Sodium fusion test

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The sodium fusion test is used in elemental analysis for the qualitative determination of the presence of halogens, nitrogen and sulfur in a sample. It was developed by J. L. Lassaigne.[1]

The test involves heating the sample strongly with clean sodium metal, "fusing" it with the sample. A variety of techniques has been described. The "fused" sample is plunged into water, and the usual qualitative tests are performed on the resultant solution for the respective possible constituents.[1]


It is a general test for the detection of halogens, nitrogen and sulfur in an organic compound. These elements are covalently bonded to the organic compounds. In order to detect them, these have to be converted into their ionic forms. This is done by fusing the organic compound with sodium metal. The ionic compounds formed during the fusion are extracted in aqueous solution and can be detected by simple chemical tests. The extract is called sodium fusion extract or Lassaigne's extract.

When an organic compound is heated strongly with sodium, any halogens, nitrogen, and sulfur will be converted into inorganic sodium salts such as sodium halide (for halides), sodium cyanide (for nitrogen), sodium sulfide (for sulfur), and sodium thiocyanate (for sulfur and nitrogen).The nitrogen is confirmed with ferrous sulfate i.e. iron sulfate.


  1. ^ a b Gower, R. P.; Rhodes, I. P. (1969). "A review of techniques in the Lassaigne sodium-fusion". J. Chem. Ed. 46 (9): 606. Bibcode:1969JChEd..46..606G. doi:10.1021/ed046p606. 

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