e safe pressure of the single riveted by 70, and
divide by 56, will give a safe pressure of a double riveted
boiler.

Q. Why is a steel boiler superior to an iron boiler?
A. Because it is much lighter and stronger.

Q. Does boiler plate become stronger or weaker as it
becomes heated?
A. It becomes tougher or stronger as it is heated, till it
reaches a temperature Of 550 degrees when it rapidly
decreases its power of resistance as it is heated beyond this
temperature.

Q. How do you account for this?
A. Because after you pass the maximum temperature
of 550 degrees, the more you raise the temperature the nearer
you approach its fusing point when its tenacity or resisting
power is nothing.

Q. What is the degree of heat necessary to fuse iron?
A. 2912 degrees.

Q. Steel?
A. 2532 degrees.

Q. What class of boilers are generally used in a threshing
engine?
A. The flue boiler and the tubular boiler.

Q. About what amount of heating and grate surface is
required per horse power in a flue boiler.
A. About 15 square feet of heating surface and 3/4 square
feet of grate surface.

Q. What would you consider a fair evaporation in a flue
boiler?
A. Six pounds of water to I pound of coal.

Q. How do these dimensions compare in a tubular boiler.
A. A tubular boiler will require I/4 less grate surface, and
will evaporate about 8 pounds of water to I pound of coal.

Q. Which do you consider the most available?
A. The tubular boiler.

Q. Why?
A. It is more economical and is less liable to "collapse?"

Q. What do you mean by "collapse?"
A. It is a crushing in of a flue by external pressure.

Q. Is a tube of a large diameter more liable to collapse than
one of small diameter?
A. Yes.

Q. Why?
A. Because its power of resistance is much less than a tube
of small diameter.

Q. Is the pressure on the shell of a boiler the same as on the
tubes?
A. No.

Q. What is the difference?
A. The shell of boiler has a tearing or internal pressure
while the tubes have a crushing or external pressure.

Q. What causes an explosion?
A. An explosion occurs generally from low water, allowing
the iron to become overheated and thereby weakened and
unable to withstand the pressure.

Q. What is a "burst?"
A. It is that which occurs when through any defect the water
and steam are allowed to escape freely without further injury
to boiler.

Q. What is the best way to prevent an explosion or b