Q. What does one square foot of half inch boiler iron weigh?

A. Twenty pounds.

Q. For steam purposes, how much wood is required to equal one ton of coal?

A. About 4000 pounds of wood.

Q. Of what does coal consist?

A. Carbon, nitrogen, sulphur, hydrogen, oxygen and ash.

Q. What are their relative proportions?

A. There are different proportions in different specimens of coal. The average per cent is carbon eighty, nitrogen one, sulphur two, hydrogen five, oxygen seven, ash five.

Q. Of what is air composed?