In hindsight, the solution was obvious.

How could he have missed it, standing up between slats on the bench?
Well, actually, that was understandable. The vial was brown-ish, the solution was brown, the bench was brown.

But why was it brown? It should be clear. Or maybe a milky-white. And why was it precipitating? C'mon, everything dissolves in a nitrate solution!

He must have disturbed the solution somewhat when he dropped it an hour ago.

He picked up the vial, and poured it in the vial he had waiting on the countertop.

In hindsight, if he still had sight, it would be obvious he had picked up the wrong vial.