The organ that used to be at Joyland Park in Wichita, Kansas,
started out as a de Kleist barrel organ built in 1905 that was sold
to Wurlitzer and converted to Style 165 at their factory.  The melody
section has a set of mixture pipes, which consists of two ranks of
violin pipes, one is tuned a perfect third above the regular violins,
and another tuned a perfect fifth above the regular violins.

When everything is turned on, it gives a fuller, richer sound to
the melody section, but not so good when used with just the flutes.
There is also a blank space (22 holes covered with a strip of wood)
where there may have been one set tuned an octave above the normal
pitch.

Mixture ranks are common in large pipe organs and are used to get
a chorus effect.  You can Google "mixture rank" to get more info.
In the Wurlitzer 165, the mixture rank was not included in most of
their factory built organs.  The registration controls in the roll
do not specifically designate it, so one can only guess as to which
control one would connect it to.

The Joyland Park organ was unique in that it used de Kleist pipework,
not Wurlitzer's.  The melody section had flutes (2 ranks), violins
(2 ranks), mixtures (2 ranks), clarinets (1 rank), and piccolos (3
ranks).  When everything was on it was quite powerful, and perfect for
outdoor use.  (The organ was supposedly designed for a large roller
rink, but it would have blown out the windows).

Gordon Ramsey - Ramsey Music Service
Wichita, Kansas