What is heavy water, and is it toxic to drink?
Chemically, heavy water is quite similar to regular water, but not identical. It looks and tastes the same, but heavy water – which has its hydrogen atoms replaced with atoms of deuterium – is somewhat toxic in large quantities. It is a little heavier than regular water, with a given volume about 10.6 percent higher. Put ice made from heavy water in a glass of regular water, and it will sink, not float. Heavy water also has the very strange property of lengthening the cycles of biological clocks of all sorts of organisms including plants and animals, but nobody knows why. It has some commercial uses, including chemistry and the slowing down, or “moderation,” of neutrons in nuclear reactors. But to really understand heavy water, a quick refresher on elements and isotopes is needed: Each chemical element is characterized by some number of negatively charged electrons whirling about (in some sense) a positively charged nucleus. The nucleus consists of positive protons (one per electron) a
