January 15, 1941
ANALYTICAL EDITION
Editor’s Note. Some time ago several notes appeared in the NEWSEDITION under the general title “Reminders”.
They made no claim to priority or originality, but reintroduced good ideas and sound practices already known to the older generation of chemists. More re-
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cently the ANALYTICAL EDITION has carried a note or two directing attention to procedures or equipment already known and used by some of the profession though not readily accessible in print. This has prompted submission of the two printed here.
Simple Vacuum Still for Purification of a Single Substance or Recovery of a Single Fraction FREDERIC E. HOLMES Children’s Hospital Research Foundation and Department of Pediatrics, College of 3Iedicine, Univ-ersity of Cincinnati, Cincinnati, Ohio
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H E X the purpose of a distillation is to obtain a substance in the distillate free from impurities from which it is to be separated, it is necessary to save only one fraction. Usually this fraction is preceded by a more volatile fraction or fractions which must be rejected. I n the conventional types of vacuum distilling apparatus it is necessary to perform one of three operations to obtain the desired distillate: (1) interrupt the distillation while the receiver is changed, ( 2 ) rotate a compound receiver of some sort that requires a n air-tight revolving joint, or (3) evacuate an outside vessel and discharge the unwanted fraction into it through a stopcock. All these difficulties can be eliminated by the use of two re-
slion.ii in the figure has the advantage of eliminating several points vliere leakage could occur and vhere contamination from rubber niight enter, especially in high-temperature distillations. The still shown is presented both for its own utility and as an example of the use of the T-connection. The apparatus involves little or no innovation in principle or design. The still is supported in a clamp or clamps having asbestoscovered jaws, in such a way that it will not slip but can ezisily be rotated around the long axis of the condenser. During tlie first part of the distillation the entire apparatus is tipped b a c k , so that the more volatile fractions to be rejected are delivered into the receiver away from the operator. As soon as the desired fraction starts to come over, it is tipped forward and this fi,:tction is collected in the clean receiver. At the end of the collection of this fraction, the apparatus is quickly tipped back again t o reject any heavier distillate that may come over before the distillation can be stopped. A t any time during the distillation of t h e desired fraction the still may be tipped back momentarily to reject contaminating material which may splash over, rvhere this can be detected. Unwanted fractions, both above and beloiv, are thus collected in one receiver, and the fraction to be saved is in the other. The apparatus illustrated proved highly satisfactory for the purification of a few milliliters of oleic acid. Because of violent bubbling in the flask and the abrupt appearance of a brownish contaminant, considerable agility was required to save the clear colorless distillate that had already been obtained, and it would have been impossible to save it if more than 2 seconds had been required to change receivers.
Removal of Stopcock Grease from Buret Tips C. B. WHITE AND R. C. MCGLENN American-LaFrance-Foamite Corporation, Elmira, N. Y.
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ceivers connected with the lower end of the condenser by a Tshaped tube. T h e distillate is directed into one or the other of the receivers by tipping the entire apparatus, thus avoiding the necessity for flexible or rotating joints or glass stopcocks. Similar T-shaped connections could be used in a variety of apparatus. A T-shaped adapter could be connected t o two flasks and to the condenser through rubber stoppers. Such a device would permit more latitude in the selection of various types of air- or water-cooled condensers, receivers, still heads, and distilling flasks; and the flexibility of the stoppers would decrease the danger of breakage. Standard taper joints could be used where advantageous. T h e one-piece construction
VERY common hindrance to the analytical chemist’s
titrations is the plugging or partial stoppage of the buret tip when too much stopcock grease has been used. The writers have seen several methods of removal employed, including hot water, pieces of wire, and the warming of the tip with a match. However, the use of carbon tetrachloride as a grease solvent gets the best results. By leaving the stopcock in the open position and dipping the tip, u p to the stopcock itself, several times in a small beaker of carbon tetrachloride, the last vestiges of grease will be removed. If the tip is not sufficiently open to permit the entrance of the carbon tetrachloride, a fine piece of wire thrust through the grease first will give the solvent the o p portunity to accomplish its task. This carbon tetrachloride method eliminates the possibility of breaking the buret by using hot water or a flame, and achieves what is wanted better than either of these methods.
