Freebase (chemistry)
Freebase refers to the standalone basic form of an amine, usually an alkaloid natural product, as opposed to its water-soluble salt form. Most alkaloids are unstable and corrosive in their freebase form, and thus are usually stored in salt form.  The salt form is the neutral amine compound with an additional proton, which is positively charged, plus a negative counterion.  Freebase amines are often found as hydrochloride salt, although other negative counterions are found, such as acetate, oxalate, bromide, et cetera.
The process of freebasing is often a key procedure during the workup chemical reaction that produces an amine.  First, the amine compound is extracted into a water away from organic solvents by the addition of acid.  Since it is protonated, and organic solvents are less likely to solubilize charged compounds, the amine migrates to the aqueous phase.  Many compounds without amines will remain in the organic phase, although some compounds may cross into the aqueous phase as well.
The second step is to extract the amine compound back into the organic layer by treating the water with base ("freebasing").  The amine compound will now be uncharged and become resolubilized into the organic layer, away from the aqueous.  Most of the non-amine compounds which crossed over into the aqueous previously will remain there, because a change of pH is unlikely to affect its phase preference.
Conversely, it is possible to take amine in the salt form, freebase it into the organic layer, and extract it back into water by acidification.  This is what is often informally done by narcotic drug users.  If impurities contain amines, or other pendant groups with similar pH profiles, however, they are likely to follow the desired compound through both stages of the freebasing process.

# Freebases in recreational drug usage
When used as a verb, it refers to smoking freebase cocaine, crack cocaine, freebase heroin or more rarely freebase PCP. Freebasing also refers to the process of freeing the active ingredients of a drug from its adulterants with which, in the slang term, it has been "cut". Adulterants are various substances which are mixed into drugs as fillers by dealers, thus increasing the amount that they can sell. Adulterants commonly include inositol and baby powder in the case of cocaine, and a wide range of substances in the case of heroin.
Drugs smoked in their freebase form are generally more powerful, and act more rapidly, than their salts. This can make freebase drugs even more powerfully addictive than their salt equivalents. Some drugs such as methamphetamine, MDMA, mescaline and dimethyltryptamine are strong-smelling, corrosive oily yellow liquids when in base form and so are rarely ingested as bases, instead almost always being encountered as the hydrochloride or sulfate salts.

## Freebase heroin
Illegal heroin is sometimes distributed in its freebase form, highly adulterated with fillers. The users then add acid to convert it to its water-soluble salt form to make it injectable. This is typically done by mixing the freebase form of the drug with a commonly available mild acid such as acetic or citric acid, and warming the mixture in a spoon or aluminum foil in order to make an injectable solution. Often the solution is injected hot to add a rush as it is felt travelling through the user's body, although it is far less dangerous to let it cool to more of a warm state.

## Freebase cocaine
As the name implies, "freebase" is the base form of cocaine, as opposed to the salt form of cocaine hydrochloride. Whereas cocaine hydrochloride is extremely soluble in water, cocaine base is insoluble in water and is therefore not suitable for drinking, snorting or injecting. Cocaine hydrochloride is not well-suited for smoking because the temperature at which it vaporizes is very high, and close to the temperature at which it burns; however, freebase cocaine base vaporizes at a low temperature, which makes it suitable for inhalation.
Smoking freebase is preferred by many users because the cocaine is absorbed immediately into blood via the lungs, where it reaches the brain in about five seconds. The rush is much more intense than sniffing the same amount of cocaine nasally, but the effects do not last as long. The peak of the freebase rush is over almost as soon as the user exhales the vapor, but the high typically lasts 510 minutes afterwards. What makes freebase a particularly dangerous drug is that users typically don't wait that long for their next hit and will continue to smoke freebase until none is left. These effects are similar to those that can be achieved by injecting or "banging" cocaine hydrochloride, but without the risks associated with intravenous drug use (although there are other serious risks associated with smoking freebase).
Freebase cocaine is produced by first dissolving cocaine hydrochloride in water. Once dissolved in water, cocaine hydrochloride (Coc HCl) dissociates into protonated cocaine ion (CocH+) and chloride ion (Cl-). Any solids that remain in the solution are not cocaine (they are part of the cut) and are removed by filtering. A base, typically ammonia (NH3) in the case of traditional "freebase" or sodium bicarbonate (baking soda) in the case of crack freebase, is added to the solution. Using ammonia as an example, the following net chemical reaction takes place:
As freebase cocaine (Coc) is insoluble in water, it precipitates and the solution becomes cloudy. To recover the freebase in the "traditional" manner, diethyl ether is added to the solution: Since freebase is highly soluble in ether, a vigorous shaking of the mixture results in the freebase being dissolved in the ether. As ether is practically insoluble in water, it can be siphoned off. The ether is then left to evaporate, leaving behind the nearly pure freebase. Alternatively, the freebase solution is simply evaporated until the freebase/cut solution "rocks up"thereby producing the form commonly known as "crack" or "rock" cocaine.
Since the manufacture of "traditional" freebase involves the use of flammable solvents, it is a dangerous process, particularly since it is often carried out outside a controlled laboratory environment without sufficient safety precautions.
The "traditional" procedure is dangerous because of the hazards of handling diethyl ether: it is extremely flammable, its vapors are heavier than air and can "creep" from an open bottle, and in the presence of oxygen it can form peroxides which can spontaneously combust. It is due both to these dangers and to the relative complexity of the "traditional" ammonia/ether method that the simpler "crack" method with sodium bicarbonate became the norm.
Although freebase cocaine prepared with ammonia and ether is generally purer than freebase cocaine prepared with baking soda but no solvent, the cocaine fumes produced when the product is smoked are approximately equally pure, and the active ingredient ingested is exactly the same. Despite this, for many years "traditional" freebase smokers scorned "crack" freebase smokersasserting incorrectly that these were fundamentally different drugs.