12 UNIVERSITY OF COLORADO 



hot water. Put filter paper containing the calcium oxalate in a 

 beaker, half fill with boiling water and add 10 cc. dilute sulphuric 

 acid, warm and titrate with potassium permanganate. 



*The nitric acid is used in the second stage to oxidize any lead 

 or copper sulphides which may be present and which are not de- 

 composed by HC1 alone. The amount of lead present will invaria- 

 bly be dissolved by the acids present and pass readily into the solu- 

 tion. 



There is invariably a small amount of carbon in the slag which 

 will make the silica look dark before ignition, but burns off in the 

 muffle. 



Care must be taken in the evaporation to dryness not to heat 

 too strongly; sometimes the iron when too strongly heated becomes 

 oxidized to Fe 2 3 and obstinately refuses to dissolve, in which case 

 a new determination is necessary. 



This, while a very rapid method for determining the lime, is 

 not free from error. The precipitate is liable to contamination 

 with zinc, manganese, lead and copper oxalates (the latter being 

 completely precipitated), hence the results usually obtained on or- 

 dinary lead slags are about \$, too high. 



The technical term "silica" embraces all that is insoluble in 

 acids. 



Manganese. — Weigh out in a No. 2 beaker \ gram of slag 

 and treat with 20 cc. water and 5 cc. nitric acid and boil well. Di- 

 lute with hot water, add enough zinc emulsion to neutralize, titrate 

 with potassium permanganate solution. Since this solution is 



165 

 standardized with iron, we have simply to multiply by =.2946 



560 

 to obtain the value in manganese. 



Another method is to add boiling water, then 4 to 5 cc. of HC1, 

 then 4 to 5 cc. of nitric acid, then 4 to 5 cc. of sulphuric and evapo- 

 rate carefully to dryness. Take up with water and boil 5 to 10 

 minutes, then add zinc emulsion and proceed as before. 



Zinc. — To \ gram of ore in a No. 3 R.B. casserole add 10 cc. 

 of chlorate mixture (a saturated solution of potassium chlorate in 



* It will be observed that no nitric acid is used during the first evaporation; this is to avoid 

 the oxidation of the sulphur which is combined in the slag as a sulphide, and which by 

 treatment with HC1 alone is eliminated as H 2 S. If the sulphur were oxidized to sul- 

 phuric acid, some barium sulphate would be formed, and remaining with the silica, 

 make the result too high. 



