178 Rock Salt and Salines of the Holston. 



deposited ; it is thence conveyed to the kettles, and evaporated 

 by rapid ebullition. As the salt is deposited, it is removed in 

 wicker baskets, and suspended over the kettles until it is dry. 

 The cast iron kettles are segments of spheres, of about the ca- 

 pacity of forty gallons ; these are arranged in pairs, in parallel 

 rows, over an oblong furnace heated by wood, the heat being ap- 

 plied directly to the bottom of the kettles. In the arrangement 

 of the kettles and the construction of the furnace, little regard 

 is paid to the economy of fuel, or heat. By direct evapora- 

 tion, at a high temperature, salt of a superior character is ex- 

 peditiously made ; but the process is attended with the serious 

 inconvenience of the formation of a hard saline incrustation on 

 the bottom of the kettles, owing to the intense heat to which 

 the salt, as it is deposited, is subjected. This incrustation, called 

 by the workmen " blocking" is sometimes fused into a vitreous 

 mass, and is generally crystalline, adhering with such tenacity 

 to the sides of the kettle, as to require the pickaxe for its remo- 

 val. A serious increase of expense attends the delay necessary 

 for the removal of this incrustation, as well as from the more 

 rapid corrosion of the iron kettles. That this incrustation is not, 

 as is generally supposed, a deposit of the more insoluble impuri- 

 ties of the brine, will be seen from the following analysis. 

 Two specimens, selected by the proprietors as representing the 

 average character of the " blocking," proved nearly pure salt. 

 They were of a snowy whiteness, compact, hard, laminated, 



highly crystalline and anhydrous. 



No. 1. No. 2. 



Sulphate of lime, 4.892 grs. 9.314 grs. 



Chloride of calcium, .068 " .050 " 



" of sodium, 95.040 " 90.510 " 



Carbonate of lime,* a trace. .126 " 



The annoyance occasioned by the " blocking," would be en- 

 tirely obviated by evaporation at a lower temperature, which 

 would also improve the character of the salt, as the slower 

 the evaporation, the more perfect the crystallization. At Chesh- 



* The occurrence of carbonate of lime in the "blocking," is probably attributable 

 to its existence in the brine in a proportion so minute as to escape detection in the 

 quantity operated upon ; or possibly it may be held in mechanical suspension in 

 the brine, that operated upon having been permitted to stand until all the mechan- 

 ical impurities were deposited and the clean water decanted off. 



