400 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



the re-enforce occur, and these are the usual directions of fractures, whether 

 the gun be made of steel or i — i 



wroug-ht or cast iron, and whether -X — b 



cast solid or hollow. It is the 01- - Cy^-- 



same, also, even if an initial '-|L— «. L^y.....7. 



strain is placed upon a cast iron — -^ — 1 \ — ^ 



gun, as in the Parrott, Blakely, or "— il 



Treadwell plan. 



Second. The muzzle drops off. It is usual to attribute this form of frac- 

 ture to the premature bursting- of shells in the g^un. 



Third. Guns burst from Haws or defects in construction. In this case 

 the direction of the fracture is governed by the direction of the weakness. 



To account for the bursting of guns, excessive measures of pressure 

 have been attributed to gunpowder. Writers on the subject seem to have 

 overlooked the fact that a certain quantity of gas must be evolved from the 

 combustion of a certain quantity of powder, and that a uniform measure of 

 pressure must be exerted upon every square inch of surface of the chamber 

 in which it is fired if it is in a closed space, whether the quantity be small 

 or great, provided the powder fills the space before firing. Yet Hutton, 

 Robbins, Count Rumford, Treadwell and Rodman, have each made esti- 

 mates varying from 15,000 to 750,000 lbs. to the square inch. If we esti- 

 mate a cubic foot of powder to weigh 60 lbs., the result of combustion of 

 gases and residuum will weigh 60 lbs. The gases being i" of the whole by 

 weight, when expanded to the pressure of the atmosphere, will occupy 

 about 417 cubic feet of space. To return 417 cubic feet of gas to ,"o of a 

 cubic foot of space, according to Marryatt's Law, would give an expansive 

 force of about 11,145 lbs, upon the square inch, with a temperature of 

 nearly 6,000^ Fah.; and this pressure can never be exceeded or even 

 attained in a gun, as there must of necessity be considerable escape of gas 

 by windage, vent and loss of expansive force from the absorption of the 

 heat that is communicated to the surrounding metal of the gun and projectile. 

 This low estimate of pressure is positively confirmed by the following facts: 



In Major Wade's book entitled " Experiments on Metals for Cannon," we 

 find that after a six-pounder cast iron gun had endured a number of charges 

 of six pounds of powder and sixteen balls without injury, it was submitted 

 to pressure by water and burst with less than 20,000 lbs. to the square 

 inch. Other experiments are recorded where guns burst with 8,000 lbs. of 

 water pressure after having endured excessive powder proof. Major Wade 

 reports, and Col. Hagner confirms his statement, that Springfield musket 

 barrels are permanently enlarged in their strongest part by a water pres- 

 sure of 5,000 lbs. to the square inch — an effect never attained by the pow- 

 der proof. 



Again, when the Great Eastern was launched, Brahma presses were 

 used, of ten inch caliber, and ten inch thickness of wall, made of the very 

 best quality of cast iron; this being the proportion of caliber to wall in 

 most ten inch guns, and such guns have endured double shotted charges 

 without bursting. Yet these Brahma presses were invariably burst when- 

 ever they were submitted to a water pressure of 5,000 lbs. to the square 

 inch. It is not the pressure of the powder alone that bursts guns. 



