Sunday, July 20, 2008

phlogiston what?

I'm still reading my Scientist Book, about the history of science seen through the lives of Scientists. both willing and unwilling. Some of the earliest scientists were just trying to prove what the Church was saying. Some were just really curious and never published their works. Some were power grabbing men. Some were down right hateful. Not much has changed over the centuries, huh?
The study of chemistry had a slow start. The technology to control variables (heat, mass, etc) was just not there for a while. Chemists used candles to heat things, or special "spirit lamps" to heat their solutions. If the wanted more heat they added more candles. But having a steady, adjustable heat source just wasn't there. But they had some interesting ideas about heat. There were two schools of thought- Caloric and phlogiston. (Both were horribly wrong, since they thought heat was a Thing)
Phlogiston refers to a compound that everything has- and is given off during burning. It's what makes burning possible (according to those who believed). Remember this is during the 1700's. Phlogistated air (carbon dioxide) was made when things were burned (true) and non-phlogistated air could not be burned (nitrogen compounds) (I don't know if you can burn nitrogen).

People still had this idea of the caloric theory- that all matter had a finite amount of caloric, also a substance that came out when objects rubbed together or where burnt or in any way heated up.

You gotta give these guys props for trying to figure out what heat is, though.

It took over 100 hundred years for some one to notice that metals and other materials actually gained mass when they burned, instead of losing caloric or phlogiston. Not that scientists were stupid at that time, but that they had other things to discover first. All of these experiments were really trying to find out the nature of heat.

Finally, after many years, well into the 19th century, scientists were able to figure out that heat is really the transfer of energy.

Reading this makes me think of my own attempts at explaining heat to my students. The study of heat is usually very confusing- I get The Empty Stare at first. Followed by "What? What?" (Reminds me of little birds when they do that) And then they start to get it (most of them any way)
I tell them there is no such thing as cold- only less hot. (That always gets them. I have to explain to them that we had the terms "hot" and "cold" before we had an understanding of the nature of energy) If heat is the transfer of heat (and it is) , then what is temperature? What is the concept of hot and cold? Temperature is a measure of the transfer of energy. Hot means a transfer (in one direction) of energy, but cold might just as easily be a transfer of energy (in the opposite direction).

I say that, and I wait a few moments to let that sink in.

And then I tell them that you can add heat, but you can't add cold. Cold is the removal of energy.

And then I wait a few moments.
I must say, it's one of my favorite things to teach. I know, I have a place waiting for me in the Hallowed Halls of Geekdom.

I just love reading this book. It's like snapshots into the past. It gives you the sense that these guys were out there looking for answers (sometimes at great personal risk) to find answers and order in the natural world. The books tells the story of their lives. Some of these guys were just in it for the science, some wanted glory, some were lying cheating spies.

More later.

1 comment:

Mrs. Who said...

Oooo- thank you ever so much. I only teach 2nd grade, but I can see applying the 'adding heat' explanation on a level they can understand.

Kudos to you!!