The weight of water

While writing a piece for Nature Chemistry about the hidden depths of the periodic table (the more than 3000 isotopes that could be stacked onto their elemental spots), I wandered across an interesting set of papers on heavy water and isotopic tracing, which led to another piece for Nature Chemistry (The weight of water). In one of the papers, future Nobelist George de Hevesy deuterates goldfish by crowding some twenty (albeit tiny) goldfish into 60 ml of water, in another he reports making thousands of distillations of urine to recapture the water, measure its density and track deuterium through the human body.

Heavy water (D₂O) is water where the hydrogens have been replaced with deuterium, an isotope of hydrogen that weighs about twice as much as standard hydrogen. Heavy water weighs just over 10% more than regular water, a tablespoon weighs only about a gram more, so it is probably not noticeable should you heft a glass of it.

And that's the question — should you heft a glass of it? In small amounts it is certainly safe to drink, and as I recently learned, used in human metabolic studies in doses of about 10 ml. An interesting question raised in the papers I read was about the taste of heavy water. One report suggests a burning sensation might be felt when drinking it, another (by Harold Urey, who discovered deuterium) suggests it tastes like undeuterated water. But other reports say it tastes sweet.

With a bit of help from my youngest son, I set up a repeat of Urey's blind taste test. And was surprised to find I could indeed taste the difference. It is sweet.

And for the next few weeks, until the last of the extra deuterium clears my systems, I'll be just a little bit heavier than usual.