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# Thread: Ok math guys/gals, need help with dilution calculations

1. Barnbaum now uses the following dilutions for TriX 320 rated at asa 160.

First he makes a stock solution of 1:3. Then he takes that and further cuts it to 1:12.5.

If you were just going from the concentrate to the final dilution what would it be? Would it be 1:37.5? I just have a mental block when it comes to ratios and dilutions etc. Duh!!

2. first: 1:3 is equal to 1 part in 4 parts total, or 1/4 =25% v/v

1:12.5 is equal to 1 part in 13.5 parts total, or 1/13.5= approx 7.4% v/v

multiply 0.074 * 0.25 = 0.0185 or 1.85% v/v or approx 1.9% v/v

then to see what the overall dilution factor is:

solve the equation for x

1/(x+1) = 0.019 x = 51.6

so overall this is equivalent to approximately 1:51.6 dilution

hope this helps,
JBJ

3. I stand in awe.

As defined:

A mixed emotion of reverence, respect, dread, and wonder inspired by authority, genius, great beauty, sublimity, or might.

So if I want to make up 1000ml of working solution would I say 1:52 so that would be 53 parts in total. So 1000 / 53 = about 19ml. So 19ml of concentrate and the rest water to make up 1000ml?

Geez this stuff drives me nuts!!

4. The main reason to do it in two successive dilutions is that it is (usually) more accurate to say dilute both 25 ml + 75 ml (1:3) and also 1:12.5 than to add simply add 18.5mL + 980.5 mL = 1:53 (999mL total)

This is more accurate than what I posted the first time, remember I rounded up in my first post from 0.0185 to 0.019. So to be more accurate is a 1:53 dilution, or 1 part in 54 total (18.5 + 980.5).

Another issue is the rate at which these solutions deteriorate. A concentrated stock solution will oxidize/deteriorate much slower than a dilute solution in which the pH is not as well buffered and more aeration has taken place (mixing fresh oxygen-rich water with concentrated developer).

But to answer the original question:

1:53 dilution is really close. That would be 18.5mL + 980.5 mL. 999mL total. I assume you have graduated cylinders that can measure an accurate half mL increment?

good luck,

JBJ

5. From a strictly practical view from someone tha have used HC-110 higly dilluted for a long time;

If you use 19ml + 1liter water, it will be VERY much OK.

I've never been able to tell the difference between 5ml concentrate to 295 or 300 ml water.

Jorge O

6. Darn! I still confused and I mix from scratch all the time. Surely I am not the only one who is still lost? (And I am not even using that combination)

7. Funny, these rounding-off errors...

1:3 gives 1/4 concentrate. So the next step is: 1/4 : 12.5, multiply both sides by 4 to get 1:50.

Why make it more complicated than it is?

8. As Jorge pointed out, for practical use it probably doesnt matter that much for this particular developer/film combination. I don't use HC-110 so I cannot comment on that.

However I do use D76 and TMX sheet and roll films. My experience with this combination, and what I have read from others, is that tight control over all aspects is important (temperature, agitation, concentration, time, age of developer, etc.)

But, with respect, in strictly technical terms 1:3 further diluted 1:12.5 is not the same as 1:50

(1/4) * (1/13.5) = 1/54 not 1/50

9. Beautiful Mind??
Governing Dynamics?

.... sorry -- I live near Hollywood

10. Originally Posted by jbj
But, with respect, in strictly technical terms 1:3 further diluted 1:12.5 is not the same as 1:50

(1/4) * (1/13.5) = 1/54 not 1/50
It ends up as 1+50, not 1/50 concentration. The final ratio is 1/51... Which is what I dislike about the convention of writing 1:12.5 when what is really meant is 1 part A plus 12.5 parts B.

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