The Locomotive - Lighthouse Survival Blog

136 THE LOCOMOTIVE, [September,
.350, and opposite .350 in the table we find 0.24498. Then 60x60x0.24498=882 square
inches, the area in question. In Table I this calculation has been made for all the sizes
of boilers that are ordinarily met with. The area to be braced has been calculated as
above in each case, the two-inch strip above the tubes and the three-inch strip around
the shell being taken into account. As an example of its use, let us suppose that upon
measuring a boiler we find that its diameter is 54 inches, and that the distance from the
upper tubes to the top of the shell is 25 inches. Then by looking in the table under 54"
and opposite 25" we find 714, Avhich is the number of square inches that requires staying
on each head.
In case the measured height from the tubes to the shell is not an exact number of
inches we may either call it the nearest even inch and take out the area as before, or we
may proceed as in the following example. Ex. What is the area to be braced in a boiler
72 inches in diameter, the distance from the top of the shell down to the upper row of
tubes being %\\ inches? For 81 inches the table gives 1,252, and for 32 inches it gives
1,317. The difference between these is 65, and one-quarter of 65 is 16, which is the
amount to be added to 1,252, on account of the measured height being %\\ inches instead
of 31 inches. Then 1,252 + 16 = 1,268 sq. in., which is the area to be braced in this case.
TABLE I. AREAS TO BE BRACED (Squake Inches).