An Automatic Continuous Percolator MILTON S. SCHECHTER AND H. L. HALLER Bureau of Entomology and Plant Quarantine, U. S. Department of Agriculture, Washington, D. C.
D
URIiYG the course of investigations of a number of plant materials, it was found necessary t o percolate the ground plants thoroughly with a solvent such as ether or petroleum ether. Large Soxhlet extractors are rather expensive and often do not work so efficiently or smoothly as the small ones. Tvhen nearly complete extraction is desired, the usual process of percolation is laborious and time-consuming. To overcome these difficulties, an automatic percolator was constructed which is simple, compact, inexpensive, and efficient, and, when once regulated, will operate for long periods without requiring attention and with T'ery little loss of solvent. The apparatus is illustrated in the diagram. The percolator, A , Tvhich holds the material to be extracted, was made by cracking off the bottom of a bottle of appropriate size and grinding down the sharp edge on a flat glass plate with a little silicon carbide powder and water. The condenser, B , is an efficient and compact distilling condenser. Tube D should be 10 mm. or more wide to permit the unobstructed passage of solvent vapor from the threeneck flask, C, to the condenser. To operate the percolator the apparatus is assembled as shown in the diagram, a small piece of cotton being packed loosely in the bottom of the percolator so that it covers the top of tube F. The material to be extracted is then packed loosely and evenly in the percolator and covered with a few sheets of filter paper to prevent particles from floating into the overflow tube, E. The filter paper may be lightly weighted down if necessary. Solvent is poured into the percolator so that it percolates through the material to be extracted and does not run into the flask through the overflow tube. Enough solvent should be poured through the material so that the three-neck flask is about half full. The percolate runs down into the flask through tube F , which
SHEET OF FILTER PAPER
A
D COTTO
0 MM. X LARGER
3
3 NECK FLASK
C
contains a stopcock and a side arm through which the percolate may be sampled at any stage of the percolat'ion. The rate of percolation is also controlled by adjusting this s t o p c o c k . The three-neck flask is heated on a steam bath (when using ether or p e t r o l e u m ether). The solvent vapors ascend tube D and are condensed in the condenser, and the fresh solvent distills into the top of the percolator through the adapter, which is inserted through a hole in the cardboard cover of the percolator. The bottom of the adapter should be kept' above the level of liquid in the percolator. In warm weather it has been found advantageous to use a compact vert,ical worm condenser in conjunction with the recovery condenser, B , in place of the adapter shown in the diagram. If the solvent distills into the percolator faster than it percolates through tube F into the flask, the excess willoverflow into tube E and be returned to the flask. A small, very loose plug of cotton may be placed at the top of tube E to filter the returning solvent free from floating particles, but care should be taken not to obstruct the overflow of solvent. The rate of distillation and the rate of percolation are regulated so that the solvent distills into the percolator slightly faster than the liquid runs into the flask from tube F; there should always be a slight return of solvent through the overflow tube, E. The three-neck flask and the percolator may be larger or smaller than those shown in the diagram. A 2-liter three-neck flask used in conjunction with a 3-liter percolator has also been used satisfactorily in this laboratory. TVhen once regulated, the percolators have been in operation for as long as 48 hours without any attention and with very little loss of solvent. Although it is possible to use rubber stoppers even with such solvents as petroleum ether, provided they fit well into the neck of the flask, i t is desirable to use special stoppers that do not swell so much. RECEIVED April 26, 1938.
