GEOPHYSICAl. RESEARCH — DAY. 363 



laboratory; can we not build a furnace in wliich an igneous rock can 

 bo formed under such conditions that we can observe its minutest 

 change ? He proposes to introduce temperature-measuring devices 

 and apparatus for the determination of pressure, to investigate the 

 character of the surrounding atmosphere and the quantity of water 

 vapor which may be present. lie insists upon the chemical purity of 

 every ingredient which goes into the furnace and guards it carefully 

 against contamination. In these various ways he will undertake to 

 ascertain the exact magnitude of all the causes, both physical and 

 chemical, which have been at work in his miniature rock producer, 

 together with the physical characteristics of the product. 



A very practical c|uestion now arises. Can he do all this suc- 

 cessfully at the temperatures where the minerals form? We must 

 press tliis question and insist upon a satisfactory answer, for it is 

 by no means obvious that the relations which the physicist and 

 chemist have established at the temperatures of everyday life — 

 energy content, density, solubility, viscosity, dissociation — will 

 continue to hold when substances are carried up to a white heat. 

 The substances, too, are different from those with which the chemist 

 and physicist have been generally familiar. Instead of simple metals, 

 aqueous solutions, and readily soluble active salts, we encounter 

 silicates and refractory oxides, inert in behavior and capable of 

 existing together in mixtures of great complexity. We must there- 

 fore extend the range of our physics and our chemistry to a scope in 

 some degree commensurate with the wide range of conditions which 

 the earth in its development has passed through. Let us follow for 

 a little the actual progress of such an attempt. 



The first step is to provide the necessary temperatures. Obvi- 

 ously, the common fire-clay ciiicible and the smelter's furnace with 

 its brick lining will not serve us here, for all these arc themselves 

 mineral aggregates. The charge, furnace lining, and cnicible would 

 go down together in a fall as disastrous as Humpty Dunipty's. But 

 experiment has taught us that platinum crucibles, magnesia furnace 

 tubes inclosing an electrically heated helix of platinum wire, and elec- 

 tric temperature-measuring devices, provide a furnace in which nearly 

 all of the important minerals can be successfully studied, which is hot 

 enough to melt zinc, silver, gold, copper, nickel, or iron readily, and 

 where any temperature up to 1,600° C. can be maintained perfectly 

 constant, if need be, for several weeks. All these temperatures can be 

 measured with no uncertainty greater than 5°. This e(|uipment pre- 

 serves the chemical purity of the mineral studied, and enables the 

 temperature to bo controlled and measured at every step of the 

 experimental work. Or an iridium furnace tube and an iridium 

 crucible can be substituted for platinum, the magnesia supports can 



