SIR DAVID BREWSTER ON THE COLOURS OF THE SOAP-RUBBLE. 497 



IV. Phenomena produced by different Solutions. 



When the films are produced from solutions of soap and water, they burst 

 much sooner than those from glycerine solutions, and the changes in the coloured 

 bands take place more quickly. 



In a solution made by Mr Dewar of the University Laboratory, according to 

 Plateau's receipt, with dry Oleate of Soda, the bands, in a vertical film, were 

 produced more slowly, and the film lasted longer than when formed from the 

 soap solution, neither of them being defended from currents of air. After stand- 

 ing half an hour, the third and fourth orders, and sometimes the second, were 

 broken up by coloured tadpole portions streaming up from the lowest point of the 

 film, as shown in Fig. 14. 



With a solution which I made according to Plateau's receipt, but with humid 

 Oleate of Soda, similar phenomena were more quickly produced. The second, 

 third, and fourth orders were more easily and completely broken up, and the 

 film burst sooner. 



When the colours upon the film, from either of these solutions, were scattered 

 by blowing, they reformed distinctly, and after being a second and a third time 

 scattered by blowing, they recovered their original position and distinctness. 



In a glycerine solution made by a London chemist, the phenomena were 

 entirely different from those produced by other solutions. It had become so 

 thick and ropy that it could not be poured out of the bottle. When a film of the 

 usual size was produced from it, and placed vertically, it exhibited none of the 

 phenomena we have described. It gave no bands, and when convex or concave, 

 and placed horizontally, no rings or portions of rings were produced. The 

 colouring matter, too thick to give colours, floated on the surface of the film in 

 currents or little streams, and sometimes remained at rest in irregular patches. 

 From these currents or fixed portions, streams of various and brilliant colours 

 rose to the apex of the vertical film, with different velocities, from the bottom 

 and sides of it, jostling one another, and, when crushed together by meeting a 

 colourless portion at rest, losing their colour. 



If, before any colour appears, we blow upon the film, it produces colourless 

 eddies, like those shown in Figs. 9 and 10. 



When the colours are produced on plane or curved films, the streams are 

 singularly beautiful, assuming the most extraordinary shapes, and running from 

 every part of the circumference. The coloured lines are sometimes serrated and 

 sometimes mottled, black portions and portions of rectilineal bands occasionally 

 appearing. 



In some films red and green colours appear the instant they are made, and 

 when this happens, the streams above described are more quickly formed. 



When the solution that exhibits these phenomena is diluted with an equal 



