MECHANICS AND USEFUL ARTS. 49 



the hardness of marble. It will take any color, and has been 

 used by the inventor for mosaics, imitations of ivory, billiard balls, 

 etc. It possesses the agglutinative property in the highest de- 

 gree, so that solid masses may be made with it at a very low cost 

 by mixing it on a large scale with substances of little value. 1 

 part of magnesia may be incorporated with upwards of 20 parts 

 of sand, limestone, and other inert substances, so as to form hard 

 blocks ; while lime and other cements will hardly admit of the 

 incorporation of two or three times their weight of extraneous 

 matter. 



By means of these artificial blocks, buildings may easily be car- 

 ried on in places where materials for the purpose are scarce. All 

 that is required is to convey a quantity of magnesia and chloride 

 of magnesium to the spot, if there be none to be had there, and 

 then to mix them with sand, pebbles, or other matter of the kind 

 close at hand ; blocks can be made of any shape, and imitating 

 hewn stone. This magnesian cement may be obtained at a very 

 low cost, especially if the magnesia be extracted from the mother 

 lye of salt-works, either by M. Balard's process, whereby magnesia 

 and hydrochloric acid are obtained at the same time, or else by 

 decomposing the lye, which always contains a large proportion of 

 chloride of magnesium, by means of quick-lime, which, by double- 

 decomposition, yields magnesia and chloride of lime containing a 

 certain quantity of chloride of magnesium, and which, with the 

 various other cheap substances, may be used for whitewashing. 



CEMENT FOR IRON. 



An exhibition of a most interesting character (says an English 

 paper) took place recently at the Albion Works, Battersea, Eng- 

 land. The exhibition consisted of a number of practical illustra- 

 tions of the uses to which a certain description of cement is 

 applied, having for its principal ingredient more or less of a par- 

 ticular gum or substance called the zepipe or " zopissa," which 

 for some years past has been identified with the name of Col. 

 Scezerelmey. It appears to be a most protean substance, for it 

 holds on with wonderful tenacity to timber, glass, brick, cement ; 

 and last, though by no means the least of its remarkable qualities, 

 it will unite iron surfaces together as completely as though they were 

 welded. The cement has the quality of being perfectly water and 

 air tight. It can be conveniently used, and hardens with the 

 greatest rapidity. About five minutes is the maximum of time 

 required for it to harden thoroughly. 



Of the value of such a material as this for engineering and 

 building purposes, it is impossible to speak too highly. Our pro- 

 fessional readers will at once perceive a variety of uses connected 

 with railway and h} 7 draulic works to which a material of this kind 

 would be of the greatest possible value. Tunnels and bridges, 

 docks and quay walls, could be constructed by its use in consider- 

 ably less time and at greatly reduced cost; and with respect to 

 sewers, an immense improvement would be effected in employing 

 a material on which fluids produce no impression. Platforms and 



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