Page:The American Cyclopædia (1879) Volume IV.djvu/191

 CEMENTS 183 Pennsylvania, appearing in Berks, Chester, Lancaster, and York counties, and passing through Maryland into Virginia, where they are found in Rockingham, Augusta, Rock- bridge, Roanoke, and other counties. The tentaculite, or water limestone of the lower Helderberg formation, however, furnishes most of the hydraulic cement that is used in the United States. Large deposits are found in Oneida, Onondaga, Madison, Niagara, Erie, Ulster, and Sullivan counties, New York. The largest development of the manufacture has taken place in Ulster county. The deposits there occupy a narrow belt in the valley of the Rondout creek, along the line of the Delaware and Hudson canal, and pass into New Jersey and Pennsylvania, but have not been found east of the Hudson river. The following table, made from a larger one in the work of Gen. Q. A. Gillmore " On Limes, Hydraulic Cements, and Mortars," gives analyses made by Prof. E. C. Boynton of four samples of hydraulic lime- stone, and the localities from which they were taken : CONSTITUENTS. Shepherdetown, Va. 8 lj gfc High Falls, Ulster co., N.Y. Layer 11. Layer 12. Carbonate of lime 58-25 11-16 17-84 4-60 74 8-26 1-70 20 85-60 19-26 &3-80 8-96 50 6-18 88 14 80-74 14-48 89-74 6'00 66 7-42 1-44 24 80-72 35-10 19-64 7-52 64 4-10 2-88 18 Silica, clay, and insoluble silica. . Alumina Sulphuric acid Chloride of sodium & potassium. Peroxide of iron Hygrometric water lost at 212 F. Total 97-75 100-82 100-72 100-28 The limestone from which cement is made, as has been intimated, varies considerably in quality even in the same locality, the difference depending much upon the relative position of the layer from which it is taken. The nearer it lies to those strata that are decidedly cal- careous, the more it approaches in character what is called a rich lime, slaking and expand- ing more or less. Again, when the more highly argillaceous strata are approached, and the deposit contains less lime, it loses energy and capability of hardening. Some of the stones require greater time for calcination than others, from 20 to 40 hours being the range. If the temperature is raised too high, the sili- cate is partially fused and the property of set- ting under water destroyed. It is therefore evident that such stones should not be burned together, although they may be mixed after- ward. Careful inspection is not always suffi- cient to detect the difference, nor is chemical analysis always to be relied on, although it is quite probable that those limes which contain much alkaline silicates should not be so highly calcined as others. Trial kilns capable of burning from 100 to 300 Ibs. should be fre- quently used. In preparing hydraulic cement for the market, similar kilns to those used for calcining common limestone are employed, and the processes are also similar. The perpetual flame kiln, or the draw kiln, such as is used on the continent of Europe, particularly the one invented by Friedrich Hoffmann of Berlin, is preferable. Kilns which are charged with alternate layers of fuel and limestone do not furnish so equable or controllable a degree of heat, and it is more important to secure this condition in calcining hydraulic limestone than in making quicklime. The process of calcina- tion is described in the article LIME. After burning, the stone is passed through a crush- ing mill and reduced to small pieces of the size of beech nuts, and is then finely pulverized by ordinary millstones. The crushers in general use are capable of preparing for the mill about 250 bbls. per day each ; and one millstone will grind about 10 bbls. per hour. One cubic yard of stone from the quarry yields about 9 bbls. of ground cement, of 300 Ibs. each. In Ulster county it is packed in barrels as it comes from the spout. The color of most of the hydraulic cement made in this country is a lighter or darker drab, the depth of hue de- pending principally upon the amount of oxide of iron which may be present. It will be ob- served from the table that the hydraulic lime- stones of Ulster and Erie counties, N. Y., as well as the one at Shepherdstown, Va., contain a large proportion of carbonate of magnesia. This might be regarded as a defect from what has been said of the effect of the presence of magnesia in common lime; but the case is altered in respect to hydraulic cements, and they are considered by Vicat and Marshal Vaillant, as well as by MM. Rivot and Cha- toney, as being superior for hydraulic pur- poses on this account. When hydraulic ce- ment is to be used, it is made into a paste with water, but no definite rules as to the propor- tion can be prescribed ; the bes't plan being to add just that quantity which will form a paste of such a consistence as can be manipulated with facility by the trowel. When the cement is used to form grout for filling in walls, it re- quires to be made thinner. The setting and hardening of hydraulic cement are processes not so distinctly separated as they are in the case of common building mortar. The setting and much of the hardening take place simul- taneously, or rather the setting and hardening are mostly one and the same process ; and with some cements it takes place almost immediately, further hardening proceeding slowly by cohe- sion, and by further chemical changes that have been commenced. The time varies with the kind and quality of the cement, some kinds taking not more than ten minutes, while others require more than as many hours, to become hard enough to fracture. MM. Rivot and Chatonay state that in calcination of an argillaceous lime- stone, when it has been just sufficient to expel the carbonic acid from the carbonate of lime, there will be formed a silicate and an aluminate of