POLYMER EVOLUTION--FROM NATURAL TO SYNTHETIC 4:1 MR. K. M. GODFREY: Fig. 2 shows variation in viscosity with pH, dropping rapidly towards pH 12 however the XlO0 000 graph is still a straight line at pH 10. Can you tell me how the curve goes after pH 107 MR. MCKEE: The cross-linked grade does not show the sharp dip of the linear grades. The difference is probably due to the exceedingly high viscosity of the XlO0 000 solutions and also the fact that solution characters are different. The linear grades appear to be nearer the true solution than the cross-lined grade which is, of course, a mucilage. In the case of X100 000 solutions, increase in the pH above 10 gives a gradual dip in viscosity until the resin precipitates as very fine particles in strong alkaline conditions. This does not happen with the linear grades, •vhere the viscosity drops without precipitation. MR. S. G. HocH: I am wondering if the application of a shear force, such as a colloid mill to emulsions as you have discussed, would improve stability. Have you done any work in this area? MR. McKEE: We have conducted high shear trials on neutralized polymer solutions but we have not connected this at all with stability. •Ve have shown that on removing the shear force, the solution viscosity almost immediately recovers. The solutions, especially the cross-linked, appear to be pseudoplastic. There is a tendency for some thixotropy, but very little. MR. S. G. HOCH: [ did not mean the solution, I meant after you had formed an emulsion. What would happen to these formulations? Would they be susceptible to viscosity drops if they were passed through a colloid mill, or can the emulsions be stabi]ised by shearing? MR. McKeE: We have never put an emulsion through a colloid mill. All our emulsions have been made up with good, fast stirring. In some cases we have used the Premier Dispersator. I do not kno•v whether it does anything to the long term stability, but high shear certainly does not break up our emulsions or reduce the viscosity.

J Soc. ½osm, t. Gh•m. 22 43-60 (1971) ¸ 1971 Society of Cosmetic Chemists of Great Britain Guar gum and its applications R. J. CHUDZIKOWSKI* Presented at the Symposium on "Gums and Thickeners", organised by the Society of Cosmetic Chemists of Great Britain, at Oxford, on 15th October 1969. Synopsis--The SOURCES and industrial PROCESSING of GUAR GUM are reviewed. An account is given of its CHEMICAL reactions and the changes in PHYSICAL preparations which accompany them. Some pitfalls in the utilization of guar gums resulting mainly from their high rate of ABSORPTION of water are discussed together with TECHNIQUES for avoiding such problems. INTRODUCTION There seems to be a semantic ambiguity about the very term "gums". According to the original definition which meant broadly "plant exudates", the term encompassed also various resins, rubber latex, etc. The present definition of "gums" is somewhat narrower and more specific. It comprises all materials that can be dissolved or dispersed in water to form more or less viscous colloidal solutions or dispersions. Whichever definition we accept, it appears that "gums" have been used in industry and commerce since the beginning of civilization. According to the Bible, myrrh and frankincense accompanied gold at the Manger. Gums were also used by the ancient Egyptians for embalming the dead and for glueing together strips of clothing for binding mummies. In different application again gum arabic was for them a convenient adhesive for mineral pigments in paint formulations. Likewise, gums were used as food and for medicinal purposes by many civilizations, up to the present day (1). Until recently, however, the use of gums was restricted to a relatively low *Rimreel Manufacturing Company Ltd., Ashford, Kent. 43