Experiments with Metol and ascorbic acid.

Now on to your second paragraph. Indeed Potassium Alum is used in fixes and it slows down fixation and causes silver retention. This is why hardening fixes began using ammonium salts to take into account the synergy between thiosulfate and ammonium ion. In effect, you can balance out the effect of potassium but only to some extent. Elimination of the potassium will allow even faster fix rates and better fixation.

As for the use of borax in fixers, they are used in many alkaline fixers as a buffer. If the level of potassium were to be too high, it would negate the effect of having an alkaline fixer entirely and make it as slow as an acidic fix of much the same formulation. Washing would probably be slowed as well.

As far as having references here, yes I do. I have hundreds of textbooks on photographic emulsion making and processing, books on theory and books on system design. So, when I wrote that note giving references, I had 3 textbooks open next to me to those pages reading exactly what was said.

And, I have done lab experiments, some of them with Haist standing next to me either guiding or observing, invovling these processing principles.

And, since we have no spec for potassium in tetraborate or boric acid in the standard you published, we don't really know how it would work in some instances.

PE

Haist's comments

Patrick;

So there is no further doubt about potassium salts in fixers, here is the passage from Haist.

Enjoy.

PE

Thio cations

I don't even remember how this got into a pissing match. All I wanted was some clear idea why 20 Mule Team Borax was not as good as so-called photo grade for my purposes and those I propose. I could get no specs for whatever grade you use for allowable soluble impurities. I could find lots of guaranteed specs for sodium tetraborate pent- and decahydrate, but never got an answer as to which one you would accept for practical use in developers. I have never proposed a formula for a fixer. I have never proposed a developer formula that I have not used myself. Until recently, I never used significant quantities of borax that I told anyone about.

I do not understand why I am accused of confusing others and am told to keep my nose out. You are the one telling others that 20 Mule Team Borax has impurities that keep it from being properly used for developers without telling them what to use in its place except to get it from a photochemical dealer, also unspecified, who might in fact be repackaging the same produce you get in the grocery store.

When I proposed a way to reduce soluble impurities by a factor of 16 or more you had a lot of "Yes, but"s. I think that AR grade is an unnecessary cost for most of us, and that for most of us who might want a small amount of more pure borax, the differential solubility method will work quite well. As I said, I did quite well in the Chemical Engineering Lab course. I was simply unable to handle courtship, being principal oboist for the University-Community Orchestra, and a 21 credit hour course load including the seond semesters of both Physical and Organic Chemistry lecture and lab courses all at once. I was not the first, nor the last to have that happen. I could have repeated Organic chemistry but chose instead to change to Aeronautical Engineering. If that makes me an idiot, then at least I am a well educated idiot.

Photo Engineer;565289]"Now on to your second paragraph. Indeed Potassium Alum is used in fixes and it slows down fixation and causes silver retention. This is why hardening fixes began using ammonium salts to take into account the synergy between thiosulfate and ammonium ion. In effect, you can balance out the effect of potassium but only to some extent. Elimination of the potassium will allow even faster fix rates and better fixation."

Yes, but...
I never proposed the use of potassium salts in any fixer.

"As for the use of borax in fixers, they are used in many alkaline fixers as a buffer. If the level of potassium were to be too high, it would negate the effect of having an alkaline fixer entirely and make it as slow as an acidic fix of much the same formulation. Washing would probably be slowed as well."

IIRC, I asked what would borax be doing in an acid hardening fixer.

"As far as having references here, yes I do. I have hundreds of textbooks on photographic emulsion making and processing, books on theory and books on system design. So, when I wrote that note giving references, I had 3 textbooks open next to me to those pages reading exactly what was said."

OK. I believe you. But it still remains difficult to see how trace amounts of potassium chloride or even potassium borate apply to those comments.

"And, I have done lab experiments, some of them with Haist standing next to me either guiding or observing, invovling these processing principles.

And, since we have no spec for potassium in tetraborate or boric acid in the standard you published, we don't really know how it would work in some instances."

I didn't publish it, I repeated it from the ANSI-PMA Standard for borax for photographic use.

Ridicule is the lowest form of argument. Argument from authority is not much higher when other bases are available.

Patrick;

You asked why I thought that the standard you published for Borax was trivial and useless for photo products. I pointed to the fact that it had no standard for presence of potassium salts and was therefore unsuitlable for application to fixers.

You questioned the authority on fixers and indeed the use in fixers, or in fact, any problem with the use of potassium alum in fixers.

So, I iterated the problems and gave the literature references which you also questioned. Then, I posted the data from the reference itself.

So, by line chapter and verse, I have tried to point out the error in the poor standard you posted, and you replied with what was essentially "yes, but" or "I can't find a reference".

So, that is how this took place. I questioned the standard and stated my reasons for both developers and even more importantly for fixers. You refused to accept my answers as being either factual or correct, and so I gave instances to prove my case.

PE

No, the problem was not my refusal to accept answers, it was my refusal to accept your interpretation of the problems. I am quite sure you provided accurate answers to the problems you posed, but they were not all the problems I wanted solved. If you had from the start identified your source for the borax you recommend and a set of specifications for it so that anyone else could search for other sources of equal product, I would have been happy. I still might have proposed a way to make cheaper product work for special occasions, who knows?

As it happens, all the impurities you have supposed might be in what I now fondly call "Mule Crap" are either very much more soluble than borax or insoluble. That includes all the likely potassium compounds. That means they may be reduced by the method I described to whatever percentage might be desired by successive solution and filtering. If you use the last solution as the product, you can dry it to powder if desired or use it as a known percentage solution. Now if I just knew the specs you require for your particular work, I could devise an engineering approach to providing it from cheap stuff and you could decide whether it is worth the trouble. I should remind you that the high quality stuff is not always available in small quantities, so you might have to buy a 50# bag to get a few ounces.

Patrick;

I'm going to lean back, relax, and let you teach us all chemistry. Have fun.

In the meantime consider whether you are doing a real service to quality photo processing or are merely putting a means into peoples hands to play around with by your use of pool and laundry chemicals and the use of volumetric measure of solids.

Remember, if some newcomer to photography follows any of your advice and gets a bad result, you may discourage him from continuing. This is the responsibility that I feel with every post I make.

There are two levels here, fun photography to see what can work, and serious photography in which we want a good, repeatable process.

I can tell you what must not be in Borax except in very tiny trace amounts.

Heavy metals
Halides
Potassium salts
Iron salts
Copper salts
Phosphate salts
Sulfate salts
Insoluable materials (dirt, sand and etc...)

Those are at the top of my list and should be absent from good Borax. And, high quality stuff is always available in small quantities. I can get 100 - 1000 grams of analytical or reagent grade Borax any time I wish. It is available on-line.

PE

Photo Engineer said:

Patrick;

You asked why I thought that the standard you published for Borax was trivial and useless for photo products. I pointed to the fact that it had no standard for presence of potassium salts and was therefore unsuitlable for application to fixers.

You questioned the authority on fixers and indeed the use in fixers, or in fact, any problem with the use of potassium alum in fixers.

So, I iterated the problems and gave the literature references which you also questioned. Then, I posted the data from the reference itself.

So, by line chapter and verse, I have tried to point out the error in the poor standard you posted, and you replied with what was essentially "yes, but" or "I can't find a reference".

So, that is how this took place. I questioned the standard and stated my reasons for both developers and even more importantly for fixers. You refused to accept my answers as being either factual or correct, and so I gave instances to prove my case.

PE

Click to expand...

I have tried to tell you that I did NOT publish the ANSI-PMA standard. I did not question the literarure references except to note that one of them is not in my copy of the third edition of "The Theory....." on the page you quoted or anywhere else. And it has not appeared there by some miracle since then. And instead of replying with the date of printing of your copy, you chose to ridicule my intelligence and my knowledge of chemistry. I'm sure your copy has a later printing date than mine, which is the fifth printing of the third edition.

I don't mind your questioning of the ANSI Standard, but please don't blame me for it. It specifically applies to most common photographic uses, and has more disclaimers than the stuff that is supposed to make a utility pole out of a penis.

gainer said:

I got the ANSI specs for Photography chemicals sodium tetraborate, pentahydrate and decahydrate, 3 pages ata cost of about $21. In a nutshell, the summary of requirements is:

Assay, Pentahydrate or Decahydrate......101% min, 105% max.
Heavy metals (as Pb)......0.002% or 20 ppm.
Iron (Fe)......0.003% or 30 ppm.
Carbonate......To pass test.
Reaction to Ammoniacal Silver Nitrate.......to pass test.
Appearance of solution........to pass test.

The tests are described in great detail. Kirk or PE could perform them. Most of us have not the equipment nor the skills to perform them.

It appears that the specs would be met or exceeded by the NF grade described at www.borax.com, and the SQ grade would come very close.

You will notice that the minimum assay is greater than 100% and less than 105%.

Click to expand...

You didn't publish them?

What is this?

PE

And I called the tests and specs trivial and meaningless after that post, and then things were off and running.

PE

Photo Engineer said:

You didn't publish them?

What is this?

PE

Click to expand...

It is a repetition of data published by ANSI.

Many, many beginners in many places have used my developers made mostly from things you can get at the grocery or hardware or country general store using common measuring spoons and have been inspired to continue photography. I made most of my photographs of musicians using homebrew without benefit of anything more accurate than a cheap spring kitchen scale.

You still haven't tried to find out if there was a reason why I could not find your reference to potassuim in fixer in my copy of Mees and James, nor explained why you should expect to find significant amounts of any potassium compound in any grade of borax. Nor have you told us what brand and grade will meet your specs and how you know it. Potassium compounds are among the first to be separated in the processing of raw borax. They are among the easiest to reduce to undetectable amounts in the purification of borax.

I don't have to explain or locate anything. I have it here in 3 texts and I took the excerpt from one and posted it here.

You had said quote: "I have tried to tell you that I did NOT publish the ANSI-PMA standard. " and here you say it is a repetition of data pulished by ANSI and posted by you here. So, you did post it.

I merely questioned the utility of the data.

In fact, photograde must apply to all stages of photochemistry, and thus you cannot have a developer photograde and a fixer photograde chemical. Photograde is photograde and a photograde borax must be free of potassium and that should be in the specifications. This alone renders the specification above suspect to me.

I'm glad people love your chemistry instructions, but I warn you that there is up to a 20% error in volumetric measurments of solids. This can affect image tone and speed among other things if the error is in bromide being used for a mix of D-72 (Dektol) for example.

So, there is playing in the darkroom for fun, and high quality darkroom work.

For that matter, in emulsion making and coating, I am restricted to what amounts to me as playing due to the limitations in chemicals and equipment available on my budget. But, I do try to keep the lab procedures as correct as possible.

PE

BS, MS, Piled Higher and Deeper.

I don't have to explain or locate anything. I have it here in 3 texts and I took the excerpt from one and posted it here."

Surely you did, and you called me an idiot for not being able to find the one quote I should have had at hand. See the attachments.


" So, you did post it.
I merely questioned the utility of the data."

And now you are trying to shoot the messenger. Make your question available to ANSI. Maybe they'll listen to you.

"In fact, photograde must apply to all stages of photochemistry, and thus you cannot have a developer photograde and a fixer photograde chemical. "

That is a stupid comment. We have had for years different grades for precision lab work and practical photo processing. You yourself or Kirk said that Kodak used ANSI specs in production.

"Photograde is photograde and a photograde borax must be free of potassium and that should be in the specifications. This alone renders the specification above suspect to me."

before you suspect it, you should look into the probability of potassium being in technical grade borax.

"I'm glad people love your chemistry instructions, but I warn you that there is up to a 20% error in volumetric measurments of solids. This can affect image tone and speed among other things if the error is in bromide being used for a mix of D-72 (Dektol) for example."

Before I "published" the article for Petersens Photographic in 1973, I did statistical sampling tests of the chemicals I proposed fot use. I also did tests where I varied the measurements by more the the 3 sigma amount. I gave methods for determining the number of teaspoons in a pound or other weight unit that came from a manufacture like Kodak so that the variation from one batch could be accounted for.

So, there is playing in the darkroom for fun, and high quality darkroom work.

"For that matter, in emulsion making and coating, I am restricted to what amounts to me as playing due to the limitations in chemicals and equipment available on my budget. But, I do try to keep the lab procedures as correct as possible."

You are not the only quality conscious person around. You may be the only one who believes implicitly in the label on the package you get.

I most assuredly did not call you an idiot. Please don't misquote me.

Now, as for your post from Mees. Do you notice that Potassium Thiosulfate is not shown? The reason is that it is not a good fixer. That is the reason it is NOT in the graph nor mentioned in the paragraph you posted. It also is the reason why I posted the definitive statement from Haist which gives further references. So, the charts show nothing but the fact that Mees and Mees and James omit Potassium and show that fixation rate varies with Cations such as Sodium, Ammonium and Lithium.

It is a shame you didn't see the adjacent table in which Potassium is cited with a "-" denoting inactivity, and in another table where an optimized Potassium fix was 4x slower than the others.

In addition, I said that there cannot be multiple standards for photo grade chemicals, otherwise we would need one for every use, such as Borax for fixers, Borax for Developers and etc. So, in fact there must be one standard for photograde Borax and it must include potassium ion. You seem to misunderstand that simple statement.

I am stating this to show you again why I said that the standard and the tests were meaningless, and that is all.

I do not believe implicitly in the label and that is the very essence of my questioning. Conversely, you appear willing to accept the label and the standard with no questions attached. I am able to spot flaws in the standards and statements on the labels through experience and questioning the label. If you do not believe what I have said, you should go back and see that I have questioned the labels and even the standards, whereas you have defended them. In fact, that is the essence of this entire disagreement.

I am surprised that you didn't know about the effects of Potassium ion on fixation. That is actually rather well known amongst Photo Engineers.

PE

Some information to add to chemical purity questions

Here are two photos I just took. They are digital, forgive that. They merely underscore a point for Analog photographers.

The first, on the left shows 3 mounds of Sodium Chloride. The one on the left is a white powder and is Analytical Grade, the one in the middle is Technical Grade and is lumpy. The one on the right is pure white and consists of pure cubes. It is food grade table salt.

The one on the left is suitable for emulsions or processing solutions. The one in the middle works in most processing applications but cannot be used in emulsion making due to aggregation and fog. The one on the right contains Iodide salts (in various states as pure NaI is unstable) and it contains silicates. It cannot be used in either processing or emusion making. Appearnce wise the one on the right appears to be the best, but it is not.

Now, the second picture shows two mounds of salts, KBr (Potassium Bromide) and both are analytical grade. One, on the right, is a powder and the other consists of cubes. The cubes cannot be measured by teaspoon due to their shape and the difficulty forming an full teaspoon evenly, so I used the small cup in the background.

That cup will contain 17.2 grams of KBr in cubic form but will contain 20.4 grams of the powder. This is the type of error to expect when measuring out solids using spoons.

I test my premises about accuracy and purity by actually running tests.

PE

You didn't pick a very good example of possible errors in volumetric measurement. Never did I suggest that potassium bromide or sodium chloride be measured by the teaspoon. There are certain chemicals that are best made up in solutions. If I buy 100 grams of, say, KBr from PF and mix it in water to make a liter, and measure it into my developer a teaspoon (5ml) or a tablespoon (15ml) at a time, where is the error? If I give a formula in grams and ml and an alternate workable formula in teaspoons what is it to you? If I give it only in spoonfuls, you can always weigh out the spoonfuls the first time and use the same weights from then on. You're going to have to do your own tests anyway.

"It is a shame you didn't see the adjacent table in which Potassium is cited with a "-" denoting inactivity, and in another table where an optimized Potassium fix was 4x slower than the others."

Well guess what? Those tables are not there. BTW, what is the number of the printing of your copy?

I have two editions. Mees - Revised Edition, and Mees and James, First Edition. But in addition to all else, I would point out that I knew Howard James personally as well as Grant Haist and others and so got a lot of information in discussions and meetings than is published.

After you look at the table I have more information for you.

As for volumetric measure of solids and chemical purity, there is ALWAYS the potential for up to 20% error regardless of chemical, and regarding purity, I test my own.

As for liquids in a teaspoon or tabelspoon, there is the meniscus to consider. That is why a graduate cylinder is transparent, or didn't you know that.

Also important is whether the liquid is wt/vol or vol/vol or wt/wt, all three of which are used commonly for solutions. Generally, viscosity and illumination level are used as criteria as to which is used in a professional darkroom.

PE

Patrick;

Here are some generic examples where people discuss your advice to use volumetric measures with solids. It covers a wide range of chemicals. Also there is a quote below. If you do a search on teaspoon+gainer+photo.net you come up with pages of text with either your generic advice to use volumetric measure or others commenting on it. In my post above, I show a simple test to reveal the fallacy in that method which can yield errors of about 10% - 30% depending on crystal habit. It does not matter that I picked KBr, what matters is crystal habit. Crystalline Ascorbic Acid vs powdered Ascorbic Acid can show the same problem. It is a sad commentary on your understanding of this that you have not recognized the error in your statement regarding my use of KBr.

I would also like to add that we have had this entire fruitless discussion a year or more ago to no avail. I gave data at that time as well but it seems that it was ignored. I even pointed out that in one bottle the crystal habit can vary as the large crystals in a jar move to the top. Thus a spoonfull of a chemical can vary as you use one single bottle.


------------------------------------------------------
References:

(there was a url link here which no longer exists)

http://photo.net/bboard/q-and-a-fetch-msg?msg_id=00Bfbh

http://photo.net/bboard/q-and-a-fetch-msg?msg_id=002bNh

Quote:

"It is easy in teaspoon measure. 2 tsp acid and 1 tsp baking soda (not powder)to the liter is close enough,......."
------------------------------------------------------

As it becomes more difficult to get prepackaged processing chemistry, we must develop and foster good lab technique in those who will follow us otherwise we fail those future analog photographers.

I myself emphatically do not recommend volumetric measure of solids for serious photographic work.

PE

Ascorbic acid powder purchased as a vitamin has on its label the gram equivalent of a teaspoonful. I have had many different brands and all have said the same.

You and I can argue all we want and we will never come to agreement. If I say you are right about something, you will find something wrong with the way I said it. Part of the problem is that you do not see the arguments I make.

How can I see the tables if I do not have them available. What do you know about potassium in borax that is not published in my copy, Third Edition, 1969, Fifth printing?

I find that the first process in production of borates from raw ore separates potassium borates. Potassium borate is 25 times more soluble than sodium borate, so it should be an easy job. If I needed a small amount of extra pure borax, I could do it myself.

Yes, it started years ago. You warned me about flashpoint, but did not seem to know the definition of flashpoint. If you wanted to prove my use of volumetric measures inaccurate, you could have weighed the volumes I presented, varied the weights by the amounts you suppose to be the probable errors and showed that they would not work. The fact is, you could not do that with any formula I proposed.

I'm not a dummy. I look for ways that allow others to enjoy photography who cannot afford even a simple powder scale, such as some underpriveleged children in New Zealand. You seem to be dedicated to telling them they are not entitled to do so if they can't afford analytical grade reagents and laboratory balances. I suggest if you want to carry on this way, you do it by PM.

Patrick;

I am all for both methodologies but one must be differentiated from the other. One is professional and one is by necessity and that must be clear to the user and he/she must know the reasions behind both.

Several years ago I did try to show you the volumetric vs gravimetric measurements and the errors involved and you disagreed with me then just as you seem to now. I gave an exact figure on Photo Net in my post about 2 years ago and here we are again at the same point.

As for flashpoint, I had to explain it to you. You were advocating a potentially dangerous method of mixing chemistry that could cause a flash fire. You see what lack of experience or knowledge can cause? It can lead to a fire in someone's home and I was trying to HELP you avoid a potential law suit.

So, what is in the Potassium data? The chart is totally in error in all versions of Mees. That is apparently why Howard left it out of Mees and James. It reports no data for Potassium and suggests that Ammonium hypo is slower to fix than Sodium hypo, a gross error. So, the figures were corrected in Haist.

It seems that the Cation of Hypo is critical in fixing and therefore must be a criterion in the purity of any generally used photochemical. We did not confirm that until just before Haist published, but after the last version of Mees. So, there must be a maximum allowed level of Potassium in the spec for Hypo itself, you see?

This, BTW, is at the root of the controversy involving TEA in fixers. I will only comment that in a TEA containing fixer, it behaves as the Cation (the ion with a positive charge) and this is where there may be problems. IDK due to uncertainties in published literature.

Design of photographic solutions requires years of work and study Patrick. I am willing to help, but not willing to see information go out with errors by omission or comission. Please see my POV for the sake of the future.

I respect the work you have done for those not able to use weight measurements, but I would like to see the differences and problems explained. The same is true of using grocery store chemiclas. It is important, or we can begin a backslide.

After all, what use is it to pay a premium for a film product from Kodak Fuji or Ilford only to process it in the equivalent of laundry detergent?

PE

Just a couple of quick comments on volume vs. mass measurements: It is well known among ammunition reloaders that the precision and accuracy of volume measurements (with respect to delivering a specified mass) can be quite sufficient for routine measurement of powder charges for reloading of ammunition. Interestingly, the precision required for powder measurements for reloading of ammunition are far more demanding than those required to make film developers, or at least that is my assertion. (The reason for this assertion is that chamber pressures are a very non-linear function of the powder charge, and both accuracy of the load and the safety of the load are strongly dependent on chamber pressures.)

It is well known that a volume measurement of a powder or granular material may give different masses if the physical properties of two different samples of material are different. However, as long as the powder or granular material is fairly uniform within a given sample and from batch to batch the uniformity of the measurement can be quite good. Many household, pharmaceutical or nutraceutical materials are quite uniform from batch to batch, and can be expected to give quite uniform results (even on a batch to batch basis) when measured by volume, as long as no serious changes take place during transport and storage, such as clumping or serious settling. Therefore, once these are calibrated by someone with a scale then someone else with only volume measurement devices (teaspoons, etc.) do a pretty good job of accurate and precise measuring. In some cases (e.g. settling) one can even manipulate a material (e.g. sift of fluff it up) to bring it back to a uniform and reproducible condition, as all home bakers know.

One person in the photo community (I forgot who) has pointed out that volume measurements may even be superior to mass measurements in certain cases. In particular, if a compound absorbs water without a large change in volume then mass measurements will often give a poorer result than volume measurements with regard to measuring the amount of active material in a sample. This is particularly the case for a hygroscopic material that has had significant exposure to atmospheric humidity.

Most scientists or engineers will agree that for a well characterized material a mass measurement using an accurate scale will almost always be more accurate and precise than a volume measurement, even using high quality volumetric devices. However, it is often the case that volumetric devices are "fit for purpose" (i.e. good enough) and are almost always more convenient than mass measurements. This is particularly the case for applications that do not require the utmost precision and accuracy. Most photographic applications probably fit into this category. The trick, of course, is to only use volume measurements on materials that are well suited to this type of measurement. Most uniform powders, granular, or liquid materials would fall into this category, but this certainly does not apply to all materials.

A final note: just in case someone is concerned about whether I am qualified to have an opinion on this matter, I am a professional chemist. I make my living by overseeing research and development of analytical methods and by overseeing some aspects of a routine testing laboratory.

Photo Engineer said:

Patrick;

It seems that the Cation of Hypo is critical in fixing...

PE

Click to expand...

A quick question for my own information: Is the cation critical mainly because of its effect on complexation of silver ions? In particular, ammonia and amines can help solublize silver compounds (e.g. silver halides) by forming so called "complex ions" Neither sodium nor potassium can do this, but ammonium ions (in the form of the non-ionic form ammonia, which exists in equilibrium with the ammonium ion in water solutions) readily forms silver complexes. Would this be the reason that the ammonium form of hypo is a more rapid fixer than the sodium, and why the addition of certain amino-compounds act as grain reducers in developers, e.g. by the mechanism of silver halide solublization?

If sodium and potassium act as "spectator ions" in the fixing process then I would expect the substitution of one for the other to have a relatively small effect. This is not to say that sodium and potassium salts would behave identically, but only that the differences would not be extreme.

Interestingly, high concentrations of chloride can also form complexes with silver ions and solublize silver compounds, which is probably the chemistry behind a discussion I recently read about using salt water as a weak fixing agent.

In answer to your first comment Alan, as you know, powder is classified into types and those types require specific settings on the powder dispenser that is commensurate with the powder size. Also, powder is made in uniform pellets or flakes (photo chemicals are not). Powders are also generally of the same or nearly the same density. Therefore, in the case of powder, you have what is effectively a calibrated variable sized spoon. Also, when rotating the dispenser, you 'cut' individual powder particles to make an even 'spoonfull'. Therefore, the argument becomes unimportant in this case as you cannot (or do not) cut up individual crystals of photographic chemicals to insure a uniform volumetric measurment, but you do in reloading. These subtle details are often missed.

BTW, I reload .223, .243, .45, .9mm and 12 guage. I encounter this quite a bit and have had a lot of time to consider the problem. I use a variety of powders and have verified the accuracy due mainly to uniformity and grain cutting! This differentiates it from the photographic use we are discussing here.

As to your second post, the cation has several functions in increasing fixation or retarding it. One is size which relates to diffusion. Potassium ion is larger than Sodium is larger than Lithium, but Lithium is about the same size as Ammonium. Therefore, where or how does the fact that Ammonium based fixers are faster than Lithium fixers come in?

Well, Ammonium ion is both a cation and a ligand and therefore the size of the Silver Ammonium Thiosulfate complex is reduced considerably by the fact that the ammonium ion becomes part of the complexation cage with the silver ion. It is not an external cation. This tends to speed the rate of both soluabilization and diffusion. The rate of dissolution of silver halide is due to the effective syngergy between ammonium ion and thiosulfate ion.

So, as a matter of actual practice, it is a fact that there is a syngergistic effect going on here. This was not fully understood until work in the 60s and 70s which I took part in. Mixtures of silver halide solvents become synergistic and speed fixation.

See my Super Fix formula posted here for an example. Jay DeFehr posted it from the thread on Photo Net. The entire thing played out there.

Hope this helps.

PE

I should add as a separate footnote that the error in the data in Mees compared to the table in Mees caused some of the confusion among workers early on. The text is correct, the table has several errors which imply that Ammonium Thiosulfate is slower than some other fixers.

This was corrected in James, not by doing work to extend the knowledge, but rather by removing the table which was in error. Our work was ongoing when Howard James was rewriting M&J and Grant Haist was aware of much of the internal and external work. It was decided to let the Haist statement with external juried references stand as the evidence and to correct the situation regarding cations in fixers.

PE

More on reloading that I almost forgot.

When you use a powder dispenser, it has a micrometer adjust, and the good reloader checks the charge on a balance while adjusting the micrometer to insure he/she is on the money so to speak. So, in effect, you have a micrometrically adjustable 'teaspoon' which you are expected to calibrate by weight for verification, and which performs optimally by slicing off excess chunks of powder to get an even level amount with each turn of the dispenser.

In addition to this, the manufacturer publishes sets of weight/volume tables in rather largish books.

And finally, the user (reloader) is expected to test the load by firing groups of loads for test purposes.

I'm glad this was brought up, because it highlights the fact that only when you have a uniform material of known density and solid form can you be sure of getting the right amount of powder by volume.

At Kodak, we dispensed solids by weight using strain guages under the container. These guages are highly sensitive to weight and are set to sense the exact weight less the tare value of the container. We do not use volume for solids.

In many situations, we even use weight for liquids.

As noted above, volume changes with the 'fluffing' of a powder, but also varies with temperature in some cases or with humidity. A caked solid has more packing density than a fluffy quantity of the same chemical. It therefore delivers more weight / volume.

PE