He familiarised himself with the new quantitative chemical theory of Antoine Lavoisier and read widely: Nicolai Tychsen's Apothekerkunst (Theoretical and practical instructions for Pharmacists, 1804); Gren's Chemistry; Adam Hauch's Principles of Natural Philosophy; and Ørsted's papers in Scandinavian Literature and Letters (his treatise on spontaneous combustion having made an especially strong impression upon him).

In the summer of 1806, he noted in his diary "a most remarkable awakening within me for something higher, for scientific creative work in general, but for Science, chiefly Chemistry, deeply and in particular".

Ørsted later recounted how he had influenced Zeise through conversations and encouraged him when he expressed the desire to take the university entrance examination (examen artium).

Zeise had at first intended to study medicine, but while attending lectures it became clear that his interests had a broader scientific base; and chemistry remained his favourite subject.

He still experimented in Ørsted's laboratory; but since at that time there was no prospect for a teaching position at the university, he took the pharmacist exam in 1815, later a master's degree (magisterkonferens), and on 21 October 1817 he defended his doctoral dissertation on The effect of alkalis upon organic substances.

As the university had no separate lecturing chair in chemistry and no scientific laboratory, Zeise decided to work and study abroad in Germany and Paris.

[3] Zeise was accordingly awarded a silver medal by the Royal Danish Academy of Sciences and Letters, and he became a member of that body the following year on the recommendation of Ørsted.

[1] Zeise's health was fragile for much of his life and he suffered greatly, possibly due to his handling of noxious chemicals in poorly ventilated rooms.

His discovery of mercaptans (thiols) in 1832 and thioethers in 1833, was once a weighty support for the influential (now obsolete) "Radical Theory" which Berzelius and Liebig developed, provoking important chemical studies.

Attempts to establish the correct structure and composition of Zeise's salt drove much basic research during the second half of the 19th century and led to a greater sophistication in organometallic chemistry.

The structure of Zeise's salt was definitively resolved only with the advent of X-ray crystallography[8][9] and the nature of its platinum to ethylene bond was not understood until the development of the Dewar–Chatt–Duncanson model in the 1950s.

[10][11][12] Shortly before he died, Zeise published his attempts to purify the pigment carotene from carrot juice while in the Polytechnic Institute; finding it to be soluble in carbon disulfide and correctly identifying it as a hydrocarbon.