A PRESSURE REGULATOR FOR DISTILLATIONS CHARLES B. DBWITT,UNIVERSITY 01. COLORADO, BOULDER, COLORADO
I n the identification of organic liquids, the determination of the boiling points is nearly always one of the first procedures, but the value of this determination is markedly decreased if the local barometric pressure is not very close to 760 mm. The pressure regulator here described makes possible the distillation of a liquid under standard pressure and eliminates the necessity for making the usual allowances when comparing observed boiling points with those recorded in the literature. The regulator is made entirely from materials that are to be found in any laboratory. It is compact, easy to use, and above all accurate. The materials needed are: a ring stand with a flat base, a board 1" X 6" X 18," a filter flask, a millimeter scale, a spring clip, some glass tubing in six-, eight-, and twelve-millimeter sizes, rubber tubing, some thin metal strips, and a buret clamp. The board is drilled with a one-inch hole about seven inches from one end, and is fastened to the ring stand with metal strips around the upright and under the base. A buret clamp attached to the upright rod projects through the hole and holds the filter flask E which is fitted with a threehole rubber stopper carrying the tubes shown in the drawing. This stopper is held in place by a metal strip passing over the top and fastened by the arms of the buret clamp. A is an open-end mercury manometer made from eightmillimeter tubing. The millimeter scale B is slotted as shown and held in place by a screw and light spring strip. F, G, and H constitute the relief valve which maintains pressure a t a constant level. His a thickwalled twelve-millimeter tube filled with mercury as shown by shading, and loosely stoppered with glass wool. The small tube G is drawn to a capillary of about one millimeter bore a t the lower end, and is connected to the tube from E with a rubber tube long enough to allow several inches vertical adjustment. F is a large-size spring-clip battery connector for holding tube G a t any desired height. For use, the side tube D of the filter flask is connected to the receiver of the distilling apparatus, and tube C is connected to a compressed air line. When air is turned on, the pressure inside the apparatus can in1174
VOL. 8.NO. 6
PRESSURE REGULATOR FOR DISTILLATIONS
1175
crease till just sufficient to overcome the head of mercury in H. Adjustment is made by raising or lowering G till the reading of the manometer added to the barometric reading equals 760 mm. With a very slow but steady current of air bubbling through H, standard pressure can be maintained with a deviation of not more than one millimeter. In the first model of this regulator built by the writer, an ordinary barometer was used instead of the open manometer, but the latter has proved far more convenient.
