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MANUFACTURE OF ALKALI. 



The works erected for the manufacture of this article generally contain 

 — Close kilns, for burning sulphur or pyrites ; leaden chambers, for con- 

 densing sulphuric acid gas ; furnaces, for making salt cake ; furnaces, for 

 making black ash ; and furnaces, for making white ash ; with the necessary 

 chimneys and flues, or sewers, for carrying off the gases evolved during the 

 process of the manufacture. 



The first process is the manufacture of 



1. SULPHURIC ACID, 



Which is produced at the works in the following manner : — Either pure 

 sulphur or pyrites is burned or heated in the close kilns. By the action of 

 the heat, sxdphuric acid gas is evolved. This gas is conducted, by means of 

 a flue, from the close kiln, in a state of vapour, into a leaden chamber, in 

 which chamber, by the help of steam driven into it, through pipes, the gas 

 is condensed into sulphuric acid, which falls in a liquid state to the bottom 

 of the chamber. 



The sulphuric acid thus obtained is either sold for the purposes of 

 commerce, or used at the works in the making of 



2. SULPHATE OP SODA, OR SALT CAKE, 



Which is obtained by the following process : — The sulphuric acid, formed 

 in the manner we have above stated, is run into a furnace upon a quantity 

 of muriate of soda, or common salt, which is a compound of muriatic acid 

 and soda. By the action of the sulphuric acid upon the salt, the muriate 

 is separated from the soda, which it leaves in the form of muriatic gas ; 

 and the soda and the sulphuric acid combine, and form sulphate of soda 

 or salt cake. 



The next process is the converting of the salt cake into what is termed 



3. BLACK ASH. 



This is effected in the following manner : — The sulphate of soda, or salt 

 cake, after being mixed with an equal weight of limestone, and a propor- 

 tionate part of small coal, is put into a separate furnace, and there sub- 

 jected to a high degree of heat, which brings the whole into a state of 

 fusion. In the corpse of this fusion the carbonic acid contained in the 

 limestone enters into combination with the soda, and forms an impure 

 carbonate of soda. 



This fused matter is drawn out in a liquid state into moulds, in which 

 it is suffered to cool. It hardens of a black colour, and something like the 

 dross of a copper smelting furnace, and in this state is called black ash. 



The next process is to refine or separate the carbonate of soda contained 

 in the black ash from its impurities — viz., sulphate of lime (which is 

 formed by the sulphuric acid in the sulphate of soda, or salt cake, leaving 

 the soda in the course of the fusion, and combining with the lime), and 

 the residium of the coal. The refinement produces a substance called 



4. WHITE ASH, 



Which is thus obtained. The solid masses of the black ash, which have 



