Sodium fusion extract, also known as Lassaignes extract, is an aqueous extract obtained from the sodium fusion test, which is used in elemental analysis for the qualitative determination of the presence of foreign elements, namely halogens, nitrogen, and sulfur, in an organic compound. The preparation of sodium fusion extract involves the following steps:

1. A small piece of dry sodium metal is taken in a fusion tube and heated until it melts to form a silver globule.
2. The organic compound is added to the tube and heated to red hot.
3. The halogens, nitrogen, and sulfur that are covalently bonded to the organic compound are converted to various sodium salts formed during the fusion.
4. The aqueous extract is made alkaline by adding NaOH, and then various tests are performed to detect the presence of nitrogen, sulfur, and halogens.

Some of the tests that can be performed on the sodium fusion extract include:

• Test for nitrogen: The extract is made alkaline by adding NaOH, and then freshly prepared FeSO4 solution is added and boiled. A few drops of FeCl3 are added, and the formation of Prussian blue (bluish green) color indicates the presence of nitrogen in the organic compound.
• Test for sulfur: The extract is acidified with acetic acid, and lead acetate is added to it. A black precipitate of lead sulfide indicates the presence of sulfur.
• Test for halogens: The extract is treated with silver nitrate, and the formation of a white precipitate indicates the presence of halogens.

The sodium fusion test is a rapid method for the detection of the presence of various elements in an organic compound, and the sodium fusion extract obtained from this test can be used for further analysis.