CEMENTS, substances employed to unite together by their solidification from a soft or liquid state, and without mechanical rivets, things of the same or of different kinds. Stony cements many be natural, as the lime employed for mortar, and the so-called Roman cements ; or they may be artificial, as Porland cement, made by calcining mixtures of chalk with clay or river-mind (see BUILDING, vol. iv. p. 459) Roman contains more clay than Portland cement, and sets more rapidly. A god artificial water cement is obtained by heating for some hours to redness a mixture of 3 parts of clay and 1 part of slaked lime by measure. Another hydraulic cement may be made by mixing powdered clay and oxide of iron with water. A very hard stone cement is prepared from 20 parts of clean river, sand, 2 of litharge, 1 of quicklime, worked into a paste with linseed-oil. Paper-pulp, mixed with size plaster of Paris is used for moulded ornaments. Keene’s marble cement is plaster of Paris which has been steeped in strong solution of alum of sulphate of potash, and calcined and ground it is slaked with alarm solution when used. In Martins’ cement, pearl-ash is employed as well as alum. Parian cement contains borax. Selenitic cement is a mixture of calcined gypsum, sand, and hydraulic lime. A cement used for cracks in boilers is a mixture of clay 6 parts and iron filings 1 part linseed-oil. For steam-joints, ox-blood thickened with quicklime is employed. The iron-rust cement consists of 100 parts of iron turnings, with 1 part of sal-ammoniac ; this is an excellent cement for ironwork. For water-tight joints, equal parts of white and red lead are worked into a paste with linseed-oil. A serviceable packing for connection pipes, making joints, filling cracks in retorts, &c., may be made by adding to asbestos powder enough of liquid silicate of soda of form a thick paste ; the composition hardens rapidly, stands great heat, and prevents the escape of acid vapours. Cracks in glass vessels required to resist head and moisture may be stopped by covering them with strips of hog’s or bullock’s bladder, which are affixed by means of a paste of caseine dissolved in cold saturated solution of borax ; after drying, the repaired portions are made capable of withstanding head by an outside coating of a mixture of concentrated solution of silicate of soda with plaster of Paris or quicklime.

A strong cement for alabaster and marbles, which sets in a day, may be prepared by mixing 12 parts of Portland cement, 8 of fine sand, and 1 of infusorial earth, and making them into a thick paste with silicate or soda ; the object to be cemented need not be heated. For stone, marble, and earthenware a strong cement, insoluble in water, can be made as follows : skimmed-milk cheese is boiled in water till of a gluey consistency, washed, kneaded well in cold water, and incorporated with quicklime ; the composition is warmed for use. A similar cement is a mixture and a little camphor ; it is made into a paste of quicklime, and a little camphor ; it is made into a paste with water when employed. A cement for Derbyshire spar and china, &c., is composed of 7 parts of resin and 1 of wax, with a little plaster of Paris ; a small quantity only should be applied to the surfaces to be united, for, as a general rule, the thinner the stratum of a cement, the more powerful its action. Quicklime mixed with white of egg, hardened Canada balsam, and thick copal or mastic varnish are also useful for cementing broken china, which should be warmed before their application. For small articles, shellac dissolved in spirits of wine is a very convenient cement. Cement such as marine glue are mixtures of shell-lac and India-rubber, or of their solutions.





There are various cements for wood. For wooden cisterns a mixture is made of 4 parts of linseed-oil boiled with litharge, and 8 parts of melted glue ; other strong cements for the same purpose are prepared by softening gelatine in cold water and dissolving it by heat in linseed-oil, or by mixing glue with _ of its weight of Venice turpentine. Solution of shell-lac in ammonia has been proposed by Mons. C Mène for the attachment of caoutchouc to wood and metals. Mahogany cement, for filling up cracks in wood, consists of 4 parts of beeswax 1 of Indian red, and yellow-ochre to give colour. Cutler’s cement is made of equal parts of brick-dust and melted resin, and is used for fixing knife-blades in their hafts. A cement used in electrical apparatus is composed of 4 parts of weight each of red ochire and beeswax, 20 parts of resin, and 1 part of plaster of Paris ; these are melted together till smooth. For covering bottle-corks a mixture of pitch, brick-dust, and resin is employed. A cheap cement, sometimes employed to fix iron rails in stone-work, is melted brimstone, or brimstone and brick-dust. Japanese cement, for uniting surfaces of paper, is made by mixing rice-flour with water and boiling it. Jewellers’ cement contains 3 parts of isinglass soft in water, and 1 part of gum ammoniacum ; these are heated together till a drop of the mixture stiffens immediately on cooling. Gold and silver chasers keep their work firm by means of a cement of pitch and resin, a little tallow, and brick-dust to thicken. Temporary cement for lathe-work, such as the polishing the grinding of jewellery and optical glasses, is compounded thus:-- resin, 4 oz.; whitening previously made red-hot, 4 oz.; wax, _ oz. Mastic alone is much employed for cementing and mending gems. It Turkey, jewellery for the ornamentation of weapons and trinkets is secured by a composition thus made:-- two small bits of gum galbanum or gum ammonicacum are dissolved by trituration in 2 oz. of a glue prepared by digesting softened isinglass in sprits, and the mixture is incorporated at a gentle heat with a thick alcoholic solution of a little gum mastic. This cement is kept in closely-stoppered phials, which must be immersed in warm water when the cement is to be liquefied for use.

The following works may be consulted:-- "On Hydraulic Lime and Cement Stones," in Knapp’s Chemistry applied to the Arts and Manufactures, vol. ii., p. 400, et seq. (1847); Burnell’s Rudimentary Treatise on Limes, Cements, &c., Weale’s series (1866); Reid’s Practical Treatise on the Manufacture of Portland Cement (1868); Cooley’s Cyclopaedia of Practical Receipts, edited by Tuson, pp. 305-311 (1872); Gwilt’s Encyclopaedia of Architecture, edited by Papworth, §§ 1868 et seq., 2231i, 225ia et seq. (1876).