98 PHYSICS. 
the funnel, enters the tube cold, and passes from it heated. In the larger 
cooling vessels, as in jig. 48 (exhibiting a sectional view), the steam-tube is 
carried in a spiral through the vessel, in order that the steam may remain 
as long as possible in contact with the cooling water, and become com- 
pletely condensed. The upper strata of water become very soon heated, 
and if the process is to be continued any considerable length of time, must 
be renewed. ‘This is done best by allowing the cold water to enter below, 
and as heated, to pass out above through an escape-pipe. 
In reality, any cooler might be employed as a means of measuring the 
amount of latent heat, provided that it were known how much moisture 
was condensed in a certain time, and how much was given off into the 
cooling water. Brix, however, has invented a special apparatus for the 
purpose, represented by fig. 49. The cylindrical vessel, C, of about three 
inches in breadth and height, served as the cooler, and the steam generated 
in the retort, R, entered, not into a cooling tub, but into the cylinder, EG, 
which had an aperture in the middle, also cylindrical. The steam entered 
at M, while the inside of the condenser was in communication with the 
open air, by the tube, L, so that the air in the condenser could escape. 
The cooler, C, was filled with a given weight of water, whose temperature 
could be ascertained by a thermometer attached to the apparatus. In the 
space between the vessel, EG, and the cylinder, C, was placed a metallic 
disk, B, which could be moved up and down by means of a wire, so as to 
keep the water in constant agitation, and thus maintain it at an uniform 
temperature. The condensing apparatus was protected from the heat 
radiant from the heating apparatus and the retort. The liquid passed over 
was determined by the quantity remaining in the retort. Brix, in this 
manner, found the latent heat of watery vapor to be 540 units; that of 
alcohol in vapor, 214 units; of the vapor of sulphuric ether, to be 90 
units, &c. From this it followed, in connexion with other experiments, 
that the latent heat of the vapor of different liquids is nearly in the inverse 
ratio of the densities of these vapors. 
If a liquid boils in the open air, it retains the same temperature, owing to 
its continually receiving from the walls of the vessel heat enough to replace 
that rendered latent in the formation of vapor. The case is different, how- 
ever, when ebullition takes place under the receiver of the air-pump: here 
the temperature continually sinks, as the latent heat derived from the water 
itself cannot be renewed. If we place under a shallow receiver on the air- 
pump, a small flat metallic capsule containing water, above a dish filled with 
sulphuric acid, and exhaust the air, the water will undergo a rapid evapo- 
ration, which is immediately absorbed by the acid. The rapid abstraction of 
heat from the water during the evaporation, will reduce its temperature to 
such an extent as finally to cause it to freeze. In Wollaston’s cryophorus (see p. 
269) [Physics, 95],water is likewise caused to freeze by its own vaporization. 
A small quantity of water is introduced into one of the bulbs aad brought to 
boil. When the other bulb and the tube are filled with steam, a small aper- 
ture left open is closed by melting the glass over it. If, now, all the water 
be collected in one bulb, and the other be immersed in a freezing mixture, 
272 
