Q.What is absolute alcohol?

Methyl alcohol (methanol, CH3OH) is known as wood spirit.

Methanol was historically prepared by the destructive distillation of wood, which is why it earned the common names wood spirit and wood alcohol (also carbinol). It …

Methyl alcohol (methanol) is added to ethyl alcohol to "denature"/poison it for industrial use.

Rectified spirit (ethyl alcohol) meant for industrial, non-drinking use is deliberately made unfit for consumption — "denatured" — by adding small amounts of a poisonous or foul substance, most commonly methyl alcohol (methanol), along with pyridine or a dye like methylene blue. This denatured spirit is called …

"Wood spirit" is the traditional name for methanol, originally obtained by the destructive distillation of wood.

Methanol (CH₃OH) was historically obtained by the destructive (dry) distillation of wood in the absence of air, which is why it earned the name "wood spirit" or "wood alcohol". Today it is manufactured industrially from carbon monoxide and hydrogen (syngas) over a ZnO–Cr₂O₃ catal …

Denatured alcohol = ethanol + additives that make it undrinkable but still chemically usable industrially.

Pure ethanol produced industrially (e.g. by fermentation followed by distillation) is chemically identical to drinking alcohol, and governments tax/regulate potable alcohol heavily. To supply cheap ethanol for industrial and laboratory use (as a solvent, in varnishes, perfumes, fuel, etc.) without it being diverted for drinking, the ethanol is denatured.

Denaturing means adding small quantities of substances that make the ethanol:

• Unfit/unpleasant to drink — e.g. pyridine (gives a bad smell/taste), or methanol (which is poisonous and can cause blindness or death if consumed).
• Sometimes also coloured, e.g. by adding copper sulphate (blue colour), so it is visually distinguishable from drinking alcohol. …

Absolute alcohol is completely water-free ethanol, made by dehydrating rectified spirit (95% ethanol).

Ordinary fermentation and fractional distillation of ethanol-water mixtures can only give rectified spirit, which is about 95% ethanol and 5% water — this composition forms an azeotrope (constant-boiling mixture) that ordinary distillation cannot separate further.

To remove this last 5% of water, rectified spirit is treated with a strong dehydrating agent such as quicklime (CaO). The CaO reacts with and absorbs the water: …