Tuesday, 24 January 2012

Captain Back's Patent Poison Producer




This bizarre contraption is my home-made experiment intended to shed some light on the question of the origin of the lead detected in the bones of participants in the Franklin Expedition. The apparatus is designed to  approximate the system originally installed on HMS Terror following the suggestion of Captain George Back on the 16th of May, 1836. A 2kw wallpaper steamer plays the part of the Fraser stove and the condenser/snow-tank is a black plastic box which normally holds paper for recycling. The five-foot length of lead piping between them is arranged so that any water condensed within it can't flow back into the steamer but instead drains via a narrow plastic tube into a glass jar on the floor. This approximates the arrangements shown on the 1837 profile drawing of HMS Terror but has the advantage, for experimental purposes, that the water which condenses in the pipe can be collected separately instead of mixing with the boiler water. 



I had been worrying how to test the lead content of the water produced. There are test strips available, for a few pounds, which give a yes/no answer to the question of whether lead is present in tap water and there are digital colorimeters, costing a few hundreds, which give an accurate measurement in terms of parts per million. In the event, no special equipment is needed. The water collected is cloudy with lead carbonate - white lead. After an hour or so the water clears leaving a powdery deposit at the bottom of the jar. When the jar is shaken it produces a pretty snow storm of glinting crystals, as shown by the middle one of the three jars in the photo above. This sample was produced as the result of 30 minutes operation. The conclusion I draw from this demonstration is: that the water making systems in place on Erebus and Terror during the fatal 1845 Franklin Expedition are likely to have introduced relatively huge quantities of lead, measurable in terms of grams per day, into the drinking water supplies, when the ships were overwintering. This seems likely to have been the major source of lead exposure, totally overwhelming any trace amounts absorbed from any other of the proposed sources.

8 comments:

  1. Peter you walk on water - with or without the lead. I think this is a huge step forward. Well done.

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  2. Thank you William. On the shoulders of giants...

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  3. Amazing, thanks so much Peter for all your work. It will be very interesting to compare this overwhelming lead content with the experiment on the reproduction Goldner cans, whatever happend with that experiment at McMasters University? I've not found any online information beyond this: http://visionsnorth.blogspot.com/2009/12/franklin-era-tin-tests-positive-for.html.

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  4. A clever and extremely useful experiment Peter, my congratualtions.

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  5. A great experiment, surely. But the view that the cloudiness of the water is due to lead carbonate, while certainly plausible, is at this point only conjecture. Two key questions I would have: 1) Is the "lead pipe" you used identical in composition, and in length proportionate to the actual apparatus; and 2) If indeed the amount of lead is measurable in grams per day, why would not every single soul on board have died of acute lead poisoning well before 1848? Lead poisoning today is often stated at 60 micrograms per decalitre of blood, so even 2 "grams per day" would equal enough lead -- if all were absorbed -- to equal 258 micrograms per crewmember per day. So though there's no question in my mind that this shows Back's system to be flawed, if it were this flawed, why would not every vessel employing it have produced a very high level of sailors with acute lead toxicity, fatal to most crewmembers?

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  6. This is excellent! In response to Prof. Potter's important observations, would the formation of scale (from minerals in the water) within the pipes form a semi-protective "barrier" against such huge amounts of precipitating lead? Does the water temperature have an impact on the rate of scale formation?

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  7. Thanks to all for the above comments.

    E.W. - Thanks. I emailed McMasters a while back but didn't get a reply so I've decided to make some reproduction Goldner cans myself.

    Russell - Excellent and valuable questions! Agreed the composition of the sediment is a conjecture. The pipe is made from clean new sheet lead from a DIY store, rolled into a tube and the join sealed with heat resistant aluminium tape. The connections are polypropylene so any debris from them will float. Mostly the dimensions were determined by what was immediately available. I'd like to build an accurately scaled replica and and attempt to replicate the whole cooking and water-making cycle, but that's for the future. For this experiment the goal was to just to produce 'some' lead contaminated water, and I'm satisfied that that is the case. The excellent question 2 requires a lengthy answer so I'll put it in a separate post.

    Jaeschylus - Thanks. In my experiment the lead is only exposed to steam and its condensate. The mineral content of the original water is not taken up with the steam so no encrusting of the pipe can happen. Corrosion of lead in damp conditions does seem to be accelerated by high temperatures.

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  8. Just a thought Peter but do you know the origin of that 'on the shoulders of giants' quip?

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