162§.] Existence of a Limit to Vaporization, 439 



If, as I have formerly shown,* some clean mercury be put at 

 the bottom of a clean dry bottle, a piece of gold leaf attached to 

 the under part of the stopper by which it is closed, and the 

 whole left for some months at a temperature of from 60° to 80°, 

 the gold leaf will be found whitened by amalgamation, in con- 

 sequence of the vapour which rises from the mercury beneath ; 

 but upon making the experiment in the winter of 1824-5, I was 

 unable to obtain the effect, however near the gold leaf was 

 brought to the surface of the mercury ; and I am now inclined 

 to believe, because the elastic force of any vapour which the 

 mercury could have produced at that temperature was less than 

 the force of gravity upon it, and that consequently the mercury 

 was then perfectly fixed. 



Sir Humphry Davy, in his experiments on the electrical phe- 

 nomena exhibited in vacuo, found, that when the temperature 

 of the vacuum above mercury was lowered to 20° F. no further 

 diminution, even down to — 20° F. was able to effect any 

 change, as to the power of transmitting electricity, or in the 

 luminous appearances ; and that these phenomena were then 

 nearly of the same intensity as in the vacuum made over tin.i* 

 Hence, in conjunction with the preceding reasoning, I am led 

 to conclude, that they were then produced independent of any 

 vapour of the metals, and that under the circumstances 

 described ; no vapour of mercury existed at temperatures 

 beneath 20° F. 



Concentrated sulphuric acid boils at about 600° F. but as the 

 temperature is Icivered, the tension of its vapour is rapidly dimi- 

 nished. Signer BellaniJ placed a thin plate of zinc at the 

 upper part of a closed bottle, at the bottom of which was some 

 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. 



* Quarterly Journal of Science, x. 354. 

 • t Phil. Trans. 1822, p. 71. . ^ Giornale di Fisica, v,- 107. 



