638 RECORD OF MEETINGS OF THE 



Iron ores are of little value in any part of the world un- 

 less they contain a minimum of 35 per cent, iron when 

 they enter the furnace, but if they are distributed in amounts 

 of from 10 to 20 per cent., in extensive masses of loose or easily 

 crushed rock in such condition that they can be cheaply con- 

 centrated up to rich percentages, they maybe profitably treated 

 and a product with 50 per cent, iron or higher be sent to the 

 furnaces. Nevertheless, speaking for the civilized world at 

 large, it holds true that as an iron ore enters the furnace it 

 cannot have less than 35 per cent., and in America with our 

 rich and pure deposits on Lake Superior two thirds of our sup- 

 ply ranges from 60 to 65 per cent. 



As regards copper, a minimum working percentage, amid 

 favorable conditions and with enormous quantities, is usually 

 about three per cent., but in the altogether exceptional deposits 

 of the native metal in the Lake Superior region, copper-rock 

 as low as three fourths of one per cent, has been profitably 

 treated. This or any similar result could only be accomplished 

 with exceptionally efficient management and with a copper 

 rock such as is practically only known on Lake Superior. With 

 the usual type of ore, not enriched by gold or silver, two per 

 cent, is the extreme, and in remote localities from 5 to 10 per 

 cent, may sometimes be too poor. 



In southeast Missouri, lead ores are profitably mined which 

 have from 5 to 10 per cent., lead, but they are concentrated to 

 65 or 70 per cent, before going to the furnace. 



Zinc ores at the furnace ought not to yield less than 25 or 

 30 per cent., and when concentrated or selected they range up 

 to 60 per cent. 



The precious metals are expressed in troy ounces to the ton 

 avoirdupois. A troy ounce in a ton is one three-hundredth 

 of one per cent., and the amount is, therefore, very small when 

 stated in percentages. If it be appreciated that in round 

 numbers silver is now worth fifty to sixty cents an ounce, and 

 gold, twenty dollars, some grasp may be had of values. Silver 

 rarely occurs by itself. On the contrary it is obtained in asso- 

 ciation with lead and copper and the ores are, as a rule, treated 

 primarily for these base metals and then from the latter the 



