Black box activities and demonstrations often involve an apparatus that performs a task or function but is designed so that it isn't obvious how it works. Students are challenged to come up with an explanation or suggestion on how it is built. Below are instructions for constructing the Black Box Siphon. One approach to its application is to make the claim that it is a water making machine. When one small beaker of water is poured into the funnel at the top, over ten times that volume comes out the tube at the bottom.
Materials
One ring stand, one 3" ring, and one 5" ring
About 1 meter of 1/4" rubber or tygon tubing
One small plastic funnel
One 2-L plastic bottle with cap
One cardboard box just large enough to cover the 2-L bottle
Ten small beakers or similar containers
Drill a hole a little smaller than the 1/4 inch tubing in the bottle cap. This is easier and safer if done with the cap on the bottle.
Remove the cap from the bottle. Cut the end of the tubing at a slant to make a point and force the tubing through the hole. Pull about 3 cm of tubing through the hole.
Carefully cut about 5 cm off the bottom of the bottle.
Screw the cap on the bottle, and mount it upside down on the ring stand as shown. Form the tubing into a loop that reaches about 80% up the side of the bottle. Leave enough slack near the bottle cap so the tubing isn't in a pinch. Tape the tubing in place.
Cut a slot down the middle of one side of the cardboard box. The slot will slide over the ring posts. When in place, the box should hide the siphon from view. Cut a hole near the bottom (open end) of the box for the tubing.
Make a hole in the top of the box for the funnel. You may want to attach a short piece of tubing to the stem.
Remove the box and fill the bottle with water up to the bend in the siphon tubing. Replace the box. Your water making machine is ready for use.
Pour 100 mL or so of water down the funnel and collect ten times that amount from the exit tube.
©2006 W.C. Deese. All Rights Reserved.