are building the machines and then take the machines away from the workers, by power of police, if necessary.
But to come back to the story. A very large part of the machinery in use is driven by steam power, which means largely coal power, and both the getting and the burning of this coal involves a terrible waste of human labor.
First the coal is dug from the mines, where one-third of it is lost or left in such shape that it cannot be used. After being brought to daylight, it is shipped by railroads or ships, sometimes thousands of miles before it comes to the steam engine. Here it is shoveled and burned beneath the boiler to transform the water into steam, by which operation perhaps 90 per cent. of the heat escapes unused through the chimneys.
The steam is led into the cylinder to give the piston the to-and-fro movement through its expansive energy, thereby turning the power wheel. It so happens that ordinarily not more than five per cent. of the stored energy in the coal becomes available for human needs. Even the finest quadruple-expansion engines with all the modern devices for superheated steam, etc., to augment their capacity, do not use more than 15 per cent.
By far a greater advance is represented by the gas engines, in which, by first turning the coal into gas and then exploding this in the motors, more than double the amount of energy now becomes available. In the best types of gas engines the yield rises as high as 25 per cent.; and in Germany the residual products from turning the coal into gas far more than pay the cost of doing this, so that the gain is clear. But all this is commercially feasible only in the great manufacturing centers and the cities, and, consequently, the gas engine, in spite of the great saving it achieves, has yet but a restricted field.
For quite other reasons the same is true of the gasoline, benzine and similar motors such as are used in automobiles. Here the price of petrol is almost pro-
