Page:The New International Encyclopædia 1st ed. v. 04.djvu/480

* CEMENT. 410 CEMENT. in two and noting the pounds of pull roquircd. Tests for soundness consist in placing cakes similar to those used in the test for setting in water and noting, after a few days, whether checks or cracks have developed, which indicate a tendency to disintegration. This is called the normal test for soundness; accelerated tests for soindness are sometimes made, and consist in immersing the cement cake in either hot or boiling water, or healing it in a hot kiln or in liame. and observing whether cracks develop. Considerable doubt exists as to the value of accelerated tests. Chemical analyses of a ce- ment are of value ehielly as a check when the other tests indicate a doubtful cement. The strengths commonly reipiired by specifica- tions in the I'nited States are based upim the recommendations of the American Society of Civil Engineers, which give the following aver- age value per square inch : usage, Canada balsam that has evaporated until rather hard is a very useful cement; from its transparency it makes an almost invisible joiul. The surfaces should be slightly warmed and the balsam brushed over them, after which they ■-liould l)e kei>t pressed together for a short time. Thick (■oi)al or mastic varnish may be used in the same manner. (Juni shellac, dissolved in alcohol in sufficient quantity to form a treacly liquid, forms a stronger cement than the above, but its color is objectionable for some purposes. The shellac may be dissolved in naphtha, but the cement thus produced is not equal to that in alcohol. The liquid glue sold in the shops is isually prepared in this manner; another kind is made of a mi.xtnre of the solutions of .shellac and india-rublier. . cement which is sold in sticks consists of shellac or gum mastic fused and molded into a convenient form. It is ap- plied by heating the surfaces to be joined just AGE OF BRIQUETTE 24 hours 7 da.vs 28 days 1 year Natural cement 4-80 lbs. 100-140 " 60-100 lbs. 250-550 •' 100-1.50 lbs. 350-700 •• 300-400 lbs. Portland " For use in structural work, cements are usu- •ally mixed with sand, to form mortar, or with sand and gravel or broken stone, to form con- crete. (See JIortar; Conckkte.) The chief hydraulic cement producing countries of the world are Germany, France, England, an<l the United States, although it is manufactured to a greater or less extent by nearly all civilized countries. In 1000 the United States manufac- tured about 8.800,000 barrels of natural cement, 8,500,000 barrels of Portland cement, and 493,- 000 barrels of slag cement, valued at about $17,000,000. Germany produces over 20.000.000 barrels of Portland cement vearly, and England between S. 000.000 and O.OOO.'oOO barrels. l'"rance makes annually aliout :!.00.000 barrels of Port- land cement and 7.0(10.000 or 8,000.000 liarrels of other cements. The principal uses of hy- draulic cement are described in the articles on AloRTAl! and (oxcRF.Ti:. Besides hydraulic cements, there are a great variety of cementing compounds uscrd for vari- ous purposes and derived from animal, vege- table, and mineral substances. Animal cements have gelatin and albumin as their basis, while the binding materials of vegetable cements arc gums, resins, and wax. S<mie of these <lill'erent cements are the following: A cenuMit used for uniting slabs of niarl)le. 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 egg, or a solution of gum, instead of with water, and is strengthened there- b}'. A cement for pipe-Joints is made of iron borings mixed with sal ammoniac and sulphur. This comi)ound is mixed with enmigh water to moisten it, and then rammed tight- ly into the joint. The proportions recom- mended are 1 pound of borings, 2 ounces of sal ammoniac, and 1 ounce of sulphur. For mending earthenware and china, etc., a variety of ce- ments are recommended. For ornamental glass or china which is not subjected to heat or rough sufficiently to fuse the shellac and then smearing them thinly with it and pressing them together. If shellac is heated uuich above its fusing-point it becomes carbonized and rotten, and therefore great care must l)e used in fusing any composi- tion of which it is an ingredient. Murine fliue, a mixture of shellac and india-rubber, is an ex- i-cllcnt 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 fall or otherwise broken again, will give way in any part rather than that cemented. Ordinary glue, so much used by joiners and cabinet-mak- ers, is couHMou or impure gelatin (qv.), ol)- tained by boiling animal stibstances, as skins, hoofs, etc.. in water. .s glue dissolves in water, it is an efficient cement only in dry places, A cement 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 When it has become quite dry. grind it in a cofVee or pepper mill, and next triturate it in a tnort.'ir until reduced to a very line ]iowder. Mix this powder with one-tenth of its weight of new, dry quicklime, also in very fine powder, and to tvery ounce of the mixture add five or six grains of powdered canqihor; trittirate the whole w'ell 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 vement is similar in com- position and u.ses. Take two parts of grated cheese and one of quicklime, in fine powder; beat these together with white of egg to form a paste, and use immediately. Ciillrr's cement, used for fixing knives and forks in handles, is made of equal weights of rosin ami loickihist melted together; or, for a superior quality, four parts of rosin, one of beeswax, and one of brick- dust, ilahofianji cement, used for stopping cracks and holes in mahogany, may be prepared by melting four parts of beeswax with one of Indian red, and as nuich yellow ochre as is found requisite to give the color. If shellac be sub-
 * it a very gentle heat, but a,s quickly as possible.