Table of Contents
Short Iodide Method
To 200 to 500 cc of solution add 10 cc HCl, 5 cc HNO3. Evaporate to about 50 cc, then cool, and add 8 cc H2SO4. Evaporate almost to dryness. Cool, add 5 cc water and 5 cc H2SO4, and again evaporate almost to dryness. Cool, add 50 cc water, and heat to boiling. Add 5 cc concentrated bromine water, and boil to expel the bromine. Cool, add ammonium hydroxide, NH4OH, drop by drop, until the ferric hydroxide precipitate just remains after stirring. Do not add an excess of NH4OH. Add 5 cc acetic acid, H(C2H3O2), and heat, stirring until the iron precipitate dissolves and the solution turns to a clear wine color. Add 1 to 2 grams sodium fluoride, NaF, the solution turning blue. Stir well, cool, and add 4 cc of 50 per cent solution of potassium iodide, KI, solution turning brown, then add a few cubic centimeters of starch solution, and titrate carefully, but quickly, with the standard sodium thiosulphate, Na2S2O3:5H2O, solution. The end point is usually sharp, the color changing from blue to a creamy white.
Standard Sodium Thiosulphate Solution
Dissolve 19.5 grams sodium thiosulphate crystals, Na2S2O3 to 5H2O, and 2 grams NaOH in a convenient amount of water, and then dilute to 1000 cc. Solution should be kept in a dark-colored bottle.
1 cc Na2S2O3 to 5H2O solution = 0.005 gram copper, Cu
On a 200-cc sample 1 cc = 0.025 gram per liter or 0.050 lb. per ton of solution.
STARCH SOLUTION
To 1.0 gram of soluble starch add sufficient water to make a paste. Then add 100 cc warm water and 0.1 gram NaOH, and bring to a boil. This solution should keep for several weeks.
Colorimetric Method
To 100 cc of solution add acids, and treat as in Method 1 to and including the second addition of H2SO4. Evaporate, and fume strongly until only 2 to 3 cc remain. Cool, add 30 cc water, and heat to dissolve the soluble salts. Filter, and wash twice with hot water. Add 50 per cent ammonium hydroxide, NH4OH, solution until just neutralized, then add 10 cc more. Warm (do not boil) until the fine precipitate just coagulates, and filter through a fine filter paper. Wash three times with hot water, then transfer to 100-cc Nessler tube, and dilute with water to the 100-cc mark.
To a second Nessler tube add 80 cc water, 10 cc NH4OH. Add the . standard copper sulphate solution 1 cc at a time until the colors match.
STANDARD COPPER SULPHATE SOLUTION. Dissolve 0.393 gram copper sulphate, CuSO4-5H2O, in water, and dilute to 1000 cc.
1 cc = 0.0001 gram copper, Cu On 100-cc sample 1 cc = 0.001 gram Cu per 1000 cc or 0.002 lb. per ton of solution.
Tins is a satisfactory method for small amounts of copper up to 0.010 gram per liter. If the copper content exceeds this figure, the method may be used on 50- or 25-cc samples.