When he returned back to work his professor advised that he take a year's leave of absence and study in Europe.
This provided a method of producing substituted benzyl compounds with interesting results, such as a synthesis of anthracene.
In the late 1880s he discovered the reaction between highly substituted aromatic halides and malonic ester in which a halogen radical is replaced by a hydrogen, his most prolific source of scientific publications.
The importance of Jackson's studies in Europe to the development of the organic chemistry industry in the United States should not be underestimated.
In the 1870s when Jackson traveled to Europe there literally was no organic synthesis being done in the United States either in academia or in industry.
Had the United States been unable to quickly develop an organic synthesis capability, the outcome of the World Wars might have been quite different.
The World Wars put this philosophy at odds with commonly held beliefs about national security, intellectual property, trade secrets and technology leakage.
Due to his interest in the student body, he was, for fifty years, a proctor in the dormitories of the Harvard Yard--Gray 5 from 1868 to 1871 and Holsworthy II from 1871 to 1918.