the blackest ingratitude
The same noun is employed by Alphonse Frankenstein in the previous chapter (I:6:37). The word conveys a sense of obligation and therefore of class difference. Again and again it is emphasized that Justine has been raised above her rank in life by the active interest of the Frankenstein household in her welfare. But has she really altered her condition? Not just the family but the whole of Geneva society condescend to her as having less than full rights to her supposedly respectable condition. The ease with which her claims to equity are abrogated implicitly places her on a par with Victor's Creature, named a wretch and denied the claim of human sympathy.