Physical Science Studies, circa 1944

If someone challenged you to come up with a demonstration of the 20-odd per cent proportion of oxygen in Earth air, could you do it?  

I'd fail.  Fortunately a little refresher course has shown up in the CAMZ class notes from Kensington High freshman science class.

"Some iron filings  were placed in a test tube
which was inverted in a dish of water.
The original level of the water was noted.
The apparatus stood for several days.."

Hold it right there.  See the illustration, below?  How are the iron filings being made to stick to the inside bottom of the test tube?  Spit?

Okay, I can't do a demo; how about understanding some practical application, such as a household hot-water system from that era?

At left, the lovely coil (great shading!)
is being heated via piped natural gas, yes?

The tank on the right has convection currents going.

So far, so good.  But what's this "coil in range," at the far right?  The kitchen stove was used as a parallel heat source. Therefore that tall convection tank had to be sitting in the kitchen.  I've never seen any setup of that kind.  Can someone send in a photo of such a system in place?

And what kinds of stoves burning what sorts of fuel were used in these systems: wood, coal, natural gas, electricity?

When did modern hot-water heaters, gas or electric, become available and replace these systems?

I'm going read up on demos by hunting up my copy of Michael Faraday's Royal Institution Christmas Lectures from a hundred years previous to this.  Or did I give that wonderful volume away to some offspring?  

Michael Faraday set the standard for scientific demonstration.