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CHAPTER XII 



SODIUM 



THE neutral salt, sodium sulphate, JSra 2 S0 4 , obtained when a mixture of 

 sulphuric acid and common salt is strongly heated (Chapter X.), 1 forms 

 a colourless saline mass consisting of fine crystals, soluble in water. It 

 is the product of many other double decompositions, sometimes carried 

 put on a large scale ; for example, when ammonium sulphate is 

 heated with common salt, in which case the sal-ammoniac is volatilised, 

 &c. 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 un- 

 changed during this reaction, PbS0 4 + 2NaCl =PbCl 2 + Na 2 S0 4 , the 

 vapours will contain lead chloride, and the residue will contain the mix- 

 ture of the three remaining salts. The cause and nature of the reaction 

 are just the same as were pointed out when considering the action of 

 sulphuric acid upon NaCl. Here too it may be shown that the double 

 decomposition is determined by the removal of PbCl 2 from the sphere ef 

 the action of the remaining substances. This is seen from the fact that 

 sodium sulphate, on being dissolved in water and mixed with a solution 

 of any lead salt (and even with a solution of lead chloride, although 

 this latter is but sparingly soluble in water), immediately gives a white 

 precipitate of lead sulphate. In this case the lead takes up the 

 elements of sulphuric acid from the sodium sulphate in the solutions. 



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

 and sodium sulphate, I wish to impart, by separate examples, an idea of the properties 

 of saline substances, but the dimensions of this work and its purpose and aim do not 

 permit 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. 



