GEOPHYSICAL-CHEMICAL PROBLEMS SOSMAN. 227 



their dry melts (to obtain their fundamental characteristics) and in 

 relation to water solutions under atmospheric pressure (problems of 

 oxidation and secondary enrichment). A distinct problem of the 

 sulfides is their relation to the silicates in the igneous rocks (differ- 

 entiation of sulfide-bearing bodies, as at Sudbury, Ontario). 



Volcanic gases and salts. — These are of particular interest in their 

 relation 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 invisi- 

 bility and intangibility of the substances handled, as well as the 

 difficulty of collecting and transporting samples of the natural prod- 

 ucts. 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 related 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 

 petroleum, and many problems of physics and physical chemistry, 

 such as adsorption, 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 experimental study, but it is hardly necessary here to make a 

 complete inventory 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 accumulated facts. 



AGGREGATES. 



In the preceding paragraphs we have mentioned some of the re- 

 searches 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. 



