160 



ILLINOIS ACADEMY OF SCIENCE 



diameter probably would have a strength about 35 per 

 cent greater than the strength of a specimen whose height is 

 equal to twice its diameter. 



Fig. 2 shows the increase in strength of gypsum with in- 

 creased age after hydration. Each value given is the average 

 strength of five 3x6-in. cylinders. Fig. 3 uses the same 

 strengths as Fig. 2, but in Fig. 3 the strengths are plotted 

 against the ratios of the weights of the specimens tested, to 

 the weight of a thoroughly dry specimen. This indicates 

 that the age affects the strength only as evaporation pro- 



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cughly dry, given the weight wet, the percentage of water used 

 in gaging the mixture, and the percentage of w T ater already 

 in the calcined gypsum. The computations are based upon 

 gresses with age. Within the accuracy of the weighings 

 made to determine the rate of drying out, it has been possible 

 to compute accurately the weight of the specimens when thor- 

 the assumption that the process of hydration continues until 

 all the gypsum becomes CaS0 4 2H 2 and that all excess 

 water is lost by evaporation. The assumptions may be in- 

 correct, but the results show this to be a practical method of 

 determining the final weight of the gypsum when the per- 

 centage of gaging water used and the percentage of water 

 in the calcined gypsum are known. 



