METHODS OF ANALYSIS 31 



to wash any salts of copper out of the precipitate. Fill the bottle 

 with water to the 350 cc. mark. The bottle is then compared with 

 the standards and the reading divided by 2. 



The mill tailings run higher in copper, hence use only 1 gram. 

 Add 5 cc. of a mixture of HN0 3 +KC10 3 , and heat for 15 minutes. 

 Now add 30 cc. water and remove. Proceed as before. 



Copper, by KCN. — Weigh 1 gram of the sample into a 500 cc. 

 flask and add 10 cc. of HN0 3 ; put on a hot plate and heat gently 

 (if heated too rapidly sulphur will collect in globules and retain 

 some copper). When no more N0 2 fumes come off, add 20 cc. cold 

 water, remove, and cool. Add 200 cc. cold water and 20 cc. strong 

 NH 4 OH and titrate with standard KCN solution (1 cc. equals 0.005 

 Cu). Take about one hour for the titration, adding a few cc.'s of 

 the standard solution from time to time, and allowing the ppt. 

 to settle after each addition. When the titration is almost fin- 

 ished, filter the contents of the flask into another flask of the same 

 size and finish the titration. 



A standard should be run with each determination, taking .200 

 grams of copper foil for the standard. Run the standard exactly 

 in the same way as the assay.* 



DETERMINATION OF COPPER IN SILVER MUD AND SIL- 

 VER MILL SLAGS. 



SILVER MUD. 



Treat \ gram with 5 cc. HN0 3 , and, when action has become 

 quiet, add 3 cc. H 2 S0 4 , and evaporate to white fumes; cool, add 

 50 cc. H 2 0, and heat to dissolve the soluble sulphates; add NaCl 

 solution in slight excess, heat to boiling, remove and filter off the 

 AgCl. To the filtrate add sodium sulphite and a small excess of 

 NH 4 CNS, stir and warm; Cu 2 (CNS) 2 will precipitate; filter, wash 

 thoroughly, ignite gently in a porcelain crucible. Dissolve the res- 

 idue in 5 cc. HN0 3 , and determine Cu electrolytic-ally. 



SLAGS. 



Treat 1 gram in a Pt. dish with 6 cc. HN0 3 and 6 cc. HF. Add 

 4 cc. H 2 S0 4 , and proceed as before. 



'All samples which contain Mn, Zn, As, or any organic matter, require the addition of a 

 little KCIO,. 



