h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Steam is invisible, vapour is visible. So why use steam interchangeably with vapour in this article? It may be common practice to call vapour 'steam' but that does not justify perpetuating the error.

Hi there, energy matters

Thanks for the comment, and I don't entirely disagree with your point; but this entry is for those who need a broader introduction to steam than that narrow band of super-heated water.

As a definition for the noun, based on current science, you may have a point, although even that is debateable. The word steam has been around a lot longer than our more modern understanding (last couple of hundred years) of the effect that heat has on water, and takes on many grey levels of meaning.

But, your comment begs the questions of what do we mean by vapour, and can a vapour be invisible. Evaporating is the process by which water become vaporous and invisible. Evaporate uses the same root as vapour, after all.

The vapour created by boiling water tends to be visible for only a short period, with most of it evaporating (although it can certainly condense as well). So, the water takes on an invisible form, becomes visible as it cools, and then becomes invisible again. Yet, it's all still water, H2O.

Thanks again for raising the point. I, and others, will be considering it in any updates.

You might also want to consider that the inclusion of a picture of a steam railway locomotive as the main illustration is slightly misleading. They are powered by what you are calling superheated water, at 150psi and up, not by the misty stuff you see condensing out of the exhaust ("chimney") which I think is the real thing you are writing about. Perhaps a picture of a boiling kettle might be better. A picture of a steaming cup of tea as well would really complete things nicely!

I think it's all a question of terminology, really, and just a little clarification might clear things up. For example, I was taught in Physics at school that "vapour" is the correct name for the gaseous state of a substance, and that visible "steam" is a mixture of vapour and minute liquid droplets which make it visible.

FYI, here in Canada where I live it gets very cold in the winter (down to -30C) and on really cold days we see steam rising from the river. Just here the river flows too fast to freeze all the way across, and because the water is so much warmer than the dry, cold air immediately above it you get evaporation and condensation. It looks pretty spectacular! I wish I could include a photo but I don't have one to hand.

Thanks for the note!

If you are recent to h2g2, you may not know that the pictures are selected by the BBC editor, not the researcher (me ).

I think that they are just running with what they have, because there's a large redesign underway taking in most of their resources.