464 SECTIONAL TRANSACTIONS.—Af, B 
and occurs at lower field values. The onset of discharge is determined 
by the approximate relation F1/r = 3,600, where F is the uniform field in 
volts /cm. and ¢ the radius of the drop. 
In ordinary atmospheric air the ions discharging from the drop attach 
themselves to condensation nuclei and form large ions. But in pure air, 
ordinary small ions only are found. No production of large ions or nuclei 
can be detected even when a drop is discharging up to 55 micro-ampéres 
and is being visibly broken up by the discharge. 
It would appear, therefore, that the low mobility ions required by C. T.R. 
Wilson’s theory of thunderstorm electrification are not rs produced 
by discharge from raindrops. 
Mr. L. H. G. Drnes.—Observations of supersaturation of water in the 
free atmosphere, and an example of a cumulus cloud composed of 
supercooled water drops (12.20). 
A number of observations of relative humidity in the upper air over 
England are summarised, made with sounding balloons carrying recording 
meteorographs. The conclusion is reached that on many occasions, in 
clouds, a state of supersaturation of water vapour exists. It is suggested 
that the degree of this supersaturation may often exceed a relative humidity 
of 120 per cent. 
SECTION B.—CHEMISTRY. 
Thursday, September 7. 
PRESIDENTIAL ADDRESS by Prof. R. Rosinson, F.R.S., on Natural 
colouring matters and their analogues (10.0). (See p. 45 .) 
Discussion on Natural colouring matters (11.0) :— 
Prof. Dr. R. Kunn.—Carotenoids and flavines. 
In recent years many new natural colouring matters of the carotene-group 
have been discovered, and a general view is given of their genetical relation- 
ships. The first products of synthesis in plants are the dyestuffs with 
40 carbon-atoms, from which carotenoids, containing fewer carbon-atoms, 
are produced by oxidative disintegration. The splitting of the carbon- 
chains may occur in different ways :— 
(1) Cyg —+> Cop + Cao, B-carotene —— 2 vitamin A. 
(2) Cy —~C,g + Cy, + Cg, lycopene —— bixin + 2 methylheptenone. 
(3) Cao —~> Cyp + Cop + Cy, proto-crocin —-—>crocin + 2 picro-crocin. 
(4) Cy —~>Cy3 + Cy,, proto-azafrin ——(ionone) + azafrin. 
a-, B- and y-carotene are provitamins A. The constitution of «- and 
Y-carotene isasymmetric; they supply only 1 mol. of vitamin A, and therefore 
their physiological activity is only half that of the symmetrical B-carotene. 
Widely distributed in nature are certain water-soluble dyestuffs, coloured 
yellow and fluorescing intense green. They have been called flavines. 
Ovoflavine from egg-albumin and lactoflavine from milk have been prepared 
