^50 GEOLOGICAL RECONNOISSANCE 



Alumina, sesquioxides of iron and manganese, 4.389 



Oxide of lead trace 



" " copper trace 



100.452 

 The air-dried ore lost 0.50 per cent, of moisture at 250 deg. F. 

 8G.49 per cent, of carbonate of zinc are equal to 5G.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 32.150 



Silica, clay, iron, lime, etc 14.519 



Oxide of zinc 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 

 zinc 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. 



