SHELL

The hardening principle of shell is generally carbonate of lime nearly pure. The animal principle, in the porcellaneous shells, is a small quantity of soluble gelatine;in the mother of pearl.shells, it is albuminous. The latter, therefore, when steeped in dilute muriatic acid, leave a membranous or cartilaginous residue; but the former are entirely soluble. For the form, structure, and mode of growth of Shell, see Contuolooy. i,i.. In Artillery, a hollow sphere of iron, which being filled wilh gunpowder and fired from a mortar, bursts into pieces; when the powder is exploded, and produces a Very destructive effect. The charge is introduced through a hole in the shell of about an inch in diameter, and tired by means of a fuze. The fuze is a wooden tube made to fit the hole, and filled with a composition of sulphur, saltpetre, and mealed powder; and is cut of such a length that the shell is calculated to explode just before or immediately after it reaches the ground. [s. 1133]