The by-products of coal can play an important part in the fuel industry. Where it is thoroughly integrated they can help in financing the development of hydroelectricity to supplement the electricity produced from coal. For while the running expenses of a hydroelectric plant are little more than the interest on the capital invested, the amount of that capital is large. Also the establishment of gas plants at the mines is a costly thing. The temptation is to revamp and repair and reorganize the present outworn and wasteful system rather than make large new investments and scrap the old equipment. But in the commercial value of the by-products from bituminous coal lies the possibility of paying for the new power to turn our factory wheels by the sale of dyes and fertilizer and medicines and tar and explosives and perfumes and a hundred other things. So it is to the chemical laboratories that we look for the new values which may make a superpower system financially possible just as it is to the electrical workshop that we look for the inventions which will integrate it into one thing. But even the recovery and sale of the by-products of coal are not all that is involved in the new way of supplying the world with power. While gas can yield the full fuel value of coal in a more efficient form than solid fuel, as well as all the commodity values, if it is converted into power through the steam engine, at least one-half of its energy value is lost. To conserve its full value, gas must be burned in the internal-combustion engine, the most familiar type of which is the one we know under the hood of the automobile and the most efficient type is the Diesel engine which has made the by-product system industrially practical. The internal-combustion engine is a relatively simple device for transforming the energy in fuel into power directly instead of indirectly as the steam engine does, of turning wheels at first hand, of cutting out steam as a middleman. It greatly enlarges the range of fuel utilization because it can burn not only fuel gas and the lighter oils--gasoline, benzol, and their close kin--but also fuel alcohol, the supply of which though hitherto only slightly developed will last as long as the sun and rain make vegetation grow in the soil. Our future success in winning and holding an economic surplus upon which the opportunity for the good life and a world civilization depends, rests almost as largely upon the internal-combustion engine as the industrial revolution depended upon the steam engine of Newcomen and Watt.