I see orange crystals on one of my cucumbers. Each crystal is a little larger than a poppy seed. What is this? Other than a few dead leaves, the plants look healthy and produce lots of cucumbers.

The main ingredients of early cosmetics were lead sulphide and lead carbonate, the most common naturally occurring lead compounds. Lead sulphide – or ‘galena’ – is grey and relatively soft with a ...

Experiments conducted in our laboratory have, however, shown the existence of the so-called volume-rectification in galena, iron pyrites and pyrolusite placed between mercury electrodes.