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of Butetown, Cardiff
Also see Loudon Foundry
1875 'PATENT CORRUGATED, AND ARCHED TOP ANNEALING POTS AND STANDS, which has been well tested. For references, apply to Aberdare Tin Works Co., Treforest Tin Co., Mellin Griffith Tin Works Co., Maesteg Tin Works Co., and others in Llanelly. Maker, Mr C. Williams, Loudoun Foundry, Cardiff.'
1877 'SUDDEN DEATH.— Mr Charles Williams, of Emlyn House, Cathays, died very suddenly early yesterday morning. Deceased was a native of Neath Abbey, from which place he removed about 15 years ago, when he purchased the Loudoun-square Foundry at Cardiff, and which since that period has been carried on very successfully by him. He enjoyed excellent health until a very short time before his death. 
1877 Advert: 'In Chancery.— The Estate of Charles Williams, late of Loudoun-square, Cardiff, Iron Founder, deceased.
FOR SALE, by PRIVATE CONTRACT, in one Lot, the GOODWILL of the Loudoun-square Iron and Brass Foundry, Cardiff, together with the Machinery, Plant, Fixtures, and Stock-in-Trade and Effects, in and about the said Premises.
The business of the said Foundry has been established for some years, and presents a rare opportunity to persons seeking such a business.
It is situate near the Docks, and a good connection can be Secured.
Apply for further particulars to Messrs John Jenkins and Co., Public Accountants, Philharmonic Chambers, St Mary-street., Cardiff, or to Mr William Jones, Solicitor, 29, St Mary-street, Cardiff.
A Horse and Crank Axle Cart belonging to the Estate can be treated for separately. 
1878 Advert: 'WANTED a LAD accustomed to drive stationary engine.— Apply to Jones & Co, Loudoun Foundry, Cardiff.'
Perhaps the successful candidate did not meet expectations, as we find a later advert:-
'WANTED, a Lad to drive an Engine; must know his duties. Apply at Loudoun Foundry, Cardiff.' 
1938 'CITY OF CARDIFF. DUMBALLS-ROAD AND LOUDOUN-SQUARE, THE TITAN AND CHRISTIES FOUNDRIES. MESSRS STEPHENSON and ALEXANDER (F.A.I.) are instructed to SELL by AUCTION. at the Mart. 5, High-street, Cardiff, on THURSDAY, October 20th. at Seven o'clock in the Evening, the above FOUNDRIES, Together with the GOODWILL OF THE BUSINESS. Further Particulars .....'
The Loudoun Foundry (Iron) was depicted on the 1880 OS 25inch map (surveyed 1876-8). It is not clear from the text on the map whether the foundry was in a small building next to the Bute Chain Testing House, or in a slightly larger triangular building wedged between the Glamorganshire Canal and a row of houses on Loudoun Square. However the 1877 sale notice describes the business as the Loudoun-square Iron and Brass Foundry, supporting the wedge-shaped building as the location. 'The Glamorganshire and Aberdare Canals' Volume 2 includes the relevant section of the OS map, and also a 1927 aerial photograph. The photograph shows that a small area of land had been reclaimed from the canal, and industrial buildings constructed there. One has what appears to have Belfast roof with ventilators. This building is also visible in this aerial photograph, as a low dark building to the left of the sunlit Loudoun Square.
See also Titan Foundry (Cardiff)