Definition of a "half glass?"
From my years of cooking, I would guess this to be about 4 oz. or 1/4 C. as we sometimes used a small 8 oz. juice glass for measuring and half a glass would be half of that or 4 oz = 1/4 C., especially with vinegar, Other than pickles I could not imagine a recipe using more vinegar than that.  Hope this is helpful.