Process for cleansing a raw material of contaminants by fractionation, with which a raw material is split up into a stream of gas with a high purity and a stream of gas with a low purity, the raw material being chlorine, the contaminants having a higher boiling-point than the raw material, the contaminants being bromine and an explosive substance, the explosive substance being NCl 3, characterised by the following steps: I. evaporating the raw material in a first evaporator to yield the raw-material gas, or making available a raw-material gas from a supply source, II. introducing the raw-material gas into a wash column in which a washing liquid for diminishing the content of contaminants trickles towards said gas, III. removal and partial condensation of the raw-material gas purified in this way at the head of the wash column, the condensate being conducted back as washing liquid towards the head of the wash column, and the remaining raw-material gas issuing from the wash column, said gas exhibiting a lower content of contaminants than the raw-material gas in step I, IV. issuing of the washing liquid as a stream of liquid at the bottom of the wash column, the washing liquid exhibiting a higher content of contaminants than in step II, V. introducing the washing liquid from above into the shell side of a second evaporator with horizontal tubes, the washing liquid entering there a tube bundle of the evaporator and being evaporated before it reaches the bottom of the evaporator, or into the tubes of a second evaporator with vertically arranged tubes, the washing liquid being evaporated inside the tubes before it reaches the bottom of the evaporator, and the gas outlet being arranged at the bottom of the evaporator, or into the tubes of a second evaporator with vertically arranged tubes, the washing liquid being evaporated inside the tubes before it reaches the bottom of the evaporator and the vapour being routed such that it once again flows upwards through a separate part of the tubes, thereby being superheated, and exiting on the upper side of the evaporator, VI. guiding of the vapour generated from the washing liquid and of the not yet evaporated washing liquid in co-current flow, VII. issuing the vapour generated from the washing liquid from the second evaporator as a stream of gas, said gas exhibiting a higher content of contaminants than the raw-material gas in step I. I. evaporating the raw material in a first evaporator to yield the raw-material gas, or making available a raw-material gas from a supply source, II. introducing the raw-material gas into a wash column in which a washing liquid for diminishing the content of contaminants trickles towards said gas, III. removal and partial condensation of the raw-material gas purified in this way at the head of the wash column, the condensate being conducted back as washing liquid towards the head of the wash column, and the remaining raw-material gas issuing from the wash column, said gas exhibiting a lower content of contaminants than the raw-material gas in step I, IV. issuing of the washing liquid as a stream of liquid at the bottom of the wash column, the washing liquid exhibiting a higher content of contaminants than in step II, V. introducing the washing liquid from above into the shell side of a second evaporator with horizontal tubes, the washing liquid entering there a tube bundle of the evaporator and being evaporated before it reaches the bottom of the evaporator, or into the tubes of a second evaporator with vertically arranged tubes, the washing liquid being evaporated inside the tubes before it reaches the bottom of the evaporator, and the gas outlet being arranged at the bottom of the evaporator, or into the tubes of a second evaporator with vertically arranged tubes, the washing liquid being evaporated inside the tubes before it reaches the bottom of the evaporator and the vapour being routed such that it once again flows upwards through a separate part of the tubes, thereby being superheated, and exiting on the upper side of the evaporator, VI. guiding of the vapour generated from the washing liquid and of the not yet evaporated washing liquid in co-current flow, VII. issuing the vapour generated from the washing liquid from the second evaporator as a stream of gas, said gas exhibiting a higher content of contaminants than the raw-material gas in step I.