418 THE WORLD OF LIFE 



Eetuming now to the different forms under which matter 

 exists in that portion of the earth which we can examine, we 

 find them to be very limited as compared with those of the 

 organic world. The crust of the earth, and presumably the 

 interior also, consists mainly of what are called minerals, which 

 is the term used for all chemical compounds of the elements 

 which have been produced under natural laws and forces, and 

 constitute the materials of the whole planet. They comprise, 

 besides the elements themselves, the various salts, alkalis, earths, 

 metallic ores, precious stones, and crystals, which have a def- 

 inite chemical constitution, a permanent form, and definite 

 characters ; forming what are termed mineral species. These, 

 when disintegrated by natural forces, intermingled in various 

 ways, and solidified in various degrees, make up the whole mass 

 of rocks and surface material of the earth. The total number 

 of mineral-species now known, almost the whole of which are 

 to be found in the fine mineralogical gallery of the British 

 Museum, is almost exactly a thousand. Many of these are 

 very rare or local, the great bulk of the rocks being made up 

 of a few score, or at most of a few hundreds of them. 



The generally accepted idea being that the whole earth was 

 once a molten mass, the crust may be supposed to give a fair 

 sample of the whole ; and the additional fact that, during all 

 geological time, matter from the interior has been brought to 



These various properties of the atoms and molecules of matter have so 

 complicated their relations, that the attempt to unravel them has led to a 

 system of equations, of diagrams, and of formulae, which are almost as 

 difficult for the general reader to follow in detail, as is the working out of 

 some abstruse mathematical investigation. As an example of this complex- 

 ity in chemical nomenclature I may refer to a recent paper by Sir William 

 Crookes, on the rare metal scandium (discovered in 1879). Near the 

 end of this paper (in the Proc. Roy. Soc, series A, vol. 84, p. 84), the 

 author says : " By the kindness of Dr. Silberrad, I have had an oppor- 

 tunity of experimenting with octamethyltetraminodihydroxyparadixunthyl- 

 bezonetetracarboxilic acid." 



He then adds : " Previous experiments would lead one to expect the 

 scandium salt of this acid to have the composition C44H4oOi4N4Se;. The 

 only scandium salt I could form with this acid has the composition 



CssHjgOoaXsSCj. 



