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INDUSTRIAL AND ENGINEERING CHEMISTRY periphery to the center will serve very well as a stopper for the ensemble. It should contain a tiny hole to admit air during the filling. After thorough cleansing with acid dichromate, the stopcock should be greased on the inner part only. Since the pycnometer is wiped after handling, a n y weight lost due to the removal of stopcock lubricant would introduce an error. The test-tube reservoir s h o u l d c o n t a i n slightly more liquid than is necessary to fill the pycnometer. If more than this is used, the pycnometer contents will be under a slight hydrostatic back pressure which when removed will cause the liquid level to fall below the mark. It is therefore well to have a mark on the test tube to indicate the proper liquid level. I n determining the density of a liquid, the procedure was as follows:
With the liquid up to the mark in the testtube reservoir, the Dvcnometer without its can FIGURE 1 was carefully inserte-dand the rubber stopper sit in place. This ensemble was clamped into a glass-walled thermostat with the lip of the test tube only a short distance from the surface of the thermostat water, and allowed to come to thermal equilibrium (about an hour). A rubber tube was connected to the stopcock, which in turn was connected to a three-way stopcock, a 100-cc. reservoir (to prevent any water from the leveling bulb from draining into the pycnometer), and a leveling bulb filled with water. The pycnometer stopcock was opened and the three-way stopcock adjusted so that water could be drawn up into the bulb. When the water was almost up to the upper capillary, the three-way stopcock was turned to allow the leveling bulb to make the careful final adjustment. Great care must be used in bringing the liquid up to the mark, as capillary action tends to draw it up. A screw arrangement on the leveling bulb will help this. The greatest accuracy is attained if the meniscus is brought up to the mark and the pycnometer stopcock closed, instead of going past the mark and then bringing it back. With the pycnometer filled to the mark, it was removed from the test tube, the stopper removed. quickly wiped with a downward sweep of a towel, and the ground-glass cap placed on it. The rest of the pycnometer was then wiped. It was suspended in the balance in a vertical position by means of a small stirrup which hooked around the stopcock. After remaining in the balance for a standardized period of time, the weight was taken. Under carefully controlled conditions and using a good analytical balance, i t was possible to check weights to 0.1 mg. The pycnometer has the disadvantage that, in working with a liquid having a high vapor pressure at room temperature, the interval between filling and weighing must be short, as the vapor pressure of the liquid tends to force it slowly out of the pycnometer. This might be overcome b y placing the small opening in the cap nearer the ground-glass joint and allowing the liquid to drip into the cap during a weighing. RECEIVED October 28, 1935.
ZINC PIGMENTS IN PAPER AFFECT ALPHACELLULOSE, COPPER NUMBER,AND ACIDITYTESTS. Consideration of fiber purity in terms of alpha cellulose content and copper number has been recommended by the National Bureau of Standards in choosing record papers that are required to have a long life. It has been found, however, that when papers contain zinc pigments, the test values obtained by the present methods are affected. P. F. Wehmer, chairman of the TAPPI Subcommittee on Chemical Methods for Paper Testing has reported that amounts of zinc sulfide commonly used in papers appreciably increase the test values for both alpha cellulose and copper number. Furthermore, that the total acidity value, obtained by titration of an aqueous extract of the paper, is reduced. Until modified testing procedures can be developed to avoid the errors caused by the zinc pigments, the probable stability of papers containing them must be judged in some other way. Another criterion recommended is the amount of folding endurance retained by paper on heating it.
VOL. 8, NO. 1
An Apparatus for Sugar and Other Titrations EDWARD S, WEST University of Oregon Medical School, Portland, Ore.
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OR a number of years t h e w r i t e r has been using a titration apparatus in sugar determinations which has made the work a great deal easier and also i m p r o v e d t h e accuracy. Because of the interest shown in the apparatus b y workers who h a v e s e e n and used it, a n illustration and brief description of it is given. As shown in the figure, a vacuum windshield motor (which may be of any good type) is connected b a s i d e a r m 6.25 cm., 2 . 5 inches long) to a vertical metal shaft (0.47 X 2 6 . 2 5 c'ml, 0.1875 X 10.5 inches) by means of a small coil spring. The shaft runs through a short glass-tube bearing. The lower end of the shaft is attached to the glass stirring rod by a short piece of pure gum tubing. The 25-cc. buret (preferably graduated in 0.05-cc. intervals) is fitted with a 20-gage stainless-steel hypodermic needle (cut to 2.5 cm., 1 inch, length) by means of a piece of pure gum tubing. The writer cuts the tip of the buret to fit snugly into the hub of the needle. The buret is fitted with a siphon automatic leveling device by fastening a glass tube, with vent hole, over the top through which passes a tube into the buret. The tip of the tube should be constricted and preferably ground. It is placed so that when the titrating solution is pumped into the buret above the zero mark and the pressure released in the flask, the solution is siphoned to the zero mark on the buret. The leveling device should be well supported. The glass stirring rod should extend almost to the bottom of the sugar tube on the down stroke. Either a loop or spiral rod is satisfactory, the spiral type being somewhat preferable. The buret, stirring rod, and sugar tube are placed so that the tube can be easily slipped into or out of the clamp when the stirring rod is raised. The vacuum motor may be driven b y a good water pump or other suitable source of vacuum and the speed of stirring controlled by inserting a T-tube and screw clamp in the vacuum line. The 20-gage needle tip delivers about 0.008 cc. of aqueous solution per drop and insures good buret drainage and accurate end points. The apparatus obviously may be used for many different kinds of titrations, though acid solutions should not be passed through the needle tip. A glass tip with fine point may be substituted for the metal tip when acid solutions are used. R E C E I V ~November D 20, 1935.
