A 33-year career as consultant and engineer took him in 1934 to Trinidad, where he worked in the oil-refining business. It was while there that he conceived the idea of an economical, keyless flute held horizontally, which might bridge the gap between the recorder and the expensive Boehm instrument.
The essence of the ``Johnstone flute'' was that it was easy to make. Edgeworth-Johnstone delighted to explain how its body could be a single length of cheap aluminium brass tubing, commonly used in oil refineries. He located shaped fingerholes where the fingers fell naturally along the tube, and found a brilliant solution to the expensive tapering required at the mouthpiece end: a tapered ``spear'' of wood several inches long which projected inside the tube and was attached to the stopper at the top of the flute. West Indian purpleheart wood was his choice for the mouthpiece and ``spear''. James Galway tried the instrument and approved. Edgeworth-Johnstone returned to this invention in his eighties, and finally published details of it in The Johnstone Flute (1993).
Edgeworth-Johnstone was born in Dublin of an Anglo-Irish family, the son of a chief commissioner of police. He attended Wellington College and the Royal Military Academy, Woolwich. Three years with the Magadi Soda Company in Kenya from 1920 gave him a taste for the chemical industry and he returned to study at Manchester College of Technology, before taking a doctorate at University College London in 1932.
Towards the end of his career in industry he was appointed, in 1960, at an unusually advanced age and without previous university experience, the first Lady Trent Professor of Chemical Engineering at Nottingham University. He impressed colleagues with his "can do" attitude and straightforward approach, considered unusual in academic circles. Anxious to produce engineers who could pull their weight in industry, he sent out a survey to members of the Institution of Chemical Engineers (IChemE) on th e daily skills they used. The response led to a syllabus with much more emphasis on economics, management and industrial administration than was then normal, anticipating by some 20 years the recommendations of the Finniston Report of 1980, the governmen t inquiry into the future of the engineering profession.
After retiring in 1967, Edgeworth-Johnstone turned his attention to the continuing education of engineers. His 1969 report to the IChemE provided the template for all subsequent development of this field.
Later in life Edgeworth-Johnstone took on the aspect of a patriarch, with a striking, bushy white beard. He moved from Brighton to the French countryside, where he led a full and vigorous life, prompting an ex-colleague to comment: ``It seemed he'd go onfor ever''.
Robert Edgeworth-Johnstone, chemical engineer: born Dublin 4 February 1900; Lady Trent Professor of Chemical Engineering, Nottingham University 1960-67; married 1931 Jessie Greig (died 1981; two sons, one daughter); died Parce-sur-Sarthe, France 3 December 1994.