in a general sense, any glutinous substance capable of uniting and keeping things together in close cohesion. In this sense the word cement comprehends mortar, solder, glue, &c. but has been generally restrained to the compositions used for holding together broken glasses, china, and earthen ware. For this purpose the juice of garlic is recommended as exceedingly proper, being both very strong, and if the operation is performed with care leaving little or no mark. Quicklime and the white of an egg mixed together and expeditiously used, are also very proper for this purpose. Dr Lewis recommends a mixture of quicklime and cheese in the following manner: "Sweet cheese shaved thin, and stirred with boiling-hot water, changes into a tenacious slime which does not mingle with the water. Worked with fresh particles of hot water, and then mixed upon a hot stone with a proper quantity of unslicked lime, to the consistence of a paste, it proves a strong and durable cement for wood, stone, earthen ware, and glass. When thoroughly dry, which will be in two or three days, it is not in the least acted upon by water. Cheese barely beat with quicklime, as directed by some of the chemists for luting cracked glasses, is not near so efficacious." A composition of the drying oil of linseed and white lead is also used for the same purposes, but is greatly inferior.

in building, is used to denote any kind of mortar of a stronger kind than ordinary. The cement commonly used is of two kinds; hot and cold. The hot cement is made of rosin, bees-wax, brick-dust, and chalk boiled together. The bricks to be cemented are heated, and rubbed one upon another, with cement between them. The cold cement is that above described for cementing china, &c. which is sometimes, though rarely, employed in building.

The ruins of the ancient Roman buildings are found to cohere so strongly, that most people have imagined The ancients were acquainted with some kind of mortar, which, in comparison of ours, might justly be called cement; and that to our want of knowledge of the materials they used, is owing the great inferiority of modern buildings in their durability. In 1779, one M. Loriot, a Frenchman, pretended to have discovered the secret of the ancient cement, which, according to him, was no more than a mixture of powdered quicklime with lime which had been long slacked and kept under water. The slacked lime was first to be made up with sand, earth, brickdust, &c. into mortar, after the common method, and then about a third part of quicklime in powder was added to the mixture. This produced an almost instantaneous petrification, something like what is called the setting of alabaster, but in a much stronger degree; and was possessed of many wonderful qualities needless here to relate, seeing it has never been known to succeed with any other person who tried it. Mr. Anderson, in his essays on agriculture, has discussed this subject at considerable length, and seemingly with great judgment. He is the only person we know who has given any rational theory of the uses of lime in building, and why it comes to be the proper basis of all cements. His account is in substance as follows:

Lime which has been slacked and mixed with sand becomes hard and consistent when dry, by a process similar to that which produces the natural stalactites in caverns. These are always formed by water dripping from the roof. By some unknown and inexplicable process of nature, this water has dissolved in it a small portion of calcareous matter in a caustic state. As long as the water continues covered from the air, it keeps the earth dissolved in it: it being the natural property of calcareous earths, when deprived of their fixed air, to dissolve in water. But when the small drop of water comes to be exposed to the air, the calcareous matter contained in it begins to attract the fixable part of the atmosphere. In proportion as it does so, it also begins to separate from the water, and to reassume its native form of limestone or marble. This process Mr. Anderson calls a crystallization: and when the calcareous matter is perfectly crystallized in this manner, he affirms, that it is to all intents and purposes limestone or marble of the same consistence as before: and in this manner (says he), within the memory of man, have huge rocks of marble been formed near Matlock in Derbyshire." If lime in a caustic state is mixed with water, part of the lime will be dissolved, and will also begin to crystallize. The water which parted with the crystallized lime will then begin to act upon the remainder, which it could not dissolve before; and thus the process will continue, either till the lime be all reduced to an effete, or (as he calls it) crystalline state, or something hinders the action of the water upon it. It is this crystallization which is observed by the workmen when a heap of lime is mixed with water, and left for some time to macerate. A hard crust is formed upon the surface, which is ignorantly called frosting, though it takes place in summer as well as in winter. If therefore the hardness of the lime, or its becoming a cement, depends entirely on the formation of its crystals, it is evident that the perfection of the cement must depend on the perfection of the crystals, and the hardness of the matters which are entangled among them. The additional substances used in making of mortar, such as sand, brickdust, or the like, according to Mr. Anderson, serve only for a purpose similar to what is answered by sticks put into a vessel full of any saline solution, namely, to afford the crystals an opportunity of fastening themselves upon it. If therefore the matter interposed between the crystals of the lime is of a friable, brittle nature, such as brickdust or chalk, the mortar will be of a weak and imperfect kind; but, when the particles are hard, angular, and very difficult to be broken, such as those of river or pit sand, the mortar turns out exceedingly good and strong. Sea sand is found to be an improper material for mortar, which Mr. Anderson ascribes to its being less angular than the other kinds. That the crystallization may be the more perfect, he also recommends a large quantity of water, that the ingredients be perfectly mixed together, and that the drying be as slow as possible. An attention to these circumstances, he thinks, would make the buildings of the moderns equally durable with those of the ancients; and from what remains of the ancient Roman works, he thinks a very strong proof of his hypothesis might be adduced. The great thickness of their walls necessarily required a vast length of time to dry. The middle of them was composed of pebbles thrown in at random, and which have evidently had mortar so thin as to be poured in among them. By this means a great quantity of the lime would be dissolved, and the crystallization performed in the most perfect manner; and the indefatigable pains and perseverance for which the Romans were so remarkable in all their undertakings, leave no room to doubt that they would take care to have the ingredients mixed together as well as possible. The consequence of all this is, that the buildings formed in this manner are all as firm as if cut out of a solid rock; the mortar being equally hard, if not more so, than the stones themselves.

Notwithstanding the bad success of those who have attempted to repeat M. Loriot's experiments, however, Dr. Black informs us, that a cement of this kind is certainly practicable. It is done, he says, by powdering the lime while hot from the kiln, and throwing it into a thin paste of sand and water; which, not slacking immediately, absorbs the water from the mortar by degrees, and forms a very hard mass. "It is plain," he adds, "that the strength of this mortar depends on using the lime hot or fresh from the kiln."

By mixing together gypsum and quicklime, and then adding water, we may form a cement of tolerable hardness, and which apparently might be used to advantage in making troughs for holding water, or lining small canals for it to run in. Mr. Wiegley says, that a good mortar or cement, which will not crack, may be obtained, by mixing three parts of a thin magma of slacked lime with one of powdered gypsum; but adds, that it is used only in a dry situation. A mixture of tarras with slacking lime acquires in time a stony hardness, and may be used for preventing water from entering. See Mortar and Stucco.

Cement, among engravers, jewellers, &c., is the same with the hot cement used in building*; and is used for* See the keeping the metals to be engraved firm to the block, forging and also for filling up what is to be chiseled.

Chemistry, is used to signify all those powders Cement powders and pastes with which any body is surrounded in pots or crucibles, and which are capable by the help of fire of producing changes upon that body. They are made of various materials; and are used for different purposes, as for parting gold from silver, converting iron into steel, copper into brass; and by cementation more considerable changes can be effected upon bodies, than by applying to them liquids of any kind; because the active matters are then in a state of vapour, and assisted by a very considerable degree of heat.

**CEMENT which quickly hardens in water.** This is described in the posthumous works of Mr Hooke, and is recommended for gilding live craw fish, carps, &c., without injuring the fish. The cement for this purpose is prepared, by putting some Burgundy pitch into a new earthen pot, and warming the vessel till it receives so much of the pitch as will stick round it, then strewing some finely-powdered amber over the pitch when growing cold, adding a mixture of three pounds of linseed oil, and one of the oil of turpentine, covering the vessel and boiling them for an hour over a gentle fire, and grinding the mixture as it is wanted with as much pumice-stone in fine powder as will reduce it to the consistence of paint. The fish being wiped dry, the mixture is spread upon it; and the gold leaf being then laid on, the fish may be immediately put into water again, without any danger of the gold coming off, for the matter quickly grows hard in the water.

**CEMENT Pots,** are those earthen pots used in the cementation of metals.

**CEMENTATION,** the act of corroding or otherwise changing a metal by means of a CEMENT.