K. MECHANICS AND ENGINEERING. 403 



statuary. Imitation ivory can be made from it for forming 

 billiard balls and other similar articles, medallions, buttons, 

 etc. By combination with mineral colors the cement may be 

 made to assume any desired tint, may be moulded like plas- 

 ter, and be employed in the manufacture, or imitation of in- 

 numerable objects of art and ornament. In practice the ce- 

 ment is never used in a pure form, but in combination with 

 other materials, which, being incorporated with it while in the 

 moist condition, are in the subsequent setting mechanically 

 bound together into a solid mass. For this purpose the mag- 

 nesia, in fine powder, is mixed with mineral substances, such 

 as sand, gravel, dust, or chips from marble or other stones, 

 or with emery, quartz, or other grits of various kinds, in va- 

 rying proportions, according to the result desired. This mix- 

 ture is then moistened with a solution of the chloride of mas:- 

 nesium, or with the bittern from salt-works. In some cases 

 it is made sufficiently wet to form a mortar, and in others only 

 enough to produce a state of dami3ness,like that of moulding 

 sand. The mixture may be effected in troughs by hand la- 

 bor, the material being worked over with shovels or hoes, or 

 more expeditiously in mixing machines designed expressly 

 for the purpose, and worked by horse or steam power. 



The materials of which this cementing substance is com- 

 posed are abundantly distributed over the surface of the 

 globe. Magnesia sufficiently pure for the purpose is obtained 

 by simply calcining mineral magnesite, large deposits of 

 which are known to exist in Prussia, Greece, Canada, Califor- 

 nia, Pennsylvania, and Maryland. Deposits will doubtless be 

 found in other places when the demand is made for the ma- 

 terial. The chloride of magnesium is readily obtained by con- 

 centrating sea-water, the bittern of salt-works being suffi- 

 ciently pure for the purpose. Sea-water concentrated to 30 

 B. precipitates nearly the whole of its chloride of sodium. 

 12 A, July, 1811, 412. 



scott's selenitic mortar. 



According to the London Mechanics' Magazine, a very im- 

 portant invention has lately been made by Colonel Scott, of 

 the Royal Engineers, of a new kind of mortar, having the 

 properties of setting very rapidly and becoming exceedingly 

 hard on account of its great cohesiveness. This termed se- 



