Touch is the sense that would help you identify something that is calcified.
We can arrive at this answer because:
Calcification is the process of accumulating calcium atoms on a surface or tissue.
This process allows the tissues or surfaces to become rigid and often difficult to identify.
However, through touch, we can feel the shapes and structure of the calcified object, allowing us to project what this object might be from its edges, angles, and shapes.
I think that the tone of Orwell’s essay progressively changes. In the beginning of the essay, Orwell’s tone is almost lecturing, telling us what’s wrong with the English language and how to fix.