NOTES ON THE WATER-JET AIR BLAST WILHELM PRANDTL University of Munich (Translated by Rolph E. Oesper, University of Cincinnati)
IF,
PEECAANCE, a student who wax using a water-jet air ?last in the chemical laboratory should he asked, "When was this instrument invented and by whom?" he would probably reply, if a t all, "It might have been Bunsen, sometime in the previous century." The answer would be incorrect; the apparatus came down from ancient times and its inventor is not known. More than 300 years ago, particularly in Italy, it was widely used, in part for physical playthings, and partly in metallurgical works. It was not brought into chemical laboratories until the second half of the 19th century. There is no mention of this blowing device, for instance, by Berzelius in his monumental Lehrbuch der Chemie. The principle of the water-jet or water-dmm air blast is as follows: A jet of water falling through a pi'pe sucks in air and carries the latter with it. The mixture of water and air is not allowed to nrd off freely, as in the familiar water aspirator or filter pump, but flows into a closed container. The water and air separate in this drum; the water flows out through a lower opening, that can be regulated, and the blast of air issues through an upper orifice. Vitruvius, architect and engineer to the Roman emperor Augustus (reigned 30-14 B.c.) described, though somewhat hazily, a water-organ that probably was actuated by a water-jet blast. The invention was forgotten in the centuries that followed. There is no mention of it in any of the'noted books that describe sovfu11v. " ,bv " word and sketch. the chemical and metallurgical practices of the 16th century. For instance, Vanoccio Birinmccio in his Pirotechnia *(Venice 15401, Georg ~ ~ r i c o l ahis l n De re metallica ( ~ k e 1556), l and ~ n ~ i db ~inv~ thei commentaries ~ ~~ ~ to~his ~ l ~ (Frankfurt h ~ ~a.M.i 1606) ~ describe only the ancient bellows. Not until the early years of the 17th century is there again mention of water-blown organs. The first description is given by the inventive French engineer, Sololson de Caus (d. circa 1635), who also proposed to propel ships by steam. I n Italy, the learned Jesuit, Athanasius Kircher (1602-1680), a native German from Thuringia, wax the first, in his Musurgia, t o describe water-organs. I n 1649, he received a commission from Innocent X to build a water-organ for the papal garden at the Quirinal palace. Such amusement devices were installed in the gardens of many of the Italian nobility for the entertainment of guests. Descriptions of these organs, etc., are given by Kircher's fellow Jesuit, P. Gaspar Schott, who was professor of physics and mathematics in the Jesuit Academy a t Wiirzburg. The accounts, written from his personal inspection of these devices, are given in his Mechanics Hydraulico-pneumatica (Wurzburg, 1657).
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The three sketches (Figure 1) taken from this work are so obvious that no detailed discussion of them is needed. In the first, the spiral inlet tube for the waterair mixture delivers its burden against a polished marble plate. In the second, a set of perforated -plates improves the separation of the water from the air, and the water drops carried along with the air are then removed by passing the mist 6hrougha spiral. Schott did not approve of the third design. The receptacles for the water-air mixtures were made of burnt clay. They were fairly large-about 5 feet high and 3 feet across. The issuing air was vented into wind chests and then sent through organ pipes, artificial singing birds, etc. Water-jet blowing engines were not used solely for amusement purposes; they were also employed for technical processes, especially for blowing fires in metallurgical operations. Figures 2 and 3 which illustrate such uses need no discussion. The sketches are taken from "Pratica Mierale Trattato, del March. Marco Antonio della Fratta et Montalbano" (Bologna, 1678). It is worth noting that these devices were constructed entirely of wood. Small-scale brass or glass adaptations of these ingenious machines for supplying compressed air were eventually installed in chemical laboratories and served their purpose quite satisfactorily. They have now been mostly supplanted by motor-driven blowers.
