04- On the existence of a Limit to Vaporization. [1826. 



the power of diminishing the tension of the vapour of camphor 

 below that point at which it could have remained unchanged 

 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 condensed, and con- 

 tinually adds to its mass. Now this can only be in conse- 

 quence of a positive power in the crystal of camphor of 

 attracting other particles to it; and the phenomena of the 

 experiment are such as to show that the force is able to over- 

 come a certain degree of elasticity in the surrounding vapour. 

 There is therefore no difficulty in conceiving, that, by dimi- 

 nishing 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 portion, 

 by the attraction of aggregation, draws the particles to it ; in 

 which case it would immediately cause the entire condensation 

 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 

 positive degree of tension in the vapour from which the 

 crystals are formed. The same power, or the force of aggre- 

 gation, is also illustrated in crystallizing solutions ; where the 

 solution 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 on 

 from these attenuated vapours, as it does in the denser states 

 of the vapours experimented upon. There is, however, no 

 good reason for supposing any difference in the force of aggre- 

 gation of a solid body, dependent upon changes in the tension 

 of the vapour about it ; and indeed, generally speaking, the 

 method I have assumed for diminishing the tension of the 

 vapour, namely, by diminishing temperature, would cause in- 

 crease in the force of aggregation. 



* Calomel, corrosive sublimate, oxide of antimony, naphthaline, oxalic 

 acid, &c. &c. 



