The authors reply to Jones

J. C. Jones's letter presents some interesting ideas. However, the availability of lignite may be a challenge to performing this demonstration. There are many other demonstrations of solvent swelling of more common opaque objects:

• pasta noodles in water
• rubber bands in toluene or cyclohexane
• cured silicone caulk in toluene
• superabsorbent polymer powder (such as one would find in a disposable diaper) in water

All of these should be readily visible on an overhead projector, though in the last case addition of food coloring to the water makes the swollen polymer more visible. Short descriptions and photographs of the last three demonstrations may be viewed here. The polydimethylsiloxane (PDMS) demonstrations described in our recent paper showed not only solvent swelling but also its connection to a controllable polymer cross-linking. Additionally, the transparency of this form of PDMS allows the observation of optically active species within the polymer.