880 NEW yoke: state museum 



manner and kept 28 days under the same conditions, shall show 

 a least average tensile strength of 220 lb per square inch. 



36 Required strength — American natural cement. Briquets of 

 neat natural cement mixed three minutes, put in the molds with, 

 thumbs and trowel and kept at a temperature of 65° to Y0° for 

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

 average tensile strength of 60 lb per square inch. 



Briquets of natural cement and standard crushed quartz in 

 equal parts, by weight, mixed and handled in the same manner 

 and kept at the same temperature for one day in moist air and 

 six days in water, shall show a least average tensile strength of 

 65 lb per square inch. 



Briquets similar to those last described and kept 28 days under 

 the same conditions, shall show a least average tensile strength of 

 150 lb per square inch. 



37 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 

 tensile strength. Since that date practice has been changed, in 

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

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



Crushed quartz was used in all the mortar tests on both natural 

 and Portland cements, that have been tabulated in this paper, 

 though in 1897 a few additional tests were made with natural 

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

 number to be of much value for comparison. 



The boiling test 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 

 is required by the specifications for Portlands, it has been mad© 



