On a Method of Freexing at a Distance. 293 
quantity of water be small, the receiver must be of large di- 
mensions ; otherwise its capacity would set too confined a 
limit to the quantity of vapour that will rise, and conse- 
quently to the degree of cold produced. 
Supposing the commonly received estimates to be cor- 
rect, as to the quantities of heat, that become latent in the 
conversion of ice into water, and of water into steam, being 
140° and 960° respectively, we should find the following 
statement to be not far from the truth. 
If 32 grains of water were taken at the temperature of 
62°, and if one grain of this were converted into vapour 
by absorbing 960°, then the whole quantity would lose 
9 o 
> =: 30°, and thus be reduced to the temperature of 32°. 
If from the 31 grains, which still remain in the state of 
water, four grains more were converted into vapour by ab- 
sorbing 960°; then the remaining 27 grains must have lost 
gt of 960°=142°, which is rather more than sufficient to 
convert the whole into ice. In an experiment conducted 
upon a small scale, the proportional quantity evaporated did 
not much differ from this ¢stimate. 
If it be also true, that water in assuming the gaseous 
state, even at a low temperature, expands to 1800 times its 
former bulk ; then, in attempting to freeze the small quan- 
tity of water above mentioned, it would be requisite to have 
adry vacuum with the capacity of 5x 1800, or equal to 
that of 9000 grains of water. 
As a means of avoiding the necessity of so large a va- 
euum, Mr. Leslie had recourse to the ingenious expedient 
of employing an extensive surface of sulphuric acid, for 
the purpose of absorbing the vapour generated in the course 
of the experiment, and by that means contrived to freeze 
much larger quantities of water than could otherwise haye 
been done, and by a far less Jaborious process. 
But even in this method the labour is not inconsiderable, 
and the apparatus, though admirably adapted to the purpose 
for which it is designed, is large and costly. I have there- 
fore thought the little instrament | am about to describe 
may possess some interest, as affording a readier and more 
simple mode of exhibiting so amusing and instructive an 
experiment. 
Let a ylass tube be taken, having its internal diameter 
about + of an inch, with a ball at each extremity of about 
ene inch diameter; Plate IV. and let the tube be bent 
to a right angle at the distance of half an inch from jour 
all. 
