Passing on to the more brilliant results obtainable from a powerful voltaic battery (of at least thirty pairs of Grove), the beautiful incandescence of platinum wire may first be noticed. If a wire of this metal is stretched between the brass standards of two ring stands, the length must be proportioned to the power of the battery; the adjustment can be made very conveniently by twisting the platinum wire on one ring stand, and then leaving the other end loose, the second ring stand may be brought nearer and nearer to the first, until the desired intensity of [Page 204] light from the incandescent wire is obtained. (Fig. 190.) If the wire is contained in a glass tube the cooling effect of currents of air is prevented, and a much greater length of wire can be made hot. [Illustration: Fig. 190. A A. Two ring stands with the battery wires B B (which should be a convenient length) attached. C. Platinum wire, fixed end. D. The other end held in one hand and shortened as the stand is moved by the other hand.] _Sixteenth Experiment._ With the same arrangement, a chain composed of alternate links of silver and platinum wire presents a very pretty effect, every alternate link of platinum being incandescent, whilst the silver, from its excellent conducting power, remains comparatively cool. _Seventeenth Experiment._ Fireworks or gunpowder, arranged in proper cases, are fired at a great distance from the voltaic battery by heating a thin iron or platinum wire contained within them by the passage of the electricity; and submarine and other explosions of gunpowder by the same agency have become a common engineering operation. (Fig. 191.) [Illustration: Fig. 191. A. A Gerb firework with two holes punctured, through which the bit of iron wire passes, and is wound round the battery wires tied to the outside of the case. C. A gut bladder containing the thin wire and powder for a miniature submarine explosion.] During the operation of blasting the hard marl rocks in the River Severn by Mr. Edwards, C.E., a number of holes were made side by side in the bed of the river, and cartridges formed of strong duck or canvas, tapered at the bottom, were filled with charges of powder from two to four pounds, according to the depth of the marl; thus, two pounds for four feet, three pounds for four feet six inches, and four pounds for five feet. Into the bag were conveyed the wires of the voltaic battery, or Bickford's fuse, and being then coated with pitch and tallow, and finally greased all over and dusted with whitening, they rarely failed, and were all fired simultaneously under water. The pitch and tallow first, and afterwards the simple tallow, effectually excluded the water from the gunpowder contained in the canvas bag. [Page 205] _Eighteenth Experiment._