62 INJURY BY SMELTEE WASTES. 



dilute with 10 cc of arsenic-free water, and boil to break up the nitro-sulphuric acid 

 formed. WTien cool, dilute with water and deliver into the Marsh-Berzelius apparatus 

 previously described. 



Soluble arsenic. 



Weigh from 1 to 3 grams of the finely ground cattle food, according to the amount of 

 soluble arsenic present, and transfer to a beaker. Extract on the steam bath with 50 

 to 100 cc of water for four hours. Filter, -wash, and evaporate the filtrate to a small 

 bulk. Transfer to a 200 cc Jena flask and evaporate to only a few cubic centimeters. 

 Add 25 cc of concentrated arsenic-free nitric acid and 5 cc of concentrated arsenic-free 

 sulphuric acid, and proceed as in the preceding method for total arsenic. 



ORES. 



Sulphur.O' 



Treat 0.5 gram of the ore in a 6-oz. flask with 10 cc of strong nitric acid. Heat very 

 gently until the red fumes have somewhat abated, and then add potassium chlorate in 

 small portions at a time (about 0.2 to 0.3 gram) until any free sulphur that has separated 

 is entirely oxidized and dissolved. The acid should not be boiled violently, nor 

 should it simply simmer. When the sulphur has entirely disappeared, boil the solu- 

 tion to complete dryness. (This may be hastened by manipulating the flask over a 

 free flame.) After cooling cautiously add 5 cc of strong hydrochloric acid. If iron 

 oxid, etc., still remains undissolved, gentle heat the hydrochloric acid mixture until 

 solution is as complete as possible, adding more acid if necessary. Finally boil to 

 dryness. Repeat this operation. Take up once more in 5 cc of hydrochloric acid 

 and dilute with about 100 cc of hot water. Make alkaline with ammonia and then 

 add 10 cc of a saturated solution of ammonium carbonate in order to convert any lead 

 sulphate present to carbonate and thus render the combined SO^ soluble as ammonium 

 sulphate. Heat to boiling, allow ferric hydroxid, etc., to settle, filter, and wash very 

 thoroughly with hot water, receiving the filtrate in a large beaker. 



Neutralize with hydrochloric acid and add 5 cc extra. Dilute to about 300 cc and 

 precipitate with barium chlorid in the ordinary way. 



Arsenica 



Thoroughly mix 0.5 gram of the finely ground ore in a large platinum crucible with 

 5 grams of a mixture of equal parts of dry sodium carbonate and potassium nitrate. 

 Reserve a portion of the mixed salts for use as a cover. Heat the mass gradually over a 

 Bunsen flame to complete fusion. Use a very low flame at first and take plenty of 

 time to avoid loss of arsenic by volatilization. Finally heat to the full power of the 

 Bunsen burner until thoroughly decomposed. The melted mass should finally present 

 a smooth and homogeneous appearance. Cool, extract the soluble portion by heating 

 with water, and filter and wash the residue with hot water. Drop a piece of litmus 

 paper into the filtrate and make slightly acid with nitric acid, adding enough to dis- 

 solve any precipitate that may have formed. Add a sufficient quantity of a solution 

 of silver nitrate, which will usually cause a white precipitate of silver chlorid, and then 

 cautiously add ammonia until, if arsenic be present, a reddish precipitate of silver 

 arsenate appears. If too much ammonia be added the precipitate first formed will 

 redissolve and may not be observed at all. Cautiously add dilute nitric acid until the 

 red precipitate just redissolves. To the faintly acid liquid add a few cubic centi- 

 meters of a strong solution of sodium acetate to replace the free nitric acid by acetic 

 acid. All the arsenic will now at once precipitate as silver arsenate (Ag3As04). 



a Low's Technical Methods of Ore Analysis, 



