MANUFACTURE AND PROPERTIES OF LIME-SAND BRICKS 135 



TABLE 48. 

 EFFECT OF FINENESS OF SAND. (PEPPEL.) 



These tests show that the bricks decrease in compressive strength 

 and increase in tensile strength as the amount of fine sand in the mix- 

 ture increases. These results of themselves appear to be unfavorable 

 to the contention of lime-sand brick manufacturers, that the strength 

 of their product is due to chemical reactions between the sand and the 

 lime. For if this contention were true, the finer sand particles would 

 certainly be more active chemically than the coarser grains, and an 

 increase in fineness of sand would necessarily mean more extensive 

 chemical inte action and consequently greater strength in both com- 

 pression and tension. 



Drying the sand. In order to secure uniformity in the product 

 it is desirable that the sand should be dried before mixing with the 

 lime. So far this point has not been realized by many manufacturers, 

 who are content to use the sand as it comes from the pit at one time 

 practically dry, at another carrying 10 to 15 per cent of moisture. 



As to methods of sand-drying, considerable differences in practice 

 exist. In the Schwarz machine, described and figured on page 137, 

 the sand is placed in a steam-jacketed drum, the drying being aided 

 by revolving paddles which stir up the sand. At a number of plants 

 live or exhaust steam is used in pipe-dryers, the sand being shoveled 

 on a series of horizontal pipes filled with steam. The best practice is 

 probably to use a rotary dryer. At one plant * a direct-heat rotary 

 dryer 22 inches in diameter and 22 feet long, set at a slope of about 

 \ inch to the foot, dries 40 to 50 yards of sand in ten hours with a fuel 

 consumption of 700 Ibs. coal. At another, a 30-foot dryer set at a slope 

 of about | inch per foot, with a fan to induce draft, is handling 40 to 

 50 yards sand in ten hours with a consumption of 600 to 800 Ibs. coal. 



Necessary properties of the lime. The lime should be carefully 

 and thoroughly slaked, and should be as free from impurities as possible. 

 The presence of more than a few per cent of clayey matter or iron oxide 



* The Clay Worker, vol. 42, p. 588. 1904. 



