Horsford eagerly seized upon Wilson's offer as he had just received his first patent for a chemical process, the use of calcium sulfite to neutralize chlorine in bleached cotton and linen fabrics. Since Wilson was interested in textile chemicals, the two men built a small calcium sulfite plant in Pleasant Valley, Rhode Island. Unfortunately, the site they picked proved unacceptable as neighbors complained about the constant escape of sulfur dioxide during the manufacturing process. In 1856 Wilson moved the equipment in the Pleasant Valley plant to a facility on a site in East Seekonk, Massachusetts, which he had purchased.

Horsford had linked up with Wilson in part because he wanted an outlet for the manufacture of calcium sulfite. At the same time, he was working on other ideas that might yield products for marketing. One of those ideas was an alternative to yeast or sour milk as a leavening agent, which would eventually be baking powder. In 1856 Horsfored received a patent for "pulverulent phosphoric acid," which coincided with the transfer of operations from Pleasant Valley to East Seekonk.

Although chemists were familiar with phosphoric acid in the 1850s, it had not been produced on a commercial scale. So Horsford and Wilson needed to develop a manufacturing process based on then available raw materials, either bones or spent bone black from sugar refining. Geologists were aware of U.S. phosphate deposits, but they were not exploited until 1869. But by the beginning of the Civil War, Horsford and Wilson had solved the supply problem and were producing sufficient amounts of calcium acid phosphate to satisfy production needs for baking powder.

Prosperity meant that the informal partnership between Horsford and Wilson needed to be converted into a corporate structure; as such, the Rumford Chemical Works was incorporated under Massachusetts law in 1859 with capital of $10,000. Horsford chose the corporate name which recognized the scientific achievements of Benjamin Thompson, Count Rumford, as well as the Rumford Chair which he occupied at Harvard and which had been founded by a grant from Count Rumford. In 1861 the boundary between Massachusetts and Rhode Island was adjusted with the result that East Seekonk Massachusetts, became part of East Providence, Rhode Island, so the corporation had to be chartered again in Rhode Island.

In addition to marketing Horsford's pulverulent phosphoric acid, the firm was producing hydrochloric and nitric acids and tin chloride. In 1864 Horsford obtained a patent for a self-rising flour containing calcium acid phosphate and sodium bicarbonate. While Horsford was developing processes, Wilson invented equipment for the implementation of Horsford's discoveries. For example, in 1868 Wilson received patents for a phosphoric acid pump with vulcanized rubber valves and for the use of porcelain-lined iron kettles for concentrating phosphoric acid. Wilson also devised methods for using bone and spent bone black in the manufacture of agricultural fertilizers.

Baking powder was the main output of the Rumford Chemical Works. By the mid-1860's "Horsford's Yeast Powder" was on the market as an already mixed leavening agent, distinct from separate packages of calcium acid phosphate and sodium bicarbonate. This was packaged in bottles, but Horsford was interested in using metal cans for packing; this meant the mixture had to be more moisture resistant. This was accomplished by the addition of corn starch, and in 1869 Rumford began the manufacture of what can truly considered baking powder.

¹ Anon., Eighty Years of Baking Powder History: 1859-1939, Rumford, RI, Rumford Chemical Works, 1939; Anon, "History of the Rumford Chemical Works," typed manuscript, dated April 15, 1947, in the East Providence Historical Society; Anon., "The Story of Baking Powder — The Story of Rumford, reprint from Oil-Power in East Providence Historical Society.