76 JOURNAL OF THE SOCIETY and much more time is called for. A good deal depends' on whether clear-cut evidence can be expected, or whether it is likely to be conflict- ing. Trying out a bubble bath is a simple matter. The consumer ex- pects it to have a pleasant smell, to make plenty of bubbles that last long enough for her to relax and enjoy them, and to leave no ring on the tub. We can judge the quantity and lasting quality of the bubbles very quickly in a laundry tull, a half a dozen women will give us a good idea of how satisfactory the product will be under varying con- ditions in the home. But if you want to know whether a face powder cakes and how well it clings, you may need 20 or more subjects because you are bound to have some contradictory results. In general, when we have a com- plicated problem, I have found that it is better to begin with a very small number of subjects, and enlarge the study after we have had some ex- perience with a product. The time required for an adequate use ,test is sometimes surprising to those who are not accustomed to this method of investigation. It may vary from a few days to a year or more. Consider, for example, a product with this claim, "Eliminates broken, brittle nails helps nails grow long and strong." This prob- lem was brought to us last spring. The plan for our test required 20 women to .come to the Beauty Clinic twice a day to have their nails treated. Since we have a OF COSMETIC CHEMISTS five-day week, they were given a supply of the product to use them- selves on Saturday and Sunday. To determine- how long the study should continue, we figured that it would take two months for the old nail to grow out completely and two months more for a new nail to grow out to the tip. So the mini- mum time was set at four months. I am sorry to report that at the end of this tedious study, we saw no difference in the quality of the nails. As I have explained, most of our practical use tests are supervised in the Beauty Clinic. Sometimes, however, we find it advisable to have groups of women make home tests. For example, in studying a plastic cuticle pusher, we thought the tip might be too sharp and in- jure the cuticle when used by un- skilled hands. A group of 20 women who used the pusher for a month de- cided this question for us. We also like to have large groups o5 home testers use products to determine whether directions for using are clear and adequate, or to learn whether they will follow directions contrary to their usual habits. These practical use tests have been of enormous value to us when we want to know whether a cos- metic works'and will satisfy the average user. They have enabled us to recommend confidently a large group of excellent cosmetics. At the same time, guided by them, we have rejected such disappointing items as a bubble bath that doesn't bubble, a cake make-up so hard it won't come off the cake, or one that

OPERATING A COSMETIC CLINIC 77 streaks badly, or a cream shampoo that disintegrates when wet fingers dip into it. They have added greatly to our knowledge both of cosmetics and the habits of users. I believe that you,• as cosmetic chemists would find such a clinic equally useful. It may be, as the consulting chemist whom I quoted at the beginning of this paper said, messy and expensive--but not nearly so messy and expensive as having an unsatisfactory product come back on your hands.