INDUSTRIAL AND ENGINEERING
158
Summary I n view of the possibility of damage, especially to the softer tissues, by regular brushing, a standard test for grading the fine powders used in dentifrices is important. An test is more satisfactory than a scratch test, although the latter is useful for detecting coarse adulterants and is more selective. Antimony has several advantages as a standard surface. Surface flow does not appreciably interfere with the test, providing proper precautions are taken. Some modifications of a convenient abrasion apparatus are described. Results obtained with this apparatus using sized powders show that particle size distribution is important, since for the same abrasion loss per unit weight of powder larger particles will give fewer but deeper scratches. The measure of experimental agreement found by Wright and Fenske between the abrasion results with a variety of powders against the antimony surface and the tissues of ex-
CHEMISTRY
tracted teeth is held to justify the use of the standard surface for testing dentifrices. The correlation between the abrasion test on extracted teeth and the wear involved in cleaning of teeth in vivo is discussed. The test with extracted teeth exaggerates the wear,
Literature Cited (1) Bowden and Hughes, Nature, 139,152 (1937). (2) Bryan, Drug CosmeticInd.,42,164 (1938). (3) Haeseler and Fain, Dental Cosmos, 77, 878 (1935). (4) Hodge and McKay, Ibid., 75,20,227(1933). Miller, W.D., Ibid., 49,1,109,225 (1907). (5) (6) Ray and Chaden, Ibid., 75,1070 (1933). (7) Smith, M.L., J. Am. Dental Assoc. (in press). (8) Smith, M. L.,J . SOC.Chem. Ind., 54,269T (1935). CHEM., Anal. Ed., 8, 191 (1936). (9) Snell and Haeseler, IND.ENCI. (lo) Souder and Schoonover, J. Am. Dental Assoc. 24,1817(1937). (11) Wright and Fenske, Ibid., 24, 1889 (1937). R~~~~~~~ Ootober 4, 1938.
A Simple Hydrogen Electrode Outfit Wa HEINLEN HALL Bowling Green State University, Bowling Green, Ohio
A
HYDROGEN electrode outfit capable of meeting established requirements for the accurate determination of the hydrogen-ion concentration of buffers is a frequent necessity in many types of work. The extensive use of glass electrodes has increased this need, because the absolute accuracy of the glass electrode technique is actually limited to the accuracy of the method used in standardizing the calibrating buffer ( 3 ) . The apparatus shown in the accompanying sketch has been useful in checking buffers according to the criteria suggested by Beans and Hammett (1). It was constructed from the following pieces: A , 180-cc. electrolyzing beaker; B, 60-cc. wide-mouthed bottle; C, ordinary 12.5-cm. (5-inch) test tube. The two electrodes, D and D’, are similar in design to the Wilson type. The saturated calomel half-cell, B, and agar gel salt bridge, E , were patterned after E. Muller’s design described by Kolthoff and Furman (2). The trap, C, should be filled with water to about 1 cm. above the end of the tube leading into the electrode chamber. The electrode chamber is made gas-tight by fitting a short piece of rubber tubing around the salt bridge a t the point where i t leaves the chamber. The position of the holes in the No. 10 rubber stopper is shown in the upper-right corner of the diagram.
Literature Cited (1) Beans, H.T.,and Hammett, L. P., J. Am. Chem. Soc., 47, 1225 (1925). (2) Kolthoff, I. M.,and Furman, N. H . , “Potentiometric Titrations,” 2nd ed., pp. 79,80,New York, John Wiley & Sons, 1931. (3) MacInnes, D. A., and Longsworth, L. G., TTans. Electrochem. Sac., 71,79-91 (1937). RECEIVED November 12, 1938.
VOL. 11, NO, 3
