632 



SCIENCE, 



[N. S. Vol. XI. No. 277. 



(2) The nearest possible approach to a purely 

 genetic classification of ore deposits is believed 

 to be found in their geological relationships, as 

 determined by the great geological processes 

 and not in their direct chemical formation, or 

 physical shapes. 



(3) The chemical reactions so widely used as 

 criteria of ore classification are to be regarded 

 as general agencies and therefore thej' are not 

 available in the specific determinations of the 

 various groups of ore bodies. 



(4) In the discovery and exploitation of ores, 

 structure is of first importance ; not so much 

 the structure of the individual ore body itself 

 as the geological structure of the enclosing 

 country rocks. 



(5) The primary groupings of ore bodies ap- 

 pear to be best indicated when based upon their 

 geological occurrence, as governed by the nature 

 of geological processes operating. 



(6) The secondary groupings appear to be 

 best based upon the general form of the ore- 

 bodies as geological formations produced by 



the grander categories of geological agencies. 



(7) The ternary groupings are best based 

 upon the specific phases of the geological proc- 

 esses involved in the formation of ores as ore 

 bodies. 



(8) The source of the ore materials is an un- 

 essential factor in their classification ; the great 

 practical question is, how are ores best ex- 

 ploited? In this connection it matters little 

 what was the original condition of the ores. 

 Nor have we to do very much with the detailed, 

 complex, and usually theoretical reactions that 

 are supposed to take place before the final 

 stage of the ore, as we find it, is reached. 



(9) Very similarly appearing ore-bodies may 

 be formed by very different methods, a fact 

 which, while apparent in all classifications, does 

 not necessarily vitiate any. 



(10) The present scheme is merely suggestive. 

 It is the barest outline of what is believed to be 

 capable of much further expansion and develop- 

 ment into a comprehensive, rational and prac- 

 tical general plan. 



Classification of Okk Deposits. 



Charles R. Keyes. 



NOTES ON INOROANIC CHEMISTHY. 

 The work of H. Brereton Baker on ex- 

 tremely dry gases is continued by a paper on 

 the vapor densities of dried mercurous chlorid 

 and dried mercury, read before the Chemical 

 Society (London). It is found that perfectly dry 

 mercurous chlorid at 443° in an atmosphere 

 of nitrogen shows a density of 217.4 which cor- 



responds to the formula HgjClj. The undried 

 substance gives a deeper density of 118.4° show- 

 ing that the dissociation of mercurous chlorid 

 like that of ammonium chlorid is dependent on 

 the presence of water vapor. The density of 

 dry mercury on the other hand was found to be 

 108.1 at 448° showing that at this temperature 

 the molecule of mercury is mouatomic. 



