Modvat credit on sulphuric acid allowed in full for detergent manufacture, with spent acid clearance and duty conditions. Modvat credit on sulphuric acid used in detergent manufacture is allowed on the full quantity of concentrated sulphuric acid physically employed in production, despite separation of a portion as 'Spent Acid'. Spent Acid classifiable with concentrated sulphuric acid must be cleared on payment of duty under the applicable clearance provision unless exempt. Existing contrary instructions are rescinded and the instruction is to be circulated to Principal Collectors and Collectors of Central Excise for compliance.