18 BULLETIN 898, U. S. DEPARTMENT OF AGRICULTURE. 
If the tank has a conical bottom, the volume, in cubic inches, of 
this part is given by the formula, 
d2 
yee (formula 2) 
in which 
a =factor 3.1416. 
d=inside diameter of tank, in inches. 
k =height (or depth) of conical portion, in inches. 
The value for V, thus obtained must be divided by 231 to ascertain 
the volume of the conical bottom in gallons. 
For cylindrical horizontal tanks, with dished ends, such as those | 
on tank cars, the calculations are more involved and difficult. The 
dished ends of such tanks are in the form of segments of a sphere. 
For most practical purposes, the capacity of such a tank may be cal- 
culated approximately, as outlined for cylindrical upright tanks, by 
assuming the total average length of the tank to be the straight 
length of the sides of the cylinder plus one-half the total outside bilge 
at each end, or the total outside depth of either tank head. For ex- 
ample, if the length of the straight part of the tank is 32 feet and the 
outside bilge of the tank heads 6 inches, the total length of the tank 
may be taken as32 feet +2 x 14 x 6 inches =32 feet 6 inches. The total 
outside bilge is measured by hoiding a straightedge against the center 
of the tank head, and measuring simultaneously with two rules from 
the butt of the end sheet on each side, adjusting the straightedge 
until both measurements are the same. 
Often it is impracticable or even impossible to measure accurately 
the inside diameter of a tank. This factor, however, can be calcu- 
lated from the measurement of the outside circumference of the tank, 
which should be determined with a steel tape. Since tanks are built 
up of short cylinders overlapping each other at the seams, it is evident 
that the inside diameter of two adjacent cylinders or sheets will not 
be exactly the same, but will differ by an amount equal to twice the 
thickness of the sheets. As every other sheet is an inside or an out- 
side lap, there are only two different values for the diameter inside. 
To determine the average inside diameter of the tank, the outside cir- 
cumference of one sheet of each size is measured, all measurements 
being converted into inches and decimal! parts thereof. Each of these 
measurements is multiplied by the number of sheets having that cir- . 
cumference, the figures thus obtained being added. The sum is then 
divided by the total number of sheets. Multiplying this value by the 
factor 0.31831 gives the outside diameter of the tank in inches. Sub- 
tracting from this the sum of the thickness of the bottom sheets and — 
of the cylindrica! or shell sheets from which the tank is constructed 
gives the average inside diameter of the tank. 
Oy 
=< 
x 
