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CHAPTER XII 



SODIUM 



WHEN common salt is submitted to the action of sulphuric acid, as we 

 saw in Chapter X., hydrochloric acid is disengaged, and a neutral salt, 

 sodium sulphate, Na. 2 SO 4 , is formed if the mixture be strongly heated 

 at the end of the reaction. This salt 1 forms a colourless saline mass 

 consisting of fine crystals, soluble in water. It is the product of many 

 other double decompositions, sometimes produced on a large scale ; for 

 instance, it is formed when ammonium sulphate is heated with common 

 salt, in which case the sal-ammoniac is vola.tilised, also when sulphuric 

 acid acts on sodium nitrate, (fee. A similar decomposition also takes 

 place when, for instance, a mixture of lead sulphate and common salt 

 is heated ; this mixture easily fuses, and if the temperature be further 

 raised heavy vapours of lead chloride appear. When the disengagement 

 of these vapours ceases, the remaining mass, on being treated with 

 water, yields a solution of sodium sulphate mixed with a solution of 

 undecomposed common salt. A considerable quantity, however, of the 

 lead sulphate remains unchanged during this reaction, PbS0 4 + 2NaCl 

 = PbCl., + Xa. 2 SO 4 , the vapours will contain lead chloride, and the 

 residue will contain the mixture of the three remaining salts. Here 

 the decomposition is produced by the lead salt as with sulphuric 

 acid. The cause and nature of the reaction are just the same as were 

 pointed out when considering Berthollet's doctrine. And here it may 

 evidently be shown that the double decomposition is not determined 

 by any other means than the removal of the substance formed from 

 the sphere of the action of the remaining substances. This is seen 



1 Whilst describing in some detail the properties of sodium chloride, hydrochloric 

 acid, and sodium sulphate, I wish to impart a conception, by separate examples, of 

 the properties of saline substances, but the dimensions of this treatise and its purpose 

 and aim do not permit the possibility of entering into particulars concerning every 

 salt, acid, or other substance. The fundamental object of this work an account of 

 the characteristics of the elements and an acquaintance with the forces acting between 

 atoms has nothing to gain from the multiplication of the number of as yet ungeneralised 

 properties and relations. 



