40 



BULLETIN 314, • TJ. S. DEPART M-ENT OP AGRICULTURE. 



X 



If* 



The cylinders are constructed for this purpose by drilling a hole in 

 fche center of the bottom of each. This hole should be slightly larger 

 than the outside diameter of the brass tubing, one end of which is 

 cemented into it by means of a litharge and glycerin mixture. The 

 upper end of the tube should be flush with the inside of the bottom 

 of the graduated cylinder and in the large cylinder a piece of 200- 

 mesh wire gauze should be soldered over the end of the tube to prevent 

 fine material passing through. 



The apparatus is set up as shown in figure 20, with the pinchcock 

 on the rubber tubing closed. The small cylinder is filled with kero- 

 sene, after which the 

 pinchcock is slowly 

 opened in order to 

 ■a permit the kerosene to 

 ■J) force any air from the 

 tubing and to come 

 flush with the bottom 

 of the large cylinder. 

 The pinchcock is then 

 closed. 



The aggregate is thor- 

 oughly mixed and quar- 

 tered, if necessary, until 

 a representative sample 

 of material of at least 

 300 cubic centimeters 

 volume is obtained. 

 This sample of aggre- 

 gate is poured into the 

 large cylinder, a scoop- 



Fig. 20. — Apparatus for determining voids in the mineral aggregate. . , . . . -, 1 • i . 



f ul at a time, with a light 

 tamping of the cylinder against the rubber pad in order to compact 

 the material. Best results are usually obtained by making a cylinder 

 of manila paper inside the glass cylinder, and introducing the aggre- 

 gate inside the paper. The paper can then be slowly withdrawn 

 while the glass cylinder is being lightly tamped. Segregation of the 

 several sizes of material must be avoided, and any fine material 

 remaining on the paper should be brushed off and added to the 

 aggregate. 



When the aggregate in the large cylinder has reached its maximum 

 state of compaction, the volume of kerosene in the small cylinder is 

 read, the pinchcock is opened and the elevation of the small cylinder 

 so regulated as to permit the kerosene to slowly percolate upward 

 through the aggregate, until it has reached a point 20 or 30 cubic centi- 



=m 



