On the 26th November 1805 Pontcysyllte Aqueduct, designed by Thomas Telford, opened to great fanfare. It carried the canal, across the River Dee at the incredible height of 126ft (38m). The aqueduct built on stone pillars carried the water in huge cast iron sections and was brilliant engineering. How Telford sealed each join surprised me and gave me an idea.
One of the great joys of writing historical fiction is weaving real characters into the story. Did you know that the canal and road engineer Thomas Telford was a bit of a practical joker? When I learned he enjoyed a tease I had to include something of his humour in my novel The Iron Masters.
The scene starts with a visit by Nye Vaughn and his son Bryn, owners of Castle Iron Works, to see Telford. They want to win an order to supply the huge iron chains that will support the Menai Bridge which Telford is constructing. Telford is at work in his office studying maps........
‘We went to see Pontcysyllte Aqueduct yesterday. It’s a beautiful piece of engineering Mr. Telford but there’s one thing I don’t understand. How did you seal the cast iron plates that carry the canal across the valley?’ asked Bryn.
Telford stopped looking at the map. ‘It’s an interesting question. What made you ask it?’
‘When I was in the boiler shop at Boulton and Watt, getting a reliable seal was always a problem. We spent a lot of time trying different materials as a sealant,’ said Bryn.
‘So you’re an engineer Mr. Vaughn. We had the same problem. The aqueduct had to be completely watertight. Believe it or not the sealant is Welsh flannel impregnated with white lead and iron filings,’ said Telford and grinned, mischievously.
‘Judging by the width of your smile I believe you are teasing us Mr. Telford,’ said Bryn. Thomas Telford roared with laughter.
‘I promise you on my dear wife’s life, it is true. What’s more, after we bolted the sections together, we filled the aqueduct with water and left it for six months to prove it was watertight,’ said Telford.
‘If I say I believe you, will you believe me when I promise you that Castle Iron should cast the chains for the Menai Bridge?’ asked Bryn.
Telford grinned again and asked to see the quotation. He read it and instructed his assistant to make out a purchase order to Castle Iron Works for 2,000 tons of cast iron chain to be delivered to the Menai Bridge. After saying goodbye, Telford returned to his map and the assistant showed them out.
‘You should know Mr. Telford is married to his work. He doesn’t have a wife,’ whispered the assistant.
‘So he was teasing us about the sealant,’ said Bryn.
The assistant grinned and returned to his master. He saw no reason to reveal that Thomas Telford had told the truth about the aqueduct.
The roadway was hung from the chains in the autumn and the bridge opened on the 30th January 1826. Telford’s reputation as the most talented bridge engineer in the world was assured and he wrote to Nye to thank him for the work Castle Iron had done;
My Dear Vaughn,
You will be pleased to learn that the bridge at Menai is finished and was opened to mail coaches last month. I confess the admiralty demand to hang the road a hundred feet above the sea to allow sailing ships to pass beneath was a daunting requirement. However the bridge is built and, I must say, I am proud of it. It seems I am to be known as the ‘Colossus of Roads’. An odd name don’t you think? Your iron chains were a devil to hang across the straits but they are firm and there is little movement when the coaches pass across, although some of the horses are unsettled by the drop. Thank your son for his suggestion to coat the chains in linseed oil to protect them from corrosion. His idea has proved better than the lead paint we planned to use. To be doubly sure we have done both. When he proposed linseed oil I believed he was repaying me for teasing you in the sealing of Pontcysyllte Aqueduct. I hope you forgive my jest. Please accept my compliments and thank your foundry men. Tell them we found no flaws in the links we tested. When I am next in need of heavy castings I will call on you.
My very best regards,
Telford did in fact use Welsh flannel, white lead and iron filing to seal the aqueduct and the cast iron chains at Menai were protected with lead paint and linseed oil. The rest, as they say, is a story.