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Proceedings of the Royal Society 
pure ; it is only faintly yellow when it has hot been exposed to 
heat, but a very slight warmth colours it brown. 
The acicular crystals dissolve readily and completely in ether and 
in alcohol; these solutions also rapidly decompose, chloride of 
ammonium being deposited, and the viscous substance above men- 
tioned remaining in solution. 
It would he premature to speculate on the nature of these sub- 
stances without quantitative analyses ; I hope before long to be 
able to lay these before the Society. 
3. On the Figures of Equilibrium of Liquid Films. By 
Sir David Brewster, K.H., F.B.S. 
In repeating some of the experiments of Professor Plateau, 
described in seven interesting memoirs published in “ The Trans- 
actions of the Belgian Academy,” and in prosecuting his own expe- 
riments on the colours of the soap-bubble, the author of this paper 
observed several new phenomena which may have escaped the 
notice of the Belgian philosopher. 
Professor Plateau has described and drawn the beautiful systems 
of soap-films, obtained by lifting from a soap solution a cube made 
of wires about one and a half inch long. This system is a poly- 
hedron, composed of twelve similar films stretching from the wires, 
and united to a plane quadrangular film in the centre. When this 
vertical film was blown upon, M. Yon Rees observed that it was 
reduced to a line, and then reproduced in a horizontal position, 
from which it could be blown again into a vertical position. 
If we suppose the quadrangular film removed, and all the twelve 
films radiating from the centre of the cube, Professor Plateau found 
that such a system could not be kept in equilibrium, unless there 
was something solid in the central point, such as the end of a wire 
or a drop of fluid. 
In repeating these experiments the author found that, after con- 
verting the horizontal into the vertical quadrangular film, and con- 
tinuing the blowing, he produced the radial system of films, which 
in an instant returned to the system with a vertical film, and then 
into the system with the horizontal film. 
M. Von Rees had found that, by immersing the wire cube with 
