Sunday, 24 July 2011

Time we put the tinned food back in the cupboard: Busting the Franklin Expedition myth of 'lead poisoning from tinned food'.


The idea that Franklin's men were poisoned by lead from tinned food has reached almost the status of dogma. For many members of the public it seems to be almost the only 'fact' they know about the expedition.

Owen Beattie and John Geiger's bestselling book 'Frozen in Time' (2004 edition) includes the statement "There is no question of the source of the lead found in the bodies of Franklin's men: it came from the tinned foods". This claim is supported by a paper by Walt Kowal and others published in the Journal of Archaeological Science in March 1991, but, contrary to that claim, the source of the lead was questioned from the very first.

ISOTOPES:

Kowal and his co-authors found that the ratios of the several isotopes of lead in solder from cans found on Beechey Island matched the ratios measured in human remains from Beechey and King William Islands. They concluded from this that the lead in both cases came from the same source. That seems reasonable - indeed it's likely that all the lead on the ships came from the same source.

No measurements were made on contemporary British samples of lead, instead the authors referred to a database of isotope ratios of 98 samples of lead ore from the British Isles published by Stephen Moorbath in 1962.

Having found no credible match, they speculated that:
"...since the isotopic ratio for the Franklin materials is so different from most lead sources in the British Isles, it is quite possible that the lead used in the solder manufacture came from some other nation".
Their argument seems to be, that because all of the other sources of lead which the members of the expedition would have been exposed would have come from British mines, then the only possible explanation for the presence of the unusual exotic lead in the human remains was that it had come from the solder of the tin cans.

Unfortunately mass-spectrometry was still in its infancy in the early sixties, and the isotope measurements published in Moorbath's paper do not bear direct comparison with those made thirty years later. In 1996 Brenda Rohl published isotope ratios of 383 samples of lead ore from the British Isles. Her introduction states:
"The data in pioneering papers such as Moorbath (1962) and Brown (1966) are now too inaccurate to be compared with modern lead isotope data".
MINING:

It is implausable that isotope data could be used to trace the origin of any industrial era lead back to a single mine. Even connecting a sample with a single mining region presents difficulties.

Veins of ore with distinct isotope ratios can occur in close proximity. Equally, veins with indistinuishable isotope signatures can occur many miles apart. A small number of smelters would serve numerous mines within a region, producing metallic lead with an isotope signature averaged from the constituent ores.

Lead is probably the most easily recycled material known to man. At the lead mills ingots of newly smelted lead would be melted together with old lead scrap to manufacture whichever products the market required, such as sheet or pipe or solder.

The isotope signature of a typical sample of manufactured lead would therefore represent an amalgam of both contemporary and previously active mining regions. The average composition of the mixture would change only gradually as established mining regions declined and new ore provinces were exploited.

In 1839, Andrew Ure published statistics showing the relative productivity of the different Lead mining regions at that time. The North Pennines (Durham, Cumberland, and Yorkshire) being the dominant region.


Click on image for source document

The following chart compares the Franklin project data with geological data from Rohl, chosen with reference to the above table, and data from 36 samples from the Northern Pennines, from a 2001 paper by Brett Scaife and others.

Click to enlarge.

Data points from the two Welsh counties are represented by the larger circles to make up for their small number. Derbyshire had been of greater significance in the preceding century hence may deserve greater prominence than Ure's figures suggest due to recycling of old lead. There has been no attempt to distinguish the relative productivity of individual mines within a region, nor to represent measurement confidence intervals.

The main feature to note in the above chart is that all the data points for the Franklin samples are within the locus of the data points for the Northern Pennines.

CONCLUSION:

It is plausible that the isotope signature shared by both the solder and the human remains is simply that of common English lead of the period and that the high levels of lead detected in the human remains could have resulted from exposure to any of a myriad of contemporary sources and certainly not uniquely to the solder of the tin cans.

That members of the expedition suffered from lead exposure is not disputed, but there is no evidence to suggest that "it was the reliance of Franklin's expedition on tinned food that was the root cause".

The supplier of the tinned food, the much vilified Stefan Goldner, is exonerated of any blame in connection with the demise of the Franklin Expedition.

The eminent Food Scientist and Science historian Keith Farrer, OBE (who even has an award named after him) was among the first to question the 'lead poisoning from tin cans' hypothesis.

In a paper published in the Journal of Archaeological Science in 1993, Farrer pointed out, among other things, that only acidic foods such as tomatoes can defeat the cathodic protection conferred on lead by the more reactive tin and iron and that the canned provisions supplied to the expedition included no acidic component. It appears that all published reports of canned food being been found with a high lead content have involved acidic foodstuffs.

Farrer's conclusion regarding the canned food was that "their contribution to the body loads of lead or to any incipient ill health in Franklin's crewmen was trivial".

However no scholarly article in a scientific journal can compete for the public consciousness with a bestseller like 'Frozen in Time'.

So I hope this small effort does something to redress the balance.
01-Aug-2011

Tuesday, 12 July 2011

Franklin's ships took refrigerators to the Arctic!

It may raise a few eyebrows when I confidently state that, for their fateful voyage to the frozen regions, HM ships Erebus and Terror were almost certainly equipped with refrigerators.

It is also a break with long held consensus, and a volte-face from my previous position, to suggest that the railway locomotive boilers fitted to these ships were modified to boil seawater instead of freshwater.

I'll start by explaining that in the context of early Victorian engineering the word refrigerator was used to refer to what is now called a heat-exchanger. The illustration below, from 1828, shows an example of the 'shell and tube' variety. The hot liquid to be cooled was passed through the array of small tubes while the cooling water flowed around them in the casing. A typical usage was in brewing - to cool the wort down to fermentation temperature after boiling.

Early nineteenth century heat exchanger



WATER:

I began to suspect that the boilers used sea water while thinking about the water consumption of the engines.

Captain Frederick William Beechey made the first proposal to fit auxiliary steam engines to Erebus and Terror with the proviso that they should only be used when there was a flat calm and the ice floes were no longer pressed together by the wind.

Beechey wrote "The openings in the ice are generally of short duration, perhaps for eight or twelve hours only."

Samuel Brees' statistics for the Rennies' engines include the information that the tender's 3.3 tons of water was sufficient for 1.87 hours operation. This equates to 21.2 tons in 12 hours.

The Terror's tanks held 6000 gallons or 26.8 tons so operating the engine for 12 hours would use 80% of the ships water, supposing that the tanks were brim full to begin with.

Alternatively the full capacity of Terror's tanks could sustain the engine for a little over 15 hours.

Fresh water is not difficult to find in an Arctic summer as melting snow forms ponds on ice flows but there would be no guarantee when the weather would allow it to be collected.

If fresh water from the ships' tanks were relied on for the boilers there would be a strong possibility that there would not be enough water on board to fully exploit the rare opportunity of an opening in the ice without endangering the crews lives.

Merely getting so much water out of the tanks in such a short time would be difficult. The ships had numerous separate tanks, most of which held around two tons, with stores piled on top of them. Merely getting at the apertures involved laboriously shifting stores around so that a hose from a force pump could be inserted.

Another useful nugget of information is found in the "Particulars of Steamships", in the National Archives.

The entry for Terror reads:
"Machinery & Boilers complete in every respect
On the 1st trial speed of the Terror was 3.6 knots per hour by Massey's log
with the disadvantage of river water priming the boilers it is expected the speed will be 3 1/2 knots per hour."
National Archives, crown copyright waived for non-commercial use.

The entry for Erebus reads:
"Machinery & boilers Reported to be complete,
on the 1st trial. speed of the "Terror" was 3.6 knots per hour by Massey's log
with the disadvantage of river water priming the boilers, the speed is expected to be 3 1/2 knots per hour"

National Archives, crown copyright waived for non-commercial use.


The Terror's speed trial is mentioned in the entries for both ships, which is perhaps another pointer that the engines were identical in each ship. Erebus, being a foot wider in the beam, would be expected to be slower.

The suggestion of using river water is a clear hint that the ships were equipped to use the water they floated in to feed their boilers. No officer in their right mind would have contemplated contaminating their ship's drinking water tanks with the filth which flowed in "the common sewer of London" - the Thames.


SALT:

I suspect that the widespread belief that the boilers could have only used fresh water is based on the assumption that they would have suffered from excessive corrosion if they had used seawater.

Using seawater certainly did cause greater corrosion. A typical lifespan of a ship's boiler using seawater was only around five years while a similar boiler on land using fresh water could easily last for twenty years. This would not be an issue during the very limited time in which the expedition's engines were expected to operate.

Around the time of the planning of the Franklin Expedition there was lively debate as to whether iron or brass was the best material for the tubes of ships' boilers.

Brass tubes conducted heat better and were resistant to scaling while iron tubes were more resistant to overheating and avoided galvanic corrosion.

A specification for paddle steamers issued by the Admiralty in January 1844, and another for screw steamers issued in September 1845, both included instructions for the tenders to include alternate costings for tubular boilers with iron tubes and with brass tubes.

More immediately dangerous than corrosion was the problem of increasing salt concentration.

A build-up of salt could cause a boiler to 'prime' or boil over, sending a mixture of water and steam to the cylinders. Worse, a boiler filled with excessively saline water could develop an insulating crust of insoluble calcium salts (essentially plaster of Paris) on the boiler tubes, diminishing the flow of heat to the boiler water and causing the tubes to fail through overheating.

In 1824 Henry Maudslay and Joshua Field had patented a method of changing water in boilers to prevent the deposition of salt and other substances.
In addition to the normal feedwater pumps common to every steam engine, the engine was equipped with what became known as 'brine pumps' which expelled a small quantity of hot supersaline water from the boiler in proportion to the quantity of seawater pumped in, thus allowing the salt concentration to remain constant. To avoid wasting heat, the hot water expelled was passed through a heat-exchanger or 'refrigerator' to transfer its heat energy to the incoming sea water.

The royal yacht Victoria and Albert (launched April 1843) had engines by Maudslay's complete with their system of brine pumps and refrigerators, and that system was also stipulated in both of the Admiralty's specifications mentioned.


CONCLUSION:

Franklin's ships were fitted with the best, most up-to-date technology of the day, including brine pumps and refrigerators (heat-exchangers). They used sea-water in their boilers.

It seems that studies of the Franklin Expedition have suffered from almost as many false trails as the searches for the Expedition itself.

Hopefully this will be the year that Parks Canada find some hard evidence to measure these speculations against.