In the German speaking countries of Europe (Germany, Austria) - this is where I live - chemicals like HCL (hydrochloric acid) can easily be obtained. The same goes for kerosene ("petroleum") and some other non-polar solvents (google what "non-polar" and "polar" means... that's common knowledge, but yes, some don't know, so google it). Several alcohols can be bought in any pharmacy, such as isopropanol, ethanol, methanol...
And a/b extraction is an
Acid/
Base extraction. I'll give you an example:
Cocaine extraction from coca leaves:
Coca leaves are put into a non-polar solvent, like kerosene (petroleum in German and some other languages). The cocaine-base gets into solution - it's extracted from the leaves. Usually, natriumcarbonate (soda) is added to this to prevent salting processes, but don't mind this, you don't have to know what this does, I just added this because it's done - not important for our a/b extr. explanatory. So the cocaine base is solved in the kerosene.
How do we get it out of the kerosene?
We make it non-polar-solvent-INsoluable. That means, we convert it to a water-soluable salt of cocaine. For example, cocaine-sulphate, or cocaine-hydrochloride. So we pour a 5% sulphuric acid solution (with water) into the kerosene, stir well, let separate, suck out the acidic water layer that forms on the bottom and that contains the cocaine-sulphate. Now we have it in the water, in a much lower volume of liquid (for example, for 20 litres of kerosene, there isn't more than 0,5 litres of sulphuric acid 5% used,).
How do we get the cocaine-sulphate out of the liquid?
We basify it. Adding ammonia causes the cocaine-sulphate to break up into cocaine-base (freebase, the substance we extracted from the coca leaves), which is water-unsoluable and precipitates out of the water. It's filtered out with a coffee filter (for example). It's recommended to wash it with some water.
A/b extraction means that you use different solvents and solubilities of different substances to extract a certain substance. In my example, we wanted to seperate the cocaine-base from the liquid (kerosene) that we extracted the cocaine with from the leaves. So we converted it to a water-soluable (that means: non-polar-solvent-UNsoluable) cocaine-salt, then converted it back to a non-water-soluable cocaine-base (freebase) that can be smoked or cooked up with an acid in water in order to be shot (cooking up with an acid converts the freebase back to a salt of cocaine, for example cocaine-citrate or cocaine-ascorbate, cocaine-sulphate or cocaine-hydrochloride; depends on what salt you use).
I'm no chemist, and I hope that everything is true that I wrote.
