Leeds, England/leeds455

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The Yorkshire squares technology uses stone (usually slate) fermentation vats for a slow-acting, top-fermentating yeast. The cool temperatures and the slow fermentation process ensures a drink richly impregnated with carbon dioxide, rendering the final draft "full of life." The effervescent nature of the beers brewed by the stone square system helps to protect them from airborne infection during fermentation, filling the vat with the heavier carbon dioxide and exposing it to close observation. This open vat with its slow fermentation process piqued the curiosity of Priestley, who began to study this gas -- thereby launching his general study of "airs." This was a watershed in Priestley's scientific life and its importance cannot be exaggerated: With Priestley's growing research with airs, he became deeply involved in chemistry, leading eventually to his discovery of oxygen.