edited by

chemi~try for kid/ RICHARD STEINER University of Utah

Salt Lake City, UT 841 12

Invitation to Chemistry through a Large Soap Bubble Chamber

Sanae Sato Yoshiwara Technical High School 2300 Hina Fuji-shi. Shizuoka. 417 Japan

A soap bubble flew; It flew to the roof. It flew to the roof, popped, and disappeared Oh, wind stop blowing! Let's blow soap bubbles and let them fly.

This famous song has been handed down in Japan for many decades. It is a special song to the Japanese people because it conveys our fascination with the soap bubbles. This fascination has resulted in our development of a soap chamber, which is the focal point of the experiment we reported a t the International Conference of Chemical Edu- cation (8-ICCE) in 1985 and subsequently published in a popular science book for children.' This article describes the preparation and use of a bubble chamber in which students can view a bubble from the inside out.

The Soap Solutlon Inexpc : imenting to find the formula for the most effective

solution to use in making huge bubbles, we found we needed to consider both the &face-tension of the solution and its viscosity. The most effective solutions for making large bub- bles were found to contain about 2% soap by weight. Addi- tion of granulated sugar increased the viscosity and helped to sustain the life of the bubble. If bar soaD is used in preparing the solution, it needs to be finely ground or shred- ded. Fifteen grams of this shredded soap is stirred into 1600 mL of water. In a separate beaker, 40 g of sugar is dissolved in 460 mL of water. The two solutions are then mixed with gentle stirring.

Alternatively the solution can be prepared by mixing 200 mL of liquid detergent and 40 mL of glycerin in 1260 mL of water. A separate sugar solution is prepared as before, again by dissolving 40 g of granulated sugar in 460 mL of water. The two solutions are again mixed with gentle stirring.

Making the Devlce A cardboard box that is bie enouzh to hold one nerson is

needed to house the setup. doorshould be cut so that a child can enter and close the door behind him. Two small holes are needed at the lower part of this box to allow two hair driers to be mounted so that cool air can be blown in. At the top of the box, a hole of about 25 cm diameter should be made at the top of the box so that a person can fit through it.

A circle about 50 cm in diameter is cut in a circular plastic washtub so that a person's head can fit through it. This is most easily accomplished by tracing the circle with a red-hot 500-W Nichrome wire, the hot tip of a glue gun, or a hot nail that has been mounted in an insulator such as a block of wood. Then place the bottomless washtub onto the box as shown in Figure 2. The tub will sit over the hole of the box and is not fastened with any external device.

' Sato, Sanae. Shabondama no Naka wa Yume no Kuni, 5th ed.; Dainippon: Tokyo, 1988.

616 Journal of Chemical Education

Figure 1. Look from the Inside out

Figure 2. Bubble chamber apparatus

Soap solution Vinyl cloth

I

Wooden stick \

Holding up a point of the wash-tub, slowly move sideways.

Figure 3. Producing the soap film on the tub.

Figure 4. Views from inside the bubble

Apply the Soap Solution Cut four pieces of wood about 5 cm in depth and 5-10 cm

in height to a length of about 70 cm. Arrange them in a square on the floor or on a desk, and drape a thin vinyl cloth over them to form a huge tray. Pour the soap solution into this tray. Remove the bottomless washtub from the box, and .dip the top into the soap. Lift one end of the tub as shown in Figure 3. I t may take a little practice to produce the desired thin soap film on the tubs.

Entering the Soap Bubble Have a student enter the box and bend down away from

the hole. Be sure the door is closed. After applying the solution, place the tuhon the cardboard box, and turn on the blowers. The wind hlows up from the bottom of the box so the soap bubble will expand upward. Once the soap bubble

Figure 5 . Dropping soap solution from an inverted dropper bonle todetermine the surface tension.

becomes big enough, the student waiting inside the box can stand up and look through the hubhle from the inside out (see Fig. 3). When the blowers are turned off, the bubble will retain its shape for several minutes. The student can look outside or talk with people outside (see Fig. 4).

Golng Further Other activities can be done in combination with this

activity. The effectiveness of different brands of soap can be tested. The surface tension of various solutions can he deter- mined based on the volume of 10 drops of solution that has dripped from an inverted dropper bottle (see Fig. 5).

Edltor's Nole: While it is not usually our policy to print short stories. we are including this anicie as an example of a creative way to introduce chemistry to young children. We encourage our readers who are interested in pursuing such work to contact the amhor of this paper orthe editor of this feature, who can provide ideasfor other outletsfor such materiais.

Chemical Tales for Children Bdla Majoros Technical University of Budapest Budapest, GeliCrt t& 4. H - I l l I . Hungary

One does not have to be at an advanced stage of intellectu- al de\,elopment in order to appreciate the chemistry relevant toe\.er\.dav life. One wa\.of introducina children (aces 7-11) ~- ~ . . . to chemistry in a nontechnical way is through stories com- bining chemistry concepts with story lines and language with which the children are familiar. This approach will, it is hoped, give students a positive feeling about chemistry so that they will not experience chemophohia when they study chemistry later in their careers.

Volume 65 Number 7 July 1986 617