TESTING OF PORTLAND CEMENT. 



329^ 



grinding lessens the deleterious effects of any under- 

 burning that may have occurred, owing to a more 

 complete distribution of any stray portions of unburnt 

 lime throughout the cement. The actual test for fineness 

 is to pass a sample of the cement through a standard 

 sieve of fine brass wire and weigh the residue which is 

 prevented by the sieve from passing through, and to 

 express the fineness as a percentage of this residue. 

 For instance, a pound of the cement may be taken and 

 put through the sieve and the residue found to weigh 

 0'151b. In this case the residue would amount to- 



FIG. 166. BAILEY'S HAND MACHINE FOR CEMK.NT TESTING. 



15 per cent, of the weight of cement tested. It is 

 important in this connection that not only should the 

 number of meshes to the square inch in the sieve be given, 

 but also the thickness of the wire used. 



In the German standard rules for testing Portland 

 cement, it is stated that the fineness must be such that 

 not more than 10 per cent, residue is left after the cement 

 has passed through a sieve having 5,806 meshes to the 



