178 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAl.. 



[Mav, 



(i. It follows necessarily from what lias i)een said above, that the combined 

 efliCts of the instantaneous ignition of the gunpowder, the absence of all 

 vent-holes, and the expansion of the enclosed column ol atmospheric air must 

 cause a much greater effect than the explosion of the powder alone in the 

 common system can produce, and consequently that a great economy in the 

 article of gunpowder must result. This is a far more important item in the 

 ( xpensc of quarrying and rock oxoavation than is generally imagined by those 

 who arc unacquainted with such works. In the excavation for the Philadelphia 

 Water Works, for example, nearly 3000^ were expended in gunpowder, and 

 at the rock-cutting for the new approach to Kdinburgli, !>y ihe Calton Hill, 

 1000/. was spent in this item alone. In granire quarries the powder for a 

 sin'^le shot oflcn costs 3/. If the method of IMr. Roberts produces a saving 

 of about two-thirds of the quantity of gunpowder required for blasting, as 

 would appear from the experiments which were made on Tuesday, some idea 

 may be formed of the great economy which would follow on the adoption of 

 the new system. 



7. The system of Mr. Roberts makes the simultaneous firing of several 

 blasts easily practised : and in many situations where the removal of the [nen 

 to a place of s.ifcty is difficult, this is an important advantage. 



The following details of the experiments made on Tuesday, by Mr. Roberts', 

 aie chiefly taken from the notes made ^by Mr. Iiirerarity, of the Madras 

 Kns:ineers. 



No. I. 15oro of the hole, t*^ inches ; depth, 3 feet; powder used, 2 lbs.; 

 column of air left in t!ie bore, only 3 inches in lieiglit ; line of least resistance, 

 18 inches; the cftect was good; the rock was much splintered, and some 

 fragments were thrown into the air. 



No. 2. Bore of hole, 2^ inches; depth ofliolc, 8 feet; half the usual 

 chaige of powder used ; column ofair left, 2 feet in height ; effect enormous ; 

 immense mass moved ; few fragments thrown into the air ; deep rents all 

 round, and large masses loosened. 



No. 3. Bore of hole, ^l inches ; depth 6 feet ; two-tliirds of the usual 

 charge of powder: column of air left 13 inches in height ; few fragments 

 thrown into the air; but large masses loosened. 



No. 4. Dimensions of hole, same as the last ; charge of powder less than 

 one-half the usual quantity ; column ofair left, •> feet in height; etl'ect very 

 good indeed ; muiii rock looscnefl ; no fragments thrown into the air. 



No. 5. 15oie of Iiolc, 2^ inches ; charge of powder, two- thirds of the com- 

 mon charge ; column of air left, two feet in height ; effect excellent ; about 

 300 tons of rock supposed to be torn away ; much rock loosened, and deep 

 rents observable ; no fragments thrown up. 



Nos. () iiud 7. No account of bore-hole taken ; powder, one quarter of 

 the usual charge ; etVect of both was good. 



No, 8. Kxperimcnt under water. In this experiment, 5 lbs. of powder 

 were put into a bladder and siuik to the depth of ten feet imder the surface of 

 the water, in a deserted ([uarry, west of ("raiglelih. The string was drawn, 

 and the effect was instantaneous ; a dull red globe of light, caused by the 

 explosion of the powder under water, was observed, and immediately there 

 followed a considerable shock which was sensibly felt on tlie margin of the 

 pool, at the distance of about 100 yards from the explosion; a mass of water, 

 about 10 feet in diameter and '■J feet in height, shaped like a flat dome, rose 

 above the surface of the j»ool, and immediately alter it disappeared, the mud 

 and biu'ned powder boiled up from below like a cauldron. 



The Directors of the ilighland Society in attendance, and all present 

 W(jic highly pleaded with the complete success of the experiments. 



EXFEKIMENTAL SUBTERRANEOUS AND SUDAQUKOUS LXPLOSluNS AX CHATHAM 

 BY THE VOLTAIC BATTERY, 



From Ihe Times of April 9, 1839. 



For several months past the Royal Engineers at Chatham, under Colonel 

 P^s' y, have been trying experiments in firing gunpowder by the voltaic 

 bitie:v, chiefly under water; and, afcer many vicissitudes of partial success 

 a d of failure, they have at last succeeded in bringing this process to as much 

 perfe Don as it seems capable of — that is, to as much certainty as the former 

 i.icihod*! ol tiring mines in dry soil. They have repeatedly fired gunpowder 

 at the disTasice of oOO feet, with their conducting wires either buried under 

 -_r,>und or led entirely under the water, excepting a few feet connected with 

 Uie iltery, wliich in their subaqueous cxploiiions was in a boat on the Med- 

 way, the powder being lodged at the bottom of that river. In their subter- 

 raneous explosion they blew up a field-work, and in one of their subaqueous 

 experiments they blew to pieces a vessel representing a wreck, the fragments 

 of which being of fir timber came up to the surface of the Medway imme- 

 diately after the column of water thrown up by the explosion. On Saturday 

 last they ap])lied their voltaic battery to the blasting of rock under water. 

 Two very large and heavy pieces of hard sandstone were each prepared with a 

 bole three incUts in diameter by a borer, after which a charge of three-quarters 

 of a pound of powder was put into eacli, and the upj>er part of the hole was 

 tamped by pouring in small fragments of broken stone round a cone fixed 

 over each charge, in a new and ingenious manner, first suggested by Mr. 

 Howe, clerk of the Morks of the Hoyal Engineer Establif-hment, more than 

 five years ago, which does not seem inferior in resistance to \.\x^ common 

 mode of tanqiing, but is much safer and far more expeditious. The con- 

 ilucting wires were led from each charge to the battery, which was placed on 

 Ihe gun-whari", whilst the stones thus prepared and loaded were lowered 

 down froiu a crane to the bottom of the river opposite, where the water was 

 fourteen i eel deep at the time. The iiist stone, being of a compact form. 



was blown to pieces, and the rope sling by which it had been lowered, and 

 wliich had not been removed, was broken. The second stone, being of a 

 more irregular shape, and much thinner, so that tliere was not sulhcient 

 resistance above and below the charge, was brought up by tlie crane after the 

 explosion, which had only blown out the solid part of the stone below the 

 bottom of the hole, apparently without injuring any other part of it. Another 

 charge was therefore placed in the same hole, which was tamped both above 

 and below in the mode before described, and the stone was tlien again let 

 down to the bottom of the river, and after firing this second charge, on being 

 hauled up by the crane it was found to have been broken into three part-, 

 one of which did not reach the surface, whilst the other two, being still held 

 together by the slings, after being raised nearly to the level of the wharf, 

 separated from each other, and fell to the bottom. One of these charges was 

 contained iu a tin cylinder fitted to the size of the hole, the two others in 

 canvass bags of the same form covered with waterproof composition. These 

 last experiments, which like several of the former, were witnessed by a great 

 number of spectators, chiefly military, have i)roved that the volt^iic battery 

 may succeed for blasting rock under water, as well as for blowing wrecks to 

 pieces, and in the former supposition the holes in the rock would be formed 

 and the charges placed by means of the diving-bell. 



The results of this course of experiments may be of great importance, es- 

 pecially for defensive military mines, because the voltaic battery affords the 

 only possible means of flring several such mines, not only instantaneously but 

 simultaneously, and at the very moment when an enemy's coluaui advancing 

 to the assault is over the spot where these mines have been prepared ; whereas 

 by the common mode of firing military mines, by a piece of portfire or slow 

 match connected to a powder hose, there can he no certainty of their taking 

 efl'ect at the precise moment required, so that the enemy's troops might either 

 have passed over, or not yet reached the spot, at the period of explosion ; and 

 the simultaneous explosions of conjunct mines by this method is out of the 

 (juestion, for no two pieces of portfire or powder hoses, though cut to the same 

 length, were ever known to bum exactly alike. For subaqueous explosions 

 the superiority of the voltaic battery is still more striking — so much so, that 

 Colonel Pasley has repeatedly declared, that if he had been possessed of the 

 same voltaic apparatus, and had known how to use it last year in his opera- 

 tions in the Thames, it would have saved a great deal of trouble and ex- 

 pense. 



Nothing can appear easier than to fire gunpowder under water by the vol- 

 taic battery, as exhibited in a lecture-room or scientific institu lion, but the 

 mode usually adopted on such occasions, of passing the conducting w ires into 

 the charge through a cork coated with sealing-wax, and of insulating the re- 

 maining length of each wire by enclosing it in small India-rubber lubes, 

 is inadequate and inexpedient, for practical purposes in a rapid tideway 

 and in deep water. In Colonel Pasley's experiments at Chatham, corks 

 and sealing-wax were rtjected, the former as being too weak, the latter 

 ftom being liable to crack, and India-rubber or caoutchouc was also re- 

 jected, as being far too expensive; instead of which a composition of pitch, 

 softened by beeswax or tallow, was adopted, the remarkable ctliciency of 

 which was proved by keeping one of those experimental charges leu days 

 under water before it was fired, when the powder was still perfectly 

 dry. Each pair of conducting wires used in these experiments was always 

 attached to a rope or line, previously saturated with boiling tar, to prevent 

 it from tearing asunder the soldered joints of the wires, by its alternate 

 contraction and expansion when wet and dry, an eflect which on one 

 occasion actually took place before the rope was so saturated. The two 

 wires and rope were bound together by tape and served round with hemp 

 yarn, and in this state they had the appearance of a single roi)e c;ipab!e of 

 being coiled and veereil out conveniently. One of the must impoi iiini points 

 necessary was to prevent all strain acting upon the conducting wires from 

 without, and thereby breaking the very small delicate platinum wire within 

 the charge, which, by interrupting the circuit, would render'explosion impos- 

 sible. To guard against this cause of failure in the shocks to which the 

 conducting wires may be exposed in a rapid tideway appeared at first u very 

 difficult task. 



The voltaic battery used was of Professor Daniell's improved construction, 

 which, from retaining its energy much longer than any former voltaic battery, 

 he has named the constant voltaic battery, and which Colonel Pasley found 

 to be much superior to the best of the former constructions, at least for the 

 peculiar purpose of firing gunpowder, either under ground or under water. 

 Sergeant- Major Jones, and the non-commissioned oflicers and privates who 

 hnve been employed in these experiments, are now as expert in the use of 

 this battery as can be desired, and, being artificers, they are able to make as 

 well as to use such batteries. 



Having described these recent interesting experiments of the engineers at 

 Chatham, we may add a brief historical notice oi' what has been done before. 

 No doubt small charges of gunpowder must have been fired by the voltaic 

 battery, as a matter of experiment and of curiosity, almost as soon as the first 

 rude battery of that description was invented, but the merit of having first 

 applied it to practical purposes is due to Dr. Ilarc, of Philadelphia, whose 

 proceedings were published some years ago in Silliman's Amencan. Jourvnl 

 tif Stic nee (vol. xxi. page 130), and more recently in a paper communicated 

 to the British Association in 1836, and published in vol. v., in the transac- 

 tions fur the sections of that year, page 45. Dr. Hare states that he used it in 

 blasting rock for the purposes of building, and that he has even lircd twelve 

 blasts simultaneously at the distance of 1 JO feet, by a powerful voltaic battery 

 of a very ingenious and peculiar construction, which be calls &calorimettr. 

 He says that the same process might be applied fur blasting under water, but 



