£hO ATE Mi BEUM 



under the conditions, Bnall sliow 



a 1. 20 II) per square inch. 



Required strength — American natural cement. Briquets of 

 neat natural cement minutes, put in the molds with 



thumbs and t and kept at a temperature of 65° to 70° for 



in moist air and 22 hours in water shall show a least 

 ^th of 60 lb per square inch. 

 of natural cement and standard crushed quartz in 

 equal parts, l>y weight, mixed and handled in the same manner 

 the Bame temperature for one day in moist air and 

 ya in water, shall show a least average tensile strength of 

 ;are inch. 

 Briquets similar to those last described and kept 28 days under 

 conditions, shall show a least average tensile strength of 

 150 lb per square inch. 



Standard crushed quartz. The standard crushed quartz used 

 in the tests shall pass a sieve of 400 meshes per square inch and 

 shall stop on a sieve of 900 meshes per square inch. 



Methods of testing 



In all the natural cements tested prior to July 1, 1900, the 



briquets were placed for two hours in air, in place of the usual 



24 hours, while the neat Portlands were given a two day test for 



rength. Since that date practice has been changed, in 



ard to the natural cements, to conform to the standard, while 



the Portlands, when tested neat, are usually given a one day test. 



( Iruehed quartz was used in all the mortar tests on both natural 



' .rtlaud cements, that have been tabulated in this paper, 



though in 1897 a few additional tests were made with natural 



1. These have been omitted, however, as being too few in 



Dumber to be of much value for comparison. 



The boilii is used on every new brand of cement sub- 



mitted; and at frequent intervals on all brands. 



The machine used is the Fairbanks 1000 lb automatic, with 



hand molded briquets. It will be noted that though a neat test 



by : '-cifications for Portlands, it has been made 



