METHODS OF ANALYSIS 11 



tion with acids is perfect when the slag is chilled, but as the slags 

 become more acid they become more difficult to decompose, and 

 when slags approach 40^ silica, the decomposition is no longer sat- 

 isfactory. 



In all lead smelters at least one sample of slag is analyzed 

 daily, and from the analysis the fluxes are adjusted. This slag 

 analysis is the first thing taken up by the chemist when he arrives 

 at the plant in the morning, and since the results are expected by 

 10 a. m., very rapid methods are required. 



The figures required, generally, are silica, iron, lime, zinc, 

 manganese, magnesium and alumina; lead and silver are deter- 

 mined by fire assay. A separate portion of ^ gram is weighed out 

 for iron, manganese, zinc and alumina; silica and lime are deter- 

 mined on one weighing. 



The slag is usually delivered to the chemist ground and 

 screened, so that he may weigh up at once. 



DETERMINATIONS. 



Iron. — To ^ gram of slag add 20 cc. boiling water and 15 cc. 

 strong HC1. Boil until action ceases. Now add three drops of 

 stannous chloride solution and allow to cool. When cool add 15 

 cc. HgCl 2 to neutralize the excess Sn. *Titrate with Bichromate so- 

 lution, using Potassium Ferro-cyanide indicator. 



Silica and Lime. — Weigh into a No. 3 R.B. casserole \ gram 

 of slag, moisten with water and add 4 to 5 cc. HC1 and stir with a 

 glass rod;-f- while stirring the silica can not gelatinize. Evaporate 

 to dryness on the hot plate, being careful to avoid "spitting." 

 Take up with 5 cc. HC1 and 5 cc. water and boil. Dilute, filter into 

 a beaker containing 10 cc. of nitric acid. Burn filter paper in a 

 porcelain crucible in the muffle, cool, and weigh. 



To the filtrate, acid with nitric acid, add ammonia until all the 

 iron is precipitated, redissolve the iron in oxalic acid and boil. 

 Filter off the calcium oxalate and wash two or three times with 



* In practice this is the first one out and is not titrated at once, being allowed to cool until 

 the manganese is also ready to titrate. This method of complete solution of the slag 

 in water and HC1 is of value in another way, as it gives an indication of incomplete 

 reduction in the furnace— i. e., if the solution has a yellow color it shows that some of 

 the iron is present in the ferric state, and when this is the case it may be necessary to 

 give an increased amount of fuel: such a fact should be noted on your report. 



tKeep stirring while adding the acid in order to keep the silica from gelatinizing into 

 lumps. 



