(2) Economies in the source of power. These will fall under four heads—
1. Substitution of cheaper for dearer kinds of human power. Displacement of men's labour by women's or children's.
2. Substitution of mechanical power for human power. Most great improvements in the "labour-saving" character of machinery properly come under this head.
3. Economies in fuel or in steam. The most momentous illustration is the adoption of the hot blast and the substitution of raw coal for coke in the iron trade.[66]
4. The substitution of a new mechanical motor for an old one derived from the same or from different stores of energy—e.g., steam for water power, natural gas for steam.
(3) Extended application of machinery. New industrial arts owing their origin to scientific inventions and their practice to machinery arise for utilising waste products. Under "waste products" we may include (a) natural materials, the services of which were not recognised or could not be utilised without machinery—e.g., nitrates and other "waste" products of the soil; (b) the refuse of manufacturing processes which figured as "waste" until some unsuspected use was found for it. Conspicuous examples of this economy are found in many trades. During the interval between great new inventions in machinery or in the application of power many of the principal improvements are of this order. Gas tar, formerly thrown into rivers so as to pollute them, or mixed with coal and burnt as fuel, is now "raw material for producing beautiful dyes, some of our most valued medicines, a saccharine substance three hundred times sweeter than sugar, and the best disinfectants for the destruction of germs of disease." "The whole of the great industries of dyeing and calico-printing have been revolutionised by the new colouring matters obtained from the old waste material gas tar."[67] These economies both in fuel and in the utilisation of waste material are largely due to the increased scale of production which comes with the development of machine industry. Many waste products can only be utilised where they exist in large quantities.
§ 4. If we trace historically the growth of modern capitalist economies in the several industries we shall find that they fall generally into three periods—
1. The period of earlier mechanical inventions, marking the displacement of domestic by factory industry.
2. The evolution of the new motor in manufacture. The application of steam to the manufacturing processes.
3. The evolution of steam locomotion, with its bearing on industry.