114 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Beckman Type E (Blue Glass), Beckman Catalog No. 4990-75. High alkalinity (low alkali error) electrode for measurements from pH 9 to pH 14. Temperature range: 5 ø to 40øC. OR Beckman Type E-2, Beckman Catalog No. 4990-72 for measure- ments over the entire pH range. Temperature range: 15 to 100øC. (3) Calomel reference electrode, such as the Beckman fiber type, Beckman Catalog No. 4970. Temperature range: -5 to 100øC. (4) Soft cotton string (at least 1/16 inch in diameter) saturated with potassium chloride solution and used while wet. Reagents Required Buffer solutions of pH 4.0, 7.0 and 10.0. Certified buffer solutions may be purchased from most laboratory supply houses in either solution form or as a fast-dissolving powder. Potassium chloride solution (KC1), saturated pH indicator test paper, such as Alkacid or Hydrion, sensitive to the nearest pH unit. Procedure Determine the approximate pH of the sample using indicator test paper. If the indicated pl-I is 9 or below, use general purpose glass electrodes designated #4990-80. If the pH is above 9, use the high alkalinity type E glass electrode designated #3990-75. The Beckman type E-2 glass elec- trode designated #4990-72 may be used as an alternate for either of the above electrodes and may be used anywhere in the pH range. P^RT I--STANDARDIZATION OF PH METER. See Note (a). (1) Attach the electrode system with the proper glass electrode described above and the calomel reference electrode to the pH meter. (2) Wash the electrodes thoroughly with distilled water and dry gently with clean absorbent tissue. See Note (b). (3) The temperature of all solutions to be tested, whether buffer or test solutions, shall be brought to 25 4- iøC. Electrodes shall be im- mersed in solution for several minutes, if necessary, to permit elec- trodes to reach same temperature as solution. (4) Buffer solution of pH 4 is used for initial standardization when the general purpose glass electrode (#4990-80) is used and pH 10 buffer solution is used for initial standardization when the high alkalinity type E glass electrode (#4990-75) is used. The pH 4 buffer solution is to be used for the initial standardization of the type E-2 glass elec- trode (#4990-72). See Note (c). (5) Place some fresh buffer solution in a beaker and in another beaker place a quantity of saturated potassium chloride solution. Set the

EVALUATION OF SHAMPOO 115 temperature adjustment dial of the meter to the temperature of the buffer (25øC). (6) Insert the glass electrode into the beaker containing the buffer solu- tion and the calomel electrode into the beaker containing the saturated potassium chloride solution. (7) Connect the buffer solution and the saturated potassium chloride solution with a 3-inch piece of string saturated with potassium chloride (wet). See note (d). (8) Check and adjust, if necessary, the pH reading with the known pH of the buffer solution used following the manufacturer's instructions. (9) Remove the glass electrode, wash thoroughly with distilled water and dry gently with clean absorbent tissue. Insert the glass elec- trode into a beaker containing fresh pH 7 buffer solution. (10) Connect the buffer solution and the saturated potassium chloride solution with a new piece of string, saturated with potassium chlo- ride, and check the pH reading. If the pH value obtained on the latter is not within +0.1 unit of the correct value for the pH 7 buffer, a faulty electrode is probably to blame and new electrodes should be installed and checked as described above. See Note (e). P^• II--DETEltMINATION OF PH (1) Wash the electrodes thoroughly with distilled water and dry gently with clean absorbent tissue. The type of electrode and standardization are based on a preliminary test for pH using indicator paper. See Part I. (2) Insert the glass electrode into the sample being tested and insert the calomel electrode into a beaker containing saturated potassium chloride solution. (3) Connect the sample being tested and the saturated potassium chloride solution with a 3-inch piece of string saturated with potassium chloride (wet). See Note (e). (4) Read the pH of the sample in accordance with the manufacturers in- structions for the instrument used. Notes (a) The pH meter should be standardized daily or before each series of tests. If a number of determinations are being made, check the meter against the two buffer solutions after every 5 determinations. (b) The pH meter should be switched to a neutral or check position when the electrodes are being handled or are not immersed. This will pre- vent the possibility of polarization of the glass electrode which will cause the pH readings to be a few tenths high and a reading drift for several minutes after re-immersion.