There are three methods of approach to the great problem of rock
formation. The first undertakes to reproduce by suitable laboratory
experiments some of the observed changes in natural rocks. The second
seeks to apply the principles of physical chemistry to a great body of
carefully gathered statistics. The third method of attack is like the
first in being a laboratory method, and like the second in seeking to
apply existing knowledge to the association of minerals as found in
rocks, but in its procedure differs widely from both. It consists of
bringing together pure materials under measurable conditions, and thus
in establishing by strictly quantitative methods the relations in which
minerals can exist together under the conditions of temperature and
pressure that have the power to affect such relations.
It is to this third method of investigation of the problems of the rocks
that the Geophysical Laboratory has been devoted since its establishment
in 1905. It has proved entirely practicable to make quantitative studies
of the relations among the principal earth-forming oxides (silica,
alumina, magnesia, lime, soda, potash, and the oxides of iron) over a
very wide range of temperatures. The resources of physics have proved
adequate to establish temperature with a high degree of precision and to
measure the quantity of energy involved in the various reactions. The
chemist has been able to obtain materials in a high degree of purity,
and to follow out in detail the chemical relationships that exist among
the earth-forming oxides. The petrographic laboratory has been available
for the comparison of synthetic laboratory products with the
corresponding natural minerals.
It has also proved entirely practicable to extend the same methods of
research to some of the principal ore minerals such as the sulphides of
copper. Other information which is certain to be of ultimate economic
value has also come out of the thorough study of the silicates, which
are basic materials for the vast variety of industries which are classed
under the name of ceramic industries. The best example of this is the
facility with which the experience and the personnel of the laboratory
has been adapted to the very important problem of manufacturing an
adequate supply of optical glass for the needs of the United States in
the present war.
It has further been possible to show within the last two years that rock
formation in which volatile ingredients play a necessary and determining
part can be completely studied in the laboratory with as much precision
as though all the components were solids or liquids.
Along with the laboratory work on the formation of minerals and rocks
has gone an increasing amount of field work on the activities of
accessible volcanoes, such as Kilauea and Vesuvius, where the fusion and
recrystallization of rocks on a large scale can be observed and studied.
There was once a time when the confidence of the laboratory in the
capacity of physics and chemistry to solve geological problems was not
shared by all geologists. There were some who were inclined to view with
considerable apprehension the vast ramifications and complications of
natural rock formation as a problem impossible of adequate solution in
the laboratory. It is, therefore, a matter of satisfaction to all those
who have participated in these efforts to see the evidences of this
apprehension disappearing gradually as the work has progressed. A
careful appraisement of the situation to-day, after ten years of
activity, reveals the fact that the tangible grounds for anxiety about
the _accessibility_ of the problems which were confronted at first are
now for the most part dissipated.
It will not be possible to review in detail the lines of work sketched
above. An outline of the synthetic work on systems of the mineral oxides
and a paragraph on the volcano researches will perhaps suffice to
indicate the general plan and purpose of the laboratory’s work. It
should be added that the results of many of the researches of the
laboratory, detailed below, have been published in the pages of the
Journal (see =21=, 89, 1906, and later volumes).
_Mineral Researches._—The mineral studies include:
I. _One-component systems_: silica, with its numerous polymorphic forms
and their relations to temperature and the conditions of rock formation;
alumina; magnesia; and lime.
II. _Two-component systems_: silica-alumina, including sillimanite and
related minerals; silica-magnesia, including the tetramorphic
metasilicate MgSiO_{3}; silica-lime, including wollastonite; the alkali
silicates, particularly with reference to their equilibria with carbon
dioxide and with water; ferric oxide-lime; alumina-lime;
alumina-magnesia, including spinel; and hematite-magnetite, a
solid-solution series of an unusual type.
III. _Three-component systems_: silica-alumina-magnesia, completed but
not yet published; silica-alumina-lime, complete, including the
compounds that enter into the composition of portland cement;
silica-magnesia-lime, completed but not yet published, including,
however, published work on the diopside-forsterite-silica system, and on
the CaSiO_{3}-MgSiO_{3} series; and alumina-magnesia-lime.
IV. _Four components_: SiO_{2}-Al_{2}O_{3}-MgO-CaO: the incomplete
system anorthite-forsterite-silica; SiO_{2}-Al_{2}O_{3}-CaO-Na_{2}O: the
series of lime-soda feldspars (albite-anorthite), and the series
nephelite (carnegieite)-anorthite; SiO_{2}-Al_{2}O_{3}-Na_{2}O-K_{2}O:
the sodium-potassium nephelites.
V. _Five components_: SiO_{2}-Al_{2}O_{3}-MgO-CaO-Na_{2}O: the ternary
system diopside-anorthite-albite (haplo-basaltic and haplo-dioritic
magmas).
Fairly complete studies have also been made of the mineral sulphides of
iron, copper, zinc, cadmium, and mercury, and the conditions controlling
the secondary enrichment of copper sulphide ores are now being
investigated. In connection with the sulphide investigations, the
hydrated oxides of iron have been studied chemically and microscopically
and the results will soon be ready for publication.
Throughout the work the mere accumulation of bodies of facts has been
held to be secondary in importance to the development of new methods of
attack and the evaluation of new general principles, and the specific
problems studied have been selected from this point of view.
_Volcano Researches._—A branch of the laboratory’s work that is of
general as well as petrological interest is the study of active
volcanoes. Observations and collections have been made at Kilauea,
Vesuvius, Etna, Stromboli, Vulcano, and (through the courtesy of the
directors of the National Geographic Society) Katmai in Alaska. The
great importance of gases in volcanicity is emphasized by all the
studies. The active gases include hydrogen and water vapor, carbon
monoxide and carbon dioxide, and sulphur and its oxides, as well as a
variety of other compounds of lesser importance. The crater of Kilauea
proves to be an active natural gas-furnace, in which reactions are
continuously occurring among the gases, often resulting in making the
lava basin hotter at the surface than it is at some depth. These
reactions are being studied in the laboratory on mixtures of the pure
constituent gases in known proportions, in order to lay the foundation
for accurate interpretation and prediction concerning the gases as
actually collected from the volcanoes themselves.
X
THE PROGRESS OF CHEMISTRY DURING THE PAST ONE HUNDRED YEARS