Final Wash Hills (Hills Type C) in the M/S Factory Dalbeattie :
Following nitration and separation, the separated Nitroglycerine went through a series of five wash columns - three
in the Nitration Hill and two in the Final Wash Hill. Subsequent to washing, the Nitroglycerine was filtered to remove any
remaining impurities, its acidity tested and then sent to the Burette Houses for blending in to Cordite. This appears a simple
process, but the risk of explosion or fire meant that the work was carried out by skilled technicians taking elaborate
precautions.
Gordon Nicholson's article on Nitroglycerine manufacture could be relied on for process detail but unfortunately very
little remains in any of the three Final Wash Hills to illustrate the process. The process and archaeology are described here
and interpreted accordingly. However, the Final Wash Hills have a further intriguing distinction - they appear to be the
interface between the trolley runways and the site's Narrow Gauge railway system.
Archaeological Evidence at the Final Wash Hills :
The internal proportions of the Final Wash Hills in both Units 1 and 2 are the same, those at Unit 1 being badly overgrown
and less evident. The Unit 2 Final Wash Hill is thankfully clear of vegetation but the Final Wash House has a single feature
in it - the low stub of a small brick-cored concrete column. The same feature exists in both the Unit 1 Hills. Bolts and the
ground floor ringbeam show that the House was a frame building clad in corrugated asbestos cement panels, with a first floor
entry and 'bridge' similar to that in the Nitration House. However, at the back of the Final Wash House there was a low
concrete platform the width of the House, beside a spur of the Narrow Gauge bogie railway used on the site. The access
tunnel for the railway has set in its floor the sleepers for the rails. A pipe tunnel in the hill bank beyond the Narrow Gauge
track leads to a line of pipe-supports clearly aligned on the site of the now-demolished Wash Settlement Hill (Type C).
The upper floor entry in the Unit 2 Final Wash Hill was very evidently linked to an asphalted trolley runway. The matching
entries in Unit 1 actually have their surviving runways, which lead by way of viaducts and a junction to the back on
Nitration Hill A2, but there is insufficient evidence in the Unit 2 Final Wash Hill to indicate whether the runway there
curved round to an entry in the Unit 2 Nitration Hill, although some displaced and demolished brick supports are near the
expected line.
Processes at the Final Washing House (after Gordon Nicholson) :
The Final Wash House held a further two wash columns that washed the soda and nitroglycerine in hot water at 40° C
and then in cold water at at least 12° C. Nitroglycerine freezes at about 12° and can be highly unstable when
thawing out. Once it had left the fifth wash column's intermediate separator, the now virtually pure nitroglycerine was collected in a lead settling
tank containing about 820 lbs of the explosive. It was then discharged into three identical four-ply flannel filters into
separate filter boxes and then into one of three separate 1200 lbs lead storage tanks. Up to 280 lbs of nitroglycerine at
a time was removed to lead weighing tanks before being moved to the next process.
As an appreciable quantity of nitroglycerine remained in the wash waters, these were first allowed to flow over a stainless
steel cataract (possibly an inclined plate with riffles, or a series of small settling tanks) to let the nitroglycerine
sink, then the wash water was discharged along a rubber-lined wooden channel into the next hill, the Waste Water
Settling Houses (Hill D).
Nitroglycerine Filtration :
Nitroglycerine from the final intermediate separator was checked with litmus to check that it was completely free of acid,
and filtered through flannel bags before discharge into one of three storage tanks. These were periodically tested, then
if acid-free, discharged into a weighing tank that held up to 280 lbs (125 Kilos) of Nitroglycerine. Although Nicholson does
not make this clear, it is suspected that one fill of the weighing tank would have been the capacity of the small trolley
bogies used between the Hills and the Burette Houses.
Testing for Purity and Stability :
Two other tests were carried out for purity - the Abel Heat Test, where the temperature was measured at which a sample
began to give off brown nitric oxide fumes - and a moisture test to check the amount of water in the mix. As these tests
could be dangerous, the writer is inclined to believe that samples were cased and carried to the nearby unidentified
Hill (for convenience designated Hill X) for lab testing onsite.
Acetone Desensitising :
The nitroglycerine had to be desensitised by mixing with alcohol, acetone or dinitrotoluene, or blended with ethylene
glycol nitrate to keep it liquid if chilled. Dalbeattie used acetone, from the evidence of other features in the Factory and
the words of former staff. This would also indicate the kind of Cordite made - Cordite MD (dual base) or Cordite N (triple
base), a matter examined futher in the Burette Houses and Cordite Milling Sections. Acetone may have been added by hand to
the Nitroglycerine storage or weighing tanks, using either sealed cans of acetone or tapping a pipeline from the Acetone
Plant. Unfortunately there is historical evidence for both methods but no physical evidence remains in or near the Final
Wash Hill, Nicholson's account also being no guide.
Interpretation of Features with Processes in the Final Wash House (Houses Type C) :
Impure but neutralised nitroglycerine from the Nitration Hills was brought either by pipe (Nicholson) or in tank trolleys
(physical evidence) to the Final Wash Hill and there treated with hot and then cold water in the wash columns. The wash water
was piped away to the Wash Settlement Hill for further treatment, whilst the Nitroglycerine from the last wash column's
separator was run into the lead settlement tank and into the filters and the storage and weighing tanks. It is suspected that
either the storage or weighing tanks are where the acetone was added to stabilise the Nitroglycerine. Following this acetone
blending process, the weighing tank was emptied into a Nitroglycerine tank on a bogie and taken away to the Burette Houses
by explosives runners.
Other enthusiasts have been surprised that the railed bogies would have gone right inside the Final Wash Houses and Burette Houses,
but the reasoning may be that the Acetone stabilised the Nitroglycerine sufficiently to prevent vibration triggering explosions.
Dennis Sawden in his history of the Carsegowan black poweder works suggested that some rails were made of brass or similar metal
to avoid sparks. This might well have been the case between the Nitroglycerine section and the Burette Houses, but the rail
fastenings in the sleepers are of rusted steel and the only in situ examples of the rail bearers at the Kirkgunzeon
Lane road bridge are definitely of steel.
Conclusions :
This Hill is of interest principally because of the trolley runway into it and the Narrow Gauge railway out of it. The
Nitroglycerine purification, testing, weighing and blending with acetone, although intriguing, is mainly a follow-on to
processes in the Nitration Hill.
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