Mr Brooke on Crystallisation, 
But the experiments which have been most frequently repeat- 
ed on the formation of artificial crystals, are those in which the 
crystals have been deposited from solution in a fluid. Mr Bro- 
chant has collected together, from various authorities, and in- 
serted in his volume on crystallisation, much interesting infor- 
mation on this head, and many of the following remarks are 
given from the authorities cited by him ; but I have also 
made many experiments on the production of artificial crystals 
from solutions, some of which have corresponded in their results 
with those described by Mr Brochant, and others have very 
widely differed. 
I propose to consider the artificial crystals produced from so- 
lution in a fluid, in reference 
To the general circumstances attending their deposition ; 
To their size ; 
To their forms ^ whether simple or compound^ regular o?' irre- 
gular ; and 
To the character of their planes. 
I shall also have to refer occasionally to natural crystals for 
the better illustration of the subject. 
The variations in the temperature and hygrometric state of 
the air, but more particularly the latter, will influence the depo- 
sition of crystals generally. 
When the air is dry, evaporation proceeds more rapidly than 
when it is moist, and crystals are then deposited more freely. 
Heat, as it promotes evaporation, predisposes a solution to de- 
|X)sit crystals ; but these are only formed when the evaporation 
has been moderate, and as the solution cools. The precipitate 
from a solution which has been entirely evaporated at a tempe- 
rature much above that of the atmosphere, does not generally 
produce crystals. A pellicle is first formed on the surface, and 
as the evaporation proceeds, an irregular mass is deposited at the 
bottom of the vessel, and it increases until the fluid is entirely 
dissipated. 
The state of atmospheric pressure sometimes influences the 
production of crystals. 
Thus, if a concentrated solution of sulphate of soda be in- 
closed, while hot, in a Lube, it will not deposit crystals on cool- 
