150 - GEOLOGICAL RECONNOISSANCE 
Alumina, sesquioxides of iron and manganese, 4.389 
Oxide of lead «es ce eee en seeeveees wea er cane trace 
« © coppers +++ seen eee ree eterenee oe trace 
100.452 
The air-dried ore lost 0.50 per cent. of moisture at 250 deg. F. 
86.49 per cent. of carbonate of zinc are equal to 56.099 per cent. of 
oxide of zinc, or to 45.045 per cent. of metallic zinc. 
No. 4. Same as No. 3; different specimen. 
The analysis of this sample was executed by igniting the ore, and 
extracting the oxide of zinc with a mixture of ammonia and carbonate of 
ammonia, (compare “ methods of analysis,” below.) 
Composition of air-dried ore: 
Carbonic acid and water. +--+ +sseeeeues 32.150 
‘Silica, clay, iron, lime, etc-++-+-+++++: s+» 14.519 
Oxide of zinc--.-- Fatale Rowad aaa EAE eae ah al FRO aie 53.331 
100.000 
53.331 per cent. of oxide of zinc are equal to 42.822 per cent. of me- 
tallic zinc. 
The residue, left after the treatment with ammonia, etc., and which 
consists essentially of clay, was found, on examination, to contain some 
oxide of zinc, showing that a small portion of this oxide must exist in the 
ore in combination with silica, forming silicate of zinc, a compound 
insoluble in ammonia. On comparing analysis No. 4 with No. 3, it 
appears that about 3 per cent. of oxide of zinc are combined with silica. 
C.—Ore from the Koch mine. 
The principal ore from this mine is a cellular, subcrystalline mass of 
brownish-white and grayish-white color; within the cavities, the surface of 
the smithsonite is botryoidal and usually covered with a very thin layer of 
red clay; this mineral is intimately associated and intermixed with an 
amorphous, grayish-yellow, massive variety of carbonate of zinc, resem- 
bling ore No.1, from the Hoppe mine. Its powder has a pale cream 
color. 
Three different specimens of this ore were analyzed; of the first speci- 
men a complete analysis was made, showing the total amount of oxide of 
zine present, and the quantitative relation of the impurities. The other 
two specimens were analyzed after the method employed for No. 4, show- 
ing only the amount of oxide of zinc that is contained in the ore in the 
state of carbonate or hydrate. 
i 
