This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1893 edition. Excerpt: ... removed and plunged into cold water, in order to set it and prevent further contraction. We may soften gutta-percba in warm water, but there is danger of some of the water remaining between the pattern and tbe mould On that account it is preferable to soften the material before a fire, or in a stove arranged for the purpose. In the case of a more deeply-cut pattern requiring or able to beur a gentle pressure only, we soften by heat the gutta-percha to the degree at which it may be pressed within the recesses of the pattern by th DEGREESl fingers, which are kept oiled. After removing thu still tepid gutta mould, dip it into cold water. There will be less danger of distortion by contraction if all the parts of the gutta-percha mould are of about the same thickness. Another method is without pressure, but by fusioL of the material. The pattern is laid in a tray, for in stance, and a ball of gutta-percha is put in the middle and on the top. The whole being put in a stove heated to the proper point, the gutta melts by degrees and finally covers the whole pattern. The hall shape given to the material is for the purpose of pushing away the air as the melting goes on. GELATIN FOR MOULDS. Another material which allows of the direct mould ing of quite deeply undercut patterns is gelatin, pure, or mixed with boiled linseed oil, as in printing rollers. For a single plaster cast, gelatin jelly aioue is sufficient; but if several casts are necessary, an addition of linseed oil will enable the mould to stand the action of dampness better. Good glue is covered with water, and is allowed to swell for twenty-four hours. Then it is heated upon a steam or water bath, and, if necessary, water and linseed oil are added. The proportions of these substance