226 



REIBLING AND REYES. 



amounts its retarding influence is less. Consequently, it was usually found un- 

 necessary to carry the investigation beyond 3 per cent. 



The results obtained by adding small amounts of plaster in increasing 

 quantities to the non-seasoned material are shown by figure 17. 



As the amount of plaster used was increased step by step in each 

 cement, the initial set took place earlier, then later, and finally again 

 earlier. In each instance, also, the amount of water required to pro- 

 duce a paste of normal consistency at fii'st decreased decidedly, and then 

 later slightly increased. However, as is readily apparent from figure 

 18, the curves of which are plotted from the data recorded in figure 17, 

 the same quantity of plaster did not effect the set and plasticity of the 

 different cements to the same extent. 



All of these cements contained free, sintered and non-sintered lime. 

 Table XXV shows that the presence of small amounts of plaster of Paris 

 such as we used has no appreciable effect upon the slaking of ignited 

 lime. 



Table XXV. " — The effect of plaster of Paris on the heat generated by the slaking 

 of freshly ignited lime in an excess of water. 



Ex- 

 peri- 

 ment 



No. 



Contents of the 



calorimeter 



in grams. 



Tem- 

 perature 

 of the 

 calori- 

 meter 

 and 

 water. 



Temperatute of the calorimeter 

 and its contents after the solids 

 had been added, the laboratory 

 temperature remaining between 

 26°. 5 and 27°.0. 



Total 

 rise in 

 temper- 

 ature. 



After 1 

 minute. 



After 2 

 minutes. 



Afters 

 minutes. 



After 4 

 minutes. 



1 

 2 

 3 



4 



5 



6 



( 75 water 



°C. 

 26.0 



I 26.0 

 !• 26.0 



I 26.5 



i 27.0 



I 27.0 



°C. 

 26.0 



53.0 

 53.0 



53.0 



54.0 



53.0 



°C. 

 26.0 



51.0 

 51.0 



51.0 



51.0 



51.0 



°C. 

 26.2 



49.5 

 49.5 



49.5 



49.0 



49.5 



°a 



26.4 

 48.5 



48.5 

 48.5 

 48.0 

 48.5 



°C. 

 0.4 



27.0 

 27.0 



26.5 



27.0 



26.0 



I 20 plaster 



75 water _ 



\ 10 lime 



[ 75 water 



i. 10 lime - 



[ 1 plaster 



( 75 water 



1 10 lime 



I 2 plaster _ 



[ "is water 



< 10 lime 



I 4 plaster _ 



[ 75 water 



\ 10 lime 



[ 8 plaster.- _ 





" The calorimeter used consisted of an asbestos-covered 250 cubic centimeter Erlen- 

 meyer flask, fitted with a rubber stopper containing the thermometer. Although rather 

 crude it is sufficiently accurate. 



Therefore, in the presence of an excess of water, other conditions 

 remaining the same, the heat generated by the slaking of the lime in 

 a given cement is independent of the amount of plaster which the cement 



