Beethoven's Pathetique sonata 2nd mov. speed?

My score says "adagio cantabile" which is about 70 bpm but, is that speed applied to a quarter of a note or an eighth of a note? Cause when I play it at 70 bpm per quearter note sounds way too fast, but it sounds perfect when I play it 70 bpm per eighth of a note. But the score doesn't tell me anything about that.