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Rh bottom half may be moulded in the sand of the floor, and the top half in an open box, which is then placed over the top of the floor mould, and pegged in place, so that the two half-moulds together will produce one casting. Usually, however, two large open boxes are employed, each containing half the mould, and the two are fastened together by pins and cotters. Nearly all the medium sized castings required for a locomotive are moulded in this manner.

Cylinders. Cylinders are the most important and difficult castings made in the foundry. The difficulty lies in the number of complicated passages which have to be moulded by means of sand cores. If a passage has to be made in a casting, that portion of the mould which represents the passage must, of course, be filled up with a piece of special sand made to the shape and dimensions of the passage, so that when the iron is poured into the mould the metal flows round this “core,” which remains in place until the casting has cooled. Afterwards, when the sand “core” is removed, the desired passage remains in the casting. These cores are made in wooden core boxes, the two halves of which are made with cavities, and when put together form a hollow pattern for moulding the core desired. The cavity is filled with a special binding sand held together by laces and nails, and the core so formed is then dried in a stove and placed in position in the cylinder mould. To form a support for the