its 

 original volume; and it appears to occupy no volume in iodate of 

 potash, assuming that iodide of potassium maintains its original 

 volume. The apparent disappearance of the volume of the 

 oxygen, in changing iodide of potassium into iodate, is ana- 

 logous to the apparent loss of volume of many salts in their 

 water of hydration, the salt occupying the volume of the crystal 

 water taken as ice, as pointed out many years ago by Playfair 

 and Joule, it is clear that, in assuming that the halogen 

 compounds of potassium retain their primitive volume in their 

 oxidized derivatives, we place these compound substances in 

 the same position as the metals in the simple oxides. Now, 

 we saw that in many oxides the volume of the oxygen varied, 

 and that, in all probability, from metallic condensation taking 

 place during the act of combination. The metals having the 

 lowest density and the greatest atomic volume condense the 

 most in combining. Generally speaking, if we examine the 

 volumes of the halogen salts in the above Table, it is clear that 

 the equivalent volumes increase, chloride of potassium being 37, 

 bromide 44, and iodide 55*3, and their relative stability dimi- 

 nishes. The equivalent volumes of chlorine, bromine,, and 

 iodine are identical in the liquid state ; and thus the formation 

 of the respective potassium compounds is one of the results of 

 unequal condensation, the coefficient of contraction in the for- 

 mation of chloride of potassium being - 46, bromide 029, iodide 

 0*23 per unit volume. Their formation is attended with the 

 evolution of very different amounts of heat. The following 

 Table contains some of the constants found with reference to 

 combination and solution. 





Constants 



of Group. 







Contrac- j 

 tion per Total 

 unit heat, 

 volume. 



Heat of 



solution. 



Diffusion 



times 

 (relative). 



Coefficient of 



expansion per 



equivalent 



volume 



Specific heat 

 per atom. 



KCl 



KBr 



KI 



0-46 | 97086 

 0-29 85666 

 0-23 | 72721 



3874 

 4522 



4847 



74-5 

 119 

 166 



0001429 

 0-001848 

 0002358 



12-88 

 13-47 

 13-60 



Generally speaking, the number found for bromide of potas- 

 sium is nearly the mean of those attached to chloride and iodide. 

 A similar observation has recently been made by M. Valsen in 

 examining the equivalent capillary constants of these bodies. 



