“To gutta-percha, which is intended to be made porous or spongy, for such purposes as aforesaid, must be added about 10 per cent. of rectified spirit of turpentine, or other proper solvent, and the whole mixed together by any convenient means. And if any of the above-mentioned compounds of gutta-percha is intended to be similarly treated, the caoutchouc or “jintawan” used therein, must be previously dissolved in from 100 to 200 per cent. of a similar solvent, the quantity of solvent being more or less, according as the product is intended to be more or less spongy and elastic. To the article which is intended to be made porous and spongy, must be added alum or carbonate of ammonia, or some other description of volatilizable substance. “If the article which is intended to be made porous and spongy, is required to be made more permanently soft and elastic, it should be combined orpiment, liver of sulphur, or a sulphuret, in the same way as described in the third part of my invention. A portion of sulphur may, in such a case, be used, but I prefer orpiment, liver of sulphur, or a sulphuret, for the reasons I have before stated. “The article which is intended to be made spongy and porous must then be thoroughly mixed with from ten to twenty per cent. of alum, carbonate of ammonia, or some readily-volatilizable substance, either in the masticating machine, or by any other convenient means. The material thus prepared, may be put into moulds, or forms, or upon trays, or confined in such a way as to cause it to assume the form which it is intended to possess. The material is then put into an oven or chamber, heated by steam or other convenient means, to a temperature of from 250° to 260° of Fahrenheit, at which temperature the article must be kept from one to two hours, according to the desired result. The effect of the exposure of the article to this high temperature will be to drive off the solvent with which it has been mixed, and at the same time, the alum, carbonate of ammonia, or other volatilizable substance before mentioned, cause the article to swell, and will render it porous and spongy. When the article has been exposed to this temperature for about one hour, it will be in the most porous and spongy state, and if the operation is further prolonged, the effect will be to render it less elastic and more rigid.”