■A FIELD MUSEUM OF NATURA L HISTORY 
of the appearance of these ores than do the smaller specimens 
of the systematic collection. 
In one table case placer gold deposits are represented by a 
collection of auriferous sands and gravels principally from 
Alaska and California. All placer specimens are separated from 
the general collections and included in this single series. 
Series of specimens and models illustrating phases of the 
extraction of metals from their ores occupy some of these cases 
and a part of one wall case. 
Series of metallurgical products illustrate the extraction of 
gold, silver, and lead from their ores. Out of a multitude of 
processes used two of the more complex methods are illustrated 
in this manner: On one side of the case is placed the ore, and 
lines are drawn from it to specimens of the materials formed 
from it by the first operation of extraction. From each of these 
specimens lines are likewise drawn to specimens of the sub- 
stances formed from them in subsequent operations, and so on 
until the final products are shown. It is thus possible for the 
visitor to follow readily each step of the operation. The meth- 
ods shown illustrate the treatment of very complex ores as 
practised in the Hartz Mountains, Germany. 
Several of the more ordinary metallurgical methods are rep- 
resented by models of the plants. Thus there is a model of a 
twenty-stamp mill which is represented at work upon ore from 
the Treadwell mines of Alaska. 
Also the well known cyanide process of gold extraction is 
represented by a model of a cyanide plant treating an ore suited 
to this method. 
A model of a blast furnace is also shown representing an 
ordinary method of smelting ores which contain lead and silver. 
A portion of one side of this furnace is shown removed to per- 
mit a view of the interior. Around the model are grouped on 
one side those materials which are fed into it and on the other, 
those products which flow from it. 
The preliminary treatment of ores by concentration is rep- 
resented by a model of a Hartz jig which is separating a pul- 
verized ore into waste rock, rich silver ore and rich gold ore. 
A table case contains a series of nearly all^ the known alloys 
of gold and silver with other metals. It contains polished plates 
of each alloy with specimens of the materials of which it is com- 
