Consolidation Coal moved coal through a 108-mile Ohio slurry pipeline in 1957.

Moving coal by rail was expensive; each heavy trainload paid a per-ton rate that did not fall with volume.

Consolidation Coal worked out that if coal is ground and suspended in water, it can be pumped as a slurry through a pipe. After small loops in 1950 and 1951, it built a 10-inch, 108-mile line from southeast Ohio mines to a Cleveland power plant.

The line opened in 1957 and carried about 7 million tons over its life, the world's first long-distance coal pipeline. A moving stream carries the solid particles, so the water is the conveyor belt.

In 1963 the line was mothballed once its purpose, forcing lower rail rates for coal, had been achieved; the idea lived on in bigger Western pipelines and pushed railroads to invent the unit train.

Make the solid flow, and a pipeline replaces a railroad

Ground coal suspended in water can flow through an ordinary pipe

A pipeline needs no crew, no track and no empty return run

The threat alone made railroads sharpen their own rates

Change the medium and you change the mode: turning a bulk solid into a flowing slurry lets it use a pipeline, but the edge lasts until incumbents price the threat away.

The line was shut in 1963 after it had driven rail rates down, but slurry pipelines were used again in the West and the threat pushed railroads to invent the unit train, changing bulk freight economics.