Thomas Holloway was a British patent medicine producer. His medicines were introduced in the United States around 1856. In the early 1860's Holloway named Joseph Haydock as his agent in the United States. In late 1862, Haydock had a private die propriety stamp prepared for Holloway’s Pills.

Holloway's Pills Stamp
Haydock apparently severed his connection with Holloway in 1866, and Holloway appointed David Pringle as his new agent. This arrangement continued until the fall of 1870, when it appears that all rights were transferred to the New York Chemical Co., which subsequently held itself out as the sole proprietors of Holloway’s Pills and Ointment.
A Holloway & Co. essay was prepared in late 1872. It appears that the essay was prepared at some point after Holloway transferred the United States operation to New York Chemical Co. Given that the essay was approved in October 1872, and Holcombe reported that the Holloway company appeared to have vanished after 1872, it appears that no stamps were ordered from the essay due to the dissolution of the company.

Holloway & Co. Essay
Holloway & Company used an "H. & Co." cancel on proprietary stamps.
H & Co. (Holloway & Co.) Printed Cancels