As a chemist, he undoubtedly came first in Scotland. He invented processes for the more perfect preparation of hydrochloric acid, muriate of morphia and oxyde of silver, besides making important observations on many other chemicals. He had an accurate command of practical chemistry, a power of condensation and clear expression, and a just perception of the value of discoveries, which made his writings unsurpassed for the use of students. In 1844 Dr William Gregory realised the dream of his youth. After a sharp contest with Dr Lyon Playfair, he was appointed to succeed Professor Hope in his chair in the University of Edinburgh. ‘The chair was given to him,’ says Sir Alexander Grant, ‘under a new title, for the Town Council now judiciously omitted “Medicine” from its province, and elected Dr Gregory to be Professor of Chemistry.’ His health was much impaired, so much so, that people even went the length of saying that he was physically unfit for his new position, and it is at any rate true that his finest teaching was given to his students in Aberdeen. He was an able teacher, if at times erratic and absent-minded. His class was always kept wide awake, for with what alarms would not the professor bring back the straying imaginations of his audience! ‘Gentlemen,’ he would say, while with his long awkward fingers he lifted up the tube of some chemical before them, ‘If this were to fall, not one of you could reach the door alive;’ and then, considering the matter over, he would place the tube carelessly upon the edge of a plate, while the students near the doorway filtered through it, and the others, hat in hand, awaited the longed-for close of the lecture, feeling a fresh tremor with every approach of Gregory’s loose fingers to the fatal vial. Good as his teaching was, the books which he wrote while in Edinburgh were his most valuable contribution to the Science of Chemistry. In the preface to the _Outlines of Chemistry_, which was published in 1845, he sketched the divisions which he intended to make in his subject for the fuller elucidation of the facts, and, had his health permitted him to carry out his plan, ‘the instruction from his class would probably have been more complete than from any other scientific chair in Europe.’ At the request of Liebig, he translated several of his more important books into English, and in the preface to the _Familiar Letters on Chemistry_, Liebig writes, ‘From his intimate familiarity with chemical science, and especially with the physiological subjects here treated, I am confident that the task could not have been entrusted to better hands than those of my friend Dr Gregory.’ Their friendship lasted throughout life, and only a few days before Professor Gregory’s death, he was propped up in his bed to write a pamphlet supporting some new theories of Liebig, which the German had just communicated to him.