ON THE CRYSTALLIZATION OF CAST IRON.

811

At one time I possessed a very large and beautifulcollection made at the Clyde Iron Works, where a con-siderable manufactory of government and other guns wascarried on during the early part of the late war. Thesecrystals were obtained in the greatest abundance, whenby accident the head or feeder of the gun had not beenfilled sufficiently high with fluid iron to overcome thequantum of subsidence that afterwards took place incooling. When the gun was carried to the cutting car-riage, and the knife applied to separate the head closeby the termination or muzzle of the gun, the deficiencywas soon discovered by the iron cutting open andspongy, and an imperfect casting indicated. A blowfrom a heavy sledge, under such circumstances, was suf-ficient to separate the head from the body of the gun.The fracture occasioned by such separation was gene-rally convex to the muzzle end of the gun, and concaveto the head or feeder ; the latter of which presented afine arrangement of crystals, inserted in the solid iron,while the convex surface presented the more perfect anddetached forms grouped base to base, or obliquely, ascircumstances had determined.

There can be no doubt that every gun, or large cast-ing, made with a head or feeder, contains a portion ofcrystallized iron, though it becomes only obvious andmost easily got when the casting is imperfect at thepoint where the knife or chisel is applied ; and probablythese opportunities are at all foundries sufficiently nu-merous to furnish an ample supply of crystallized iron,though a supply might be obtained from a more perfectcasting, particularly a mortar or cannon, by first measur-ing the depth of the shrinkage on the head or feeder,and applying the cutting knife from 4 to 6 inches lowerthan the ascertained point. As soon as the iron beginsto cut open and spongy, the operation is to be stopped,and the upper part of the head broken off by means of