BISCUIT. In sculpture, a species of porcelain, of which groups and figures in miniature are formed, which are twice passed through the furnace or oven. It is executed without glaze upon it. In pottery, this term is applied to earthen ware and porcelain, after it has been hardened in the fire, and before it re ceives the glaze : in this state it is per meable to water. On which account it is now largely used as porous cells for elec trotype purposes.
Bison IT. An unfermented bread, which, when well prepared, may be kept for a long time ; and hence valuable as a common form of bread at sea. In Eng land, the sea biscuit manufacture by hand for government-contract has been sus pended by the machinery invented by T. T. Grant, Esq., of the Royal Clarence yard, which is this : the meal or flour is conveyed into a hollow cylinder four or five feet long and about three feet in dia meter, and the water, the quantity of which is regulated by a gauge, is ad mitted to it ; a shaft, armed with long knives, works rapidly round in the cylin der with such astonishing effect, that in the short space of three minutes, 340 lbs. of dough are produced, infinitely better made than that mixed by the naked arms of a man. The dough is removed from the cylinder and placed under the break mg-rollers ; these latter, which perform the office of kneading, are two in num ber, and weigh 15 cwt. each ; they are rolled to and fro over the surface of the dough by means of machinery, and in five minutes the dough is perfectly knead ed. The sheet of dough, which is about two inches thick, is then cut into pieces half a yard square, which pass under a second set of rollers, by which each piece is extended to the size of six feet by three, and reduced to the proper thickness for biscuits. The sheet of dough is now to be cut up into biscuits, and no part of the operation is more beautiful than the mode by which it is accomplished. The dough is brought under a stamping or cutting-out press, similar in effect, but not in detail, to that by which circular pieces for coins are cut out of a sheet of metal. A series of sharp knives are so arranged that, by one movement, they cut out of a piece of dough a yard square about sixty hexagonal biscuits. The rea son for a hexagonal (six-sided) shape is, that not a particle of waste is thereby occasioned, as the sides of the hexagonals accurately fit into those of the adjoining biscuits ; whereas circular pieces cut out of a large surface always leave vacant spaces between. That a flat sheet can be divided into hexagonal pieces without any waste of material is obvious.
Each biscuit is stamped with the queen's mark, as well as punctured with holes, by the same movement which cuts it out of the piece of dough. The hexa gonal cutters do not sever the biscuits completely asunder • so that a whole sheet of them can be put into the oven at once on a large peel or shovel adapted for the purpose. About fifteen minutes are sufficient to bake them ; they are then withdrawn and broken asunder by the hand.
The corn for the biscuits is purchased at the markets, and cleaned, ground, and dressed at the government mills. In
quality it is a mixture of fine flour and middlings, the bran and pollard being removed. The ovens for baking are formed of fire-brick and tile, with an area of about 160 feet. About 112 lbs. weight of biscuits are put into the ovens at once. This is called a suit, and is reduced to about 110 lbs. by the baking. From twelve to sixteen suits can be baked in each oven every day, or after the rate of 224 lbs. per hour. The men engaged are dressed in clean check shirts and white linen trowsers, apron, and cap ; and every endeavor is made to observe the most scrupulous cleanliness : 450 lbs. of dough may be mixed by the machine in four minutes, and kneaded in five or six minutes ; we need hardly say how much quicker this is than men's hands could effect it. The biscuits are cut out and stamped sixty at a time, instead of singly : besides the time thus saved, the biscuits become more equally baked, by the oven being more speedily filled. The nine ovens at Gosport used to employ 45 men to produce about 1,500 lbs. of bis cuit per hour ; 16 men and boys will now produce, by the same number of ovens, 2,240 lbs. of biscuit (one ton) per hour.
The comparative expense is thus stat ed: Under the old system, wages, and wear and tear of utensils, cost about 18.6d. per cwt. of biscuit : under the new sys tem, the cost is 5d. British money. BISMUTH. A brittle, yellowish-white metal, of crystalline texture. Its specific gravity is 10• it fuses at 476°, and at a red heat it sublimes in close vessels. It conducts heat less perfectly than most of the othermetals. When strongly heat ed it burns with a bluish white flame, and is rapidly oxidized. Its equivalent upon the hydrogen scale is 71 ; and it forms only one salifiable oxide, the equi valent of which is 79. When nitrate of bismuth is dropped into water, a white powder is thrown down, formerly called magistery of bismuth or pearl white : it is a subnitrate. This is used as a cosmetic. A brown peroxide of bismuth is obtained by fusing the protoxide with caustic potash. Some of the alloys of bismuth are remarkable for their fusibility : a compound of 8 parts of bismuth, 5 of lead, and 3 of tin, melts in boiling water, and is commonly called fusible metal. The ores of bismuth are not common ; but it occurs native, and combined with oxygen, sulphur, and arsenic. The Ger mans call it wismuth.
Bismuth, alloyed with lead and tin, has been used as the patent safety plug in steam boilers to guard against explosion. It was supposed that at a high tempera ture, the alloy would melt and allow the steam to blow itself out. This has not been found the case, for this alloy, when exposed a long time to the action of steam, undergoes a process of change by which the more fusible alloy is melted out, and what remains is so hard as not to fuse : after the explosion of boilers, these plugs have been found unmelted.
Fusible metal has been used for casts for anatomical preparations, casts from medals, and even the surfaces of .wood and paper. Cake moulds for toilet soap manufacture, are made of this metal.