A. Carbon, hydrogen, nitrogen, sulphur, oxygen and ash.
Q. What are the relative proportions of these that enter into coal?
A. There are different proportions in different specimens of coal, but the following shows the average per cent: Carbon, 80; hydrogen, 5; nitrogen, 1; sulphur, 2; oxygen, 7; ash, 5.
Q. What must be mixed with coal before it will burn?
A. Atmospheric air.
Q. What is air composed of?
A. It is composed of nitrogen and oxygen in the proportion of 77 of nitrogen to 23 of oxygen.
Q. What parts of the air mix with what parts of the coal?
A. The oxygen of the air mixes with the carbon and hydrogen of the coal.
Q. How much air must mix with the coal?