DISCOVERY BY EXAMINING PECULIAR MINERALS. 503 



paraffin, to isolate the pure substance and discover its 

 chief properties. 1 



g. By investigating peculiar minerals. Similar pro- 

 cesses of concentration to those employed in the arts occur 

 upon the grandest scale in the operations of inorganic 

 nature, upon the surface and in the interior of the earth, 

 and determine the occurrence of particular substances in 

 certain localities ; and, in consequence of this, all peculiar 

 solids, liquids, and gases found in such places are worthy 

 of examination, and especially the still further concentrated 

 residues of the manufacturing treatment of such bodies. 

 We know that bromine is concentrated in the Dead Sea ; 

 borate of soda in Death Valley, California ; tellurium in the 

 gold ores of Hungary ; selenium in certain copper ores of 

 Cuba ; thallium in certain mineral springs in Cornwall and 

 the Hartz Mountains ; vanadium in certain deposits in 

 Cheshire and in Scotland ; lithium, rubidium, and csesium 

 in the lepidolite of Mount Hebron, U.S., America ; indium 

 in the zinc ores of Frieberg, &c. 



The processes by means of which minute ingredients 

 are naturally and may be artificially concentrated depend 

 upon the properties of the substances. Those substances 

 which are volatile are obtained artificially by distillation 

 or sublimation ; soluble ones are obtained by digestion in 

 liquids, filtering, and evaporating the solution ; fixed ones, 

 by expelling foreign bodies by means of heat or com- 

 bustion; electro-positive ones, by solution, and stirring 

 the liquid with a more positive metal, or by the ordinary 

 precipitation processes of chemical analysis. It was in 

 consequence of long-continued contact of the copper sheath- 

 ing of ships, sailing to and fro during several years on the 

 western coast of South America, that silver was discovered 



1 Philosophical Transactions of the Royal Society, 1869. 



