858 



SODA, CARBONATE OF 



forated sheet-iron vessels, H IT, which can be raised or lowered into outer lixiviating 

 vessels, also made of iron, by means of the cords and pulleys, i, K. When a charge is 

 received from the furnace, it is introduced into the lowest vessels, o, where it is sub- 

 mitted to the dissolving action of a liquid already highly charged with alkali from 

 digestion upon the black ash contained in the tanks above it ; after a certain time, 

 this charge is raised by the rope from G into the tank F, where it is submitted to a 

 weaker liquid, and so on, successively. The alkali at each stage becomes more com- 

 pletely exhausted, and the residue is successively submitted to the action of weaker 

 lye, till at length, in A, it is acted on by water only, supplied from the cistern, L. 

 When fresh water is admitted from M, to the top of the vessel, A, as it is specifically 

 lighter than the saline solution, it lies upon its surface, and gradually displaces the 

 solution from A, through the bent tube, whilst the water takes its place ; the liquid 

 thus displaced from it, acts in like manner upon that contained inn; and this dis- 

 placement proceeds simultaneously through each successive tier of the arrangement, 

 until the concentrated lye flows off from o, and is transferred to the evaporating pans. 

 The residue which remains after this treatment contains nearly all the sulplaur present 

 in the ball alkali, in the form of oxysulphido of calcium, together with the other in- 

 soluble portions, and is of no value ; it accumulates to an immense extent in large 

 soda works, and is thus a source of annoyance. Many trials have been made to 

 obtain the sulphur contained in it, and to use it for the reproduction of sulphuric acid, 

 but without much success hitherto. 



The solution obtained by thus lixiviating the ball soda, contains principally car- 

 bonate of soda and hydrate of soda, as well as some sulphide and chloride of sodium, 

 and a little sulphate of soda. It is allowed to settle ; then the clear liquor is drawn 

 off into evaporating vessels. These may be of two kinds. The surface-evaporating 

 furnace, shown in fig. 1860, is a very admirable invention for economising vessels, 

 time, and fuel. The grate A, and fire-place, are separated from the evaporating labo- 

 ratory D, by a double fire-bridge B, c, having an interstitial space in the middle, to 

 arrest the cemmunication of a melting or igniting heat towards the lead-lined 

 cistern D. This cistern may be 8, 10, or 20 feet long, according to the magnitude 

 of the soda-work, and 4 feet or more wide. Its depth should be about 4 feet. It 

 consists of sheet lead, of about 6 pounds weight to the square foot, and it is lined with 

 one layer of bricks, set in Koman or hydraulic cement, both along the bottom and up 

 the sides and ends. The lead comes up to the top of c, and the liquor, or lye, may be 

 filled in to nearly that height. Things being thus arranged, a fire is kindled upon the 



grate A ; the flame and hot air 



I860 __^\S$SSM$S^^^WSS^^ sweep along the surface of the 



'liquor, raise its temperature there 

 rapidly to the boiling point, and 

 carry off the watery parts in vapour 

 up the chimney E, which should be 

 15 or 20 feet high, to command a 

 good draught. But, indeed, it will 

 be most economical to build one 

 high capacious chimney stack, as is 

 now done at Glasgow, Manchester, 

 and Newcastle, and to lead the 

 flues of the several furnaces above described into it. In this evaporating furnace 

 the heavier and stronger lye goes to the bottom, as well as the impurities, where 

 they remain undisturbed. Whenever the liquor has attained to the density of T3, 

 or thereby, it is pumped up into evaporating cast-iron pans, of a flattened some- 

 what hemispherical shape, and evaporated to dryncss while being diligently stirred 

 with an iron rake and iron semper. 



This alkali gets partially carbonated by the above surface-evaporating furnace. 

 When pure carbonate is wanted, that dry mass must be mixed with its own bulk of 

 ground coal. Stawdust or charcoal, and thrown into a reverberatory furnace, like fg. 

 1857i but with the solo all upon one level. Hero it must bo exposed to a heat not 

 exceeding G. r >0 or 700 F. ; that is, a little above the melting heat of lead ; the only 

 object being to volatilise the sulphur present in the mass, and carbonate the alkali. 

 Now, it has been found, that if the heat be raised to distinct redness, the sulphur will 

 not go qff, but will continue in intimate union with the soda. This process is called 

 calking, and the furnace is called a calker furnace. It may be 6 or 8 feet long, and 

 4 or 5 feet broad in the hearth, and requires only one door in its side, with a hanging 

 iron frame filled with a fire-tile or bricks, as above described. 



This carbonating process may lie pecfivmed upon several cwts. of the impure soda, 

 mixed with sawdust, at a time. It takes three or four hours to finish the desulphur- 

 ation ; and it must be carefully turned over by the oar and the rake, in order to burn 



