Moulding in baked or used sand

—The mechanical part of this proce is the same as of the preceding. But when the castings are large, and especially if they are tall, the hydrostatic pre ure of the melted metal upon the sides of the mould cannot be counteracted by the force of cohesion which the sand acquires by ramming. We must in that case adapt to each of these frames a solid side, pierced with numerous small holes to give i ue to the gases. This does not form one body with the rest of the frame, but is attached extemporaneously to it by bars and wedged bolts. In general no ground coal is mixed with this sand. Whenever the mould is finished, it is transferred to the drying stove, where it may remain from 12 to 24 hours at most, till it be deprived of all its humidity. The sand is then said to be baked, or annealed. The experienced moulder knows how to mix the different sands placed at his disposal, so that the ma of the mould as it comes out of the stove, may preserve its form, and be sufficiently porous. Such moulds allow the gases to pa through them much more readily than those made of green sand; and in general the castings they turn out are le vesicular, and smoother upon the surface. Sometimes in a large piece, the three kinds of moulding, that in green sand, in baked sand, and in loam, are combined to produce the best result.