MANUFACTURE AND PROPERTIES OF LIME-SAND BRICKS. 139 



The first of these processes is slow, since the hardening takes place 

 only as rapidly as the lime in the brick can absorb water and carbon 

 dioxide from the atmosphere. The second process is more rapid, but 

 the change of slaked lime to lime carbonate is still incomplete. In 

 the third process, which is the one used at practically all lime-sand 

 brick plants to-day, the reactions are rapid, and its advocates claim 

 in addition that the steam under pressure causes the combination o 

 the lime with the sand, so as to form a greater or lesser amount of sili- 

 cate of lime. The truth of this contention seems to be more than ques- 

 tionable; but the process is in increasing use and therefore demands 

 a somewhat more detailed description. 



In the process as now followed, the bricks are loaded onto trucks 

 and these are run into a long horizontal cylinder. This hardening 

 cylinder is then closed and steam under pressure is admitted. 



The experiments, whose results are given in table, were undertaken 

 by S. V. Peppel to determine the most advantageous steam pressure 

 and time of hardening. In discussing these results, Peppel states that 

 "this table shows that four hours' time at 150 Ibs. steam pressure is 

 sufficient; that six or eight hours are required at 120 Ibs.; that eight 

 to twelve hours are required at 100 Ibs." 



To the present writer, however, the table seems to show that very 

 little relation of any kind exists between pressure and time and the 

 strength of the resulting brick. 



TABLE 51. 



EFFECTS OF STEAM PRESSURE AND TIME OF HARDENING. 

 Strength in pounds per square inch. 



(PEPPEL.) 



Trans. Amer. Ceramic Soc., vol. 5. Page 25 of pamphlet edition. 



