Hello,  A Mixture rank is used in most of the German-made fairground
organs, such as Gebr. Bruder, Gebr. Richter, Gebr. Wellershaus, Alfred
Bruder and A. Ruth & Sohn and -- sometimes in early and large organs --
also by Wilhelm Bruder Soehne.

A Mixture is, in fact, a fortification for the Accompaniment and Melody
section in a traditional German fair organ and it plays never alone.
A traditional German fair organ has only few register stops/keys,
mostly only "Forte" and "Piano" (meaning "Mixture on" and "Mixture off")
for the Melody and Accompaniment.

A traditional Mixture has two (in larger fair organs three or
sometimes, seldom four) ranks of different tuned "Principal", or
so-called "Diapason" type of open pipes.  Mixture pipes are normally
not violins.  The Mixture stop was used in church organs since the
16th century and also today.  It fortifies the natural overtones of
the basic ranks and gives the organ a "silver glossy sound".

In a fair organ, the basic stops (or "Piano" mode) are normally two or
three ranks of Violin 8' and a Stopped 8'.  The Forte-Mixture ranks in
a large organ are tuned mostly in octave (8th) 4', quint (12th) 2-2/3',
Super Octave (15th) 2', sometimes (in large organs) in Accompaniment
also Tierce (17th?) 1-3/5' in relation to the basic rank.  Sometimes
organs, especially organs by Richter and Wellershaus, have an additional
harmonic flute 4' in their Mixture composition, to get more power.

Smaller fair organs (less than circa 65 keyless) have normally only
a two-ranks "Forte" -- of Octave 4' plus Super Octave 2' -- and that
combination is not a really true mixture.

Thus in a large Ruth organ (Style 36/37) or Gebr. Bruder organ (Style
104/105), the Melody section contains normally one rank of Stopped
pipes plus three ranks of Violin, plus 3 ranks Mixture additional in
"Forte" = 7 ranks of pipes for every note.  Hope that helps.

Regards from Waldkirch, Germany,
Raphael Lüthi

 [ Raphael is an organ builder/restorer employed at Paul Fleck
 [ Sons Organ Builders in Waldkirch, Germany.  He owns a nice
 [ Gebr. Bruder Model 111 42-key fairground organ pictured at
 [ http://fleck-orgelbau.de/Museumorgeln.htm  -- Robbie