20 



NATURE 



{_May I, 1879 



cottoa is transmitted instantaneously in all directions by the 

 water, and the shell is thus broken up into a number of frag- 

 ments averaging fourteen times the number produced by bursting 

 a .'■hell of the same size by means of the full amount of powder 

 which it will contain (13 oz.). Employing I oz. of powder, in 

 place of \ oz. of gun-cotton, in the shell tilled with water, the 

 comparatively very gradurd explosion of the powder charge is 

 rendered evident by the result ; the shell being broken up into 

 le-s than twenty fragments by the shock produced by the first 

 ignition of the charge, transmitted by the water. In this case 

 the shell is broken up by the minimum amount of force neces- 

 sary for the purpose, before the explosive force of the powder 

 charge is properly developed. Extensive comparative experi- 

 ments carried on not long since by the Royal Artillery at 

 Okehampton, demonstrated that this simple expedient of filling 

 common shells with water and attaching a small charge of 

 gun-cotton with its detonator to the fuse usually employed, 

 allowed of their application as efficient substitutes for the 

 comparatively complicated and costly shrapnel and segment 

 shells. 



Another illustration of the sharpness of action developed by 

 detonation as compared with explosion, consequent upon the 

 almost instantaneous character of the metamorphosis w hich the 

 explosive agent undergoes in the case of detonation, is afforded 

 by a method which the lecturer applied some years since for 

 comparing the violence of action of charges of gun-cotton and 

 of dynamite arranged in different ways. The charges (5 lb.) to 

 be detonated were freely suspended over the centres of plates 

 of very soft steel of the best quality, which rested upon the flat 

 face of a massive block, or anvil, of iron, having a large central 

 circular cavity. The distance between the upper surface of the 

 plate and the charge suspended over it, was 4 feet. The sharp 

 blow delivered upon the plate by the air suddenly projected 

 against it by the force of the detonation when the charge was 

 fired, forced the metal down into the cavity of the anvil, pro- 

 ducing cup-shaped indentations, the dimensions of which afforded 

 means of comparing the violence of the detonation. A much 

 larger charge of powder exploded in actual contact with the 

 plate, would produce no alteration of form in the metal, and 

 the same negative result would be furnished by the explosion 

 over the plate of a heap of loose gun-cotton of the same or 

 greater weight than the charges detonated. The above method 

 of experiment was devised, in the first instance by Mr. Abel, in 

 July 1875, for comparing the quality of some specimens of 

 Llandore steel proposed to be used by the Admiralty for 

 ship-building purposes, with samples of malleable iron, and it 

 has since been employed by Mr. Adamson in carrying out a 

 very useful series of experiments, recently communicated to the 

 Iron and .Steel Institute. 



It has been stated that detonation can be transmitted from 

 one mass of gun-cotton or dynamite to another through inter- 

 vening air-spaces. The extent to which such spaces can be 

 introduced without checking detonation is obviously re- 

 gulated by the size of the masses of ex]>losivc detonated ; 

 but the distances of air-space through which the detonation of 

 a moderate quantity of the explosive agent will communicate to 

 similar masses, are very limited, a space of 2 inches being 

 sufficient to prevent the detonation produced by a ma- s of 8 oz. of 

 gun cotton, freely exposed, from communicating to contiguous 

 ones. If the dispersion of force is prevented in jiart, and 

 direction is given to the gases violently prrjecled from the 

 centre of detonation, the power of transmitting detonation to 

 separated masses of explosive is increased to a remarkable 

 degree. This is readily accomplished through the agency 

 of tubes, the charge first detonated being just inserted into 

 one extremity, while that to which the detonation is to be 

 transmitted is inserted into the other ; or separate charges maybe 

 placed at different distances inside a long tube, with long in- 

 tervening spaces, the initiative charge being inserted at one end. 

 Thus, the detonation of a I-oz. disk of gun-cotton in open air 

 will not transmit detonation w ith certainly to other disks placed 

 at a greater distance than half an inch from it ; but if it be just 

 inserted into one end of an iron tube 2 feet long and i"25 inch 

 in diameter, a similar disk, inserted into the other extremity of 

 the tube, will invariably be detonated. In tubes of the same 

 kind, of very considerable length, 2-oz. disks of gun-cotton 

 placed at intervals of 2 feet, were detonated through the initia- 

 tive detonation of one such disk inserted into one extremity 

 of the tube. The results obtained with equal quantities of gun- 

 cotton varied with the diameter, strength, and nature of the 



material of the tubes used. Dynamite and mercuric fulminate, 

 applied to their own detonation, furnished results quite analo- 

 gous to those obtained with gun-cotton ; but in applying ful- 

 minate to the detonation of gun-cotton through ihe agency of 

 tubes, some singularly exceptional results were obtained. 



Silver fulminate was employed for the purpose of instituting 

 more precise experiments than could be made in operating on a 

 larger scale, with gun-cotton, on the influence of the material 

 compo-ing the tubes, of the condition of their inner surfaces^ 

 and of other variable circumstances, upon the transmission 

 of detonation. Half a grain of silver fulminate freely ex- 

 posed and ignited by a heated body, will transmit detonation to 

 some of the compound placed at a distance of 3 inches from it, 

 but does not do so with certainty through a distance of 4 

 inches. But when the quantity of the fulminate is just inserted 

 into one end of a stout glass tube 0'5 inch in diameter, and 3 

 feet long, its detonation is invariably induced by that of a 

 similar quantity of the fulminate plnced just inside the other 

 extremity of the tube. Glass tubes were found to transmit the 

 detonation of silver fulminate much more rapidly than tubes 

 of several other materials of the same diameter and thickness 

 of substance. Thus, with the employment of double the 

 quantity of fulminate required to transmit the detonation with 

 certainty through a glass tube of the kind described, 3 feet in 

 length, it was only possible to obtain a similar result through a 

 pewter tube 31 •$ inches long, a brass tube 23"7 inches long, an 

 indiarubber tube 15-8 inches long, and a paper tube II -8 

 inches long. The difference in the results obtained was not 

 ascribable to a difference in the escape of force on the instant of 

 detonation, in consequence of the fracture of the tube, nor to 

 the expenditure of force in work done upon the tube at the 

 seat of detonation. The transmission of detonation ajipeared 

 also not to be favoured by the sonorosity or the pitch of the tube 

 employed, as the sonorous brass tube was not found to favour 

 the transmission to the same extent as the pewter tube. These 

 differences appeared on further investigation not to be ascrib- 

 able, to any important extent, if at all, to the difference in the 

 nature of the material composing the tulies, but to be simply, or 

 at any rate almost entirely, due to differences in the condition of 

 the inner surfaces of the tubes. Thus, brass tubes, the inner 

 surfaces of which were highly polished, and paper tubes, when 

 coated inside with highly glazed paper, transmitted the detona- 

 tion of the silver fulminate to about the same distance as the glass 

 tubes ; on the other hand, when the inner surfaces of the latter 

 were slightly roughened by coating them with a film of fine 

 powder, such as French chalk, they no longer transmitted de- 

 tonation to anything like the distance which they did when the 

 inner surfaces were in the normally smooth condition. Other 

 very slight obstacles to the unimpeded passage of the gas wave 

 through the tubes were found greatly to reduce the facility with 

 which detonation could be transmitted by means of tubes ; thus, 

 when a diaphragm of thin bibulous paper was inserted into the 

 glass tube about halfway between the two extremities, detona- 

 tion was not transmitted, even with the employment of about 

 six times the quantity of fulminate that gave the result with 

 certainty under ordinary conditions. 



Among several other interesting results furnished by an ex- 

 amination into the conditions governing and results attending the 

 transmission of detonation by tubes, a remarkable want of reci- 

 procity was found to exist between mercuric fulminate and gun- 

 cotton. The latter substance is more susceptible to the detona- 

 tive power of mercuric fulminate than of any other substance. 

 The quantity of fulminate required to detonate gun-cotton is 

 regulated by the degree to which the sharpness of dts oivn 

 detonation is increased by the amount of resistance to rupture 

 offered by the envelope in which the fulminate is confined. 

 From 20 to 30 grains are required if the detonative agent is con- 

 fined in a thin case of wood, or in several wrappings of paper ; 

 but as small a quantity as 2 grains of the fulminate suffices to 

 effect the detonation of compressed gun-cotton, provided the 

 fulminate be confined in a case of stout metal (sheet tin) and be 

 closely surrounded by being tightly imbedded in the mass of gun- 

 cotton. If there be no close contact between the two, the 

 quantity of fulminate must be very considerably increased to 

 ensure the detonation of the gun-cotton, and, in attempting to 

 transmit detonation from mercuric fulminate to gun-cotton by 

 means of tubes, it was found necessary to employ comparatively 

 very large quantities of fulminate in order to accomplish this, 

 even through short lengths of tubes. But when the quantity of 

 fulminate used reaches certain limits, the detonation may be 



