clogz said:
clogz said:
RalphLambrecht said:That's not what I meant. Of course, agitation helps diffusion, because the greater the concentration differential the faster the diffusion, and optimum agitation ensures the highest differential possible until equilibrium is reached. After that, only an exchange with fresh water will do. But I was looking for something else. Absorption?
If you want to have a couple of minutes to do something else, do the Ilford process for the first 5 and 10 inversions. If you used initial rinse and vigorous agitation, the residual thiosulfate level is already very low at this point. Instead of the last step of 20 inversions, fill with fresh water, and leave it for a few minutes (or longer). Feel free to boil water and make a cup of tea. By the time you come back the film is ready to dry. This saves a lot of water with little extra work.Roger Hicks said:Some find it quicker and easier to wash with running water because they can do something else while the film is washing. If I lived somewhere that there is never a shortage of water I might do the same.
RalphLambrecht said:Adsorption. That's the one.
So talking about paper now, how does diffusion and desorption influence the wash? I assume diffusion comes first, but then 'total' desorption has to take place before a final diffusion can do the rest, or do we depend on wash-aid to take care of desorption. This is not clear to me.
I know, but I still suggest that you search first and come back if there's any specific question. That question came up so many times and, besides someone often come up with bizarre theory or implausible mechanisms, the conclusion is always the same, and it hasn't changed for decades. I have no fun repeating it. And I'm not hired to do public lecture on APUG or anything. It's taking my time. My Wiki has the answer to your question and more info. It gets several thousand hits each week and there is no reason to expect difficulty in searching there.RalphLambrecht said:That's not very helpful, [...]
I'll bite. Why is that?Ryuji said:Using demineralized water for washing is not recommended. The author probably used it for conductivimetry in his laboratory, and that's fine, but tap water is generally much more effective washing water than distilled, demineralized or deionized water.
RalphLambrecht said:I wish Richard Knoppow would be on APUG.
Because tap water contains a small amount o f carbonic acid and bicarbonate, which act as a very mild (but effective) washing aid. If you use sulfite washing aid, the difference is relatively unimportant. Or you can add some bicarbonate to deionized water for washing purpose.Bruce Watson said:I'll bite. Why is that?
Agreed.Kirk Keyes said:I've done the methylene blue test on microfilms and it's not really a hard test. Not as easy as a single solution spot test, but not difficult by chemistry lab levels.
I've got instructions on how to do this type of test (i.e. not the ANSI or ISO standard, but a company SOP) if anyone is interested.
Kirk Keyes said:Ryuji - can you find a working link on Kodak's web site for the reference you give? Module 3 seems dead from what I can see. http://www.kodak.com/US/en/motion/support/processing/h24.shtml
But if the mechanism is actually diffusion, this shouldn't matter. I don't see how this would cause diffusion to work any better or faster. One would think (and I'm certainly not a chemist, so this one might think this wrongly) that deionized water would make the diffusion process as fast as it's going to get.Ryuji said:Because tap water contains a small amount o f carbonic acid and bicarbonate, which act as a very mild (but effective) washing aid.
Again, diffusion is only one part of washing, and it is not even rate-limiting stage. The rate limiting stage is desorption, especially if deionized or distilled water is used.Bruce Watson said:But if the mechanism is actually diffusion, this shouldn't matter. I don't see how this would cause diffusion to work any better or faster. One would think (and I'm certainly not a chemist, so this one might think this wrongly) that deionized water would make the diffusion process as fast as it's going to get.
Ryuji said:I have a link to their PDF file (methylene blue test section only) from my wiki page "residual thiosulfate tests" just stick this in the search, and click on the section on methylene blue test.
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