30 UNIVERSITY OF COLORADO 



15 cc.'s of 1 to 10 sulphuric acid. Place platinum cylinder into 

 the solution, connecting it with the negative or zinc element of the 

 batten-; inside the cylinder place a platinum wire spiral, reaching 

 almost to the bottom of the beaker, being careful not to allow the 

 spiral to touch the cylinder. 



A very good battery for this purpose is a Bunsen cell; about 

 eight hours is usually required for a total precipitation of the 

 copper. To determine whether or not all the copper has been 

 ppt., remove a few drops of the solution in a pipette and 

 test it with ELS water. If the test shows that all copper has been 

 removed, then, without turning off the current, remove the cylinder 

 and place immediately into a beaker of warm water, so as to wash 

 off as quickly as possible all acid from the cylinder. After the 

 cylinder has been thoroughly washed, place it in a beaker of alco- 

 hol, which removes the water, then dry as quickly and carefully 

 as possible, avoiding the oxidation of the copper on the cylinder. 

 The ppt. copper should be a bright rose-red color. 



In case the ore contains only a trace of arsenic, antimony, or 

 bismuth, the precipitation of the copper on the aluminum foil may 

 be dispensed with. In that case, after the ore has been dissolved 

 and the mass disintegrated, add enough ammonia to just neutralize 

 this solution, add ^ gram NH 4 N0 3 and 15 cc. of 1 to 10 H 2 S0 4 , and 

 place on the battery as before.* 



COLORIMETRIC COPPER DETERMINATION. 



To make up the standard: One gram of C.P. copper foil is 

 dissolved in just as little HN0 3 as possible, then 10 cc. more of 

 HN0 3 is added. Thoroughly boil off the red fumes, and add dis- 

 tilled water up to 1000 cc. From this solution 1 cc. is used for 

 every 1/10^. Make alkaline with 20 cc. NH 4 OH, and add enough 

 distilled water to bring the bulk up to 350 cc. The standards are 

 placed in large salt-mouthed bottles of colorless glass, with glass 

 stoppers. These are kept in a suitable rack, which is lined with 

 white paper, and placed in a well-lighted part of the room. 



Slags and Tailings. — Weigh 2 grams of the pulp into a No. 2 

 beaker, add 5 cc. HC1, and take to dryness on the steam bath. Take 

 up with 5 cc. HNO3 and boil until copious fumes are driven off. Now 

 add distilled water and remove from the plate. Add 20 cc. NH 4 OH, 

 and filter into the glass bottles. Wash twice with boiling water, 



* From Chemists' Handbook. Western Chemical Co. 



