GEOPHYSICAL LABORATORY. 129 



on the same terms as the other atmospheric gases, for the reason 

 that the critical temperature of water is but 374° and the effect of 

 the salts which might chance to be in solution in it will hardly prove 

 adequate to raise this temperature to the order of magnitude of the 

 lava temperature (1000° or more). 



It is also of interest to note that the exhalation contains but a 

 trace of chlorine (about one part in a thousand). 



THE SECONDARY ENRICHMENT OF COPPER SULPHIDE ORES. 



To be both broad and thorough the investigation of such a problem 

 as the secondary enrichment of copper sulphide ores must be under- 

 taken partly in the field and partly in the laboratory, and it will 

 involve the application of a number of different sciences. The 

 actual processes of deposition, however, are unquestionably chemical 

 and will fall to the share of the laboratory for elucidation. 



The general direction which such a chemical investigation should 

 take is clear, though the path may be difficult. The plain task of 

 the chemist is to test the natural conditions supposed to have been 

 active in the deposition of the ore, or in a word to reproduce the 

 results of nature in the laboratory and under conditions which can 

 be carefully controlled and measured — and these conditions, it should 

 be added, must include the conditions either known or supposed to 

 have existed during the deposition in nature. It is not sufficient 

 merely to reproduce the results. 



Not only must the conditions which attend such deposition be 

 known and measurable, but a chemical investigation like this also 

 demands a considerable body of precise information about the min- 

 erals involved. Now, the majority of these minerals have never 

 been regarded as definite chemical substances. An examination of 

 the chemical text-books, even the fullest, reveals but a meager and 

 unsystematic knowledge of them and that which has been recorded 

 is commonly relegated to the fine print. Such chemical tests as 

 have been made were undertaken by mineralogists, generally for pur- 

 poses of identification. 



A systematic knowledge of the mineral sulphides does not exist . We 

 must learn the individual composition of these substances, whether it 

 is fixed or variable; and, if variable, within what limits. We shall 

 require a systematic knowledge of their chemical reactions one with 

 another, such as we have of the more common compounds of everyday 

 laboratory experience. The temperature range within which these 

 substances can have a stable existence must be known, whence ther- 

 mal studies are indispensable. A knowledge of their dissociation 

 pressures would be of great practical value, both to chemistry and to 

 geology, and an investigation of these ought to be begun in the not dis- 

 tant future. Methods of separation and identification of the sulphides 



