If you want it to throw a ball of stone, make the length of the gun to be 6, or as much as 7 diameters of the ball; and if the ball is to be of iron make it as much as 12 balls, and if the ball is to be of lead, make it as much as 18 balls. I mean when the gun is to have the mouth fitted to receive 600 lbs. of stone ball, and more.
OF THE THICKNESS OF SMALL GUNS.
The thickness at the muzzle of small guns should be from a half to one third of the diameter of the ball, and the length from 30 to 36 balls.
740.
OF LUTING THE FURNACE WITHIN.
The furnace must be luted before you put the metal in it, with earth from Valenza, and over that with ashes.
[Footnote 1. 2.: Terra di Valenza.—Valenza is north of
Alessandria on the Po.]
OF RESTORING THE METAL WHEN IT IS BECOMING COOL.
When you see that the bronze is congealing take some willow-wood cut in small chips and make up the fire with it.