INDUSTRIAL AND ENGINEERING CHEMISTRY
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amount of cresol red indicator to yield the same concentration as in the assay solution at the pH 7.65 end point. COLORSTANDARD B. To 50 ml. of 0.2 M acid potassium phthalate solution add 5.75 ml. of 0.2 J4 hydrochloric acid and dilute to 200 ml. with water. To a quantity of the solution, add sufficient cresol red and bromophenol blue indicator to yield approximately the same concentration of both indicators as in the assay solution at the pH 3.15 end point.
Vol. 14, No. 1
the results obtained have been checked by gravimetric assay and by potentiometric titration. In addition, numerous pharmaceuticals and detergents have also been assayed b y both the gravimetric and the authors’ method. In all of the assays, no deviation greater than 0.2 per cent from the potentiometric or gravimetric method has occurred.
Literature Cited Discussion The method has been applied to the assay of reagent grade orthophosphoric acid and alkali-metal orthophosphates and
(1) Kolthoff, I. M., Chen. Feekblad, 12, 644 (1915). (2) Rosin, Joseph, “Reagent Chemicals and Standards”, pp. 415,417, (3)
New York, D. Van Nostrand Co., U.S. Pharmacopoeia XI, p. 25.
1937.
Anchor-Type Laboratory Stirrer for Viscous or Foamy Materials RALPH E. FORREST’, Research Laboratory, Autoxygen, Inc., New York, N. Y.
I
N THE course of an investigation made in this laboratory it became necessary to reflux a troublesome reaction mixture with stirring. The mixture foamed a t first, became viscous and pasty as the reaction proceeded, and finally became hard and adhered to the inside of the flask. Several wellknown types of stirrer were found to be useless. Various stirrers, different from the ordinary propeller, have been described-e. g., the chain type ( f ) , the bicycle-chain type ( 2 ) , and a gas-tight stirrer for pasty materials ( 3 ) . It was thought that a n adaptation of the anchor type of stirrer, well known in industry, might be effective here, because of the scraping action. The stirrer was to be used in a 500-ml. P rex 3-necked flask. Measurement of the circumference of the iask with a flexible steel tape gave a value of about 32 cm. (12.625 inches). Accordingly, a circle with a 5.1-cm. (2-inch) radius was drawn on a sheet of cardboard. Since the inside diameter of either side neck of the flask was 1.6 cm. (0.625 inch), a second circle was drawn, concentric with the first, having a radius of 3.5 cm. (1.375 inches). A diameter was drawn, and with a pair of scissors the cardboard was cut along the diameter and along both circles, producing two semiannular tem lates. Before a t e m p i t e would pass freely into the flask by way of a side neck, it was necessary to reduce the width of the cardboard strip somewhat. The radius of the outside edge also had to be reduced, in order to make the edge of the template exactly fit the curvature of the glass. After the dimensions of the template had been established by trial, the curves were laid out on No. 25 gage (or slightly heavier) Alleghany stainless-steel sheet. They were very carefully cut out with a pair of heavy tinsmith’s shears, a trifle oversize, so that the outside edge could afterward be smoothed with a file to the exact radius determined by the template. (Any suitable sheet metal may be used instead of stainless steel.) As no two flasks have identical inside diameters, it is necessary to make an individual sheet-metal blade for each flask used. For the shaft a 30.5-cm. (12-inch) length of 0.635-cm. (0.25inch) stainless-steel rod was used. This was slotted along a diameter with a hacksaw, the slot being 0.635 cm. (0.25 inch) deep ( A , Figure 1). At the center of the sheet-steel blade a corresponding slot was filed, 0 . 6 3 5 cm. (0.25 inch) wide by 0.32 cm. (0.125 inch) deep or slightly deeper (B,Figure 1). To set up the stirrer, the blade is introduced into the clean flask through a side neck, from the position shown in dotted lines (Figure 2) by rotating it about its center of curvature. The shaft is next introduced through the center neck, and the slots in the blade and shaft are caused to engage one another. The flask is then charged with the desired materials, and a stuffing box (or a perforated cork) is slipped over the shaft and seated in the neck of the flask. The whole is clamped into position on a ring stand and the upper end of the shaft engaged in the chuck of a variable1
Present address, Kelton Cosmetic Co., 230 West 17th St., New York,
N. Y.
speed stirring motor (or a pulley for leather belting may be attached by means of its setscrew). During all the operations subsequent to the engagement of the shaft with the blade, care must be exercised not t o raise the shaft at all, for otherwise the shaft may become disengaged from the blade. The rate of stirring must be fairly slow (250 to 300 r. p. m.) to avoid splashing into the side necks of the flask, and for the same reason not more than 200 ml. of liquid may be placed in a 500-ml. flask.
n
FIGURE 1
FIGURE 2
For a stirrer to fit a 1-liter flask, the same shaft may be used, but the blade must be cut from heavier sheet metal, about No, 19 gage (or slight1 heavier). The radii in this case are approximately 6.2 cm. $2.4375inches) and 5.1 cm. (2 inches). The blade should be sufficiently flexible to permit of some deformation, in order to be able to introduce it into the flask without difficulty, especially in the case of the 1-liter flask.
When this type of stirrer was used with the reaction mixture mentioned above, the liquid was thrown against the wall of the flask, forming a hollow sphere. This suppressed foaming over. Finally, when solid material was precipitated, t h e scraping action of the blade proved effective to prevent t h e solid from adhering to the inside of the flask.
Literature Cited (1) Herahberg,
IND. ENQ.CHEM., .%NIL. ED.,8, 313
(2) Lippincott, Ibid., 4, 9 3 (1932). (3) Maude, Ibid., 9, 196 (1937).
(1936).
