The dibrominated product so obtained was then fused with caustic potash, the melt dissolved in water, and on the addition of hydrochloric acid to the solution, alizarin was precipitated.
The precipitated alizarin is then well washed and made into a paste with water, in which form it is put on to the market.
The first step in the synthetical production of alizarin was the discovery in 1868 of C. Graebe and C. Liebermann that on heating with zinc dust, alizarin was converted into anthracene.
Numerous derivatives of alizarin are known.
This compound is hydrolysed by hydriodic acid and alizarin is obtained.
This he did in 1869, thus securing for the Greenford Green works a monopoly of alizarin manufacture for several years.
Caustic soda is used in very large quantities in the manufacture of soap, paper, textile fabrics, alizarin and other colouring matters, and for many other purposes.