Chemical Artion in the Crystalline State. 575 



followed as above. From experiments V. and VI. the values 

 of n for the $2 per cent, solid solution were 0*62 and 0*64. 

 The large crystals of potassium permanganate give values of 

 n which vary considerably with x, n being greater than unity 

 for small values of a? and diminishing as a? increases. 



Influence of Temperature. 



The influence of temperature is complex since both k and 

 a+f(x) vary. The variation of k is the true temperature 

 coefficient in the ordinary sense of the term. If for the 

 same substance in the same • state of subdivision a+f(x) 

 could be assumed not to vary with temperature, k could be 

 directly determined. In this case the curves for two 

 temperatures should be similar. But the figures given below 

 show that this is not so. 



Pot; 



issium Pi 



Esrmang 



anate. 





Tetraniti 



•oaniline. 



X. 



w 



*217- 



Ratio ^ 



^•240 



X. 



^lio- 



W 



Ratio *!20.. 



^l to 















545 



14 



50 



36 



7-9 



19-1 



94 



49 



15-4 



203 



79 



39 



121 



22-2 



118 



53 



26*2 



267 



110 



4-1 



244 



27 



167 



62 



400 



30 



140 



4-9 



435 



32 



214 



67 



56-0 



33'5 



170 



51 



57-8 



35-5 



239 



6-7 



65-0 



35*5 



185 



5-2 



733 



395 



262 



6-6 



85-0 



41-2 



230 



56 











Extrapolated to #=0 3*4 Extrapolated to x—0 4"4 



If we could assume that a were constant, then the above 

 ratios extrapolated to .r = would serve to measure the true 

 temperature effect. 



Conclusion and Summary. 



When reactions take place in the crystalline state the 

 change appears to be confined to those molecules in the 

 neighbourhood of the surface. Where a progressive dis- 

 integration of the crystal structure takes place the change is 

 strongly accelerated. Solution in another solid causes a 

 reduction in the rate of reaction. 



It is clear that the molecules in the interior are under 

 some kind of restraint. This may be connected with the 

 fact that in the interior the molecules are bound by valency 

 forces on all sides, or it may be referred to the internal 

 pressure. The two points of view are probably equivalent. 



We have pleasure in thanking Brig. -Gen. H. Hartley for 

 the interest he has taken in these experiments. 



