1896 - 97 .] Mr W. W. J. Nicol on Super saturation. 
477 
solutions of this salt is 35° C. The fused crystals when evaporated 
in a thermostat at 40" C. deposited crystals containing, at the most, 
one molecule of water. 
2. Supersaturation due to the existence of allotropic forms, 
whether enantiotropic or monotropic. 
(a.) Potassium nitrate, already described. 
( b .) Ammonium nitrate, fully described by Lehmann, forms 
supersaturated solutions. 
(c.) Silver nitrate, hitherto known only in the rhombic modi- 
fication, deposits hexagonal rhombohedra (?) when a drop is allowed 
to evaporate spontaneously ; and when the drop saturated to this 
modification is touched with a needle point which lias been in 
contact with the rhombic variety, instant crystallisation of the 
whole ensues, showing supersaturation. Supersaturated solutions 
on a larger scale can also be prepared by the exercise of some care 
Organic Compounds. 
(d.) Acetanilid. A hot concentrated solution deposits, at different 
parts of the microscope field, rhombic ordinary crystals and 
(rhombic?) crystals of a modification. These, when in the imme- 
diate neighbourhood of the stable form, are gradually dissolved ; 
but if the two come in actual contact they become opaque, owing 
to change of their internal structure. Supersaturated solutions on 
the large scale can be readily prepared. 
(e.) Hydroquinone. A hot strong solution deposits a net-work of 
crystals of an unstable modification (hexagonal?). After a time 
monoclinic prisms of the ordinary modification put in an appear- 
ance, and gradually eat their way through the unstable form. 
Supersaturated solutions can be easily prepared. 
(/.) Acetamide. A concentrated solution deposits crystals pris- 
matic in shape of an unstable form. When the edge of the drop 
is touched with a trace of the ordinary hexagonal form, the whole 
crystallises, the original crystals becoming opaque. Supersatura- 
tion on the large scale is very marked. 
(g.) Malonic acid. This substance forms supersaturated solu- 
tions very readily. When a hot strong solution is observed under 
the microscope, prismatic crystals of the unstable modification soon 
