ANALYTICAL CHEMISTRY
230 powder, other than the easy loading of the pycnometer with the powder to he tested, have not been solved, and the minor, but universal, problem common to all pycnometers equipped with ground-glass joints-that is, the diifficulty in obtaining repro.. . . .. .. ducible seating of such joints- is mmmizea but not eimunatea by the use of alignment marks on the separate pieces of the pycnometer. Design. Tho pycnometer illustrated consists of a container similar to a standard weighing bottle, into which is fitted the special stopper which includes 8 thermometer and a capillary overflow tube equipped with a. vented cap. All parts have groundglass connections which facilitate removal for cleaning. The underside of the speeisl stopper is concave-elliptiesl, with the apex of concavity a t the entrance to the capillary overflow tube, to aid in getting rid of trapped air bubbles.
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of Dorothy Appleton and Theresa Hudock, Metallurgicd Depart ment, American Brake Shoe Co., in the rrreuaration of the accompanying illustrations.
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IXI'ERATURE CITED
(1) Am. 800. Testing Materials, Philadelphia, "A.S.T.M. Standards." Designation D 70-27. (2) mid.. D 153-39. (3) Ibid.. D 792-48 T. (4) Fifteen-Year Collective Index, IND.END.CHEX., ANALEo., 115(1F^^
A Gas Trap or Large Lapaciry. uean n. itexfora, r ne^ Lhemicai Laboratory, Princeton University, Princeton, N. J. QAS
trap of large capacity has been designed for use a t
A atmospheric pressure with water-soluble gases. Its unique advantage is that i t creates a slight reduction in pressure within
Test Technique. A large number of containers can be manufactured in such 8 manner that the special stopper is interchangeable. Therefore, only two special stoppers need he purchased; one for test use and one, tared with its container, to serve as a counterbalance to correct for the adsorption of moisture on the exposed surface of pycnometers during weighing. These containers, which are relatively inexpensive, can he cdihrated and marked, and used when multiple determinations are desired. This is partioularly important in the case of powders and synthetic resins, where the preliminsry preparation is timeconsuming hut where many samples can he prepared, withant much extra effort, in approximately the time necessary far one sample. Usually, in such preliminary preparation, the contaiuer remains open and the special stopper is needed only for a short time a t the end of the t e s t 4 u r i n g the volume-adjustment and weighing process. If, a t any other time, it is necessary to close the containers, standard weighing bottle Ptoppers can be used. Accuracy and Reproducibility. The pycnometer is calibrated and used in exaotly the same manner as any standard pyenometer ( 1 4 ) . With a laboratory, torsion-type, analytical balance having a sensitivity of =tO.OOOl gram and with a constanttemperature water bath controlled to 25.0" =t 0.1' C., this laboratory has checked to +0.002 gram per cc. the density data forwarded by various resin manufacturers. I n many cases, specifications for commercial resins are set up for ranges such a8 1.03 to 1.04, 1.20 to 1.30, etc. This appears to he close enough far practical purposes, but occasionally both the supplier and the customer feel the need to check separate batches to three decimal places. The ABSCO pycnometer yields reproducible results to the aeeuraoy noted above, provides for speed in loading, testing, and cleaning, and thereby enables an industrial laboratory to effect an appreciable saving in time and money. ACKNOWLEDGMENT
the apparatus to which i t is connected. This contributes greatly t o safety in handling disagreeable gases, as the gases we allowed t o escape only 'hrough the trap. The device has een used in this Lhoratory for the a s t two years. t has successfully "apped hydrogen hloride, hydrogen r o m i d e , iodine, 2 nd bromine apors, hydrogen yanide, a n d certain lachrymators. The construction of the all-glass device is simple. It is well to keep the clearance between the bell, 5, and the outer wall to 1 mm. or less; otherwise n C,
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.Tj wn,r,er Lias nevcr pressure in the SJ of gas). The d e via the side arm, ~
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dryirig tube. I" substitution bromination ieactions a small trap of this design (22 mm. in outside diameter, and 160 mm. in over-all bur "I I A l l Y l r ' ",I lengt.,, '.,app'"u"y"L"g"L' U l Y l l l l U r To all appearances, the absolute capacity of a trap of these small. dimensions lies well beyond this limit. lC3.Y.z
The authors wish to acknowledge the assistance of J. P. Bader, Emil Greiner Co., in the construction of this pycnometer, and
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Water is allowed to flow in a t 1 in sufficient space between the bell, 5, and the outer wall. The bottom part of the main barrel fills up to the overflow, 3. It is important that the device he mounted high enough above the drain to establish a. "head" of a t least 1foot above the sink. This is accomplished by mounting the device on ringstand about a foot above the bench and allowing the overflow water to drain through a lenkth oi burner tubing into the sink. When the device is connected to a closed system, air is drawn in through the side arm, 2. The distance from the bottom of arm 3 to the top of arm 2 regulates the reduction in pressure in theequipment. In the authors' device this was about 0.25 inch. A bulb is blown in arm 2 to prevent water being blown out of the device by sudden increase in pressure within the system.
LIYUL.
