176 ANNUAL OF SCIENTIFIC DISCOVERY. 



pressure at any instant on the interior of the gun at one inch from the breech 

 varied between 19.000 and 21,000 Ibs. per square inch. At one foot from 

 the breech the greatest pressure was only about 8,000 Ibs. ; at two feet 

 about the same; at three feet about G, 000, and at four feet about 5,900 Ibs. 

 The pressure of a small quantity of Hazzard's rifle powder, fired in a cavity 

 from which there was absolutely no escape, was not sufficient to burst the 

 box, the strength of which was estimated sufficient to sustain an internal 

 pressure of about 93,000 Ibs. per square inch. These facts are interesting, 

 as they serve to show how the metal should be distributed hi casting 

 cannon, and also to remove the belief which exists among practical men 

 that one grain of powder absolutely confined would exert an infinite force. 



EXPERIMENTS ON THE STRENGTH OF METALS. 



During the last year an elaborate and comprehensive work on the above 

 subject has been published by the authority of the War Department, made 

 up of reports of experiments by officers of the Engineers and Ordnance, and 

 more especially those conducted by Major Wade, U.S.A. The experiments 

 were extended over a series of years, and were made to test the strength 

 and other properties of metals employed in the manufacture of cannon. One 

 new fact developed by them is, that iron fused a number of times up to 

 a certain point, is thereby greatly improved in strength. In trials with some 

 iron, it was found that its transverse strength was nearly doubled by being . 

 melted and cast four times. At the South Boston Foundry, experiments 

 were made to test the strength of cast iron which had been submitted to 

 fusion during different periods of time. Eleven thousand pounds of iron were 

 cast into four six-pounder guns ; one, after the metal had been under fusion 

 or melted half an 'hour; the second, under fusion an hour and a half; the 

 third, under fusion three hours; and the fourth, under fusion three hours and 

 three quarters. The gun first cast burst at the thirty-first fire ; the second, 

 at the thirty-fourth; the third was fired thirty-eight times, and remained 

 unbroken. Thus the strength of the metal seemed to increase in a ratio 

 corresponding to the period of fusion, or under which it was kept in a highly 

 molten state, and it might have been inferred from this that the fourth gun 

 would have been the strongest of all. Instead of this being so, however, it 

 proved to be the weakest, for it burst at the twenty-fifth discharge. In view 

 of these experiments, Major Wade, in this report, says, "these results appear 

 to establish satisfactorily the fact, that a prolonged exposure of liquid iron to 

 an intense heat, does augment its cohesive power, and this power increases 

 as the time of the exposure up to some (not well ascertained) limit, beyond 

 which the strength of the iron is diminished." Experiments were also made 

 to test the transverse strength of ra&t iron bars, two inches square and 

 twenty-four inches long, the metal of which was kept under fusion during 

 different periods of time. These bars were set on supports twenty inches 

 apart, and the breaking force was applied at the middle. The results obtained 

 from four castings were in favor of that which was kept fused longest three 

 hours. On this head the report says, " from this it appears that the cohesive 

 power of the iron, so far as it can be shown by its capacity to resist trans- 



