Pre-treatment methods are used for the even preparation of textile webs; in order to prepare it for all subsequent finishing processes like dyeing, printing and finishing. These are generally scouring and bleaching processes which are designed to remove dirt and contaminants from the fibres. Analyses of raw cotton have revealed surprisingly high variation in levels of calcium, magnesium and iron. The metal ions are transferred to the cotton through contamination with soil in the cotton plantation area. Modern harvesting methods, processing systems and packaging plants increase the iron content of the fabric. In peroxide bleaching processes, these metallic contaminants result in the feared catalytic damage which - in extreme cases - can cause holes in the fabric and the destruction of individual threads. Various extraction methods can be employed at the pre-treatment stage to prevent this from happening. From a chemical point of view, demineralisation with the aid of hydrochloric acid is the simplest solution. Complex metallic compounds (e.g. iron (III) oxide, which is also known more simply as "rust") are converted into water soluble ferric chlorides which can then be simply washed out. The treatment of cotton with hydrochloric acid is very risky, as the cotton can be completely destroyed if the acid is not applied correctly. This makes Benninger's job of delivering an operationally safe and efficient plant for demineralisation with inorganic acids all the more challenging.