NEW YORK BTATB MUSEUM 



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

 h in 28 days is aot more than 5 kilograms per sq. cm 

 (71.12 pounds per Bqnare inch) in excess of that at seven days, 

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

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

 ,i m . ( l u it must he exceeded in S4 days. 



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

 ard duced by crushing quartzite obtained from the 

 quarries mar Cherbourg, ami Bifting it through sieves of G4 and 

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

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

 and constitutes the Btandard Band. 375 grams (13.25 ounces) of 

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

 wat added in the proportion of 12 parts by weight to 10O 

 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 

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

 h 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 23 

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

 grams per sq. cm (2S.45 pounds per square inch). In 84 

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

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

 day tests are only considered indispensable for those cements 

 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 GRINDING 



The degree of fineness to which the cement must be ground 



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



a the Btrength chiefly during the duration of the tests, and 



that subsequent increase of strength is less with fine than with 



coarse cement. 



TIME OF SETTING 



This practically agrees with the German specifications. Any 

 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 Bet must have taken place within 12 hours. In each case 

 the lime is reckoned from the moment the water is poured on 

 the cement 



