Tests for tensile strength are made by break ing test pieces, briqutqles, whose smallest sec tion is one Melt square, in special tensile testing machines. The cement paste or is made into briquettes in small molds, and is allowed to remain in the molds until set; the briquettes are then removed and kept in a moist ;itmos 'Mere for 24 hours, and then immersed in water. where they remain until tested. Tests ;ire usu ally Made when the briquettes are 7 and 2s days old, and they consist in pulling the briquette in two and noting the pounds of pull required. Tests for soundness consist M placing cakes similar to those tied in the test for setting in water and noting, after a few days. whether cheeks or cracks have developed. which indicate a tendency to disintegration. This is called the normal test for soundness; accelerated tests for soundness are sometimes made, and consist in immersing the cement cake in either hot, or boiling water, or heating it. in a hot kiln or in flame, and observing 1\ hether cracks develop. Considerable doubt exists as to the value of accelerated tests. Chemical analyses of a ce ment are of value ehi•lly as a cheek when the other tests indicate a doubtful cement.
The strengths commonly required by speei lions in the United States are based upon the recommendations of the American Society of Civil Engith.ers, which give the following aver age value per square inch: usage, Canada halsain that has evaporated until rather hard is a very useful cement from its transparency it makes an almost iuci,ible joint. The surfaces should he slightly warmed and the balsam brushed over them, after which they should he kept pressed together for a short time. Thick copal or mastic varnish may be used in the same manner. ;unt shellac•, dissolved in alcohol in sufficient quantity to form a treacly liquid. forms a stronger cement than the above, hut its color is for some purposes. The shellac may he dissolved in naphtha, but the cement thus produced is not equal to that in alcohol. The liquid glue sold in the shops is usually prepared in this manner: another kind is made of a mixture of the solutions of shellac and india-rubber. A cement which is sold in sticks eonsists of shellac or gum mastic fused and molded into a convenient form. It is ap plied by heating the surfaces to be joined just For use in structural work, cements are usu ally mixed with sand. to form mortar. or with sand and gravel or brokcn stone. to form con cr•te. AloaTAat CoN('RETE.) ?HRe chief hydraulic cement producing eountries of the world are t;ermany, France, England. and the United States, although it is manufactured to a greater or less extent by nearly all civilized countries. In 1900 the Cnited States nutintfae tured about 8,800,000 barrels of natural cement, 8.500,000 barrels of Portland cement. and -WS, Om barrels of slag cement, valued at about, :417,000,000. Germany produces over 20.000,000 barrels of Portland cement yearly, and England between S.000,000 and 9,000.1mo barrels. France makes annually about 3.000.000 barrels of Port land cement and 7,000.000 or 8,000,000 barrels of other cements. The principal uses of hy draulic. cement are described in the articles on Atom xi; and Besides hydraulic cements. there are a great variety of cementing compounds used for vari ous 11111'1)0Se:A and derived front animal, vegc• table, and mineral substances. Animal cements have gelatin and albumin as their basis, while the binding materials of vegetable cements are gums, resins, and wax, `once of these different cements are the following: A cement used for nniting slabs of marble. alabaster, and for many
similar purposes consists of plaster of Paris mixed with water to the consistency of thick cream and then applied. The plaster of Paris may be mixed with thin glue, with diluted white of e or a solution of gum. instead of with water, and is strengthened there by. A cement for pipe-joint, is made of iron borings mixed with sal ammoniac and sulphur. compound is mixed with enough water to moisten it, and then rammed tight ly into the joint. The proporthins recom mended art. 1 pound of borings, . ounces of sal ammoniac, and I outlet. of sulphur. Vol- mending earthenware and china. etc., a variety of ce ments are recommended. For ornamental glass Or china which is not subjected to heat (Jr rough sufficiently to fuse the shellac and then smearing them thinly with it and pressing them together. If shellac is heated much above its fusing-point it becomes carbonized and rotten. and therefore great care must be used in fusing any composi tion of which it is an ingredient. Mere, ue, mixture of shellac and Mina-rubber. is an ex cellent cement, and. when applied with the pre cautions just alluded to, is so strong that glass or china cemented with it, and then allowed to tall or otherwise broken again. will give way in any part rather than that cemented. (t•dinary glue. so much used by joiners and cabinet-mak crs, is common ur impure gelatin tq v.), ob tained by boiling animal substances, as skins, Roofs, et•., in water. As glue dissolves in water, it is an effieient cement only in dry places. A. Ce1111•11t which can be used for many purposes is made as follows: Curdle skim milk with rennet, or vinegar, press out the whey, and dry the curd at a very gentle heat. but as quickly as possible. When it has become quite dry, grind it in a coffee or pepper mill. and next triturate it in a morta• until reduced to a very fine powder. Al ix this powder with one•tenth of its weight of new, dry quieklime, also in very fine powder, and to every ounce of the mixture add five or six grains of powdered camphor; triturate the whole well together. and keep it. in small. wide-mouthed vials, well corked. When required for use, make it into a paste with a little water and apply it immediately. Cheese cement is similar in coin position and uses. Take two parts of grated cheese and one of quicklime, in line powder; heat these together with white of egg to form a paste, and use immediately. Cu ler's cement, used for fixing knives and forks in handles, is made of equal weights of rosin and 1)rick-dust. melted together: or. for a superior quality, four parts of rosin, one of beeswax, and one of brick dust. .,1Iahogoned central , used for stopping (•acks and holes in mahogany, may be prepared by melting four parts of beeswax with one of Indian red, and as inuelt yellow ochre as is found requisite to give the color. If shellac be sub stituted for the beeswax, and less red used, a much better cement is made. Mucilage is a name applied to a great variety of sticky or gummy preparations used for fastening paper and other light materials together. It is some times a thickened aqueous solution of gum, and sometimes a preparation of dextrin, glue. or other adhesive materials generally containing sonic preservative substance or eompoutol, as creosote or salicylic acid.
env. Among the best books treat ing of hydraulic cements are: Spalding, Notes on History and Use of Hydraulic Cement (Itha ca, 1893) ; Treatise on Masonry Con struction (New York, 1889) Candlot, Ciments et chaux hydraaliques (Paris, 1897). See, also, Britm NG :MORTAR: CONCRETE FOUNDATIONS; _MASONRY; KILNS.