a calcination of upwards of forty hours, is cooled down to moderate ignition by sliding in the dampers and sliding up the doors, which had been partially closed during the latter part of the process. It is now observed to form prismatic concretions, somewhat like a columnar mass of basalt. These are loosened by means of iron bars, lifted out upon shovels furnished with long iron shanks, which are poised upon swung chains with hooked ends, and the lumps are thrown upon the pavement, to be extinguished by sprinkling water upon them from the rose of a watering can, or they may be transferred into a large chest of sheet iron set on wheels, and then covered up. Good coals, thus treated, yield eighty per cent. of an excellent, compact, glistening coke, weighing fourteen cwt. per chaldron.” Illustration: (‡ OVEN TOOLS.) Coke burns without smoke, and not so rapidly by far as charcoal, it is, moreover, considerably cheaper than that article is. GUNPOWDER. Gunpowder is a mixture of nitre, sulphur, and charcoal, and the more completely they are mixed, the more finely ground, and the purer they are, the more perfect will be the gunpowder. The proportions used of these ingredients differ slightly in different powder mills; but the average is about seventy-four parts nitre, ten sulphur, and fourteen charcoal, by weight; the sulphur and nitre can easily be completely purified, but the charcoal differs very much in almost every specimen, and charcoal that has been burnt long ago and exposed to the air and moisture is almost unfit for the purpose, that charcoal which has the least ash when burnt is found to be the best, and the charcoal which has been made in iron cylinders, is better than that made in the usual way, when each of the ingredients are separately powdered and sifted through a kind of sieve of silk called a bolting machine (such as is used in dressing flour), they are mixed in the proper proportions and taken to the mill, where they are moistened with water and ground to a smooth paste, this is pressed hard and then broken up into pieces which are put into a copper sieve, the bottom of which is perforated with small hole; a flat wooden ball is put into each sieve with the pieces of damp powder, and the sieves are all put into a circular motion by machinery, this causes the wooden ball to turn round in the sieve and so rub the damp powder through the little holes; it is collected below in small grains or “corns,” this process is called “corning,” this is now dried, and then put into a “reel” (a sort of barrel which turns round) and the grains, by rubbing against each other, become smoothed on the surface; the dust is now removed by a sieve, too fine to let the grains through; the powder is now fit for use.