680 
points 8 and 4 do not lie on the line drawn through 1 and 2 5. 
If we use the first two observations to extrapolate to the compo- 
sition O atom °/, Hg, which is, of course, a rather inaccurate method, 
we find 200°,5 for the transition point of pure tin. 
At all events it appeared from this that the transition point of pure 
tin must lie in the neighbourhood of 200°, and as it had appeared 
from the preceding experiments that the conversion in the transition 
points of mixtures containing Hg is attended with a distinct though 
small diminution of volume, it must also be possible to find the transition 
point for perfectly pure tin by dilatometrical way. 
It was clear that the conversion in pure tin proceeds slowly, and 
that at every temperature we should have to wait long to attain 
reliable results. 
When the thermostat, in which the dilatometer which contained 
250 gr. of tin, was placed, was first regulated at 240°, so that the 
tin melted, and when then comparatively rapidly the thermostat was 
brought to 190°, it appeared that after the dilatometer had assumed 
the temperature of 190°, no change of volume worth mentioning took 
place even after 24 hours, from which it was inferred that on soli- 
dification exclusively the tetragonal modification had been formed, 
and that therefore the tin had solidified at the metastable point of 
solidification. 
In agreement with this experiment it appeared that when the bath 
was regulated at 206°, and also the tin had assumed this temperature, 
an increase of volume took place, which could not practically be 
considered as completed until after 48 hours. If then the thermostat 
was again put at 190°, a diminution of the volume set in again at con- 
stant temperature. 
This phenomenon, which points to the conversion : 
tetragonal tin = rhombic tin, 
shed a great deal of light on the fact of tin becoming trittle at about 
200°, on the preparation of corn tin, and also on KALISCHER’S obser- 
vation, particularly because it is very probable that the above 
conversion proceeds most slowly in pure material. 
It further appeared from these experiments, just as from those 
made with tin containing mercury, that the difference in specific 
gravity between the tetragonal and the rhombic modification is much 
smaller at + 200° than at the ordinary temperature, as the variation 
of volume found, which, it is true, had probably not yet reached its 
1) This investigation is being continued to get to know more about the system 
tin-mercury. 
