T. E. James, Dictionary of National Biography… (1912)
“ On the completion of the prescribed three years' course of study he joined the teaching staff of the Royal College of Chemistry, London, as a student assistant under Prof. A. W. von Hofmann, who recognised O'Sullivan's promise, and on becoming professor of chemistry at Berlin in 1865 made O'Sullivan his private assistant. A year later the professor's influence secured him the post of assistant brewer and chemist to Messrs. Bass & Co., Burton-on-Trent. In that capacity he applied his chemical knowledge and aptitude for original research to the scientific and practical issues of brewing. ”
