My challenge is to provide a low-tech (DIY) way to purify the glycerol produced from soapmaking or biodiesel production. Simple distillation is out because the boiling point for glycerol is above its smoke point. Vacuum distillation and electrolysis do not count as low-tech. :) The input mixture is a mixture of glycerol, water, sodium hydroxide, and sodium chloride. The desired output is concentrated (>80%, preferably 100%) glycerol in water. Someone suggested a gelatin-and-salt bridge to some distilled water, but I'm not sure how that would work. Any suggestions or pointers to tech that might solve this are welcome.