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I am developing film using a solution I purchased online that is supposed to create one liter of developer. However, I do not need one liter, I need 625ml, which is all that I need.

The instructions say to mix the 66.3 grams of of powdered developer with 800ml of water, and to keep adding water until I get a total of 1000ml (1 liter). How do I modify these instructions to create a solution that would yield about ~625ml? Mixing the 66.3 grams of powder with 500ml of water and then adding more water would obviously make it too strong. How much powder would I need to use? An equation with variables would be helpful because I may need to change the amount.

I am unsure what tags to use, math is not my stron suit, feel free to edit for the proper ones.

ToastHouse
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2 Answers2

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You want to make a solution of identical concentration. Call that concentration C; let the amounts of solute you add be denoted by A, and V the volumes. Then you have $$ A_1/V_1 = C = A_2/V_2. $$

Daniel Y. Poon Syverson
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    This is above my mathematical understanding. I am unsure if the slash is denoting to divide, and have forgotten what the "lower exponent number" means. I haven't done this stuff in years, and haven't had a reason to use it until today. – ToastHouse Oct 23 '17 at 04:06
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You want to create $\frac{625}{1000}$ of the original recipe, so you simply multiply all the parts by $\frac{625}{1000}$ or $0.625$.

$66.3 \cdot \frac{625}{1000} = 41.4371$g, and $800 \cdot \frac{625}{1000} = 500$ml. So you should add $41.4371$g of powder and $500$ml of water. Originally, you add $200$ml after, so you also multiply this; $200 \cdot \frac{625}{1000} = 125$ml.

You mix $41.44$g of powder with $375$ml of water, then add $125$ml of water aftwerards, giving you a grand total of $625$ml.

Travis
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