154. The ordinary cements, known as the Rosendales, comprising the Cumberland, Round Top, James River, Louisville, and others, are manufactured from natural cement stones existing in most of the states, and are known as light, quick-setting cements. These stones are calcined in a kiln; the product is then very finely ground and packed in barrels or sacks. For mortar they should not have more than 3 parts of sand to 1 of cement.

155. What are known as the heavy, slow-setting cements are almost entirely artificial products; these are called Portland cements, such as the German, English, French, and American brands. They are composed of pure clay and pure lime, combined in certain definite proportions determined by experiment, thoroughly mixed, and calcined at a very high temperature, then ground to a fine powder, and carefully packed in strong, light barrels, generally lined with paper to prevent any possible absorption of moisture. These cements will stand 4 parts of sand to 1 of cement, for cement mortar.

156. As to different cement brands, we must first be guided by tests that have been made, and select that one which seems best suited for the purpose in view; and in addition, simple tests should be made on delivery. All broken barrels should be rejected, especially if the cement is to be stored for any length of time, as by exposure to the air it will "take a set " and become useless.

It is well to test a number of barrels by feeling, in order to determine the fineness to which it is ground. A little experience will enable this to be determined by the sensitiveness of the touch. In addition, small cakes of mortar made with good sand and cement, in proportions used on the work, will give a very good idea of its setting qualities, either in air or water. In general, the Portland cements can be relied on, especially if made by the standard companies, who cannot afford to put inferior grades on the market.