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 : 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. * 



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. * 



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 be 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. 



