Safe sodium carbonate.

I have received from www.chemistrystore.com a 17 pound pail of

anhydrous sodium carbonate. The MSDS sheet accompanyinf it saya it is

100% sodium carbonate. The price was $15.98 + shipping. Is there a

reason I should not use this in any of my B&W photographic solutioons

that call for sodium carbonate?

I don't see why not.

Only remember the conversion factors between anhydrous and hydrated carbonate

Well, right off the bat we know they're lying. Nothing is 100%- there have to be some traces of something in there. Now that we've established they can't be trusted, it's just a question of how far they'll go to mislead you. Heck, the stuff might be more contaminated than my pool chemicals. BTW, I don't place any stock in MSDS sheets for content anyway. They fulfill a regulatory need, but they have nothing in common with an assay of what's really there. Ok, seriously, I wouldn't hesitate to use the stuff. Now, where's the cheapest sulfite?

Conrad,

 

I can tell by your reply that you know my question was rhetorical. I was planning to use it anyway.

 

100% in engineering terms means a purity greater than 99% that rounds off to 100, such as 99.6. If it was claimed to be 100.0% pure, it would have to be 99.95% pure or better.

That's pretty cheap Patrick! I called a local pool supply house for a price on the sodium sulfite you cited in another thread (Chemout), and it's the same price ($12/2 lbs) as Photographer's formulary , but no shipping! Thanks.

Not to go too far off topic, but I've got a partially filled container of sodium sulfite that's about 25 years old. I haven't opened it lately but I recall it being in a plastic bag-liner inside the container, which is one of those heavy cardboard/fiber pail jobs. I think it was 100 lbs when I bought it, back when I was a mixin' fool.

 

Is it still good, or even maybe good? Or should I just forget about it?

When I used to buy Analar quality chemicals, an entire assay was given listing other compounds present down to five places of decimals. If sodium carbonate is listed as 100 % then this cannot be strictly true but sufficently pure for all practical purposes. The sodium carbonate I currently buy does not come with an assay but is clearly suffciently pure for photographic applications.

That's a very good price, given that I paid more than $2 for a box of three pounds of washing soda not long ago. Now, the washing soda is about 98% pure, works fine in every photographic application I've tried, but it's (most likely) decahydrate, which means it's about three times the price (not counting shipping).

 

Of course, I now have about a year's supply of soda, but I'll try to remember www.chemistrystore.com when I next need to shop. Did they have other photographically interesting chemicals, like metol, phenidone, hydroquinone, etc.?

www.chemistrystore.com appears to be oriented toward cosmetics and detergents. Best look them up and scan their product list. They do have potassium carbonate, propylene glycol, triethanolamine and many other chemicals we can use, but I don't remember seeing any developing agents.

Guys;

 

At that price, I doubt that the purity is higher than 98%, and may be less. As noted on another thread, mining and purifying sodium carbonate is a big business. I know how hard it is to get these chemicals free of halides, so I question any purity claims.

 

Read the comments on the other thread below.

 

Ron Mowrey

chemistry store is targeted to cosmetics?

then all the products should be of high quality, maybe some halides but worth a try at that rpice.

 

Their PG and TEA should be USP grade.. have to look again

While their MSDS claims 100% Na-Carbonate I'd take it as 99.xxxx but probably good enough for photographic uses. Let us know how the test go

Patrick - I posted this at the end of the other thread, but I'll put it here too.

 

An MSDS is not a certification of purity - it is a safety guideline that the Dept. of Transportation, industrial hygenists, firefighters and other use to determine the safety associated with a substance. That 100% figure you see most probably means that the sodium carbonate does not have any other added ingredients and that for all practical (read - safety) purposes, is behaves as 100% sodium carbonate. Firefighters do not care if there are minor amounts of something in the sodium carbonate unless it would cause it to behave differently, such as when they spray water all over it. But a MSDS is not an assay of purity.

 

You mention accuracy, but what about the error associated with those numbers? If an MSDS says 100%, is that 100 +/- 0.1%, or 0.5%, or 1.7%? We can't tell. That's where having an analyzed reagent or at the least tested to meet the criteria set out in the product specifications is better. Error limits are given to truly know what the error limits are - you can not really be certain that the error is equal to the rounding step, as you assumed above. It most likely is not.

 

I've also seen assays on analyzed reagents come up above 100% - that just kind of reflects the nature of the chemical and the method used to determine the assay. It may not really mean the assay is wrong or bad, but it may be just as accurate as an assay that comes up a little under 100%. It's just the nature of the methods used...

 

And it's not that the supplier is "lying" about anything. They are just following the guidelines set out by their industry, and those guidelines may not match the guidlelines that the photographic industry follows.

 

All that said, enjoy your bargain!

 

Kirk

Kirk;

 

That was right on.

 

Different industries have different standards. What is right and useful and uncontaminated to one, might be bad in another.

 

I have tried to make that clear myself in my posts.

 

If people wish to use cosmetic grade, or food grade or 'pool grade' chemicals in their photographic chemicals, let them. I think that you and I have pointed out that it may not make any difference, but then again, it might. And, if it does, they have no cause for complaint.

 

After all, you can hammer in a nail with a wrench, but it wasn't designed for that purpose either, but it is heavy and has a handle, so it 'kinda' meets the specs for a hammer.

 

Which, when you look at it, is just what I've been trying to point out when it comes to choosing chemicals.

 

Thanks.

 

Ron Mowrey

So, Ron, what do you ask for when you want the utmost quality of sodium carbonate? How do you know when you have gotten it? More to the point, how do you know when you need the utmost purity? I am presuming that most of us are not doing quantitative analysis on every chemical we buy and are not using our chemicals for quantitative analysis of other chemicals. In practical photography, if it looks like sodium carbonate, acts like sodium carbonate, and has no measurable unwanted reactions, then for my purposes it IS sodium carbonate. If it is not, at least it does the same job, and at much less than $5 a pound.

 

When the manufacturer specifies 100% anhydrous sodium carbonate, I take that to mean that the actual percentage rounds off to 100 and is within 1 unit of 100. If that statement is not true, you can hold the manufacturer responsible for whatever damage the difference causes.

 

The Chemistry Store does not specify any limitations on what their product is to be used for. They sell many products beside raw chemicals, and from those products one may judge that they cater to people who make food, cosmetics and detergents.

Patrick;

 

Since I rely mostly on prepackaged chemistry with the exception of some esoteric color chemistry and B&W printing from time to time, I can't answer your question definitively.

 

Kirk and others in this thread and the previous one that was referenced above have made very definitive statements about purity.

 

I keep repeating that my purpose was to heighten awareness and spark discussion on a potential weak point in scratch mixing developers. It has done just that.

 

I buy from Photographers Formulary, trusting that they supply a photographic grade set of chemicals. So far, after three batches (no, I don't know if they are truly batches, but they came from three orders over the period of about a year) and starting the fourth, I find good repeatability in my color printing work, and in my B&W paper developers. I do have a slight amount of sediment that I let settle out before use, and I don't use the developers for film. From the tests I am able to run, their sodium carbonate is free of halides for all practical purposes, and I can repeat Dektol very well, thank you, except for the sediment mentioned above.

 

OTOH, there is a chemistry supply firm here in Rochester that deals with very high purity chemistry. I may investigate their analytical grade if I need to. But, I won't use 'pool grade'.

 

I will also weigh things in grams or grains, and not use teaspoons and tablespoons. I guess I'm too much of a purist, and have seen too many things go wrong using approximations.

 

If I'm going to develop a $2 sheet of color film or a $1 sheet of color paper, I want to be sure that the results are right on and repeatable, and that others can repeat my work if necessary.

 

I have listend closely and objectively to what Kirk and others have said, and I have developed a healthy respect for their POV regarding standards and purity (or lack thereof unfortunately, or confusion therein... whichever way you want to look at it)

 

Since I have nothing to lose or gain by whatever anyone does here, only they do, I say that you should use what appears to work. If it fails, does something unexpected, or whatever, it is on the shoulders of the user(s). I will continue to use what works for me and if it fails, I will take issue with the company supplying me. You, OTOH, will have short shrift if you try to complain to a pool supply company that their sodium carbonate ruined your photos of your newest grandchild or something like that.

 

Ron Mowrey

I had a similar discussion with some friends in 1973 after I wrote for Petersen's Photographic about using volumetric measurements. I demonstrated the consistency of such measurements. The mean deviation of ten teaspoons of several chemicals was less than the accuracy recommended by Kodak of a balance or scale for weighing chemicals for developers. They went out and bought analytical balances. I will never convince you that the accuracy required of black and white film or paper developers is not as great as some of us would believe. But tell me, are all the formulae in "The Darkroom Cookbook" in any one category so much different from one another? I see a number of developers that differ from one another by more than the error that would be introduced by 98% carbonate, yet they are claimed to give the same results.

 

You might go so far as to ask Photographer's Formulary about the purity of their sodium carbonate.

 

I am not about to tell any amateur or professional photographer what he must do, but I see no harm in telling all what they can do.

 

By the way, the article "Salt to Taste" is in Volume 23, #1 of Photo Techniques and is still available among the back issues.

Patrick;

 

I have had problems desigining photographic coatings or processing solutions, and I have seen others with the same problems, when the experiments were designed improperly, when tests were not repeated, or when they were repeated improperly. I have left out tests that I should have run, and seen others do it as well.

 

What I learned was that you can prove, or disprove, just about anything with film or paper by running the appropriate or inappropriate test. I see print tests claiming sharper images, but what I see sometimes is contrastier images which can be mistaken for sharpness. I see claims for finer grain, but it is really an increase in sharpness that makes the grain look finer, but in other cases they claim more grain, but again it is sharper grain due to increased overall sharpness.

 

So, basically, I rely on my eyes supplemented by intrumental tests. A real proof of sharpness or grain, for example, cannot be just stated by comparing two pictures of a chart. You should have appropriate tests run to verify that the contrasts are comparable before you make the statement. (that is a generic you, I'm not pointing any fingers) In many cases, this involves very sophisticated equipment and these tests are also hard to run.

 

In regards to the standard deviation of tablespoons, I'm just making the comment that measures by that method, done by one person, on one batch of chemicals, might work and in your case did, but if another batch has a different crystal habit (powder vs spheres), there can be over a 50% difference in packing density and therefore weight. You may never have run into that particular problem, but I have using a powder vs granular materials. The person trying to duplicate a 'spherical' measurement with a powder could be off by over 50%. A person who uses spherical chemical particles, vs an ellipsoid particle could be off by 20% or so.

 

One of the most famous of all chemical mixtures compounded by volume was gunpowder. However, IIRC, the makers recommended pulverizing to a powder, each ingredient, in its own mortar and pestle before measuring out the powders by volume, because in those days the making of uniform crystals was a primitive science. Lump charcoal, sulfur, and saltpeter were well known, but purifying them was not, so they crushed them to uniform powder and only then were they able to get repreatability.

 

So, unless everyone is using a mortar and pestle, and crushing materials to a uniform powder, I doubt that everyone will get uniform results from volumetric measure due to variation in the chemicals supplied.

 

I have gotten crystalline phenidone, and powdered phenidone. I have crystalline sodium sulfite and powdered sodium sulfite. I have potassium bromide in large cubic crystals and in small cubic crystals like table salt. Which one is volumetrically the 'correct' amount?

 

Therefore, although it is possible, over the long term I doubt that it will work for evreyone in every case with every chemical. There are just too many variables.

 

I say, good luck to them and I hope that they don't ruin any valuable pictures. I will stick to gravimetric measures. Sorry I can't agree with you.

 

Ron Mowrey

I don't know if you've noticed, but every time you buy a pound of any photo chemical it comes in the same size container and has about the same empty space. Now if you are smart, you will measure the whole pound in a graduate or kitchen measuring cup to find the actual volume. If you know how many ml are in the whole pound, you know how many grams are in a tea or tablespoon full by a simple calculation. If you are making black and white developers, you will soon learn that when a formula in some book specifies something like 45.25 grams of something, that number was not arrived at by scientific calculation, but was the number that "worked" in the original formula and could just as well been 40 or 50.

 

Though developing agents may be more critical because of their smaller amounts, you will be able to find a volumetric measurement that "works" and will continue to work the same way every time you make it up as long as you use the same batches of chemicals.

 

Please note I deal only with black and white. I am sure there are tolerances in color developer also, but I don't know what they are.

 

The way to find out what tolerances there are in black and white is to weigh carefully the ingredients and mix a batch of your favorite developer. Then do a series of experiments in which you vary the amounts of ingredients according to an experimental plan such as "magic squares" and compare the results of each test with the original. You will be interested in grain, resolution, film speed, curve shape, and if you are Ron Mowery, in proving Pat Gainer wrong. (Couldn't resist the dig.)

Patrick;

 

You of all people here, having taken chemistry, should be well aware of the fact that the packing density of a chemical varies with crystal habit. I have also mentioned that I have 2 bottles of Sodium Sulfite (anh) on my shelf, one from Aldrich and another from Kodak. They are totally different in crystal form and probably density. I have not measured them to prove anything one way or another. I'm not interested in trying to prove or disprove anyone, as I weigh things.

 

In addition, the chemical levels that I worked with were molar quantities adjusted to acheive the optimum ratio of chemicals based on extensive experimentation. That is why you use 800 ml of water, add chemicals, then dilute to 1 liter, so you have a measured molar concentration of chemicals determined by these experiments. I worked in both g/l and moles/l, and in some cases you will find precise molar ratios of ingredients when the weights look odd to you. In other cases, chemicals are adjusted to a molar level based on the seasoning or aerial oxidation effects. It would be far easier to work with molal concentrations for the average user, but it would not be as accurate.

 

The reason I brought up volumetric vs gravimetric measurement, and have current information as well, is not to dig anyone, but rather is due to the fact that Science News has reported at least 3 times in the last few months on the effect of packing density on the shape and size of a given material. Recent research shows that previous data stating that spheres packed the most densely of all materials has now been proven mathematically wrong and oblate spheroids are now the most densely packing material.

 

I was quite taken with the variations in mass that can be packed volumetrically with various particle shapes and realized that it could have a very negative impact on volumetric measurements as I see being mentioned on this forum.

 

Empiricism can be used Patrick, but does not always work when others are asked to repeat the results. I didn't say it would not work, I said it does not always work. I know, having spent many years designing developers, fixes, hardeners, bleaches, and blixes. I am trying to heighten awareness to the dangers of some of these empirical, qualitative, and volumetric methodologies, not take pot shots at people or their ideas.

 

Granted that probably more than 80% of my work was with color systems, that is beside the point really. The fundamental research methods are what are important. Also, the principles of photography in B&W and color are nearly identical as well. You do use an MQ for processing reversal color films for example, and you use antioxidants in color and B&W developers. I could go on and on, but basically, I learned to do factorial experiments and apply statistics to gain a full understanding of photographic processing solutions. Some of what I learned came from Grant Haist personally, with whom I worked for a while. He and I exchanged a lot of ideas on B&W and color processing.

 

I'm sorry if what I have said has offended you. No offence was intended. I was and am trying to help scratch mixers get better results. If my suggestions go unheeded, there is no loss to me. If they heed you rather than me for whatever reason, that is also no loss to me. My position here is simply this. I will not knowingly give any incorrect or inappropriate advice to anyone. I will do no harm. I will not reveal any information given to me in confidence.

 

If you can show in this thread or the previous one that I started, that I have gone against my principles stated above, I will apologize to all concerned. Otherwise I stand by what I have said.

 

If, on the other hand, what I have said bothers you, and if you see any truth in what I have said whatsoever, then perhaps you should look to your own advice to others for possible or potential faults.

 

Ron Mowrey

"Recent research shows that previous data stating that spheres packed the most densely of all materials has now been proven mathematically wrong and oblate spheroids are now the most densely packing material."

 

============================

 

Isn't that the "M&M Theory"?

Yes Lex, you have it right.

 

And this is the fundamental problem with volumetric measurement of solids. It is going to eventually fail for someone.

 

So, aside from chemical purity there is also the issue of measuring out solids by volume rather than by weight. The actual amount measured depends completely on particle shape.

 

Ron Mowrey

I'm a believer in following what's known as "best practice". If you have the ability to weigh stuff accurately, why not do it? If you don't, you do what you have to do. Also, if you have a method that has worked in the past, and appears to continue to work, why worry. There are too many things that concievably can go wrong to fixate on the purity of a few chemicals. If you don't think so, you just don't have a good imagination. The hobby can be enjoyed on many different levels. Mine is fairly technical, but artistically iccky. Nor do I spel two good. And you don't have to be consistant. I'm generally fussy about fresh materials, but I just posted an image in the classic camera forum that I shot today on Plus-X that expired in 1977 and was sitting out in the bright sun at a flea market for most of a day. I doubt that film knew if the developer was weighed out on my Mettler, or the bathroom scale, much less where the carbonate came from!

I thought the problem with weighing chemicals was they pick up moisture. You end up weighing water. OTOH volume measurement doesn't have that issue. It's not exactly hard to weigh a sample when you buy new chemicals and check how much they weigh.

Robert - I don't know if that is a common misconception, but it is a misconception. Chemicals most certainly will change density as they absorb (or loose) water or react with other agents, such as carbon dioxide or oxygen from the air.

 

Looking up in a CRC Handbook of Chemistry and Physics (or your favourite chemistry handbook) what the density of compounds at different levels of hydration, and you will see the density most certainly changes, and so therefore does the volume of a given amount.

 

Here's an example - I'f you've ever looked at the mortar in an old building, you will probably see that it is cracking or even falling apart - this is because the lime in the mortar is reacting with both water and CO2 and it is changing molar volume (or loosing water depending on the enivoronment it is in). There are still the same number of lime molecules as in the mortar when it was made, but because it is aging and reacting with other things in it's environment, it is changing chemical composition - if it is in a moist evironment it is becoming limestone. This new compound has a different crystal habit or density, and the mortar expands and starts to crack and fall apart. The volume most certainly does change.

 

I'm with Conrad and Ron. Using volumetric measurements is interesting and could be used in a pinch, but why not minimize any errors you may have by simply weighing out your chemicals? There are electronic scales nowadays that are soo inexpensive (I guess we can thank the illicite drug trade for that) that there is really no excuse not to be able to wiegh things out.

 

And are all you teaspoon photochemists really wieghing out every chemical you are buying when you first get the bottle, or are you guys just taking the word of someone else as to the density of these compounds? And what happened to everyones concern about being poisoned by some of these things - like pyro and other developers? If you want to minimize exposures, you will probably want to avoid dumping all your new chemicals out of the bottles and then assuming the stated amount on the bottle is accurate to make your volumetric measurements. It's just too much fussing around when there is a simpler and more accurate way to do things, just weigh it!

 

Rube Goldberg, where are you?

 

Kirk

Robert, Kirk;

 

I'm kind of hard pressed to think of many chemicals that absorb moisture out of air so rapidly that they affect normal weighing operations.

 

The only two used photographically that come to mind are NaOH anhydrous pellets and certain hydration grades of Sodium Thiosulfate ( I forget the grades now, I'm sorry ). You can see the weight change of a sample as you watch the balance with these two, but you need a RH in the room of about 50% or higher to see it.

 

The thiocyanate salts are hygroscopic, but act very slowly in absorbing moisure. Carbonate and sulfite are even slower IIRC.

 

Anhydrous copper sulfate is also subject to absorbing moisture from air, but it is so hygroscopic you generally have trouble even storing it anhydrous. I have rarely seen it anyhdrous. It is not a common photographic chemical.

 

Aluminum chloride is another. It actually begins to react violently to air when you open it up, as it reacts with moisture and liberates HCl. It is not used photographically, only in organic chemical syntheses. Even with its high reactivity, I was able to weigh it out and use it with accuracy when doing syntheses. I just worked fast.

 

My main concern is not with absorbing moisture rapidly, but rather with the variation in density due to variations in crystal type and purity of chemical depending on source.

 

Thanks for the post Kirk. Good information. Conrad, you have a vaild point, as I said above. Use what works. But, I added that volumetric measure or incorrect measure may bite you sometime. It has bitten me.

 

Ron Mowrey