154 REIBMNG AND SALINGER. 



into consideration. This is produced by the heating of the cement after 

 it is gauged and molded. Many cements heat considerably at some jieriod 

 of the stage of early setting and Imrdening, the rise in temperature often 

 being as much as 10°C.; it may take place in five minutes, or it may not 

 occur until many hours after the gauging. 



C. Prussing ^^ states that "many slow setting cements of excellent 

 quality begin to set after five or six hours and then set conipletelj^ in 

 one hour, giving a rise of temperature of 5° to 7°C." The heat gen- 

 erated by briquettes placed under a damp cloth is not confined, as it is 

 readily conducted away into the surrounding atmosphere. Moist-air 

 closets are constructed to insulate the interior from outside heat in- 

 fluences as much as possil^le, and as a result the heat generated by the 

 briquettes is confined ; so that in a cubical moist-air closet of 2 feet on 

 the side which was used to store briquettes after they were removed from 

 the molds, the temperature often rose to 40° (30° being room tempera- 

 ture) when it held from 80 to 100 briquettes. A number of slow- 

 setting briquettes made at different, successive intervals of time, or worse 

 still a mixture of quick, normal, and slow-setting cements, will under 

 these conditions not be sul^jected to the same rmiform temperature, or 

 to a temperature change that is characteristic of it during its most 

 critical setting and hardening period ; and the same is true of the storage 

 of pats made for the time of setting when man}' are placed in one com- 

 partment after gauging. 



It is well known that the temperature conditions under which cement 

 sets and hardens will influence its "tensile strength. Therefore, the 

 practice of storing numerous briquettes in one compartment of a moist- 

 air closet is very liable to cause abnormal one, seven and twenty-eight 

 day breaks of some of them. Pats for time of setting similarly stored 

 may be also afl:ected to such a degree that an otherwise slow-setting 

 cement may become quick setting. 



We suggest two ways of overcoming this objectional feature of the 

 ordinary closet. The heat generated by the setting cements may be 

 conducted away by means of a forced ventilation of air saturated with 

 moisture; or only briquettes and setting jDats of the same cenrent made 

 at practically the same time should be placed in a small, insulated com- 

 partment. The former method will maintain the interior of the compart- 

 ment at nearly the same temperature as that of the laboratory, while the 

 latter will meet the conditions of actual service, as the heat generated 

 by the cement is not readily conducted away. Laboratory tests should 

 coincide as closely as is possible with the actual conditions of construction 

 work, where large volumes of concrete are tamped into wooden frames. 

 The heat generated in such a large mass (especially in the center of it) 

 is not conducted away hj ventilation and it is in fact partly insulated 



''•Tlioniiul. Zcit. (1804), 18, 251. 



