Quote Originally Posted by pdeeh View Post
So, just to clarify for people like me (gave up mathematics and chemistry age 14, find ratios difficult to grasp sometimes, has to calculate the dilution on a scrap of paper each time I make up some developer) ...

10g/l = 1% solution
100g/l = 10% solution
200g/l = 20% solution ... and so on, up to the solubility limit of KBr in water I presume.

SO, when I am making up a litre of developer that requires 1g of KBr per litre, I would substitute 100ml of a 10% solution for 100ml of the total volume of water required by the formula ?

(I imagine a lot of sighing, eye rolling and shaking of heads from all the scientificky types at this point)
No quite 100ml. You see, 100ml of 10% solution contains exactly 10g of KBr. If you need 1g, you use 1/10th of it, or 10ml, not 100.

Think of it in terms of bromide in the bottle. Say you dissolved 100g of KBr in some amount of water. If a formula calls for 50g of KBr, you use half of the solution, if a formula calls for 1g, you use 1/100ths of the solution, 5g - 5/100ths, etc.