Should you not eat snow?

Natalie Henderson wonders if a friend can be right when she says that eating snow is bad for you (Natalie has actually been wondering for quite a while now, alas I got snowed under). It may seem strange but Natalie’s friend is correct.

The odd mouthful is fine — if it wasn’t then snow cone vendors would be have a lot to answer for — so connoisseurs of frosty treats don’t need to worry. But there is a big difference between a refreshing tub of flavoured ice on a hot day and desperation for water half way up a frozen mountain.

A snowfield is about as useful in a survival situation as an ocean: water, water everywhere and not a drop to drink. The problem with seawater is chemical — you shouldn’t drink it unless you get the salt out. The problem with snow is physical — you shouldn’t drink it unless you melt it.

It’s all about heat energy. Physicists love arguments based on energy, as they usually let you beat a short cut through a problem without worrying too much about the details — and with the space I have here I need all the shortcuts I can get.

Anyway, if snow seems like a tempting source of water then you probably haven’t heard of the latent heat of melting. That’s not surprising, though: like latent fingerprints or latent hostility the point is that it is hidden. Melting ice isn’t just about raising its temperature. You have to apply extra heat to change it from solid to liquid and that’s the latent heat of melting.

It turns out that the latent heat of melting for ice is equivalent to the heat needed to warm the same weight of water by 79.8 degrees Celsius. Or, put another way, eating a mouthful of snow is like taking a swig of water cooled to 79.8 degrees below freezing. Chilly enough for you?

Eating snow will suck all your heat away, possibly leading to hypothermia and even, ironically, dehydration. So today’s hot tip is that eating snow is just not cool.

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