234 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS more light than one in which the droplets are coarsely dispersed. Therefore, when light is passed through a thin layer of an emulsion, the amount of light transmitted will be determined by the size and size distribution of the droplets in the emulsion. The simple Photometer which is demonstrated consists of a hght source, a cell of standard thickness and a photo-electric cell. The meter is set at 100 per cent transmission without any sample in place and the reading then taken with the sample in position. In general, the lower the amount of light transmitted, the finer will be the emul'sion. This reading is an average which cannot distinguish between the various possible particle size distributions. It should therefore be used in conjunction with a microscope in order to assess the effect of the varying particle size distributions in the experimental systems. The instrument thus forms, for a system of constant com- position, a rapid quality control check on the average degree of homo- genisation or dispersion of many two-phased dispersions. Exhibited by Dr. A. M. Posner. o ROTATING CUP VISCOMETER. The apparatus shown is a modification of an oscillating disc vis- cometer in which the cup is rotated on a constant speed. The sample is carefully placed into the cup and the disc gently lowered into it and covered with the cream. The disc is then attached to the weighted bob at the lower end of the torsion wire and the motor switched on. The maximum deflection on the scale is noted and this gives the approximate measure of the yield point. The way in which the viscosity changes with time may then be determined by reading off the values of varying times. If necessary, the instrument may be calibrated using liquids or systems of known viscosity. Exhibited by Dr. A. M. Posner. . HAIR STRETCHING MACHINE. It is often necessary to assess the changes in the mechardcal strength of hair brought about by various treatments. This can be most simply done by the apparatus described below: The apparatus consists of a balance beam, to one end of which is attached the hair to be stretched, the other end being loaded at a constant rate by a varying length of chain. The change in the length of the hair and the load applied are recorded by means of a pen or• the drum at right angles to one a_aother. The curve produced is a load/extension curve. The ler•gth of the initial straight line portion of the curve, the

SOCIETY OF COSMETIC CHEMISTS OF GREAT BRITAIN 235 Hooke's Law length, is reproducible under certain conditions, and changes in this length after chemical or mechanical treat- ments to the hair are used as a measure of damage done during the treatment. Exhibited by Dr. A. M. Posner. 10. EXTRUSION TEST FOR PASTES. One of the important features of a paste or cream is the ease or difficulty of squeezing it from the tube. To measure this, a simple test has been developed in which air pressure is applied to the opened crimp end of the tube and the time required for $ cc of the product to be extruded through a standard metal nozzle is determined. The nozzle is fixed into a normal cap and can then be quickly screwed into the tube. Since temperature has a considerable effect on flow of products, the tubes are warmed to the required temperature in a thermostatted water bath before the test and are kept in a water jacket during extrusion. Exhibited by Dr. A. •VI. Posner. 11. AIR CONTENT OF PASTES AND CREAMS. A common method for estimating air content of pastes and creams is to measure the apparent density. If the real density of the product in the absence of air is known, the air content can then be calculated. With many products, this method is unsatisfactory, particularly if the real density is either unknown or can vary. In the apparatus shown, the product is contained in a cylinder of known volume and the compression of the air is measured as a function of the applied air pressure by measuring the movement of water in the calibrated tube connected to the container. By simple application of Boyle's Law in the absence of volatile components or with correction for condensed yapours in their presence, the air content can then be calculated without any knowledge of the density of the paste at all. Exhibited by Dr..4. M. Posner. 12. PARTICLE SIZE OF FINELY DIVIDED SOLIDS. This apparatus has been modified from one described by Pechukas. and Gage in Industrial and Engineering Chemistry, Analytical Edition, 18, June 1946. The original apparatus has the disadvantage that the pressure driving the air through the porous material is variable and the air is saturated with water. In this modification, the method of measuring the volume of air has been changed from sucking water' into a pipette to measuring the movement of small droplets of mer-