26 ON RIFLED GUNS. 



and solving with respect to c, 



~- m- I " 2 — 4 P -, 



(14) 



/> 

 which is much greater than the value for c, as given by Eq. (13), and which shows that a gun 

 having its dimensions properly adjusted to slow powder might fail under the action of one 

 much quicker. Indeed, there can be no doubt that many good guns have been broken by the 

 use of powder rendered unfit for cannon practice by reason of its superior quickness. Quick 

 powder gives no better range, often crushes the projectile in shell firing, and unnecessarily 

 taxes, if it do not destroy, the gun. Its use should be avoided. 



The velocity of molecular disturbance increases with an increase of elasticity and 

 diminution of density. Gun metal should, therefore, possess the greatest elasticity and least 

 density consistent with high tenacity. 



(19) — In the report of Major Wade on the metals for cannon, page 269, the tenacity of 



the Greenwood gun iron is given at 35,538 pounds. This is the value of M — at the breaking 



point for this quality of iron. Taking the case of the 42-pounder, we shall have 



M — = 3553S lbs 

 P 



,9 = f .29166 



c = f .70S33. 



which, in Eq. (10), give 



P = 150100 lbs 



for the pressure on a square inch of bore, which would be sufficient to break a gun made of 

 the Greenwood iron and having the dimensions of the 42-pounder. 



(20) — In his report upon gun metals and powder, page 200, Major Rodman gives, as the 

 mean of five experiments, 51800 pounds to the square inch, as the pressure due to 8 pounds 

 of powder, (grain 0,1 inch in diameter), a solid shot and sabot, fired in a 42-pounder. Hence, 

 making 



P — 51800 lbs 



// = 0'.29166 



c — f .70S33 

 and substituting in Eq. (9), give 



M. — =35541 lbs 



t> 



for the tensile strain on a square inch. 



(21) — From the experiments of Major Rodman, of which the results are given at page 

 158 of his work on the properties of metals and qualities of powder, it appears that cast 

 iron — of the kind tested — when subjected to a tensile strain of 5,000 pounds to the square 

 (338) 



