184G.J 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



371 



bore hole wonUl be the centre, and its bottom the apex, so that four adjoin- 

 ing shots would leave between them a pyraraidical piece of marl, where the 

 powder would have produced little or no effect. By carrying the shot holes 

 lower than the bottom of the intended dredging, the apex only of this 

 pyramid was left to lie removed, and in practice this was found to form but 

 a small impediment (figs. 1 and 2). A second reason was, that if the re- 

 moval of the shoals should cause the level of the summer water to fall 

 lower than was e.'spected, the marl might still be found suiiicieutly broken, 

 to enable a greater depth to be obtained without further blasting. 



The cartridges, or charges, were formed of strong duck or canvas bags, 

 somewhat tapered at the bottom ; these were filled with the required charge 

 of powder, virying from 2 lb. to 4 lb., according to the depth of the marl ;* 

 the end of a cnii of Bickford's patent fuse was inserted to the centre of the 

 powder, and the neck of the bag was carefnily gathered up round the fuse, 

 and well tied with small twine. If the cartridge was small, it was then 

 dipped into melted pitch, which had about one-fourth of tallow melted with 

 it, or otherwise the melted pitch was ladled over it, till it was uniformly 

 coated; in this state, the cartridges were hung to drain and stiffen. When 

 hard, they were well rubbed over with tallow, and lastly powdered over with 

 dry whiting. The tallow, whilst it insured the stopping of any little 

 cracks in the pitch, facilitated the passage of the cartridge down the hole ; 

 the whiting also prevented the pitch from adhering to anything. It has 

 already been stated, that the powder was ignited by means of Bickford's 

 patent fuse; but as this material is never made in lengths exceeding 48 feet, 

 it was found expedient, in order to save waste, to use the whole coil, cutting 

 it off at the requisite length when absolutely in the hole, and using the 

 remainder in the same way till the whole was used up.f 



The charge was carefully pushed down into the hole hy a wooden ramrod 

 of suitable diameter, with the end rounded ; the same instrument was used 

 for ramming down the tamping. The material found to answer best for this 

 purpose was the small fragments of hard marl, separated hy the action of 

 the weather from the lofty escarpment at each of these shoals; this was 

 gradually filled into tlie holes, and rammed solidly, till the bore was full up 

 to the surface ; the timber dogs which held the pipes were then removed, 

 the pipes were loosened from the marl, ropes were attached to the pipes and 

 to the raft, or to some loose pieces of timber, and the shnts were fired. 

 Generally there was little external effect beyond the pipes being lifted a few 

 inches, though sometimes they would be blov,-u up several feet, and occa- 

 sionally the water would be forced up through the pipe to a height of 40 or 

 50 feet. All the gangs commenced their holes in the morning, and they 

 were generally all ready to fire at the same time, which was always done, as 

 it caused least interruption to the work. 



It was a rare occurrence for a shot to miss fire — probably not once in a 

 hundred shots ; the failure arising generally from a leak at the joint between 

 the fuse and the hag. If the leak was not very serious, the shots were often 

 saved by the following somewhat singular expedient. An iron bar, | inch 

 in diameter and of sufficient length, pointed at the end, was kept in readi- 

 ness, and when required the end was heated red hot, put quickly through 

 the water into the tamping, through which it was driven as rapidly as possi- 

 bly into the powder, which in nine cases out of ten it was still hot enough 

 to ignite. 



The result of the whole work being invisible, great care was necessary in 

 order to prevent mistakes and omissions. As each shot was ignited, a red 

 mark was laid against its corresponding stake upon the bank ; when it had 

 gone off, each shot was carefully examined with a steel chisel-pointed 

 searcher, to prove that the required effect had been produced to the deter- 

 mined depth ; when so found, the red mark was inserted into the top of the 

 stake, as a certificate of that shot having passed examination; the numbers 

 so certified were then transferred to a book kept for that purpose, and if a 

 shot was found ineffective, another was j)ut in the same place. 



To afford space for the workmen, every alternate hole was first made, and 

 afterwards those which had been left between them ; one line being com- 

 pleted, the whole line of raft was moved 6 feet outwards to the next line, 

 and so on till the required width was obtained. The whole estalihshment 

 was then dropped down the length of the rafts, and the process was repeated. 

 When the men had become used to the work, each gang would sometimes 

 get down four shots per day, to that with fifteen gangs sixty shots have been 

 fired per day. 



It may be objected to the use of the patent fuse, that the ignition of a 

 number of charges simultaneously by the galvanic battery would have pro- 

 duced better effect, at less cost, and in a more scientific manner. The author 

 commenced the work under a different impression, and subsequent experience 

 with the battery has not altered his opinion. When it is required to separate 

 a large stone from its bed in the quarry without breaking it, nothing can be 

 better than the numerous simultaneous discharges, which can only be ob- 

 tained by the use of the battery, but the object in this work, on the con- 

 trary, was to break the mass to pieces as much as possible, which it is con- 

 ceived would be more likely to be effected hy distinct discharges. 



Then as regards cost : the patent fuse No. 3, carriage included, cost -^ths 



* Tlie weigt\ts of powMer used for deptlis of 4 feet, 4 feet 6 incties, and 5 feet, were 

 respectively about 2 lb., 3 lb., aud 4 lb. 



t The short remaining ends, though useful for less depths, were of little value, from 

 the diilicu'ty of splicing them to^fther. This oper.ition. though troublesome, was re- 

 sorted to with success on one occasion ivJiiKt waiting the arrival of a parcel of t ise. On 

 returning the short ends to Messrs. Bickford they atlowed half the length of new fuse 

 in exchange, I 



of a penny per foot; if the average length is taken at lo feet, that is just 

 nine-pence per shot, a sum which would barely pay for making the arrange- 

 ment of wires necessary for the galvanic ignition. It was also foumi, from 

 the compressihle nature of the canvas cartridges, that the arrangement of the 

 wires was very liable to be disturbed, during the insertion of the cartridge 

 into the hole, or by the subsequent ramming of the tamping. After con- 

 siderable experience, therefore, aud the use of nearly 100,000 feet of the 

 patent fuse, the author feels that he is only doing an act of justice to the 

 M.-ssrs. Bickfords, in stating the perfect satisfaction which the use of their 

 ingeniously manufactured material has afforded him, iu the prosecution of 

 the work now described. 



There now only remains to be given the cost of the operation above de- 

 scribed. The first cost of the establishment or pl,;nt, sufficient for 6 months' 

 work, was £300. This includes the waste and use of timber, in the raft, 

 stages, booms, c^c, hire of barges, and cost of fitting them up for the work] 

 cost of pipes for boring, iron and steel for tools, deducting estimated value 

 when done with, sundry ironmongery, waste and loss of ropes and other small 

 stores. 



More than four thousand shots have already been fired, and in the six 

 months, at a low computation, six thousand will have been fired. This num- 

 ber gives just one shilling per shot, as the proportionate share per shot of 

 the cost of the plant ; this would of course be much less if the work was to 

 be continued. 



The cost of labour per shot varies from 2s. Gd. to 4s.; this sum, however, 

 must be understood to cover the wages of tfie whole establishment as under' 

 Superintenileut of the work. — Foreman and timekeeper. — Examiner of the 

 shots. — Maker of cartridge and two assistants. — Carpenter. — Blacksmith and 



hammerman. — Labourers, some at 3s.; majority at 2s. 6(/. and 2s. 9d. 



Watchman. — Thus the total cost per shot is as under : 



s. d. 

 Use of material . . . . . . ..10 



Labour, average . . . . ..33 



Pitched bag . . , . . . ..03 



3 lb. of powder, at Sjf/. .. .. ..14.!- 



15 feet of patent fuse .. .. ..0 9 



Pitch, tallow, twine, coals, &c., say .. .. 4i 



7 

 If, therefore, the shots are 6 feet ap.irt, and an average depth of 3 feet is 

 broken up, 4 cubic yards are prepared for dredging at the cost of one shot; 

 or the cost of the whole operation is Is. 9d. per cubic yard. Distances of 5 

 feet apart were used in some very hard shoals, and spaces of 7 feet were 

 tried in some that were softer than usual ; spaces of 6 feet apart, however 

 appeared to be generally sufhcient. ' 



ON THE CORROSION OF METALS. 



P,iper ijR. Adie, of Liverpool, read ut the Inslitution of Civil Engi- 

 neers. " 



This communication is intended to give an experimental proof of the 

 fact, that Wilier saturated with common salt, preserves to a great extent 

 the surface of the oxidizable metals from corrosion by the joint action of 

 air and water. From some trials upon metals placed beside water in 

 closed glass tubes, it was shown that water, or water containing a saline 

 solution, does not act as a corroding agent, without the aid of the oxyo-en 

 of our atmosphere. The details of some experiments, made to ascertain 

 the quantity of oxygen dissolved by water under different circumstances 

 showed that brine and some other saline solutions contain much less dis' 

 solved oxygen than sea or ordinary water, which was the fact that induced 

 the trial of salt water as a preserver of iron. The object of the last set of 

 experiments v^-as to determine by trial, the rates of corrosion of metals in 

 fresh water, sea water, and brine; the results of these show that sea water 

 corrodes the quickest, fresh water less rapidly, and brine very much slower 

 than either. 



Ore the rate of action of brine, sea and fresh water, in currodin". 



These experiments were made with weighed pieces of metal immersed 

 in the three solutions under examination. Those which are compared to 

 gether, were tried in every re.-pect under similar circumstances, as to wei<'ht 

 and surface of metal ; size and form of vessel ; quantity of water emnlovp°d • 

 light and temperature. I'^^t 



The experiments on zinc were made with that metal in connexion with a 

 piece of copper, so as to form a galvanic couple ; for zinc, when uncon 

 uected with a less oxidizable mdal, is soon covered with a crust of oxide 

 so that pieces, after a month's immersion in wafer, are found to be sli^htlv 

 heavier than at the beginning of the experiment. This is not the case when 

 a piece of silver or copper is in metallic connexion with zinc; for then the 

 white oxide of the metal is gradually precipitated to the bottom of the rnn 

 tain ing vessel. = i.uu- 



A plate of zinc, 1 superficial inch in area, immersed 



for 60 days in sea water . . . lost 1-0 grains. 



A similar experiment in fresh water . . 1-15 



A plate of zinc, 7 superficial inches in area, immersed 

 for 90 days in fresh water • . . 4-9 



48* 



