26 UNIVERSITY OF COLORADO 



ing water, discard the solution in the casserole, being careful that no 

 lead has escaped. Now remove the Al foil and, with the finger cot, 

 remove any adhering lead, wash the foil with boiling water, decant- 

 ing as closely as possible the last time. Pour over the piece of Al 

 foil 6 cc. dilute nitric acid, to dissolve any particles of lead adher- 

 ing to it, remove the foil with a glass rod, washing it slightly with 

 a stream of water from the wash bottle, heat the acid in the cas- 

 serole to boiling so as to dissolve the particles of lead, then pour 

 it upon the greater portion of lead in the beaker, heat until dis- 

 solved, add a few drops of an acid solution of phenolphthalein, then 

 add a solution of sodium hydroxide until slightly alkaline, then 

 10 cc. of a solution of oxalic acid (1 in 10), cool, filter, wash with 

 cold water several times until excess of oxalic acid is removed. 

 Remove the filter paper from the funnel, open against the side of 

 a No. 2 beaker, wash the ppt. from the paper into the beaker with 

 hot water, add 5 cc. dilute sulphuric acid and titrate with a solution 

 of potassium permanganate made by diluting 1 volume of the 1$ 

 solution with 4 volumes of water, making a solution of which 1 

 ce.=.002 Fe. Multiply the value of the solution in Fe by 1.85 to 

 obtain its value in Pb. 



Comparing the equations, 



10 FeS<V2KMn0 4 +8H 2 S0 4 = 5Fe 2 (S0 4 ) 3 +K 2 S0 4 +2MnS0 4 +8H 2 

 and 



5 PbC 2 O 4 +2KMnO 4 +8H 2 SO 4 =10 C0 2 +2MnS0 4 +K 2 S0 4 +5PbS0 4 +8H 2 

 we see that the same amount of potassium permanganate will ox- 

 idize 5 equivalents of Pb oxalate, or 10 equivalents of ferrous sul- 

 phate. 5x207, the atomic weight of lead, therefore, are equivalent 

 to 10x56, the atomic weight of Fe. From this we obtain the above 

 factor. 



5X 207 



560 



=1.85. 



Copper. — Cyanide Method. — Weigh 1 gram into an 8-oz. flask, 

 add from 8 to 15 cc. strong nitric acid (according to the amount of 

 sulphides in the ore), then add 5 cc. strong H 2 S0 4 , and evaporate 

 to white fumes over a strong heat, eliminating all nitric acid. 

 When the flask is full of white fumes, remove and place on a piece 

 of asbestos to cool; when cold, add 30 cc. cold water and 6 grams 

 of sheet zinc in strips; allow to stand until the evolution of hydro- 

 gen has nearly ceased, then add 10 cc. strong commercial H 2 S0 4 



