Dissolving salt

[penelopejane]

I suspect you would have to use more than "full water" (a lye concentration below 28%) to get a perfectly clear mixture with no precipitated salt, but that's not practical from a soap-making standpoint. We'd have to have a solubility chart of salt-NaOH-water to know for sure.

It makes little or no difference if you dissolve the salt in one portion of water-based liquid and the NaOH in the another separate half and then use the two to make a batch of soap. That's like putting chocolate in a 1/2 glass of milk and strawberry in the another 1/2 glass and hope the two won't mix together in your stomach when you drink each 1/2 glass separately. When you combine the two portions of liquid with the fat in your soap pot, some of the salt will still precipitate out. You just won't see it.

I mix some salt with the water and then add the lye but I mix all the rest of the additives (and everything if I'm not making soleseife soap) into some reserved water because I was worried that the precipitate was lye. Good to know it is salt.

Even if they do precipitate out when my reserved water and additives are mixed into the oils and then the salt and lye solution added I can't see it and that makes a huge psychological difference to me. (It really worries me to see it precipitate out and sometimes it seems lumpy so it looks more like the lye than salt and I worry it won't saponify properly.)

Also by adding sugar and citric acid to reserved water (or to the milk if using it) and then to the oils you avoid the lye burning the sugar and making the batter brown.

 

[Steve85569]

Does anyone know how much water it would take to properly dissolve 2.45 ounces of lye AND 1.55 ounces of salt (putting both in the same container)? Is there a formula for salt and lye absorbtion?

The salt would take a minimum of 6.2 ounces of water to dissolve. Lye will dissolve in a 1:1 solution. 2.45 plus 6.2 is 8.65. Using those numbers you can *probably* get the salt to dissolve in a 50:50 mix.
That gives a water : lye ratio of 3.53:1 which would make the soap very, very wet.

Why not just add salt to the water at 25%? You would still have a 12.5% brine and not have to worry about precipitants.

 

[BrewerGeorge]

The salt would take a minimum of 6.2 ounces of water to dissolve. Lye will dissolve in a 1:1 solution. 2.45 plus 6.2 is 8.65. Using those numbers you can *probably* get the salt to dissolve in a 50:50 mix.
That gives a water : lye ratio of 3.53:1 which would make the soap very, very wet.

Why not just add salt to the water at 25%? You would still have a 12.5% brine and not have to worry about precipitants.

With respect, that's not right. The solutions are not additive because of the common ion interference with the solubility of NaCl. From a higher perspective, all the differences in procedure would be irrelevant if we could form a stable solution. Dissolving the salt first, dissolving both separately and mixing the resulting solutions, etc processes are not about forming a complete solution of both ions. We're just not going to practicably be using enough water to do that in soaping. What the procedures ARE about is controlling the salt precipitate - when it forms and how big it is.

 

[DeeAnna]

Kudos to Brewer George -- his perspective is closer to my understanding. The obvious "common sense" explanation is not necessarily the correct one, especially when we're talking about chemistry.

 

[Steve85569]

^^ All true. Point is we would end up with too much water in the soap. I count on those like BrewerGeorge and DeeAnna to help me out with the chemistry since I am "challenged" in that area.