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Remove the pan from the heat and add the salt. Allow the mixture to cool. Skim the top layer from the mixture. Pour the glycerin into a glass bottle.
Once the mixture has reached the proper consistency, take the pan off the heat. Mix in cup (150 g) of salt, and stir well so it is thoroughly incorporated. Make sure that the mixture is still hot when you add in the salt. After you've mixed the salt into the lye and oil mixture, leave it to cool completely, which should take 20 to 30 minutes. As it cools, the soap and glycerin will gradually separate into different layers. The soap will solidify into a thick layer on the top of the mixture, while the glycerine will remain liquid-y on the bottom. When the mixture has cooled completely, pour off the top soap layer from the top of the glycerin. You may find it easier to use a spoon to gently lift the soap off, though. If you want to use the soap, add it to a soap mold and put it in the freezer for 24 hours. Let the soap bars air dry for at least 2 to 3 weeks to finish curing them. If you don't want to make soap, you can discard the soap layer. Once you've removed the soap from the top of the mixture, transfer the liquid vegetable glycerine to a glass bottle. Seal the container tightly, and store it in the refrigerator. The vegetable glycerin should keep in the fridge for at least 3 to 4 weeks. You'll know that it has gone bad if it is no longer clear and instead appears cloudy. Glycerin that has gone bad may also develop a foul smell.