288 ON METALS. 



Howitzers. ewt. qr. Ib. 



10 inches . . . 31 2 16 



8 . . . 12 1 16 



5| . . . 4 18 



Mortars (Land Service). 

 13 inches . . 



10 ... 



8 . 



5 . . . 



4f . . . 



Mortars (Sea Service). 



13 inches . . . 81 1 8 



10 . . . 32 3 7 



In casting these pieces of cannon, they generally make the thick, 

 ness of the sides, near the muzzle, half the diameter of the shot) 

 and at the touch-hole, or charging cylinder, three-fourths of the 

 diameter. Brass cannons are dearer than those made of iron ; 

 and, which is a disadvantage, they give a louder report at the 

 time of explosion, so as to occasion a tingling in the ears of the 

 persons on shipboard, which takes away for a time the faculty of 

 hearing. 



Cannon might be cast of copper alone ; but the mixture of tin 

 and copper is harder and denser, and less liable to rust than pure 

 copper is, and upon these accounts it is preferable to copper. 

 Tin melts with a small degree of heat, copper requires a very 

 great heat to melt it ; a mixture of copper and tin melts much 

 easier than pure copper, and upon this account also, a mixture of 

 copper and tin is preferred to pure copper, not only for the cast- 

 ing of cannon, but of statues, &c. for pure copper, in running 

 through the various parts of the mould, would lose so much of its 

 heat as to set before it ought to do. 



Bell, metal consists also of tin and copper. Authors do not 

 agree in the proportions ; some ordering one part of tin to be 

 melted with four parts of copper* ; others making the proportion 

 for bell. metal to be the same as that for gun. metal ; or one part of 

 tin to about ten parts of copper, to which they order a little brass 



* Pemb. Chcm.ii.32l. 



