Just realized that all of futura's very helpful salting dilutions are based on weight / weight calculations.

So let's say that you find muriatic acid at a hardware store. The bottle says 30% HCl. Now let's get more specific here; 30% of what measurement is HCl?

It turns out that the 30% is calculated from the weight of HCl gas divided by the total weight of the solution (which is HCl gas weight + water weight). For instance, 30g HCl / (30g HCl + 70g water) = 30% (weight/weight)

So when futura is talking about making a 10% HCl solution from the store bought HCl, which reads 30% on the label, futura is sticking with the weight/weight (or w/w) designation of percentage when he says mix 33 mL of 30% HCl with 67 mL of water. This is essentially a (1/3) dilution of the original 30%. 30% (w/w) multiplied by a dilution factor of (1/3) equals 10% (w/w).

Now you're thinking, yeah so?

Well, if you think you can just take a shortcut and buy 10% HCl that is fine but beware that it could actually be 10% HCl (volume/volume). In other words a 10% dilution of the original store bought 30% HCl solution by volume and not by weight.

This means that, for example, 10 mL of the 30% store bought HCl solution was added to 90 mL of water. Or in other words a (1/10) dilution factor using volume/volume as the meaning of percentage. ** This would actually be the equivalent of a 3% (weight/weight) HCl solution **

So, to get straight to the point it will change your calculations of how many drops of HCl to add per however many hundreds of mLs of water used depending on how the percentage of your HCl solution is measured; whether its (weight of HCl / weight of solution) OR (volume of original stock HCl / volume of solution).

Please, if this is totally wrong, let me know, but this is what I'm decyphering from reading through these threads