Scientific question

Sorry I'm not sure of the right words, so I will try and ask in my own :wink:

How much water does it take to dissolve salt in water? I have a faint memory of it being more than 1 part water to disolve 1 part salt.

The reason I am asking - I made a batch of OMH, dissolved the lye in minimum water, then added salt, naturally it didnt dissolve because there was no 'free' water left (only a couple of grams). I am assuming Lye is 1 part to 1 part as it can be mixed until clear.

The thing that is confussing me - the water should go clear to ensure the salt is completely dissolved (just been reading up on this), but that is actually really hard to do, so its making me think that the ratio of water needs to be quite high?

Next scientific question:

Can salt 'push out' the dissolved lye? (lol sorry not very scientific) What I mean is - if you had previously dissolved lye and added salt and there was not enough 'free water' would parts of the lye then become undissolved.

The reason for this question is - My OMH did have granules on the bottom of the lye water after I added the salt. I assumed it was only salt as all the lye crystals were dissolved when salt was added. i sieved the lye water and used it - but my soap is VERY over superfatted and slick.

I know next time to add some extra water for the salt, I'm just not sure how much :?:

1 part lye to one part water might not be enough to dissolve all your lye. Some of the lye might precipitate out. I would do a 40% lye solution instead. How much salt were you trying to add?

I used 162 grams of lye to 180 grams of water then add 260 of milk at trace. I tried to add 30 grams of salt.

I ran it through soap calc and a 40% solution would have needed 244grams. Is a 40% solution needed even when adding liquids at trace?

The amount of salt or NaOH that water can hold in solution depends on the temperature of the water. If you don't use enough water to make your lye solution, it will precipitate out as it cools.

When I use a 1:1 ratio, it clouds as it cools, but I don't have lye sitting on the bottom of the container.

Many soap makers use the 1:1 ratio, but it isn't necessary. You can use more liquid. Why are you reducing your liquid amount? Perhaps you can get the same affect with another technique.

I'm not sure if the salt would cause sodium hydroxide to come out of solution, exactly, but yes - you will impact how much of something the water can hold by dissolving something else in it. Think of it as marbles in a jar - if you add rocks, then there isn't as much room for the marbles.

The solubility of salt and the solubility of NaOH are available online http://en.wikipedia.org/wiki/Solubility_table and in books - and they are temperature related. In general, room temp water can hold approximately the same amount of NaOH. Heat the water and it'll hold more (until it cools). Salt is less soluble.

O.K

So if the lye disolves completely at a ratio of 1:1 and I soap at 110 deg and there is no sign of cloudyness or lye crystals my soap will be fine? (this is what I usually do)

And if I decided to soap at room temp and it was cloudy it is still O.K as long as there are no crystals in the solution (I'm thinking this might be risky)

As for the salt - i dissolved the lye, but the water was still cloudy, I'm thinking the salt pushed some of the lye out of the way.

I'll do some research via the links and figure out how much water to add next time, or just skip the salt.

Thanks for the explanation everyone, and the link Carebear, I'm off to read it now

Wow that was interesting. Salt isnt very soluble at all, @ 100deg its only 39g/100g of water. And when brought down to soaping temp of around 40deg its only about 36/100grams.

That would mean I needed between 80 and 90grams of extra water to dissolve the salt if using a lye ratio of 1:1

So even a 40% lye solution wouldnt have been enough water.

I have a dumb question: just curious: why are you adding so much salt to your lye water?

I usually add only a tsp (6gms) to 24 ounces of water, hoping it might harden the soap a bit more. I stir like crazy when the lye/water is really hot, and it does dissolve.

For soap hardness, try 1 tsp. of salt per lb. Otherwise I would reformulate your recipe with harder oils.

Can salt 'push out' the dissolved lye?

Click to expand...

Shortly: YES, and your greasy soap is proof of this.

Googling, I wasn't able to find any table showing mixed solubilities so that you can find out exactly how much water to add.

I have just tried a salt bar, and added add salt (finely ground) at medium trace. You probably can do the same.

An alternative suggestion for your recipe is to add the salt to the milk.

For soap hardness, try 1 tsp. of salt per lb. Otherwise I would reformulate your recipe with harder oils.

Click to expand...

Do you mean that more salt than 1 tsp won't make the soap harder (harder than with 1 single tsp) ?

Starum said:

Can salt 'push out' the dissolved lye?

Click to expand...

Shortly: YES, and your greasy soap is proof of this.

Googling, I wasn't able to find any table showing mixed solubilities so that you can find out exactly how much water to add.

I have just tried a salt bar, and added add salt (finely ground) at medium trace. You probably can do the same.

An alternative suggestion for your recipe is to add the salt to the milk.

[quote:2pdoa5ut]For soap hardness, try 1 tsp. of salt per lb. Otherwise I would reformulate your recipe with harder oils.

Click to expand...

Do you mean that more salt than 1 tsp won't make the soap harder (harder than with 1 single tsp) ?[/quote:2pdoa5ut]
Using salt will only marginally harden your soap if your formula is soft to begin with. You could make a salt bar by adding salt AFTER lye water and oils have been combined. Start with 1:2 ratio, plain table salt to raw soap batch. Be aware that this type of soap hardens fast, so it will need to be cut sooner.

Ok.

But it does make sense that 20 tablespoons of salt will make a harder bar than 1 single tablespoon, right ?

This is how I see things: if after 20 tsp, the soap is still not hard enough for our liking, the only thing left to do is to change the recipe.

Be aware that this type of soap hardens fast, so it will need to be cut sooner.

Click to expand...

I learned this the hard way

I've made this recipe 2 other times (with salt) and it works perfectly.

I am new to using salt for hardening, here is my research:

http://soapmakingforum.com/forum/viewto ... ight=quest

On researching there was such a variation between salt recommendations. Most were between 1 and 2.5 %, some of total batch some on oils.

I went for 1.5% of total batch, or 2.1% of oils.

My issues are only because of the large water discount.

On reflection, I could most definately reduce the amount of salt, and next time will try 10grams per kg, this will solve the dissolving issue.

Starum said:

Can salt 'push out' the dissolved lye?

Click to expand...

Shortly: YES, and your greasy soap is proof of this.

Click to expand...

I wouldn't consider greasy soap made by someone with limited experience proof of this. In a controlled study I'd consider it potentially compelling but not yet.

The inclusion of another soluble item in a solution can "push" something out of solution, or the initially solubulized item could keep the second from dissolving fully or at all. Or a combination. If you have technical proof I'd love to see it - my degree was a long time ago.