TO PREVENT THE COPPER COOLING IN THE FURNACE. When the copper cools in the furnace, be ready, as soon as you perceive it, to cut it with a long stick while it is still in a paste; or if it is quite cold cut it as lead is cut with broad and large chisels. IF YOU HAVE TO MAKE A LARGE CAST. If you have to make a cast of a hundred thousand pounds do it with two furnaces and with 2000 pounds in each, or as much as 3000 pounds at most. 738. HOW TO PROCEED TO BREAK A LARGE MASS OF BRONZE. If you want to break up a large mass of bronze, first suspend it, and then make round it a wall on the four sides, like a trough of bricks, and make a great fire therein. When it is quite red hot give it a blow with a heavy weight raised above it, and with great force. 739. TO COMBINE LEAD WITH OTHER METAL. If you wish for economy in combining lead with the metal in order to lessen the amount of tin which is necessary in the metal, first alloy the lead with the tin and then add the molten copper. How TO MELT [METAL] IN A FURNACE. The furnace should be between four well founded pillars. OF THE THICKNESS OF THE COATING. The coating should not be more than two fingers thick, it should be laid on in four thicknesses over fine clay and then well fixed, and it should be fired only on the inside and then carefully covered with ashes and cow's dung. OF THE THICKNESS OF THE GUN. The gun being made to carry 600 Ibs. of ball and more, by this rule you will take the measure of the diameter of the ball and divide it into 6 parts and one of these parts will be its thickness at the muzzle; but at the breech it must always be half. And if the ball is to be 700 lbs., 1/7th of the diameter of the ball must be its thickness in front; and if the ball is to be 800, the eighth of its diameter in front; and if 900, 1/8th and 1/2 [3/16], and if 1000, 1/9th. OF THE LENGTH OF THE BODY OF THE GUN. 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. THE CAUSE OF ITS CURDLING. I say that the cause of this congealing often proceeds from too much fire, or from ill-dried wood. TO KNOW THE CONDITION OF THE FIRE.