244 REPOET OF NATIONAL MUSEUM, 1899. 



The kiln works continuously, calcined ore being withdrawn and 

 fresh charges made without interruption. The ore is subjected for 

 forty-eight hours to the heat, which expels the moisture, sulphur, and 

 carbon dioxide. About li tons of calcined ore are withdrawn every 

 three hours during the day. The outside of the lumps of calcined ore 

 has a light-brown color, while the interior shows upon fracture a 

 darker brown. Great care is necessary to regulute the heat so that 

 the ore is not overburnt. When this happens the product has a black, 

 scoriaceous appearance, and is unfit for the manufacture of metallic 

 paint, as it is extremely hard to grind. 



The calcined ore is carried from the kiln in wagons to the mill, 

 where it is broken to the size of grains of corn in a rotating crusher. 

 The broken ore is carried by elevators to the stock bins at the top of 

 the building, and thence by shutes to the hopper of the mills, which 

 grind it to the necessary degree of fineness. Elevators again carrj^ it 

 to the packing machine by a spout, and it is packed into barrels hold- 

 ing 500, 300, or 100 pounds each. 



A "mineral paint"" mined on Porter Creek, near Healdsburg, Sonoma 

 County, California, is said ^ to consist of hematite and silicate of iron 

 in the form of a compact mass lying between hornblendic rock, actin- 

 olite and mica schist on the one side and rotten serpentine on the 

 other. The vein has a north of east course, and is some 60 feet in 

 width. The material is mined from a tunnel, crushed, ground between 

 buhrstones, and bolted, making a paint fit for mixing with oils or japan. 



Uses. — The ochers are among the most widespread and readily 

 accessible of coloring materials, and have been used by savage and 

 civilized people both ancient and modern. The war paint of the 

 American Indian was not infrequently an ocher mixed with oil or 

 grease. 



According to William J. Russell,^ the pigments used by the Egyptians 

 and others since the earliest times were of hematite, and moi^tly of an 

 oolitic variety, apparently closely corresponding to the Clinton hema- 

 tites of New York State. As tested, such were found to contain from 

 79.11 to 81.34 per cent ferrio oxide. 



Yellow ocherous pigments, presumably limonite, are also described 

 by the same authority. These jdeld only al)out 33 per cent ferric oxide 

 and some 7 to 10 per cent of water, together with clay. The ochers 

 are now used mainly in the manufacture of paints for exteriors, as of 

 buildings, the rolling stock of railways, bridges, and metal roofing. 

 They are also used as a pigment for coloring mortars, and in the 

 manufacture of linoleums and oilcloths. Mixed with a certain pro- 

 portion of oxide of manganese, the ochers have been used to produce 

 desirable colors in earthenware. 



1 Twelfth Annual Report of the State Mineralogist, 1894, p. 406. 



2 Nature, XLIX, 1894, p. 374. 



