The rolling of plate has been described thus in detail that a slight conception can be obtained of the refinement and the minutia which is a necessary part of modern mill practice. American outputs which have grown to as much as several hundred tons per twelve-hour turn, require that every operation move along with “clock-like” precision. But with this immense tonnage and with all of the handicaps of occasional broken rolls and machine parts, electric crane delays, and illness of important men, the work must be and usually is kept up without serious delay. Modern metallurgical and rolling mill practice is a marvel. Sheets [Illustration: THE ROLLING OF SHEETS ] Most plates are rolled from slabs which are about 36 inches wide, but “sheets,” which are plates less than ³⁄₁₆″ thick are rolled from much smaller-sized slabs known as “sheet bars.” After “pulling out” into sheets these may be folded once or even more times, so that from two to eight thinner sheets are rolled at once. That they may not weld or stick together under the heavy pressure, they must be rolled colder than are single plates. They are later trimmed and pulled apart. Some mills start sheet bars of smaller size, for each sheet a separate piece, which, after drawing out somewhat are piled, two, three, four or five high. With coal or charcoal dust—either dry or mixed with water—between them, they are heated and rolled, the charcoal and coal dust keeping them from sticking together. After annealing, pickling, etc., they may be cold finished in polished rolls or otherwise treated according to the purpose for which they are intended. After straightening some are galvanized, others are tinned, blued or painted. Most of them are sold “black,” i.e., with no coating at all. Terneplate has a coating of 75% of lead and 25% of tin. The Rolling of Rails and Structural Shapes It will be readily understood after reading the above, that, instead of using plain rolls, mills for rolling steel rails, I beams, channels, angles, Z bars, rods, etc., must have grooved rolls. For these products the first pass will be through a groove slightly smaller than the bloom or billet. Successive passes will be through other grooves in the same set of rolls which will gradually make smaller and bring more nearly to the finished shape the piece being rolled. [Illustration: RAIL IN THE FINISHING ROLLS ]