"Black's research began in an attempt to produce a milder [for medicinal use] from Epsom salts. ...He commenced by studying the different forms of lime. , when heated in a fire, became activated, and this quicklime, when placed in water, generated much heat, and was transformed into slaked lime. The limestone was supposed to have absorbed phlogiston from the fire and later to have lost it to the water. Black heated a weighed quantity of marble and found that in the process it lost weight, thus giving the first blow to the phlogiston theory. He next showed that if slaked lime be treated with a mild alkali, such as , it is changed again to chalk, while the mild alkali becomes caustic alkali."