Mance: Quarry Industry of Southern Indiana 



197 



bicarbonate is but slightly soluble in cold ammoniacal solution 

 of common salt. The most important part of the process depends 

 upon a careful regulation of temperature. The chemical reactions 

 involved in the process are as follows: 



KaCl + XH.3 + HoO + COo = XaHCOs + XH4CI 



This formula means that salt, plus ammonia gas, plus water^ 

 plus carbon dioxide, equals sodium bicarbonate plus ammonium 

 chloride. 



The carbon dioxide is obtained by burning limestone in a 

 specialh' constructed kiln which is arranged for saving the carbon 

 dioxide. This gas is forced upward thru a tower where a con- 

 centrated brine of common salt charged with ammonia is flowing 

 down. The temperature of the whole is kept at 35 degrees 

 Centigrade. The sodium bicarbonate, being less soluble than the 

 other constituents, is separated from them on filters. The bi- 

 carbonate is readily changed to the carbonate by heating. The 

 liquor which passes the filters is treated with the lime formed 

 in the producing of the carbon dioxide gas used in the tower and 

 the following reaction takes place: 



2XH4CI + CaO = 2XH3 + CaCl. + H^O 



The liquor will contain calcium chloride and some sodium 

 chloride. After this reaction these are separated by crystalliza- 

 tion, since the salt is more soluble and remains in solution. 

 The ammonia and salt solution can be used again in the tower, 

 so there is no waste. The limestone used in either this or the 

 LeBlanc process must be yeiy pure because the presence of iron, 

 silica, or magnesia interferes with the reactions and the purit}^ 

 of the product. 



Carbon Dioxide Recovery in the Manufacture of Lime. 



In the manufacture of lime there are large quantities of carbon 

 dioxide drii^en off. This gas is now used extensively in charging 

 mineral water and in the manufacture of paints. It is usually 

 made for these industries b}^ the action of weak acids on lime 

 carbonate, using marble or limestone in the operation. Since 

 this gas can be condensed to a colorless liquid under a pressure 

 of 50 atmospheres and is easily handled, it seems like an 

 unnecessary loss to allow it to escape in the manufacture of 

 lime, and then produce it as it is needed in other industries. 

 This recovery process is already in operation in England and 



