Dunn was appointed the founding Principal of the Northern Polytechnic Institute in Holloway, London, and head of its Chemistry Department, in 1895.

[5] The institute was opened with aid from the City of London Parochial Foundation and substantial donations from the Worshipful Company of Clothworkers.

Under the terms of its royal charter its objective was: "to promote the industrial skill, general knowledge, health, and wellbeing of young men and women belonging to the poorer classes of Islington and to provide for the inhabitants of Islington and the neighbouring parts of North London, and especially for the Industrial Classes, the means of acquiring a sound General, Scientific, Technical, and Commercial Education at small cost.

Courses ranged from English, mathematics, chemistry and physics to more vocational classes such as machine construction, plumbing, dress-making, and millinery.

New buildings began to be erected during Dunn's time in charge there, with the Great Hall being opened in 1897,[9] and other large additions completed in 1902.

In January 1900 at the prize-giving, Dunn was able to report that the institute had grown very rapidly and was still growing, the number of students by then being two thousand.

[10] A year later Dunn was able to record a further rise in student numbers and to report that there was a growing tendency to take advantage of the institute, especially in the trade and industrial classes.

[12] The firm had been founded in the year of Dunn's birth – 1858 – and set up offices and a laboratory at 75 The Side in Newcastle upon Tyne,[13] where they concentrated on coal purity testing and food analysis.

[14] With Dunn as a partner they moved to larger offices and laboratories nearby at 10 Dean Street in Newcastle[13] and vastly extended their operations.

[4][5] Dunn remained as the senior partner of J and H S Pattinson until his death in 1939, giving up his public appointments only with the onset of illness in 1937.

The book was a success, being regarded as an intermediate course in Physics and Chemistry for London Matriculation, and also being adopted by the Admiralty for teaching elementary Science.

It was well-reviewed by Dunn's peers, with the author congratulated on his success in bringing under one cover the many sources of information on the subject.

[4] His junior partner Charles Bloxam wrote in the journal of the Royal Society of Chemistry that: "An eminent man has gone from us, but his example remains, and fortunately the many who came in contact with him during his early scholastic and university life, and later in his numerous public and professional activities, have had the opportunity to profit by it.

A cultured and scholarly man, of quiet and kindly disposition, tolerant of the views of others, yet ever ready stoutly to defend his own opinions with a vigour that surprised those who were unacquainted with the depths of his character".