( 149 ) 
Chemistry. — “On the Enantiotropy of Tin (11).” By Dr. Ernst 
ConEen and Dr. C. van Eyk. (Communicated by Prof. H. W. 
Bakuuts Roozesoom). 
(Read in the meeting of September 30th 1899.) 
1. Continuing our researches on grey (stable) and white (meta- 
stable) tin!) we first attacked the question of the velocity of change 
of the white into the grey modification. 
According to our first communication the velocity is zero at 
+ 20° C, the transition point. 
In the course of our experiments we had received the impression 
that the change white tin — grey tin, took place more slowly at 
— 83° than at somewhat higher temperatures. 
Such a phenomenon recalls the solidification of super-cooled fused 
substances where the rate of crystallisation increases as the tempe- 
rature falls below the melting point until a maximum is reached 
after which jt decreases again *). 
2. A dilatometer, of 2 cc. capacity, was filled with grey tin 
which had already repeatedly undergone transformation in both 
directions. By warming the dilatometer for a few moments to 50° 
a part of the contents was converted into white tin. The dilatometer 
was then filled with a solution of pink-salt in alcohol, in order to 
avoid complications which might arise from crystallisation of the 
salt at very low temperatures. 
The dilatometer was then placed successively in different baths 
at constant temperatures. 
Since the conversion of white tin into grey tin is Bat 
by a considerable increase of volume the rise (per minute) of the 
liquid in the capillary of the dilatometer is a measure of the velo- 
city of transformation. It is necessary, of course, to take care that 
the quantity of white tin undergoing change remains constant during 
the whole course of the experiments. For this reason the capillary 
tube of the dilatometer was made very narrow; the conversion of 
a very small quantity of white tin then gives a sufficient rise. One 
mm. of the capillary = 0,00028 cc. Taking the specific gravity of 
white as 7.3, and that of grey tin as 5.8 the transformation of 
8 mgrm. of white tin into the grey modification gives a rise of 
1 mm. In this way the following results were obtained. 
~ 1) These Proceedings, June 24 1899. 
2) Compare GERNRZ, Journal de Physique (2) 4. (1885) p. 349. 
TAMMANN, Zeitschr. fiir phys. Chemie 23, 326 (1888). 
COHEN, These Proceedings, February 25 1899, 
