wire upon the different gases. After many unsuccessful experiments this decomposition was effected by means of the following apparatus: Fig. 53. A bent glass tube, open at one end, (fig. 53) was connected at its other end by a narrow neck, with a bulb into which the platinum wire passed, as represented in the figure. The whole tube was filled with water previously freed from air, and its open end immersed in a vessel of water. On applying a battery of two zinc-platinum cells, the air in the bulb was expanded and expelled so that the water entered it and then soon boiled, and at a certain period the wire became ignited in the vapor. "At this instant a tremulous motion was perceptible, and separate bubbles of the size of pin-heads ascended and collected in the bend of the tube. It was not a continuous evolution of gas as in electrolysis, but appeared to be a series of jerks; the water in returning through the narrow neck formed a natural valve, which cut off by an intermitting action portions of the atmosphere surrounding the wire." The collected gas was detonating gas. That this evolution of detonating gas can certainly not be attributed to electrolysis has been satisfactorily demonstrated by Grove. I give below the most important of his arguments. 1. A battery of two cups produces in distilled water, even under the most favorable conditions, a scarcely perceptible electrolysis. 2. The decomposition did not commence until the wire became ignited. 3. When the wire was divided no gas was evolved. Grove now endeavored to produce the decomposition of aqueous vapor in such a manner that the red hot platinum wire could only come in contact with the vapor. A glass tube, as in fig. 54, which Fig. 54. at its closed end had a curved platinum wire melted in, was filled with water which had been carefully freed from air by long boiling and the air pump; it was then inverted in a vessel of the same water, and a spirit lamp applied to its closed extremity until the upper half was filled with vapor, which therefore surrounded the platinum wire. The wire was then brought to full ignition. After the connexion was broken and the lamp removed, the water gradually ascended again, but a bubble of the size of a mustard seed remained in the tube, and detonated when touched by a lighted match at the surface of the water trough. The experiment was repeated, the wire being kept ignited for a longer time, but the gas could not be increased beyond a very limited quantity. The experiment just described was repeated and the gas bubble transferred to another tube, the wire was then again ignited in vapor, the bubble formed again removed, until a sufficient quantity of gas was collected for analysis, which required the labor of ten hours. This gas was now detonated in a eudiometer and left a residue of 0.35 of its original volume, which consisted of nitrogen. The experiment was repeated several times with the same result; sometimes a trace of oxygen was found in the residue. Here electrolysis was completely excluded; the wire was ignited in dry steam. When in the apparatus of fig. 55 the sparks of a large hydro-electric machine were passed between platinum points through the vapor, a small bubble of detonating gas was also formed. As in the previous experiments a whole day's work did not increase the bubble, but when it was transferred, another instantly formed. The gas similarly collected detonated and left a residue of 0.4 Fig. 55. of its original volume of nitrogen with a trace of oxygen. By an estimation, which could of course only be approximate, the detonating gas formed, was found to be about of the volume of the vapor. Grove, considered this evolution of detonating gas not to be a specific effect of electricity at all, but of heat alone, and indeed, succeeded also in decomposing aqueous vapor merely by heat without electricity. Omitting the less successful experiments, we shall at once proceed to those that gave very decisive results. With a constant battery of 30 zinc-platinum cells the end of a thick platinum wire was melted into a globule of the size of a pepper corn; between this and the carbon point of the negative pole the voltaic arc was taken until the gobule was again near its melting point. It was then rapidly plunged into water, freed from air, that was kept boiling by means of a spirit lamp, and into which a tube filled with the same water was inverted. Separate bubbles of gas rose into the tube. This process was repeated until a sufficient quantity of gas was collected, which, after explosion, once left a residue of 0.4; another time only 0.25 of the original volume, consisting, as usual, of nitrogen and traces of oxyen. The galvanic battery here served evidently only to bring the platinum to ignition. When melted and heated by means of the oxy-hydrogen blow-pipe, it acted exactly in the same manner. In this way more than cubic inch of detonating gas was obtained. The heated globule is evidently, when immersed in the water, immediately surrounded by a stratum of vapor, from which then the small quantity of detonating gas is developed. To obtain a continuous evolution of the mixed gases from water subjected to the action of heat alone, Grove constructed the apparatus Fig. 56. shown in fig. 56; a and b are tubes of silver 4 inches in length and 0.3 in diameter, connected by two platinum caps to a tube of a perforated platinum wire 0.125 inches diameter, the bore having the diameter of a large pin; a is closed at the extremity, and to the extremity of b is fitted, by means of a coiled strip of The whole apparatus is filled with water freed from air, and, after having expelled the air from a by heat, the end of the glass tube was immersed in a vessel of boiling water. Heat is now applied by a spirit lamp, first to b and then to a, until the whole boils; after this the flame of an oxy-hydrogen blowpipe is directed upon the middle part of the platinum tube c, and when this has obtained a high degree of ignition gas is evolved which, mixed with vapor, soon fills the whole apparatus, and escapes through the open end either into the open air or into a gas collector. bladder, the bent glass tube d. The gas thus obtained left, after its detonation, a residue of 0.3 of its volume, consisting of nitrogen and a trace of oxygen. That, in all these cases, the remnant consists of nitrogen is caused by the great difficulty or even impossibility of absolutely removing all the air from the water. This series of phenomena is very remarkable. While the detonating gas, under the influence of heat, is condensed to vapor of water, we have here exactly the opposite action, though to a very limited extent only. The elaboration of the more intimate conditions and relations of this decomposition of aqueous vapor, which might lead to an explanation of the phenomenon, we must leave to the future. When Grove says "that these experiments afford some promise of our being, at no distant period, able to produce mixed gases for purposes of illumination, &c., by simply boiling water and passing it through highly ignited platinum tubes, or by other methods," I cannot help expressing my doubts whether, even if the manufacture on a large scale should succeed, the detonating gas thus produced could give more light and heat than the fuel consumed in its formation. § 63. Application of galvanic ignition to blasting rocks.-It has for a long time been known that gunpowder can be ignited by the electric spark, as shown long ago by Franklin, and still repeated as one of the usual experiments in the lecture room. But, although blasting by means of frictional electricity is therefore possible, still there are too many difficulties in the way of the process to allow us to expect its introduction into practice. Hare was the first to employ the ignition of metallic wires by the galvanic current in blasting. But his apparatus was too complex and unsuited for every day use by common laborers, and, therefore never was used to a great extent.* In consequence of the many fatal accidents in mines and quarries, Roberts, of England, directed his attention to this subject. After many endeavors he succeeded in making the application of the galvanic current to blasting so simple that his process deserves general commendation. It was first described in the Mechanics' Magazine, May, 1842, p. 353.-(Dingler's Polytech. Journal, LXXXV, 275.) We shall be brief in this notice, as probably much that is contained in the article mentioned is well known. In order to avoid the necessity of arranging before each charge the fine iron wire between the conductors, Roberts invented cartridges, a number of which can always be prepared in advance. They are made in the following manner: two copper wires, each 10 feet long and 1 line thick, well covered with waxed cotton or woolen yarn, are placed side by side close together; at one end they are twisted together for about 6 inches, as represented in Fig. 57, and their extremities left to form a fork, a little over inch long, with its extremities inch apart; the ends of this fork are then laid bare, cleaned by filing, and the fine iron wire is stretched between them. The iron wire is wound around the extremities of the copper wires, and may then be soldered with tin. The iron igniting wire is, of course, destroyed by each explosion; to save the conducting copper wires they are firmly tied together with twine, as indicated in the figure, and then wound around with fine binding wire. The body of the cartridge is a tin tube, 3 inches in length and to 1 inch in width, soldered and perfectly water tight. (A glass tube might probably answer.) The fine iron or steel wire is placed at about the middle of the cylinder, and is kept in its place by means of a cork which closes the cylinder, and through which the twisted copper wires pass. It is best to cut this cork lengthwise, and after putting the wire between the two halves, to press them into the tube. But on account of the thickness of the conducting wires it will probably be found more convenient to make a groove in the cork for their reception. The cork being put in so that the fork is nowhere in contact with the sides of the tube, it is covered with a good cement. Roberts recommends a mixture of one part beeswax and two parts rosin. The tube is then to be filled through its open end with dry sporting powder, and closed by another cork, which must also be covered with the cement. Figure 58 represents the entire cartridge. the cartridge is placed in the hole. Fig. 57. Figure 59 shows how *Our author could not possibly have seen Dr. Hare's description of his apparatus when he wrote this sentence. The original notice (Am. Jour. Science and Arts, vol. 21, p. 139, 1832,) shows that Dr. Hare's apparatus was not complex, and that it was essentially the same as that here described as the contrivance of Roberts. G. C. S. After all dust and moisture are properly removed from it, one half of the intended charge is put into the hole, the cartridge is inserted Fig. 58. and the remaining gunpowder A wadding of straw or tow is Fig. 59. The two separate ends of the cartridge wires must now be brought into connexion by conducting wires with the battery 60 to 90 feet off. The conductors are also covered wires about one line in diameter, placed side by side. and kept close together by being wound over with twine throughout their whole length, with the exception of their extremities, where they are to be connected with the battery and with the cartridge wires. It is sometimes necessary that the person who has to ignite the charge should still be further off from the charge than the battery is, and for this purpose an arrangement must be made by which the circuit may be closed from a distance. Roberts contrived the following arrangement for this purpose: upon two opposite ends of the box which contains the battery two wooden posts are erected, connected above by a wooden rod of one inch in diameter. At one end a tin disk, A, fig. 60, three to four inches in diameter, is fastened, to which a wire is soldered conducting to one, say the positive pole of the battery. Another tin disk, B, is fastened to a tin tube, made to slide easily on the rod, and this is kept from A by a spiral spring. One end, D, of this spiral is connected with one of the conducting wires, while the other conducting wire leads to the negative pole of the battery. The disk B is therefore connected |
