356
MODERN GASWORKS PRACTICE
analysis may almost be said to be of academic interest alone, and—according to one authority—is “ as likely to afEord an idea of the constitution. of coal as the total weights of stone, metal, glass, and other materials forming a cathedral would convey an idea of its architecture and design.”
The methods now in vogue for the examination of coal may be classified into two gi’onps, namely, (a) Destructive methods, and (6) Non-destructive methods. Destructive methods have proved of certain usefulness in the past, but it is now generally realized that the constitution must be determined by such means as will not involve any radical change in the Chemical constitution of any one of the com-ponent parts of the substance. The non-destructive methods which comply with this condition are, notably, microscopic examination of sections by transmitted light, the use of special solvent, and contact photography. The solvent processes, perhaps, can scarcely claim to come within the sphere of non-destructive methods, but their application. has proceeded along with the scientific, as opposed to the directly Chemical, means, and has resulted in the unearthing of mucli of the valuable information now at our disposal.
THE ORIGIN OF COAL
Vegetable Matter
• Cellulose
- Peat (Dry)
- Lignite
- Bituminous Coal
- steam Coal Anthracite
Carbon
Volatile Matter
Specific Gravity
Hydrogen
Oxygen
Nitrogen
Calonfc Power
(Very Variable)
Fig. 255.—The Formation of Co al.
(The figures for the various properties and constituents vary con-siderably for the same types of coal. Those given above represent the average.)
It is not proposed to follow out in detail the gradual formation of coal from the original vegetable matter. Sufficient it is to say that the respective changes are partly physical and structural, and partly Chemical. The accompanying diagram (Fig. 255) enables the changes, so far as the salient properties and con-stituents of the coal are con-cerned, to be followedup. From this it will be noticed that the looseness of structure of the original matter gradually gives way to a more compact and homogeneous mass, whilst the volatile bodies are progressively displaced by constituents of a “ fixed ” nature. The moisture (i.e. the hygroscopic water), hydrogen, oxygen, and nitrogen of the cellulose all tend to be expelled, whereas the carbon remains, and increases in propor-