432 SECTIONAL TRANSACTIONS.—A, B. 
65, whereas that on the other side increases towards a maximum @;. At every 
speed $(0,;+0,)=0. Beyond the critical speed of 0.44mm. per second 6, is 
constant (113° 10’) and also 0, (96° 20’). 
Drops of water sessile on a plane wax surface have been photographed, and 
the plates obtained projected through a lantern, and the angles of contact 
measured. For a fresh horizontal surface 6=104° 40’; for the surface inclined 
until the drop just slips 6;=113°00' and 6,.=96° 00’. 
These results clearly account for the hitherto unexplained discrepancy in 
the values of @ obtained by different methods—some obviously giving values 
between 6 and 6, and others between 6 and 6, according to the type of 
experiment involved. 
25. Report of the Seismology Committee. (See p. 283.) 
SECTION B.—CHEMISTRY. 
(For references to the publication elsewhere of communications entered in 
the following list of transactions, see p. 504.) 
Thursday, September 13. 
1. Joint Discussion with Sections A and G on Cohesion and 
Molecular Forces, opened by Sir Wiuu1am H. Braae, F.R.S. 
2. Prof. Sven Opnn.—The Formation of Precipitates. 
3. Prof. G. 8. Wuirsy.—The Nature and Significance of the Resin 
of Hevea Rubber. 
The resin of raw rubber, which constitutes about 3 per cent. of the material,- 
has been found to contain liquid unsaturated acids, a new solid fatty acid 
(Heveic acid), a phytosterol glucoside, a phytosterol ester, a free phytosterol, 
quebrachitol, and d-valine. The acids have a marked influence on the vulcanisa- 
tion of rubber in the presence of catalysts. The introduction into the rubber 
of strong bases has a striking effect in increasing the rate of vulcanisation 
with catalysts and in enhancing the tensile strength of the product. This effect 
is not due merely or mostly to the elimination, by neutralisation, of the retarding 
influence of acids, but is due largely to the dispersing action on the caoutchouc 
of the soaps produced. The total resin-acid-content of different samples of raw 
rubber varies greatly. Such variation is probably an important factor in 
vulcanisation by rubber samples. The ability of the resin constituents and of 
certain related substances to act as emulsifying agents has been studied. The 
ability of a wide range of organic substances to swell rubber has been studied 
in relation to the question of the mode of occurrence of the resin constituents 
in latex and in rubber. 
Friday, September 14. 
4. Presidential Address by Prof. F. G. Donnan, F.R.S., on The 
Physical Chemistry of Interfaces. (See p. 59.) 
5. Prof. G. N. Lewis.—The Quantum Theory in Chemistry. 
6. Dr. N. V. Sipewicx, F.R.S.—The Bohr Atom and the Periodic 
Law. 
7. Dr. G. Hevesy.—The Chemistry of Hafnium. 
Though hafnium is to be placed in the periodic table between zirconium 
and thorium where formerly cerium happened to be placed, its chemical pro- — 
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