LOOKING AT THINGS How? When? and Why? In looking at a piece of mechanism the eye should enable the "how" to be appreciated. This process is a sort of differentiation. The reverse process-- a sort of integration--is when a problem has to be looked at from the end- point to the means. Packaging problems often come under this heading, and like integrals, can be completely solved only when the differential is known. For example, a cardboard box is to be made. It is known that if a thin card is folded over and pressed, the fold can be straightened out so the cardboard is more or less flat, but on applying a slight sideways pressure the fold will re-form. Because this is known it becomes easy to see the mode to be employed in fabricating a folding carton. Many other ways have been found for producing an incipient fold, e.g., scoring, and because of this it becomes possible to construct mechanical devices to enable folding cartons to be made. Many such problems can be worked out in the brain, but they are almost wholly dependent on having seen similar things by means of observant eyes. And the problems need not be mechanical ones. Let us take a method of analysis for control purposes in a product the composition of which is known. It will undoubtedly be true that an extensive time-consuming assay can be drawn up which will give the right answers. But for control purposes it would mean delay in production. A shorter but sufficiently accurate estima- tion is needed. To do this the whole product and method of manufacture must be looked at. First of all, the point has to be cleared up as to whether the specified ingredients are present. This is best accomplished by making sure that they are up to standard as soon as they are delivered into the factory. If their quality be right, then they have to be weighed out correctly and put into the mixing vessel. This is best done by the foreman checking the weights, initialing the process sheet and watching the various additions. If this routine is followed the composition should be correct, but a final means of assessment is necessary. This is when the looking starts. If the product is a cream then it should have certain physical attributes which will characterise its quality. According to each individual firm's product these particulars will be or should be known and should be easily identifiable. It may be colour, opacity, consistency or body, aeration or non- aeration, easy of liquefying, etc. Most of these are susceptible of quick tests which can be made objective instead of subjective. Colour can be matched in a comparator or tintometer. More exact assays, which in certain products are imperative, can be done by the more expensive photo-electric photo- meters. Opacify is best assessed by a simple photo-electric device, the per- centage of light passing through a thin film of precise thickness being meas- ured. Such a film can be obtained by the use of the Lovibond method in which an optical flat with three accurately ground "legs" is superimposed on a plain flat. Films of 0.25, 0.50 and 1.00 mm. can be obtained. The extent of 153

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS aeration can be measured by such a means. Consistency is not so easy because temperature has a profound influence on any measurement involving viscosity. Nevertheless, measurements can be obtained with some reason- able accuracy and reproducibility if a rotating cup viscometer be employed. These tests are all looking tests put on to a numerical scale. As regards a general assay of composition, inspection of the formula will normally indicate one ingredient which is large in amount and which can be positively determined. For example, a brushless shaving cream will contain 70 or more per cent of water. Drying the water off is not satisfactory. In the first place desiccation takes time and involves at least two weighings (three if the dish is not already tared). Cooling time affects the speed of the method and, as it is a difference method, losses other than that of water may affect the result. It is better to deternfine the acid value. Since the acid value of the fatty acids is known or certainly ought to be known, varia- tions in the amounts of the other ingredients will affect the titrimetric deter- mination. Limits of pernfissible variations can indeed easily be set up. Looking now at the "when," everybody knows, that in making a cos- metical product there is generally some sequence in adding the ingredients. Firstly, there are the instances where some chemical reaction is to occur. For example, in making an emulsion using a soap to disperse a fatty material. If a soap is to be employed the question will arise as to whether the soap is to be dissolved in the water, or in the oil or made in situ. Every cosmetic chemist knows that these three methods, although presumably ending up as an emulsion of identical constitution, give different emulsions. Before a chemist can, therefore, decide at what stage, or when, the soap has to be present, it is necessary for him to look very closely in order to discern why these differences should be. If he can form some picture of the mechanism of emulsification then he can decide which is probably the better way of doing the job. It is true that at the present moment the view-point on emulsification is in the state of flux, especially as the latest work is indi- cating that all interfaces are fundamentally mosaic in character. Neverthe- less, for the purpose of this talk, a simple view mxy be taken. It is easy to imagine that if oil containing stearic acid is brought into contact with water, then at the interface the stearic acid will orientate itself so that the carboxyl group will push out of the oil into the water, but the long length of hydrocarbon chain will want to remain in the oil since it is oleophilic. The extent to which the chain will be pulled into the water will depend on the hydrophilic character of the polar ending, and the carboxyl group is not so strongly hydrophilic as one associated with a sodium or mono-valent ion. This means that if the interface is allowed to form and the projecting carboxyl groups are then changed into soap, the nett results will be that the polar end will become more hydrophilic and will tend to draw •the hydrocarbon chain further into the water phase. At the same time, 154