388 THE WORLD OF LIFE CHAP. 



Returning 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 them- 

 selves, the various salts, alkalis, earths, metallic ores, 

 precious stones, and crystals, which have a definite 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 the surface by volcanoes and hot springs, renders 

 it probable that very few either of the elements or com- 

 pounds remain unknown. 



The skill of the chemist, however, has led to the pro- 

 duction of a much greater number of stable chemical 

 compounds than occur in nature. These are used in 



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 complexity 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 opportunity of experimenting with octamethyltetramino- 

 dihydroxyparadixunthylbezonetetracarboxilic acid. " 



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

 salt of this acid to have the composition C 44 H 40 O 14 N 4 Sc 2 . The only scandium 

 salt I could form with this acid has the composition CggHygOjgNgScj. 



