ramtimram said:
That would be either extracting some other chemical that is dangerous, a chemical from the extraction remaining in the yield, or chemicals mixing and reacting to make a chemical that is dangerous.
To check the quality of the end result of your extraction, you can buy colorimetric reagent tests. Include some thin layer chromatography in the procedure, and you'll have a pretty good estimate of identity and purity.
If you work properly, the only extraction chemical that could possibly remain in the end product is a possible impurity in your naphta. You can check this by doing an evaporation test before using it. If want to be certain, destillation of the naphta will make sure no nonvolatiles are left. In any case, assure yourself that the naphta is low on aromatics (benzen, toluene) because those mess up freeze precipitations.
The only dangerous reactions I can see happening is mixing lye and water, which generates a lot of heat. Hot lye is very caustic. Wear glasses. Wear gloves. Be careful not to inhale the fine mist of lye droplets that may occur if the water gets too hot from the dissolving lye.
Additional dangers are: glassware breaking from thermal shock or slipping through your fingers (fingerfat + lye => soap). Spilling corrosive uneraseable black paint all over the floor is nasty, the flammable naphta doesn't make it better. And yeah, naphta is flammable.
The wrong people may walk in at the wrong moment.
ramtimram said:
I guess this is extremely naive, but I don't know anything about chemistry.
Good, so at least you know that you may have to learn some things. Most important safety advice is to think ahead of anything that can go wrong and then take precautions for such mishaps. One good precaution is to start really small, that way most mishaps will cause only small problems.
Overall, I would say driving a car is more dangerous. But people take their time to learn it and it works most of the time.