Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/340

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 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 may be natural, as the lime employed for mortar, and the so-called Roman cements ; or they may be artificial, as Portland cement, made by calcining mixtures of chalk with clay or river-mud (see BUILDING, vol. iv. p. 459) Roman contains more clay than Portland cement, and sets more rapidly. A good 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 and 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 or sulphate of potash, and calcined and ground. It is slaked with alum solution when used. In Martin s cement, pearl-ash is employed as well as alurn. 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 G parts and iron filings 1 part with linseed-oil. For steam-joints, ox-blood thickened with quicklime is employed. The iron-riist cement consists of 100 parts of iron turnings, with 1 part of sal-ammoniac ; this is an excellent cement for iron- w T ork. For water-tight joints, equal parts of white and red lead are worked into a paste with linseed-oil. A serviceable packing for connecting pipes, making joints, filling cracks in retorts, ttc., may be made by adding to asbestos powder enough of liquid silicate of soda to form a thick paste ; the composition hardens rapidly, stands great heat, and prevents the escape of acid vapours. Cracks in glas3 vessels required to resist heat 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 caseiue dissolved in cold saturated solution of borax ; after drying, the repaired portions are made capable of withstanding heat 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 marbls, 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 of 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 com position is wanned for use. A similar cement is a mixture of dried fresh curd with T Vth of its weight of quicklime, and a little camphor ; it is made into a paste with water when employed. A cement for Derbyshire spar and china, &amp;lt;fec., 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, shell- lac dissolved in spirits of wine is a very convenient cement. Cements 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-Lc in ammonia has been proposed by Mons. C. Mene 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 yello w-ochre to give colour. Cutlers 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 by weight each of red ochre 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. Jap anese cement, for uniting surfaces of paper, is made by mixing rice-flour with water and boiling it. Jeivellers* cement contains 3 parts of isinglass made 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 and 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. In Turkey, jewellery for the ornamentation of weapons and trinkets is secured by a composition thus made : two small bits of gum galbanum or gum ammoniacum are dissolved by trituration in 2 oz. of a glue prepared by digesting softened isinglass in spirits, 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 musfc be immersed in warm water when the cement is to be liquefied for use.

1em  CEMETERY ([ Greek ], from /cot^aco, to sleep), lite rally a sleeping-plac !, was the name applied by the early Christians to the places set apart for the burial of their dead. These were generally extra-mural and unconnected with churches, the practice of interment in churches or churchyards being unknown in the first centuries of the Christian era. The term cometery Las, therefore, boe:* 