The subject of this thesis was the interaction of the three dinitrobenzenes with potassium cyanide in alcoholic solution, an investigation to which he several times returned, and the first results of which he published in 1904.

[1][2] About this time De Bruyn went to Paris and worked for a few months in the laboratories of Charles-Adolphe Wurtz and of Charles Friedel, returning to Leiden in 1884, where he remained until the following year.

Having been appointed as a chemist to the Government Department of Marine, his official duties naturally brought before his notice new problems, especially those connected with the manufacture and properties of explosives, and to this work he devoted much attention for 11 years.

During this period he began the study of methyl and ethyl alcohols in the character of solvents, which led him on to the isolation of hydroxylamine and hydrazine.

[1] In 1896, de Bruyn was appointed to succeed Gunning as Professor of organic chemistry and pharmacy in the University of Amsterdam, having declined the position of State Chemist offered to him in 1895 by the Government of the Transvaal.