530 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS properly set up. With tl•e method you are proposing, it is possible that one could end up with a mixture of dispersed and undispersed colour, unless great care is taken by the process operator. MR. J. M. TRmGnE: I have absolutely no knowledge of the sand mill, but when grinding various pigments on a three-roller mill, it is necessary to have entirely different conditions on the mill, for the optimum conditions of different pigments. Now, where you have a mixture of pigments going through the sand mill under one condition, is there any flexibility within the sand mill to allow for the different con- ditions necessary for each pigment? T•E LECTURER: We have not found any problem in this respect. We have established a compromise setting for the mill and find that we achieve satisfactory results if we process our various shades of lipstick in this way. MR. J. M. TRm•nE: IS the setting constant for all shades and the single pigments as well? THE LECTURER: Yes. MR. R. SOMERV•nnE: Have you noticed any degradation of the wax base when keeping it in the molten state for long periods? THE LECTURER: We make up sufficient wax base to last us for approximately one week. The tests carried out with molten wax stored in an inert atmosphere indicate that it is slightly better when standing hot for a period, because of the settling of unwanted debris which would pass through normal screening gauzes. MR. J. C. MCCARTHY: Did you ever consider a carborundum mill instead of a sand tnill, and i[ so, why did you reject it? T•E LECTURnR: The drawbacks were that a fair degree of skill is needed to set this mill up, and a multiple pass is also necessary. Admittedly one could use a "cas- cade" process but we felt that the sand mill offered more advantages. MR. A. FOSTER: Could you comment on the rather formidable cleaning problems which I envisage? We see that the only proof you have of the sand mill being clean is that clean oil has gone through it. THE LECTURER: We are quite certain that there are no pockets at the feed in and feed out stages of the mill because we are able to strip off the parts and clean them in the degreaser. As far as the grinding shell itself is concerned, by exposing its integral sieving screens, it is quite obvious when the machine is running clean. If the mill is run whilst the sand is being cleaned, because of the turbulence it is inconceivable that the sand itself would not be thoroughly cleared of colour. MR. A. McGEE: Could you give us some indication of the speed of the process compared with other methods? ThE LECTURER: For a 4 min dwell within the sand mill, one needs approx. 6 hr running in the ball mill.

J. Soc. Cosmetic Chemists 19 531-549 (1968) ¸ 19o8 Socieo, of Cosmetic Chemists of Great Britain Synergism in vitro microbial agents of certain anti- E. E. BOEHM* A lecture delivered before the Society on 4th January 1968. Synopsis•The need for broad-spectrum antimicrobial systems, active against both gram- positive and gram-negative micro-organisms, which function not only as preservative systems but also exert a rapid bactericidal and fungicidal effect is discussed. The desired antiseptic effect can result from the synergism obtained when using different combinations of anti- microbial agents. The existence of antimicrobial compounds has been recognized for many years and chemically they represent a very heterogenous group of compounds. By definition, an antimicrobial agent is one that interferes with the growth and activity of microbes it can be microbicidal (any agent that kills microbes) or microbiostatic ( a condition in which the growth of the organism is prevented), or both, depending on the contact time. Although an antimicrobial which is microbiostatic is considered sufficient for the preservation of some cosmetics this is a dangerous state of affairs. A change in storage conditions can lead to a change of state where microbial growth becomes possible and therefore it is always best to use a microbicidal. The specific nature of activity of any antimicrobial agent, i.e. whether it is essentially active against bacteria, moulds or yeasts or whether it has a more broad-spectrum of activity and is active against bacteria, moulds and yeasts has initially to be considered. One has then to distinguish between antimicrobial agents which are essentially active against gram-positive organisms e.g. Staphylococci, Streptococci and gram-negative organisms, •Nipa Laboratories Ltd., Pontypridd, Glare. $31