Help for the Math-Impaired

1+50 -> 9.8 concentrate + 491.2 water but I suggest using 10 ml of concnetrate + 500 water = 510 ml

1+100 -> 4.95 concnetrate + 495.05 water --> 5 concentrate + 500 water

 

but, 1:1 == 1+1.

 

What about 1:2:100 My god two colons? This was on the Unblinking Eye web site.

 

1 part of solution A, 2 parts of solution B and 100 parts of solution C.

 

including, I believe, the BIG one in the yellow box. to wit...

• D-76 (1:1)
• HC-110(b) == HC-110(1:31)
• X-tol (1:3)
• etc...

I heartily agree with you Ole but the 800 pound gorilla says otherwise....

 

craigclu,

once you get the impression that someone made an acceptable explanation to the 1+x and 1:x solutions, just buy a beaker and put several markings on it for the amount of water PLUS x amount of developer (or watherever).
I've got one beaker with marks for the amount of water used to develop 1 135 film, 1 120 film, 2 ... and the amount of Rodinal to add to the water in dillutions of 1+25 and 1+50 (I tend to use the latter mostly).

I hope this is clear to you as English is not my mother tongue.

G

 

I am not a chemist so strictly speaking I can not say that you are right on wrong in this, but what I can say for fact is that much of the photographic literature establishes equivalency between 1:1 and 1+1 when describing the mixing of solutions. And I don't just refer to the literature by people who are not scientists but also to the literature written by trained research scientists. See, for example, Chapter 7 - Photographic Solutions of Grant Haist's Modern Photographic Processing, Volume 1. On page 345, for example, in describing mixing a 1:3 solution of Kodak D-76 working solution from a stock solution, Haist writes: "For the 1:3 dilution, take 250 ml (one part) of the stock solution and add it to 750 ml (three parts of water) . . . "

There is something strongly counter intuitive in the statement that “1:50 is the same as 1+49, so that makes 10ml concentrate to 490ml water, or that 1:100 = 1+99.” I personally find a great deal of linguistic ambiguity in this statement, even if in fact it is correct scientific terminology, if for no other reason the fact that the common defiition of *ratio* is far from completely unambiguous.

Now, if we talking about percent solutions this makes sense, because a one/half percent solution would indeed be one/half part of something in water (or some other solution) to make 100 total parts, or one part of something to to make a total of 100 parts.


But the basic point is that most photographic texts, and much if not all of Kodak literature, establish an equivalency between solutions that are expressed as 1:2:100 and one part A + two parts B + 100 parts C.


Sandy

 

Thanks, Shyguy and Ole. I agree, Ole, the the "plusses should be used. And, to "split hairs" your latter statement (1+2+97) is more precise.

 

Yes, and the amibuity does come from the irrational (really incorrect) use of ratios. The ":" sign indicates a ratio. Kodak uses it as a plus sign. That's the irrational part. "1:50" should be read as one part taken to a final volume of 50 parts, hence the equivalence to 1 part + 49 parts = 50 parts.

The "part plus parts" system really does make the most sense. Have you noticed that you never see anyone asking questions about "if I take 1 part of this and add it to 99 parts of that, how many parts do I have?"

Despite the usage by Haist and even Kodak today, it really is too bad that Kodak and others promote this expression today.

Sandy, I'm sure you meant that a 1/2% solution would be 1 part into a final volume of 200 parts, not 50 parts, as that makes a 2% solution.

Anyway, I'm just glad they don't use normal (N) concentrations. Molar, I could live with that...

 

Hi Kirk,

Thanks. I corrected the statement. At least I think it was corrected!

Sandy

 

Craig, it's much, much simpler, at least for spreadsheet purposes, if you just include the number of grams or ml of component X and enough water to dissolve the components, and finish with "water to make 1 liter". Then for 500 ml, you use X/2 and water to make 500 ml. And for a concentrate, if you're making it yourself, you'd decide if you want 50 ml concentrate and water to make 500 ml (what I think of as 1:9, but by Ole's nomenclature would correctly be 1+9), or if you'd find it easier to use 45.5 ml concentrate and water to make 500 ml (1+10). For my money, if working in metric, 1+9 is about the simplest dilution you can possibly use.

Of course, different systems give advantages different places. Back around 1967, Kodak picked 1+31 (or 1:31, as they call it) for HC-110 Dilution B because it was one ounce concentrate per quart of working solution (and then they complicated the whole situation by recommending you mix the whole bottle of concentrate into stock solution, 1+3, and then use the stock solution at 1+7 -- it's tricky to get into the right mental viewing angle for that combination to add up the same as 1+31).

Now, just to bollix the works a bit, if you're mixing your own chemisty, the simple way is to make up packets of dry chemicals containing the premeasured amount of each ingredient to make 500 ml of working solution, and if you need a liter, use two packets. The only time there's a significant disadvantage to doing this is if a) you have a formula that is difficult to dissolve (has a lot of borax or sodium sulfite, for instance), or b) you have an ingredient that doesn't keep well in dry form, such as glycin. If you routinely use several different size batches, however, and have a concentrate that keeps well (say, dissolved in TEA or glycol, so the alkali isn't ionized and thus the phenidone doesn't deteriorate), then a concentrate will be easier than using the correct number of small-batch packets or keeping several packet sizes on hand; this is also the case if your formula is difficult to fully dissolve at room temperature.