1843.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



337 



l ii 

 24 



Orf. each) 



6 in. Pipes. 

 12 lb. of lead in joints, at Is. 2d. 

 4 lb. of yarn 



1 yarner, 1 clayer and rammer, 1 pelter up, 3s 

 two labourers, 2s. Gtf., 1 fireboy to 55 joints 



Excavation per length 

 Filling and Paving ditto 



Labour per yard, Is. Gd. 

 Metal per yard, Os. M. 



Total cost per yard, 8s. 3d. 



16 in. Pipes. 



321b. of lead 



Excavation per length 

 Filling and paving ditto 



2 lb. of gaskin 



Labour per yard, 3s. 8d. 



Metal per yard, 24s. 2d. 



Total cost per yard, 27*. Md 4 3 6 



Table of Weight and Dimensions of Flanched Pipes. 



Cost of laying pipes, inclading digging, filling in, and lead for joiuts, but 

 exclusive of pipes and carting superfluous earth, and making good roads, per 

 yard. 



Inch. 



2 .. 

 24 



3 .. 



Inch. 



1 

 1 1 



1 3 

 1 4J 



Relaying, paving, or making good roads, ptr yard 

 Boxes for plugs, each 

 Ditto with flaps, each 

 Spiggots, each 

 Boring Plugs, each 



! 





ELECTRO -GALVANIC BLASTING. 



Sir — Having read with much interest, in your Journal for August, 

 the account of the various applications of the electric fluid to the 

 useful arts, by Mr. Alexander Bain, I beg to communicate to you 

 another application of the conducting power of water, which, with 

 the approval of Major-General Pasley, I have lately adopted in liring 

 sub-marine charges over the wreck of the " Royal George," at Spit- 

 head, and which the General and myself both consider a great im- 

 provement on the mode hitherto practised. 



My attention had been for some time led to this subject, in carrying 

 on some experiments in June and July last, on the relative power of 

 different lengths of wire conductors in use over the wreck, for trans- 

 mitting the electric fluid. These conductors consist of two stout 

 copper wires, separated by an 14 inch rope ; the wires are care- 

 fully insulated and paid over with tape, yarn, and waterproof compo- 

 sition : the rope is saturated with the same composition, being im- 

 mersed in it while boiling, and yarn is then bound round the whole 

 with a second coat of the composition over it. 



The apparatus used for the experiments was the voltameter, con- 

 sisting of a glass vessel with inverted tubes, two pieces of platinum 

 wire were fixed into the sides of the vessel, and bent at right angles, 

 to enter the tubes ; on connecting the two ends of the conducting 

 wires at one extremity, placing a voltaic battery at the other, and the 

 voltameter within the circuit, the water in it was rapidly decom- 

 posed, gas was emitted and passed into the tubes, which being gra- 

 duated with a scale divided to tenths of inches, showed the relative 

 power of each length of the wire conductors by the quantity of gai 

 delivered in a certain time. 



I was, however, surprised to find that decomposition of water en- 

 sued, even when the ends of the wires furthest from the battery were 

 disconnected, and it soon became evident, that as these wires had 

 been frequently used for firing charges at a depth of 13 fathoms under 

 water, a certain degree of moisture must have been forced in by the 

 great pressure at that depth through the exterior coating, notwith- 

 standing the precautions used to make it and the wires waterproof, 

 and thus the electric fluid must have been led from one wire to the 

 other, causing action in the voltameter; this became still more apparent 

 on applying the voltameter and battery to a length of wire conductor 

 which had never been under water, as unless the ends of the wires 

 were connected, there was no gas emitted. There was another con- 

 vincing proof of the power of water as a conductor, though it in some 

 measure frustrated the object of my first experiments; but prose- 

 cuting the subject still further, I have since been enabled to turn thiJ 

 power to account, by using the water as a conductor in conjunction 

 with a single wire for firing charges, which are daily required over 

 the wreck. 



The method of doing this will now be stated. 



From Mr. Bain's experiments as well as my own, it appeared that 

 using water as a conductor in conjunction with a single wire, a certain 

 metallic surface must be present at each extremity of the wire, to 

 ensure the transmission of a sufficiently powerful current of electri- 

 city. In the case of sub-marine explosions, it would therefore be ne- 

 cessary to have one surface of metal at the bottom of the sea, and 

 another at the top, the depth of water forming the conductor between 

 them, and as the greater part of the charges used at Spithead are 

 common oil cans of tin, (a good conducting metal,) varying from two 

 to five gallons, it occurred to me to make use of the tin can a3 the 

 metal required at the bottom, and at the surface of the water to use 

 plates of zinc. 



Before lowering the charge to the bottom, the single wire is con- 

 nected to one of the priming or short wires inserted in the bursting 

 tube of the charge, and the other priming wire is turned down on the 

 tin and connected with it. The charge is taken down by a diver, 

 who places it, and after he has come up, the zinc plates are immersed, 

 (I found by experiment, that three plates of 10 in. by 7 in. were re- 

 quired) connected by copper wire passed through a hole in the top of 



■ f id 



/ J 



