350
INDUSTRIAL AND ENGINEERING CHEMISTRY
The large internal volume of the still made it impractical to pack the interior with jack chain as was done in the original and much smaller still. Coarse aluminum turnings were found to be ideally suited as a packing material. Temperatures in the packed column are measured by means of a number of thermocouples mounted in thin, small-bore glass tubes bound together by asbestos cord and situated in the axis of the column, and also by red reflecting mercurial thermometers placed in the packing next to the interior front surface. Both thermocouples and thermometers are supported and maintained in their proper positions by the packing material; and, a t equilibrium, their readings differ by not more than 2" t o 3" C. As in the case of the original still, the present column is heated internally by refluxing over the packing material a suitable solvent such as kerosene or an Arochlor. The flask containing the reflux liquid is heated on the bottom by a variac-controlled resistance coil and on the sides by a woven basket of resistance wire. An auxiliary mechanical pump, immediately below the one shoivn in Figure 2, is used for controlling the pressure above the liquid in the reflux boiler, as well as for lowering the mercury in the McLeod gage. -4manometer in the reflux line shown just to the upper right-hand side of the column is graduated to correspond to approximate temperatures produced in the still rather than to actual pressure. The condensing surface of the column is cooled by air jets directed against its surface from a perforated spiral of 1.25-em. (0.5-inch) copper tubing as shown in Figure 2. The helix was formed on a mandrel and then perforated around the inside with holes drilled a t intervals of 2.5 cm. (1 inch). The spiral ITas fitted with four feed lines for compressed air and the completed coil screwed over the column prior to sealing on the reflux boiler a t the point indicated by the dashed line in Figure 1. The accessory vacuum-producing equipment is of the conventional type and consists essentially of a mechanical pump, mercury diffusion pump, and a cooling trap. The free air pressure is measured by means of a McLeod gage, and total pressure within the still is approximately measured by a thermal conductivity gage. No stopcocks are used in the high vacuum line except in the by-pass to the McLeod gage, the fraction cutter, and the residue receiver. The first-mentioned is of the mercury-sealed type, and the latter two are sealed with glycol phthalate resin ( 7 ) which is solid except for the interval in which it is heated during the operation of removing fractions. I n the low vacuum lines either double 15-mm. bore vacuum-ground, grease-lubricated stopcocks or single mercury-sealed stopcocks are used. Only dry air is admitted to the system, except during charging and cleaning. Consequently, the mercury in the diffusion pump and in the McLeod gage has remained brilliant and free from fouling after more than
VOL. 12, NO. 6
2 years of service. Dry ice and acetone are used in the cooling trap during cleaning operations to prevent diffusion of the solvent backward to the pumps and McLeod gage.
K h e n the still was first placed in operation, a crude soybean oil which had been partially degassed was passed through the column to complete the degassing. Practically all the remaining gas appeared to be liberated a t the dripping prongs and, consequently, the oil spread smoothly over the distilling surface. The temperature of the column during this operation was maintained a t 100" to 130" C., and it was noted t h a t in this temperature range appreciable distillation occurred; approximately 15 ml. of distillate per liter of distilland collected in the receiver, and considerable crystalline material collected on the condensing surface. (The nature and properties of the distillate will be discussed in a later publication dealing with the composition of soybean oil.) I n a considerable number of previous runs which were made with soybean oil i n the older type of still, no appreciable distillation was evident below 180" C. A similar b u t less marked lowering of the distillation temperatures of other products, including the glyceride components of the oil, was likewise observed in the modified still as compared with the previous still. The improved efficiency of distillation appears to have resulted from the better distribution of the film over the distilling surface, the increased time required for passage of the oil through the system, and the turbulence in the flow xhich resulted from roughening the distilling surface.
Literature Cited (1) Detwiler, S. B., Jr., and Markley, K. S., Oil & S o a p , 16, 2-5 (1939). (2) Fawcett, E. W.hl., J . SOC.Chem. I n d . , 58, 43 (1939). (3) Fawcett, E. W., Burrows, G., and Imperial Chemical Industries, Ltd., British Patent 480.265 (Feb. 21, 1938). (4) Hickman, K. C. D., ISD. Exvc. CHEX.,29, 968 (1937). (5) Jewell, W., Mead, T. H., and Phipps, J. W.,J . SOC.Chem. I n d . , 58, 56 (1939). ( 6 ) Mair, B. J., Schicktanz, S. T., and Rose, F. W., Jr., J . Research Natl. BUT.Standards, 15, 557 (1935). (7) Sager, T. P., and Kennedy, R. G., Jr., J . Physics, 1,352 (1931).
A Small Biichner Funnel for Qualitative Organic Analysis C. A. ROSWELL University of Kentucky, Lexington, Ky.
IK
THE analysis of organic compounds small amounts of crystalline derivatives must often be filtered with suction. The usual method, employing a small 60" funnel with a loose Witt plate and a side-arm test tube, is not always satisfactory. Considerable trouble may be encountered in obtaining a tight fit between the filter paper and the funnel, t e n t tube and the loose plate invariably tilts to one side or the other, giving a n unW i t t plate even deposit of crystals. The funnel shown in the drawing is a more convenient arrangement. A Witt plate of a size that just slipped into a 200 X 25 mm. Pyrex test tube was placed so that its edges rested against the curved portion of the
bottom of the tube, and was sealed in by rotating the tube in an oxgyen gas flame and annealing well in a smoky flame. A small tube was then sealed to the bottom of the test tube, cut off, and ground to a 60" angle. The funnel was completed by cutting off the test tube 20 mm. above the plate and flaring the edge out slightly with a carbon rod.
It is easy t o seal in the porcelain plate, as porcelain will seal readily to Pyrex glass (1). Funnels of various sizes may be made by choosing the appropriate plate and tubing sizes. Filter circles to fit the funnel closely may be made from larger paper by cutting them out with a cork borer of the correct size.
Literature Cited (1) Frary, F. C., Taylor C. S., and Edwards, J. D., "Laboratory
Glass Blowing", 2nd ed., p. 91, S e w York, McGraw-Hill Book Co., 1928.
