This method is to purify liquids from non-volatile impurities, and used for separating the constituents of a liquid mixture which differ in their boiling points.
There are various methods of distillation depending upon the difference in the boiling points of the constituents. The methods are
(i) simple distillation
(ii) fractional distillation and
(iii) steam distillation.
The process of distillation involves the impure liquid when boiled gives out vapour and the vapour so formed is collected and condensed to give back the pure liquid in the receiver. is method is called simple distillation. Liquids with large difference in boiling point (about 40K) and do not decompose under ordinary pressure can be purified by simply distillation Eg. The mixture of C₆H₅NO₂ (b.p 484K) & C₆H₆(354K) and mixture of diethyl ether (b.p 308K) and ethyl alcohol (b.p 351K)

Few substances like benzoic acid, naphthalene and camphor when heated pass directly from solid to vapor without melting (ie liquid). On cooling the vapours will give back solids. Such phenomenon is called sublimation. It is a useful technique to separate volatile and non-volatile solid. It has limited application because only a few substance will sublime.
Substances to be purified is taken in a beaker. It is covered with a watch glass. The beaker is heated for a while and the resulting vapours condense on the bottom of the watch glass. Then the watch glass is removed and the crystals are collected. This method is applicable for organic substance which has high vapour pressure at temperature below their melting point. Substances like naphthalene, benzoic acid can be sublimed quickly. Substance which has very small vapour pressure will decompose upon heating are puried by sublimation under reduced pressure. This apparatus consists of large heating and large cooling surface with small distance in between because the amount of the substance in the vapour phase is much too small in case of a substance with low vapour pressure.

(i) Test for halogens:To a portion of the Lassaigne's filtrate add dil HNO₃ warm gently and add AgNO₃ solution.
a) Appearance of curdy white precipitate soluble in ammonia solution indicates the presence of chlorine.
b) Appearance of pale yellow precipitate sparingly soluble in ammonia solution indicates the presence of bromine.
c) Appearance of a yellow precipitate insoluble in ammonia solution indicates I the presence of iodine.
\(Na+\underset { from\quad organic\\ compound }{ X } \overset { heat }{ \rightarrow } \quad \quad Na{ X }_{ (Where\quad X=Cl,\quad Br,I) }\)
Nax + AgNO₃ AgX + NaNO₃
(ii) If N or S is present in the compound along with the halogen, we might obtain NaCN and Na₂S in the solution, which interfere with the detection of the halogen in the AgNO₃ test Therefore we boil the Lassaignes extract with HNO₃ which decomposes NaCN and Na₂S as
\(NaCN+{ HNO }_{ 3 }\overset { \Delta }{ \rightarrow } { NaNO }_{ 3 }+HCN\uparrow \)
\({ Na }_{ 2 }S+{ 2HNO }_{ 3 }\overset { \Delta }{ \rightarrow } { aNaNO }_{ 3 }+{ H }_{ 2 }S\uparrow \)
\(NaCN+{ AgNO }_{ 3 }\overset { further }{ \rightarrow } \underset { white\quad ppt\quad confusing\quad with\quad AgCl }{ AgCN } +{ NaNO }_{ 3 }\)
\(\\ { Na }_{ 2 }S+{ AgNO }_{ 3 }\rightarrow \underset { black\quad ppt }{ { Ag }_{ 2 }S } \downarrow { NaNO }_{ 3 }\)

The organic substance is mixed with about three times its weight of dry copper oxide by grinding. The mixture is then placed in a hard glass test tube fitted with a bent delivery tube. The other end of which is dipping into lime water in an another test tube. The mixture is heated strongly and the following reaction take place.
\(C+2CuO\longrightarrow { CO }_{ 2 }+2Cu\)
\(2H+CuO\longrightarrow { H }_{ 2 }O+Cu\)
Thus if carbon is present, it is oxidized to CO₂ which  turns lime water milky. Ifhydrogen is also present, it  will be oxidized to water which condenses in small  droplets on the cooler wall of the test tube and inside  the bulb. Water is collected on anhydrous CuSO₄  which turns anhydrous CuSO₄ blue. This confirms  the presence of C and H in the compound

A carbon atom whose tetra valency is satisfied by four different substituents (atoms or groups) is called asymmetric carbon or chiral carbon. It is indicated by an asterisk as C*. A molecule possessing chiral carbon atom and non-super impossible to its own mirror image is said to be a chiral molecule or asymmetric, and the property is called chirality or dissymmetry.