Fill a container about half way or more with distilled\xa0water, add the acid, and then bring up to volume with more\xa0water. In the example above, fill a flask with about 150 mL or more with distilled\xa0water, add 6.9 mL of concentrated sulfuric acid, then continue to dilute with\xa0water\xa0to the 250 mL mark.)\xa0Sulfuric acid\xa0is\xa0prepared\xa0industrially by the reaction of water with sulfur trioxide (see sulfur oxide), which in turn is made by chemical combination of sulfur dioxide and oxygen either by the contact process or the chamber process.