8 r\ivi;i;srn OF COLORADO 



the siiii has completely dissolved, titrate with the volumetric so- 



lu I ion. 



:*.. Potassium Ferrocyanide. Ignite in a porcelain crucible 

 abort i gram of O.P. zinc oxide When cold weigh np two por- 

 lions of .— « m > grams, place each portion in a No. - beaker, add 25 cc. 

 boiling distilled water and 5 cc. BC1, and stir until completely dis- 

 Bolved. in another No. 2 beaker place 7 grama of ammonium chlo- 

 ride, dissolve it in LOO cc. boiling water, add L5 cc. cone ammonia 

 wiiior to It, carefully, (hen filter it Into the solution of zinc in HC1. 

 W'nsii with a little water so thai the entice bulk of solution fills the 

 beaker two-thirds full. Place on the ho1 plate, after adding a spoon- 

 ful of granulated O.P. lend,* and boil. 



Fill the burette with the standard solution and liave the spot 

 plate iend\ willi ii i:t ii i i j in acetate indicator. Now take the beaker 

 oil' the liol plate, add 1 or 2 CC. Of a concentrated solution of so- 

 dium sulphite (the solution should smell of SO.,), and titrate. The 

 end reaction is a vevy fainl pink. 



The writer has found it a good plan to divide the solution be- 

 fore adding t he sodium sulphite, leaving 20 to JJO cc. on the lead in 

 oim beaker, to this pari adding the Na.S() 3 . Titrate the other por- 

 tion rapidly until B good end reaction is reached, then pour in the 

 other part, had and all, rinse carefully and complete the titration 

 slowlv. This precaution prevents running past the end point. 



4. Potassium Cyanide. — Weigh in duplicate a piece of Cu. 

 foil approximately .200 gram, place in an 8-oz. flask and dissolve 

 in 5 CC. strong nitric acid. Boil off the red fumes, cool by dipping 

 in cold water; when cold add 20 cc. cold water, then 10 cc. strong 

 ammonia, then 5 cc. cold water, mix and titrate with the volumet- 

 ric solution of KCN until colorless. Divide the weight of the Cu. 

 taken by the number of <■<•. used. 



5. Sodium Hyposulphite. — Weigh accurately about .2 grams 

 of Cu. foil and place in an 8-OZ. flask, add 5 cc. strong nitric acid, 

 and boil off all the red fumes. (This must be carefully done, other- 

 wise trouble will follow due to nitrous acid liberating iodine.) Re- 

 move from the heat and add LB vr. water and 6 to 7 grams of zinc 



♦The addition of lead is not necessary here, but since we use it to take care of the Cu when 

 we are testing for zinc in ores (Low's Method), we desire to have the same conditions 

 present in standardizing. 



