CHAPTER XXVII. 
CHEMICAL ANALYSES. 
Native copper ore.—San pedro marl.—Carboniferous limestone.—Argentiferous galena.—Trachytes.—Soil from mesa of 
SONORA DESERT.-SOIL FROM PIMAS PLAINS.-SOIL 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 boty- 
roidal excrescences ; masses I f inch thick, the breadth of the seam ; small cavities in the inte¬ 
rior, with incrustations of malachite. 
Analysis of two specimens. 
Found. 
Calculated. 
1 . 
2. 
1 . 
2. 
Copper--- 
11. 00 
8.97 
81. 84 
80. 66 
Silica___ 
Water. 
1. 30 
1.29 
9. 67 
11.61 
Carbonic acid_ 
1 1.10 
.77 
8.18 
6.96 
Loss_ 
.04 
.05 
.31 
.77 
13. 44 
11.08 
100. 00 
100. 00 
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¬ 
phur et. 
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. Specimen 2. 
Hydrated carbonate of copper—“green malachite ”. 28.63 24.36 
Native copper. 61.39 63.36 
90.02 87.72 
The difference representing the silica and impurities. 
