James Neilson’s Hot Blast: Pierre Armand Dufrénoy and Lady Charlotte Guest – part 1

by Victoria Owens

Many thanks to Victoria Owens who provided the following fascinating article.

When James Beaumont Neilson, engineer of the Glasgow gas works, patented his ‘hot-blast’ of 1828 – the system of pre-heating air by passing it through a hot ‘vessel or receptacle’ before it entered the blast furnace – he was confident that it would save fuel and reduce costs. Encouraged by three Scots iron manufacturers – Colin Dunlop of Tollcross, Charles McIntosh of Crossbasket, and John Wilson of Dundyvan, all of whom acquired shares in his patent rights – Neilson conducted  experiments at the Clyde Ironworks which demonstrated that use of the hot blast could reduce fuel consumption by about a third. News of its merits spread fast. Not only did many English, Scots and Welsh ironmasters adopt Neilson’s system, but the French inspector of mines, Ours-Pierre-Armand Petit-Dufrénoy, (1792-1857), visited Britain to analyse the economic and metallurgical consequences of its application.

Ours-Pierre-Armand Petit-Dufrénoy

Dufrénoy’s Rapportsur l’emploi de l’air chaud dans les mines à fer de l’Ecosse et de l’Angleterre’ appeared in the 1833 issue of the French Annales des Mines. By chance, Edward Hutchins, nephew of Josiah John Guest of the Dowlais Iron Company, obtained a copy, in autumn 1834 and, recognising the British iron trade’s likely interest in its content, asked his uncle’s wife Charlotte to translate it into English.

The previous year, John Guest had married Lady Charlotte Bertie, daughter of the late ninth earl of Lindsey. An able linguist, she was fluent in Latin, Greek, Persian, Arabic and Hebrew. Soon after her marriage, she began to learn Welsh from the Revd. Evan Jenkins, Rector of Dowlais, and would in time publish a best-selling translation of the mediaeval Welsh story-cycle known as the Mabinogion. That she had a fair working knowledge of French goes without saying.

She started work on her translation of Dufrénoy’s article on 3 December 1834, while John Guest, MP for Merthyr Tydfil, was canvassing votes for the coming general election. She found the text ‘full of technicalities’ and foresaw that producing an English version would take a long time. Nevertheless, she continued throughout the following day, and calculated that by the evening, she had completed about a sixth of it. Here, to give some flavour of the task, is Dufrénoy’s description of Neilson’s methods:- ‘Dans la première experience,’ he writes

l’air fut chauffé dans une espèce de coffer rectangulaire en tôle de 10 pieds de long, sur 4 pieds he haut et 3 de large, semblable aux chaudières des machines à vapeur. L’air provenant de la machine soufflanteé tait introduit dans cette capacité, oùil s’échauffait avant de sa render dans le haut-fourneau. Malgré l’imperfection de ceprocédé, qui ne permit d’élever la temperature de l’air qu’a 200⁰ Fahrenheit (93.3 cent), on pouvait déjà pressentir que l’idée de M. Nielson était destinée à produire une revolution dans le travail du fer.

‘In the first experiment,’ offers Lady Charlotte, ‘the air was heated in a kind of rectangular box of sheet iron, ten feet long, four high and three wide, similar to the boilers of steam engines. The air proceeding from the blowing machine was introduced into this space, where it was heated, previous to being conveyed into the blast furnace. Notwithstanding the imperfection of this process, which did not admit of the air being heated above 200⁰ Fahr, it became immediately apparent that Mr Neilson’s idea was destined to produce a revolution in the manufacture of iron.’

If terms such as tôle [sheet metal] and chaudières [boilers] sent her to the dictionary, her rendition of the idiomatic phrase on pouvait  déjà pressentir, [literally, ‘one could already foresee’] as ‘it became immediately apparent…’ shows her ready command of the syntax.

Lady Charlotte Guest. Photo courtesy of Cyfarthfa Castle Museum & Art Gallery

First caught up in the excitement surrounding the election and, later, dismayed by an outbreak of cholera, Charlotte does not mention the hot blast again in her journal until February 1835. By this time, she and John and their infant daughter Maria were visiting Charlotte’s mother and step-father at their Lincolnshire home – Uffington House near Stamford. ‘Wet Day,’ Charlotte wrote on Friday 13 February; ‘Merthyr (her private name for her husband) […] corrected iron hot air [sic] for me.’

For all its brevity, her statement raises intriguing questions. That John Guest should have been interested in the observations of a highly qualified mining engineer from a rival nation upon the production process of every ironworks from Calder to Merthyr Tydfil by way of Monkland, Codnor and Wednesbury was understandable. Whether he also wished to explore Dufrénoy’s account in the hope of discovering some means of using the hot blast technique without having to pay Neilson royalties is a matter for speculation. The fact that on 12 March 1836 an injunction was issued against Guest and partners restraining them from infringement of Neilson’s patent suggests that by the time Lady Charlotte was translating the French treatise, the Dowlais Ironworks had already introduced the hot blast. In the event, John Guest, was quick to settle with Neilson and his fellow patentees, and pay the shilling-per-ton royalty on iron produced by their method.

Furthermore, Lady Charlotte’s reference to her husband’s ‘correction’ of her work, suggests that, rather than treat her translation of the treatise as a work of private reference, the two of them thought it deserved publication. Certainly the English edition of On the use of hot air includes a number of observations – each designated ‘Note by the Translator’ –which, to judge from their detailed knowledge of the ironworks and coal deposits of South Wales, are the work of an industry insider. The remark, for instance, that before they introduced the hot blast, both Guest at Dowlais and Samuel Homfray of the Penydarren ironworks were using raw coal rather than coke to fuel their furnaces evinces considerable local knowledge. Incidentally the concluding ‘Note by the Translator’ not only gives a complete overview of the hot blast apparatus in use respectively at Dundivan in Scotland and Pentwyn, Clydach and Dowlais in Wales but also appraises the efficiency of the system and the quality of the iron produced in each place. Dufrénoy includes no corresponding commentary and this state-of-the-art survey of British iron manufacture offers an authoritative epilogue to the English version of his treatise.

To be continued in the next post……

Leave a Reply

Your email address will not be published. Required fields are marked *