Solignac mixed boiler system. 19th-century artwork of a longitudinal section through a Solignac mixed boiler system. This shows S-tube bundles through which water is passed from a reservoir tank or drum (upper right). This tube is heated by the furnace (bottom) and the steam passed to the moving parts of the engine. This was a compact and relatively safe boiler that was built to order. It was a French design, by an engineer named Solignac, and was patented in the UK in 1894. Artwork from the first volume (1897) of 'La Revue Scientifique et Industrielle' by French chemist and inventor Jules-Louis Breton (1872-1940).