2 20 Bulletin of Laboratories of Demsoii University. i\'"i. mi 



work, including cleaning of the troughs, etc., is readily per- 

 formed by three ordinary laborers. 



The ocher passes from the washer, through a line of troughs, 

 into a series of settling-vats dug in the ground, and is exposed 

 throughout the day to the direct heat of the sun. After it has 

 settled, and as much as possible of the water siphoned off by 

 rubber-hose, the remainder of the water is expelled by evapora- 

 tion. As soon as it is stiff enough to be handled, the ocher is 

 removed from the vats and placed on drying-racks under a shed 

 where the drying-process is completed. (See Fig.- 7). The 

 time required for the evaporation of the water from the ocher 

 in the vats sufficient to admit of handling will average about ten 

 days in clear summer weather. It requires from eight to twelve 

 days of similar weather to complete the drying on the racks be- 

 fore the ocher can be pulverized. 



Evaporation is either by natural means — exposure to the 

 heat of the sun — or by artificial means promoted b)' steam- 

 heating. Several of the plants in the district are fully equipped 

 for both natural and artificial evaporation. The artificial drying 

 is in vats or tanks, arranged in series, in which iron-pipes are 

 run at close intervals along the sides and bottoms for steam- 

 heating. Drying by this method requires usually not longer 

 than one or two days, when the ocher is ready to be removed 

 to the racks and the drying continued for the usual time, from 

 eight to twelve days, before it is dry enough to be pulverized. 

 While the time is much shortened by the steam-drying over 

 that of the natural evaporation by the sun, the ocher is less de- 

 sirable than the sun-dried material ; the reason for this being 

 that near the pipes the heat is strong enough to dehydrate par- 

 tially or calcine the ocher, changing its color from )ellow to 

 dark red. For this reason some plants in the district have not 

 included an equipment for artificial drying. 



After being thoroughly dried, the ocher is pulverized and 

 packed under steam-pressure in barrels and bags of uniform 

 size, ready for shipment. 



Fig. 8 presents a view of the plant of the American Ocher 



