1504
ANALYTICAL CHEMISTRY
The accuracy with which 2 grams of polymer can be measured volumetrically in these small test tubes is shown in Table 11. Sixty tubes were calibrated, 30 n-ith cube-rut Lucite 140 and 30 with granular Lucite 40. Each calibrated tube was checked by two analysts, who weighed the amount of sample required t o fill the tube to the mark. The average weight was very close to 2 grams in each case. The larger standard deviation obtained for ctul,e-cut molding powder is not surprising, as cubes to inch on edge) would not be expected to pack as uniformly and reproducibly as fine granules. .Iccurate measurement of samples requires tubes ivith a favorable ratio of inside diameter to length, with consideration for the particle size range and distribritiou. STABILIZED K.ARL FISCHER REAGENT
ur:ite results using the moisture kit deaci,ibed 't:tlile Iiurl Fischer reagent. This reagent is a powerful desiccnrit. Contact ivith moisture from any source results in instantarieous reaction and an attendant decrease in strength. In small sealed vessels the reageut is adequately protected. However, the us;ial Fischer reagent, ivhich is a niixture of methaiiol. pyridine, sillfur dioxide: and iodine, undergoes an unavoiddble deterioration even 17-heii protected from contiict with water ( 5 ): daily standardization is iircrw;sry to obtain accurate resiilts. Consequently, it c:innot he wr:l for an :ipplication such as the moisture kit, where daily stantl:ti~tlizntion is not practical. In the fall of 1953 the Fishrr Scientific Co. marketed a s:abilized Fischer reagent (Catalog T o . SO-K-3). Shelf-life tests shoved that this reagent had good stability. Hon-ever, as sold it is much too roilrentrated for use in the nioisture kit, having an equivalenre factor of more than 6 nig. of water per ml. of reagent and a density of about 1.28. I t was necessary, therefore, to reduce its strength n-ithout impairing its stability. Three methods were investigited: ( 1 ) dilution viith methanol, ( 2 ) ) dilution v-ith methyl Cellosolve. iddition of water, a i i l 11:ivr demonstrated that relatively Peters and Jungnicltel stable Karl Fischer reagent ca i he p r e p r e d by use of nieth>-l Cellosolve in place of mz:h ino!. Ililution with methanol IYJS unsuccessful. I11 I45 days the strength of SO-Ii-3 Karl Fiachcr reagrnt, which 11-as diluted with xpproximately 2 parts by volume of methanol, decreased almost liuearlg from 2.11 to 1.20 mg. of water per ml. This as not surprising, because it is known ( 5 ) t h a t ordinary Fischer reagent prepared with methanol is unstable. Reducing the strength of SO-K-3 Fischer reagent b y adding water resulted in a reagent of i'tiirly good stability. I n 138 days ivater-weakened SO-K-3 decreased in strength from 2.28 to 2.09 mg. of water per nil. l l e t h y l Cellosolve-diluted SO-K-3, hoxvever, had excellent stability. Over a period of 110 days SO-K-3 reagent diluted with 2 volumes of methyl Cellosolve maintained its water equiv:ilvnce factor unchanged at 2.16 mg. of n-ater per ml. T h e shelf-life tests of the three modifications of SO-K-3 disc-iiased ivere all run in the same manner. A number of dried 20ml. serum bottles were filled with the formulation to be tested aiid stoppered v-ith pressure-seal rubber stoppers. T h e vials \\.we stored at room temperature with no special protection ag.iinst light. The stoppers were not coated with beeswax. Oiie bottle of each formulation was standardized a t approximately m-eekly intervals. This v-as a severe test of the reagent. I t demonstrate'd not only t h a t the methyl Cellosolve-diluted rc:tgent was stable but also t h a t the small serum bottle$ capped ivith pressure-seal rubber stoppers adequately protect t'he reagent from atmospheric moisture. This method of testing shelf-life \vas chosen because the conditions simulated storage of the reagent in the moisture kit. .ilthough a tight seal was maintained b y t h e stoppers during the course of the tests, the outer surface of the stopperE deteriorated badly, on-ing t o oxidative t l r g i d a t i o n of the stretched rubber. I n order to prolong their
life, the stoppers of all serum bottles containing reagent were sribsequeJit1.v coated r i t h beesn-ax, Tvhich effectively prevented .such degradation. The moisture kit principle should be applicable to the determination of water in other resins. In many c:tses the primary practical problem bo be overcome is that of finding solvents which ivill dissolve the polymers quickly to form solntions of not inconveniently high viscosity. LITERkTL-RE CITED
(1) Dean. R. B., Hawley, R. L.. Paci.fic Sci. 1 , 108-15 (1947).
12) Harrison, S. A . , Lieincke, E. R., ASAL. CHEM.20,47-8 (1948). (3) Houston, R. J.. Ibid., 20, 49-51 (1948). (4) Levy, G. B., Murtaugh, J . J.. Rosenblatt, 11.. ISD. Esc. CHEM., - \ s . i L . ED. 17, 193-5 (1945). ( 5 ) IIitchell, J., J r . , Smith. D. LI., "hquametry." pp. 54 ff, Interscience, Sew York, 1948. ( 6 ) Peters, E. D., Jungnickel, J. L.. . h . 4 ~ CHmr. . 27,450-3 (1955). ( i ) Smith. D. A I . , 1Iitchel1, J., J r . , Billmeyer, A. AT., I b i d . , 24, 1847-9 (1952).
Cover Glass for Erlenmeyer Flasks Frank R. Short and Gordon Good, Chemical Research Department, Monsanto Chemical
Co., Dayton, Ohio
arose in this laboratory for a cover glass that would permit rapid evaporation of liquids. particularly organic solvents, from Erlenmeyer flasks. Neither a small plain watch glass nor a chemical funnel permits very rapid evaporation. No quitable n-atch glass was found in any s~ipplycatalog, so the cover g l a a ~shon-n in the photograph v-as designed and made for t h e p u r p o s e . I t will f i t 125-. 200-. and 300-1n1. conical flask^ I n addition to the advantage of rapid evaporation, the flasks may b e wirled, or tipped to about 45' witho u t l o s s of t h e cover \~EED
~
deal or blon- a round (test tube) bot,toni at one end of a 15-em. (6-inch) length of glass tubing 25 mm. in outside diameter. To the center of the bottom seal about 15 cm. of 4- or 5-mm. glass rod to serve as a handle for further working. \Then the glass has cooled, sa\\-off the tube about 10 t o 12 mm. above the point where the bottom curvature begins. Sccure the glass rod in the chuck of a glass lathe and heat the open end of the tube until it is soft and gloning. With a carbon rod ( 7 t o 8 mm. in diameter) flare the end back t o the point of c.urvatme until it is at right angle t o the axis of the tube and about 1 em. in diameter. It may be necessary to reheat and rotate against a carbon paddle to flatten the flare evenly. Cool and remove from the lathe. I n a small flame heat a portion of the flare a t n time and make the three indentations in the top surface with a tungsten rod ( 2 mm.) or a carpenter's pencil. If a pencil is used, whittle the viood from about 15 mm. of the lead, which is then shaved t o a \\-edge shape. Finally, heat and wniove the glass rod from the bottom of the cover. The cover glaqs may he made entirely by hand working, b u t i l the fi:~ringis done by hand the cover may not fit the three sizes mentioned above. I t may be necessary to start with a different size of tubing for each size of flask, depending on the skill of the glass blower. For hand working, a glass tube is chosen v i t h an outside diameter within 1 mm. of t h e inside diameter of the neck of the flask. If desired, rovers for 500-ml. flasks may be made from tubing 35 mm. in outside diameter and for liter flasks from 38-mm. tubing. The latter also serve as cover glasses for 50-ml. beakers. Covers for flasks with 24/40 Ptandard-taper outer joints can be made from 20-mm. tubing.
