SPECIFICATIONS FOR PORTLAND CEMENT. 623 



including the time of setting in air, they shall be immersed in the hot 

 water and allowed to remain there for eighteen hours. After removal 

 from the water the samples shall not be curled up, shall not have fine 

 hair cracks, nor large expansion cracks, nor shall they be distorted. 

 If separated from the glass, the samples shall break with a sharp, crisp 

 ring. 



(6) Tensile est (neat cement). Briquettes made of neat cement 

 mixed with about 20 per cent of water, by weight, after remaining 

 one day in air, in a moist atmosphere, shall be immersed in water, 

 and shall be capable of sustaining a tensile stress of 250 Ibs. per square 

 inch after submersion for two days, 400 Ibs. per square inch after sub- 

 mersion for six days, 500 Ibs. per square inch after submersion for 

 twenty-seven days. The tensile test shall be considered as the aver- 

 age of the strength of five briquettes, and any cement showing a decrease 

 in tensile strength on or before the twenty-eighth day shall be rejected. 

 (Sand and cement.) The sand for standard tests shall be clean quartz, 

 crushed so that the whole shall pass through a sieve of 400 meshes to 

 the square inch, but shall be retained on a sieve of 900 meshes per square 

 inch. The sand and cement shall be thoroughly mixed dry, and then 

 about 10 per cent of their weight of water shall be added, when the 

 briquettes are to be formed in suitable molds. After remaining in a 

 damp chamber for twenty-four hours the briquettes shall be immersed 

 in water, and briquettes made in the proportion of one of cement to 

 three of sand, by weight, shall bear a tensile stress of 125 Ibs. per square 

 inch after submersion for six days, and 200 Ibs. per square inch after 

 submersion for twenty-eight days. Sand and cement briquettes shall 

 not show a decrease in tensile strength at the end of twenty-eight days 

 or subsequently. 



(4) The manufacturer shall, if required, supply chemical analyses 

 of the cement. 



(5) Packing. The cement shall be packed either in stout air- and 

 water-tight casks, carefully lined with strong brown paper, or in strong 

 air- and water-tight bags. 



(6) The manufacturer shall give a certificate with each shipment 

 of cement, stating (1) the date of manufacture; (2) the tests and 

 analyses which have been obtained for the cement in question at the 

 manufacturer's laboratory; (3) that the cement does not contain any 

 adulteration. 



