750 NEW YORK STATE MUSEUM 



pounds per square incli) at the end of 84 days. If, however, the 

 strength in 28 days is not more than 5 kilograms per sq. cm 

 (71.12 pounds per square inch) in excess of that at seven days^ 

 then it must be at least 55 kilograms per sq. cm (727.8 pounds- 

 per square inch) in 28 days, and in any case where this is not 

 attained in 28 days it must be exceeded in 84 days. 



Tests of cement mixed with sand are also specified. The stand- 

 ard sand is produced by crushing quartzite obtained from the 

 quarries near Cherbourg, and sifting it through sieves of 64 and 

 144 meshes per sq. cm (413 and 929 meshes per square inch). 

 That which remains between these two sieves is washed and dried^ 

 and constitutes the standard sand. 375 grams (13.25 ounces) of 

 this sand is mixed with 125 grams (4.41 ounces) of cement, and 

 water is added in the proportion of 12 parts by weight to lOO 

 parts of sand and cement combined. The sand and cement are 

 first carefully mixed in a basin or capsule, then the whole of 

 the sea water is added at once, and the mixture stirred with a 

 spatula for 5 minutes. At the expiration of seven days the 

 strength of the sand cement briquets should be at least 8 kilo- 

 grams per sq. cm (113.78 pounds) and in 28 days 15 kilo- 

 grams per sq. cm (213.35 pounds per square inch). In 28- 

 days the strength should exceed that at seven days by 2 kilo- 

 grams per sq. cm (28.45 pounds per square inch). In 84 

 days the strength mast be greater than at 28 days, and at least 

 18 kilograms per sq. cm (256 pounds per square inch). The 

 84 day tests are only considered indispensable for those cementa 

 which may have stood the two previous tests; but if, while the 

 cement is in store, the 84 day tests should be unsatisfactory, it 

 may be rejected. 



FINENESS OF GETT^TDIKa 



The degree of fineness to which the cement must be ground 

 is not specified, it being considered that very fine grinding in- 

 creases the strength chiefly during the duration of the tefe*ts, and 

 that subsequent increase of strength is less with fine than with 

 coarse cement. 



TIME OF SETTING 



This practically agrees with the German specifications. Anjr 

 cement commencing to set in less than 30 minutes, or failing to- 

 commence to set within three hours is to be rejected; and the 

 final set must have taken place within 12 hours. In each case 

 the time is reckoned from the moment the water is poured or 

 the cement. 



