138 



CEMENTS, LIMES, AND PLASTERS. 



Proportions of mixture. The slaked lime is mixed with sand in 

 the usual proportion of 5 to 10 Ibs. of lime to 100 Ibs. of sand. Peppel 

 experimented on this point by preparing mixtures carrying various pro- 

 portions of lime and sand. His results are shown in the following table. 



TABLE 50. 

 EFFECT OF PERCENTAGE OF LIME. (PEPPEL.) 



Trans. Amer. Chem. Soc., vol. 5. Page 13 of pamphlet edition. 



The mixture may be accomplished in pug-mills, edge-runner mills, 

 wet pans or dry pans. 



Methods of molding. The mixture is shaped into bricks in a press. 

 Peppel states * that a press should fulfil the following requirements : 



"(1) The press must be able to regularly deliver a pressure of from 

 200 to 250 tons per brick and yet not break down if by accident the 

 pressure rises somewhat higher. 



" (2) The filling of the mold must be accomplished with great ac- 

 curacy and uniformity. 



" (3) All working parts must be so arranged that they will be free from 

 contact with loose sand, otherwise they will cut out at an alarming rate. 



" (4) The dies and mold linings must be made of the hardest mate- 

 rial obtainable." 



Many presses, both of American and German design, are now on the 

 market for use in the lime-sand brick industry. Any machine that will 

 press clay brick has power and strength enough to handle lime-sand 

 brick, but the new product is so fragile as to require delicate handling 

 in taking off the press. 



Methods of hardening the bricks. Three general types of harden- 

 ing processes have been in use. These are: (1) hardening by simple 

 exposure to the atmosphere; (2) hardening in an atmosphere saturated 

 with carbon dioxide; (3) hardening in a cylinder filled with steam 

 under pressure. 



* Trans. American Ceramic Society, vol. 5, pp. 33-35 of pamphlet edition. 



