SECT. II.] 
PROPERTIES OF STEAM. 
81 
The idea of employing very powerful pressures, acting through a short space, 
seems more valuable at first sight than it proves on examination. It is considered 
that an engine of high power can be got into a small place, and will be of less 
weight. But the real inconveniences are, the large mass of fuel required to 
supply the engine a given time, and the immense surface that must be exposed 
to an intense heat to obtain a given quantity of heat in a given time. Besides, 
when we attempt to use high degrees of pressure, an accuracy of workmanship, 
and attention to the elasticity of materials, becomes necessary, which renders the 
work expensive and of short duration. 
The success of Mr. Faraday in reducing various gases into the liquid state is 
not however the less important. His method consisted in generating the sub 
stances in a bent tube of glass hermetically sealed at both ends. Then, by cooling 
one end of the bent tube and heating the other, when heat was necessary, the gas 
was condensed in a liquid state at the cold end of the tube. 
117. Carbonic acid required the greatest precautions to effect the conden 
sation with safety. The liquid obtained is a limpid, colourless body, extremely 
fluid, and floated upon the contents of the tube without mixing. It distils readily 
at the difference of temperature between 32° and 0°: its refractive power is much 
less than that of water, and its vapour exerts a pressure of 36 atmospheres 
at a temperature of 32°. In endeavouring to open the tubes which contained 
it, at one end, Mr. Faraday states, that they uniformly burst with powerful 
explosions. 1 
The gases reduced to a liquid state by Mr. Faraday, with their densities as far 
as they are known, are collected in the following table, with a column to show 
the mechanical power compared with steam. 2 
1 The ingenious Mr. Brunei is attempting to work an engine where the acting vapour is to be 
from liquid carbonic acid. It is to he regretted that his great talent for mechanical combination 
should be employed where there is so little chance of success. 
2 The power is as the force and the space through which the gas passes in its reduction to the 
state of liquid. (See Sect, iv.) The space is found by comparing the density of the body in the 
liquid state with its density in the gaseous under the same pressure ; and as the weight of air is 
to water as 1: 828, to find the mechanical power of equal volumes of the liquid, we have simply 
to multiply 828 by the specific gravity of the liquid, and divide the product by the specific gravity 
of the body in the state of gas. The force does not enter into the calculation, because the density 
of the gas must obviously be greater in the same proportion. The quantity of heat is most pro 
bably in the ratio of the power : if this be the case, all substances will afford equal powers with 
equal quantities of heat. 
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