It appears therefore from this reasoning, that when the direct force of steam of greater pressure than the atmosphere is used without condensation, the total mechanical effect is always less than that produced by the condensation of atmospheric steam without expansion; but that the greater the pressure under which the steam is produced, the less will be the difference between these effects. In general, the proportion of the mechanical effect of high-pressure steam to the effect produced by the condensation of atmospheric steam, will be as the number of atmospheres expressing the pressure of the steam to the same number increased by one. Thus, if steam be produced under the pressure of six atmospheres, the proportion of its effect to that of the condensation of atmospheric steam will be as six to seven.
(133.) Another method of applying the power of steam mechanically is, to combine its direct action with condensation but without expansion.
The piston being, as before, loaded with one ton, the evaporation of the water will raise it through six perpendicular inches, and the result so far will be equivalent to a ton raised half a foot; but if the piston-rod be supposed also to act by a chain or cord over a wheel, so as to pull a weight up, the steam which has just raised the ton weight through six inches, may be condensed, and the piston will descend with a force of one ton into the vacuum thus produced, and another ton may be thus raised through half a foot. The total mechanical power thus yielded by the steam, adding to its direct action its effect by condensation, will then be one ton raised through one foot, being an effect exactly equal to that obtained by the condensation of atmospheric steam.
If the piston be loaded with two tons, its direct action will, as we have shown, raise these two tons through four inches, which is equivalent to two thirds of a ton raised a foot. By condensing this steam a ton weight may be raised in the same manner, by the descent of the piston through a third of a foot, which is equivalent to the third of a ton raised through one foot.
By pursuing like reasoning, it will appear that, if the direct force of high-pressure steam be combined with the indirect force produced by its condensation, the total mechanical effect will be precisely equal to the mechanical effect by the mere condensation of atmospheric steam.