18 BULLETIN 949, U. S. DEPARTMENT OF AGRICULTURE. 



CHEMICAL PROPERTIES. 



(2) The following limits shall not be exceeded: 



Per cent. 



Loss on ignition 4. 00 



Insoluble residue 85 



Sulphuric anhydride (S0 3 ) 2. 00 



Magnesia (MgO) 5. 00 



PHYSICAL PROPERTIES. 



(3) The specific gravity of cement shall not be less than 3.10 (3.07 for white Port- 

 land cement). Should the test of cement as received fall below this requirement 

 a second test may be made upon an ignited sample. The specific gravity test will not 

 be made unless specifically ordered. 



(4) The residue on a standard No. 200 sieve shall not exceed 22 per cent by weight. 



(5) A pat of neat cement shall remain firm and hard and show no signs of distortion, 

 cracking, checking, or disintegration in the steam test for soundness. 



(6) The cement shall not develop initial set in less than 45 minutes when the Vicat 

 needle is used or 60 minutes when the Gillmore needle is used. Final set shall be 

 attained within 10 hours. 



(7) The average tensile strength, in pounds per square inch, of not less than three 

 standard mortar briquettes (see par. 51) composed of one part cement and three 

 parts standard sand, by weight, shall be equal to or higher than the following: 



Age 



at 

 test. 



Days. 



7 

 28 



Storage of briquettes. 



1 day in moist air, 6 days in water.. 

 1 day in moist air, 27 days in water. 



Tensile 

 strength 



per 

 square 

 inch. 



Puuvds. 

 200 

 300 



(8) The average tensile strength of standard mortar at 28 days shall be higher than 

 the strength at 7 days. 



PACKAGES, MARKING, AND STORAGE. 



(9) The cement shall be delivered in suitable bags or barrels with the brand and 

 name of the manufacturer plainly marked thereon unless shipped in bulk. A bag 

 shall contain 94 pounds net. A barrel shall contain 376 pounds net. 



(10) The cement shall be stored in such a manner as to permit easy access for proper 

 inspection and identification of each shipment and in a suitable weather-tight building 

 which will protect the cement from dampness. 



INSPECTION. 



(11) Every facility shall be provided the purchaser for careful sampling and inspec- 

 tion at either the mill or at the site of the work as may be specified by the purchaser. 

 At least 10 days from the time of sampling shall be allowed for the completion of the 

 7-day test and at least 31 days shall be allowed for the completion of the 28-day test. 

 The cement shall be tested in accordance with the methods hereinafter prescribed. 

 The 28-day test shall be waived only when specifically so ordered. 



REJECTION. 



(12) The cement may be rejected if it fails to meet any of the requirements of these 

 specifications. 



