QUANTITATIVE ESTIMATION OF DETERGENCY OF SHAMPOOS 653 by the results of preliminary experiments using controls, which showed no improvement of precision over those using no controls. The fact that certain major factors included in the experimental design (see below) were shown to be significant gave additional evidence that this procedure was sufficiently sensitive. Lengths of yarn (25" long, for convenience) in the form of bundles, were tied with string to the underside of the phalanges of the hairdresser's fingers, as close as possible to the finger tips. The hairdresser then carried out the appropriate shampoo on a subject's head, followed by rinsing. The yarn bundles were taken from the fingers and, after rcmoval of extraneous strands of hair, vere squeezed between tissues to remove most of the water. Finally, drying to constant weight was carried out, as described above. All weighings were done in small, well-stoppered bottles to prevent moisture uptake from the atmosphere. Preliminary experiments assessed possible differences due to using either the right or the left hand for the shampooing and rinsing. Depending on the habit of the hairdresser, one or other hand will spend a longer time involved in the actual shampooing action, the other hand being used for some periods in turning taps and manipulating the rinsing hose, etc. No difference was found, however, between the use of the two hands. Never- theless, the left hand was consistently used in subsequent experiments. Certain other ancillary procedures needed standardisation to ensure minimum variability. These included:-- (a) The concentration of shampoo solution on the head. (b) The time of shampooing. (c) The time of rinsing. (d) The mechanical intensity with which the shampooing was carried out. These factors were determined as follows:-- Concentration of shampoo solution To find the concentration of shampoo solution one required to know the average amount of water retained by a head of hair immediately before the shampoo solution was applied. For normal salon tests, the quantity and concentration of a particular shampoo stock solution applied to a head is chosen arbitrarily. The amount of water retained by a head of hair was found by wetting the head with water from a 1000 ml cylinder, filled to the mark, and collecting the water in a bo•vl placed in the basin, under the

654 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS person's head. When the water had ceased to leave the head in a continuous stream and was limited to a relatively slow succession of drops the portion in the bowl was returned to the measuring cylinder and the volume noted. The difference between this and the initial 1000 ml was taken as the amount retained by the head of hair. Where 1000 ml was insufficient to wet the hair satisfactorily the operation was repeated with the same portion of water. An appropriate volume of shampoo stock solution was then added to give the final required concentration of shampoo on the head. The average quantity of water retained by the hair of eighteen women, chosen at random was: 93 ml (S.D. =38 ml). The Standard Deviation is given in brackets. Time of shampooing The time of shampooing was noted from ten observations (using a stop watch) on each of two hairdressers during the course of their normal work. The minimum and maximum times used (for any single application) by either of them, were 1 min and 2 min. The time was measured from the instant the shampoo solution was put on the head. Time of rinsing The times of rinsing were determined similarly to the shampoo times, the extremes being 1 min and 2 min 15 sec. Mechanical intensity of shampooing The mechanical intensity of shampooing was found to have no effect on detergency. This was established by the subsequent factorial experiments in which extreme conditions of agitation with the hands were used. These conditions were, on the one hand, the minimum movement of the hair- dresser's hand compatible with some agitation and on the other hand, the maximum speed and pressure compatible with the subject's comfort. No attempt was made to control the temperature, other than ensuring that the water coming from the hand hose was at 40øC + 1 øC. The most suitable replication for each experiment was found to be the use of three models per condition of treatment and three samples of wool per model. Greater replication, either of subjects or samples, did not sufficiently improve the precision of results to compensate for the additional