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The reason for this peculiarity of mercury is that the pull between the particles of mercury themselves is stronger than the pull between them and your finger or handkerchief. In scientific language, the cohesion of the mercury is stronger than its adhesion to your finger or handkerchief. Although this seems unusual for a liquid, it is what we naturally expect of solid things; you would be amazed if part of the wood of your school seat stuck to you when you got up, for you expect the particles in solid things to cohere—to have cohesion—much more strongly than they adhere to something else. It is because solids have such strong cohesion that they are solids.

Application 13. Explain why mercury cannot wet your fingers; why rain falls in drops; why it is harder to drive a nail into wood than into soap; why steel is hard.