Early experiments

[Jean Berko Gleason]

I'm looking for a reference to an "experiment" carried out by one of the
German kings (Frederick the ?), who purportedly raised children without
allowing them to hear spoken language because he was sure that they
would then speak the REAL language, German.  Can anyone tell me which
Fred it was and point me to a reference that details this?  (I know all
about
Psammetichus, and really mean this story....)  Thanks.

Jean Berko Gleason