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This department welcomes brief communications reporting new demonstrations, laboratory equipment, techniques, or materials of interest to teachers of physics. Notes on new applications of older apparatus, measurements supplementing data supplied by manufacturers, information which, while not new, is not generally known, procurement information, and news about apparatus under development may be suitable for publication in this section. Neither the American Journal of Physics nor the Editors assume responsibility for the correctness of the information presented. Manuscripts should be submitted using the web-based system that can be accessed via the American

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Measurements of contact angle of ethanol-water solutions were performed on crystalline silicon and on mesoporous silicon films with porosities up to ∼72%. Water contact angles of 44 • and 76 • were measured for untreated and HF-dipped crystalline silicon, respectively, consistent with previous studies. The contact angle for ethanol-water mixtures was found to decrease with increasing ethanol concentration for both untreated crystalline silicon and also for HF-dipped crystalline silicon up to an ethanol concentration of ∼80%; at higher concentrations the contact angle approached zero. Similar behaviour was observed on mesoporous silicon surfaces for ethanol concentrations 40%, above which the contact angle dropped abruptly to an immeasurably small value. This behaviour is attributed to a decrease in surface tension with increasing ethanol concentration. For all ethanol-water solutions, a minimum value of contact angle was observed at a porosity of ∼40%, above which it remained approximately constant. The behaviour of contact angle with porosity can be explained by a change in the Wenzel roughness parameter due to changes in the specific surface area of the film.

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NOTES ON EXPERIMENTS 'Notes on experiments' enables teachers at both school and tertiary level to share their ideas with other readers. Physics Edurolion welcomes submissions from readers who know of some simple improvement to a commercially made piece of apparatus, or who have designed a new gadget or improved a standard experiment. In particular the Editor would welcome brief descriptions ofexperiments devised or procedures evolved during the course of project work or investigations undertaken by students; such submissions should be made under the joint name of the teacher and the student.

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The graph is a tool for the analysis of data, but like any tool is only as effective as a student’s ability to interpret it in a meaningful way. This article suggests ways that graphs can be plotted to extract the maximum information from an experiment.