Vol. 6, 1920 
GEOPHYSICS: R. B. SOSMAN 
593 
CaO 
MgO 
NasO 
K2O 
H2O 
CO2 
About 4.9 per cent by weight 
About 3.7 per cent by weight 
About 3.3 per cent by weight 
About 3.0 per cent by weight 
About 2.0 per cent by weight 
About 0.7 per cent by weight 
An understanding of the chemistry of these oxides and their combina- 
tions is essential to the progress of petrology. Their study should pro- 
ceed from the simple to the complex, i.e., should begin with the individual 
oxides, then proceed to their two-component systems, then the ternary 
systems, and so on. Upon this fundamental basis is then erected the 
structure of physical properties for each system: densities at all accessible 
temperatures, mechanical properties, fluidity, surface tension, specific and 
latent heats, etc. 
The study of these systems may be divided on practical grounds into 
(1) investigations of the anhydrous oxides and silicates (taking in the 
first eight oxides in the list above); (2) investigations involving hydrous 
silicates, as well as combinations containing both carbon dioxide and 
water. 
(1) Anhydrous Silicates. — Work on the first group involves high-tem- 
perature researches under ordinary atmospheric pressure conditions, ex- 
cept in the case of systems containing the oxides of iron, where the oxygen 
pressure must be controlled, and systems containing the alkali silicates, 
where attention to moisture, carbon dioxide, and volatility of the oxides 
is necessary in certain cases. Considerable progress has been made in 
the study of the anhydrous silicates. The phase rule diagrams of the 
four ternary systems of Si02, AI2O3, MgO, and CaO are now complete, 
and a large amount of data is at hand on the alkali feldspars, the forms 
of silica, portions of several quaternary silicate systems, etc. 
(2) Silicates with Volatile Components. — Work on systems involving 
the volatile components CO2 and H2O must be done, for the most part, 
under pressure, and with apparatus designed especially for this purpose. 
The methods are well in hand and progress is being made in assembling 
experimental data. The theoretical side, involving the complications 
due to pressure as a variable in addition to temperature, is also being car- 
ried forward by several investigators. 
So much for the 98%. But the remaining 2% contains many natural 
substances of such great economic as well as geologic interest that they 
must also receive attention. These may be roughly classified as in the 
following examples: 
The Sulfide Ores (e.g., sulfides of iron, nickel, zinc, copper, lead, cobalt, 
cadmium, mercury, silver). — These must be studied both in their dry 
melts (to obtain their fundamental characteristics) and in relation to 
water solutions under atmospheric pressure (problems of oxidation and 
