The 1883 edition of the Colorado Mining Directory noted that Edward Posen, Ph. D. maintained his business at 350 Curtis Street, Denver. Presumably, most of his business came from gold mined in the district to the west of Denver which included Central City, Black Hawk, and several other mining communities.

The cited directory listing noted the following:

Edward Posen, Ph.D. Bureau of Mines, Assay Office, Analytical Laboratory, 350 Curtis Street, Denver, Colorado.

Makes investigations of mines, reporting on the same. Makes assays for gold, silver, quick-silver, lead, copper, tin, zinc, nickel, cobalt, antimony, arsenic, coal, and sulphur, and etc. etc.

Also makes analysis of mineral waters and those in use for all technical purposes. Finest display of minerals — the celebrated collection or Dr. Eisner can be seen in my office.