Mr. Perry F. Nursey a few weeks ago read a paper on the above subject before the Society of Engineers, of London, from which we extract the following : Although many attempts have been made to supersede gunpowder, but fewhave practically succeeded, and this arises not so much from any inadequacy on the part of the substitutes, as regards power, bait on account of the extreme liability of most of them to premature explosion from varying j causes. Gunpowder itself is open to this objection, and hence the propositions to reduce the risk by mixing it with protecting ingredients. But this is not enough, we must go a step i further. What is required is a material over which we can have perfect command, one which shall do more than burn when in contact with air, but which shall equal, if not exceed, gunpowder in its power when ignited in an air-tight chamber, as in a bore hole, or the barrel of a gun. The necessity for this is evidenced almost daily in one or other of our mining districts, where a large percentage of the explosions occur in the blasting operations. How frequently is gunpowder ignited by stray sparks, even when standing about, but much more frequently do accidents arise when tamping is going on. Here the contact of the metal rod with the rock leads to many a fearful accident. So much is this so, that the Royal Cornwall Polytechnic Society have taken the matter up, and have suggested safe methods of performing this dangerous operation. But however careful a miner may be, there never can be perfect immunity while he has to deal with a material which carries within itself all the elements of danger and destruction. To meet the case a perfectly inexplosive material is required, one which will not explode so long as the at- mosphere has access to it, but in which all the active energy of gunpowder is developed immediately it is fired out of contact with the air. Gunpowder itself is at present more largely used than any other explosive material, and it is a remarkable fact that, notwithstanding the centuries which have elapsed since its first discovery, no radical or permanent change has been effected in its composition. Slight variations, it is true, have been made from time to time in the proportion of its constituents, but, in the main, gunpowder remains much as it was 600 years ago. But the danger ever present in handling this material has always been so patent, that many years since means were devised for rendering it harmless while in store, and to restore to it its power at the time of use. Colonel Ryley was the first to propound this theory, and he submitted his plans for enveloping the grains of gunpowder in bone dust, to the Government some twenty-five years since. In later times—in fact, very recently—Mr. Gales proposition to render gunpowder non-explosive and explosive at will has been much before the public. His plan was to mix ground glass with the powder for storage and transport, and to sift it from it again when it was required for use. This addition to a large amount of a foreign substance with the powder no doubt answers the purpose most effectually; but unfortunately there are practical difficulties in the way of its adoption. The objections are, increased bulk and weight for transport, the necessity of numerous sets of mixing and shifting apparatus, and the utter impropriety of having to prepare an explosive material just when it is required for use. Beside, in blasting operations, the accidents usually occur in charging the mine; therefore a system of this kind would be of no value whatever. Before quitting the subject of gunpowder, it may be interesting to notice the force this material is capable of exerting when used for blasting purposes. The following particulars show the amount of earth or rock thrown down or removed by 1 pound of powder, under various circumstances, the results being taken from actual practice. At the Round Cliff, Dover, 85,232 pounds of chalk were thrown down by 1 pound of powder. In the Leith cutting, Tunbridge, 31,860 pounds of hard white sand were moved by the same weight of powder. At Plymouth 22,000 pounds of limestone were moved per I pound; in small charges only 8,900 pounds were moved. In I Antrim, 45,084 pounds of white limestone, and 32,430 pounds of whinstone or basalt were moved by 1 pound of powder. At East Dunmore, 14,280 pounds of hard conglomerate were moved; and on the Londonderry and Coleraine Railway, 22,-I 400 pounds were thrown down by 1 pound of powder. Taking the mean of these results, we have 32,832 pounds of material to I pound of powder. Numerous compounds have been brought forward from time to time, for which it was claimed they perfectly superseded gunpowder. But, until very recently, no material has been found which would answer all the practical purposes, and fulfill perfectly all the conditions and requirements of that most important material. Saltpeter is the agent to which the characteristics of gunpowder, as an explosive material of permanent character, are mainly due. It is tojhe substitution of other nitrates for this constituent that most attention has been given, and the nitrates of sodium, lead, and barium have been successively tried. But although the products, which have been known by the names of soda gunpowder and barytic powder, etc., have obtained a certain amount of temporary success, they have ultimately been abandoned. In fact, all mixtures of this class, when compared with gunpow-dsr proper, have been found to exhibit important and radical defects. Chlorate of potash has been a favorite substance with inventors, notwithstanding its violently explosive nature. The object has, of course, been to tone down its vio- lence by proper admixture with other ingredients, and there-suiting products have been to some extent successful One of the earliest mixtures of this class was German or white gunpowder, which was tried, but proved unsuccessful. Many preparations of a similar character have also been brought before the public. Of this class is Ehrhardts powder, the invention of which is also claimed by Mr. Horsley.. M.Ehrhardts compositions are as follows: BLASTING POWDER. Chlorateof potash......................- part Nitrate of potash........................$ Tannin of cachou......................1 Charcoal................................9 POWDER FOR ARTILLEHY. Chlorate of potash......................1 part Nitrate of potash.. v.....................1 Tannin................................1 POWDER FOR SHELLS, Chlorate of potash......................1 part Tannin................................. 1 Mr. Horsleys powder is a compound of chlorate of potash and gall nuts in proportion by weight of three to one. The ingredients are ground separately to a state of fine powder, and then passed, also separately, through a very fine wire sieve. The two ingredients So prepared and thoroughly dried are blended when required to form the explosive compound. The blending of the ingredients is. safely and easily accomplished by passing them in a mixed state through a series of horsehair sieves, arranged one below the other and set in motion. Upon the upper sieve the two ingredients are first mixed by being run together from two receptacles placed above the sieve, one containing a given weight of chlorate of potassa, and the other one-third of such weight of gall nuts. As the chlorate of potash is much heavier than the gall nuts, the volumes or measures of the two receptacles are about equal. Motion being imparted to the sieves, and as the two finely ground ingredients pass downwards through the sieves, they become blended, and form the explosive compound. Pow -ders in which chlorate of potash is an ingredient are undoubtedly somewhat dangerous. The fact, however, of cannon-priming tubes, which are composed of chlorate of potash and ter-sulphide of antimony, having been prepared, stored, and used for more than thirty years past without accident, ought to relieve apprehension on that score. When treated, as it should be, with care, and not improperly blended with combustibles, chlorate of potash is practically safe. With regard to the explosive power of Horsleys powder, it may here be interesting to adduce a fe facts in the shape of results of trials which came under the authors notice, and which were made tft institute a comparison of its strength as against gunpowder. An eprauvette, weighing with its carriage 10 pounds, 2 ounces, was placed on a fir plank in a perfectly level position. The charge in each instance consisted of 50 grains of the various powders, and was kept in place by a small wad- of thin paper. The recoil of the eprouvette, when charged with fine grain sporting powder, was -g inch; with very fine grain sporting powder, -j-Jf inch. Fine grain sporting powder in a state of meal, and compressed by a weight of 400 pounds on the square inch, gave a recoil of 4 inches. Horsleys powder in a similar state of meal, and with a similar pressure of 4G0 pounds per square inch, showed a recoil of no less than 11 inches. These results afford some idea of the relative power of Horsleys powder and the best gunpowder. The author has examined some blocks of elm which had been submitted to experiment to show the comparative disruptive force of Horsleys powder and of common gimpowder. In each case equal charges were used, and the eprouvette was discharged one inch from the wood and at right angles to its face. The disruptive force of Horsleys powder on the wood was as if a solid body had been driven into it, separating the fibers and tearing a hole completely into it. The force of the small grain best sporting powder merely left a mark upon the surface of the blocks. A Wooden Railway. A description of the Wooden Railway recently constructed for the Clifton Iron Company between Clifton and the Adiron-dac mines in New York is given as follows by Mr. C. G. Myers, late President of the Company. The rails are of hard maple scantling, 4x6 inches, set on round ties, on which arc framed slots 6x4 The rails, set on edge and keyed in the slots by two wooden wedges driven against each other, project two inches above the ties. The rails admit of bending sufficiently to make the curves. The ties are laid on the earth and ballasted in the usual manner to two inches of the bottom of the rail. It takes 21,120 feet, board measure, of scantling for a mile, and 1,760 ties at three feet apart. Our road is a very rough one. We have a great deal 6f trestle work, some of it over thirty fijet high, which is vastly more expensive then a level Mute. The engines used weigh from ten to fourteen tuns. The rails will probably last about five or sis years. An engine will move about thirty tkns of freight at about six or eight miles an hour, with hevy grades and sharp curves. The Company expects to movgxver the road nexfyear from 50,000 to 100,000 tens of freight. Trains have passed over the road, light, at the rate of twenty miles, n hour, but this would not do for freight. 168 Bench Punch for Perforating Sheet Metals, A handy punch for ordinary and shop purposes, for light work, and which may be used on the work bench, is a desideratum in any machine shop. In the machine shown in the accompanying engraving, the old device of the togglejoint is used, the most powerful form of the lever when moving short distances. The machine is very simple in construction, and almost impossible to get out of order. A brief description will show its build and use perfectly. The frame, or bed plate, is a single casting, screwed to the bench. To the handle, A, is pivoted a sliding arbor moving through holes in the snugs, B, and carrying a punch at its end, held in the arbor by a set screw. The matrix, or die, is similarly held in an adjustable seat bolted to the snug, C. A lever, D, is pivoted to a snug, E, at the rear of the bed plate, and also to the handle, A, just behind the sliding arbor. The operation is so easily understood that nothing more than a reference to it is required. The sheet or piece of metal to be punched, is placed between the punch and die, the handle de pressed forcing the punch forward and through the metal, when the handle is raised, and the punch moves back, the holder, F, releasing it from the metal. It is apparent that punches and dies of any form may be used on this machine, as one of either may be instantly removed and others substituted. The machines may be made of different sizes, but one veighlrig only 21 lbs. will punch wrought iron or brass one-eighth of an inch thick. It may be used for cutting saw teeth or severing wire by employing the proper dies and punches. Patented July 31, 1866. Orders should be addressed to Goodnow & Wightman, manufacturers and sole agents, 23 Comhill, Boston, Mass. See advertisement on another page. Manufacture of Clay Tobacco Pipes. The clay of which these are made is obtained in Devonshire, in large lumps, which are purified by dissolving in water in large pits, where the solution is well stirred up, by which the stones and coarse matter are deposited; the clayey solution is then poured off into another, where it subsides and deposits the clay. The water, when clear, is drawn off, and the clay at the bottom is left sufficiently dry for use. Thus prepared, the clay is spread on a board, and beaten with an iron bar to temper and mix it; then it is divided into pieces of the proper sizes to form a. tobacco pipe; each of these pieces is rolled under the hand intcua long roll, with a bulb at one end to form the bowl; and in this state they are laid up in parcels for a day or two, until they become sufficiency dry for pressing, which is the next process, and is conducted in the following manner: The roll of clay is put between two iron molds, each of which is impressed with the figure of one-half of the pipe; before these are brought together a piece of wire of the size of the bore is inserted midway between them; they are then forced together in a press by means of a screw upon a bench. A lever is next depressed, by which a tool enters the bulb at the end, and compresses it into the form of a bowl; and the wire in the pipe is afterward thrust backwards and forwards to carry the tube perfectly through into the bowl. The press is now opened by turning back the screw, and the mold taken out. A knife is next thrust into a cleft of the mold left for the purpose, to cut the end of the bowl smooth and flat; the wire is carefully withdrawn, and the pipe taken out of the mold. The pipes when so far completed, are laid by two or three days, properly arranged, to let the air have access to all their parts, till they become stiff, when they are dressed with scrapers to take off the impressions of the joints of the molds; they are afterwards smoothed and polished with a piece of hard wood. The next process is that of baking or burning; and this is performed in a furnace of peculiar construction. It is built within a cylinder of brickwork, having a dome at top. and a chimney rising from it to a considerable hight.to promote the draft. Within this is a lining of fire-brick, having a fireplace at the bottom of it. The pot which contains the pipes is formed of broken pieces of pipes cemented together by fresh clay, and hardened by burning; it has a number of vertical flues surrounding it, conducting the flame from the fire-grate up to the dome, and through a hole in the dome into the chimney. Within the pot several projecting rings are made; and upon these the bowls of the pipes are supported, the ends resting upon circular pieces of pottery, which stand on small loose pillars rising up in the center. By this arrangement a small pot or crucible can be made to contain fifty gross of pipes without the risk of damaging any of them. The pipes are put into the pot at one side, when the crucible is open; but when filled, this orifice is made up with broken pipes and fresh clay. At first the fire is but gentle, but it is increased by degrees to the proper temperature, and so continued for seven or eight hours, when it is damped and suffered to cool gradually; and when cold, the pipes are taken out ready for sale. Dentistry in Japan. This trade, for such it may be more fitly considered in Jap an, is carried on by a very low class of people, usually peri- patetic in their habits, and who carry with them a box covered with brass ornaments, by which their occupation is recognized. Now, the extraction of a tooth by one of these gentry is regarded by the Japanese as a capital operation, and not without reason, if the information given me i8 reliable, that death (from tetanus, I presume) is not unfrequently the result. The tooth is extracted by the operators fingers, but not urftil it has been well.loosened by means of a stick and a mallet vigorously wielded. The operation is seldom performed, but I saw some teeth in possession of one of these charlatans that had large portions of the alveolar process attached. In the face of these facts it can scarcely be credited that artificial teeth, sustained by atmospheric pressure, have been in use from time immemorial. These teeth are carved out of seahorse ivory, the molars being plentifully studded with little brass bosses, and the whole strongly mounted upon a base cut from the hard shell of a species of gourd, and carved to conform to the irregularities of the gums and palate. I have several sets of these teeth in my possession; they are not expensive, the very best, a complete upper set, costing about five boos, or about one dollar and sixty cents. Colossal fortunes are not accumulated from dentistry in Japan, as may be inferred from the foregoing.—Dr. A. M. Vedder.