In the last-mentioned specification, the patentee recommends that the sulphuretting of the gutta-percha should be effected by means of sulphurets, such as orpiment or liver of sulphur, in preference to sulphur itself; and he there states that though a portion of sulphur might be used in place of an equal portion of sulphuret, yet he conceives the use of sulphur to be altogether objectionable, because of its offensive smell and tendency to effervesce. He has since ascertained that if a minute portion of sulphur be used along with a sulphuret, a better result is obtained from a combination of the two than from either substance alone. The proportions which he finds to be the best are, 6 parts of sulphuret of antimony, or hydrosulphate of lime, or some analogous sulphuret, and 1 part of sulphur to 48 parts of gutta-percha: when these materials have been mixed, the compound is to be put into a boiler and heated (under pressure) to a temperature of from 260° to 300° Fah.; and it is to be left in this state for a period varying from half an hour to two hours, according to the thickness of the materials; by which times the gutta-percha becomes completely sulphuretted or metallo-thionized. The patentee applies precisely the same combination of materials (i. e., a sulphuret and a small quantity of sulphur) to the sulphuretting of India-rubber and jintawan, and in the same way. * * * The _fourth_ mode consists in making a paste of the sulphuret and sulphur with the addition of a small quantity of gutta-percha or caoutchouc solution, brushing it over the material to be sulphuretted, and then subjecting the same to one of the three processes as described. The invention consists, _fourthly_, in the following means of improving gutta-percha, both in a sulphuretted and unsulphuretted state, and in the application of the same to caoutchouc and jintawan in the like conditions. The patentee either exposes the material for a minute or two to the action of binoxide of nitrogen gas, (obtained by the usual method of dissolving a metal, such as zinc, copper, mercury, in nitric acid) or he immerses it in a boiling and concentrated solution of chloride of zinc, for a period varying from one to five minutes, according to the strength of the solution; and in either case, he afterwards washes the material with some alkaline solution, or with soft water. The material may be subjected to the action of the binoxide of nitrogen gas, either by putting it into the acid while the metal is in the course of being dissolved and the gas evolved, or by introducing it into a chamber in which the gas has been collected for the purpose.