Ruins of Washburn A Mill after explosion, Minneapolis, 1878.
Minnesota Historical Society Photograph Collection, Location no. MH5.9 MP3.1W r46; Negative no. 7286-A
The A Mill had used the middlings purifier, which made
the flour better but produced a large amount of dust. It was this dust
that sparked the explosion that wiped out most of the milling district
and killed 18 workers.