491 
existence of a limit to vaporization. 
the power of diminishing the tension of the vapour of cam- 
phor, below that point at which it could have remained un- 
changed in contact with the glass, or in space : for the vapour 
of the camphor is of a certain tension in the cooled end of 
the tube, which it can retain in contact with the glass, and 
therefore it remains unchanged ; but which it cannot retain 
in contact with the crystal of camphor, for there it is con- 
densed, and continually adds to its mass. Now, this can only 
be in consequence of a positive power in the crystal of cam- 
phor of attracting other particles to it ; and the phenomena 
of the experiment are such as to show, that the force is able 
to overcome a certain degree of elasticity in the surrounding 
vapour. There is therefore no difficulty in conceiving, that, 
by diminishing the temperature of a body and its atmosphere 
of vapour, the tension of the latter may be so far decreased, 
as at last to be inferior to the force with which the solid por- 
tion, by the attraction of aggregation, draws the particles to 
it ; in which case it would immediately cause the entire con- 
densation of the vapour. 
The preceding experiment may be made with iodine, and 
many other substances ; and indeed there is no case of distinct 
crystallization by sublimation * which does not equally afford 
evidence of the power of the solid matter, to overcome a po- 
sitive degree of tension in the vapour from which the crystals 
are formed. The same power, or the force of aggregation, 
is also illustrated in crystallizing solutions ; where the solu- 
tion has a tendency to deposit upon a crystal, when it has not 
the same tendency to deposit elsewhere. 
It may be imagined that crystallization would scarcely go 
* Calomel, corrosive sublimate, oxide of antimony, naphthaline, oxalic acid, &c. & c. 
