178 JOSEPH HYDE PRATT 



in California, and for a few years a number of thousands 

 of tons were shipped to Baltimore. When, however, the 

 importation of chrome ore began, about 1884, the chrome 

 mining industry in the United States began to decline. There 

 are known deposits of this mineral in quantity in California 

 and North Carolina, and probably deposits exist in Pennsyl- 

 vania and Maryland; but, on account of the low price at 

 which the foreign ore can be landed at Baltimore, but a small 

 portion of that used in the United States is mined here. 

 New uses for chromium and the construction of railroads 

 through some of the chrome fields will undoubtedly cause an 

 increase in this industry during the next few years. 



The uses of chromite, at present the only source of chro- 

 mium, can be readily divided into three heads : 



1. As a mineral: In the manufacture of bricks as 

 hearth linings for basic, open hearth furnaces, and for water 

 jacket furnaces in copper smelting. For these purposes ores 

 carrying as low as 40 per cent of chromic oxide can be used. 

 It is also probable that chromite can be used to advantage 

 in other furnaces, especially where it is desirable to use fluor- 

 spar as a flux. 



2. In chromium alloys: Chromite is used to a consid- 

 erable extent in the preparation of a ferro-chromium alloy. 

 The preparation of this alloy, which is used in the manufac- 

 ture of armor plates and armor plate piercing projectiles, 

 has become a very important industry. The ferro-nickel 

 alloy is also used in the manufacture of armor plate. It is 

 generally made by the addition of these two alloys of iron 

 to molten steel before it is cast into the ingot; they produce 

 a more or less homogeneous triple alloy. 



3. In chromium salts: The first use of chromite was 

 in the preparation of the salts, chromate and bichromate 

 of potash, used in dyeing, tanning, and in the manufacture 

 of pigments; this continues to be its chief use. It was about 

 1800 that the value of these salts as pigments was discovered, 

 but it was not until the discovery of deposits of chromite 

 that they were used commercially. Some chromium salts are 

 also used for medicinal purposes. 



Nickel and cobalt mining in the United States began 



