Page:Popular Science Monthly Volume 16.djvu/894

 is ground in water to a fine pulp; the pulp is then subjected to powerful pressure in a perforated vessel, to extract the bulk of the moisture, but still leaving it slightly moist for the next operation, which consists in thoroughly incorporating finely comminuted gum-camphor with the moist gun-cotton pulp. The proportions employed are said to be one part by weight of the camphor to two parts by weight of the pulp. Any pigments, coloring matter, or other materials that may be adapted to the requirements of the articles into which the product is to be manufactured, may be incorporated at this stage. The mass is next subjected to a powerful pressure, to expel from it the remaining moisture, and incidentally to effect, also, the more immediate contact of the camphor with the pulp. The dried and compressed mass is next placed in a mold open at the top, into which fits a solid plunger, when a heavy pressure applied to the plunger is brought to bear upon the mixture. While thus under pressure, the mixture is heated to a temperature of about 300°, at which temperature the camphor fuses, and, its volatilization being impossible, the melted camphor dissolves, or "converts," the gun-cotton pulp. The process of transformation is rapidly effected when the right temperature is reached, and the product is celluloid. After the mass is taken from the press it hardens and becomes tough and elastic. A noteworthy circumstance is, that a large portion of the camphor appears to be permanently held in the mixture, so that its property of volatilization, when exposed to the air, is arrested. Celluloid is so extensively used as a substitute for ivory that it is said to have seriously affected the business of ivory importers and workers. It has all the strength and elasticity of this substance, and does not warp or discolor with age. It is used in place of tortoise-shell, malachite, amber, pink coral, and other costly and elegant materials, which it is made to imitate very closely. Its latest use is in combination with linen, cotton, or paper, for shirt bosoms, cuffs, and collars.

Experimental Glaciers.—Mr. J. T. Bottomley describes in "Nature" a successful experiment which has been arranged by himself and Mr. D. Macfarlane for constructing a model glacier with shoemaker's wax. A little wooden ravine was prepared, with steep declivities and gentle slopes, and a point where the space was narrowed by projections inward. At the upper end of the ravine a flat place was fixed, on which shoemaker's wax was piled, as snow collects at the upper end of the natural ravine. A supply of shoemaker's wax was put on the top at the beginning of each winter's session, whence a flow of semi-solid material went on steadily during the session, hardly perceptible from day to day, but progressing from week to week and from month to month. Several of the glacial phenomena were beautifully imitated with the wax; among them the more rapid flow of the middle with the less rapid flow at the edges. Little crevasses were sometimes formed, though not often, owing to the great effect of temperature on the plasticity of the material. Sir William Thomson, in order to test the qualities of shoemaker's wax as a viscous material, a year ago prepared a large cake of it, at the bottom of which he put some corks, and on the top some bullets. The corks at the end of the year had floated up through the wax, and were coming out at the top, while the bullets had sunk down and come through the bottom; and, while this was going on, the wax was all the time in such a condition as to be excessively brittle to any force suddenly applied.

Source of the Niger.—Information has reached Marseilles of a successful journey to the source of the Niger, which has been made by two men in the employment of the commercial house of M. Verminck, of Sierra Leone. The expedition, it appears, originated with M. Verminck himself, who sent forth two of his clerks, MM. Zweifel and Moustier, with an equipment of surveying instruments, maps, and goods, for the express purpose of reaching the spot on the northern side of the Kong Mountains, some two hundred miles from Sierra Leone, where both Major Laing, in 1822, and Winwood Reade, in 1869, were informed by the natives lay the sources of the "Joliba." The two envoys ascended the river Rokelle to the foot of the mountains, and seem to have met with none of that opposition, from