136 



CEMENTS, LIMES, AND PLASTERS. 



is undesirable, not so much because of its effect on the strength or dura- 

 bility of the brick as because of its effect on the color. 



The following experiments on high-calcium vs. magnesian limes 

 appear to prove that the latter give bricks inferior in strength. In view 

 of the results attained elsewhere, however, those in the table below 

 should be accepted with caution. 



TABLE 49. 



COMPARATIVE TESTS OF HIGH-CALCIUM AND MAGNESIAN LIME 

 BRICKS. (PEPPEL.) 



Trans. Amer. Ceramic Soc., vol. 5. Page 15 of pamphlet edition. 



The lime-sand bricks whose results are shown in the above table 

 were made up of two parts coarse sand and one part fine sand, to which 

 base was added 10 per cent of lime. The blocks were molded under 

 a pressure of 15,000 Ibs. per square inch and hardened by exposure 

 for four to fourteen hours to a steam pressure of 150 Ibs. per square 

 inch at a temperature of 185 C. Each of the results given in the table 

 is the average of twelve tests. 



Methods of slaking the lime. The lime may be either slaked to a 

 paste by the addition of more water than is theoretically required 

 or slaked to a dry powder. The general methods employed are usually 

 similar to those in the lime-hydrate industry. In one process, however, 

 a machine of entirely different type is employed, which requires some 

 notice. 



The Schwarz process is described * as follows: 



" The first operation in the Schwarz process is the mixing of the 

 sand and lime, which is done in a vacuum mixing-machine. This 

 machine is shown in transverse and longitudinal section in Fig. 26. 

 Briefly described, the machine consists of a steam- jacketed drum with 

 interior rotary blades operated by suitable gearing outside and at one 

 end. This drum, which has a capacity of about three tons of sand, 



* Engineering News, vol. 49, p. 179. Feb. 19, 1903, 



