( 79 ) 
If the tube containing the grey tin is immersed in warm water 
the tin immediately takes on the colour of ordinary tin. The recon- 
version into grey tin occurs when the tube is cooled: At — 83°, 
in a paste of solid carbonic anhydride and alcohol the change from 
white to grey tin took place in about 24 hours. Prolonged cooling 
to a temperature not lower than —20° was fruitless. On the other 
hand the change of grey into white tin was only observed at tem- 
peratures above -++ 30°. From this point, however, the velocity of 
the change increased very rapidly with rising temperature. It appeared 
therefore to be difficult to find a transition point. It is, however, 
known that transition phenomena are accelerated when the materials 
undergoing the change are present in a finely divided state, and 
also that solvents accelerate the change }). 
After a number of preliminary experiments we found that a so- 
lution of ammonium stannic chloride afforded an excellent means 
of causing the change to take place readily in either direction. 
For example, the change white tin — grey tin, which without 
the ammonium stannic chloride solution required 24 hours at —83°, 
took place in 6 hours when a few drops of a 10°/, solution of the 
salt in water were added to the tin. When the change has been 
carried out in both directions several times with the same quantity 
of tin, it takes place more and more readily. In general, it may be 
said that the phenomena are here quite analogous to those observed 
with salts containing water of crystallisation when they are heated 
above their transition points and again cooled. 
6. In order to determine the transition point of the change 
grey tin = white tin 
we used the dilatometric- and the electric methods. 
a. Determinations with the dilatometer. 
The dilatometer contained about 2 cc. and was filled with white 
tin; a 10°/, aqucous solution of ammonium stannic chloride served as 
measuring liquid. The position of the liquid in the very narrow 
capillary was read on a porcelain millimeter scale. 
The following table contains the observations. 
1) See for example: L. Tu. Retcner, De temperatuur der allotropische verandering 
van de zwavel. Dissertatie, Amsterdam, 1883 
