Processing kodak motion picture films, module 3 analytical procedures

Determination of Silver in Thiosulfate Fixing Baths
(A Non-Instrumental Method Using Thioacetamide)
1209D
Process ECN-2 ECP-2D VNF-1/LC RVNP
Formulas F-34a F-35b
F-35c
F-36 F-38
PRINCIPLE
This technique is basted on the work of Bush, Zuehlke, and
Ballard, * but no instrument is required. The silver in a fixing
bath is titrated, in effect, by adding graduated amounts of a
thioacetamide solution to samples of the bath that have been
adjusted to a pH greater than 12. At this alkalinity,
thioacetamide decomposes to sulfide which immediately
precipitates a chemically equivalent amount of silver sulfide.
The silver sulfide is filtered and the filtrate is tested for
completeness of silver precipitation by adding more
thioacetamide.
It is probable that this method will be used most frequently
to determine the amount of silver in a fixing bath before and/
or after the fixing bath has passed through the Kodak
Chemical Recovery Cartridge and associated Kodak
Circulating Unit. A fix which has passed through this silver
recovery unfit contains moderate amounts of ferrous iron
ion. This method assumes that every fixer contains Iron II
ions and includes a step to remove their effect before the
conventional silver determination.
The fixing solution must not have very much color,
although some can be tolerated if a suitable blank is used.
The practical extremes of measuring silver concentration
by this technique are presented as Procedures A and B.
Procedures C and D illustrate very useful specific
modifications.
Procedure A – Rapid Determination of the Approximate
Silver Concentration in Thiosulfate Fixing Baths.
Procedure B – Determination of Silver in Thiosulfate
Fixing Baths. (This is a more precise procedure making
use of pipets and burets.)
Procedure C – Determination of Silver in Thiosulfate
Fixing Baths When Concentration of Silver is Less Than
0.5 Grams per Liter.
Procedure D – Special Application of Procedure C for
Determination of Exhaustion of Kodak Chemical
Recovery Cartridge.
* D. G. Bush, C. W. Zuehlke, and A. E. Ballard, Analytical Chemistry, 31,
1368 (1959).
RELIABILITY
Eight fixing baths were prepared containing known amounts
of silver and varying in pH from 4 to 10. Each contained
some of the following items: conventional sequestering
agents, sulfite (bisulfite), carbonate (bicarbonate),
thiosulfate (sodium or ammonium), formaldehyde, acetate,
borate, potassium alum, anti foaming agent, and citrate.
The fixers were analyzed using Procedure B. End points
were determined to 0.05 g/L. Of 30 results in the range from
0.50 to 6.00 g/L all were within 0.10 g/L of the nominal
value and there appeared to be no bias.
Ten acid hardening fixes were prepared to contain either
0.50 g or 5.00 g of silver and 0.1 to 10 g of Iron II ions.
These were analyzed according to Procedure B and all
results were within ± 0.2 g/L of the mix level.
SPECIAL APPARATUS
100-ml Glass-Stoppered Graduated Cylinder
(VWR Scientific, catalog no. 24760-100)
10-ml Graduated Cylinder
(VWR Scientific, catalog no. 24710-044)
Filter Paper, Whatman No. 3 (12.5 cm diameter)
(VWR Scientific, catalog no. 28456-101)
Torsion Balance, sensitivity 0.01 g
REAGENTS
6.0 N Accelerator Reagent
0.00926 N Thioacetamide
0.1 M Potassium Ferricyanide
0.2 M Potassium Ferricyanide
Processing KODAK Motion Picture Films, Module 3, Analytical Procedures H24.03 1