MECHANICS AND USEFUL ARTS. 41 



malleability. The President remarked that the art of making such large 

 castings of thin metal was unknown in England. 



STRENGTH OF GUN-METAL. 



" We were never so powerfully impressed," says the Liverpool Albion, 

 "with the improvements in the manufacture of gun-metal, as during a 

 recent visit to the Mersey Steel and Iron Works, where we witnessed various 

 attempts to burst a two-pounder gun. The experiments took place in a 

 chamber excavated in the sandstone rock, covered over with loose sheets of 

 iron, which, of course, made a considerable rattle when each explosion took 

 place. The gun in question, which is five feet two inches in the bore, and 

 weighs somewhere about four hundred pounds, after being charged with 

 one pound of powder, was filled to the muzzle with one-pound balls, and 

 fired by means of a string. When the smoke had cleared away, it was found 

 that the gun was all right, and that so great had been the force of the ex- 

 plosion that many of the shot were shattered, and others deeply buried in 

 the rock. The gun was again charged, and filled with balls, and a cylinder, 

 or round bar of iron, which projected from the mouth. It was then fired, 

 with equally satisfactory results. The next trial was with one and a half 

 pounds of powder and three cylinders, weighing seventy-six pounds all to- 

 gether. This is a test which few guns are calculated to withstand; but, 

 though the noise of the explosion was very great, the metal of the gun was 

 so tough that it remained uninjured. The weight of the metal was after- 

 wards gradually increased to nearly ninety pounds, Avith safety. 



EXPERIMENTS WITH CAST IRON. 



A series of interesting experiments has recently been carried on, under 

 the managemeat of Colonel Eardley Wilmot, Superintendent of the Royal 

 Gun Factories at Woolwich, England, with a view to determine the most suita- 

 ble variety of iron for casting cannon ; and the results have been printed in the 

 form of a parliamentary report. Information regarding the several brands 

 of iron experimented with would be of little interest to our readers, but 

 there is other information in it interesting to all those who work in cast 

 iron, and the substance of this we give, as follows : The general mean 

 tensile strength of 8-30 specimens of cast iron was 23,257 pounds on the inch ; 

 the transverse strength of 564 specimens was 7,102; while the crushing 

 strength of 273 specimens was 91,001 pounds, and the torsion but 0,0-30. 



It was found, during these experiments, that when the specific gravity of 

 cast iron was 7'3, and upwards, it was too hard, and did not possess suffi- 

 cient elasticity for casting cannon. A marked superiority was the result in 

 bars cast horizontally over those cast vertically. Bars which were cooled 

 quickly were also much stronger than others cooled slowly. 



It was also found that, by repeated re-melting of the cast iron, its quality 

 was greatly improved. This etfect, however, was not so marked when 

 large masses of several tons were operated upon at once. It is believed 

 that by re-melting, although such impurities as phosphorus, sulphur, and 

 silica, may not be expelled, some of the graphite in the iron is converted 

 into combined carbon, which enables the contraction and crystallization of 

 the metal to be more complete. But if the melted iron is allowed to cool 

 very slowly, the carbon, it is thought bv some, is reconverted into graphite, 



4*' 



