[3] After attending the local gymnasium Karl Arnold began training as a pharmacist with his Father, also working as an assistant apothecary in pharmacies in Zofingen, Hamburg, Frankfurt am Main and Magdeburg.

[6] During his time in Munich, he became a member of an academic singing association, the Akademische Gesangverein (AGV) München in the Sondershäuser Verband.

[7] Arnold went on to study chemistry and physics at the University of Tübingen, where he worked with Julius Lothar Meyer.

He completed his doctoral thesis with Robert Wilhelm Bunsen at the University of Heidelberg, studying inorganic and physical chemistry.

[6] Following the mandate given to Begemann to expand and modernize the chemistry department, Arnold developed an expansion plan including chemical labs and an auditorium.

[5] In organic chemistry, Arnold studied the determination of chlorides, urea, uric acid, phosphates, alkaloids and sugar under physiological conditions.

His Repetitorium der Chemie ("Chemistry Revision Course") was a standard work for veterinarians, medical students and pharmacists.

Arnold also published a three-volume work, Tierärztliche Arzneibuch für Studierende und praktische Tierärzte ("Veterinary Medicinal Book for Students and Practising Veterinarians" with professor of physiology Josef Tereg.

[3] He was a member of the German-Austrian Alpine Association (Deutscher und Österreichischer Alpenverein) for almost 45 years, and chairman of the Hanover section.

[11] After making an ascent of the Ankogel in 1885, he encouraged development of the town of Mallnitz in Carinthia, now part of High Tauern National Park as a locale for mountaineers.