1873J Engineering. 267 



The little green pebbles commonly sold to tourists in Iona have been 

 analysed by Mr. E. C. C. Stanford, and found to be a variety of serpentine, 

 notable for containing manganese. 



ENGINEERING— CIVIL AND MECHANICAL. 



Guns. — The first 35-ton gun, known by the name of the " Woolwich Infant," 1 

 has recently formed the subject of a report, as to the state of its interior, by 

 the Inspector of Ordnance. After thirty-eight horizontal discharges, after its 

 bore had been enlarged to 12 inches, the interior had sustained injuries, caused 

 by four cracks, four fissures, and some deep roughnesses : two of the cracks 

 were on the lower side of the bore, and all the other injuries on the upper 

 side, their centres coinciding with the point where the front studs of the shot- 

 hammer and the rear studs come into driving bearing. The gun is being rebuilt 

 at a cost of about ,£700 or ^800. 



On the gth of January last Commander Dawson, R.N., reaa a paper, at the 

 Royal United Service Institution, on the " Powder-Pressures in the First 

 35-ton Gun," illustrated by diagrams showing the state of its interior on 

 leaving and on returning to the gun-fadtories, and by corresponding diagrams 

 of some other disabled Woolwich guns. After thirty-five discharges from the 

 ii-6-inch bore, this gun was reduced by boring it up to 12-inch calibre, with a 

 corresponding reduction of the pressures. But after thirty-eight horizontal 

 discharges the 12-inch bore was so injured by the projectiles as to necessitate 

 the rebuilding of the gun. The table of pressures shows that when the 

 12-inch bore was fresh from the factory, no-lb. W. A. P. charges gave very 

 regular maximum pressures of 20* 1 tons; but when the 12-inch bore had sus- 

 tained thirty-four to thirty-eight discharges the registers were very irregular, 

 and averaged 31*3 tons. Similarly, the first 115-lb. W. A. P. charges, in the 

 12-inch bore, gave very regular mean maximum pressures of 22*5 tons, but 

 subsequently increased to 44-5 tons ; and the 120-lb. charges began at 20 tons 

 and increased to 66 tons. The whole of the injuries in the bore of the gun 

 are, however, recorded in a certain short part of the bore outside the area of 

 maximum pressures, and precisely where the oblique movement of the axis of 

 the projectile about its studs would have its greatest force. The same mis- 

 direction of mechanical forces was shown to be in operation in other guns 

 similarly rifled, tending to impede the free exit of the shot, to injure the 

 projectile and the guns, and to diminish the velocities and striking force, whilst 

 giving rise to accumulation of gases and elevation of pressures in the bore. 



Shells. — A series of experiments have recently been carried out in Austria 

 in order to test the relative merits of steel and chilled iron shells. These 

 trials appear to have been very exhaustive, and the results confirm what had 

 previously been arrived at, namely, that the former are superior for naval 

 purposes. The steel projectiles were found to pierce the shield with a consi- 

 derable excess of force without breaking up, whilst the chilled shells only 

 penetrate to the second plate and break up. The effect of the live shells also 

 accords with this; the steel shells explode in the wood backing, and their 

 fragments are hurled behind the target. The chilled shells burst in front of 

 the second plate, and thus virtually produce no effect, being kept by the side 

 far from the interior of the ship. 



Dynamite. — A very interesting series of experiments have recently been 

 carried out with this powerful explosive, among the sand-hills of Ardeer, on 

 the coast of Ayrshire, where the British Dynamite Company have erected 

 their factory. These experiments were carried out in order to satisfy the 

 traffic-managers of the Scotch railways of the almost total immunity from 

 danger that is displayed by this valuable material under all conditions of 

 carriage. They were conducted under the superintendence of Mr. A. Nobel, 

 the patentee and technical director of the Company. The results were most 

 conclusive and satisfactory, proving the dynamite to be perfectly harmless under 

 mere percussion, or when subjected to flame, but capable of exerting a most 

 powerful effect when exploded in the usual manner with a Bickford fuse., 



