Existence of a Limit to Vaporization. 347 



stances indeed which boil under common circumstances at 

 600° or 700° F. 



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

 at the bottom of a clean dry bottle, a piece of gold leaf at- 

 tached 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 amalga- 

 mation, in consequence 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 

 phaenomena exhibited in vacuo, found, that when the tempe- 

 rature 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 phsenomena 

 were then nearly of the same intensity as in the vacuum made 

 over tinf. Hence, in conjunction with the preceding reason- 

 ing, I am led to conclude, that they were then produced in- 

 dependent 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 lowered the tension of its vapour is rapidly 

 diminished. Signor Bellamy 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 tempera- 

 tures, with respect to the silver, and with all bodies which 

 bear a high temperature without appreciable loss by volatili- 



* Quarterly Journal of Sciences, x. 354. 



t Phil. Trans. 1832, p. 71. % Giornale di Fisica, v. 197. 



2X2 zation, 



