Impressments of flour.
--It is understood that the Government agents in this city have, within the past two days, impressed a large quantity of flour, mostly, it is said, in the hands of the millers and speculators. The price allowed was $17 50 for superfine, and $19 50 for extra. A few days before the seizure a great mania prevailed in the city on the subject of flour, thousands of barrels having been bought up for speculative purposes.