854 



SODA, CARBONATE OF 



commercial value. Soda (oxide of sodium'), thus prepared, is a -white solid, which 

 absorbs moisture rapidly, the whole of which cannot be again removed by heat alone, the 

 hydrate NaO.HO (WaHO) remaining. This hydrate of soda, which is largely used in 

 the manufacture of soap, is not prepared from the anhydrous oxide, but by removing 

 the carbonic acid from carbonate of soda by the means of hydrate of lime. When 

 the soda is required in the solid state, the carbonate of lime thus formed is allowed 

 to settle, the clear supernatant liquid is poured off and evaporated to dryness, fused in 

 a silver vessel, and cast into sticks. 



The following is a table of the quantities of real eoda (NaO) in the solutions of dif- 

 ferent specific gravities. By Bichter. 



SOBA-AXiTTM. See A i.or. 



SODA, BZBORATE OF. See BoRACic ACID, and BORAX 



SOBA, BISUI.PHATE. UaO.H0.2S0 3 (NaHSO 4 ). This is obtained in the 

 same manner as bisulphate of potash, with which it corresponds. 



SODA, CARBONATE OP (Kohl ensaures Natron, Ger.), is the 'soda' of commerce 

 5n various states, either crystallised, in lumps, or in a cmde powder called ' soda -ash.' 

 It exists in small quantities in certain mineral waters ; as, for example, in those of 

 Seltzer, Seydschutz, Carlsbad, and the volcanic springs of Iceland, especially the 

 Geyser; it frequently occurs as an efflorescence in slender needles upon damp walls, 

 being produced by the action of the lime upon the sea-salt present in the mortar. The 

 mineral soda is the sesquicarbonate, to be afterwards described. 



Of manufactured soda, the variety most anciently known is barilla, the incinerated 

 ash of the Salsola soda. This plant is cultivated with great care by the Spaniards, 

 especially in the vicinity of Alicant. The seed is sown in light low soils, which are 

 embanked towards the sea-shore, and furnished with sluices, for admitting an occasional 

 overflow of salt water. "When the plants are ripe, the crop is cut down and dried ; the 

 seeds are rubbed out and preserved ; the rest of the plant is burnt in rude furnaces, at 

 a temperature just sufficient to cause the ashes to enter into a state of semi-fusion, so as 

 to concrete on cooling into cellular masses comparatively compact. The most valuable 

 variety of this article is called sweet barilla. It lias a greyish-blue colour, and becomes 

 covered with a saline efflorescence when exposed for some time to the air. It is hard 

 and difficult to break; when applied to the tongue, it excites a pungent alkaline taste. 

 Another method of manufacturing crudo soda, is by burning sea-weed into kdp. 

 [Formerly, very large revenues were derived by the proprietors of the shores of the 

 Scottish islands and-Highlands, from the incineration of sea-weeds by their tenants, 

 who usually paid their rents in kelp; but since the tax has been taken off salt, and 

 the manufacture of a crude soda from it has been generally established, the price of 

 kelp has fallen low, its principal use being now to obtain iodine. See BAKII.LA, IODINK, 

 KELP. 



The crystals of soda carbonate, as well as the soda-ash of British commerce are 

 now made altogether by the decomposition of sea-salt. 



Soda-manufacture. The manufacture divides itself into three branches: 1. The 

 conversion of sea-salt, or common salt (chloride of sodium), into sulphate of soda. 

 2. The decomposition of this sulphate into crude soda, called black balls by the work- 

 men. 3. The purification of these balls, either into a dry white soda-ash or into 

 crystals. 



Preparation of Sulphate of Soda. The decomposition of common salt is effected 

 by sulphuric acid in furnaces of whicli Jig. 1855 is a section. A, the smaller of the 

 two compartments which compose the furnace, is of cast iron; into this (the decomposer) 

 from five to six hundred weight of common salt are introduced, and an equal weight 

 of sulphuric acid, of specific gravity 1*6, is gradually mixed with it ; a gentle heat 

 being applied to the outside, enormous volumes of hydrochloric acid gas are disengaged, 

 and pass off by the flue, d, to the condensing towers, E and F; these towers are filled 

 with fragments of broken coke or stone, over which a continuous stream of water is 

 caused to trickle slowly from h h. A steady current of air is drawn through the 



