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.
Gregory’s appearance was most noticeable. He was of great proportions, obese, slouching and loosely hung together. In later years his body was a great burden to him, but the mind kept the mastery.
He was, like his father, a keen student of language, and would wile away many of the weary hours of forced inaction by the study of foreign tongues. French and German were to him as familiar as English. With a microscope, too, he did beautiful work, and was in his day, the greatest authority on the Diatomaceae. The slides which he made of these microscopic water-plants with their sculptured valves, were another resource of his declining years. He presented valuable memoirs on this subject to the Royal Society of Edinburgh, of which he was a member.
Professor William Gregory died in Edinburgh in April 1858, and was honoured with a public funeral.
He was succeeded in the university by Dr Lyon Playfair (afterwards Lord Playfair) who had contested the chair unsuccessfully at the time of Gregory’s appointment.
William Gregory was survived by an only son, who was called after his father’s far-famed friend, James Liebig Gregory.