606 CEMENTS, LIMES, AND PLASTERS. 



removed in a similar manner by pouring into the flask a small quantity 

 of clean liquid and repeating the operation. 



18. More accurate determinations may be made with the pic- 

 nometer. 



FINENESS. 



19. Significance. It is generally accepted that the coarser particles 

 in cement are practically inert, and it is only the extremely fine powder 

 that possesses adhesive or cementing qualities. The more finely cement 

 is pulverized, all other conditions being the same, the more sand it will 

 carry and produce a mortar of a given strength. 



20. The degree of final pulverization which the cement receives at 

 the place of manufacture is ascertained by measuring the residue re- 

 tained on certain sieves. Those known as the No. 100 and No. 200 

 sieves are recommended for this purpose. 



21. Apparatus. The sieves should be circular, about 20 cm. (7.87 

 inches) in diameter, 6 cm. (2.36 inches) high, and provided with a pan, 

 5 cm. (1.97 inches) deep, and a cover. 



22. The wire cloth should be woven (not twilled) from brass wire 

 having the following diameters: 



No. 100, 0.0045 inch; No. 200, 0.0024 inch. 



23. This cloth should be mounted on the frames without distortion; 

 the mesh should be regular in spacing, and be within the following limits : 



No. 100, 96 to 100 meshes to the linear inch. 

 No. 200, 188 to 200 " " " 



24. Fifty grams (1.76 oz.) or 100 gr. (3.52 oz.) should be used for 

 the test, and dried at a temperature of 100 C. (212 F.) prior to sieving. 



25. Method. The Committee, after careful investigation, has reached 

 the conclusion that mechanical sieving is not as practicable or efficient 

 as hand-work, and, therefore, recommends the following method: 



26. The thoroughly dried and coarsely screened sample is weighed 

 and placed on the No. 200 sieve, which, with pan and cover attached, 

 is held in one hand in a slightly inclined position, and moved forward 

 and backward, at the same time striking the side gently with the palm 

 of the other hand, at the rate of about 200 strokes per minute. The 

 -operation is continued until not more than one tenth of 1 per cent 

 passes through after one minute of continuous sieving. The residue is 

 weighed, then placed on the No. 100 sieve and the operation repeated. 



