This reduction involves a 30% decrease in volume, which makes the rust lay-
ers more porous and allows the solution to reach the deeply-buried chlorides.
The conservation must be carried out in sealed containers as ingress of oxygen
into the solution would convert the sulfite to sulfate, and hence no reduction
would take place. Some conservators have heated the solutions up to 60°C to
speed upthe reduction rates, and hence the removal of chloride ions. The two
major problems with this particular formulation are that the chloride analysis is
rather difficult and is not very efficient for artefacts covered in thick layers of
corrosion products.
The conservation of the first submarine of the British Royal Navy, Holland 1,
was carried out by aqueous washing method (Figure 7). The submarine was
launched in October 1901. She had a crew of nine and weighed 105 tons with
a length of 19 m and a maximum diameter of 3.7 m at her widest point. A four-
cylinder petrol engine producing 160 Hp and weighing 4 tons, gave the sub-
marine a top surface speed of 7.4 knots. Underwater propulsion was provided
by a 74 Hp electric motor powered by 60 lead acid battery cells each weigh-
ing 108.5 kg. This gave a maximum underwater speed of 7 knots. There were
two ballast tanks into which water was admitted to increase the vessel’s weight
and allow her to dive to a maximum of 30 m. However, the normal operating
depth was 15 m, which took approximately 40 min to reach from the surface.
Holland 1saw 12 years service before she was superseded by more advanced
and powerful craft and she was sold for scrap in 1913. While being towed to the
breaker’s yard, she sank off the Plymouth coast and remained on the seabed
until her discovery by a Royal Navy minesweeper in April 1981.
146 Chapter 6
Figure 7Holland 1 at the submarine museum Gosport, England prior to conservation