—It is essential to the success of subaqueous blasting operations, that the explosive substance used should be suitable to the conditions under which it is to be applied. This is true of all blasting, but the requirement is frequently overlooked in some of the operations that have to be performed under water. In clearing a wreck for salvage purposes, gunpowder will in most cases act more effectually than either gun-cotton or dynamite. Also, in many cases, this compound will prove more suitable than the stronger substances in removing obstructions in water-courses. Examples of this will be given hereafter. But when a wreck has to be broken up, when piles, or objects of a similar character, have to be removed, or when rocks have to be blasted, the more violent compounds will be found to accomplish the purpose much more effectively. Generally, it may be stated that when it is required merely to remove objects, gunpowder is the most suitable explosive agent to employ; and that when it is required to break objects, the nitro-cotton and the nitro-glycerine compounds are the agents whose application is likely to be attended with the greatest degree of success.

When gunpowder is used, means must be adopted to protect it from the water, since a small proportion of moisture is sufficient to lessen, in a very important degree, the force developed, while a large proportion of moisture will destroy altogether its explosive properties. It is no easy matter, under the most favourable circumstances, to keep the water from the charge; but when the depth of water is considerable, it becomes very difficult to attain that object. The pressure of a considerable “head” will force the water through substances that, without a pressure, are sufficiently impervious. At ordinary depths, metal canisters are usually employed to contain gunpowder. Old oil-cans are as good as anything for this purpose. The fuse, whether safety or electric, is passed through the cork, and the latter is luted with some waterproofing composition. The best consists of:

Instead of metal canisters, indiarubber bags are sometimes used. These are, however, more expensive than the oil-cans, and, in many cases, they are scarcely more efficient or suitable. Small charges of gunpowder may be put into short lengths of indiarubber tubing, so as to form a kind of cartridge. But care must be taken to close the ends securely. The best way is to insert a cork, or if that cannot be obtained, a cylindrical piece of wood, and to tie the tubing to this very tightly with twine. The ends should then be dipped into the luting composition described above. Tubing suitable for this purpose is sold under the designation of “blasting tubes.” For large blasts, wooden casks are the most suitable receptacle for the charge. The casks should be well tarred, or, if the depth of water be great, laid over with pitch applied very hot. Great care must be taken to protect the aperture through which the safety fuse, or the wire of the electric fuse, passes.

In blasting under water with gunpowder, only the best and strongest qualities of that compound should be used. The extra strong mining powder of the Messrs. Curtis’s and Harvey’s, commercially known as the E.S.M. powder, is, of all, the most suitable. It is also highly conducive to success to detonate the charge. If the charge be not detonated, the enclosing vessel is ruptured when only a small proportion of the number of grains have been ignited, and, consequently, a large proportion of the charge is blown away into the water unburned. Were gunpowder in blasting charges always fired by a detonation, it would compare in its effects far more favourably with the nitro-cotton and the nitro-glycerine compounds than it does under the circumstances attending the common method of firing it.

When gun-cotton is used, the difficulty of waterproofing is much lessened, but not wholly removed. Inasmuch as this compound may be detonated in the wet state, it is not required to take those precautions which are necessary in the case of gunpowder. But, as we have pointed out in a former chapter, the detonation of wet gun-cotton is effected by means of that of a small quantity of the dry substance. This quantity, which is generally employed in the form of a cylinder, and is called the “priming,” must be thoroughly protected from the water. For this purpose, indiarubber tubing may be used, or, if the primer be large, indiarubber bags. When the pressure of the water is not great, a very efficient protective covering is obtained by dipping the primer into melted paraffine. Care should be taken to avoid raising the temperature of the paraffine above the degree required to melt it completely. The primer should be placed in contact with the charge, and it is desirable that the latter, when it can be conveniently made to do so, should surround the former.

Charges of gun-cotton for subaqueous blasts are usually made up of discs of a large diameter, or of slabs of a rectangular form. When, however, the charge has to be put into a bore-hole in rock, the common cartridge is employed.

Tonite, or cotton powder, is largely used in subaqueous blasting operations. This substance is always applied in a dry state, and requires, therefore, to be protected from the water. This protection it is however, not difficult to give. Being prepared for use in a very highly compressed state, it does not readily absorb moisture. In this state, it is enclosed in cartridges, which are subsequently dipped into melted paraffine. This is the form and preparation adopted for ordinary use. For application under water, especially when the depth is considerable, additional protection is given. For wreckage purposes, tonite may be obtained in convenient charges, made up in suitable forms, and sufficiently protected.

When dynamite is used, the conditions are similar to those prevailing in the case of gun-cotton. Since nitro-glycerine is unaffected by water, no necessity exists for protecting it from moisture. But when a charge of dynamite is immersed in water, and not contained in a bore-hole, the nitro-glycerine rapidly exudes. The writer once made several ineffectual attempts to explode a charge of dynamite at a depth of 70 fathoms beneath the surface. The cause of failure was found to be this exudation; for subsequent experiments showed that, though the dynamite was in the form of the ordinary parchment paper cartridges, and was contained in a stout canvas bag, the kieselguhr retained hardly a trace of nitro-glycerine when the charge reached the surface from that depth, after being rapidly lowered and raised. Hence it becomes necessary to enclose dynamite within some fairly impervious substance, to prevent the exudation of the nitro-glycerine. Waxed linen, or fine canvas overlaid with the composition already described, may be used as a protective covering; for blasts in deep water, indiarubber bags and tubing are employed. When the charge is contained in a bore-hole in rock, exudation can hardly occur, and therefore in such cases waterproofing is unnecessary.

For firing subaqueous blasts with safety fuse, only the guttapercha covered kinds are suitable. Great care must be taken to render the junction of the fuse and the detonator water-tight. A stronger detonator is required under water than in dry ground. Electric fuses offer not only a cheaper, but a far more certain and suitable means of firing in water. This means is now very generally employed. When tension currents are used, the insulation must be very good. In all cases, ample power should be possessed by the firing machine or battery.

The shattering class of explosives are very suitable for subaqueous-rock blasting. In many cases, their employment renders the boring of shot-holes unnecessary, an advantage of obviously great importance. When detached or projecting masses of rock have to be broken up, it is sufficient to place the charges upon them. Of course, when so applied, larger quantities of the explosive are required; but though the method is wasteful of explosive, it is very economical of labour and time. Even when large undetached masses of rock have to be removed, the same method may often be successfully followed. Suppose a level surface of rock, for example. A few heavy charges judiciously distributed over this surface will blow out craters of a considerable radius, and more or less fracture the rock in their immediate neighbourhood. A few other blasts then fired between these shattered points will break up the intervening solid portions. Sometimes the rock will be disintegrated to a considerable depth, and so broken up generally that it may be removed by dredging. By proceeding in this way, the whole of the rock may often be removed without any labour of boring.

But when the rock is too tough to be removed in this way, recourse must be had to boring, though even when boring is necessary, an occasional “loose” shot may be found to be very efficacious.

Boring under Water.

—The percussive drills, one of which, the Darlington, was described in a former chapter, may be used effectively under water. Compressed air is used as the motor fluid. The tripod stand, having its legs weighted to give it stability, is generally the most suitable support. These drills need the immediate attention of a diver. Sometimes the boring is carried on by hand from the deck of a vessel or from a raft provided for the purpose. The following description will give a general notion of the operations involved in subaqueous boring:—

The working vessel having been moored over the rock by means of mooring-lines attached to buoys placed about 50 yards from each quarter of the vessel, the diver descends and selects the most suitable position for the blast; he then signals, by a certain number of pulls upon his signal line, to have the drill and stand lowered to him. This being quickly done by means of a steam derrick, he guides the drill-stand to its place, and finally fixes it in position by means of its adjustable legs. This being done, he signals for air to commence drilling.

It has been found that the drill can be worked in a rapid current as well as in slack water. This allows the operations of drilling and blasting, by a proper division of time and labour, to be conducted in an extremely rapid tidal current, so that the principal work of the diver, in inserting charges for blasting and slinging stone, may be done near the periods of slack water, while the drilling may be advantageously continued during the period of rapid flow. In a rapid current, the stoppage of the drill for the purpose of “spooning out” the hole becomes unnecessary, as the motion of the drill works up the dÉbris to the mouth of the hole, whence it is sucked out and carried off by the current in a dark stream, like the smoke from the funnel of a locomotive. In a sluggish current, or during slack water, the hose of the air-pump is sometimes introduced, and air forced into the bore-hole to create a current of water, by which means the hole is cleared more thoroughly than by the most careful “spooning out.”

As soon as the hole is drilled to the required depth, the drill is stopped; the diver then fastens the derrick chain, which is lowered to him for the purpose, to the drill-stand, and signals to hoist away, whereupon the machine is quickly hoisted on deck.

After having examined the hole and cleared away any dÉbris remaining at the bottom, the diver comes to the surface, and taking in his hand the charge contained in a water-tight cartridge, and provided with its electric fuse to which a sufficient length of insulated wire is attached, returns with it, and inserts it into the drill hole, carefully pressing it to the bottom with a rod. The tamping, if any is used, is then inserted above the cartridge, and the diver comes up.

The working vessel having been quickly hauled by the mooring-lines to a safe distance by means of capstans worked, whenever practicable, by the steam-engine, the wires are attached to the machine, and at the signal “all ready” the charge is fired.

The working vessel is then hauled back to her position, and as soon as the water becomes sufficiently cleared of the dark muddy matter stirred up by the blast, to enable the diver to see in it, he descends and examines the result.

If the blast has been effective, he signals for the stone chains to be lowered to him; which being done, he proceeds to sling the large pieces of broken rock, one after another, as they are hoisted up and deposited on deck. All the pieces large enough to sling having been thus removed, he signals for the tub and shovel, and upon their being lowered to him, proceeds to shovel into the tub the small fragments, and to have them hoisted up and piled on deck, until the surface of the rock is sufficiently cleared to place the drill for a new blast.

Submarine Rocks.

—The following brief account of the removal of the “Tower” and the “Corwin” Rocks from the Narrows, at the entrance of Boston Harbour, U.S., from the pen of J. G. Foster, is instructive as illustrating the method of procedure in submarine blasting, and as showing the unfitness, for work of that character, of the slow-burning explosives:—

“Tower Rock,” being the smaller of the two, was selected as the one to be first removed. Its horizontal dimensions being only 50 by 26 feet, it was estimated that one large central charge surrounded by five or six others, all in large and deep drill-holes, would be able to rend the rock into pieces.

The working vessel, the sloop “Hamilton,” of 70 tons, was moored over this rock on the 30th of July, 1867, and the new submarine drilling machine, designed for this work, by Mr. Townsend, the contractor, was placed in position and tried.

Several imperfections were found at the first trial, which prevented its efficient working. While these were being remedied, a trial was made of surface blasts, placed in and around the rock in the positions most favourable to their action. These proved to be entirely without effect. No seams or breaks were made by them in the smooth surface of the rock.

As soon as the submarine drilling machine was perfected, it was put in operation, and successfully worked. The central and the surrounding holes were drilled to depths varying from 2 to 8 feet, each hole being 3¹/₂ inches in diameter. These were well charged with black blasting powder, and tamped with sand. In some holes, the charges produced no visible effect, the tamping being blown out like the charge from a cannon. In others, a crater was formed, but with a radius only about one-half the line of least resistance. The holes that were intact were then deepened, and new ones drilled; these were charged with Dupont’s sporting powder. The result was much better, but not what was desired. The pressure of the water, from 23 to 33 feet in depth, seemed to diminish largely the ordinary explosive effect of gunpowder upon rock, as seen in blasts in the open air.

Trial was then made of the patent safety blasting powder, manufactured by the Oriental Company of Boston, the proportions of the ingredients having been modified to increase its strength for this especial use. This produced the desired effect. The rock was rent in pieces; and by drilling additional holes and continuing large charges of the powder, the rock was finally reduced to the required depth.

To smooth off its upper surface and break down the sharp projecting points, large surface charges of sporting powder were employed. These accomplished the result to a limited extent, but not completely. A large 15-inch shell was then placed in a crevice near the centre of the rock and fired. Its explosion swept the rock completely, breaking down and levelling the projecting points.

The work upon this rock occupied eight weeks. In that time, 80 tons of stone had been blasted out, hoisted up, and deposited on shore, attaining the required depth of 23 feet at mean low water. About 70 tons of small fragments were suffered to remain on the bottom around the rock, where they had been thrown by the blasts, and where they could do no harm.

The cost per ton of the quantity hoisted up and deposited on shore was 64·93 dollars, no account being taken of the quantity blown, in small fragments, into deep water.

“Tower Rock” having been entirely removed to the required depth, the moorings of the working vessel were at once removed to “Corwin Rock,” and work commenced upon it on the 1st of October, 1867. This rock was found to be much more difficult to blast, on account of its extremely tortuous lamination, its great toughness, and the presence of a great number of iron pyrites.

Surface blasts were also tried upon this rock at the outset, in hopes that, by being placed in the most favourable positions between the sharp ridges of the rock, they might break them down. These, however, like those upon Tower Rock, entirely failed to produce any noticeable effect, even when they contained four and five hundred pounds of the best sporting powder. The drilling machine was therefore called into requisition as before, and used continuously till the completion of the work.

On account of the extent of this rock, a different plan of operations for its removal was adopted. One side of the rock most favourable for blasting was selected, and a row of holes drilled parallel to the edge, and at a distance from it equal to the depth of the holes, which was taken to extend 1 foot below the required level, 23 feet at mean low tide. After blasting out these holes, a new line of holes was drilled parallel to the former line, or to the “face” left by the blasts, and these also were blasted out; then a third line, and so on, progressing regularly across the rock, continually blasting it off in parallel blocks, extending downward a little below the depth required.

The advantages of this mode of operation were that it enabled the blasts to act laterally, in which direction they were the most powerful; and the rock was left, after each series of blasts, with a nearly vertical side, or “face,” in which the presence of seams could be more readily detected, and the character of the strata observed, so that the most favourable positions could be selected for the next blasts.

Sometimes the craters, following the strata, ran under, or left an overhanging “face,” in which case a large charge placed under its projecting edge, usually had the effect of throwing off the overhanging portion, and sometimes of dislodging large masses.

After the rock had been in this way blasted entirely across, and to the general depth required, a careful survey was made, the soundings being taken in lines from 5 to 10 feet apart, and at right angles to each other, the lower end of the sounding pole being placed by the diver alternately upon the highest and the lowest points.

This survey showed that although more than the required depth had been generally attained, yet many points projected above this level by distances varying from 2 to 14 inches.

To remove these, large surface charges were again tried, but with the same ineffective result. Their only effect was to pile up the sand and small fragments of stone into irregular windrows on the surface of the rock. Small holes had, therefore, to be drilled at each of these points to blast them off. This occupied much more time than could reasonably have been expected; so that it was not until two months’ labour had been expended, that all the points were finally reduced to the required level.

Obstructions in Water-courses.

—The removal of obstructions from water-courses often leads to much subaqueous blasting. Trees that have fallen into the stream are most effectively broken up by charges of gunpowder fired by a detonation. The success of the operation will, however, be greatly dependent upon the judicious placing of the charges. Brickwork may also be very effectively dealt with by charges of gunpowder. But stone masonry and blocks of rock may be more effectively broken up by gun-cotton, tonite, or dynamite. For work of this character, electrical firing offers great advantages, for, besides its convenience, it allows of several charges being exploded simultaneously, a condition that is always favourable, and in many cases essential, to success.

The following highly interesting and instructive account of the removal by blasting of some obstructions in certain rivers in India is given by Lieut. A. O. Green, R.E.

He, in company with some assistants, left Calcutta for Maldah on the 8th of April, 1874, where they commenced work on the following day upon the wreck of a large county boat, which lay on the top of a tree in mid-stream, as shown in Fig. 51. Soundings were taken over and around this tree, which was found to be about 3 feet 6 inches in diameter at its base. The gunpowder intended to be used in these operations not having arrived, three 5-lb. charges of gun-cotton were made up; it was thought that under the 15-feet head of water, these would have been sufficient to break the tree in half. The gun-cotton was in the form of compressed discs, 2¹/₂ inches in diameter, and 2 inches thick, each disc weighing about 5 ounces. These discs were filled into a tin cylinder to within about 4 inches of the top. An electric fuse, with wires attached, having been securely pushed into the hole in the centre of the top disc, the empty space above was filled up, with first a layer of sawdust, and then a layer of plastic clay, well rammed. The whole was then painted over, and the upper end tied up in a covering of waxed cloth, the holes through which the fuse wires passed being carefully luted. The charge, thus made up, is shown in section in Fig. 52. It was fired by means of a dynamo-electric machine.

The first charge produced but little effect; a second failed from the case not being water-tight; a third charge was more effective, as it lifted the tree and the boat partially out of the water. The positions of these gun-cotton charges are indicated by circles on the figure. The next day, two charges of gunpowder, of about 70 lb. each, were placed under the boat, these charges being lashed on to the snag by the divers. These charges consisted simply of common oil-tins, carefully cleaned and painted over with red-lead paint. The bunghole was closed by a wooden plug, bored through to allow the fuse wires to pass. This plug, after being inserted, was coated over with a waterproofing compound. The effect of the two charges was to completely demolish the boat. Another charge of 50 lb. removed the tree underneath. The positions of these gunpowder charges are indicated by squares in Fig. 51.

The next obstruction met with was a sand bank caused by a boat which had broken in half and then sunk. The sand nearly covered the boat, so that there was little else to operate upon. A charge of 80 lb. (one large charge being considered preferable to two or three small ones in getting rid of the sand), placed close to the part of the boat that was visible, made a considerable crater, and a second charge of 80 lb. was placed in a much more favourable position, as nearly all the boat was removed except portions of the bow and stern, which required two separate charges of 50 lb. each before they disappeared. In half an hour, the whole of the sand bank had been washed away by the stream, and there was from 3 to 4 feet of water over the spot where before the sand was high and dry out of the water. The removal of this obstruction was dangerous, owing to the nearness of the boat to the surface, the consequent small resistance offered to the projection of its pieces through the air, and the largeness of the charges used. Had, however, small charges been used, it is more than probable that the small craters made by them would have become too quickly filled up again to have been of any good in facilitating the placing in position of subsequent ones.

The following day, a large mango tree, about 4 feet 6 inches in diameter, was destroyed by two 50-lb. charges, which broke it up into three pieces, easily removable ashore.

A few days later, a large trunk of a tree, about 3 feet in diameter, was removed with two 50-lb. charges; but the depth of water over it was so small that a large portion of the trunk was thrown a considerable distance on shore. The next day a large tree which had formed a sand bank was very successfully removed by a charge of 50 lb. placed among the roots, it being considered that a smaller charge than 50 lb. would not have effected the purpose. Opposite to KÁsimpore, a boat was removed with a charge of 50 lb. placed in the centre up-stream, which entirely demolished it, the pieces being all dragged ashore. At MootyÁ, a large cotton tree, the wood of which is extremely tough, was found with many large branches projecting out of the water. A charge of 70 lb. tied under the tree at the springing of the branches effectually broke it up, and the pieces were all hauled to land. Three miles farther down the river, an attempt was made to destroy another large cotton tree with a similar charge, but it only broke it into three pieces, and two more charges of 50 lb. each were necessary to clear it away effectually. This tree was, if anything, slightly larger than the last, i. e. from 3 to 4 feet in diameter, and there was less water over it.

Farther on, the party came across a collection of three or four trees, with their branches interlaced, lying on a sand bank near Alumpore DÁldah; these were sufficiently broken up by a 70-lb. charge to make them easy of removal by coolie labour. Opposite to the village, another awkward snag, in the shape of a large tree sticking up in 30 feet of water, was destroyed by tying a 70-lb. charge at its base. A charge of 50 lb. of powder under this head of water, or even a smaller amount, might have been sufficient, but as the work had to be done quickly, not much account was taken of a few pounds of powder more or less, provided the object was attained. At Gomashtapore, a large tree, branches and all, was found in 25 feet of water, lying in the channel under the bank. The current here was considerable, and some difficulty was experienced in placing the charges. One charge of 70 lb. broke the tree in half; another of 50 lb. at the springing of the branches broke them up; and another of the same weight got rid of the roots. Below Gomashtapore, a large mango tree was demolished with 60 lb. of powder. A short distance farther on, a bad bamboo snag was met with. These bamboo snags, which were merely the roots of the bamboos with perhaps a dozen or so whole ones left, gave much trouble. Fig. 53 gives an idea of what these snags are like. It was found impossible to place a charge underneath this one, so an opening was prized between the bamboos, and a charge of 70 lb. rammed down pretty well into the middle. This cleared the whole of it away and opened the channel.

At Chandpore, at a re-entering angle of the river and in a place peculiarly dangerous to navigation during the rains, was an enormous banyan tree (Ficus Indica), the main trunk of which, to judge from the branches, must have been at least from 12 to 15 feet in diameter. An approximate measurement was made with a pole, but any such measurement can only have been a very rough one.

The trunk was lying in deep water, but the branches, more like an accumulation of large trees, were lying stretched out for a considerable distance over the bank, covering an area of more than 80 square feet. A charge of 200 lb. of powder was made up in an indiarubber bag, and placed by the divers in about 28 feet of water, well under the trunk of the tree. The effect of this was to split the trunk up into several pieces, each of which subsequently required separate removal. A 70-lb. charge was next fired under two of the largest pieces in 18 feet of water, and this broke them up completely. Having now run out of all the cases for powder, three charges of gun-cotton, similar to the first, were made up, and fired separately, each placed under a good thick branch, about 8 feet in girth. The effect of all three was prodigious; seemingly greater than that of the 70 lb. of gunpowder. As there were no more cases left, and time was precious, some common earthenware ghurrahs were obtained from the village as a makeshift. These held about 20 lb. of powder; the fuse was placed in the centre in a disc of gun-cotton, and the neck was closed up with damp earth, white-lead paint, &c., just in the same way as the gun-cotton charges had been. A rope for lashing them to the obstacle was securely fastened round the neck, and the fuse wires were tied under, this lashing, leaving a small loop towards the fuse free, so as to avoid any chance of a strain being brought on the fuse in lowering the charge. Figs. 54 and 55 show the arrangement of this charge. The first one tried had but little effect when placed under a branch of the tree in deep water, and it was accordingly determined to wait for cases from Calcutta; but after waiting five days without their appearing, three more of these charges were tried, and this time with very excellent results. They were indeed so satisfactory, that the same evening four more were made up and fired. The first under a mango tree a little farther down the river. This broke it in half, throwing one part high and dry on shore, and the other into deep water. The other three were fired under the remaining branches of the banyan tree with very good effect, cutting them away.

It is more than probable, observes Lieut. Green, that the good results obtained with all these ghurrah charges were entirely due to the gun-cotton disc inside causing the gunpowder itself to detonate, so that the thinness of the envelope was of little moment in determining the force of the explosion.

The tin cases having arrived, the rest of the powder was made up into five charges of 48 lb. and three ghurrah charges of 20 lb each. About four miles farther down the river, there was an old peepul tree lying in mid-channel, with several of the branches above water. Two tins, one placed under the springing of the branches and the other under the roots, blew away the lower branches on which the tree was resting, and it sank slightly in the water. A ghurrah was next fired under the trunk with splendid results, the tree disappearing entirely except one branch, which required another small charge to remove it. The trunk of this tree was nearly 8 feet in diameter, but of soft stringy wood.

On returning to camp, a small charge of 2 lb. of gun-cotton was made up in a section of bamboo, and used against the banyan tree with very good effect, and a ghurrah charge demolished the last branch but one. The next day 1¹/₂ lb. of gun-cotton in a piece of bamboo finished the last of this enormous tree.

After clearing away several more trees, the foundations of an old factory, which had slipped into the stream, were removed by introducing two charges of 1¹/₂ lb. of gun-cotton, in the ends of two bamboos, well into the crevices of the masonry under the water.

Another obstruction consisted of a row of old piles, about 15 inches square, stretching across the river below the surface of the water. Six of the most dangerous of these were removed from the dry season channel with ghurrah charges tied to the foot of the piles.

An old well that had fallen bodily into the water was afterwards met with. The position of this well is shown in Fig. 56. A charge of 4 lb. of gun-cotton completely destroyed it.

Near Azimgunge, the trunk of a very large peepul tree was found sunk in deep water. It was so large that it was thought necessary to place a 100-lb. charge underneath it; this charge broke it up completely, but two small charges of 20 lb. each were subsequently required to remove the pieces.

Later on, a well, similar to the one previously destroyed, was met with. The brickwork was remarkably good and about 3 feet thick, and the mortar was excellent. One charge of 4 lb. of gun-cotton broke it up into large pieces; but it took another similar charge, and two charges of 20 lb. of gunpowder to destroy it completely. On the same day, two trees were removed with ghurrah charges, which had been used throughout, for small charges, with unvarying success.

At a place called Farrashdangah, there was a very bad obstruction in the river, caused by the remains of an old bathing ghat and bridge having been cut out from the bank by the water getting underneath the masonry. Both were projecting about 3 feet above the water, and in the rainy season they formed the centre of a very nasty and dangerous whirlpool, in which many boats had, according to the Executive Engineer of the Nuddea Rivers Division, been lost. There was an immense mass of masonry, but no means of getting a charge placed underneath it; so a charge of 100 lb. of powder was placed close alongside it in about 15 feet of water. This shunted the mass bodily over and underneath the water. Two 50-lb. charges were next placed underneath the mass, and these shattered it all up, except one piece, which was got rid of with a fourth charge of 20 lb. placed well underneath it. The Executive Engineer wishing that the wing-wall of the bridge, which was on dry land during the dry season, might be removed as well, a small hole was made at the foot of the visible portion of the brickwork, and a charge of 2 lb. of gun-cotton was introduced into this, and fired with only a tolerable effect, the brickwork being cracked for a distance of 3 or 4 feet from the centre of the charge. A hole was next dug down about 5 feet at one side of the wing-wall, and a charge of 4 lb. of gun-cotton well tamped was fired. The tamping was blown out, and the wall foundations cracked a good deal. The excavation was now deepened to 6 feet, and a hole made under the brickwork big enough to contain a 100-lb. charge. It was then well tamped up and fired. Its effect was excellent. All the brickwork of the wing-wall was got rid of, and a crater about 30 feet in width at the top blown out in the point of the bank that was required to be removed, and which was one of the chief causes of the whirlpool, so that the next rise of the river was sure to carry it all away. The following day an old pucka ghat opposite to Berhampore was entirely broken up with three 20-lb. charges, and an enormous quantity of old bricks were thrown into the river.

The last operation undertaken consisted in the blowing up of a very large ghat opposite to the NawÁb of MoorshedabÁd’s palaces. The river during successive rains had cut into and underneath the steps of the ghat, bringing down large masses of it into the river, where they formed most dangerous obstacles to navigation. The work was necessarily carried out in a very rough way, for want of the proper tools. Deep excavations were made under the three largest masses of masonry, at about 25 feet apart, and into these were introduced three 50-lb. and one 20-lb. charges of powder. These charges were well tamped, connected up in divided circuit, and fired simultaneously. All the masonry was broken up completely, so as to be easily removable afterwards by coolie labour, which was all that was required.

The conclusions to be drawn from the foregoing notes are, that large trees lying in shallow water require charges of 50 lb. of gunpowder and upwards for their effectual removal; but that where there is plenty of water, and the trees are not very large, 20 lb. is sufficient.

For these small charges, it has been seen that the common earthenware ghurrah answers admirably, and under similar circumstances it would undoubtedly be advantageous to use them, as they are inexpensive, and obtainable in nearly every Indian village.

The charges used might, in many cases, at first have been no doubt made smaller with advantage, both for safety and economy; but as speed was the great object, these were not so much thought of.

For the removal of masonry under water, it is not necessary to place the charge underneath the mass, which is often impossible; a large charge alongside it being generally quite sufficient to break it up pretty effectually where there is sufficient head of water. Smaller charges can of course be easily used afterwards, whenever required, and for these small charges, gun-cotton is very effective, as it can be easily introduced, in the end of a bamboo, into holes and crevices where it would be impossible to get any but the smallest charges of gunpowder.

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