Given the diameter of a cylinder in inches, and the pressure in lb. per square inch, to find the load on the piston in tons. Set pressure in lb. per square inch on B to 2852 on A, and over cylinder diameter in inches on D read load on piston in tons on B. EX.—Steam pressure 180 lb. per square inch; cylinder diameter, 42 in. Find load in tons on piston. Set 180 on B to 2852 on A, and over 42 on D read 111 tons, the gross load, on B. Given admission period and absolute initial pressure of steam in a cylinder, to find the pressure at various points in the expansion period (isothermal expansion). Invert the slide and set the admission period, in inches, on Ɔ to the initial pressure on D; then under any point in the expansion stroke on Ɔ find the corresponding pressure on D. EX.—Admission period 12 in., stroke 42 in., initial pressure 80 lb. per square inch. Find pressure at successive fifths of the expansion period. Set 12 on Ɔ to 80 on D, and opposite 18, 24, 30, 36 and 42 in. of the whole stroke on Ɔ find the corresponding pressures on D:—53·3, 40, 32, 26·6 and 22·8 lb. per square inch. To find the mean pressure constant for isothermally expanding steam, given the cut-off as a fraction of the stroke. Find the logarithm of the ratio of the expansion _r_, by the method previously explained (page 46). Prefix the characteristic and to the number thus obtained, on D, set 1 on C. Then under 2·302 on C read _x_ on D. To _x_ + 1 on D set _r_ on C, and under index of C read mean pressure constant on D. The latter, multiplied by the initial pressure, gives the mean forward pressure throughout the stroke. (N.B.—Common log. × 2·302 = hyperbolic log.) EX.—Find the mean pressure constant for a cut-off of ¼th, or a ratio of expansion of 4. Set (L.H.) index of C to 4 on D, and on the reverse side of the slide read 0·602 on the logarithmic scale. The characteristic = 0; hence to 0·602 on D set (R.H.) index of C, and under 2·302 on C read 1·384 on D. Add 1, and to 2·384 thus obtained on D set _r_ (= 4) on C, and under 1 on C read 0·596, the mean pressure constant required. Mean pressure constants for the most usual degrees of cut-off are given below:—