480 Proceedings of Eoyed Society of Edinburgh. [sess. 
fusion, subject to the same laws as supersaturation, and differing 
from it only in the absence of a solvent. 
In very many instances it may not be possible to obtain the 
unstable form, whether it be crystalline or amorphous ; but if it is 
found on further investigation that supersaturation is possible in 
all cases where tico forms can be obtained, I would submit that 
this will equally establish the truth of the law laid down in the 
early part of this paper, and it is in this direction that I propose 
to continue the work, at the same time endeavouring to ascertain 
the limits within which supersaturation is possible, and the examin- 
ation of the border region within which the supersaturation or 
superfusion is terminable by shock or other mechanical means. 
That such a region exists is, I believe, ndicated by many experi- 
ments already made, and its existence would explain the many 
conflicting statements made by previous observers as to the causes 
which bring about the crystallisation of supersaturated solutions. 
