A hundred years of development have passed since the streets of the city of London were first lighted with coal gas. This beginning of preparing coal gas by the distillation of cial has been expanded and developed into our modern great by-products recovery industries. The history of these years plainly shows how the proper utilization of by-products can revolutionize an industry. No attention was given to the recovery of by-products of coal as a factor in reducing the cost of production, when coal gas was produced first by the distillation of coal. Special laws were enacted in England at one time to prevent the contamination of streams and lakes with tar. We are now beginning to realize how wasteful our methods of coking coal have been and how necessary it is to conserve our supplies of fuel.