£0 BULLETIN 314, U. S. DEPARTMENT OF AGRICULTURE. 
METHOD. 
The cylinders are constructed for this purpose by drilling a hole in — 
the 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 pmchcock 
on the rubber tubing closed. The smali eyed is filled with kero- 
sene, after which the 
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a aC” 
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aienoue: is slowly 
z=! opened in order to 
- “s“|—a@ permit the kerosene to 
eee ae ; 
a -=-|—f force any air from the 
— =u ll| tubing and to come 
flush with the bottom 
of the large cylinder. 
The pincheock 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- 
ful ata time, withalight 
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 The paper can then be slowly withdrawn 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 
ageregate. 
When the aggregate in the large cylinder has reached its maxumum 
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- 
Fic. 20.—Apparatus for determining voids in the mineral aggregate. 
