50 
BULLETIN 949, U. S. DEPARTMENT OF AGRICULTURE. 
fig. 27). A ring burner is used, starting with a small flame at the top of the still and 
gradually lowering it, if necessary, until all the water has been driven off. The dis- 
tillate is collected in a 200-c. c. separatory funnel with the tube cut off close to the 
stopcock. When all the water has been driven over and the distillate has settled out 
the water is drawn off and the oils returned to the residue in the still. The contents 
of the still shall have cooled to below 100° C. before the oils are returned, and they 
shall be well stirred and mixed with the residue. 
(3) The apparatus shall consist of the following standard parts (see fig. 28): 
(a) Flash. — The distillation flask shall be a 250-c. c. Engler distilling flask, having 
the following dimensions: 
Diameter of bulb 8. cm. 
Length of neck 15. cm. 
Diameter of neck 1.7 cm. 
Surface of material to lower side of tubulature 11.0 cm. 
Length of tubulature 15.0 cm. 
Diameter of tubulature 0. 9 cm. 
Angle of tubulature 75 deg. 
Fig. 27.— Dehydrating apparatus 
A variation of 3 per cent from the above measurements will be allowed. 
(b) Thermometer. — The thermometer shall conform to the following requirements: 
It shall be made of thermometric glass of a quality equivalent to suitable grades of 
Jena or Corning make. It shall be thoroughly annealed. It shall be filled above the 
mercury with inert gas which will not act chemically on or contaminate the mercury.. 
The pressure of the gas shall be sufficient to prevent separation of the mercury column 
at all temperatures of the scale. There shall be a reservoir above the final graduation 
large enough so that the pressure will not become excessive at the highest temperature.. 
The thermometer shall be finished at the top with a small glass ring or button suitable 
for attaching a tag. Each thermometer shall have for identification the maker's, 
name, a serial number, and the letters "A. S. T. M. Distillation." 
The thermometer shall be graduated from 0° to 400° C. at interval o£ 1° C. Every 
fifth graduation shall be longer than the intermediate ones, and e^^rydsnth gradua- 
tion beginning at zero shall be numbered. The graduation marks and numbers shall 
be clear-cut and distinct. 
