How many ML of D-76 powder do I mix with how many ML of water.

Paul Verizzo said:

Wow, let's make an easy thing really complicated and subject to many more possible errors.

Dump it all into a mixer, mix, apportion by volume. Simple.

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You've still got to get the initial quantities right, and as Gainer points out, when you do it as you're suggesting, you're relying on factors that are hard to measure to get the proportions right, which makes QC more difficult. At least with each machine measuring precise quantities, it's easy to do QC checks along the way -- program the assembly line to dump only metol in the package once every 1,000 packages, then only hydroquinone in the next one, and so on, and pull those packages to check that they've got the right amounts.

Besides, as I say, lots of things are made in precisely this way. It may be more important that the ratio of, say, metol to hydroquinone is right in D-76 than it is that the ratio of filling to cake is right in a Twinkie, but this sort of manufacturing is a precise science. Check out some TV shows like "How It's Made" or "Modern Marvels" and you'll see examples.

I've never noticed the different chemicals in packaged developers, or lumps, or strata.

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Presumably they either get mixed up in ordinary normal handling as the bags are sealed up, put in boxes, and shipped; or some station exists to deliberately mix the contents up.

Of course, we're both just speculating here. I for one am not trying to present a case that this is definitely how it's done; I'm just trying to present an alternative to your proposal, since you said you "...can not believe that the little 1 gallon packet of dry chemicals didn't come from some huge cement mixer...." Perhaps you still won't believe it, but IMHO, it's a perfectly plausible idea.

gainer said:

You could ask someone at Kodak how they do it. It shouldn't be proprietary information. I'll bet the only time they do it your way is with liquid developers like HC110. Mixing dry ingredients in large quantities is probably more expensive and more likely to damage the ingredients by frictional heating, as well as being more likely to result in inconsistent product quality. But suppose that you have periodic tests of samples from the packaging line and you find a defective sample. The contents of your cement mixer must be assumed defective after the last good sample. The first half of your cement mixer's contents may have contained 90% of the Metol without showing any defective samples. Now you have a problem. Do you add more Metol, or throw away the rest of the mix? The major cost of D-76 is in the sulfite. More than that, the ability to determine that the problem is in the Metol depends on a quantitative analysis. You will be stopping production as well as increasing the cost of production more by testing than any other part.

Let us not forget that you had to weigh out the ingredients you put into the blender. A chef with the same type of problem would use volumetric measurements of each ingredient that gos into the blender.

Enough.

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20 pounds of Metol, 50 pounds of hydroquinone, 100 pounds of sodium sulfite, 20 pounds of borax (IIRC). Mix for ???? hours.

It's done all of the time with dry cement mixing. As long as the ingredients are in the mixer long enough, it will be a uniform mixture.

I was hoping PE could "weigh" in on this.

Maybe it would be OK if you were going to make glue out of the ingredients, but I just cannot imagine Kodak trusting that each of the 5000 or so liter packs of D-76 would be the same. If one is off, at least one other is also off. In such a production line, you try to avoid depending on probabilities. You would like the probable error of measurement of each ingredient to be less than 1/3 the tolerable error in that ingredient.

If Kodak did it your way, how would the contents of the mixer be transferred equally into ~1000 5 liter packages? Would a worker with a scoop and a scale or balance do it manually? Would someone design an automatic weigher-loader device to do the package filling on an assembly line? If such a contraption can be designed, why not use 4 of them to put each of the ingredients into packages as they move along the line, thus eliminating the expense of a huge mixer and the uncertainty of its output?

gainer said:

Maybe it would be OK if you were going to make glue out of the ingredients, but I just cannot imagine Kodak trusting that each of the 5000 or so liter packs of D-76 would be the same. If one is off, at least one other is also off. In such a production line, you try to avoid depending on probabilities. You would like the probable error of measurement of each ingredient to be less than 1/3 the tolerable error in that ingredient.

If Kodak did it your way, how would the contents of the mixer be transferred equally into ~1000 5 liter packages? Would a worker with a scoop and a scale or balance do it manually? Would someone design an automatic weigher-loader device to do the package filling on an assembly line? If such a contraption can be designed, why not use 4 of them to put each of the ingredients into packages as they move along the line, thus eliminating the expense of a huge mixer and the uncertainty of its output?

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I seldom have a chance to argue with a rocket scientist! So you mix and mix until uniform. The amount of variability between a scoop of the batch here and one there will be difficult to ascertain. The concrete made from a cement mixer is uniform.

So, with some simple calculations of weight and volume, you get your amount to put into that one gallon foil packet. In production, it's easy to measure volume and then drop it into something with a sliding measure. Position A, load. Position B, drop.

I would far more trust a scenario I envision than measuring four separate ingredients down to the 8 gram level, rapidly, no less. That's four times the possible error of one "scoop" measurement.

Where's PE?

Have you ever put a bag of dry cement in a cement mixer? When you put it in there and turn it on all the lighter powders go to the bottom and the rocks float up to the top what you end up doing is giving the perfect situation for the powders to go to their natural position by density.

Paul Verizzo said:

The concrete made from a cement mixer is uniform.

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Only if you were smart enough to add water. To my mind this thread has have moved way beyond what is relevant in the lab. I did mix partial packets from XTol years ago and the inconsitency between batches was no fun at all. Lesson learned.

best

Stefan

If the argument is whether Kodak could make their developer packages properly packaged by premixing the chemicals, of course it's possible. It just seems that it would be far easier for them to insert the individual ingredients one at a time. It would eliminate extra steps, and the extra complication of doing the chemicals one at a time for each pouch is really not that big of a complication.

Some things you learn along the way toward being an aeronautical research scientist: concrete is not mixed dry. The huge trucks are filled with dry ingredients in the proper amounts to make the amount ordered. Along the way to the construction site, water is added and then mixing begins. Concrete does not dry: it sets. The water is part of a chemical reaction. Too little is not good and neither is too much. It is important to keep the concrete from drying after it is poured, so it is kept covered with wet burlap. I don't think there is a lot we can learn from making good concrete that applies to measuring photographic chemicals.

I do a lot of consulting work for the medical industry. Powders are compounded in large batches and then dispensed into smaller packets. I have never seen a packaging line with powders getting added to packets a dose at a time, but they may exist. Pharmaceuticals are all mixed first, made into tablets or capsules second.

Mixing powders is an art form. The equipment ranges from cement-mixer clones to canisters that gyrate, shake & swirl at the same time.

http://www.glenmills.com/product_showcase/index-dynamix.shtml

Learn more:

http://www.amazon.com/gp/product/0412403404, cheap.

Nicholas:
I have been trying to find the definition of USP<2091> without success. I can find innumerable lists of products that conform to it, but that tells me nothing about the standard deviation it allows. Perhaps you are the one who can tell me what variation in weight of ascorbic acid I can expect in nominal 500 mg tablets.

Pat - you need to find a copy of the USP-National Formulary. I think the lastest one is USP 32–NF 27, Vol. 1.

I doubt anyone around here has one. I thought I might buy one, but the price to an individual is $595. All I want to know is the tolerance specified in USP<2091>. There seems to be a graet reluctance to say what it means when a product claims conformity to USP<2091> for weight.

We who play with improbable sources of developing agents such as Vitamin C and Tylenol tablets and capsules would like to know, especially if we want to argue.

gainer said:

All I want to know is the tolerance specified in USP<2091>.

There seems to be a graet reluctance to say what it means when a product claims conformity to USP<2091> for weight.

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Well, for the first one, I would suggest your local library. Looking on Google Maps, if looks like the town you live in (Gilmer?) has about 4 houses in it? Well, if that doesn't work, call up your doctor or your local hospital and see if you can come and look at their copy.

Here's an idea, look in your phone book and find a local company that makes nutritional suppliments and call and ask for their QC officer. Then ask them what the specs for USP 2091 are.

For the second one, I have a feeling when you see "conforms to USP 2091" on the label of a dietary suppliment, you are seeing how the suppliment industry is trying to look like they have ligitimate scientific standards behing their sometimes dubious products. Certainly there is a basis behind Vitamin C, but a lot of other things that fall under the heading "Nutritional Suppliments" are pure snake oil.

Also, my understanding is that Vitamin C would be covered by USP 2091, as it is a nutritional suppliment and 2091 is for nutritional supliments. To find the variation in acetaminophen, you need to find another specification as it is a medication and it then falls under the regulations for drugs. That's not the same as a nutritional suppliment. You can sell pretty much anything you want to the public as a nutritional suppliment - you just can't say it cures any particular ailment. You can say nebulous stuff like "helps with liver function" - well, maybe it does, maybe it doesn't.

For drug regulations, I would suspect that there should be something in the Code of the Federal Register, which is online. CFR 21 looks like it covers the FDA.

Here - not an official method, but it looks like it has what you want, at least for the acetaminophen: Dead Link Removed
or http://www.medscape.com/viewarticle/436633

Based on those, it looks like each of 10 tablets tested must have between 85 and 115% of the drug specified with a std dev of 6%.

I beleive that PE has stated in the past that Kodak dry powder developers were produced in large mixed batches and that the individual containers were filled by weight. He's said it's a science of it's own as to how they have to mill each component in the mix so that they can be done that way. But even then, on sitting and transportation, one should expect the individual components to separate based on density in the package.

gainer said:

I have been trying to find the definition of USP<2091>

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I'd take a bare-arsed guess: CV of 20 samples < 5%

CV is the standard deviation expressed as a percentage of the mean.

You might try contacting the reference librarian at a good sized library or medical school. "This is Proffessor Gainer, I need to check a value in the USP for a paper I'm writing, of course I would include you in the list of authors, very prestigious journal .... the A.P.U.G., in fact."

ajuk said:

I have a bag of D-76 raw powder, it says there are 415 grams to make 3.8 liters of the stuff. SO I think that means if I just want to mix up 700ML of stock solution I need 76 grams (how appropriate!) however I don't have any really accurate scales, does anybody if I can use a liquid measure tube to measure the amount of powder rather than weighing it, and how many ML of powder I need?

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All other considerations aside, yes. Approx. 76.5 g is what you need to mix 700mL of the stuff. As far as using a graduate to measure that much out, it could work if you dump all the powder into the graduate, and, since 700mL is approx 0.185 of 3.8L, take out 18.5 percent of the height of the total amount that is there and use it to make your 700mL. (It must be a straight graduate, of course.) Like I said, "All other considerations aside." Have fun!

I live in Gilmer County. Gilmer is one of those unincorporated communities where there used to be a post office. There is (or was) one of those communities called Thursday because that was the day the postman came. The city of Glenville is the county seat of Gilmer County, wherein lies the Glenville State College which has a pretty good library. I couldn't fool the librarian. I'm sure she knew my late father who was Dr. Patrick W. Gainer, a Professor of English and American Literature at West Virginia University for many years and who started the West Virginia Folk Festival in Glenville while teaching an extension course in American Folklore. Glenville State Colege also had a pretty good football coach named Rodriguez.

If I could walk as well as I talk, I could just walk into the library and look around. I know where they keep the reference books like Merck, etc.

Anyway, if the deviation is a Gaussian random variable, we might expect an error of 15% in fewer than 1% of the samples. Would Kodak tolerate that kind of variability to pass without 1 or so out of a hundred customers complaining? Add to the cost of manufacturing the cost of replacing defective merchandise before you speculate on how Kodak does it.

Patrick;

One of the reasons that a concrete truck continues to mix during transportation is that if there is no rotation the mixed in gravel will eventually end up on top as the truck vibrates its way through traffic. If you mix sand and gravel evenly in a wide mouth jar and shake it, the large particles (gravel) will eventually vibrate to the top and the sand will settle to the bottom. At the present time, several mathematicians and materials scientists are trying to determine a math model for this and there are several proposals.

In making the chemicals that Kodak dispenses as a powder, and also dispensing and packing pharmeceuticals, the delivery drum is constantly rotating just like that concrete truck to keep things evenly mixed, but one of the key things is to try to mill all ingredients to the same size as much as is possible. Many ingredients are placed into binders to achieve this and so we see starch used in pharmaceuticals to bind ingredients into similarly sized particles.

In any event, mixing a small quantity of a solution from a large bag of powder is not a good idea. Kodak's error is better than 15% in everything because, as you know, errors build up so 15% here and 15% there can cause a total failure when it is least expected.

PE

Since everyone is interested in talking about concrete here, I'll add the following:

By the way, another reason the concrete truck keeps revolving on the way to delivery is that when the cement (which partially makes up the concrete (aggregate (sand, gravel, and or crushed rock) and water are the other two ingredients in concrete) sits, the dehydrated minerals that make up the cement begin to grow crystals. I used to do chemical analysis on concrete, cement, and mortar, and it's been a while, but I remember that there were 3 main minerals that would grow over time. One crystal would grow in about 4 hours, the second in about 24 hours, and the third one took up to a month. That's why concrete and cement need long times to cure, and the must remain moist so that the minerals have enough water to form all the crystals needed for strength. As long as you keep the concrete mxing, the formation of those crystals is delayed, and the concrete will still be workable. (Within reason, of course...)

Kirk Keyes said:

Since everyone is interested in talking about concrete here, I'll add the following:

By the way, another reason the concrete truck keeps revolving on the way to delivery is that when the cement (which partially makes up the concrete (aggregate (sand, gravel, and or crushed rock) and water are the other two ingredients in concrete) sits, the dehydrated minerals that make up the cement begin to grow crystals. I used to do chemical analysis on concrete, cement, and mortar, and it's been a while, but I remember that there were 3 main minerals that would grow over time. One crystal would grow in about 4 hours, the second in about 24 hours, and the third one took up to a month. That's why concrete and cement need long times to cure, and the must remain moist so that the minerals have enough water to form all the crystals needed for strength. As long as you keep the concrete mxing, the formation of those crystals is delayed, and the concrete will still be workable. (Within reason, of course...)

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The things you can learn on this forum!

As an afterthought I would add the follwoing:

I said "one of the reasons", Kirk has given another. The third is to keep the concrete from solidifying in the drum! They use explosive charges to break up concrete that has solidified in a drum. It works. They demonstrated it on Mythbusters about a year ago. Another reason is that wet concrete generates quite a bit of heat as the reactions begin to take place. The rotating drum distributes the heat. This heat can keep the water from freezing in wet concrete in very cold weather. Falling snow will melt more rapidly on fresh new concrete while curing than on old concrete.

Also, relevant to Kodak's variability, if I made a film that was 15% low in contrast as an error and this was allowed, and then someone processed it in a developer which was 15% low in alkali which was allowed, the film could be very low in contrast when run through such a developer, but another film that was 15% high in contrast might appear normal. The tolerances in the photographic chain can be shown to be either additive or mulitplicative depending on circumstance, and therefore must be kept under rigid control to prevent the system from falling apart.

PE

OK. One more concrete story. My father used to make fun of his fellow English professors' lack of practical knowledge. He told me about one who undertook to lay the concrete for a new patio floor. He ordered ready mix. The truck arrived before he was ready to spread. He told the driver "Just pour it under the porch. I'll spread it tomorrow."

How does the constant rolling and tumbling of the powders not cause premature oxidation of the developing agents?

An inert atmosphere not uncommon in industrial processes.

Freestyle sells 1L packages for $4.79 or 5L for $5.79. For $1 more, you get 4L additional. Even if you only used a fraction, your money ahead.

The other alternative is mix from scratch (I plan to learn to do this for other reasons) and have no waste and save money.

Risking a roll of film as well as maybe a really once in a lifetime shot on non recommended procedure is not worth it, IMHO.

gainer said:

How does the constant rolling and tumbling of the powders not cause premature oxidation of the developing agents?

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The tumbler is filled with dry nitrogen.

PE