1839.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



177 



and Skenyvore; each one halfpenny per ton, if British, or Id. per ton if 

 foreign. By piissing tlirough the Canal there will be only two lights to pay, 

 viz. Tiirbot Ness and Lismore ; being a saving of 2d. per ton, if British, and 

 4d. Taton, if foreign. 



In case of war, and the English Channel being infested by steam privateers, 

 the caniil will afford a passage of comparative safety for the trade between the 

 West Indies or America, and the east coast of Gfeat Britain. 



1 have not said that the Caledonian Canal is, as a money account, ever to be 

 a profitable concern, but that it will be a useful public work ; that being 

 made, there appears to me no alternative but to tioish it; and (this granted) 

 that to finish it properly will be, even as a money account, the proper course to 

 adopt. The time, ho.vever, may come, and may not be very distant, when, 

 even as a money speculation, it will appear in a very different light from the 

 present ; this partly from the increase in the quantity of tonnage, and partly 

 from the rate. The act allows 'id. per ton per mile, the present charge is a 

 farthing ; to raise it without aftbrding increased facilities, would reduce the 

 trade, but with better accommodation ; the facts I have stated would justify an 

 addition to the rate. 



The Forth and Cli/dc Canal is a parallel canal, and in some degree a parallel 

 case, although comparatively small, the locks being only 20 feet wide, with a 

 depth of eight feet ; it is therefore suited only for small craft under 100 tons. 

 This canal was opened in 1777, and was at work for .30 years before it paid 

 any interest. The toils are charged not upon the tonnage of the vessels, but at 

 various rates upon goods. On referring to the table of tolls, I find that by far 

 the greatest number of articles is charged 2d. per ton per mile, which is the 

 liigl:e.st rate allowed by the Caledonian Canal Act, or eight times the present 

 rate charged upon the latter. The trade and profits of the Forth and Clyde 

 Canal are now such that the shares which were originally £100, exclusive of 

 accumulated interest, are now .-t'GOO in the market. The accumulated interest 

 upon the original share of £100, taken, I suppose, at compound interest, 

 amounts to four times the original sura, but still shows the canal to be a pro- 

 fitable investment. 



i\Ir. May has, at my request, prepared a table of the tonnage to and from 

 the eastern ports, to show the extent of trade, a portion of which he considers 

 would be likely to use the canal ; it is so great, that a small portion of it 

 would make the concern not only useful, but profitable. I dislike the appear- 

 ing to calculate profits, which is not my department, and ought always to be 

 received with caution, as a basis for any calculation. I would only remark, 

 that, at a halfpenny per ton, the rates upon 100 tons would amount to 

 £1'2 lOs.; and that 400 tons passing daily would produce a gross income of 

 £18,000 per annum, without any material increase of the present outgoings, 

 but rather the contrary, if the works be put in repair. 



The limit to the number of vessels passing is caused by the eight continuous 

 locks at Bannavie, near the west end of the canal, through the whole of which, 

 owing to their being no chamber or passing-place, a vessel must pass up or 

 down before another can enter in the opposite direction. This is a great delay 

 and evil ; its effects might partly be remedied by dividing the trade, the 

 ascending vessels one part of the day, the descending vessels the other part. 

 A more effectual, but more expensive remedy, as respects money and water, 

 would be making a siding or passing-place in the middle of the chain of locks. 

 As, however, with its present imperfections, the locks can pass more than four 

 times the trade I have named, 400 tons per day, I have not included in the 

 estipiate any thing for an alteration in these locks. 



Mr. Gladstone, whose long and extensive mercantile concerns and general 

 knowledge are well known, Iiaving applied to Mr. May to know if his vessel of 

 250 tons, bound for Liverpool, could be passed through the canal, was referred 

 to me by Mr. May. After a couferenco at his desire, I requested Mr. Glad, 

 stone to favour me with his opinion, wliich he has kindly done. His letter has 

 given me no reason to cluinge iht' f.iv.Mirahle opinion I certainly have of what 

 this canal is likely to be at a future period. It has never yet had a chance, and 

 I consider that all its bearings and prospects are completely altered by the 

 introduction of steam ; so that the evidence given previous to its formation, and 

 much less its working, since it was opened, has but little to do with the present 

 prospect. 



[The report concludes with some remarks on the state of the Crinan Canal 

 which we shall give in the next Journal. — Editor.] 



BLASTING BY THE AID OF GALVANISM. 



INTEntStlNO EXrEIUMliiM'S ON EL.VSIINO AT CR,VIGLEITU QLiRUY. 



(From the Edinburgh Advertiser.) 



On Tuesday, 26th of March last, a large party of gentlemen assembled in 

 Craigleith Quarry, to ^vitness some experiments on blasting by means of 

 galvanism, \vhich were made at the request of the Directors of the High- 

 land and Agricultural Society of Scotland by Martyn Roberts, Esq. 



It has long been known that the ignition of gimpowdcr can be very effec- 

 tually produced by the application of the electric fluid; but Mr. Roberts 

 has succeeded in producing an apparatus for this purpose, which is simple 

 in its structure, very portable, and wliich, above all, is easily managed, lie 

 has also, in the application of thi.s ajiparatus to blasting rucks, introduced 

 various luodificatioiis of its arrangements, and effected great improvements 

 in the mode of charging. 



The apparatus consists of a small trough, about a foot in length, and four 

 inches square on the end, and a battery containing ten pairs of plates. 

 Along the battery runs a bar upon which a tin (Use slides freely. This disc, 

 when drawn to the end of the bar, touches another disc, and thus completes 

 the ttfiuitxioJi b6t^YeeI^ tlic opposite poles el' Uie battery. To prevent acci- 



dents, the sliding disc is kept in the middle of the bar by means of a spring 

 of coiled wire ; and it is impossible to put the battery in action nllhough 

 sunk in the trough without shifting the plate along tlie bar to the opposite 

 end of the trough. The copper wires which convey tlie electric fluid to the 

 gunpowder are kept separate during their whole course by a sheath of cot- 

 ton thread, which is wrapped closely round them in the same nia)]ner as in 

 the strings of a guitar, in- as in the wm: which stiflens the rim of a lady's 

 bonnet. At their terminatinn these wires are bent outwards, and their ex- 

 tremities are connrcted by means of a line steel wircj half an inch long, so 

 as to form a small triangle, like the Greek capital delta. This triangular 

 end is inserted into a small tin cartridge, and ignition of tlic powder con- 

 tained in the cartridge is produced by the deflagration of the steel wire 

 which connects the ends of the two cu])per wires. So rapid is the progress 

 of the electric fluid, that it is impossible to measure the interval of time 

 which elapses between the action at the trough and the explosion of the car- 

 tridge. The cost of this app^i^atus is only about lifteen shillings; aiul the 

 price of the materials required for the solution is such, that a shilling will 

 cover the expense of keeping the trough in a working state for months. 

 The copper wire which, if properly shielded, may last for years, costs about 

 one farthing for each yard. In applying this apparatus to blasting, Mr. Ro- 

 berts makes the fnUowing arrangements : — In regard to the mode of charg- 

 ing, which is perhaps the most important peculiarity of his method, he 

 leaves a space of about one fool, containing atmospheric air, above and be- 

 low the gunpowder ; and thus obtains, over and above the effect of the giui- 

 powder, all the power wliich the sudden increase of its i oluine produces ; 

 and thus the same eli'cct is obtained from a smaller charge. He also inserts 

 the tin cartridge into the heart of the charge of powder, and as the cartridge 

 explodes at both ends, the gunpowder is much more instantaneously ig- 

 nited. Lastly, in lamping, no vent-hole is left, as in the connnon system, 

 by the withdrawing of the needle ; but the tamping is pressed closely round 

 the wire which conveys the electric fluid from the trough to the cartridge. 

 When the tamping is completed, the battery is plunged into the trough, 

 v^iich is at the distance of 40 feet from the bore-hole, and may of course 

 be removed as far as may seem desirable, by giving a small increase to 

 the power of the battery if required, which is easily effected by adding a 

 pair of plates. The spring of coiled wire still keeping the tin disc in the 

 middle of the bar, tlicie is no risk of an une.\pected explosion, a danger 

 which occasionally liap|)en3 by the too rapid ignition of a train or fuze in 

 the common method of blasting. Every one iiaving retired, a person 

 stationed at any safe distance, pulls a siring, which makes the tin disc pass 

 along the bar, and the instant the coimection of the opposite jioles of the 

 battery is established, the explosion takes place. We sliall liricfly detail 

 the chief advantage of this new system of blasting, which we conceive to 

 be as f.iUows :— 



1. Freedom from tlie dangers which alwiiys attend blasting is obtained 

 from various causes. In the comraim system, the fuse or train must be 

 fixed at or very near the bore-hole, long trains being expensive and un- 

 certain in their actimi ; ami accidents, Ironi the too rapid burning of the 

 fuze, are unfortunately very common. But in Mr. Roberts' system, the 

 person who pulls the string which puts the battery in action, may be sta- 

 tioned at any convenient distance. In the ;present sysiem, perhaps the 

 most common source of aceiilent is the withdrawing of the needle ; and 

 this is completely avoided in Mr. Roberts' plan. Lastly, there is less 

 chance of failure, and when failure does occur, the bore-hole may be 

 at once, approached without risk of accident, as the moment the siring is 

 slackened, "the action of the battery ceases. 



2. The next advantage is, the great facility which this mode gives for 

 blasting under water. 'J'liis is one of the most inconvenient, expensive, 

 and uncertain of all engineering operations, it involves much trouljle and 

 expense in laying hoses for the train or fuse, which are destroyed every 

 lime ; and after all, there are, perhaps, three failures out often trials. AH 

 this is avoided by Mr. Roberts' system, which is as efficient underwater as 

 above it and involves not one^lartliing of loss under water more than on 

 land. 



3. The great advantage of a much more rapid ignition of the gunpowder, 

 which incloses the cartridge on all sides, and receives the action of the 

 flame over the greater part of its surface at the same instant, gives the itew 

 system a great superiority. This is a most important element in the eC'ect 

 of the charge, as its full force is thus secured. In the present method, on 

 the other hand, the powder is fired from the tap, and when bard rammed fre- 

 quently burns away in a series of smaller explosions, producing successive 

 shocks, separated, it is true, by imperceptible intervals of time, but yei pro- 

 ducin" an effect greatly less powerful than they could have done if concen- 

 trated in one shock, so <is to act simultaneously. 



4. There is absolutely no vent-hole in the mode of tamping pursued by 

 ]Mr. Roberts, which mode cannot be applied to the present system of blasting. 

 This is an important gain, the vent-hole being a decided loss of poiver, 

 which is well known to gunners, and to counteract which, the Turks are in the 

 habit of covering the touch-hole of their guns with a bag of sand the moment 

 the priming is fired. _ _ 



5. Tlie advantage of enclosing a column of atmospheric air, as practised 

 by Blr. Roberts, is obvious, for the force exerted during its expansion is 

 added to that of the gunpowder itself. What that expansion may be it is 

 dillicuU to tell, as we have no good means of ascertaining the increase of 

 temperature which accompanies the explosion of gunpowder : but as the 

 volume of atmospheric air is doubled for every increase of temperature of 4ftO 

 deg. of Fahrenheit, the force produced bv the expansion of the inclosed 

 column of atmospheric air must Ibrm an important addition to the effect of 

 the gunpowde;-. 



