22 BULLETIN 949, IT. S. DEPARTMENT OP AGRICULTURE. 



DETERMINATION OF FINENESS. 



(32) Wire cloth for standard sieves for cement shall be woven (not twilled) from 

 brass, bronze, or other suitable wire and mounted without distortion on frames not 

 less than 1J inches below the top of the frame. The sieve frames shall be circular, 

 approximately 8 inches in diameter, and may be provided with a pan and cover. 



(33) A standard No. 200 sieve is one having nominally a 0.0029-inch opening 

 and 200 wires per inch standardized by the United States Bureau of Standards and 

 conforming to the following requirements: 



The No. 200 sieve should have 200 wires per inch, and the number of wires in any 

 whole inch shall not be outside the limits of 192 to 208. No opening between adja- 

 cent parallel wires shall be more than 0.0050 inch in width. The diameter of the 

 wire should be 0.0021 inch, and the average diameter shall not be outside the limits 

 0.0019 to 0.0023 inch. The value of the sieve as determined by sieving tests made 

 in conformity with the standard specification for these tests on a standardized cement 

 which gives a residue of 25 to 20 per cent on the No. 200 sieve, or on other similar 

 graded material, shall not show a variation of more than 1.5 per cent above or below 

 the standards maintained at the Bureau of Standards. 



(34) The test shall be made with 50 grams of cement. The sieve shall be thor- 

 oughly clean and dry. The cement shall be placed on the No. 200 sieve, with pan 

 and cover attached, if desired, and shall be held in one hand in a slightly inclined 

 position, so that the sample will be well distributed over the sieve, at the same time 

 gently striking the side about 150 times per minute against the palm of the other 

 hand on the upstroke. The sieve shall be turned every 25 strokes about one-sixth 

 of a revolution in the same direction. The operation shall continue until not more 

 than 0.05 gram passes through in one minute of continuous sieving. The fineness 

 shall be determined from the weight of the residue on the sieve expressed as a per- 

 centage of the weight of the original sample. 



(35) Mechanical sieving devices may be used, but the cement shall not be rejected 

 if it meets the fineness requirement when tested by the hand method described in 

 paragraph 34. 



(36) A permissible variation of 1 will be allowed, and all results in excess of the 

 specified limit but within this permissible variation shall be reported as 22 per cent. 5 



MIXING CEMENT PASTES AND MORTARS. 



(37) The quantity of dry material to be mixed at one time shall not exceed 1,000 

 grams nor be less than 500 grams. The proportions of cement or cement and sand shall 

 be stated by weight in grams of the dry materials; the quantity of water shall be 

 expressed in cubic centimeters (1 c. c. of water=l gram). The dry materials shall be 

 weighed, placed upon a nonabsorbent surface, thoroughly mixed dry if sand is used, 

 and a crater formed in the center, into which the proper percentage of clean water 

 shall be poured ; the material on the outer edge shall be turned into the crater by the 

 aid of a trowel. After an interval of one-half minute for the absorption of the water 

 the operation shall be completed by continuous, vigorous mixing, squeezing and 

 kneading with the hands for at least one minute. During the operation of mixing, 

 the hands should be protected by rubber gloves. 



(38) The temperature of the room and the mixing water shall be maintained as 

 nearly as practicable at 21° C. (70° F.). 



NORMAL CONSISTENCY. 



C39; The Vicat apparatus consists of a frame A (fig. 10) bearing a movable rod, B, 

 weighing 300 grams, one end, C, being 1 cm. in diameter for a distance of 6 cm., the 

 other having a removable needle, D, 1 mm. in diameter, 6 cm. long. The rod is 



'- Article 36 is to be withdrawn from these specifications, effective Jan. 1 1921. 



