Benjamin Thompson, Count of Rumford, was born in Massachusetts in 1753 and taught in Concord, New Hampshire before emigrating to England. He was an inventor, and was married to the widow of Lavoiser. The Rumford Chemical Works had little to do with him, but his shillouette appears on the private die stamps the company had designed for them in 1880.

Professor Eben N. Horsford was the president of the Rumford Chemical Works. His specialty was use of phosphates in food production, and his products were not specifically intended to be proprietary medicines. One, Horsford's Acid Phosphate, was marketed as a drink, but was touted as preventing cholera, and in 1880 was required to bear a tax stamp. Private die stamps were issued on January 24, 1881 and May 1, 1883. 1,219,050 were printed, all on watermarked paper. An unknown quantity of the second delivery were left imperforate.

The cancel on this stamp has been identified as having been used by Rumford Chemical Works. If so, why would they have needed a proprietary stamp before 1880?

Horsford's first product containing his patented phosphate was a Self-Raising Bread Preparation. This was not considered a patent medicine in any way.

A trade card for Horsford's Acid Phosphate, which eventually was considered to be a patent medicine.

The center of a fold-out card advertising Horsford's Acid Phosphate, showing the claim about cholera which resulted in the product being taxed as a medicine.

Professor Horsford's Phosphatic Baking Powder was introduced around 1890.

The cancels on these general issue Spanish American War proprietary stamps are also identified as belonging to Rumford Chemical Works. Acid Phosphate was still considered to be a medicine at the turn of the century.

An Acid Phosphate advertisement from early in the twentieth century.