This film, possibly made at the Royal Institution in the early 1930s by A.S.G. Lawrence, demonstrates the colours produced in soap films when a steady jet of air is directed over the surface.
Soap films are thin layers of liquid surrounded by air. The soap film shown has been created by dipping a wire ring into a soap solution to form a thin film of the solution stretched flat across the ring.
The viewer sees the switch from black and white during the setting up of the demonstration, to colour to allow for the observance of the bright, iridescent colours produced by the interfering of reflected light waves, a process called thin film interference which is determined by the thickness of the film.
The air jet over the soap film allows streams and vortex patterns in a great variety of colours to form themselves over the film. On stopping the air jet, the colours re-arrange themselves to their previous positions, rising or falling in coloured showers according to their thickness relative to the position on the film at which they are released from motion.
This early demonstration film shows the further phenomena of soap films, the symmetrical patterns produced when the air jet is glanced off the film surface, the response of the soap film to sound disturbance, and the effect known as the ‘black’ condition, whereby the soap film thins out to a few molecules of soap and water, passing beyond the stage at which interference colours can be produced.
The demonstration goes on to show the effect that a wet pad of ammonia solution has on the soap film when held near. There is a further demonstration of rapidly producing the ‘black’ stage across the soap film, with the normally smoothly graded bands seen now being broken up by the rapid development, as the black area quickly extends by the aggregations of black ‘clots’ all over the soap film.
The film ends with a nozzle pierced with four air holes sending air jets over the soap film surface, producing patterns of extended symmetry and beauty of contrast.
This excerpt shows the experimental setup used in the above film, in full.
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