Which preposition to use with gratuitous

in Occurrences 2%

Even the man who keeps a carriage will let it out for hire; and the manner in which money is accepted, and even asked for by persons in easy circumstances, and for things that would be gratuitous in the Middle States, often causes disappointment, and sometimes disgust.

on Occurrences 2%

But this tone is gratuitous on the part of those who assume it.

as Occurrences 1%

This introduction during the past season was, however, as perfectly gratuitous as that of the rain was uncalled for.

for Occurrences 1%

Gratuitous for Unwarranted.

Which preposition to use with  gratuitous