228 



REIBLING AND REYES. 



contains, and the influence of tliis factor remains practically a constant 

 for each cement. With this fact thoroughly in mind the effects of dif- 

 ferent amounts of plaster upon the plastic and setting properties of 

 non-seasoned cements may readily be explained. 



Thus, from figure 17 and calorimetric tests with brand L cement 

 we obtained the figures in Table XXVI. 



Table XXVI. — The effects of various amounts of plaster on the heat generated, 

 and the plastic and setting properties of non-seasoned, brand L cement. 



Contents of the calori- 

 meter, in grams. 



Total 

 rise in 

 tem- 

 pera- 

 ture in 

 4 min- 

 utes. 



Per 

 cent 

 of wa- 

 ter re- 

 quired 

 to pro- 

 duce a 

 paste of 

 norma) 

 con- 

 sist- 

 ency; 



Time 



of 

 initial 

 set in 

 min- 

 utes. 



Remarks. 



"5 water 



°C. 



1 " 

 1" 



I 1.8 

 I 1.8 



29.0 

 24.0 



21.0 



21.5 



270 

 80 



40 



100 



A regauged cement paste. 



jA partially regauged cement 

 I paste. 



A normal cement paste. 

 Do. 



50 cement- 



75 water 



50cement + 0. 5 per 



cent of plaster. 

 75 water__ __ __ ___ 



50 cement-fl.O per 



cent of plaster. 



75 water 



50cement + 2. per 



cent of plaster. 



From these figures it is seen that the constant rise in temperature 

 due to the heat generated by the slaking of the lime in this cement is 

 1°.8. Any excess above this must be due to the chemical activity of 

 the compounds which cause the cement to set. When no plaster had 

 been added to the cement, the temperature of the calorimeter rose 4°.l, 

 or 3°. 3 in excess of the lime factor. As already stated, the normal con- 

 sistency-paste made from this cement was that of a regauged, freshly 

 set cement, which therefore required a large amount of water and set 

 very slowly. 



The use of 1 per cent of plaster reduced the rise in temperature of 

 the calorimeter to the constant lime factor (1°.8). It also retarded the 

 rate of reaction of the setting compounds until long after the cement 

 had been molded ^^ (40 minutes). Consequently this cement was not 



'- In this calorimetric work we only took the early rise in temperature, pro- 

 Tided it remained constant at the end of 4 minutes. The reason for so doing is 

 that according to the American Society specifications which were used it requires 

 about 4 minutes to knead and mold and to test the consistency of the cement. 



