A Simple Large-Capacity Extractor NATHANL. DRAKEAND JOSEPH R. SPIES University of Maryland Station, Insecticide Division, Bureau of Chemistry and Soils, College Park, Md.
N
EED for an extractor of the Soxhlet type which could be operated with a charge of approximately 10 pounds of ground roots or seeds prompted the design of the apparatus shown in Figure 1. This extractor can be constructed a t low cost, is relatively durable, absolutely free from any fire hazard, and can be assembled from material generally available in the laboratory. Although designed primarily for use with methanol, it could be used with few changes for any solvent boiling below 100" C.
FIGURE1
A 1Zliter short-necked Pyrex flask, A , serves as the extractor body. To the bottom of this flask is sealed a 3-in. (7.5-cm.) length of 25-mm. tubing which ends in a short piece of 5-mm. tubing, and serves as an adapter for connecting the siphon tube which returns the solution to the boiler. Connection between the extracto? and the glass siphon tube is made by rubber tubing within which there is a glass-to-glass contact. A large thin cork bored in the center to hold the breather tube, B, and pierced with several holes to allow free passage of solvent, serves to support a thin layer of absorbent cotton, C, upon which rests the material to be extracted. The broad cotton surface promotes rapid draining and effectively filters the returning solvent. The breather tube promotes clean siphoning by eliminating the resistance of the marc to the passage of air, The return
siphon, D,is of 5-mm. tubing, connected to the boiler through a rubber stopper and to the extractor as described above. The boiler, E, is a 12-liter, three-necked +Pyrexdistilling flask. One small neck serves to admit the returning solution and the other to conduct solvent vapor to the condensers. The large neck is closed by a rubber stopper through which pass the inlet and outlet of a small copper steam coil. Such a heating coil can be easily constructed by winding 0.25-in. (0.62-cm.) outside diameter copper tubing on a piece of iron pipe of suitable diameter. Inlet and outlet can then be attached by soldering 0.125-in. (0.3-cm.) brass pipe nipples of appropriate length to the ends of the copper coil. The outlet of the heating coil is not throttled during operation so that there is little pressure within the coil. A suitable steam valve on the inlet controls the steam flow. Solvents whose boiling points are below 100" C. can be boiled very conveniently in the apparatus without the slightest fire hazard. The riser tube, F , ends in a short partial condenser, G, constructed from a piece of 0.5-in. (1.3-cm.) outside diameter copper tubing with a glass water jacket. This condenser discharges into flask A through a triply bored stopper. Through the other holes in this stopper pass the vapor tube of the total condenser, H , and its solvent return line. Condenser H is similar to a glass condenser' described by Cameron (1). It is constructed entirely of metal, and can be easily assembled from standard copper tubing. The vapor inlet tube, h, is capped a t the end and pierced by a number of small holes. Solvent vapor passes through these holes and impinges on the cold wall of the condenser. The resulting condensate flows down through the small annular space between the vapor riser tube and the condenser wall to the bottom of the condenser, whence it returns through trap j to flask A . The return trap, j, is of glass, connected to a metal nipple soldered to the condenser by means of a rubber joint. A condenser of this type is free from the disadvantage of flooding even when used a t very high condensation rates. When methanol is used as solvent, siphoning takes place every 45 minutes. The connection between boiler and partial condenser is made of Pyrex tubing of suitable diameter, jacketed with asbestos. A bored stopper affords a means of connection at the condenser end, and a tightly fitting rubber tube within which there is glass-to-glass contact makes the joint to the boiler. During operation it is not necessary to move boiler or vapor riser tube. The extractor body can be detached from the rest of the apparatus for charging and discharging, and solvent can easily be removed from the boiler by siphoning. I n the authors' apparatus a pipe union makes it possible to break the steam inlet lines, and consequently the steam coil can be lifted from the boiler for convenience in siphoning off its contents. An apparatus like the one described has been in operation constantly for several months and has proved highly satisfactory in every respect. (1) Cameron,
LITERATURE CITED A. E.,IND.ENG.CHEM.,Anal. Ed.,4, 394 (1932).
RECEIVBD April 5 , 1933.
284
