hunnymonster said:henkverhaar said:b] cold water dissolves less fatty acid salts and it is therefore more difficult to make a good lather with cold water -- solubility is what makes potassium salts superior latherers over sodium salts
Does the solubility of the anion vary with the cation by that much?
Yes, apparently it does. Haven't looked up the actual solubilities/ion products, but surfactants are funny things, physicochemically speaking. It may have something to do with the local ion strength at the aequeous side of the air/water interface in the lather (the bubbles' edges...), where the larger size of the potassium ion stabilizes the surfactant layer? Again, just theorizing here.
And should we seek out Rubidium or Caesium salts for even better experience? (I'll let others suggest Francium salts - although I read glowing reports of their efficacy :lol: )
Well, the Francium soaps would be interesting, especially if you make an autoradiogram after shaving ;-) But other than that, no, all other alkali and alkaline earth salts of fatty acids are insoluble in water (remember soap scum?).
If soaps would behave normally (i.e. not as a surfactant, I guess), the potassium salt would be less soluble than the sodium salt.