A Continuous Distillation Apparatus for the Laboratory The operation of a laboratory distillation apparatus is generally hased m o m 01 co*mnaua m*"lo"cr *warotur (mito riole, on a hatch principle or an excess feed constant overflow principle. The former is very easy to set up hut requires frequent attention. The latter can be used in a laboratory which has a built-in distilled water supply from a central distillation system, hut it is wasteful unless the overflow is saved for recycling or for other purposes. Apparatuses hased on the "chicken-waterer" principle1 and on the "siphon" principle2 were designed to eliminate the feeding problem. Both are convenient and operate satisfactorily. However, they both require periodic maintenance, the siphon of the latter needing to be checked each time the reservoir is filled. We have designed a continuous distillation apparatus to feed the water dropwise hased on the principles of gravity and surface tension. I t is easy to set up and easy to operate. I t operates as well as the other apparatuses mentioned ahove. The only major requirement is to refill the reservoir periodically. heating mantel (H), and condenser The apparatus is shown in the figure. The distillation part consists of flask (F), (C). A side tuhe (A) connected to the flask has two outlets. The upper outlet connects to a sink bottle (S) and stands not over 3/n height of the body of the flask. The lower outlet leads to a drying tube (B). The top of tube A is covered with a stopper. The outlet tuhe of the reservoir (R)has two three-way stopcocks (TI and Tz). The downward tuhe in TIcan be used for releasing the water in the reservoir. The upward tuhe in T2is open to the air. The downward tube in Tz is connected to tube B and is used as the dropping tuhe to feed water from the reservoir. The position of the reservoir is not so crucial as in the siphon-type apparatus as long as the reservoir is arranged in such e position that the tip of thedropping tube in T2is above the upper outlet in tuhe A. To start the distillation, turn an the heater and open the cooling system. When the rate of distilled water coming out of the condenser is steady, measure the time (tlw) taken to receive 100 ml of distilled water. Open TI and Tp tolead water out of the reservoir. Then, adjust the dropping rate by turning Tz so that it will feed 100 ml of water in tlw or a little shorter but not longer. After the dropping rate is adjusted, Tz can then he left untouched. T o open or close the reservoir, one can just use TL.I t is recommended that the dropping rate he checked by inspection and experience. The reservoir can be refilled while it is distilling and it is not necessary to turn TI off. No special attention is required. The reservoir in our apparatus can be filled with deionized water up to 60 X 15 X 15 cm3, and it is sufficient for an eight-hour continuous distillation. (Reservoirs of larger capacity than this can be constructed.) If the power goes off while it is distilling, the water will be fed continuously to the flask. However, the upper outlet in tube A will lead the overflow to the sink bottle S which has a capacity of about 5 1. Theoverflowcan besavedforrecyeling. In case bottleB is filled, theside tubein it will lead theoverflow to the drain. When the power comes on again, the distillation will also start to operate. Overnight distillation using this type of apparatus is not recommended. Burrhus, K. D., and Hart, S. R., Anal. Chem., 44,432 (1972). Shen, C., and Melius, P., J. CHEM. EDUC., 53,262 (1976). 3 Mr. Wu is ateaching assistant in the Chemistry Department. 4 Address correspondence to this author. Cheng Rung University Tainan, Taiwan 700 Republic of China
Cheng Kuei WuJ J i n g - J e r Jwo4
Volume 55. Number 10, October 1978 1 677
