Air Thermometer: Blackened Tin Box and Water U-Tube (Boy Mechanic, 1913)

"This instrument will measure the amount of heat given by a candle some 20 or 30 ft. away."

Take a small tin box about 1-1/4 in deep and 2 in across. Solder a 1 in piece of 1/4 in brass tube into its side, then solder the cover on so air can only escape through the tube.

Take 1/4 in glass tube at least 18 in long and bend it into a U as in the figure by holding it across a broad flame until it sags under its own weight. Join it to the brass tube with a short rubber hose, bound with fine copper wire if loose.

Make the standard from No. 10 wire about 10 in long on an oak base, with a No. 14 wire soldered across it and bent round the brass tube and the glass tube.

Smoke the bottom of the box black over a little burning cotton soaked in turpentine (after any painting of the rest). Put water in the U-tube with a dropper and paint a scale on the glass.

From **The Boy Mechanic, Book 1** (Popular Mechanics, 1913), pp. 152-153, by J. Thos. Rhamstine (checked on the archive.org scan boymechanic0000unse_n5a8). It shows relative warmth, not degrees. He also mentions etching the scale with hydrofluoric acid; we use paint only. The spirit lamp in place of a gas jet is ours.