538 



CEMENTS, LIMES, AND PLASTERS. 



Effect of calcium sulphate on set of cement. Experiments on the 

 effect of setting time of the addition of gypsum or plaster are fairly 

 numerous. Unfortunately, such records mean very little, unless they 

 are accompanied by sufficient data, as to the chemical composition, 



700 



500 



300 



200 



100 



\ 



12345 

 Per cent of Plaster. 



FIG. 134. Effect of plaster on tensile strength of Portland cement. (Lewis.) 



fineness, etc., of the cement; to enable some idea to be formed con- 

 cerning the general type of cement tested. Experiments on low-limed 

 cement can not be fairly compared with those carried out on high-limed 

 cements; and cement made in stationary kilns behaves differently from 

 the usual product of the rotary. 



