133 



This clip is to be used without cushioning at the points 

 of contact with the test specimen. The bearing at each 

 point of contact should be ^4 in. wide, and the distance 

 between the center of contact on the same clip should be 

 1% in. 



47. Test pieces should be broken as soon as they are 

 removed from the water. Care should be observed in 

 centering the briquettes in the testing machine, as cross- 

 strains, produced by improper centering, tend to lower 

 the breaking strength. The load should not be applied 

 too suddenly, as it may produce vibration, the shock from 

 which often breaks the briquette before the ultimate 

 strength is reached. Care must be taken that the clips 



nm 



Fig. 5. 



and the sides of the briquette be clean and free from 

 grains of sand or dirt, which would prevent a good bear- 

 ing. The load should be applied at the rate of 600 Ib. per 

 minute. The average of the briquettes of each sample 

 tested should be taken as the test, excluding any results 

 which are manifestly faulty. 



Constancy of Volume. 



48. Methods: Tests for constancy of volume are di- 

 vided into two classes: (1) normal tests, or those made 

 In either air or water maintained at about 21 C. (70 F.), 

 and (2) accelerated tests, or those made in air. steam or 

 water at a temperature of 45 C. (115 F.) and upward. 

 The test pieces should be allowed to remain 24 hours in 

 moist air before immersion in water or steam, or preser- 

 vation in air. 



