Given the absolute initial pressure, length of stroke, and
admission period, to find the absolute pressure at any point
in the expansion period, it being assumed that the steam

P
expands adiabatically. (P2 = ~ro. in which P^ = initial

pressure and Pg the pressure corresponding to a ratio of
expansion E.)



56 THE SLIDE RULE:

Set L.H. index of C to ratio of expansion on D, and read
on the back of the shde the decimal of the logarithm. Add
the characteristic, and to the number thus obtained on D
set 9 on C, and read off the value found on D under the
index of C. Set this number on the logarithmic scale to
the index mark, in the opening on the back of the rule, and

10

under l.h, index of C read the value of E ^ on D. The
initial pressure divided by this value gives the corresponding
pressure due to the expansion.
Ex. — Absolute initial pressure 1201b. per square inch ; stroke, 4ft. ;

cut-off i. Find the respective pressures when | and Jths of the stroke

have been completed.
