Dennis G. M. Diaper and Arnis Kuksis 1 A Large Capacity Laboratory

Royal Militory College Kingston, Ontario I khad ion Apparatus

A Soxhlet extractor of large capacity is a welcome adjunct to the laboratory facilities of a smaU college for demonstration purposes, student experiments in natural products, and research work. An all-glass apparatus is pedagogically preferable to and cleaner than the more robust devices of metal'-J but commercial models are expensive. Our apparatus may be speedily made by an unskilled glass-blower and has been employed by us for some years in extraction of solids with volatile solvents such as ether.

It differs from previous e q ~ i p m e n t ~ . ~ chiefly in siphon design-a vital factor in proper operation. Narrow tubing cannot be used because slugs of liquid stay in the downward limb and promote premature siphoning. A tight glass wool pad or sintered disc in the upward limb is even more undesirable, for air cannot enter the siphon tube after draining and there- fore extraction continues with the siphon tube full and the chamber almost empty.

Wide tubing in the siphon, on the other hand, causes the apparatus to run with the chamber full and the siphon tube almost empty. Liquid "dribbles" over the top bend of the siphon and runs down the walls of the downward limb. To avoid this form of mal- function, Cameron5 constricted the bend and tip of his siphon, while a downward tube which is narrower than the other is used in the Corning apparatuso.

In our apparatus, wide tubing is used with a single loop a t the upper end. After drainage, a slug of liquid is trapped in the loop. As the liquid level rises again in the chamber, the slug moves up and down in the vertical part of the loop, releasing air from the siphon until only a small bubble remains and the siphon is

' RMP, K. E., WOODMANSEE, C. W., AND MCHARGUE, J. S., Ind. Eng. Chem., Anal. Ed., 15,351 (1943).

SALXIN, R. AND KAYE, I. A., Ind. Eng. Chem., Anal. Ed., 18, 215 f 19461.

MIICCA, C. M., Ind. Eng. Chem., Anal. Ed. 5 , 213 (1933). ' BURRELL, R. C. AND WOLFE, A. C., J. CREM. EDUC., 18,

5 1 1 (14411 - \ A A -, . CA~~ERON, A . E., Ind. Eng. Chem., Anal. Ed., 4,394 (1932). Corning Glass Co. No. 3885, Corning Glasa Works, Corning,

N. Y.

about to "dribble." Because liquid then begins to run down the downward limb, the air bubble is drawn around the bend and proper siphoning commences.

A Cliter aspirator makes a good extraction chamber. By rotating the joint, the effective height of the siphon may be adjusted so that the siphoning level is in the narrow neck. When the liquid reaches this level, the rapidly increasing hydrostatic pressure in the siphon overcornea any tendency to "dribble." For fast and complete extraction, inert material such as sand or glass beads should be placed in t,he bottom where the liquid is relatively stagnant. A lining of filter paper is placed in the aspirator before introducing the material to be extracted. This is achieved by cutting a rectangle, 18 cm X GO, cm which is rolled into a tight cylinder and introduced through the neck. I t is unrolled in place by using long forceps and wetting the glass with solvent. During extraction, liquid flows rapidly between the glass and paper and therefore solvent flows radially outwards inside the chamber. A loose plug of glass wool is placed in the siphon joint which is lubricated with glycerol-starch and wired in place.

The chamber capacity is l L / r G lb of solid, and three extract,ions per hour can he achieved using ether.

CONDENSER

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BOILER ~. Left, extraction chamber and siphon; right, detail of siphon.

532 / Journal of Chemical Education