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R. J. FRIESEN, editor univenity of Waterloo Waterloo, Ontario, Canada
Solid State Labs: The Bubble Raft
P. D. McCormick Thorold Secondagv School Ormond Street Thorold, Ontario The lack of explicit methods for interpreting the patterns observed in soap bubble rafts has, for the most part, precluded the use of this fascinating experiment as a two-dimensional dynamic model of a crystalline solid. The following activities provide considerable insight into the orderly packing of spherical objects and, by inference, into the properties of metallic crystals. The Equipment A ripple tank with either bottom or top illumination serves admirably as a bubble raft container, and a fine glass U-tube connected to a low pressure gas supply, such as a balloon, a gas tap or any gas metering device that you can control, can he manipulated to produce l-mm bubbles in a raft form (Fig. 1). Solutions of dishwashing detergent to which glycerin is added produce stable bubble rafts. These can be swept with a glass rod into clusters, and close packing areas become readily apparent.
Figure 1 . Ripple tank for bubble raft production
Try These Experiments 1) A group of bubbles that constitutes a "crystal" has rows of bubbles that form concentric equilateral triangles. This can he demonstrated by cutting cardboard triangles of the proper size, and superimposing them on the projected image. 2) Neighboring cj s t a l s have their rows oriented in different directions and this can be demonstrated using two or more triangles, whereupon their orientations are seen to be different. The less organized regions between neighhorinr crvstals are then eood renresentations of cwstal houn&ari& 3) The effect of "im~uritv"atoms on the cwstal stmct& of the raft can be demonstrated by inGoducing a larger or smaller bubble, and examining the orientation using the triangles. 4) The effect of compressive or tensile forces on a solid can he illustrated by placing two plastic or wooden sticks parallel to one another at each end of the raft, and alternately pressing and stretching the raft. Ohyeme the vacancies, grain boundaries and dislocations under compression and tension. This illustrates what happens when you bend a metal bar and i t springs back. Permanent deformation can he illustrated by increasing the tension or compression. 5) Dislocations in crystals are defined by a change in direction of grain patterns, by movement within the crystal, and by changes in the structure of the crystal itself. If a parallelogram ABCD is used to define a crystal orientation, and is placed over an area containing a dislocation, i t does not close exactly (Fig. 2), and the resulting vector AE is called the Burgers vector and defines the dislocation. A parallelogram around a perfect crystal, or a crystal
Figure 2. represented
by
and illustrating the
paralleiogram
urgers
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containing a vacancy only, will close perfectly and the Burgers vector will be zero. 6) Dislocations can he introduced by bursting one or more bubbles with a hot wire, and the ways in which they move can he studied under conditions of tension and compression. The interaction of two or more dislocations can be noted, and the effect of vacancies on dislocations can be studied. 7) Any other ideas?
The synthesis of the hexafluorochlorine ion is reported in an article in Inorganic Chemistry, 12, (7). 1580 (1973). The CIFs+ cation was prepared in the form of its PtFssalt. It is a canary yellow solid and a powerful oxidizer reacting explosively with organic materials or water. The cation is octahedral. Would you expect this?
Ks, Experiment: The Solubility Product for Barium Hydroxide John P. Reynolds l'Amoreaux Collegiate Institute 2501 Bridletowne Circle Agincourt, Ontario M I W 1 W7 The soluhility product experiment most often used in high school is that involving silver acetate. There are no others mentioned in most high school texts. I have found that an experiment, using barium hydroxide, Ba(OHh, yields results just as valid; two completely separate approaches are used, and the cost involved is very much less. The concepts involved in the treatment of solubility product are much more clearly impressed on the student. Volume 52, Number 8. August 1975 / 521
