OCTOBER 15, 1937
ANALYTICAL EDITION
in the position shown (fume inlet). The tube is ready for use as soon as it has cooled. The tube is first filled with glass beads or glass wool to a point somewhat above the fume inlet. The glass beads or wool support a column of loosely packed soda lime or other suitable absorbent. A wad of cotton may be placed above this. The filled tube is fitted tightly into the neck of the Kjeldahl flask by means of a collar of folded filter paper, as suggested by Henwood and Garey (1). The tube must not project down too far into the neck of the flask; otherwise spray may collect on it. Before beginning the digestion, the cotton wad is removed and the soda lime moistened with a little distilled water. The wad may then be replaced. The charge in one tube may last for several digestions. The filling and fitting of the tube require only a few minutes. This type of absorber has been used with Kjeldahl flasks of 100- to 500-cc. capacity and with a variety of digestions, including feeds, sugars, and pure organic compounds. It has shown itself satisfactory, enabling the digestions to be carried out in the open room without inconvenience. Occasionally a small amount of sulfuric acid mist has escaped from the tube at the beginning of a digestion, but this has always ceased after a few minutes. Because of the shape of the opening, any spray which spat-
479
ters u p onto the bottom of the tube may readily be washed off the rounded end with the stream from a wash bottle, and any small condensate which forms inside the tube will collect safely inside the rounded end.
Summary A test tube, perforated near the bottom, is filled with moist soda lime or other suitable absorbent, the perforation being first shielded with glass beads or glass wool, and is then tightly fastened into the neck of the Kjeldahl flask by means of a collar of folded filter paper. This device absorbs and prevents the escape of practically all irritating fumes during the digestion, and thus permits it to be carried out in the open room without inconvenience. It may be modified for use in other reactions which evolve unpleasant fumes. Literature Cited (1) Henwood, A,, and Garey, R. M., S. Franklin Inst., 221, 531-8 (1936). (2) Henwood, A.,and Garey, R. M., Science, 76, 524 (1932). RECIDIVSD J U ~ Y9,1937
A Self-Filling Pycnometer G, F. HENNION University of Notre Dame, Notre Dame, Ind.
T
HE pipet type of pycnometer is widely used for the determination of densities, particularly of organic liquids, but has the serious inconvenience that filling requires suction. As this is frequently accomplished orally, obnoxious vapors may be drawn into the mouth. Precise adjustment of the liquid volume is also frequently troublesome. By making a few minor changes in construction, pycnometers have been made in this laboratory which are entirely self-filling and extremely easy to adjust. Figure 1 illustrates one of these. The dimensions are somewhat variable except for the capillary tip, A, and tube D. The pycnometer is used as follows: Hold with thumb and second finger at oint F , place index finger over opening G, and dip capillary tip beneath the surface of the liquid whose density is t o be determined, contained in a small crucible or beaker. Remove pressure at G . The pycnometer fills automatically, owing to capillary rise of liquid at A and overflow at B. When the liquid reaches the calibration mark, apply pressure at G and withdraw A from the liquid. Wipe the capillary tip, rock the pycnometer gently to withdraw the li uid from A B , suspend in a balance, and weigh. desired, the pycnometer may be filled beyond the calibration mark and suspended in a constant-temperature bath maintained at the desired temperature. Excess liquid may be subsequently withdrawn at A in the usual manner. The capillary section at A B must extend beyond both sides of bend B . Too fine a capillary causes very slow filling. A 2ml. pycnometer used by the author fills with water in 18 seconds at 25" C. If tube D has an internal diameter greater than 2 mm. the descending column of liquid tends to break, causing air bubbles. Naturally the pycnometer must be cleaned and dried before use. The presence of a small slug of liquid at E prevents liquid rise at A .
B
1
2 mm. i.d.
If
A number of these pycnometers have been constructed by the author, with volumes varying from 0.75 t o 10 ml., and have been used with organic liquids of various densities and surface tensions. The pycnometers are readily constructed from selected pipets and are calibrated without difficulty in
FIOURE1. SELF-FILLINO PYCNOMETER the usual manner. A fine wire, connected a t C and F, serves for suspending the pycnometer in the balance. RECEIVED August 13, 1937.
