A FORM OF CONDENSER FOR USE WITH HIGH-BOILINGPOINT LIQUIDS
For purposes of purification of mercury, a still was required which, while simple in construction, would yet have a high rate of distillation. It had been observed that mercury in a glass condensation pump distilled over rapidly, and the still described below was then constructed on the same principles as a simple condensation pump. The apparatus has since been found of use in the distillation of high-boiling-point liquids under vacuum.
Description of Apparatus Constructed of Pyrex glass, the air inlet A was first sealed into a 100 cc. round-bottomed flask. The tube A consisted of a piece of 5-mm. bore
tubing drawn out to a capillary. The tap-funnel B was then sealed in, the inside end of the tube C being drawn out to form a dropper so that the entering cold liquid did not touch the hot sides of the flask. A jet D, 5 cm. long and of 5 mm. bore, was fused into a length of 10 mm. bore tubing, at a distance of 10 to 15 cm. from one end E, which was then sealed into the neck of the flask just below the seal A . A water jacket was then attached as shown in the diagram. Asbestos string was wound on the boiler and as far as the jet on the condenser R. By means of the tap-funnel B, 30 to 40 cc. of liquid was introduced into the flask and a vacuum was produced at the receiving end of the apparatus. The amount of air allowed to bubble in through the tube A was controlled by means of a screw clip on a short piece of rubber tubing. For compara2963
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JOURNAL OF CHEMICAL EDUCATION
DECEMBER, 1930
tive purposes an exactly similar piece of apparatus was constructed, but without the jet. It had been observed, that when a mercury condensation pump was in operation, the level of the mercury in the return pipe was considerably higher than that of the mercury within the boiler. In order to record any changes of pressure within the apparatus described above, vacuum pressure gages were connected, G' to the tap-funnel B, G" to the pump end of the condenser. Experimental Data Distillations were carried out under known conditions of temperature and pressure, using liquids of various boiling points. In each distillation using the apparatus with the jet, an increase of pressure in the boiler was recorded by the pressure gage G', while in no case was such increase of pressure observed using the apparatus without the jet. Since no comparison of rates of distillation could be made unless the liquids boiled at the same temperature in both forms of apparatus, it was so arranged that the pressure in the boiler of the apparatus without the jet was the same as that in the boiler of the apparatus with the jet, and the temperature of the hath was kept constant in both cases. Ethyl Malonate: Boiling Point 198'C. (at atmospheric pressure). The innease of pressure in the hoiler of the apparatus with the jet was found t o be 3 mm. of mercury on haling with the hath a t a temperature of 160°C. The yield of distillate from the apparatus without the jet was almost as great as that from the apparatus with the jet. Nitro-benzene: Boiling Point 207'C. (at atmospheric pressure). The increase of pressure in the hoiler of the apparatus with the jet was found t o he 3.5 mm. with the bath a t a temperature of 180°C. The yield of distillate from the apparatus without the jet was 85% of that from the apparatus with the jet. Glycerin: Boding Point 290DC.(at atmospheric pressure). The increase of pressure in the bailer of the apparatus with the jet was found to he 4 mm. with the bath a t a temperature of 240PC. The yield of distillate from the apparatus without the jet w3s 80% of that from the apparatus with the jet. Mercury: Boiling Point 357-C. (at atmospheric pressure). The increase in the hoiler pressure of the apparatus with the jet was found t o he 7.5 mm. with a bath temperature of 260°C. The yield of distillate from the apparatus without the jet was 55% of that from the apparatus with the jet. An experiment was carried out using the apparatus without the jet, the vacuum attained in the hoiler being the greatest obtainable with the pump used, i . e., the boiler pressure in this case was 7.5 mm. less than that in the apparatus with the jet. It was then found that the yield of distillate was 75% of that obtained in the case of the apparatus with the jet. Trouble was, however, experienced with the burning of stoppers on the apparatus without the jet.
I t has been shown that with the lower-boiling liquids, little is gained by use of a jet in the condenser. In the case of liquids boiling above 200°C.
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an inaeased speed of distillation is obtained while owing to the construction of the condenser with the jet, water cooling can be used. It is thought that the increased speed of distillation is due to two factors. The constriction of the outlet from the boiler caused by introducing the jet causes an increase of pressure in the boiler, which forces the vapor through to the condenser a t a greater velocity. This vapor shooting through the jet a d s in the same way as in a condensation pump and a vacuum is created in the space around the jet, thus tending to draw the vapor through a t a higher speed.
