28 BULLETIN 1036, U. S. DEPAETMEISTT OF AGEICULTUEE. 



an angle of 75° with the neck of the flask, and is one-fourth inch in 

 diameter and 8^ 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^ 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 by 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. 



