28 BULLETIN 1036, U. S. DEPARTMENT OF AGRICULTURE. 
an angle of 75° with the neck of the flask, and is one-fourth inch in 
diameter and 8J inches long. The neck of the flask is constricted at 
its junction with the bulb to three-fourths inch in diameter. This 
constriction is made so that a loose plug of wire, preferably platinum, 
may be dropped into the neck to support a column of glass beads. 
In making the plugs used at the Forest Products Laboratory, two 
circles of heavy wire were fastened together at right angles to each 
other, and another circle of heavy wire was fastened to them in such 
a manner that the plane of this circle was perpendicular to the 
plane of the other two. Using these three circles as a framework, 
wire was used to fill up the spaces on the surface of the sphere and 
form a network through which the beads would not slip. Another 
device which serves the purpose equally well may be made from per- 
forated sheet metal bent in the shape of a truncated cone. In con- 
structing these, a circle 1 J inches in diameter was cut from perforated 
sheet brass of 23 B. S. gauge, having 23 perforations 0.023 inch in 
diameter to the linear inch. On the outside of the circle was cut a 
number of irregular notches one-fourth inch across and one-fourth 
inch deep. A sector was next cut from the whole, so that the re- 
maining portion contained about two-thirds of the total area of the 
circle. The edges of this section were then drawn together and 
fastened by a wire in the form of a cone. Lastly, a small weight was 
hung from the center of the cone like the clapper in a bell, so that the 
cone would stand upright when it was dropped into the flask. This 
would support the column of beads fully as well as platinum wire, 
and had the advantage of being somewhat cheaper. 
The bead column is composed of approximately 200 glass beads, 
but its height should be kept constant at 5 inches with a variation 
of not more than one-fourth inch. Some previous work b}^ the 
Forest Products Laboratory on the distillation of turpentine (Forest 
Service Bulletin 105) has shown that the most important factor in 
the use of a Hempel column in distillation is the height of the bead 
column. The diameter of the column and the size of the beads have 
apparently but little effect, so far as the efficiency of separation is 
concerned, but do affect the speed at which the distillation can be 
run. If the same speed and the same height are used, the results 
obtained are identical, irrespective of the size of the beads or the 
diameter of the bead column, provided that the speed is not great 
enough to prevent the condensed liquid from returning to the flask. 
The distillations were run at a rate as nearly uniform as possible. 
The speed of the dropping was timed by the use of a metronome set 
at 90 a minute and kept as near this rate as possible. At no time, 
however, was it allowed to exceed 120 drops or to go below 60 when 
once the distillation had been started. 
