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connexion with the zinc plate it may be other, and if the lanyard be slackened, called the negative pole, and if a wire at. the spring separates the two discs, the actached to the positive pole is brought into tion of the battery is stopped, and there contact with the disc the battery is put is then no danger in approaching the into action. Another tin disc E, of si. charge of gunpowder, should it not have milar size to that of the negative pole, exploded when the electricity circulated must slide freely along the round cross through the fine wire. bar: the central aperture in this disc To prevent the possibility of the dises should be about an inch and a half in touching each other before the workmen diameter, and to it a tin pipe, of the same are prepared for the explosion, a wooden diameter and about 2 inches in length, is pin p, is placed between them; this is fixed, (this is to be on one side only of inserted into a hole bored through the the disc and must project towards the cross-bar about midway between the discs. positive pole of the battery.) The use When all is prepared for firing the charge, of the pipe is to keep the moveable disc this pin, which Mr. Roberts calls the steady during its motion along the bar : safety pin, is removed from the hole beit must not project on both sides of the fore the lanyard is pulled. moveable disc, because it is necessary We come now to the method of conthat the surfaces of the discs be in perfect necting the long-conducting wire with the contact with each other when the battery battery: is in action.

In the practice of blasting, the conSuppose then, a wire connected with ducting wire should be of copper, and the positive pole to be fastened to the about one-eighth of an inch in diameter; moveablc disc, and this disc to be then its length must of course vary according moved along the cross-bar until it comes to circumstances; but, in general, if the in contact with the fixed disc, the battery battery be placed 20 or 30 yards from the is in action, because there is a metallic rock to be blown up, it will be in perfect communication from one pole to the other. safety: To enable an operator standing at a dis If the battery is to be 30 yards from tance from the battery to bring these discs the explosion, 60 yards of stout copper into contact, a string S, is fastened to the wire covered with cotton thread well was. moveable disc and reeved through two ed will be required. The 60 yards of wire holes bored in the fixed disc, and the two are cut in half, and the two lengths of 30 ends tied together about a foot behind yards each laid side by side, and bound the fixed disc, so as to form a span or together with twine nearly in the same double cord proceeding from the moveable manner as each wire is covered with disc. To this double cord is tied a string cotton. As an additional security, this of any convenient length, which Mr. double wire may be done over with seal. Roberts calls the lanyard; the end of ing-wax varnish. About a foot in length this lanyard is carried to some place where of the ends of these wires is left free, the operator may be in safety, and on that is, not bound together in the manner pulling it, the moveable disc slides along the rest of their length has been. (See the cross-bar into close contact with the fig. 2.) fixed disc, and the battery is thus put into We have now a kind of rope 30 yards action.

long, consisting of two wires bound toA further contrivance must however gether, and the four ends projecting. be provided to prevent the discs touching Take one end of this rope, and fasten its each other before the lanyard is pulled, two projecting ends to the galvanic batand this Mr. R. effects by fastening to the tery in the following manner: Solder one pipe of the sliding disc a spiral wire, F, projecting end to the sliding tin disc, and (such as a bell spring), which encircles the other projecting end of the same ex. the cross-bar, and has one end fixed to tremity of the rope) to the wire attached the wooden upright on the positive side to the positive pole of the battery. The of the battery. The length of the wire rope must be permanently fixed in spring when unextended is such, that the this manner; in fact, it thus forms a part moveable disc attached to it stands about of the battery. When not extended for 7 inches from the fixed disc, but when use, it may be coiled up, or wound upon a the lanyard is pulled, the spring extends, reel. Let us now suppose the wire rope and the discs come in contact with each extended, two of its projecting ends fixed

battery.

ROBERTS'S GALVANIC BLASTING APPARATUS.

357 to the battery, and let the other ends be The details of making the cartridges connected by a few inches of fine wire ; are as follow : let us also suppose the plates immersed in the exciting liquid: if the lanyard be

"Take 20 feet of stout copper wire coverpulled, the sliding disc will move for ed with cotton thread, double it, and twist ward into contact with the fixed disc or

the two parts at the looped end closely tonegative pole, the electricity circulates

gether for about 6 inches of their length, from the positive pole through one part

A, fig. 3; then, with a file or cutting pliers,

cut off the round end of the loop, and the of the conducting wire, then through the fine wire (fusing it) back through the

ends will project as horns of half an inch in

length B B ; then bare the extreme points other part of the conducting wire to the

of these horns (being about half an inch sliding disc, and from this to the fixed

asunder) of the cotton thread that is around disc, which is the negative pole of the them, and clean them with a file : now take

half an inch of the fine steel wire, lay it The wire immersed in the gunpowder is across from horn to horn of the stout wire, generally of steel, and very fine, (of the and there (C) let it be firmly soldered. We sort called by watch-makers, balance wire) have now two long stout copper wires conbecause the degree of heat raised in me nected at one extremity by a fine steel wire : tals by electricity is in proportion to the

the end of these wires are twisted together minuteness of their diameter. A reel of to prevent the horns slipping into contact this fine steel wire containing six or eight

with each other, and also to preserve the fine yards, costs 3d., and will perhaps serve

wire from being broken by any pull or jerk for a hundred explosions. “A very short given to one of the communicating wires. piece of it is employed at one time, be

As this combination of wires is placed in the

bore-hole, it will be exposed to the action of cause the obstruction to the

progress of

the ignited charge of gunpowder, and, with. electricity through a conductor is in pro

out some precaution to secure it, would be portion to its length, and, if the fine

destroyed by every explosion : to prevent wire be too long, it will prevent the pas this waste, the communicating wire is first sage of electricity in sufficient quantity to covered with cord (in the same manner as fuse it.

the conducting wire of the battery is coverBut as it would be inconvenient to ed), and an additional covering is then given have at every explosion the trouble of of hard whip-cord or of fine binding-wire, attaching a fine wire to the ends of the (binding-wire will perhaps be found best, as conducting wire, Mr. Roberts has con it effectually prevents the included commutrived a cartridge, a number of which nicating wires being injured by the broken may be kept ready for use, and one

fragments of the rock). The fine wire sol. fastened without loss of time to the con

dered to the ends of the communicating wire ducting wire whenever required. The

will be destroyed at each discharge, for the

electricity will fuse it, but this fine wire is cartridge is a tin tube filled with gun

easily replaced at a cost of three-halfpence powder, and in this are placed the ends

for every dozen cartridges. of two stout copper wires connected by a

“ The body of the cartridge is a tin tube, fine steel wire; the copper wires are each 3 inches long, and 4 of an inch or an inch in about 10 feet long, and serve to convey diameter, of which the joint is soldered and the electricity from the conducting wire rendered perfectly water-tight: the fine wire of the battery to the fine wire immersed across the hords of the twisted wire is placed in the powder of the cartridge. These in the centre of the tube, and retained firmly copper wires he calls communicating in this position by a cork at the end of the wires. The tube is stopped at both ends tube, through which the twisted wires pass, by corks covered with cement to keep fig. 4. The best way of fixing the twisted the gunpowder dry; when thus corked

wires is to split a bit of cork half through, and cemented the cartridge may be fired

lay them in the slit, then force the cork into

the tube, and this will jam the wires firmly under water without a risk of failure.

in the slit : taking care that the horns do not The communicating wires must be of

touch the sides of the cartridge, and that the sufficient length to extend from the bot

cork is covered with a good cement, as this tom of the bore-hole in the rock to a few

assists in preserving the horns in their proper feet above the surface, and as the holes position. The cement I generally use is are seldom more than 6 or 8 feet deep, composed of one part of bees'-wax and two 10 feet may be taken as the average length of resin, which, if put on hot, readily sets, of the communicating wires.

is very strong, and does not crack in cooling:

but any cement that has these properties, and powder. In practice Mr. Roberts has effectually keeps out damp, will answer the found it of great importan:e to allow this purpose. Having now the tin tube with the

distance to exist between the powder and fine wire firmly fixed in the centre, the next

the wad, for the expansion of the air by operation is to fill the cartridge with gun

the flame of the ignited powder adds to powder. It must be fine sporting powder the rending force, and there is also an and thoroughly dry; unless this be attended to, the fine wire may be fused by the electric ball is rammed but half-way down s

effect produced similar to that when a fluid without igniting the charge, for the action is so rapid, that if the powder be damp,

musket barrel. When the wad is in its it will hardly be dried, much less ignited by proper place fill the hole up to the sur. the fusion of the wire. The best method of

face of the rock with dry sand. The bole ensuring this dryness, when a great number of is now charged, and about 4 feet of the cartridges are made at one time, is to dry cartridge communicating wires project the powder over a steam-tight box filled with above the surface of the rock. boiling water ; but, when a few dozen only Having filled the box of the battery of cartridges are required, heat a soup plate with a saturated solution of sulphate of by a fire, and when it is a little hotter than copper mixed with a little sulphuric acid, the hand can bear, take the plate from the place it at some convenient distance from fire, and throw into the plate a sufficient the rock, behind a large stone, or in any quantity of powder to fill two or three car

situation where it is not likely to receive tridges; shake it in the hot plate for two or

injury from the falling fragments of the three minutes, and then fill the cartridge tubes with the powder, which will now be

rock; put the frame of plates on the perfectly dry and warm :-while in this state

ground by the side of the box, and be cork the ends of the cartridges, and cover

careful the safety pin p, is in the bole prethe corks with the same kind of cement as

pared for it; then unroll the conducting that used for the corks through which the

wire, and attach the ends that are free to wire passes."

the cartridge communicating wires pro

jecting above the surface of the rock. It only remains now to detail the actual This attachment may be done by twisting process of blasting with the apparatus be them together, but it will be better that fore described.

a binding-screw, fig. 5, be soldered to When a rock is to rent by the ex. each free end of the conducting wire, and plosive force of gunpowder, the first thing to these the communicating wires are done is to bore in the rock a hole, of a readily attached by inserting an end into depth and diameter proportioned to the each screw, two or three turns of which strength of the stone and the quantity we will make the contact perfect. Fig. 5, wish detached. Let us, for example, represents the screw; b, hole for insersuppose the hole to be 6 feet deep and 2 tion of the communicating wire; c, the inches in diameter : cleanse it from dust conducting wire soldered to the bindingand moisture by passing a straw or oakum screw, and d, the screw. This contrir. wad several times through it, then lightly ance will be found of great service, bepour into the hole half the intended charge cause the cartridge can be attached to the of gunpowder; put a cartridge upon this conducting wire without loss of time, a and upon the cartridge pour the remain good metallic contact between them is der of the charge ; do not ram the powder ensured, and, if the binding screws are down, for the lighter it lies together the covered with cotton, varnish, or some better: the cartridge will thus be in the other insulating substance, there will be centre of the charge, and its long com no metallic contact between the separate municating wires will project 3 or 4 feet parts of the conducting wire; and this above the surface of the rock: the charge should be avoided, because it would open of powder and cartridge will fill about 8 a channel to divert the electric fuid from or 10 inches of the hole.

its proper course, The next operation is tamping. Thrust When the cartridge has been fastened a straw or oakum wad gently down the to the conducting wire of the battery, bore-hole until it is about 21 feet from unroll the lanyard, and carry the end to the surface; this done, there remains an a situation where the operator can stand empty space (that is to say, containing in perfect safety. Every one must now merely atmospheric air,) of about 24 feet retire from the rock, except one person, in depth between the wad and the gun whose office will be to ascertain that the

ADULTERATION OF ZINC.

359 safety-pin is in its place, and that the a tub of water, for the space of five or discs do not touch each other; lie is then ten minutes, or allow the plates to reto place the box in such a position, that main for a few minutes in the battery its end shall be towards the point from cells before the lanyard is pulled. which the lanyard is pulled, taking care Mr. Roberts gives, also, a description this and the double cord are clear; he of a method by which several charges then puts the frame of plates into the may be fired simultaneously, which is box,-a pair of plates into each cell, stated to have been found of great service being careful the fixed disc is towards at Skerry Vore Lighthouse, now erecting the place where he stands to pull the under the superintendance of Mr. Allan lanyard : the safety-pin must now be Stevenson; but for this, as for many taken out, and the operator retires to the other illustrative details, we must once place where the lanyard has already been more refer to the pamphlet itself, which laid; he then pulls the lanyard slowly does altogether great credit to the sciand steadily, without a jerking motion ; entific sagacity and practical skill of the moveable disc slides into contact with its author. the fixed disc, the electricity circulates, and the charge of powder is exploded. Fig. 6 shows all the apparatus in proper order for firing.

ADULTERATION OP ZINC. In this figure a a are the communica Sir,-I beg to direct public notice, ting wires of cartridge.

through your pages, to an important C. Cartridge.

fraud in the market of metals, which I p. Powder.

have recently discovered. Having had ocw. Straw or oakum wad.

casion for a considerable quantity of zinc, b b. Binding screw.

in as great a state of purity as I could x x. Conducting wire.

readily obtain it, for the purposes of my 1. Lanyard.

patented method of preventing the corm. Man to pull the lanyard.

rosion of iron, I purchased and emd. Battery.

ployed a quantity of waste clippings of 8. Vacant space.

sheet or patent zinc, obtained from a t. Tamping stuff.

zinc-worker's establishment, and stated The operator must after the explosion to consist principally of the best Belgian return to the battery, and remove the zinc. Circumstances occurred, during plates from the cells, coil up the lanyard, its use, to make me suspect this zinc detach the conducting wire from the cart contained some foreign metal; and on ridge communicating wires, and coil it up. submitting to analysis several different The communicating wires, most probably, specimens of the sheet zinc, just as rewill be found jammed between the frag ceived, I found them all to consist of ments of the rock, and there they must variable mixtures of lead and zinc. The remain until released by carrying away alloy of lead in some amounted to nearly the stones, when the wires will be found one-fourth the amount of the zinc, in uninjured :-if they are forcibly pulled one specimen, to one-third; and in the out from the fragments of rock, they greater number to between a sixth and a may be broken : the tin tube and fine fifth of the weight of zinc. My curiosity wire of the cartridge will be destroyed having been excited, I have since examined by the force of the explosion, but the several other specimens of sheet zinc, comrnunicating wires will serve for an and find most of them alloyed with lead. other cartridge. It sometimes happens This adulteration is obviously of the that, if the battery has not been used for most mischievous tendency, as regards some days, the papers that are round the the chief purposes to which sheet zinc is zinc become so dry, that time is required applied, promoting its oxidation, and infor the exciting solution to penetrate creasing its weight as a covering. through them to the zinc, and if an at The end in view in the adulteration is, tempt be made to work the battery be however, abundantly plain. Zinc is now fore the paper is well saturated with the about 491. per ton, in sheets; lead is liquid, it is probable no electricity will only 191. per ton : hence, a metal concirculate: to avoid such a disappoint- sisting of three parts zinc, and one part ment, either dip the frame of plates into lead-crude zinc being 371. per ton—will

only cost 321. 108. per ton, and can be its superior flexibility to that which is sold at 491. per ton, so that there is a pure. clear profit upon the adulteration of 51. As such frauds are of public importper ton; added to which, the base metal ance, and deserve exposure and repreis denser than zinc, and hence more hension, I have deemed this notice not weight must be sold to cover the same unsuited to your journal, and am, Sir, surface.

Your obedient servant, The adulterated zinc might be at once

ROBERT MALLET. recognized, by an experienced hand, by Dublin, April 24, 1842.

CENTRIFUGAL RAILWAY.

[From the Liverpool Courier, April 20.)

" Those who have visited the exhibition a man or a woman, is loaded with beary held some time since at the Mechanics' In weights, and despatched down a plane stitution, will probably recollect a small which reaches from the upper portion of the model railway in the room appropriated to gallery down to the orchestra; here, by its illustrations of hydrostatics, in which a tiny own impulse, it traverses a vertical circle of iron carriage was made to run down an in. 40 feet diameter, and the remaining force is clined plane, traverse an iron circle, and expended in carrying it forward up another ascend an inclined plane on the opposite slope, which reaches to the back of the stage. side. The curiosity attracted much atten The journey having been performed with tion, and those who did not fully compre fifty-six pound weights, a bucket of water, hend the principle of its operation were not &c., without either of the weights or a drop a little puzzled at the wonderful precision of liquid having been displaced ; a young with which the little vehicle performed its man, and subsequently a young lady, entered rapid journey. If the miniature railway the car, and each performed the apparently was deemed wonderful, we know not what perilous journey in perfect safety, and with. the public will now think of that exhibiting out the slightest inconvenience. The exhi. at the theatre. We had the pleasure of bition is exceedingly curious, and well worthy viewing it in its full operation on Friday the attention of the public.” last. A carriage, sufficiently large to hold

The invention noticed in the preceding extract, is the same, we believe, which our readers will find included in our List of Registered Designs for the last month, No. 1196, April 14, Messrs. Hutchinson, Higgins and others, proprietors. The principle of the thing is well known, though the application of it to enabling people to travel with their heels uppermost is, doubtless, new. The prefixed engravings are copies on a reduced scale of those depo. sited at the Registration Office,

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