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analog what is that?
02-08-2012, 11:12 PM
...

analog what is that?
02-08-2012, 11:13 PM
,,,,,,,

Gerald C Koch
02-08-2012, 11:13 PM
It's probably best not to make any generalities about APUG. I think that the contributers are a diversified group. What binds them together is a love of photography. I don't usually toot my own horn as that is not my style. Very briefly for the record I have a BS in chemistry, an MS in nuclear chemistry, and a BS in computer programming. For a number of years I worked at the Kennedy Space Center.

Jerry

Kirk Keyes
02-08-2012, 11:39 PM
Sweet, Jerry! What did you do there?

The only thing I've done at KSC is visit and buy t-shirts!

albada
02-09-2012, 12:01 AM
I might need a new pH probe. A few questions:

1. What brand/model would you recommend for a price of around US$60?
2. Should I pay extra for a high-salinity/high-alkalinity probe?
3. Is it normal for a probe to need a few minutes to acclimate to a high sulfite solution?

My Hanna pHEP-5 probably needs a new probe. It has always needed about 4 minutes to acclimate to a sulfite solution. Once acclimated, it responded quickly to changes in pH. But this evening, the pH started dropping as I was watching it. Adding alkali failed to raise pH. Due to Hanna's poor packaging, this probe was dry when I got it a month ago, so I expected it to be a short-liver.

Based on my Internet research, I discovered that all pH probes have the same electrical behavior at the connector. So I figure I'll hack a BNC-connector onto my pHEP-5 meter, and attach a better probe to it. Does anyone know of a reason this will not work?

TIA!

BTW, I'm a computer science geek. But in college, I almost became an EE (electrical engineer), and I've tinkered with electronics all my life, so I know enough about electronics that companies have me work with their EEs, since I'm one of the few programmers around who can read circuit-diagrams and talk EE-lingo. EEs and I get along great.

Mark Overton

Ryuji
02-09-2012, 01:47 AM
It's probably best not to make any generalities about APUG. I think that the contributers are a diversified group. What binds them together is a love of photography.

I take this as your reaction to my previous post, which I think was overstated my sentiment, but I hope people understand that I spent a LOT of time posting information online, this site and several other places before APUG started. But I was seriously troubled by several people on this website, who demanded information as if they were entitled to anything and everything I know or figured out. I simply donít shouldnít be obligated to share information when I know from experience that Iíll be facing a lot of questions or requests that I canít help. That ďopen sourceĒ phrase, while I used it myself in relation to darkroom chemistry, was also previously used by some in the very context above and I personally donít need to see that again. When people say whatver to justify pressuring me to share information I get irritated!!!

Ryuji
02-09-2012, 01:56 AM
I might need a new pH probe. A few questions:

1. What brand/model would you recommend for a price of around US$60?
2. Should I pay extra for a high-salinity/high-alkalinity probe?
3. Is it normal for a probe to need a few minutes to acclimate to a high sulfite solution?

My Hanna pHEP-5 probably needs a new probe. It has always needed about 4 minutes to acclimate to a sulfite solution. Once acclimated, it responded quickly to changes in pH. But this evening, the pH started dropping as I was watching it. Adding alkali failed to raise pH. Due to Hanna's poor packaging, this probe was dry when I got it a month ago, so I expected it to be a short-liver.


What you described is one of the typical symptoms of clogged or chemically deteriorated reference electrode junction.

You should get a double junction and refillable probe. Replace the fill solution every time you use the probe. It is usually best to replace the fill solution at the end of shift.

High alkalinity electrodes use slightly different glass membrane, which is important at pH 13 and above. They are not really needed for photographic applications. The place that gets shot in photographic applications is the reference junction.

Usually, high salt solutions are faster to settle/stabilize reading. If your reading doesnít stabilize in a few minutes at 25C, the reference electrode is the first place to check.

There are two common causes for unstable reading, when the electrode is perfectly normal. One is low temperature. Measurement at 20C is not very good idea for this reason. This 5C difference is big for the glass membrane. Another cause is when you clean the electrode. If you use brush or other mechanical means to clean the glass membrane, forget it. Put the electrode in 3M KCl solution and go for lunch. You wonít be making any meaningful reading for about 2 hours. You can't even calibrate the system. This is yet another reason why it is best to clean the electrode at the end of each shift.

Another possible place to go wrong is moisture or conductance leak. The input impedance of the pH meter amplifier is REALLY high. Slight moisture can cause significant leakage that affects the sensitivity "slope" of the electrode. This is common with cheap pH "tester" type devices. I remember throwing away a few of those testers for this. (But all of them used gel filled reference junction, that gets killed by the test solution in a few weeks anyway.)

The least expensive electrode I know suitable for photographic work is Hanna HI-1333. It's cheap because Hanna sells it as "student lab grade" or "fish tank" or "field monitoring" use and not really rated for analytical lab use. At least that's what Hanna tech support told me years ago. That's good enough for routine darkroom use. When I had a deep tank line for film, and slot processor set up for prints, HI-1333 was used in the processing station to monitor the health of those solutions, but it never failed on me unexpectedly. I think I replaced the electrode only once in a 10 year period (but I did take very good care of it. most people kill the electrode in less than 2 years.) and the second electrode is still alive (I just took it out of the storage).

Ryuji
02-09-2012, 02:46 AM
Based on my Internet research, I discovered that all pH probes have the same electrical behavior at the connector. So I figure I'll hack a BNC-connector onto my pHEP-5 meter, and attach a better probe to it. Does anyone know of a reason this will not work?

You need to be very careful in choosing low leakage BNC connectors, wiring and whatever connector used in your pHEP-5 (Molex maybe?). Those lines have to be VERY high impedance (on the order of hundreds of megohms) and well shielded from noise. The bandwidth of the amp is very low, so you mostly worry about low frequency inductive noise. Also be very careful about each connection. You want to minimize flicker noise (a.k.a. 1/f noise or pink noise), which will appear as the drift in the reading. Usually, you get most of the noise from the electrode itself but just try not to add any.

BNC connectors are usually designed for constant RF impedance, but that actually doesn't matter for pH measurement. What matters for this is leakage.

Ian Grant
02-09-2012, 08:26 AM
How many people here actually have experience in debugging misconceptions, gross oversimplifications, and other errors in popular darkroom "chemistry" books?
How many people here actually identified a problem, formed a design objective and offered practical solutions to it through a systematic approach?
How many people here have a paper on photographic chemistry published in a peer reviewed academic journal?

There used to be a couple, but they've moved on.

I seem to remember a section on your own website based around a misprint in a US book of amount of Bromide in the ID-78 formula, and despite the error being pointed out to you many times over a few years you never corrected it even though you quoted elsewhere from two primary sources with the correct version of the formula (one an Ilford Manual, the other a book by an Ilford chemist - LFA Mason). Hardly good academic practice.

One problem with many of the Darkroom "Chemistry" books published in the US was they were riddled with errors and mistakes because nearly all the formulae were taken from copies of he Photo Lab Index (where the mistakes were first made) andnot original primary sources. Steve Anchells 3rd Edition of "The Darkroom Coobook" was the first book to be cross-checked where ever possible with manufacturers published data and as a consequence many formulae were corrected.

A classic example of the misprints is the Pyrocatechin compensating formula attributed to Hans Windish (he doesn't clain it as his own in his books) this was published correctly in Jacobson's Devloping (1st Edition) as well as in Windisch's own book, however a BJP Almanac in the late 1940's or early 50's publishes a US version of the formula where the qunatities of Pyrocatechin and Sulphite have been transposed, this version happened to work as well although differently.

How many people here actually identified a problem, formed a design objective and offered practical solutions to it through a systematic approach?

Quite a number of us actually, however often work could not be published due to commercial secrecy.

Ian

Photo Engineer
02-09-2012, 09:29 AM
Mark;

I have had 3 Hanna electrodes, and none have given me any problems. I used many at work as well. We never used "special" electrodes for high salt or high pH and always got good results.

The symptom you describe could also be due to a cracked glass bulb on the electrode. This would also give the result that the electrode would eventually empty of all solution. This has been my experience when having problems. A broken electrode.

PE

Gerald C Koch
02-09-2012, 03:16 PM
I take this as your reaction to my previous post, ...

Hi Ryugi,

My post was only to caution everyone that we really know very little about others that post on APUG and shouldn't make generalities about their knowledge and qualifications. In my own experience I have said things which I soon regretted. Now commuicating with people in this wonderful age on a text only basis is difficult. Things that are easily understood verbally are often misunderstood as text.

Jerry

albada
02-10-2012, 01:26 PM
Thanks for the interesting info about pH-probes. I ordered a compatible replacement, which lets me procrastinate on hacking a BNC with its potential problems.

You can drive water out of propylene glycol by heating.

Last night, I verified that one can drive water out of propylene glycol by heating it to close to 100C. My idea came from Tom Hoskinson's observation in this thread:
http://www.apug.org/forums/forum37/33112-any-hazards-mixing-catechol-hot-propylene-glycol.html
In it, he states that "If you heat straight propylene glycol to 160F it will give off some water vapor."

This is important to me because sodium metaborate contains some water (as Rudeofus pointed out), and Borax has much more. Plus, some reactions with ascorbic acid produce water. I want as little water in a concentrate as possible to avoid absorbing oxygen and oxidizing developer. So I put 2.5 ml of PG in a beaker, weighed it, and added 1 gram of water. Then I heated it to just under 100C, and weighed it every 5 minutes. Here are the water-weights (ie, initial weight was subtracted):

Min ... Water
0 ...... 1.00
5 ...... 0.76
10 .... 0.32
15 .... 0.16
20 .... -0.08
25 .... -0.16
30 .... -0.23

I could see a wisp of steam rising from the beaker the whole time. The negative numbers mean I lost more than 1 gram, which I attribute to (1) A couple of drops of carry-out on the thermometer-stem, and (2) water in the original PG.
My conclusion: Heating PG drives water out of it.

But a couple of warnings: (1) Keep the temperature below the 99C flash-point of PG. Above that, flammable PG-vapor can run down the outside of the beaker onto the heater and ignite. (2) Staying below 100C also avoids what chemists call a "bump" wherein a sudden bubble of steam blasts hot PG everywhere, including your hands and face. So go ahead and heat your PG-based concentrate to dry it -- but I suggest not going over 90C.

Mark Overton

albada
02-10-2012, 01:53 PM
My second posting to this thread today...

Last night, I also discovered a way to dissolve a large amount of ascorbic acid into propylene glycol (PG). The trick is to include enough alkali to convert the ascorbic acid into ascorbate. Here's what I mixed:

Propylene glycol ................. 9.75 ml
Ascorbic acid ..................... 5.5 g
Sodium metaborate 4 mol ..... 4.25 g

This is a developer I'm working on, but without the Dimezone in it yet. I chose 9.75 ml of glycol because 9.75 is the weight of the two powders, so the g/ml ratio (powders/PG) is 1.0. I figured there's no way so much powder could dissolve at such a high ratio, so I planned to add more PG as I went. I heated the above to 70-90C, and... you guessed it... it all dissolved! It took 20-30 minutes of constant stirring followed by intermittent stirring, but it all dissolved. And there's no precipitation upon cooling to room-temperature.

So the good news is: You can achieve a very high concentration by converting some/all of the ascorbic acid to ascorbate in situ. For comparison, the g/ml ratio for Gainer's PC-Glycol is only 0.1333. But there's a cost to such high concentration: Its viscosity at room-temperature is like honey or cool pancake-syrup. It's still pourable and measurable, but I don't think I'd want to push that ratio much above 1.0.

Mark Overton

Rudeofus
02-10-2012, 05:14 PM
You can drive water out of propylene glycol by heating.
Chemists call this distilling, you take advantage of sufficiently different boiling points of two substances and it is a process not only used by chemists :p

This is important to me because sodium metaborate contains some water (as Rudeofus pointed out), and Borax has much more. Plus, some reactions with ascorbic acid produce water. I want as little water in a concentrate as possible to avoid absorbing oxygen and oxidizing developer.

I think I also pointed out that traces of water barely matter when it comes to trapping oxygen, and I'm not even sure whether trapped oxygen actually mattered that much in such a solution. Pat Gainer apparently mentioned (http://www.flickr.com/groups/pc-tea/discuss/72157622857551374/) that a few ml of water in the concentrate did not affect shelf live. Sorry, I didn't find the original quote from him.

albada
02-10-2012, 07:32 PM
I think I also pointed out that traces of water barely matter when it comes to trapping oxygen

What concerns me is the molar ratio of liquids. In my formula at the top of this page, for example, the metaborate will produce 1.13 g of H2O after reacting with the ascorbic acid. That sounds small, but on a molar-basis, that's one third of the molecules of liquid. That's enough to concern me, and is a question for the chemists here: Will a solution of 67% PG and 33% H2O (molar ratios) absorb a significant amount of oxygen?


Pat Gainer apparently mentioned (http://www.flickr.com/groups/pc-tea/discuss/72157622857551374/) that a few ml of water in the concentrate did not affect shelf live. Sorry, I didn't find the original quote from him.

I seem to recall reading that quote also. He was suggesting adding a little water to PG to help dissolution. But a quantity of water that's small on a volumetric basis is surprisingly high on a molar basis, so I'm being cautious.

I'm thinking that mixing hot PG has two benefits: Speedy dissolution, and removal of water. The question is: Is the amount of water harmful? If not, dissolution can be accomplished using Gerald Koch's method: Let the brew sit for hours at room-temperature, shake the bottle on occasion, and all will eventually dissolve with no heating needed.

Mark Overton

Kirk Keyes
02-11-2012, 12:38 AM
Will a solution of 67% PG and 33% H2O (molar ratios) absorb a significant amount of oxygen?

OK - I'm a chemist that has worked with dissolved oxygen in water.

At 20C, a saturated solution of oxygen in water has a concentration of 9 mg of oxygen per liter of water. That's a saturated solution. A supersaturated solution can have a higher concentration of oxygen in it, but it will loose oxygen until it becomes a saturated solution. And as the temperature of the water goes up, the solubility of oxygen in it rapidly decreases.

I can't say what effect having glycol in there will do to the solubility of oxygen in water.

A liter of water really can't hold a lot of oxygen. What kills developers is exposure to oxygen through permeable bottles and caps, poorly sealed bottles, or agitation of the developer in an oxygen environment. Like using bottles fitted with a rubber bulb is a poor choice as a storage container.

Anyone that's used pyro developers can tell you how fast they oxydize in a Jobo tank. And anyone that's used pyro developers in a Jobo tank fitted with a nitrogen-purge line will tell you how well pyro developers can work in a Jobo tank.

Rudeofus
02-11-2012, 04:20 AM
I can't say what effect having glycol in there will do to the solubility of oxygen in water.
The problem as stated by Mark is exactly the other way round: he has traces of water in glycol. Developer in pure glycol is known to last forever, but he/we would like to know how much water is acceptable in that mix before it deteriorates too fast. Since developer action differs when it's anionic, cationic or not ionized at all (http://encyclopedia.jrank.org/articles/pages/1212/The-Chemistry-of-Developers-and-the-Development-Processe.html), the oxygen content alone may not be the only determining factor.

Alan Johnson
02-11-2012, 12:16 PM
It might be possible to get some idea of the effect of water content on rate of oxidation by dipping into the concentrate clean pieces of copper and aluminium and measuring the current flowing between them.
Or there is a test for accelerated corrosion in brake fluid:
http://www.mossmotors.com/SiteGraphics/Pages/Brake_Fluid/brake_fluid_long.html
Otherwise it may take months to find the rate of oxidation.

Rudeofus
02-11-2012, 01:53 PM
It might be possible to get some idea of the effect of water content on rate of oxidation by dipping into the concentrate clean pieces of copper and aluminium and measuring the current flowing between them.
Or there is a test for accelerated corrosion in brake fluid:
http://www.mossmotors.com/SiteGraphics/Pages/Brake_Fluid/brake_fluid_long.html

Brake fluids are tested with metal test strips because that's what's in the break lines or pistons. In our case we deal with reducing agents which work differently depending on their state of ionization. To my best knowledge, ascorbic acid lasts for a long time as a powder even if oxygen is present, yet deteriorates quickly in aqueous solution. That oxygen trapped in the glycol/water may or may not attack the ascorbic acid (or whatever dev) in there. Another factor may be catalysts: some dev deterioration processes happen rapidly if certain ions are present (e.g. iron & ascorbic acid). I don't know whether this reaction takes place in water contaminated glycol/TEA/...

Photo Engineer
02-11-2012, 01:55 PM
It has already been stated that Ferric ion in water will rapidly oxidize AA.

PE