COMPOSITION OF SLAGS. 707 



of carburet of iron ; it is possibly part of the. carburet of iron of the iron reduced in 

 the furnace at a certain stage of the smelting operation, and subsequently fluxed down 

 by sulphur, arsenic, and silica. That carbon is thus liberated there is no doubt, for 

 the writer has been able to isolate graphite blown off with the lead fumes in the cham- 

 ber-dust. 



Strange as it may appear, there is no doubt whatever about the presence of small 

 quantities of carbonateof lime in the slag. This quantity is undoubtedly proportionate 

 to the rapidity with which the furnace is run. 



The large proportion of phosphate of lime in the slag, derived from the pyro- 

 inorphite of the ore, is one of the causes of its opacity, it being well known that 

 phosphate-of-lime glasses are opaque. The presence of large quantities of sulphide 

 of calcium in the crystalline portions of the slags is another very clear indication that 

 sulphide of calcium is really combined with the silicates, either chemically in the 

 state of sulpho-silicate, or possibly crystallographically. 



Although we are in possession of a good many facts relative to slags, it seems 

 necessary to postpone an attempt at a rational definition of these products until we 

 have examined the mattes of Leadville. (See observations on mattes, and final defi- 

 nition of slag.) 



Assays of slags made in the laboratory of the Survey In Table XI is given the fol- 

 lowing information concerning the slags collected in Leadville and assayed in the lab- 

 oratory of the Survey: 



1. Reference uumbe.rs for discussion. 

 2. Names of the smelters. 



3. Character of the slag. 



4. Color of the powdered slag. 



5. Remarks as to whether the slags are normal or accidental. 



6. Number of specimens mixed for assay. 



7. Places where the slags were collected. 



8. Portions of the cakes from which the specimens were taken. 



9. Assays of the slag in silver, ounces to the ton. 

 10. Assays of the slag in gold, ounces to the ton. 



