He went to the field with the Lutzow Jagers, and soon after made the acquaintance among his comrades of the theological students Langethal and Middendorf.

When, after the Peace of Paris, the young friends parted, they vowed eternal fidelity, and each solemnly promised to obey the other's summons, should it ever come.

As soon as Froebel took off the dark uniform of the black Jagers he received a position as curator of the museum of mineralogy in the Berlin University, which he filled so admirably that the position of Professor of Mineralogy was offered to him from Sweden.

But he declined, for another vocation summoned him which duty and inclination forbade him to refuse.
His brother, a pastor in the Thuringian village of Griesheim on the Ilm, died, leaving three sons who needed an instructor.

The widow wished her brother-in-law Friedrich to fill this office, and another brother, a farmer in Osterode, wanted his two boys to join the trio.