SOAP BUBBLE SCIENCE

Evening Star, Issue 19022, 18 August 1925, Page 8

SOAP BUBBLE SCIENCE

A PAGEANT OF SBIEHGE Sir Wiliam Bragg lectured recently at (ho Royal Institution in London mi 'Tho investigation of tho Properties of Thin Film's by Means of X-rays,’ and gave to his audience a pageant of gorgeous coloring and an explanation, based on the latest work, with X-rays, of the hues of tho soap bubble, of the peculiar arrangement in Katifta that turns a solid into an efficient lubrication, and of tho mysterious property known as catalysis, which is being found to outer more closely in manutacturing processes. Tho thin film with which substances were often ooatocl, said Sir William, played a» very important part in everyday life. A drop of oil could spread over a. vast expanse of water. Water in a thin tube rose, far above the level of the mass of water with which it was in contact. The surface of a pond served to suppmt small animal life, antli the non-wetting of fruit by rain was duo to the film by which the fruit was covered.

Tho study of these films by moans of X-rays showed the strong tendency to regularity and order displayed by Mature, and 1 the black spot seen in a soap film just before the film bust- was a very instructive' object of study. It was so thin that it would reflect very little light, aiulf its thickness bore the same proportion to tho size of a soap bubble, as tho length of a fountain pen did to the diameter of the earth.

The molecules of which it was composed stood side by side in a double layer. They were far longer than they were wide, and held together much more strongly sideways than end to cud. Tho thin black film was subjected to a pull of one or two urns to tho square inch by the tendency of (ho rest of the film to contract. Its suvfakv l was very slippery, and other films of the same kind wore often found, to slide about on it with great case.

X-ray investigation showed (hat flier* was a tendency of substances to lorro flakes, and this property of forming flakes was very possibly a. distinguishing character istio of solid lubricants. Bow could the strength of this black spot be explained;' Ju putting a crystal together Nature arranged tho molecules in much the si mo way as boots would be stored in a p.ck’iig case so as to save room. This stnictuie, however, was supplemented by the presence of another moKculc, arranged ddi’ercuLy, that knitted tho groups together. This helped to explain the strength of tho bbH: spot of the soap film. There were two sides to the film. On each side tho long molecules of colc-ic acid derived from the soap in solution were ail standing erect. One ond of the molecule, had a special attraction lor water, and was rooted in it. Tho other end was froo to the outside air. Tho black spots commenced wdien the Iwo opposite skins happened to come into contact inside. Tho water between them was expelled, and (he two faces joined up, molecules on one side tying together those on the other, and tho. Whole acquiring tho form and strength the o’mpets crystal.

Magnified onorinouely, the black spot would have the, appearance of a thin sheet bordered at its edge by great mountainous masses rising above and dipping below its surface. Dealing in conclusion with dialysis, Sir William compared t-hn cauly-t with a chaperon who, by the action of an introduction, brought a couple together. Lake tho chaperon, (he catalyst remained unchanged throughout (he whole operation, and it seemed lo have tho power of drawing two or more molecules of the liquor or gas on which it was aiding. Ju Ibis temporary and constrained pe-filum change.-, could'occur that were impo-iblo during the, usual rapid and unentered mol ion. Ono of the points emphasised by the application of X-rays to tho study of bodies was, he concluded, that it was always arrangement that counted.