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360 Field Museum of Natural History — ■ Reports, Vol. III. 



these lights are removable entire when it is desired to open the case. 

 The other floor cases are of the type already in use in Hall 68. Before 

 reinstallation of the specimens they were carefully cleaned and any 

 essentially duplicate material eliminated. The general plan of in- 

 stallation which had been previously adopted was retained, the ores 

 being placed in geographic order in the wall cases. As before, the 

 ores of a group of mining districts have been placed together and for 

 all such groups an individual label has been prepared. It may be 

 said that most of the important mining districts of the precious metals 

 of the world are represented in this collection. The large specimens 

 on the floor of the Hall are grouped geographically also as far as 

 possible. Specimens too large for these cases were removed to the 

 West Dome. All of the specimens in Hall 72 are now protected by 

 glass, so that much better preservation of them is insured than has 

 been possible hitherto. In addition to the large specimens the floor 

 cases contain a number of special collections, such as those illustrat- 

 ing alloys of gold and silver, salvage of gold and silver waste, and 

 platinum ores from various parts of the world. Three floor cases 

 are also devoted to the metallurgy of the precious metals and lead. 

 In one of these is exhibited an elaborate German method of treating 

 silver and lead ores, the results of the different processes being con- 

 nected by lines to show the course of treatment. A collection illus- 

 trating smelting of silver-lead ores in the ordinary manner occupies 

 another case. In order to make the representation of the process 

 somewhat more graphic, this collection has been provided with a 

 model of a blast furnace. In this model, which was constructed in 

 the Department, the various features of the blast furnace are shown 

 in detail and a portion of the wall of the furnace is represented as 

 removed from the rear so that the interior charge of the furnace 

 may be seen. A model of a cyanide plant for the extraction of gold 

 has also been constructed and placed in one of the floor cases. The 

 model shows five wooden tanks placed upon trestles and filled with 

 representations of the solutions and ores used in the processes. The 

 tanks are connected by pipings shown in the model and a steam 

 pump and zinc box are shown. A summary of the collections at pres- 

 ent exhibited in the Hall and their distribution is as follows : One 

 case, synoptic collection, placer gold ores, Canadian ores and Appala- 

 chian Mountain ores; one-half case, lead ores of the Mississippi Valley; 

 two and one-half cases, Colorado ores; one case Nevada, Montana, 

 Idaho, South Dakota, Washington, and Utah ores; one case, Califor- 

 nia and Arizona ores; one-half case, New Mexico ores; one case, Mex- 



