PORTLAND CEMENT TESTING. 



157 



sixty minutes. However, this uncertainty can be greatly overcome if tire 

 needle is carefully aijplied at intervals of five, ten, fifteen, or twenty 

 minutes according to the rapidity of set, indentations being made in a 

 row. After the pat has become dry, the point where the needle ceases 

 to penetrate is easily recognized (especially so if the surface is slightly 

 moistened), and the time can then be calculated according to the number 

 of previous indentations. 



Pigs. 2 and 3 illustrate a quick and a normal setting cement, worlced 

 according to these directions. 



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Fig. 2. 



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Fig. 3. 



This method, once the details are mastered, is just as convenient and 

 quick as a less accurate one. For research work and for cements the 

 setting qualities of which are close to the requirements of specifications, 

 it is especially valuable, as we have found that two pats of the same paste 

 will compare almost eiactly, and that even different operators will not 

 vary 10 per cent if they are careful and efiicient. 



