CHAPTER XXVIl. 



CHEMICAL ANALYSES. 



Native copper ore. — San pedro marl. — CARsoNiPERons limestone. — Argentiferous galena. — Trachytes. — Soil prom mesa op 



SONORA DESERT. — SolL FROM PIMAS PLAINS. SolL NEAR MOUTH OF THE GILA RIVER. — -REMARKS UPON THE SOILS. 



1. NATIVE COPPER OF RIO GILA. 



Crystallized in small cubes and octagonal prisms, from apparent passage of the octahedra 

 into the prism ; surface rough, and coated with a layer, ^ inch thick, of malachite, in hoty- 

 roidal excrescences ; masses li inch thick, the breadth of the seam ; small cavities in the inte- 

 rior, with incrustations of malachite. 



Analysis of tioo specimens. 



Before the blowpipe faint traces of arsenic were detected. No. 1 was determined in the way 

 used at the New York assay office — by solution in nitro-sulphuric acid, and evaporation to expel 

 the acid — treating the residue with hydrochloric acid and precipitation on an iron plate. 



No. 2 was determined by a plan recommended by M. Rivot, in the Annales des Mines'. 



The ore was dissolved in nitric acid, and the solution diluted ; sulphurous acid passed in 

 until the solution smelled strongly ; then a solution of sulpho-cyanide potassium added, until 

 no more precipitation occurred. 



The precipitate, dried and burned with an equal weight of sulphur, gave the copper as sul- 

 phuret. 



In the analysis the silica separated as quartz sand, and was not combined with the green 

 carbonate of copper. The ore might then be represented as made up in 100 parts of— 



Specimen 1. 



Hydrated carbonate ot copper — "green malachite " 28.63 



Native copper 61.39 



90.02 



Specimen 2. 

 24.36 

 63.36 



87.72 



The difference representing the silica and impurities. 



