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Paul - Belated thanks for your comments and refs to Bourne (1861 edn) and Stephenson, et al (1829) and your second message yesterday suggesting the Boulton & Watt Collection (deposited in Birmingham Central Library. I have indeed had several very helpful replies from Ind Arch and am copying this back to the list. a) Boiler pre-dating the prison? The boiler is so integrated with the 1780s structure it cannot reasonably be older, and the historic maps of the castle show no building anywhere near this. b) Boiler providing steam power for construction?: I think if the boiler had related to construction it would have been installed in a more accessible position. c) Boiler for a steam powered water pump? This could be, assuming it was a steam generator, but the obvious water source is at the opposite corner of the prison beside the river, with tanks surviving in adjacent St George's Tower, and a capstan arrangement designed to use a different power source (i.e. the prisoners). d) Boiler for a laundry? Jason Lucas was first to suggest this, because he felt this was a water boiler rather than steam generator. He referred me to Dr. Eleanor Casella at the University of Manchester, and I'm hoping to hear from her. It looks promising because the later laundry is on this side of the range. John Ferris notes `Water boilers didn't start appearing until after c1820, before then they were usually steam at low pressure, about 5psi', but this could still give it up to 50 years operation before abandonment in 1868. However John Ferris asks `Are we sure it is a boiler and not a warm air stove', and I have to say that the bore size of the (?Inlet) pipe seems extravagant for water (see photo, use hand-shovel for scale, maybe 75-100 mm bore). But the Victorian prison has hot air ducts of massive scale (1 m square section), and this pipe looks puny by comparison. Perhaps after all it is about right for a water-hearing system using convection circulation? Two questions have been raised which I can't answer from memory, so I will need to consult with the site staff. 1) Pat Achon asks was the "external" tubing made from steel/bronze/ are they soldered ? any more tubing present around the boiler ? Provisionally I think a lot of this went as the general contractor was digging out upper part of the vault, before the significance of the boiler was recognised. 2) Jason Lucas points out that some indication whether the boiler was original may come from how the connecting pipe-work goes through the masonry, i.e. if there is evidence of hacking through it is more likely to have been a later installation. Thanks again to all. Incidentally for those of a stronger constitution there is a forthcoming `Meet the Ancestors' programme on a different aspect of the Oxford Castle work, which may briefly show the hanging cell next door, though filmed before the boiler was discovered. Said to be BBC2 16 Feb, but I can't find confirmation on the Beeb website. - Brian -- Brian Durham ([log in to unmask]) also Oxford City Council ([log in to unmask])