Please read content below and look at the photos - Merrill Patent Firearm Manufacturing Company and Pearl Hominy Company are one and the same building. I'm working with the Maryland Historical Society for any additional information that will be shared here.
Pearl Hominy Mill
From the Baltimore City and County Mills A-C
Northeast corner of Chase and North Street [Guilford Avenue], on October 17, 1867 (City Deeds AM 353:106, MSA). Photo below is from the E. Sachse’s 1869 lithograph. E. Sachse's 1869 lithograph showed this works as an Italianate villa with a cupola, a three-story structure between Belvidere Street and the west bank of Jones Falls. A fire caused by a boiler took place at the Pearl Hominy Mill on North Street near John (later called Preston) Street, May 19, 1872; the works was owned by MacGregor & Co., Fire Marshall’s Report, p. 106. Baltimore Pearl Hominy mill was described as “recently established” in Monumental City, p. 138 (1873). It produced 2500 bu/diem of kiln-dried pearl hominy and grists, pearl maizene, corn flour, corn meal, and chop. The site was below the extinct Hansons Mill at Belvidere Bridge. Maps of 1851, 1863, and 1868 did not show this works. Possibly it replaced the Wait & Caldwell Spice Factory shown on the 1851 Poppleton city plan. The Baltimore Pearl Hominy Company was the first U. S. corporation to patent a trademark according to a display about “Firsts” at the MHS. The Baltimore Pearl Hominy Company’s mill was shown blocking Biddle Street just east of Guilford Avenue [then called North Street] in the 1877 G. M. Hopkins City atlas, Volume II, plate 60-61.
Merrill Patent Fire-Arm Manufacturing Company
From the Baltimore City and County Mills A-C
The firearm company had acquired the ground from the Mayor and City Council in November 1864 (Deeds AM 263:435). C. C. Hall in Baltimore, Its History and Its People (1912), 1:44, noted that the Pearl Hominy Mill occupied the site of a water pumping station erected by the Baltimore Water Company, that early privately managed utility—the pump ran on the water from the Lanvale Cotton Factory dam according to C. C. Hall. The Baltimore American of July 26, 1868, reported that the “dam of the Pearl Hominy Co. at Belvidere Bridge was destroyed” by the flood.
From the Wednesday, July 27, 1864 article in the Baltimore Sun (my greatest find to date):
An Extensive Improvement - The Merrill Patent Fire Arm Manufacturing Company - This well-known company, chartered by the Legislature of Maryland, who for some years carried on its extensive gun manufactory in the upper stories of the Sun Iron Building, found its business increasing to such an extent as to induce the president and directors to look out for more extended accommodations. They purchased the lot from the Water Company on which was located what was known in former days as the "Pump House." The lot contains 6 1/2 acres of ground, with a water front on Jones's falls extending from the Belvidere bridge, a distance of fully a quarter of a mile. The have recently erected on this lot, and have now in full operation, one of the most extensive gun manufactories in the country, every department being filled with the most ingenious labor-saving machines yet invented, and which perform their several functions with a perfection with which the human hand can never compare. The buildings are all of brick, the main one being 220 feet front by 60 feet deep, and four stories high. This building is used exclusively for the manufacture of firearms; others being appropriated as blacksmith shops, cartridge factory, magazine, etc.
The main building is surmounted by a handsome cupola. affording a fine view of the surrounding country. Every portion of the factory is used for some special purpose connected with the manufacture of firearms, and all are comfortably and indeed handsomely finished. The company's counting-room is in the second story, and is a large and airy apartment, furnished with every convenience for those employed as well as those who have business to transact. The old mansion on the premises has been thoroughly repaired and is now occupied by the foreman of one of the shops.
The power for driving the vast machinery connected with the manufactory is derived from Jones's falls, the company owning the water-right up to the Charles Street bridge over that stream. With two powerful water-wheels they have a power equal to more than one hundred horses, the only steam used on the premises being that intended for heating the entire building during the winter season. Every room in the building is lighted with gas from the Baltimore Gas Company's works. On the basement floor, adjoining the water-power, is a furnace for annealing or softening the iron; and in adjoining apartment is an equally ingeniously contrived furnace for case-hardening the metal after it has been put in the desired shape. On the same floor is a fan for blowing the ten different furnaces, a trip-hammer for drawing out heavy work or welding, and a number of highly improved drop hammers, which, by a single blow, cuts off any portion of the lock. The first floor is one entire room, 108 by 54 feet, filled with all kinds of the most ingenious machinery, intended for the various processes through which the gun must pass before it reaches the finishing shop. On the third story, among a vast amount of machinery, there is one machine deserving of particular attention; it is designated as the "stocking-machine," and by its peculiar construction a piece of hard walnut is made a perfectly finished gun-stock in a less time than is required to describe it. On the same floor is what is called the buff or finishing-room, where the pieces are thoroughly finished and mounted. The company has ample room to accommodate one thousand workmen and can readily turn out the same number of firearms per week.
One of the most interesting features of the establishment is in the upper story, and is termed the inspection room, where is constantly employed a number of gentlemen appointed by the Government to test and inspect the pieces before they are finally delivered; here every arm is taken to pieces, each part carefully examined and passed upon, and when a piece leaves the premises is ready for immediate use without further trial. The front of the factory is most delightfully shaded by the well-known row of willow trees brought from the tomb of Napoleon Bonaparte at St. Helena by Columbus O'Donnell, Esq., the former president of the Water Company. The entire grounds belonging to the company are very tastefully laid out, and the choicest flowers and vegetables are now growing in the greatest profusion. Much credit is due to the superintendent of the establishment, Mr. Wm. Merrill, a son of the President of the Company, for the admirable condition and entire perfection of the manufactory; under his guiding eye the establishment is conducted on perfect Governmental principles; he is ever on hand superintending the work.
The cartridge factory, in a building separate and distinct from the main factory, is under the immediate superintendence of Mr. J.L. Merrill, another son of the president of the company, and is in truth quite a novelty. Although several millions have been made since the first of January, the company have met with no accident whatever, although constantly employing over one hundred females. Adjoining the cartridge factory are two dressing rooms for the accommodation of the female employees. The bullets are made in the basement of the building, by a simple and ingenious process, the invention of Mr. Merrill, by which some fifty thousand are turned out a day. From the care and caution practiced in the factory, it is almost a matter of impossibility that an accident should occur, as although a vast amount of powder is used but a small quantity is brought in at a time, the balance being kept in a well secured magazine.
This is certainly one of the greatest establishments of the kind in the country. That it is one of the permanent institutions of our city - giving employment to hundreds of industrious mechanics the year round - cannot be doubted, for in the case of a total cessation of demand on the part of the government for fire arms, he works and factory are so constructed that the company can at any time turn out a first-class locomotive or stationary engine with the same facility that they can furnish a Merrill Patent Rifle.