SPECIFICATIONS FOR PORTLAND CEMENT. 629 



15 to 30 minutes and kept boiling for six hours. After cooling, the 

 distance between the points is again measured; the difference between 

 the two measurements represents the expansion of the cement, which 

 must not exceed the limits laid down in this specification. 



(14) The tests and analyses hereinbefore referred to shall in no case 

 relate to a larger quantity of cement than 250 tons sampled at one time. 



Acceptance. (15) No cement is to be approved or accepted unless 

 it fully complies with the foregoing conditions. 



American Society for Testing Materials, 1904. 



GENERAL OBSERVATIONS. 



1. These remarks have been prepared with a view of pointing out 

 the pertinent features of the various requirements and the precautions 

 to be observed in the interpretation of the results of the tests. 



2. The committee would suggest that the acceptance or rejection 

 under these specifications be based on tests made by an experienced 

 person having the proper means for making the tests. 



3. Specific gravity. Specific gravity is useful in detecting adultera- 

 tion or uriderburning. The result of tests of specific gravity are not 

 necessarily conclusive as an indication of the quality of the cement, but 

 when in combination with the results of other tests may afferd valuable 

 indications. 



4. Fineness. The sieves should be kept thoroughly dry. 



5. Time of setting. Great care should be exercised to maintain 

 the test pieces under as uniform conditions as possible. A sudden 

 change or wide range of temperature in the room in which the tests are 

 made, a very dry or humid atmosphere, and other irregularities vitally 

 affect the rate of setting. 



6. Tensile strength. Each consumer must fix the minimum re- 

 quirements for tensile strength to suit his own conditions. They shall, 

 however, be within the limits stated. 



7. Constancy of volume. The tests for constancy of volume are 

 divided into two classes, the first normal, the second accelerated. The 

 latter should be regarded as a precautionary test only, and not infallible. 

 So many conditions enter into the making and interpreting of it that 

 it should be used with extreme care. 



8. In making the pats the greatest care should be exercised to avoid 

 initial strains due to molding or to too rapid drying out during the first 

 twenty-four hours. The pats should be preserved under the most 



