
Lord Pendragon |

As a DM, I would give this an infinitesimal chance of being effective. Sand in the eyes is effective because when you throw it, it spreads out in a sorta cloud that is hard to dodge and easy to get in the eyes. In your case, the sack is going to make it much easier to dodge the glass.
Unless you wanted to reach into the sack with your hand, grab a handful, and throw that at your foe. Powdered glass is nasty, nasty stuff.
Of course, that has its own drawbacks. *evil grin*