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# Thread: Consensus on the notation of dilutions

1. It is common to use 1:3 or 1:4 (1+3 or 1+4) with film and 1:9 (or 1+9) for paper. But, with conflicting instructions it is hard to day. Either 1+3 or 1+4 will work with most all fixers if you adjust fix times to compensate.

PE

2. Originally Posted by Steve Smith
You're probably better off just ignoring it as most manufacturers use the + notation anyway.

Steve.
Sure, i will use + notation, even if some will use : i will consider it as +.

3. Originally Posted by TareqPhoto
Sure, i will use + notation, even if some will use : i will consider it as +.
That's what most of us do.

Steve.

4. As long as you are consistent in your own practice, you'll be fine.

5. I have been surprised by the wide variety of methods used in all areas regarding dilution. I think that we must agree to disagree. But,when we post or publish something, we should write or dilution down in clear and unambiguous terms so that everyone else can understand what you have done.

PE

6. The problem is what we individually think of as clear and unambiguous might not be to someone else.

Before this topic was raised on APUG a few years ago I thought that everyone treated 1:3 the same way as me. i.e. one part to three parts making a total of four and didn't know that anyone thought of it in a different way.

I think we should all use + rather than : As far as I can tell, that is clear and unambiguous.

Steve.

7. Originally Posted by Tony-S
Yuckity yuck.......
It is suprising as you insist on your true. One true.
Sorry, but I regret your students that they don’t teach other ways of the solution preparations, that they won’t meet with other possibilities how to describe a composition of different mixtures (solutions).

Your consideration is based on simple dilution equation:
V(f) × c(f) = V(i) × c(i)
Where V(f) and V(i) are volumes (final and initial) for example in mL and c(f) and c(i) are concentrations (final and initial) for example in mg/L (or mol/L).

From this equation so-called dilution faktor (DF) can be derived.
DF = V(f) / V(i) = c(i) / c(f)
It says how many times the final solution is diluted against the initial solution.
Or, how many times the final solution should be diluted against the initial solution if there is such instructions for preparing the final solution from the initial solution.
DF is greater than 1 and it is expressed by one figure, not by ratio! (Usually)
The reciprocal value can be admited, but I don't like it.
OK, DF (reciprocal value) is your criterion.

But there are more possibilities how to describe composition of mixture.
For example mass fraction, often expressed in percentage, which is fraction of mass of one component to total mass of mixture. Its using is (I hope) very simple. For example water solution of some soluble salt at concentration 20 % (mass fraction = 0,20) means 20 g salt plus 80 g (mL) water.

And now I recommend you to study the following material from IUPAC:
http://pac.iupac.org/publications/pa.../8002x0233.pdf
It si enough to find „mass ratio“.
Do you see that it is possible to describe a composition of mixture by means of such fraction?
This fraction expresses mass of one component to mass of the second component! And the above mentioned example looks 20/80 (=0,25). It is very near to our 1:4. And just such unusual notation gives signal that is 1+4.
And mixing ratio for example 1:0,5 is 1+0,5 etc. (what is your explanation with such recipe?).
And as example I thing was stated earlier. Prepare four components mixture (solids, liquids) in mass ratio 1:0,5:4:20 (where will your explanation be?)
It is no matter if the principle of mass ratio is applied to mixing liquids in volume units.

This mass ratio is known to chemists as relative mass fraction and its application is comfortable in calculations in such technologies as are drying or adsorption. In this case it should be better use for the „normal“ or ordinary mass fraction (related to total mass) name absolute mass fraction, but it is not necessary in ordinary life.

(Two notes to your „serial_dilution“.
1.
The explanation is based on similar dilution equation as is described above:
V(f) × c(f) = V(i) × c(i) + V(s) × c(s)
(s) means solvent and in your case c(s) = 0; V(s) = 9 mL,
But!
This equation is true if V(f) = V(i) + V(s), so-called additivity of volumes is assumed.
Yes, in many many cases of water solutions is true, but this assumption MUST be stressed, especially to students during pedagogical process.
2.
It si important after additon of initial solution to mix final solution before taking a new amount. I am not sure how this mixing is important in bacterial cultivation but I am
fully sure that mixing for preparation the most chemical solutions is very very important.

Both notes (by my opinion) are missing in your serial.)

And in the end some pictures (my serial what means 1:X). It is not necessary to understand in German (even I know very pure German :-))

8. Originally Posted by H2O
It is suprising as you insist on your true. One true.
No where did I say this, so please don't say I did. There are many ways to do dilution problems and I am not disputing any of the methods described here. What I, and others, are saying is that communicating to others using the ':' is ambiguous, while using the '+' is not.

9. Kind of an interesting conflict. I believe in British usage they read that 1:50 as 1 in 50, or 1+49. In American usage we would actually read 1:50 as 50 to 1, or 1 + 50. As Winston Churchill said, "Two countries divided by a common language".

What surprised me is the Americans in the thread that think 1:50 means 1 + 49. They certainly weren't taught that in school, unless they had a foreign teacher who was unfamiliar with American usage.

What confuses me is why anyone in either camp would think 1:1 = "stock solution", why would you label some thing as a mixture if it was not????? I think anyone would be more likely to say, "Do Not Dilute", if it was labeled 1:1, I would think they were using the American notation for (1 + 1). And just for the hell of it I ran upstairs to check my old bottle of Rodinal, we usually say 1:50 (50 to 1) when talking about diluting it, it is labeled 1 + 50, so those Germans seem to be using the notation in the same way we Americans do. On the other hand, my fixer is labeled 1 + 9.

Please do not let this interfere with your "MY way is the WAY" debate.

10. So, what is unambiguous?

How about 1 part A and 1 part B to make 2 total parts. Or 1 part A and 9 parts B to make 10 total parts. You can substitute liters, ml, oz or quarts for the word parts! This is not ambiguous.

PE

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