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Time of Setting: It shall not develop init1a..1- ret in :Less than thirty (30) minutesi and must develop hara set in not lese than one hcur, nor more than ten hovxs. Tensile Strength: Thi riirimum requirements for tensile strength for briquettes one square inc'-,i in cross-sections shall be as follows, and. the cement shall show no retrogression in strength wit yin the Periods specified: Age. Strength. Neat Cement lb. per sq. inch, 24 tours in n.oist air......... ........................ 275 7 days ( 1 day in moist air, 6 days in water ) 650 28 days ( 1 day in moist air, 27 days in water ) 700 ONE PART CRIFETL T, TULEE PARTS STANDARD OTTAWA SA??D 7 days ( 1 day in moist air, 6 days in water )....... 275 28 days ( 1 day in moist air, 27 days in eater ) 325 Constancy of Vo?ume. Pats of neat cement about three (3) inches in diameter, one-half inch thick at the center, and tapering to a thin edge, .hall be kept in moist air for z period of twenty-four (24) hours. (a) A pat is then kept in air at normal temperature and observed at i.r.tervals for at least twenty-eight (28) days. (b) Another pat is kept in water maintained as near seventy degrees, (70) Pahrenheit as practicarle, and observed at intervals for at least twenty-eight (28) days. (c) A third pat is placed in boiling water, and kept therein for a. period of six (6) hours. These patsy to satisfactorily pass the requirements, shall retrain firn and hard and show no signs of disTortior_, checiring, cracking, or disintegrat- ing. Sulphuric Acid and ?.Tagnesia. The cement shall not contain .more than one and seventy-five one hundred1ths of one per cent (1675%) of anhydrous sulpburic acid (SO3) nor more than four per cent (4%) of magnesia (MgO), Section 111. Any person, firm or corporation, who by itself or agents shall use or at cerapt to use any cement for Lne construction of any public work or improvement in the City of Colton, which has not been duly passed upon by the City Engineer and certified to by him tbaz it -. -