MEASUREMENTS ON FINGERNAILS ... Figure 7. Apparatus for performing impact absorption experiments 423 that there was no suitable equipment available for testing samples of this size. Unlike the previous tests, however, this experiment could not be performed in the Instron or by modifying any other existing equipment. The simple apparatus which we have developed for this purpose is shown in Fig. 7.

424 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS IMPACT ABSORPTION EXPERIMENTS The operation of the apparatus is as follows: a conditioned and inspected fingernail sample is placed in the clamp at the lower right hand side of the tester. The sample is clamped so that 1/8 in. of the nail protrudes from the top of the clamp. The pendulum, which has been resting in a horizontal position on the stop at the upper left side of the apparatus, is released and strikes the sample 1/16 in. above the clamp. After striking the sample, the pendulum rebounds, and the rebound is observed and recorded. The pendulum continues to strike the sample, and the continually decreasing rebounds are observed and recorded. We have found it convenient to use a tape recorder to preserve the operator's observations, since it allows him to devote full at- tention to the mechanism. The actual rebound in degrees is converted to rebound ratio by dividing the height in degrees of observed rebound by height in degrees of the starting point. For example, if the first rebound was observed to be 56.4 degrees, dividing by the starting point (90 ø ) we would obtain a rebound ratio of 0.6267. If the second rebound was then observed to be 35.2 degrees, dividing by the starting point (56.9% we would obtain a value of 0.6241. The first 5 rebounds are converted in this manner, and the rebound ratios averaged, and the standard deviation determined. The procedure is repeated 3 times for each sample in order to reduce the chances of error due to an incorrect measurement and as a check against possible sample degradation due to the test itself. In the experiments performed to date, a total of 64 different fingernail samples have been tested. The rebound ratio values obtained have ranged from 0.4632 to 0.7273. SUMMARY We have described 4 pieces of apparatus for measuring physical properties of finger- nails. We have also presented a brief description of the operation of each apparatus and a range of experimental results which we have obtained from each. In our opinion, the tests provide a much needed addition to the state of the art in this area, and we hope that others will find them as useful as we have. We regret that, due to space limitations, we could not include statistical interpretations of the results obtained. We are currently preparing another paper in which we intend to include this information. Also included will be data demonstrating differences in physical properties attributable to age and sex of the donor as well as hand and digit of nail origin. ACKNOWLEDGMENTS The authors wish to express their gratitude to Del Laboratories, Inc., who provided the financial support, which made this program possible, and to Patrick Harding who prepared the photographs of the apparatus.