NOTES ON THE DEMONSTRATION OF "WETTER" WATER C. R. CARYL American Cyanamid Company. Stamford, Connecticut
I N THE August, 1939,,issue of this JOURNAL, Drs. Hauser and Reynolds complimented the author's sinking of a duck in "wetter" wateias an ingenious method of demonstrating the action of a powerful wetting agent. Pointing out the disadvantages in the use of ducks, they presented a simpler demonstration of reduction of surface tension, using toy battleships so constructed that they would sink when a wetting agent was added to the water. Witnesses of this demonstration have reported it to be most effective. However, with both the ducks and the battleships, considerable preparation is needed in advance. The following suggestions are therefore made for those who wish to demonstrate the remarkable surface-tension reducing powers of the modern synthetic wetting agents, but who may have only a few minutes in which t o prepare the experiments for the lecture table. As everyone knows, powdered sulfur will float indefinitely on the surface of water without becoming wet. The addition of a few drops of a concentrated solution of Aerosol OT (the di-octyl ester of sodium sulfosuccinate) t o the surface of the water on which the sulfur floats causes it to sink immediately-a very effective
demonstration. All that is necessary is a beaker of water, a few grams of powdered sulfur, the solution of Aerosol OT, and a stirring rod or eyedropper. An even more startling demonstration is illustrated in Figure 1. The beaker on the right contains only water, that on the left water plus 0.1 per cent Aerosol OT. Powdered sulfur is poured from both hands into the beakers and as shown, it does not penetrate the surface of the pure water but pours like sand into the beaker of "wetter" water containing the Aerosol OT. Everything necessary for this demonstration can be assembled in a few minutes. Similarly, in Figure 2, ordinary string is let slowly down into the two beakers. It does not get wet in the pure water and floats on top, but in the beaker containing Aerosol OT i t wets instantly and sinks beneath the surface. Two wads of raw wool or cotton may be used instead of the string, with equally startling results. If the lecturer prefers to show a ship sailing on the water instead of the sinking of enemy battleships, a little more preparation is needed than for the abovementioned experiments. A-gram of Aerosol OT pressed onto the stern of a toy ship (preferably a balsa-wood model) will propel it back and forth across a tank of water for hours. Taken home after the lecture, this device launched in the bathtub full of water is guaranteed to keep the children amused for many a rainy day. The warmer the water,.the greater the speed of the boat will be.
