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BLACK pleasure in noticing and assisting the efforus of his pupils, took him under his particular direction Mr. Black was unwilling to trast toj the reports of, chemical processes, until he had himself repeated, them; the accuracy and dexterity with which he performed his experiments, toge ther with the attachment of the professor, caused him to be, regarded as Cullen's assistant, in which, capacity he frequently acted, and his ex periments at this early age were often referred to as good authority. His note books, which are still preserved, point out the compre- bensive plan of study which he had laid down for himself, and are particularly curious, as they exhibit the germs of his ideas, and their after-progress, until they ripened into those great discoveries which produced so complete a 108 revolution in chemical science. The action of lithontriptics on the human frame, at that time excited great attention, and the professors in the university of Edinbargh were much divided in their opinions on the subject. The pupils then engaged in their studies, of course warmly entered into the contest, and when Black left Glasgow to finish his medical education at Edinburgh, in 1750, the differences of opinion were at their height The natural bent of his inclination engaged him in the controversys and, daring his residence at the bouse of, his cousin-german, Mr. Russell, professor of natural philosophy in the university, he entered into a course of experiments to investigate the cause of causticity, ai property in which all the lithontriptics ithen in use, ágreed. He at first adopted the idoctrine of the older chemists, that lime, during the burning of ity absorbs something from the fire, which, entering into combination with it, renders caustic what was before mild and inno- cuous.j This he attempted to separate, and collect from the caustic lime, but without effect; and, in the prosecution of his experiments, he found reason to conceive that caus- ticity depended on the removal, rather than the addition, of some other substance.oThis suspicion took possession of