IN this very concise treatise the author has summarized the history of the industrially important diazo-compounds since their earliest recognition by Peter Gries in 1858 until the present time. The various methods of preparing diazonium salts are reviewed, including the recent outstanding discovery made independently by Hodgson and Schoutissen that o-diamines can be made to give the reactions of bisdiazonium compounds. The Aromatic Diazo-Compounds and their Technical Applications By K. H. Saunders. Pp. xii + 224. (London: Edward Arnold and Co., 1936.) 12s. 6d. net.