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.

Unbending the bends

Sometime before dawn this morning, we took our oldest son to the airport. He's bound for the Caribbean for a pre-orientation trip for college (learning to sail with a team of other freshmen). They will get the chance to do a little snorkeling, but when his dad asked him about whether or not they'd be doing any scuba diving, he replied enigmatically,"There is no hyperbaric chamber in the Virgin Islands. They'd have to fly you to Puerto Rico, I guess."

My first response was to wonder how they would do that, given that most aircraft are pressurized to something around 10,000 to 15,000 feet, which would certainly exacerbate the bends - the outgassing of nitrogen from the blood, which can cause embolisms (blockages) in your blood vessels and painful swelling in your joints.

Henry's law governs the amount of gas dissolved in a liquid: the amount of dissolved gas depends on the external pressure of the gas. For example as the pressure of carbon dixoide increases, so does the amount of dissolved carbon dioxide. Some portion of that dissolved CO₂ turns into carbonic acid (H₂CO₃), and lowers the pH, which gives soda water it's characteristic bite. It also means that acidification of the ocean is a risk of fossil fuel burning, and the resultant carbon dioxide in the atmosphere. Climate deniers will say that there is no data linking CO₂ levels with changes in the ocean pH, suggesting it's because the oceans aren't plain water, and that this will complicate the chemistry. True. But your blood is pretty chemically complicated, and this is essentially the system that is used to control your blood's pH.

So why would flying make the bends worse? As the external pressure of nitrogen falls with altitude, more nitrogren comes out of solution in your blood stream and joints. Neither are places where you want more bubbles. If possible, victims of the bends are evacuated on planes that can be pressurized to lower altitudes (an expensive proposition, and one often not covered by travel insurance).

Bariatric chambers allow the external pressure to be increased, and then slowly decreased to prevent the formation of large bubbles. It can take several "dives" to assuage the symptoms. I sat with my mother while she underwent treatment in a hyperbaric chamber, it's not for those with claustrophobia is all I will say.

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Photo is from Wikimedia.

Don't drink the water

"Don't drink the water from the sink!” read a sign taped to the mirror. As I was in rather desperate need of a glass of water before rehearsing the piece I would sing solo at Christmas, I was glad to find someone had left a gallon jug of distilled water and a stack of paper cups. Rehearsing the next day, as I went to grab a cup of water, a colleague pointed out that yesterday someone had mistakenly put out distilled water, which he had swapped for spring water. “Hopefully no one drank it!” he said.

“Why not?” I inquired.

“You’re not supposed to drink distilled water.”

Ah. Yes and no.

Distilled water is water that has been boiled, trapped as steam and condensed, leaving behind the non-volatile impurities (the stuff that doesn’t easily turn into a gas, like metal salts). Other components, like alcohols can still be carried along into the distillate.

Distilled water lacks most of the ions that tap water has, and thus, much of its flavor. Some of the ions (such as fluoride) in regular tap water may have health benefits, so a steady diet of distilled water may deprive you of certain useful trace elements. Conversely, drink water that is too hard (has a lot of ions in it) is correlated with kidney stones. It’s unlikely that the ionic content of your drinking water has a huge impact on your health (despite claims found here and there). All of the trace elements (including fluoride) can be found in other food sources. And distilled water’s osmotic pressure isn’t so different from that of plain water, therefore drinking it will not cause the cells in your body to suck up water until they burst and you begin to bleed internally (yes, this theory is out there, for both distilled water and deionized water). Bottom line, yes, you can drink distilled water.

That said, you probably shouldn’t drink the distilled water in most labs, as it is not tested to be free of bacterial contamination (which it can pick up in storage tanks) or volatile organic compounds. The same goes for bottled distilled water that hasn’t been tested to be certain it’s potable.

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And while we're on urban myths about water, it's impossible to completely remove all the ions from water. Water is always in equilibrium with hydronium ions (H₃O⁺) and hydroxide (OH^-).

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Image Copyright Filipe B. Varela, 2011. Used under license from Shutterstock.com