1826.] On the existence of a Limit to Vaporization. 203 



concentrated sulphuric acid. No action had taken place at 

 the end of two years, the zinc then remaining as bright as at 

 first ; and this fact is very properly adduced in illustration of 

 the fixedness of sulphuric acid at common temperatures. Here 

 I should again presume, that the elastic force which tended to 

 form vapour was surpassed by the force of gravity. 



Whether it be admitted or not, that in these experiments 

 the limit of volatilization, according to the principle of the 

 balance of forces before stated, had been obtained, I think we 

 can hardly doubt that such is the case at common temperatures 

 with respect to the silver and with all bodies which bear a 

 high temperature without appreciable loss by volatilization, as 

 platina, gold, iron, nickel, silica, alumina, charcoal, c. ; and 

 consequently, that, at common temperatures, no portion of 

 vapour rises from these bodies or surrounds them ; that they 

 are really and truly fixed ; and that none of them can exist in 

 the atmosphere in the state of vapour. 



But there is another force, independent of that of gravity, 

 at least of the general gravity of the earth, which appears to 

 me sufficient to overcome a certain degree of vaporous elasticity, 

 and consequently competent to the condensation of vapour of 

 inferior tension, even though gravity should be suspended ; I 

 mean the force of homogeneous attraction. 



Into a clean glass tube, about half an inch in diameter, in- 

 troduce a piece of camphor ; contract the tube at the lamp 

 about 4 inches from the extremity ; then exhaust it, and 

 seal it hermetically at the contracted part; collect the camphor 

 to one end of the tube ; and then, having placed the tube in a 

 convenient position, cool the other end slightly, as by covering 

 it with a piece of bibulous paper preserved in a moist state by 

 a basin of water and thread of cotton ; in this way, a difference 

 in temperature of a few degrees will be occasioned between 

 the ends of the tube, and after some days, or a week or two, 

 crystals of camphor will be deposited in the cooled part ; there 

 will not, however, be more than three or four of them, and 

 these will continue to increase in size as long as the experiment 

 is undisturbed, without the formation of any new crystals, unless 

 the difference of temperature be considerable. 



A little consideration will, I think, satisfy us that, after 

 the first formation of the crystals in the cooled part, they have 



