Gretna, Hm Factory, Eastriggs Explosives Factory, Acids Section

ACIDS SECTION

NY26SW 38.1 Grillo Oleum Plant

NY26SW 38.2 Mannheim Oleum Plant

NY26SW 38.3 Sulphur Store, Pyrites Store, Fines Store

NY26SW 38.11 North Nitric Acid Retort House

NY26SW 38.12 South Nitric Acid Retort House

NY26SW 38.7 Nitre Stores

NY26SW 38.13 Cummer Dryer

NY26SW 38.14 Nitre Bag Washing plant

NY26SW 38.31 Spent Nitrocotton Acids Stillhouse

NY26NE 140.4 Nitrocotton Acid Mixing, Storage and Blending plant NY26SW 38.17 Nitroglycerine Acid Mixing plant

NY26SW 38.28 Nitroglycerine Spent Acids Denitration plant

NY26SW 38.27 Nitroglycerine Spent Acid Storage system

NY26SW 38.26 Gaillard Concentrating Towers plant

NY26SW 38.25 Cottrell Precipitation plant

NY26SW 38.29 Gas Producer plant

The Acids Section (NY26SW 38) is located immediately to the SSW of the Nitrocotton Production plant (NY26NE 140) in the W part of the First World War National Factory, Gretna (Site 3: Eastriggs). This was where the oleum, sulphuric acids and nitric acid were produced and mixed for use in the production processes carried out elsewhere on the site (MMW 1919, 21-2, 35-115). This section comprised the Grillo Oleum plant (NY26SW 38.1) and Sulphur Stores (NY26SW 38.3), the Mannheim Oleum plant (NY26SW 38.2) and Pyrites Stores (NY26SW 38.3), the North and South Nitric Acid Retort Houses (NY26SW 38.11, NY26SW 38.12) with three Nitre Stores (NY26SW 38.7) and the Cummer Dryer (NY26SW 38.13), the Nitre Bag Washing plant (NY26SW 38.14), the Spent Nitrocotton Acids Stillhouse (NY26SW 38.31), the Nitrocotton Acid Mixing, Storage and Blending plant (NY26NE 140.4), the Nitroglycerine Acid Mixing plant (NY26SW 38.17), the Nitroglycerine Spent Acids Denitration plant (NY26SW 38.28), the Nitroglycerine Spent Acid Storage system (NY26SW 38.27), the Gaillard Concentrating Towers plant (NY26SW 38.26), the Cottrell Precipitation plant (NY26SW 38.25) and the Gas Producer plant (NY26SW 38.29).

There were two types of plant used in the production of oleum - the Grillo Oleum plant and the Mannheim Oleum plant. These backed up one another in the event of breakdown. They were still relatively experimental and potentially temperamental. The Grillo Oleum plant was situated to the WNW of the Mannheim Oleum plant, both of which were associated with dedicated warehouses to their N. These contained their respective raw materials – sulphur and pyrites. The Grillo Oleum plant stretched over three ranges, but also included a storehouse for magnesium sulphate and a Platinising Laboratory (NY26SW 38.47), where the converter mass used in the plant was created. These buildings lay to its NW, while Oleum Storage Tanks were situated between them and the Grillo Oleum Compound (NY26SW 30.49). By contrast, the Mannheim Oleum plant was more compact. However, the pyrites used in the process had to be conveyed to a Crusher (NY26SW 38.4) and a Screening House (NY26SW 38.5) before being weighed and processed. There were further Oleum Tanks for storage (NY26SW 38.46) situated to its ESE and a small laboratory to its NE. These Oleum Tanks supplied a Mixing Station (NY26SW 38.51), before this acid was exported by rail (NY26NW 46.10) or pipeline elsewhere about the site.

Nitric Acid was also produced in this area and this plant lay immediately NE and SE of the Mannheim Oleum plant. The nitre (sodium nitrate) powder was delivered by rail in bags to the three Nitre Stores via a branch of the Glasgow and South Western railway. The empty bags were then sent to the Nitre Bag Washing plant, which comprised three separate buildings - a dirty bag store, a clean bag store with a washing plant in between. The waste nitre traces were recovered here and then reintroduced into the process. The nitre in the stores was sent to a Dryer situated between these buildings and the two Retort Houses. After drying, it was put into bogey trucks, which were weighed and raised by elevators to the charging platforms situated high within the two Retort Houses. The dried nitre was tipped into the twenty-four retorts in each Retort House and sulphuric acid was added from feed tanks in the roof. The mixture was heated, using coal gas from the Gas Producer plant, in order to manufacture the nitric acid gas. This gas was sent to a series of Hartz-type condensers which modulated its strength, allowing a strong or weak acid to be created. These acids were then run into separate receiver tanks: six lead receivers were provided in a lean-to at each Retort House for the strong acid and ten stoneware receivers were provided for the weak acid. The latter were situated outside and to the ESE of the buildings.

Any remaining fumes from this process were conveyed to the Condensing Towers situated to the ESE of the northern Retort House, where all traces of any residual acid were removed. The waste gases from the combustion process were directed via flues to a tall chimney situated on the WNW, midway along each Retort House, while a railway entering the northern Retort House removed the waste solids (nitre cake) from the retorts. The weak and strong acids produced that these produced were then sent to the Preliminary Acid Mixing Houses (NY26SW 38.36 and NY26SW 38.37) where they were combined with sulphuric acid and oleum to form an approximate mixture of nitroglycerine acid and nitrocotton acid. The nitroglycerine acid was then adjusted in the the Nitroglycerine Acid Mixing plant and sent to Storage Tanks (NY26SW 38.7). It was pumped from there via overhead pipes on trestles to the Mixed Acid Settling Tanks (NY26SE 17.4) situated S of Nitroglycerine Hills 2 and 3 (NY26SE 16.2 and NY26SE 16.3). By contrast, the nitrocotton acid was sent (via overhead pipes) to the Blending Plant S of the Nitrating House (NY26NE 140.3), where there were tanks for the weak and strong acids used in the final mixing, as well as nitrocotton acid storage tanks.

Spent mixed acids recovered from the Nitrating House were conveyed to the Spent Nitrocotton Acids Stillhouse situated ESE of the northern Retort House. Here the weak and strong nitric acids were separated from the sulphuric acid and recycled through the system, while the sulphuric acid was sent for concentration to the Gaillard Towers. Any residual sulphuric acid in a gaseous form was removed by the Cottrell Precipitation plant to which the towers were linked.

The nitroglycerine spent acid was returned from the Nitroglycerine Hills (NY26SE 16.1-5) to a storage house and from there a feed line led into the Nitroglycerine Spent Acids Denitration plant where the nitric and sulphuric acids were recovered. These acids were then recycled back through the system.

Wherever acid was run throughout the factory, earthenware pipes and pans were employed. These supplies were brought in by the Glasgow and South Western Railway and stockpiled in the Pottery Store (NY26SW 38.8) situated to the NW of the Retort Houses.

The energy for these processes came from a large Boiler House (NY26NE 139) situated immediately NNE of the Acids Compound (NY26SW 38.19-38.21, 38.42) and NNE of the Gas Producer plant (NY26SW 38.29).

Information from HES Heritage Recording (MMD, ATW), 22 May 2023.