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

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• 10-22-2003, 05:00 PM
Eric Rose
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!!
• 10-22-2003, 05:21 PM
jbj
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
• 10-22-2003, 05:56 PM
Eric Rose
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!!
• 10-22-2003, 06:26 PM
jbj
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
• 10-22-2003, 06:55 PM
Jorge Oliveira
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
• 10-22-2003, 10:20 PM
ann
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)
• 10-23-2003, 01:53 AM
Ole
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?
• 10-24-2003, 12:41 PM
jbj
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
• 10-24-2003, 12:50 PM
fhovie
Beautiful Mind??
Governing Dynamics?

.... sorry -- I live near Hollywood
• 10-25-2003, 09:17 AM
Ole
Quote:

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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