52 THE STEAM-ENGINE AS A SIMPLE MACHINE.
coal, igniting that in turn, and, as claimed by Papin, the combustion was complete, and the formation of smoke was entirely prevented. He states, in "Acta Eruditorum," that the beat was intense, the saving of fuel very great, and that the only difficulty was to find a refractory mate- rial which would withstand the high temperature attained. This is the first fire-box and flue boiler of which we have record. The experiment is supposed to have led Papin to suggest the use of a hot-blast, as practised by Neilson more. than a century later, for reducing metals from their ores. Papin made another boiler having a flue winding through the water-space, and presenting a heating surface of near- ly 80 square feet. The flue had a length of 24 feet, and was about 10 inches square. It is not stated what were the maximum pressures carried on these boilers; but it is known that Papin had used very high pressures in his digesters-probably between 1,200 and 1,500 pounds per square inch.
In the year 1705, Leibnitz, then visiting England, had seen a Savery engine, and, on his return, described it to Papin, sending him a sketch of the machine. Papin read the letter and exhibited the sketch to the Landgrave of Hesse, and Charles at once urged him to endeavor to perfect his own machine, and to continue the researches which he had been intermittently pursuing since the earlier machine had been exhibited in public.
In a small pamphlet printed at Cassel in 1707, Papin describes a new form of engine, in which he discards the original plan of a modified Huyghens engine, with tight- fitting piston and cylinder, raising its load by indirect ac- tion, and makes a modified Savery engine, which he calls the "Elector's Engine," in honor of his patron. This is the engine shown in the engraving, and as proposed to be used by him in turning a water-wheel.
“Nouvelle manière d'élever l'Eau par la Force du Feu, mis en Lu. mière," par D. Papin. Cassel, 1707.
