SODA, SULPHATE OP 863 



second tower, down which they may pass and thence either to the chimney or to a 

 third and fourth tower. 



3rd. A tower may be divided in two parts. The gases may pass up ono sido and 

 down the other. This merely treats one as if it were two. 



4th. The gases may pass up one tower and down earthenware pipes to the bottom 

 of the second tower, up which they rise. By this method the gases pass up the towers 

 only, and down tubes only. 



5th. Condensers may bo vessels of stone or of earthenware ; when of stone they 

 may be several feet in length, breadth, or depth. In these vessels a large amount of 

 acid is frequently condensed before it passes to the towers. The gases may pass 

 through several of these tanks. 



6th. As the gases come from the roaster very hot, it is found of advantage to 

 cool them before they enter the condenser. This is done by allowing them to pass 

 along earthenware pipes for a great distance before entering the condensers. When 

 these pipes are not used, the condenser is heated very highly and filled more or less 

 with hot instead of cold water. This is the case sometimes to such an extent as to 

 warm the whole tower. A great supply of water cools the tower but weakens the 

 acid, and may even obstruct the passage of the gas too far. 



7th. The first condenser is made largo enough to condense all the gas, or several 

 may be required. The greater part of the gas may bo removed by one or more 

 towers, leaving a small amount to be condensed by a post-condenser flushed with a 

 great excess of water. This acid is not intended for use. Sometimes several condensers 

 are connected with one post-condenser for a final washing. A greater amount of 

 space and water being required to remove acid when it exists to the extent of only 

 two or three per cent., the acid from these washings is often very dilute, sometimes 

 so much as not to be sensible to the taste. 



Figs. 1863 and 1864 are drawings in elevation of the fine towers at Messrs. Allhu- 

 sen's. The stairs are entirely within the enclosure made by the six towers, and can be 

 ascended with perfect safety. The chamber at the top contains the cistern and arrange- 

 ments for the distribution of the water. At the very top are openings for the uncon- 

 densed gases. There are two rows of three towers, making six towers, for the pan-gases. 



SODA FELSPAR. Usually called Albitc. See FELSPAR. 



SODA, HYPOCHLORITE OF. NaO.CIO (WaClO). This is obtained in the 

 same manner as hypochlorite of lime, or by decomposing a solution of this latter by 

 carbonate of soda. Its uses are the same as those of the hypochlorite of lime. 



SODA, HYPOSULPHITE OP. This is now largely prepared for photo- 

 graphic purposes. See HYPOSULPHITE of SODA. 



SODA, XUXTRATE, OP. NaO.NO 5 (KTaWO 3 ). Syn. cubic nitre; Chile salt- 

 petre. (Nitrate de soude, Fr. ; Wiirfctsalpeter, Ger.) This important salt is found 

 native in immense quantities in Chili and Peru. It is, in some parts, found in beds of 

 several feet in thickness. As found in nature it is tolerably pure, the principal impu- 

 rities being chlorine, sulphuric acid, and lime. Nitrate of soda can be formed artifici- 

 ally by saturating nitric acid with soda or its carbonate, and evaporating the solution. 



Nitrate of soda is extensively and economically employed as a source of nitric acid. 

 It is also used for the purpose of being converted by double decomposition with 

 chloride of potassium into nitrate of potash. (See NITKATE OF POTASH.) It is em- 

 ployed as a manure. 



A good sample of nitrate of soda should not contain more than two per cent, of 

 chloride of sodium. The nitric acid may be determined by the process described under 

 NITRATE OF POTASH. 



Nitrate of soda is not applicable for the preparation of gunpowder or fireworks, 

 partly in consequence of its tendency to attract moisture from the air, and partly 

 owing to the fact that mixtures made in imitation of gunpowder, but having nitrate of 

 soda in place of nitrate of potash. It has, however, been prepared and used for 

 blasting-powder, with some apparent advantage. See CUBIC NITBE. 



SODA, NITRITE OP. NaO.NO 3 (NaNO 2 ). This salt is not nnfrequently 

 employed as a source of nitrous acid, especially in researches on the volatile organic 

 bases. Nitrite of soda possesses some advantages over nitrite of potash, owing to 

 the comparative ease with which -it is prepared. 



SODA, PHOSPHATES OP. Several of these are known, but are not impor- 

 tant in the arts. The principal are the normal tribasic phosphate, the well-known 

 rhombic phosphate, the pyrophosphate, and the metaphosphate of soda. 



SODA, STTXiPHATE OP. NaO.S0 3 + 10HO (Wa'-SO* + lOH'O). This salt 

 is obtained as a residue in several chemical processes, as in the manufacture of hydro- 

 chloric and nitric acids, &c., but owing to the enormous quantity used in the manu- 

 facture of carbonate of soda, it is made purposely as described under SODA, CARBONATE 

 OF. It is known as Glauber's salt, and has been found native near Madrid, nearly 



