Air-holes must be cut round the bottom
of the lining to give good ventilation.
A boiler of this size will keep a 1 by 1-1/2 inch cylinder well supplied
with steam at from 30 to 40 lbs. per square inch.
A Horizontal Boiler.
[Illustration: FIG. 82.--Longitudinal section of large water-tube
boiler.]
The boiler illustrated by Fig. 81 is designed for heating with a large
paraffin or petrol blow-lamp. It has considerably greater water capacity,
heating surface--the furnace being entirely enclosed--and water surface
than the boiler just described. The last at high-water level is about 60,
and at low-water level 70, square inches.
The vertical section (Fig. 82) shows 1/16-inch barrel, 13 inches long over
all and 12 inches long between the end plates, and 6 inches in diameter.
The furnace flue is 2-1/2 inches across outside, and contains eleven
1/2-inch cross tubes, set as indicated by the end view (Fig. 83), and 3/4
inch apart, centre to centre. This arrangement gives a total heating
surface of about 140 square inches. If somewhat smaller tubes are used and
doubled (see Fig.
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