72 G NEW YOKK STATE MUSETTM 



Portland cement becomes slow setting through long storage, 

 though at first it may gain in its setting speed if kept in a dry- 

 place free from drafts. 



Jameson also states that some cement, when taken from the 

 mill and gaged with Avater, is found to be moderately slow setting, 

 but after 24 to 30 hours will set almost before it can be mixed. 

 Store it in a cool, dry place and in a few days it will become slow 

 setting. 



The speed of setting usually decreases with the age of the 

 cement, provided it has been stored in a dry place. Some con- 

 sider that slow setting is due to free lime, but other factors also 

 enter into the problem, such as the underburning or overburning 

 of the cement, the underburned setting quicker. A vitrified 

 cement will never set. 



Boiling test 



This is the one that has been recommended as the best for 

 determining the soundness of a cement. At the fifth interna- 

 tional convention for unifying methods for testing construction 

 materials, held in Zurich in September 1895, the rules for con- 

 ducting this test were laid down as follows. 



1 The rapidity test of hydraulic cements for constancy of vol- 

 ume consists in the application of warm baths at temperatures 

 of from 50° to 100° C. 



2 Manner of making test pieces. Enough water is used to 

 bring the neat cement after proper working into a plastic state. 

 Two balls from 1.5-2 inches diameter are formed by hand and 

 kept in moist air resting on some non-absorbent material. (Sand 

 mixtures are not subjected to this test, neither are briquets that 

 arc to be tested for tensile strength.) The employment of ten- 

 sion briquets and cylindric disks from 2 to 4 inches in diameter, 

 from 4 to I4 inches thick, is likewise permitted. 



3 Duration of previous hardening. Till set has taken place, 

 test pieces must be kept in moist air. Portland, slag, po;^zuolana, 

 and Roman cement will be kept uniformly thus for 24 hours, 



