The Collaborative International Dictionary of English v.0.48:

Commixtion \Com*mix"tion\ (?; 106), n. [L. commixtio.]
   Commixture; mingling. [R.]
   [1913 Webster]

         An exact commixtion of the ingredients.  --Boyle.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

COMMIXTION, civil law. This term is used to signify the act by which goods
are mixed together.
     2. The matters which are mixed are dry or liquid. In the commixtion of
the former, the matter retains its substance and individuality; in the
latter, the substances no longer remain distinct. The commixtion of liquids
is called confusion, (q.v.) and that of solids, a mixture. Lec. Elem. du
Dr. Rom. Sec. 370, 371; Story, Bailm. Sec. 40; 1 Bouv. Inst. n. 506.