from the fact that sodium sulphate, on being dissolved in water and 

 mixed with a solution of any lead -ah land even with a solution of lead 

 chloride, although thi- latter i- but -paringlv soluble in water), imme- 

 diately gives a white precipitate of lead -ulphate. In this case the 

 lead lake- up the elements of sulphuric acid from the sodium sulphate 

 in the solutions. ( >n heating, the reverse phenomenon is observed. 

 The contrary reaction in i he solution i- founded on the insolubility of 

 the lead sulphate, and the phenomenon which takes place on heating is 

 founded on the volatility of the lead chloride. Let us cite other ex- 

 amples of double decompositions, in solutions giving sodium sulphate. 

 Silver sulphate. Ag.,S<)j. \vhen treated \\ith common salt, gives silver 

 chloride, because ii is insoluble in water. Ag,S<>, -f- -_'Na('l = Na.,Sn, 

 -f l'Ag('l. Sodium carbonate, mixed in -olution with sulphates of 

 iron, copper, manganese, magnesium, iVc.. gives in solution sodium 

 sulphate, and in the precipitate a carbonate of the corresponding metal, 

 because these salts of carbonic acid are insoluble in water: for instance, 

 .MgS<), 4- Na. ,('(),,= Na.,S<), + .Mu'( '<),,. In precisely the same way 

 sodium hvdro.xide acts on solution- of the majoritv of the salts of 

 sulphuric acid containing metal-, i he hvdroxides of which are insoluble. 

 in water for instance, ('uS<>. + L'Nal 1 <) = Cu( I [<>)., + Na.,S<),. 

 Sulphates of magnesium, aluminum, iron, iVc.. on being mixed in 

 solution with common salt, ought to form chlorides of magnesium, 

 aluminium. iVc., and sodium sulphate, as the above-mentioned chlorides 

 are more -oluble in water than sodium sulphate. ( >n cooling the 

 mixture ot stich (concentrated) solution- -odium sulphate is deposited. 

 This i- made u.-e ot tor preparing it on the large scale in works where 1 

 -ea water is treated. In a similar wav -odium sulphate is prepared bv 

 the aid ot the magnesium sulphate which is found in large (juantities 

 in Stas-fiirl in the seams if common -a.lt. In this case, on cooling, 

 the reaction L'NaCl -f .MgSOj Mg('l -f Na.,S(), takes place. 



Thus \\here suljihates and -alls if sodium are in contact, it mav 

 alway- be expected that sodium -ulphate will be formed and sepa- 

 rated it' the conditions are favourable; for 'his reason it is not sur- 

 prising; to often lind -odium -ulphale in the native state. Some of the 

 springs and sail lakes in the steppes Uvond the Volga, and in the 

 ( 'auca-.il . ' -on ! a i n a considerable <|iia nt it v of sodium std] hate, and yield 

 it bv -imple evaporation of the solutions. lleds of t his salt; are also 

 met with : tint- at a depth of onlv ~> feet, alioiit .">S \crsts to the 

 east of Tillis, al the foot of the range of t he * Wolf 's mane ' ( Voltchia 

 gri\a) moii n ' a i us. a deep stratum ot verv pure (daubers sail, 

 NaS< ).. I n| | ( . ha., been found.' A aver two metres thick of the 



n, ..I. is known ii 



