47* Decompojilion of the Muriate of Soda by Lead, 



colour, and flew ofF in fmoke, without leaving any metallic lead ; effefts which prove that 

 this fubflance is the common muriate of lead. The portion diflblved in the nitric acid 

 being evaporated by a gentle heat, afforded cryftals of the nitrate of lead, amting which 

 there were fome needles of the muriate of lead, which had been diflblved by the nitric 

 acid. 



4. 100 other parts of the fame fubftance, heated with_ boiling water, were not percep- 

 tibly diflblved, and the fluid afforded fcarcely any Cgns of lead, by the hydro-fulphuret of 

 potafli. 



Thefe experiments appear to mc to prove : i. That litharge, after it has decompofed the 

 muriate of foda, is'a muriate of lead, with excefs\of oxide. 2. That the cauftic alkilis 

 diflblve this fait without decompofing it. 3. That it is by virtue of the affinity which the 

 muriate of lead has for this oxide that litharge decompofes fea fait. 4. That it is this quan- 

 tity of oxide, exceeding the proportion of common muriate of lead, which communicates to 

 this fait the property of acquiring a lemon yellow colour by heat ; an event which does 

 not happen with the true or common muriate of lead. 5. That it is this excefs which 

 renders this muriate of lead nearly infoluble in water. 6. And that laftly it isJ*l!is which 

 is difTolved in the nitric acid, and forms the nitrate of lead, leaving behind it the common 

 neutral muriate of lead. 



• ~ It is fo true that the oxide of lead does not decompofe the muriate of foda, but by forming 

 a muriate of lead with excefs of oxide ; that when tlie common muriate of lead is decom- 

 pofed by cauftic foda, it is impoflible even to deprive it of the whole of its muriatic acid. 

 There conflantly remains a fufhcieiit quantity to put the lead into the ftate in which it 

 is found after the decompofition of the muriate of foda. This is proved by the yellow 

 colour it acquires in the fire, by its decompofition with the nitric acid, the feparation of the 

 common muriate of lead, and the formation of the nitrate of lead, which takes place in this 

 operation. 



It is therefore truly, by virtue of a double aflSnity, that the oxide of lead decompofes the 

 muriate of foda : namely, by the united forces of the oxide of lead for the muriatic acid, and 

 the muriate of lead for an excefs of oxide. 



This confideration fhcjvs why fo large a quantity of the oxide of lead is required for 

 completely decompofing the muriate of foda ; becaufe five-fixths at leaft of this oxide are 

 employed, not in decompofing the marine fait, but in forming the muriate of lead with 

 excef^ of oxide ; and the fourth part at leafl of this oxide unites with the muriatic acid in 

 the ftate of true muriate of lead. It will therefore be proper to aflert that litharge com- 

 pleatly decompofes the muriate of foda, when the dofe is fufficient, and that foda never 

 totally decompofes the muriate of lead, however confiderable the dofe. 



If the carbonate of lead do not decompofe the muriate of foda, it ought -to follow that 

 the carbonate of foda fliould compleatly decompofe the muriate of lead ; and this in fad is 

 confirmed by experience. 



It may moreover be obferved, that the muriate of lead is not the only fait of this kind 



which 



