34 
BULLETIN' 1216, r. S. DEPARTMENT OF AGRICULTURE. 
the cement paste shall first 1>< V flattened on the glass and the pat 
then formed by drawing the trowel from tin* outer edge toward 
the center. 
43. The pat shall then he placed in an atmosphere of steam at 
a temperature between 08° and 100° C. upon a suitable support 
1 inch above boiling water tor .") hours. 
H. Should the pat leave the phite, distortion may he de- 
tected host with a straight edge applied to the surface which 
was in contact with the plate. I Sec Plate I.) 
XIII. DETERMINATION OF TIME OF SETTING. 
Time ol 4o. The following are alternate methods, either of which may 
setting. he used as ordered : 
46. The time of setting shall he determined with the Yicat 
apparatus described in section 38. 
47. A paste of normal consistency shall he molded in the hard- 
rubber ring as described in section .">!>, and placed tmder the rod, 
the smaller end of which shall then he carefully brought in con- 
tact with the surface of the paste, and the rod quickly released. 
The initial set shall he said to have occurred when the needle 
ceases to pass a point 5 millimeters above the glass in one- 
half minute after being released; and the final sot. when the 
needle does not sink visibly into the paste. The test pieces shall 
he kept in moist air during the test. This may he accomplished 
by placing them on a rack over water contained in a pan and cov- 
ered by a damp cloth, kept from contact with them by means of 
a wire screen; or they may he stored in a moist closet Care 
shall he taken %to keep the needle clean, as the collection of cement 
on the sides of the needle retards the penetration, while cement 
on the point may Increase the penetration. The time of setting 
is affected not only by the percentage and temperature of the 
water used and the amount of kneading the paste receives but 
by the temperature and humidity of the air, and its determina- 
tion is therefore only approximate. 
48. The time of setting shall he determined by the Gillmore 
needles. 
49. The time of setting shall he determined as follows: A pat 
of neat cement paste about 3 inches in diameter and one half inch 
in thickness with a flat to]), mixed to a normal consistency, shall 
he kept in moist air at a temperature maintained as nearly as 
practicable at 21° C. (70° F. ). The cement shall he considered 
to have acquired its initial set when the pat will hear, without 
appreciable indentation, the Gillmore needle one-twelfth inch in 
diameter, loaded to weigh one-quarter pound. The final set has 
been acquired when the pat will hear without appreciable inden- 
tation, the Gillmore needle one twenty-fourth inch in diameter, 
loaded to weigh 1 pound. In making the test the needles shall he 
held in a vertical position and applied lightly to the surface of 
the pat. 
XIV. TENSION TESTS. 
Tension tests. 50. The standard form of test piece shall be used. The molds 
shall he made of noncorroding metal and have sufficient material 
in the sides to prevent spreading during molding. (Jang molds 
may he used. .Molds shall he wiped with an oily cloth hefore 
using. 
51. The sand to he used shall he natural sand from Ottawa. 111., 
screened to pass a No. 20 sieve and retained on a No. 30 sieve. 
This sand may be obtained from the Ottawa Silica Co., at a cost 
of :; cents per pound, f. o. b, cars, Ottawa, in. 
52. This sand, having passed the No. 20 sieve, shall he consid- 
ered standard when not more than ."> grams pass the No. 30 sieve 
after one minute continuous sieving of a 500-gram sample. 
53. The sieve shall conform to the following specifications: 
The Xo. 20 sieve shall have between 19.5 and 20.5 wires per 
whole inch of the warp wires and hetween 19 and 21 wires per 
