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GEOPHYSICS: R. B. SOSMAN 
Proc. N. a. 
secondary enrichment). A distinct problem of the sulfides is their rela- 
tion to the silicates in the igneous rocks (differentiation of sulfide-bearing 
bodies, as at Sudbury, Ontario). 
Volcanic Gases and Salts. — These are of particular interest in their re- 
lation to volcanic activity, as at Kilauea and Vesuvius. Research on 
gases, including the various gas mixtures evolved from volcanic vents, is 
of a peculiarly trying character on account of the invisibility and intangi- 
bility of the substances handled, as well as the difficulty of collecting and 
transporting samples of the natural products. A special phase of this 
work is the study of the complex gases given off by fumaroles and hot 
springs. In addition to chemical composition and equilibria of the gases, 
data are needed on the physics of the flow of such gases from vents, as re- 
lated to volume, temperature, and pressure at the point of emission. 
The volcanic "sublimates", such as sulfur, ammonium chloride, arsenic 
sulfide, copper chloride, magnetite, may be mentioned in this connection, 
as well as the minerals accompanying fumarole and hot-spring activity. 
The Oxide Ores (e.g., ores of iron, chromium, manganese, tin). — The 
study of these ores involves high-temperature investigations similar to 
those on the silicates, and also studies of the hydrated and colloidal oxides. 
The Natural Hydrocarbons. — Organic chemistry of a very complex 
kind is involved in the formation and alteration of natural gas and petro- 
leum, and many problems of physics and physical chemistry, such as ad- 
sorption, surface tension, and colloid phenomena, are also involved in 
their underground storage and movements. 
Other substances — for example, the silicate ores, the carbonate ores, 
the titanium minerals — may be similarly grouped for purposes of experi- 
mental study, but it is hardly necessary here to make a complete inven- 
tory of such groups. 
Running along with all these investigations is the general research 
necessary to develop experimental methods and apparatus, and to keep 
the general theory of physics and chemistry abreast of the newly accumu- 
lated facts. 
Aggregates 
In the preceding paragraphs we have mentioned some of the researches 
that are necessary on the chemical substances of the earth's surface. We 
come next to aggregates, including the igneous rocks, the pyroclastic and 
sedimentary rocks, the oceans and other bodies of water, and the 
atmosphere. 
Igneous Rocks and Magmas. — Among the aggregates the igneous rocks 
are the most important, constituting as they do the original matter from 
which the others have been derived. They are poly-component systems 
with seldom fewer than six oxides, and it seems out of the question at 
present to give a complete phase-rule discussion of the chemistry of any 
