native Phosphates and Arseniates of' Lead. 137 



Green Lead- Brown Lead- Green Lead- Yellow Lead- 

 Spar from Spar from Spar from Spar from 

 Zschopau. Huelgoet. Hoffsgrund. Wai'.lock-Head. 



Oxide of lead, 78.40 78.58 77.10 80-00 



Phosphoric acid, 18.37 19.73 19.00 18.00 



Muriatic acid, - 1.70 1.65 1.54 1.62 



Oxide of iron, - 10 000 0.10 0.00 



98.57 99.96 97.74 99.62 



It is commonly supposed that the phosphoric acid and oxide 

 of lead exist in these minerals as a neutral phosphate ; but, on 

 calculating their composition on this idea, they will be found 

 to contain too much oxide of lead for converting the phospho- 

 ric acid into a neutral compound, and too little for forming 

 any known sub-salt with it. This circumstance led M. Wbh- 

 ler to suspect some inaccuracy in these analyses, and it is ob- 

 vious, on reading Klaproth's account of them, that the results 

 cannot be altogether exact. Klaproth determined his oxide 

 of lead, by precipitating it from a dilute solution of the mine- 

 ral in nitric acid by sulphuric acid ; — a method which is inex- 

 act, because a considerable portion of the sulphate of lead re- 

 mains in solution. Having collected the sulphate of lead on 

 a filtre, and removed the excess of sulphuric acid, the phos- 

 phoric acid was thrown down by the acetate of lead, the solu- 

 tion having been previously neutralized as far as possible by 

 ammonia. Now the phosphate of lead, so formed, is not uni- 

 form in composition, unless certain precautions are taken which 

 Klaproth did not employ ; and the effect of this error was to 

 cause the quantity of phosphoric acid to appear greater than 

 it ought to have been. Another circumstance which attract- 

 ed the attention of M. Wdhler, was the constant occurrence of 

 muriatic acid in all the varieties which were analyzed by Klap- 

 roth ; a coincidence which could hardly be accidental, since 

 the proportion of that acid to the other constituents of the mi- 

 neral is so nearly the same in all of them. 



The first variety examined by M. Wohler, was the green 

 lead-spar from Zschopau, being one of those which Klaproth 

 had analyzed. The muriatic acid was determined by adding 

 nitrate of silver to the solution of the mineral in nitric acid. 

 To ascertain the quantity of lead, a fresh portion was dissol- 



