rial; this is the more liable to happen where the core has not body enough to be able to resist the action of the wet concrete.

The material for cores may be of many different mixtures; where to be modeled by hand the sand mixture, either green or to be baked, is the best and most easily worked. Where the same core is to be used in a number of casts it can be made of plaster of Paris, wall plaster, or even of concrete with success; the practice of using wood cores is not advisable as the excessive moisture in the concrete used is very liable to swell the wood and injure same.

The value of a separate core is shown most strongly in the illustration at (a) Fig. 5; the core is designated by the dotted lines and as illustrated, shows it extending at an angle into the face of the pattern, which would be the case in many deep under-cuttings; in the ordinary process of molding it would be an impossibility to mold this core with the pattern, as the lifting of the pattern would disturb the sand at the point of core in every case; hence the necessity of making this a separate part of the mold.

As shown by dotted lines the base of core sets into the sand of mold, so that the action of pouring in the concrete will not displace same. In making the sand mold, a small block of wood or anything of the exact size of the body of core is placed over the opening in pattern where the core is demanded; this molds in the sand the opening where the core is to be placed, and as well prevents the sand mixture from entering the part of pattern that is to be molded with a separate core.

After the sand mold is finished and pattern freed, a small box form is placed on the face of pattern, this box form should be the exact size or a trifle smaller, on the inside; than the block of wood used to mold the opening for core in sand mold; the mixture for core is now placed inside this box, using every care that it fills completely the opening in pattern. When a plaster mixture is used it is allowed to harden and can then be removed by turning to conform to the curve of the opening in the pattern. With a sand mixture the pattern must be turned over so to be uppermost and then by turning

the pattern to conform to the curve of opening in same, it can be removed from the core easily.

In molding the work in concrete, this separate core is placed within the opening made by the block of wood and the cast made; when it is to be removed from the mold, if possible to remove without injuring mold, the core lifts or draws from the main body of mold, when made of a hardened material, and is then removed from the concrete cast in the same manner as the core is removed from the pattern. When made of green sand the core is of course broken into small particles, the same as mold, in removing the concrete cast from the mold; this allows the easy removal of the material for core from any design, such as a very deep and curved opening in the work, or from the inside of a hollow ball cast in concrete.

The style of core employed to mold the opening inside a vase, jug, or any similar article is shown at (b) and (c); this must be of the green sand mixture for the reason that the neck of the article cast is smaller than the largest part of core, hence the core cannot be removed only in

small pieces; the sand mixture when dry easily disintegrates and in many cases can be removed by breaking up with a small stick, then is easily poured out of the inside of the concrete work. This is the only method of molding concrete work that permits a concrete article to be molded in one piece, with an opening many times smaller than the body of core, as by this method the opening to jug may be even 11⁄2" in diameter and the diameter of the main body of core ten or fifteen inches and yet be easily removed; in such work the core is held upright by a round piece of wood placed at the neck and to extend up into the core, so to support it; this piece of wood must not be larger than the neck to the jug or vase, and thus is easily withdrawn first and the main body of core removed by breaking into pieces and pouring out. For practical purposes the method of molding such articles in two sections and then joining with cement cannot be recommended, for while it is strong enough if not subjected to usage, yet for practical use it cannot compare with the strength of a monolithic piece of work.