Techniques useful for the separation of mixtures include the following: DISTILLATION is the purification of a liquid by heating it to its boiling point, causing vaporization, and then condensing the vapors into the liquid state and collecting the liquid. Separation of two or more liquids requires that they have different boiling temperatures. All boiling temperatures can be reduced by decreasing the pressure on the liquid. EXTRACTION is the removal of one substance from a mixture because of its greater solubility in a given solvent. FILTRATION is the process of removing or "straining" a solid (the chemical term is precipitate) from a liquid by the use of filter paper or other porous material. DECANTING is the pouring of a liquid from a solid-liquid mixture, leaving the solid behind. CENTRIFUGING is the process of separating a suspended solid from a liquid by whirling the mixture at high speed. SUBLIMATION is the physical property of some substances to pass directly from the solid state to the gaseous state without the appearance of the liquid state. Not all substances possess this characteristic. If one component of a mixture sublimates, this property may be used to separate it from the other components of the mixture. Iodine (I2), naphthalene (C10H8, mothballs), ammonium chloride (NH4Cl) and dry ice (solid CO2) are some substances which sublime. CHROMATOGRAPHY is the process of separating a mixture by the distribution of its components between two phases, one phase being stationary and the other phase moving. Some examples of chromatography are gas chromatography, paper chromatography, and thin-layer chromatography.