I'm not a chemist - help Mr. Wizard.

Kirk Keyes · Jan 24, 2009

It's not about minutia, it's about learning and using language and techniques that can be used by anyone without concern that they are interpreting particular instruction one way vs. another way. A professional like Anchell must be held to a higher standard, and the correct standard. Joe Analogtog can certainly do what he feels like doing, proper technique or not. It's just when he starts talking to others, and they are doing things one way and they are doing things the other way, then confusion, uncertainty, and doubt may get in the way of good results.

10% error in adding alkali to a developer will certain have an effect. Now it may not be one that ruins a photo, but it may not be one that gives a better photo.

And remember Denise, you've got a science background, not everyone does. Reread some the posts at the beginning of this thread and see how people can get confused without good info.

pnance · Jan 24, 2009

I don't think it's been clearly stated, but almost all lab glassware are only accurate at 20 C/68 F. This is especially true for graduated cylinders, as most graduated beakers and other flasks are usually only marked approximately.

You have to return the liquid being measured to this temperature before measuring.

Paul

Photo Engineer · Jan 24, 2009

That is correct. Therefore, 1 liter of water is 998.23 grams at 20 deg C but is 1 KG at 4 degrees C where the density specification is defined. This is why a percent solution should be defined at wt/wt, wt/vol, vol/wt, or vol/vol to be more precise. Of course, this is about a 0.2% error, and that is well below what is usually problematic.

I try to stay below 5% error and more generally below 1% error as best I can.

My formulas provide for up to 10% error in any ONE item though, but if two or more are in error, then the errors compound and things will go awry. I build them that way as I expect exactly the type of problem demonstrated in this thread.

PE

dwross · Jan 24, 2009

Hi Kirk,

Far be it from me to argue with my favorite chemist in the whole, wide world... but

The problem with this kind of conversation is the complete loss of perspective. It's kind of like a fundamentalist who thinks a guitar in church is a End Times sign.

Let me leave this with just one point, and then I promise to quit. My post was about making % solutions. If I make a 1% KI solution by adding 1 g of KI to 100 ml of water, or if I make it by adding 1 g of KI to 95 ml of water and then bring the total solution to 100 ml, the difference in KI concentrations is infinitesimal. Talking about a 10% error in adding alkali to a developer is from a different Universe. To confuse the two points...well, it confuses the two points (and to no one's advantage.)

d

Photo Engineer · Jan 24, 2009

Denise, you are again right and wrong.

Your statement is right. The error in the KI solution is infinitesimal.

You are wrong in that this teaches someone the wrong way to do something, and generalizing it to the OP, the error becomes rather large. It also introduces a difference into your formula for whatever, and my formula for the ostensibly same whatever. So, what if we differ by 1/3 stop in speed or 1/2 grade in contrast? Then we argue!

PE

dwross · Jan 24, 2009

Photo Engineer said:
Then we argue!
PE

Not me. I would celebrate our differences, and the opportunity for discovery. If I particularly admired your work, I'd ask your technique and try to emulate it. Chances are I'd miss, because technique is more than the significant figures on a scale.

Please note one last time that I am advocating perspective, not sloppiness. Remember, I'm the one who insisted we stop your workshop long enough to completely clean the darkroom and remix the chemistry.

Photo Engineer · Jan 24, 2009

Well, Denise that was a collective "we" above followed by a smiley.

And yes, we did have a problem with a contaminant in the lab when the workshop started. And no, I didn't have problems the year before, or the year after. So cleanup and remixing is always indicated when there is a problem. This is why emulsion making can be hard as well as easy. I don't want anyone to be blindsided and thereby discouraged just as you don't want anyone to be discouraged by what appears to be complexity.

I believe that anyone going into scratch mixing solutions or emulsion making can do it easily once they learn the proper techniques, which are not hard at all. Making a 10% solution the right way is certainly not hard. Teaching it is not hard, but explaining the reasoning behind it has taken nearly 6 pages.

PE

Ray Rogers · Jan 24, 2009

Denise,

Well, darn it, while I was writing whats below, you'all been busy working things out already! Which is good... and makes me consider not posting what I wrote, humm... what should I do? humm hum OK, you mentioned perspective, so before I crawl back into my cave to get some sleep I will leave you with my perspective...

dwross said:
Here's an opinion (mine):

I seriously doubt the technique used to make a 10% solution has much effect on speed, grain, contrast, etc.

More problems arise from the obsession with minutely quantifiable results than any variations from technique.

Photography (the whole, not the individual components of chemistry, optics, and the rest) is far more qualitative than quantitative.

I believe digital photography actually got the foothold it did, at the speed it did, precisely because there has always been a group of photographers

If we continue to frame our dialogue around technical minutia....

d

dwross said:
I worry that a learning darkroom worker could be seriously put off by the seeming complexity of all this - perhaps never to attempt mixing a custom recipe.

???

Denise,

Well, I agree with you on some levels, for example, I feel that the book "problem" is mostly an English language problem and the tone voiced aginst Steve was infact a bit harsh... however - wrong is wrong and it is important to be told when something we may come across, is known to be false.

On the otherhand,
I disagree with many of your opinions quoted above, but I will only addess the things I feel most strongly about.

These are my opinions:
Digital took over so quick because our societies thrive on speed...
Digital quality is... fair to OK, digital is quick! AND digital is reusable!

Now, you have repeatedly come to the "rescue" of those suffering from someone's "technical minutia" here for fear of them being "discouraged".

I think your concern is well meant, but somewhat quaint.

If you don't like or don't need Geekese (techno-babble, technical minutia) that is OK, nobody says you have to read it and certainly no one says you have to participate in it; but are you really prepared to take that right away from others?

APUG... is like an experimental 60's school in concept... One big classroom with K-12 under one roof. It is our choice if we want it to remain a place of remedial learning or if we wish to nuture it into a more powerful institution providing tutelage for people of any age/background, engaged in serious independant study/research.

Stated another way, I worry that you may be putting off the "chemgeeks" as you say, by implying they have no place here...
we do not all have the same goals, Denise...

Please let this be a place of learning, for all of us.

Ray

Related Quotes:

"The supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience."

or

"Everything should be made as simple as possible, but no simpler".
Albert Einstein

dwross · Jan 24, 2009

UNCLE!!

I think we're agreeing that people don't need the interests or skills of a professional chemist to do accurate, repeatable darkroom work, and that's good enough for me. No one would argue the the value of your contributions to the dialog, Ron.

d

RMP-NikonPro · Jan 24, 2009

Errrr! What's a Darkroom? :rolleyes: LOL

dwross · Jan 24, 2009

Ray Rogers;741270 APUG... is like an experimental 60's school in concept... One big classroom with K-12 under one roof. It is our choice if we want it to remain a place of remedial learning or if we wish to nuture it into a more powerful institution providing tutelage for people of any age/background said:
Actually, Ray, that's very nicely put and I couldn't agree more. I'm not for shunning geeks (Heavens, if you only knew what a geek I am.) But, it is precisely because I understand quite a bit of chemistry that I recognize the times a simple question goes the graduate chemistry class route without ever answering the original question. To add injury to insult, the resulting dialog often makes it look like the answer is necessarily complex. That's about the only time you see me weighing in as a counter voice of simplicity. The rest of the time I thoroughly enjoy reading the techno threads.

d

Kirk Keyes · Jan 25, 2009

Wasn't the original question answered? I think it was and then the question as to why was asked and our fine discussion ensued.

By the way, I hear "why" about every 2 minutes from my soon to be 3 year old these days. It's reflex for me to try and answer them. Sometimes with more complexity than may be needed. But I think it is good for her to hear these things in more depth than needed occasionally. And besides, it's so gratifying when I point at a drawing (not even a photo) of Saturn, I ask "What is that?" and I get the right answer back.

Ray Rogers · Jan 25, 2009

dwross said:
Actually, Ray, that's very nicely put and I couldn't agree more.
d

Thanks Denise.

Actually, the thread got sidetracked I think due to my curiosity about a statement and an observation the explanation for which has not yet fully crystalized.

It is interesting how many things are "understood" by science, but when explanation is requested, there is no one who can do the explaining and no book can be found that answers adequately either.

What is needed is a computer, taught everything including how to think, that can find data and suggest possible solutions.

Data may be perfect, but personally, I would prefer Dr. Spock!

Live Long and Prosper,

Ray

Photo Engineer · Jan 25, 2009

Ray;

I had the entire proof and derivation of the proof once demonstrated to me by a professor in graduate school. He took two walls of the classroom to do it in fine print erasing the entire thing once to continue with the rest of the math. He ran out of space!

We were told it was going to be on the exam so I studied the derivation he gave us, and then he gave us a problem using it instead. I failed that question. I could prove it but not use it.

Then, I ended up on the Kodak Density committee and had to use the general principles and ideas or die! (metaphorically speaking of course)

It can be reduced to some simple but time consuming calculations on a sheet of paper, but the math to explain it and the reasoning behind it would take pages and pages, perhaps half a textbook to explain. It is a specific topic in a broad type of Physical Chemistry called Thermodynamics.

PE

Kirk Keyes · Jan 25, 2009

Ray Rogers said:
Data may be perfect, but personally, I would prefer Dr. Spock!

Ray, I'm sure Dr. Spock could explain all about bottle feeding and diapering one could ask for, but I suspect you are referring to Mr. Spock...

Kirk Keyes · Jan 25, 2009

Photo Engineer said:
Then, I ended up on the Kodak Density committee and had to use the general principles and ideas or die!

Going back to the silver nitrate solution and density. I I tried the APUG google search and I get either 3 threads threads that don't have the equation and 185 threads that I don't have time to go through (although the first page or so it doesn't look hopeful).

If you post an equation again or scan a page of tabular output, that would be quite fully appreciated!

Photo Engineer · Jan 25, 2009

Kirk;

Sorry, I never posted the equation. I did post some densities from my notes, I thought, but just in case I have dug some up for you.

Here they are:

1.0 Molar AgNO3 = 1.13775
0.5 Molar AgNO3 = 1.06826
0.1 Molar AgNO3 = 1.01229

1.0 Molar NaBr = 1.07633
0.5 Molar NaBr = 1.03752
0.1 Molar NaBr = 1.00613

These are all at 20 degrees C and verified with a handy dandy pyknometer to within 1%

PE

Kirk Keyes · Jan 25, 2009

I usually spell it "pycnometer". but thanks!

Photo Engineer · Jan 25, 2009

However we spell it, I have an engraved one sitting here with me, thermometer, ground glass joints and all. It was given out to members of the Density Standards Committe by the Analytical Chemistry Division at Kodak Park.

BTW, the equations take the form:

Density = a + b * conc + c * conc^2 etc... out to the 8th power. Going from Density to Molarity or to Molality or from conc to Molality is possible to do by iteration. The constants, a, b, c, d... etc are derived from doing the actual measurements and then a regression to get the equation. Temperature is done the same way and mixtures the same way again. It took years to compile the tables for the plant.

Molality becomes important when making an emulsion as everything starts molar, but ends up requiring molal calculations due to the change in volume. Well, then if you are running the UF as you make, it is at constant volume and then you have to have a model for the UF. Nasty tricky stuff.

Gelatin and Silver Halide crystals also must be calculated for in this case.

PE

Kirk Keyes · Jan 25, 2009

Are you saying it's conc in molality that needs a polynomial to model? I just plotted your 3 points plus one for 0.00 M and all 4 points look extremely linear on my computer screen when I plot them g/L vs. sp.gr. As a check, I did my KBr data from my CRC Handbook, and it's very linear when plotted that way too.

Kirk Keyes · Jan 25, 2009

By the way, here's the KBr data:

Sp. Gr., % KBr, g/L
1.0054, 1, 10.05
1.0127, 2, 20.25
1.0275, 4, 41.1
1.0426, 6, 62.56
1.0581, 8, 84.65
1.074, 10, 107.4
1.0903, 12, 130.8
1.107, 14, 155
1.1242, 16, 179.9
1.1419, 18, 205.5
1.1601, 20, 232
1.1788, 22, 259.3
1.198, 24, 287.5
1.2178, 26, 316.6
1.2383, 28, 346.7
1.2593, 30, 377.8
1.3147, 35, 460.1
1.3746, 40, 549.8

Ray, these are the things that need to be in a publicly available form/wiki. Don't you think?

Photo Engineer · Jan 25, 2009

All of them need polynomials. Some constants are negative giving bumps to the curve between some points as the solution undergoes transitions.

Try 4.0 molar AgNO3 at 1.54563 and see if it fits.

PE

Photo Engineer · Jan 25, 2009

Kirk, I match at the lowest value, but at the highest I have 1.37364. Quite a difference.

PE

Kirk Keyes · Jan 25, 2009

Still linear. I took 4 M converted to g/L => 679.48. Then plotted against sp. gr. of 1.54563 and it's right in line with the other values when calculated the same way.
?

Photo Engineer · Jan 25, 2009

Well, I have thought it over for about an hour or so, and I can't give you an answer. The equation, as I remember working with it, is high order, not linear. Sorry.

But the KBr datum above may show us a direction. The result is quite different from what you posted. I know that my notes are correct.

PE

I'm not a chemist - help Mr. Wizard.

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