Excise duty exemption for Chapter 68 goods using substantial fly ash or phospho gypsum content, excluding specified headings. Full exemption from excise duty is provided for goods of Chapter 68, excluding Heading 68.04, in which more than 30% by weight (minus the water content) of fly ash or phospho gypsum or both has been used, exercised under the power conferred by sub section (1) of section 5A of the Central Excises and Salt Act, 1944.