COMPOSITION, PROPERTIES, AND TESTS OF PLASTERS. 



59 



briquettes were sufficiently set, which usually took about three hours, 

 the molds were removed". Some of the briquettes were kept in air 

 and some in water for various lengths of time, and they were finally 

 broken in a Fairbanks cement-testing machine. Preliminary tests, 

 using various percentages of water, showed that 30 to 35 per cent of 

 water gave the maximum strength of briquettes. As 35 per cent gave 

 a mixture that was more readily handled in the making of briquettes 

 than the 30 per cent mixture, it was adopted for the final series of tests 

 whose results follow. 



A series of 220-day tests were made, but the results are of little value, 

 because the briquettes were allowed to stand in very moist air between 

 the 28- and 220-day periods, and therefore all showed a marked falling 

 off in strength. For this reason the results of the 220-day tests are 

 omitted here. 



TABLE 13. 

 FINENESS OF PLASTERS TESTED. 



TABLE 14. 

 TESTS OF TENSILE STRENGTH AND EFFECT OF SAND. 



