264 



CEMENTS, LIMES, AND PLASTERS. 



TABLE 127. 

 EFFECT OF AERATION ON SETTING TIME OF NATURAL CEMENT. 



(SABIN.) 



Effects of gypsum or plaster on natural cements. Natural cements 

 are affected by the addition of gypsum in regard to setting time and 

 strength in much the same manner as Portland cement would be. 

 The degree to which these effects are produced, for the same per- 

 centage of gypsum, depends entirely upon the chemical composition 

 of the respective cements. This fact seems to have been entirely over- 

 looked by experimenters, and in consequence the tests which have been 

 made are deprived of much of their value, because the analysis of the 

 cement is rarely included in the report of the test. 



Experiments on the effect of gypsum on the rate of set have been 

 carried out by Sabin,* and the results are embodied in Table 128, below, 

 and are shown diagrammatically in Fig. 50. 



TABLE 128. 

 EFFECT OF PLASTER ON SETTING. TIME OF NATURAL CEMENT. (SABIN.) 



* Report Chief of Engineers, U. S. A., 1895, p. 2938. 



