I’ve mentioned autoclaves in my science posts in the past. Autoclaves are one of the basic sterilization tools in a lab.

The autoclave pictured above is one of the bigger ones around used by the people in my rice lab.

What is an autoclave? Basically a its a steam oven.

When scientists were first trying to sterilize stuff, boiling a solution on a stove was the easiest way.

But boiling has a problem.

Say you want to create a solution of 3 liters of water with 4 grams of salt per liter. You measure out 3 liters of water and you pour in 12 grams of salt.

But now you need to sterilize it. You put it on the stove to boil.

After it boils you measure the volume of your solution and now only 2.5 liters are left!

So the solution is sterile, but its no longer the concentration you wanted.

There are ways to work around this obviously by adding more water or less salt, but that gets tiresome.

Eventually a French scientist, Charles Chamberland, invented the autoclave to avoid this sort of problem.

The temperature inside an autoclave heats up to 121°C (250°F). This is a higher temperature than boiling.

Normally water would boil in an autoclave and you’d have the same problem, but heating isn’t the only thing an autoclave does.

The air pressure inside is about 20 times room pressure. This air pressure forces the liquids you place in an autoclave to stay liquid instead of evaporating into gas.

Thus the temperature can be raised to kill any bacteria, microbes, or other nasty things in your solution of salt water, but the solution does not changed its concentration.

The most interesting part for me is why the machine is called an autoclave.

Autoclave is a Greco-Latin word that means self-locking.

With a normal oven you can open it at 250°F (121°C) and you’ll be fine.

But what if that oven was full of 20 times the amount of steam that normally would be in there?

The steam would fly out of the oven and give you horrible burns if the autoclave was opened suddenly.

Thus it was very important for Chamberland to prevent that accident.

The autoclave cannot be opened until the steam has been condensed into water and removed from the machine. The bottom left of the picture on this blog shows the pipe where the hot water comes out of the autoclave.

That’s all for today!

-Mister Ed