carbon dioxide in carbonated water. The dissolution of CO2 in a liquid, gives rise to effervescence or fizz. Carbon dioxide is only weakly soluble in water, therefore it separates into a gas when the pressure is released. The process usually involves injecting carbon dioxide under high pressure. When the pressure is removed, the carbon dioxide is released from the solution as small bubbles, which causes the solution to become effervescent, or fizzy. Carbonated beverages are prepared by mixing chilled flavored syrup with chilled carbonated water. Carbonation levels range up to 5 volumes of CO2 per liquid volume. Ginger ale, colas, and related drinks are carbonated with 3.5 volumes. Other drinks, often fruity ones, are carbonated less. In the late 18th century, scientists made important progress in replicating naturally carbonated mineral waters. In 1767, Englishman Joseph Priestley first discovered a method of infusing water with carbon dioxide to make carbonated water when he suspended a bowl of distilled water above a beer vat at a local brewery in Leeds, England. His invention of carbonated water (later known as soda water, for the use of soda powders in its commercial manufacture) is the major and defining component of most soft drinks. Priestley found that water treated in this manner had a pleasant taste, and he offered it to his friends as a refreshing drink. In 1772, Priestley published a paper entitled Impregnating Water with Fixed Air in which he describes dripping oil of vitriol (or sulfuric acid as it is now called) onto chalk to produce carbon dioxide gas, and encouraging the gas to dissolve into an agitated bowl of water. Another Englishman, John Mervin Nooth, improved Priestley's design and sold his apparatus for commercial use in pharmacies. Swedish chemist Torbern Bergman invented a generating apparatus that made carbonated water from chalk by the use of sulfuric acid. Bergman's apparatus allowed imitation mineral water to be produced in large amounts. Swedish chemist Jöns Jacob Berzelius started to add flavors (spices, juices, and wine) to carbonated water in the late eighteenth century. Thomas Henry, an apothecary from Manchester, was the first to sell artificial mineral water to the general public for medicinal purposes, beginning in the 1770s. His recipe for 'Bewley's Mephitic Julep' consisted of 3 drachms of fossil alkali to a quart of water, and the manufacture had to 'throw in streams of fixed air until all the alkaline taste is destroyed'.