132 CEMENTS, LIMES, AND PLASTERS. 



blocks have so far perfected the product as to bring this stone into 

 successful competition with the very best of the natural and artifi- 

 cial building materials: The action of lime upon silica, forming a 

 silicate of lime (calcmakit) , and thus binding together particles of 

 sand, as in mortar, has been known from the remotest ages, and con- 

 crete walls of great antiquity are now standing, vying with the natural 

 rock in hardness and durability. Some years since a concrete block, 

 compacted by pressure, was brought out in this country and used to 

 some extent as a building material, but the slowness of the induration 

 and uncertainty in the product hindered its general introduction. 

 The improvements referred to consist in the use of heat in connection 

 with quicklime and sand, by which the formation of the silicate of lime 

 is hastened, and the same effect, which formerly took years to be con- 

 summated, is now produced in a few days. Ground quicklime is thor- 

 oughly mixed with clean, sharp sand, and is then subjected to the action 

 of either superheated or high-pressure steam, which slaks the lime 

 and causes it to attack the silica. This process continues for from 

 twenty minutes to ten days, according to the degree of heat employed, 

 when the material is molded and compressed by a heavy steam-ham- 

 mer into blocks of any desired form. The ordinary building-block 

 made by this process is 10 inches wide and 4 inches deep, having a 

 hollow space in the center 6 inches long by 1 inch broad; when the 

 blocks are placed upon each other, so as to break joints, a continuous 

 and connected series of air-chambers will be formed within the wall. 

 Thirty days' exposure of the block, after it is first formed, to the air, 

 produces an induration quite sufficient for all ordinary building pur- 

 poses, but the block continues to harden for an unlimited period. A 

 church built entirely of this material was recently dedicated at Morris- 

 ania. A number of fine buildings have already been constructed of 

 this material in Chicago, among which may be mentioned a handsome 

 block of dwellings on Sixteenth Street, and the Young Men's Christian 

 Association of the same city, which was recently burned. The endur- 

 ance of this stone when submitted to repeated freezing and thawing 

 is quite remarkable, and experiment proves it to be equal in this respect 

 to granite." 



The theory of lime-sand brick. When ordinary quicklime is slaked, 

 mixed with sand, and used as mortar the mixture hardens very slowly 

 and never attains much strength. The hardening is due to the fact 

 that the slaked 'lime gradually absorbs carbon dioxide from the atmos- 

 phere and recarbonates, forming a sort of artificial limestone. So 

 far as known, there is no chemical action between the lime and the 



