Conversion of anhydrous ammonia to aqueous solution not manufacture, so no additional excise duty where original ammonia is duty paid. Conversion of duty paid anhydrous ammonia into aqueous ammonia is not manufacture under Section 2(f) of the Central Excise Act, 1944. The process is a simple, reversible dissolution done for transportation; both forms fall within the same tariff description, and no chapter or section note treats the conversion as manufacture. Therefore, no further excise is payable where the anhydrous ammonia is duty paid, and pending disputes should be settled in line with these guidelines.