Henry Dickinson started the Connecticut River Paper Mill in 1870 on the Third Level Canal. They are a maker of fine paper with one type being No. 1 High Grade. They were called the Connecticut River Paper Company from the 1870s to the 1890s.
The Purcell Envelope Company which formed in 1894 is a maker of United States stamped envelopes. They in 1896 joined with the Connecticut River Paper Mill.
Then they were the Union Paper Mill.
Sanborn map analysis:
Sanborn 1949 map they are the United Folding Box Mill