THE PROMISE AND THE PRODUCT 5O3 support to the development chemist. In fact proliferation of techniques is one of the problems. Quot homines, tot sententiae certainly applies here. There is also the problem of what happens to the Mark I technique when Mark II arrives unless the results are carefully correlated, earlier work becomes unrelatable and the temptation is always to continue with both. It is also an area of steady publication and I believe that something approaching a standard methods handbook could well be now timely if we could ever reach agreement. This is one of the declared aims of the I.F.S.C.C. (6) which has survived unchanged from the original draft put up by the US Society on 13th August 1958. Screening techniques Even simpler concepts based on even more comprehensive assumptions must be used to screen materials as opposed to assessing products. In this field there is greater inter-laboratory agreement and also, or because of, very many fewer problems of commercial security. I am thinking of such tests as foam tests for a detergent raw material, minimum inhibitory concentration of germicides, abrasivity of abrasives, Sward hardness of resins. Many of these tests are so standardized now that they will be handled by the raw materials section of the analytical laboratory and quoted by potential sup- pliers as part of their materials specification. Nevertheless there are some more specialized and local techniques in this category which will be deeply rooted in a locally-generated hypothesis, perhaps of a very fundamental nature and certainly a matter of commercial security, at least until the patents are solid! Summary Physical evaluation is thus largely a question of measurement of properties. Some of the properties we wish to quantify are easily measured and in some circumstances attention is mostly required to determine that it is indeed the right quantity that is measured. Viscosity measurement, for example, is not a technical problem, but selection of what method of measurement, under what conditions, does in fact measure the property most relevant to the attributes may be a difficult decision. It is the properties of the product-in-use that have to be quantified

504 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS and this may involve measurement both on the product itself (e.g. viscosity of a shampoo) and on the total system (e.g. viscosity of lather in the presence of greasy hair). The selection process is far more critical than the elaboration of techniques. Furthermore the selected property may need to be examined in the appropriate light at each of the stages we have just discussed. Taking them in reverse order, we start first with the screening process whereby an in- gredient or very simple formulation is checked against the basic hypothesis. Such a hypothesis will be that an improved functional performance should be obtained by a certain change--a new ingredient, a new solvent or vehicle, etc. The first stage must therefore always be to check whether the hypo- thesis can be invalidated. Note--not that 'it is correct' but that 'it cannot be invalidated': a hypothesis cannot be proved, it can only be disproved. Since it is most important to reject incorrect hypotheses which cause vast wastes of time and plug up the whole research process, the initial screening of properties must be done under the conditions most favourable for a positive result, because if the test system fails in these conditions, it can be happily written off. Typically this means using apparently excessive dosage, long dwell times, etc. This screening stage gives the scientist con- fidence to proceed to the next stage and is typically on-bench in vitro, although occasionally animals or even humans must be used (such as in screening new perfume ingredients). In the second stage, which I called assessment, a prototype system is created by the development chemist so that he may check that the sought- for properties do indeed exist. Again favourable conditions are used and standardized techniques with high levels of control to reduce intrinsic variability. This stage also is essentially in vitro, although small animals or small panels may be used if no in vitro technique exists. This stage not only gives further confidence and information to the scientist, but may be essential for giving authority to Patents, Marketing or external authorities. A further value of the use of instrumental methods in early development is that of economy in safety testing. Unless a development is shown as potentially worthwhile, the time and expense of rigorous consumer safety testing is not incurred the resource is then available for the extensive testing needed by favourable developments. Having obtained confidence that proceeding to the rationale can pro- duce the desired effect, the next stage is the in-use confirmation, the physical evaluation of functional performance. Incidentally, it may be that the hypothesis is scientifically not too sound, but in some circumstances