(101.)

If the law of Mariotte were strictly applicable to steam, its mechanical effect would be the same as has been already explained in all states of density; but since its temperature will rise and fall as its density is increased or diminished, a corresponding change will be produced in its [Pg174] mechanical efficacy. It is therefore necessary in the calculation of the mechanical effect of steam, whether it be used at a uniform pressure without the principle of expansion, or with the application of that principle to any given extent, to take into account the combined operation of the laws of Mariotte and Dalton. Formulæ exhibiting the relation between the temperatures, pressures, volumes, and densities of steam, and the mechanical effect produced by the evaporation of water, whether acting with or without expansion, together with the tables necessary for the practical application of these, will be found in the Appendix.