856' 



SODA, CARBONATE OF 



preparatory shelf, where the mixture to bo decomposed is first laid in order to be 

 thoroughly heated, so that when transferred to the lower or decomposing hearth, B, 



it may not essentially chill it, and 

 throw back the operation, c is the 

 fire-bridge, and D is the grate. In 

 the horizontal section, or ground 

 plan, fig. 1858, we see an opening 

 in the front corresponding to each 

 hearth. There is a door, as shown 

 in the side view or elevation of tho 

 furnace, fig. 1856 ; and each door 

 is shut by an square iron frame 

 filled with a fire-tile or bricks, and 

 suspended by a chain over a pulley 

 fixed in any convenient place. (See 

 COKE.) The workman, on pushing 

 up the door lightly, makes it 

 rise, because there is a counter- 

 weight at the other end of each 

 chain, which balances the weight 

 of tho frame and bricks. In 

 the ground plan, only one smoke- 

 flue is shown ; and this construc- 

 tion is preferred -by many manu- 

 facturers ; but others choose to have 

 two flues, one from each shoulder, 

 as at a, b ; which two flues after- 

 wards unite in one vertical chimney, 

 from 25 to 40 feet high ; because 

 the draught of a soda furnace must 

 be very sharp. Having sufficiently 

 explained the construction of this improved furnace, we shall now proceed to describe 

 the mode of making soda with it. 



The quantity of the mixture required for a charge depends, of course, on the size 

 of the furnace. This charge must be shovelled in upon the hearth, A, or shelf of pre- 

 paration (fig. 1857); and whenever it has become hot (the. furnace having been 

 previously brought to bright ignition), it is to be transferred to the decomposing 

 hearth or laboratory, B, by an iron tool, shaped exactly like an oar, called the 

 spreader. This tool has the flattened part from 2 to 3 feet long, and tho round part, 

 for laying hold of and working by, from 6 to 7 feet long. Two other tools are used : 

 one, a rake, bent down with a garden hoe at the end ; and another, a small shovel, 

 consisting of a long iron rod terminated like a piece of iron plate, about 6 inches long, 

 4 broad, sharpened and tipped with steel, for cleaning the bottom of the hearth from 

 ndhering cakes or crusts. Whenever the charge is shoved by the sliding motion of 

 the oar down upon the working hearth, a fresh charge should be thrown into tho 

 preparation shelf, and evenly spread over its surface. 



The hot and partially-carbonised charge being also evenly spread upon the hearth, 

 is, is to be left untouched for about ten minutes, during which time it becomes ignited, 

 find begins to fuse upon the surface. A view may be taken of it through a peep-hole 

 in the door, which should be shut immediately, in order to prevent the reduction of 

 the temperature. When the mass is seen to be in a state of incipient fusion, the 

 workman takes the oar and turns it over breadth by breadth in regular layers, 

 till he has reversed the position of the whole mass, placing on the surface the particles 

 which were formerly in contact with the hearth. Having done this, he immediately 

 shuts the door, and lets the whole get another decomposing heat. After five or six 

 minutes, jets of flame begin to issue from various parts of the pasty-consistenced 

 mass. Now is the time to incorporate the materials together, turning and spreading 

 by the oar, gathering them together by tho rake, and then distributing them on the 

 reverse part of the hearth ; that is, the oar should transfer to the part next tho 

 fire-bridge the portion of tho mass lying next tho shelf, and vice versd. The dex- 

 terous management of this transposition characterises a good soda-furnacer. A little 

 practice and instruction will render this operation easy to a robust clever workman. 

 After this transposition, incorporation, and spreading, the door may be shut again for 

 a few minutes, to raise the heat for the finishing off. Lastly, the rake must be dex- 

 terously employed to mix, shift, spread, and incorporate. Tho jets, called candles, 

 are very numerous, and bright at first; and whenever they begin to fade, the mass 



