Complex sentence: This smell was not typical of arsenic, but a similar odor was known from tellurium compounds, and so Berzelius' first letter to Alexander Marcet stated that it was a tellurium compound.
Split into simpler sentences: This smell was not typical of arsenic, but a similar odor was known from tellurium compounds. Hence, Berzelius's first letter to Alexander Marcet stated that this was a tellurium compound.