1889-90.] Mr C. Michie Smith on Surface Tension. 121 
reduction in the surface-tension, though the action may he a purely 
mechanical one. 
I hope to continue and extend the experiments at an early date ; 
meanwhile my thanks are due to Professor Tait for many valuable 
suggestions, and to Mr D. J. Graham who has assisted me in all 
the experiments. 
The Absorption Spectra of Certain Vegetable Colouring 
Matters. By C. Michie Smith. (With a Plate.) 
(Read March 17, 1890.) 
For the substances dealt with in this paper I have been indebted 
at various times, to the kindness of Mr David Hooper, Quinologist 
to the Madras Government. The observations have been made 
with several instruments, but have all been reduced to the scale of 
the direct vision spectroscope of the Chemical Laboratory of the 
Edinburgh University, kindly placed at my disposal for the most 
important part of the work. The illumination used with this 
instrument is a 10-candle power incandescent lamp; with the 
other instruments sun-light was used. I have thought it better for 
practical purposes to draw the spectra to the natural scale of the 
instrument than to reduce them to a scale of wave-lengths, but 
data are supplied for finding the wave-length corresponding to any 
part of the spectrum. To represent the varying shades of an 
absorption spectrum is extremely difficult, and the results usually 
obtained are, at best, far from satisfactory. The method I have 
employed is to draw the spectra on a large scale, shading the 
various parts by aid of a light curve, and then reduce this drawing 
to the required size by photography. The result, though not all 
that could be desired, is fairly satisfactory. 
Colouring Matter from Trichosanthes palmata. — Mr Hooper has 
given me the following notes on this substance : — “ The plant which 
yields it is the Trichosanthes jpalmata , one of the Gourd tribe or 
Cucurbitaceae, and the rounded scarlet fruits have their seeds im- 
bedded in a green bitter pulp. The bitter principle is a glucoside, 
soluble in water and alcohol, and affords a red solution, changing 
to purple with sulphuric acid. I have named it ‘ trichosanthin,’ as 
