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-

'236 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 13. -14. -15. 16. 17. cury along a horizontal tube. This gives a constant pressure and the advantage that dry air or air of pre-determined humidity can be used for the determination. The apparatus is particularly quick and easy to use. Exhibited by Mr. C. Pugh. MECHANICAL BRUSHING MACHINE. Human teeth, mounted in holders, are held in nylon troughs while being brushed with experimental toothpastes. Surface examina- tion by microscopy of the tooth surface before and after this brushing treatment yields valuable information regarding the polishing power and abrasive quality of these pastes. Exhibited by Dr. D. J. Alexander. SPINNING CELL ATTACHMENT FOR THE TRISTIMULUS COLORIMETER. This attachment has been designed to provide a method for measur- ing the colour of a composite surface, e.g. either a piece of fabric or a sample of talcum powder, with the tristimulus colorimeter. The specimen is placed in a cell which Is rotated at 200 r.p.m. in front of the annular photo-cell of the instrument. Exhibited by Dr. D. J. Alexander. APPARATUS FOR THE AUTOMATIC DETERMINATION OF BULK DENSITY. Exhibited by Dr. A. W. Middleton. SACHET TESTER. The instrument was designed to examine shampoo sachets for comparison of the mechanical strength of various laminates (especially to evaluate sealing efficiency) and to permit control of delivered reels. It comprises an anvil under controllable pressure on one side from a hydraulic jack and on the other side connected to gauges, fitted with pointers indicating the pressure at which failure occurs. Exhibited by Mr. N.J. Van A bbe. TILTING TABLE. The apparatus was constructed as a modification of Train's tech- nique (J. Pharm. Pharmacol. 1958: X Supp. 127 T) for measuring the repose angle of powders. The technique provides information on the flow properties of powders and the lubricant effect of additives. Exhibited by Mr. N.J. Van Abbe.