His friends were Lemans, Somerhausen, and Ullman, all of them members of the circle Tongeleth, who applied themselves to the study of the Hebrew language.
Mulder composed at this time a Hebrew romance, "Beruria," and a psalm (see Delitzsch, "Zur Geschichte der Jüdischen Poesie," Leipzig, 1836).
In 1812 Mulder became a Sabbath-school teacher; in 1817, a sworn translator at the tribunal; in 1835, inspector of religious schools; and in 1849, secretary of the Amsterdam congregation.
From 1826 Mulder was regent (director) of the theological seminary Sa'adat Baḥurim, which was reformed by him and which became in 1836 an institution subsidized by the state.
In addition he published many books on the study of Hebrew, e.g.: "Chronologisch Handboekje," 1836; "Rudimenta" (a revision of Lehman), 1840; "Aardrijkskunde van het Heilig.