MORSE AND PIERCE. — SUPERSATURATION IN GELATINE. 



637 



from which the value of a that most nearly satisfies equation (12) is seen 

 to be 1.80. 



1.80 



a 



2a 



4.25 X lO" 3 . 



The corresponding value A of the integral is .009668. 

 Therefore from equation (11) 



H= JL (.009668)* = 1.6 x 10- f Gm ' MoL Y. 



7o 7T v ' \ liter ) 



The diffusion constant is not «, but a 2 , which, reduced to the usual 

 units with the day as unit of time by multiplying a 2 by 8.64 X 10 4 , 

 becomes 



* = 1.56 (%- 



V 



In this calculation of H the reacting substances have been assumed to 

 be completely dissociated. The result of the calculation shows that the 

 concentration of the silver ion was about ^io Normal and that of the 

 chromate ion ^ Normal when precipitation occurred. The dissociation 

 of g.^ silver nitrate differs so little from that of T ^ , which enters into 

 the calculation of subsequent cases, that the assumption of its complete 

 dissociation introduces no appreciable inaccuracy. On the other hand, 

 the dissociation of T f ¥ potassium chromate is about 1.05 times the dis- 

 sociation of j^ , and this factor representing the ratio of dissociation must 

 be introduced into calculations involving different concentrations of potas- 

 sium chromate in the gelatine. 



Observing this precaution we obtain the following values for a' 2 and H 

 from other sets of data of Table III. 



