Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
admistĭo (better admixt-, q. v.), ōnis, f. [admisceo], a mixture: olei admistione conspersus, Vulg. Lev. 7, 12.
admixtĭo (better than admist-), ōnis, f. [admisceo], a mingling; in concreto, an admixture: animus omni admixtione corporis liberatus, Cic. de Sen. 22, 79; so, terreni, Pall. 1, 5, 1: ardor nulla admixtione concretus, Cic. N. D. 2, 45, 117.
In plur., Varr. R. R. 1, 9, 2 al.