Contact electrification, or tribocharging, is pertinent to a broad range of industrial and natural processes involving dielectric materials. However, the basic mechanism by which charge is transferred between insulators is still unclear. Here, we use a simple apparatus that brings two macroscopic surfaces into repeated contact and measures the charge on the surfaces after each contact. We vary the temperature of the surfaces, and find that increasing temperature leads to a decrease in the magnitude of charge transfer. When paired with a Monte-Carlo simulation and TGA measurements, our results support a mechanism where adsorbed surface water is crucial for charge exchange. Our setup is easily extendable to a variety of industrially relevant materials.

The dissolution rates for 20‐ to 500‐μm‐diameter air bubbles in water and seawater at 50% and 100% air saturation are presented. The data indicate a dissolution rate that is independent of diameter for bubbles larger than ∼70 μm but is strongly dependent on diameter for smaller bubbles. Rise velocity data from a companion study were used in conjunction with Levich's “dirty bubble” formula to predict dissolution rates for the bubbles. There is good agreement with theory for bubbles in saturated liquids and for bubbles with diameters larger than 70 μm. Agreement is fair for smaller bubbles in 50% saturated water and seawater.

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SUMMARYOe~trone-4-~~C in dimethyl sulphoxide solutioii has been treated with lithium acetylide (ethylene diamine complex) to give ethynyloestradi01-4-~~C. INTRODUCTION.

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