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CHLORATE OF POTASH POWDER.

A so-called "safety explosive compound" has been patented in England, by Mr. Percy A. Blake, of Aberdeen Park. The constituents of this compound are sulphur and chlorate of potash, in the ratio of one of the former to two of the latter. These substances are kept separately and dry, and are mixed when required. The powder burns slowly when ignited, but explodes under percussion. This explosion is effected by means of a detonating tube of metal, about an inch long and of an inch in diameter, partly filled with the compound and with fulminating mercury, and lastly with powder. This powder may be ignited by any ordinary ignition apparatus.

The first attempts to make powder with chlorate of potash, sulphur, and carbon, were those of Berthollet, in 1788. In 1792, experiments in its manufacture were made at the works of Essonne under his direction; but they were stopped by a terrible explosion which destroyed the lives of the director of the works, his daughter, and four workmen. Berthollet, who was with the director, had a wonderful escape. The explosion was caused by the end of the director's cane striking some of the powder upon the floor.

It has also been attempted to use various mixtures of the chlorate with white sugar and prussiate of potash and with charcoal and sulphuret of antimony and starch; but all these compounds are exceedingly dangerous to manufacture or transport, and it does not appear probable that they can ever come into general use.

For mining purposes a mixture of tan-bark, chlorate of potash and sulphur has been made at Plymouth, England. The tan is soaked in a warm solution of the chlorate, and afterward covered with a film or layer of powdered sulphur. This preparation is said to burn but slowly in the open air, but when confined, as in the hole of a boring, it explodes with great energy.

Picrate of potash has also been experimented with, and used for torpedoes, but its preparation has led to some frightful accidents; that at the Sorbonne, in 1869, killing five persons and wounding many more.

EXPLODING CHARGES BY ELECTRICITY.

Franklin, in 1751, and Priestley, in 1761, suggested the possibility of applying the electric spark for the ignition of gunpowder charges; but electricity was not practically applied until about thirty years ago, by the French military engineers, since which its use has become general. It was employed to ignite the great blasts that destroyed the Round Cliff at Dover, and to remove the wreck of the Royal George; and has been largely used in heavy blasting with powder and nitro-glycerine in California and for exploding torpedoes under water.

The variety of contrivances is very great. Many exploders have been devised to act either by heating a piece of thin wire, introduced in the circuit of a battery and placed in the charge, or by the passage of a spark produced by an electro-magnetic machine or Ritchie coil through a sensitive explosive compound, thus causing a local explosion sufficient to ignite the whole charge.

Among those who have given great attention to this subject, Baron Von Ebner, of the Austrian military engineers, may be specially mentioned, and Mr. Abel, of the British war department, who has devised one of the best exploders known. A spark generated by revolving magnets is made to pass through a mixture of subphosphide and sub

sulphide of copper and chlorate of potash-materials of high conducting power and extremely sensitive to the spark. One of the great difficulties in the way of making such exploders is the liability of the materials to be merely thrown aside and not exploded by the passage of the spark.

In the United States inventors have been active in devising different forms of apparatus for igniting explosives. They all depend upon either the direct passage of a spark or the heating up of an imperfect con ductor, immersed in an explosive mixture. This mixture and the arrangement of wires are inclosed in a small cartridge of paper or wood, which can be readily placed in the midst of the powder in the hole to be exploded. Mr. Stowell patented, in 1862, a peculiar form of cartridge containing the ends of the conducting wires and a strip of platina. Beardslee, in 1863, patented a very simple mode of making an imper fect conductor between the ends of two wires, by drawing a pencil mark, of graphite, upon the surface of a piece of dry wood. Mowbray, in July, 1869, patented an improved electrical fuse for exploding charges of nitro-glycerine. It consists of a small cartridge of powder, in the top of which is placed a small quantity of a composition, like that used by Mr. Abel, made of sulphide of copper, 9 parts; subphosphide of copper, 2 parts; chlorate of potash, 3 parts, the whole intimately mixed. The ends of the wires are immersed in this mixture. It is designed especially to be inserted in cans of nitro-glycerine, to be exploded in oil wells.

The dealers in the new explosive compounds, such as nitro-glycerine, dynamite, and dualin, farnish exploders especially designed for the several preparations. These various exploders may be fired either by the voltaic current or by a spark from a suitable electrical machine, or the Page coil. An electrical machine has recently been invented and patented by Mr. H. J. Smith. The following is a description and the claim

The object of this invention is the production of an electrical machine constructed with especial reference to portability, and to working in all conditions of the atmosphere. It is designed more especially for igniting charges of powder by means of the electric spark which it evolves.

It is well known that the electrical machine, as commonly constructed of glass, be comes wholly inefficient in a damp atmosphere, such as prevails in tunnels and mines. This is due to the fact that glass so very readily condenses moisture upon its surface, in the form of a continuous film. Vulcanite, on the contrary, does not so readily condense moisture. Nor does it condense moisture in the form of a film, but rather in the form of detached drops.

The machine consists of an outer covering or shallow box, containing a frame plate, a Leyden jar or condenser, a generating plate of vulcanite, and devices for operating the generating plate and condenser in connection.

The frame plate, the condenser, and the generating plate are placed parallel to each other, and parallel to the sides of a box about a foot in diameter.

The condenser is connected to the frame plate by four posts, 1, 2, 3, and 4. The generating plate of vulcanite lies between the condenser and frame plate, and is revolved on its axis by means of a handle or crank.

The axis of the generating plate passes tightly through a stuffing box, which may be made to grasp the axis more or less tightly, by means of a packing screw.

The outer end of the axis has its bearing in a small hole sunk in the outer vulcanized plate of the condenser.

The generating plate of vulcanite revolves between two cushions, the surfaces of which are coated with an amalgam, as is usual with electrical machines.

The cushions are provided with flaps, which flaps serve to prevent the electricity from escaping from the generating plate until the excited portion of its surface arrives in the neighborhood of the collectors, which are serrated strips of metal, placed one on each side of the generating plate, and both collectors are attached to and in metallic

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connection with the frame post 4, and by it are brought into connection with the inner plate or surface of the Leyden jar or condenser.

The two outer plates or surfaces of the condenser are in metallic connection with the post 2, and also with the cushions by means of post 3.

The inner plate connects with post 1, as well as with post 4.

The condenser is constructed in the following manner:

When the vulcanite is in a plastic state, upon a layer of vulcanite is placed a layer of tin-foil. Over the layer of tin-foil there is placed a second layer of plastic vulcanite, and then a second layer of tin-foil. A third layer of plastic vulcanite, a third of tin-foil, and a fourth of vulcanite, complete the jar or condenser.

The first and third layers of tin-foil form the outer surfaces of the condenser, the middle layer forming the inner surface.

Care must be taken that the diameter of the tin-foil plates be less than that of the layers of plastic rubber, excepting a small projection from each tin-foil plate, intended to connect with the posts of the frame. The condenser, thus made up, is then substripmitted to the baking or vulcanizing process, at the end of which it becomes hard and rigid. Its surfaces will forever remain in a perfectly dry condition.

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The posts 1, 2, 3, and 4, are now screwed into the condenser, posts 1 and 4, as before stated, connecting with the inner surface, while posts 2 and 3 connect with the outer

surfaces.

To the outer casing are attached two knobs. These knobs are electrodes, or paths for the discharge of the electricity when they are brought into contact with the inner and outer surfaces of the condenser, which is done by turning the handle of the machine backward a little, until the post 1 comes into contact with a projection from one knob, and the post 2 comes into contact with the projection from another knob.

There is a stop, which serves to prevent the framework of the machine from revolving by the action of the crank, except through a small arc. The post 1 is limited in its forward motion by the stop, and in its backward motion by the projection from the knob.

The casing is made of vulcanite. Two forms of casing are made: one, a box in halves, which are screwed together, with a packing of soft rubber or other air-tight material between them; the other, a box with a cover, having a rubber band placed over and around the outer edge.

The operation of the machine is as follows:

By turning the crank the generating plate is revolved between the cushions. The electricity generated is collected by the collectors, and from them carried by post 4 to the inner surface of the condenser. The opposite electricity appearing at the rubbers, is conducted from them by post 3 to the outer surface of the condenser.

By continued turning of the crank, the condenser may be charged sufficiently to give a spark of three-eighths or one-half an inch in small machines of five or six inches in diameter.

The first motion of the crank turns the frame, as well as the generating plate, until post 1 strikes the stop. Turning the crank backward brings posts 1 and 2 in contact with the knobs, when the condenser may be discharged. It is desirable that the condenser be discharged by the posts 1 and 2, rather than by posts 3 and 4, which are used for charging, as the tendency to escape during accumulation is thereby avoided.

The frame plate and the generating plate are both made of plastic rubber, and vulcanized.

The capacity of a Leyden jar or condenser constructed of plastic rubber and metallic plates, as above directed, may be increased by adding successive layers of metal and vulcanite. Such a condenser will be of use for electrical purposes independently of the generating apparatus herein described.

The inventor claims:

1. A generating plate and a flat condenser, placed parallel to each other within the same casing, substantially as described.

2. A Leyden jar or condenser constructed of vulcanized rubber and metallic plates, substantially as described.

3. So arranging the jar or condenser that the forward motion of the crank, to generate electricity and charge the jar, moves the jar forward through a small arc, whereby its terminals are moved away from the discharging knobs.

4. The device for discharging the jar by the retrograde motion of the crank bringing the posts 1 and 2 into contact with the projections from knobs V and W.

Placing the firing points of the condenser at a distance from the collecting points, substantially as described.

6. The stop X, limiting the forward movement of the jar, substantially as described. 7. The combination of a generating plate, a condenser, and a casing, made air-tight, as described, by packing or a rubber band, together with knobs in the casing, and their projections, by which the condenser is discharged, substantially as described.

SECTION II.-BORING AND EXCAVATING BY

MACHINERY.

CHAPTER LXVII.

MACHINES FOR DRILLING ROCKS.

Machines for rock-drilling originated in the United States, where one was put into practical operation as early as 1838. The attention of mechanicians and inventors being thus early directed to this great desideratum, a machine that could be economically and easily substituted for hand labor, so great a variety of contrivances and forms have been proposed and experimented with, that their number renders it difficult even to enumerate them. Our Patent Office and the patent offices of Europe contain many models of machines; but most of them are of the class known as "drop drills," where the tool cuts by percussion. There are other forms of machines, fitted with revolving disks or cutters, and designed to bore out the drift or tunnel to its full size at one operation; and others, again, in which a number of drills are mounted in a frame, so as to cut an annular space around a central core of rock, which can afterward be broken out with powder or otherwise. There is still another type, in which diamonds are made to do the cutting by pressure and rotation, without percussion. Rock-drilling machines may therefore be grouped in two great classes: 1. Those that bore by percussion; 2. Those that bore by constant pressure and rotation.

The drop drills belong to the first class, and will be first considered. In these machines the drill or bar of iron or steel-either a single rod or provided with a steel bit or point at the lower end-is raised by means of a crank, cam, or other mechanism, and then allowed to fall by its own weight upon the rock to be bored. There are also numerous contrivances to accelerate the speed of the fall and increase the force of the blow. Metallic and rubber springs have been used, and, in some cases, the elasticity of air; but in all these modifications but little has been gained over the form in which gravity acts unaided. With springs, the greatest compression and force is exerted when the drill is at its highest or furthest from its striking point, and as the drill descends this force becomes less and less-the reverse of the most desirable condition given by gravity.

It is desirable to note a few of the more important of these inventions which have been in use practically during the past thirty years, and which, by successive modifications and improvements, have led to the present very considerable degree of perfection of rock-drilling machines. As early as 1838, Messrs. J. M. and John N. Singer experimented with a large drop drill on section 64 of the Illinois and Michigan Canal, about thirty miles below Chicago. This machine was patented in May, 1839, and some ten or twelve machines were built for, and used upon, the canal until the suspension of that work in 1841-42. They were also used in the Mount Washington cut, near Hinsdale, for the Western railroad of Massachusetts. Two machines were built at Lockport, in 1840, and used upon the enlargement of the Erie Canal. Modifica