2193. Black Cement

2193.    Black Cement. Sulphide of antimony and iron dust, in equal proportions, stirred in with soluble glass (see No. 2182 (Colored Cements)), afford an exceedingly firm black cement.

2194. Dark Grey Cement

2194.    Dark Grey Cement. Zinc dust and iron in equal proportions, used as in No. 2182, yield a hard dark grey cement.

2195. Portland Cement

2195.    Portland Cement. Portland cement is formed of clay and limestone, generally containing some silica, the properties of which may vary without injury to the cement. The proportion of clay may also vary from 19 to 25 per cent, without detriment. The only necessary condition for the formation of a good artificial Portland cement, is an intimate and homogeneous mixture of carbonate of lime and clay, the proportion of clay being as above stated. The materials are raised to a white heat in kilns of the proper form, so that they are almost vitrified. After the calcination all pulverulent and scorified portions are carefully pricked out and thrown away. The remainder is then finely ground and becomes ready for use. The amount of water which enters into combination with it in mixing is about .366 by weight. It sets slowly, from 12 to 18 hours being required. Made into a thin solution like whitewash, this cement gives woodwork all the appearance of having been painted and sanded. Piles of stone may be set together with common mortar, and then the whole washed over with this cement, making it look like one immense rock of grey sandstone. For temporary use a flour-barrel may have the hoops nailed, and the inside washed with a little Portland cement, and it will do for a year or more to hold water. Boards nailed together, and washed with it, make good hot-water tanks. Its water-resisting properties make it useful for a variety of purposes.

2196. Mastic Cements, or Pierre Ar-tificielle

2196.    Mastic Cements, or Pierre Ar-tificielle. Boettger says that these cements are mixtures of 100 parts each of sand, limestone, and litharge, with 7 parts linseed oil. These ingredients, carefully mixed and well worked together, will have the consistency of moist sand, and at first but little coherence. When pressed, however, the mixture gradually acquires the hardness of ordinary sandstone, and in six months time will emit sparks when struck with steel. The binding agents in such cements are the litharge and oil, the sand giving the body, and limestone or chalk filling up the interstices.

2197. Coarse Stuff for Plastering

2197. Coarse Stuff for Plastering. Coarse stuff, or lime and hair, as it is sometimes called, is prepared in the same way as common mortar, with the addition of hair procured from the tanner, which must be well mixed with the mortar by means of a three-pronged rake, until the hair is equally distributed throughout the composition. The mortar should be first formed, and when the lime and sand have been thoroughly mixed, the hair should be added by degrees, and the whole so thoroughly united that the hair shall appear to be equally distributed throughout.