138. Q.--In what way does the specific heat of a body enable the quantity of heat in it to be determined?
A.--If any body has only half the specific heat of water, then a pound of that body will, at any given temperature, have only half the heat in it that is in a pound of water at the same temperature. The specific heat of air is .2669, that of water being 1; or it is 3.75 times less than that of water. An amount of heat, therefore, which would raise a pound of water 1 degree would raise a pound of air 3.75 degrees.
COMBUSTION.
139. Q.--What is the nature of combustion?
A.--Combustion is nothing more than an energetic chemical combination, or, in other words, it is the mutual neutralization of opposing electricities. When coal is brought to a high temperature it acquires a strong affinity for oxygen, and combination with oxygen will produce more than sufficient heat to maintain the original temperature; so that part of the heat is rendered applicable to other purposes.
140. Q.--Does air consist of oxygen?
A.--Air consists of oxygen and nitrogen mixed together in the proportion of 3.29 lbs. of nitrogen to 1 lb. of oxygen. Every pound of coal requires about 2.66 lbs. of oxygen for its saturation, and therefore for every pound of coal burned, 8.75 pounds of nitrogen must pass through the fire, supposing all the oxygen to enter into combination. In practice, however, this perfection of combination does not exist; from one-third to one-half of the oxygen will pass through the fire without entering into combination at all; so that from 16 to 18 lbs. of air are required for every pound of coal burned. 18 lbs. of air are about 240 cubic feet, which may be taken as the quantity of air required for the combustion of a pound of coal in practice.
141. Q.--What are the constituents of coal?
A.--The chief constituent of coal is carbon or pure charcoal, which is associated in various proportions with volatile and earthy matters. English coal contains 80 to 90 per cent. of carbon, and from 8 to 18 per cent. of volatile and earthy matters, but sometimes more than this. The volatile matters are hydrogen, nitrogen, oxygen, and sulphur.
142. Q.--What is the difference between anthracite and bituminous coal?