Gilles Chouinard said, "Mixtures are not made to be played solo all by
themselves.  They are made to complement the palette of other stops so
they are used in conjunction with these."

I think the metal pipes in the Raffin Model R 20/78 crank organ probably
qualify as a "mixture rank" although they are only one set of pipes and
are not linked to other sets.

The organ is well described in Gordie Davidson's article at

  http://www.coaa.us/index_archive/Issues_31_to_40/The%20Raffin%2020-78%20Concert%20Street%20Organ%20-%20A%20Profile%20_%20Gordie%20Davidson_%20_40.pdf 

although the word "mixture" is not used there.  Another on-line
description says they are "11 Metal flute pipes quint 2-2/3' "

The Raffin Orgelbau website is silent on this question.

Wallace Venable