Experimental Inquiries respecting Heat and Vapor. 311» 
to give a maximum energy of action between it and the spirit. By 
several trials for this purpose, it was found to be three and a half 
seconds. ‘The greatest length of time during which the same quan- 
tity had been found to remain was one hundred and fifty seconds+ 
Whence it appears, that the relation between the two is 2:5 = 1,, 
or; nearly. ‘The only remaining question was the actual temper- 
ature at which the spirit disappeared in the least time. For this pur- 
pose, recourse was had to the bar with mercurial reservoirs and cups, 
already described. On raising the temperature to 312°, where wa- 
ter had been observed to be most rapidly vaporized, it was manifest 
that the alcohol was clearly and strongly repelled. 
The temperature was then lowered to 280°, when occasional signs 
of adhesion were manifested, and a corresponding diminution in the 
time of evaporating a given quantity of liquid was the result. 
By lowering the temperature of the iron to 260°, the time was 
again perceived to increase on account of a deficiency of heat. By 
thus passing and repassing several times between 260° and 280°, 
limits of range became circumscribed between 270° and 278°, 
and finally the point of most vigorous action seemed to rest at 274°, 
the arithmetical mean of the above mentioned limits. This, it will 
be recollected, is 100° above the boiling point of alcohol. It will 
be observed also, that this is exactly as much above its boiling point, 
asthe temperature of most activity on water is above the boiling point 
of that liquid. 
6. Anallusion has already been made to the opinion of some writers, 
that the repulsion of a liquid from metal begins at the temperature of 
Incandescence, and increases as the temperature rises. The facts 
already detailed in this paper, will serve to show that the former opin- 
on is wholly without foundation. Indeed, when we reflect for a mo- 
Ment on the nature amd cause of that diminution of the liquid which 
takes place after vaperization has ceased through an excess of tem- 
Perature, we must perceive that as the effect is an evaporation, due 
0 the radiation of heat, the rapidity with which the latter will dis- 
Perse a given quantity of water must be proportionate to the tension 
of the heat at the radiating source ; that is, the surface of the metal. 
Yaporation must commence where vaporization ceases, and the 
mer must be slow when the tension is barely sufficient to elevate 
the liquid out of the sphere of contact, or of contiguous attraction. 
iS cannot however prevent an increase of rapidity, when the ten- 
“on at the source is sufficiently elevated to allow the radiated heat to 
Communicate temperature to a transparent medium. 
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