in Figure 2. It is desirable to mount the heater at the 3 o’clock position as shown. This permits the heater to set up an efficient self-circulating action and allows omission of mechanical circulators and thermoregulators. I n designs of the type described here, where separate thermostating of the column and conductivity cell is not used, the use of the conventional “on-off” type of thermoregulator will usually cause base-line fluctuations due to temperature cycling of the system. Once temperature equilibrium has been obtained (usually less than 1 hour), recorder base-line drift due to temperature fluctuations is less than 0.1 mv. over a 12-hour period, if the heater is supplied with a regulated voltage. d 4-quart wide-mouthed Dewar flask is used for insulation. A thin strip of foam rubber is glued to the lip of the Dewar flask, which is then supported in position by two steel rods and a steel b u t t plate. The lip of the Dewar flask is held tightly in the recess around the circumference of the SIicarta block by tightening the bolts on the end of the two steel rods supporting the butt plate. Copper tubing (l/c-inch) and standard flared fittings were used for all connections. The sample injection port (Figure 1, G) is a standard 1/4-inch flare-fitting copper tubing tee, modified to provide flat bearing surfaces for a silicone rubber dkk (Perkin-Elmer part 154-1043),
. .
PRESSURE GAUGE. 0-30 LE osiaIN
* DIFFERENTIAL TYPE PRESSURE REGULATOR- - -
MEASURING C E L L S A’
Figure
4.
CHROMATOGRAPHIC COLUMN
2
Schematic diagram of eluting gas flow
Components enclosed by shaded area maintained at same temperature
through which liquid samples are injected b y use of a hypodermic syringe. A 26gage Sinch hypodermic needle is used to administer the sample to the column through the silicone rubber septum, which retains an effective seal until it has been punctured 50 to 60 times. The wiring diagram for the thermal conductivity cell is shown in Figure 3. Figure 4 illustrates the flow diagram of the eluting gas. The chromatographic column of I/dinch stainless steel is bent into a helical shape after packing, and attached between points L (Figure 1). The 4quart D e m r flask accommodates a
l/rinch column a t least 50 feet long. The eluting gas is introduced into thc instrument at M . When the instrument has been completed, a l/s-inch hole is drilled through the relay rack panel and Micarta block to alloTT insertion of a metal dial thermometer in tht, Dewar flask. The thermometer is not in place in Figure 1. A recording potentiometer with a 0to 10-mv. sensitivity range and a chart speed of 8 inches per hour was used in this laboratory to record the output of the thermal conductivity cell. Complete dimensional details of the entire instrument will be willingly supplied by the author.
Modified Pot Molecular Still Kermit Groves and R. R. Legault, Department of Agricultural Chemistry, State College of Washington, Pullman, Wash.
T
pot molecular still designed by Hickman and Sanford [Hickman, K. C. D.. Sanford, C. R., J . Phys. Chem. 34, 637 (1930)l is simple and more convenient to operate than many of the more elaborate stills available for the purification of small quantities of high boiling liquids in the laboratory. This still has been modified by adding a chamber below the evaporating liquid to provide heating by the vapor of a boiling liquid. A uniform constant temperature is maintained on the HE
Table I.
Sample 2-Hydrox~-diethylsulfide Octoil 1724
bottom of the eraporation chamber. and the temperature can be varied by using different liquids or liquid mixtures in the heating chamber. U p to 20 grams of sample can be distilled and collected in five fractions in the sample collector. Ball joints provide convenient connections to the water supply for cooling the condensing surface and to the high vacuum system. The 50-sq. em. condensing surface gives fairly rapid distill a t’ion.
Distillation Rates of Molecular Still
Boiling Point Microns
c.
O
54 126
ANALYTICAL CHEMISTRY
3 10
Heating Liquid
Distillation Rat e, bIin./Ml.
Acetone Water
4 1.5
-
1
