METHODS OP ANALYSIS 25 



slag is mixed with about 3 times as much fusion mixture, and 

 ^ gram of potassium nitrate (this is added to keep the lead from 

 reducing and spoiling the crucible) and fuse in a platinum crucible 

 in the muffle. Cool the crucible and place in a No. 4 casserole 

 with about 50 cc. boiling water, boil until clean, take out crucible, 

 rinse with hot water, using finger cot if necessary, boil until dis- 

 solved. Cover with a watch glass and add through a pipette 10 cc. 

 strong HC1, wash off the cover, remove it, and evaporate to dryness. 

 Treat the dry mass with 50 cc. dilute HC1, boil, dilute with 50 cc. 

 water, filter, wash, ignite, and weigh silica. 



Iron. — To the filtrate add ammonia in slight excess to ppt. the 

 iron, filter and wash, dissolve the ppt. in dilute HC1, and proceed 

 in the usual way. 



Lime. — To the filtrate from the iron add 10 cc. of a 10$ solu- 

 tion of oxalic acid, then make slightly alkaline with ammonia, boil, 

 allow to settle, filter, wash, proceed in the usual manner. 



Lead. — The purchase and sale of lead ores is at present based 

 on the fire assay. This method, though inaccurate, appears to meet 

 the commercial requirements.* The titration by ammonium molyb- 

 date already given is the method in general use where lead is 

 determined in the wet way, but another way, by titration with 

 potassium permanganate, is also in use. 



In this method the lead is separated first as metal, then dis- 

 solved and ppted. as oxalate, the acid oxalate being titrated with 

 permanganate of potassium. 



Treat ^ gram of ore with 15 cc. strong nitric and 10 cc. strong 

 sulphuric acids, and evaporate to white fumes over a strong heat, 

 cool, add 50 cc. cold water and 2 grams of Rochelle salts, boil, filter, 

 wash with dilute sulphuric acid (1 to 1), and then with water. 



Wash the lead sulphate back into the casserole, add 10 grama 

 ammonium chloride, 25 cc. water, and boil until dissolved; filter 

 and wash with a little more solution of ammonium chloride, wash 

 with boiling water. The filtrate should be received in a No. 2 

 beaker, containing the Al foil, such as was used in the Cu deter- 

 mination. Boil five minutes, when the lead will be completely ppt., 

 and, if in considerable quantity, will usually separate from the 

 foil and unite into a spongy mass. Decant the solution from the 

 lead and aluminum into the casserole and fill the beaker with boil- 



* The Colorado Scientific Society are at present gathering information regarding: the best 

 method of determining lead. 



