240 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS and in any case a control treatment was included in any series of tests, the value of K is not of importance. Since it was difficult to remove the charge from the comb completely, it was necessary to take two readings in each determination. The first to ascertain the amount of residual charge on the comb from the previous determination, and the second to determine the amount of charge after the present determination. To correct for the residual charge the following relationship was used' Charge produced on the hair (a)= total charge- residual charge •:(do• -- d D where d r is the comb/leaf distance giving a just perceptible leaf movement before charge generation, and d o the corresponding distance after generation of the new charge. Humidity control Attempts to control the humidity using saturated salt solutions were not successful for the following reasons: (i) Since the chamber was not hermetically sealed, movement of the rack and pinion, or glove, caused uncontrollable changes in the relative humidity. (ii) A large amount of salt solution was required and a long time was needed to reach equilibrium. (iii) Circulation of air within the chamber is desirable to maintain a uniform humidity and it was difficult to incorporate a fan within the space available. A laboratory air compressor was used to circulate the air through the salt solutions, but removal of the last traces of oil and contamination in the air which derived from the pump and salt solu- tions was difficult. The presence of this contamination caused erratic results. Finally, air from a cylinder of compressed air was passed into the chamber through glass and polythene (not rubber) tubing only. A by-pass, through a series of water bubblers, was so arranged that any relative humidity was obtainable by varying the proportion of air passed through the bubblers. The gas was allowed to leak out of the chamber through a small orifice, a small positive pressure being main- tained at the inlet. The humidity was measured by a hair hygrometer, suspended in the chamber, and by another one placed in a small chamber on the inlet pipe which served as a check on the relative humidity and facilitated control of the incoming gas. By adjusting the flow of gas, whenever necessary, it was possible to maintain the relative humidity at a specified value, to within -+- 1 per cent.

STUDYING STATIC ELECTRICITY PRODUCED ON HAIR BY COMBING 241 The calibration of the meters was checked using saturated salt solutions, and appropriate correction factors were employed wherever necessary. }V[ATERIALS AND TREATMENT The hair used was of good quality and cleaned by the suppliers, using a mild soapless shampoo, and was otherwise untreated. Some natural grease still remained, as shown by solvent extraction on one or two samples. It was supplied in one-ounce locks, each lock being reputed to come from the same head, and care was therefore taken that all samples for one test came from the same lock. The hair locks were cut to 8 '• in length, largely eliminating the curled ends, weighed into one gram samples and tied one inch from the root end. Since most comparisons were made between different shampoo treat- ments, the following standard shampooing technique was evolved: (a) The hair was pre-wetted by immersing ten times in 200 mls of tap water at 35 ø C. (b) The hair was immersed in 200 mls of shampoo solution (made up with tap water) at 35 ø C for 3 minutes, occupied as follows: l st minute--hair pulled repeatedly through a comb, 2nd minute-hair pulled repeatedly between the fingers, and 3rd minute--hair pulled repeatedly through a comb. (c) The hair was rinsed ten times in each of three 200 ml tap water at 35 ø C, being squeezed dry between the fingers after each lot of rinsing. (d) The wet hair was combed free of snags and put between clean linen cloths until all samples in the experiment were shampooed. (e) When all samples had been treated, they were hung in the air to dry for two hours and then suspended freely in the experimental chamber. The air supply was turned on, adjusted to the desired relative humidity and left for at least one hour to reach equilibrium. Each sample was then tested in turn to determine the amount of static electricity gener- ated on combing. RESULTS AND DISCUSSION The rate of the leakage of the charge from the comb Although every attempt was made to insulate the comb, it was inevitable that some loss of charge should occur with time. A 1 g lock of hair was shampooed using the standard technique. The hair was pulled through the comb ten times (i.e., ten strokes), and the charge on the comb determined at regular intervals. The relative humidity in the chamber was set at 70 per cent, so as to produce conditions most favourable to charge leakage. The results are shown plotted in Fig. 2.