AIR ENGINES. Many attempts have been made within the last few years to pro duce engines which should have the power of steam-engines without the use of steam. The compression or the rarefaction of air, brought about in some one of many different ways, is the agentrelied upon for producing a moving force. In 1840 Mr. Stirling patented such a machine, and read a description of it before the Institute of Civil Engineers in 1840. In this engine two strong air-tight vessels are connected with the opposite ends of a e,,, tinder, in which a piston works in the usual manlier. About four-fifths of the interior space in these vessels is occupied by two similar air-vessels, or plungers, suspended to the opposite extre mities of a beam, and capable of being alter nately moved up and down to the extent of the remaining fifth. By the motion of these in terior vessels the air to be operated upon is moved from one end of the exterior vessel to the other ; and as one end is kept at a high temperature, and the other as cold as possible, when the air is brought to the hot end, it becomes heated, and has its pressure increased, whereas its heat and pressure are diminished when it is forced to the cold end. Now as the interior vessels necessarily move in opposite directions, it follows that the pressure of the enclosed air in the one vessel is increased, while that of the other is diminished ; a dif ference of pressure is thus produced upon the opposite sides of the piston, which is thereby made to move from one end of the cylinder to the other ; and by continually reversing the motion of the suspended vessels or plungers, the greater pressure is successively thrown upon a different side, and a reciprocating mo tion of the pistpn is kept up. The piston is connected with a fly-wheel, in any of the usual modes, so as to communicate motion to ma chinery. There is a furnace to heat one end of the air-vessels, and a water-pipe refrigerator to cool the other ; and the air traverses nume rous small channels in its course from the one' end to the other, in such a mode as to econo mise the beat. An engine on this construc tion has been used in an iron foundry at Dundee.
One of the most remarkable projects for an air-engine is the Carbonic Acid Locomotive, for which Mr. Baggs took out a patent in 1842. Carbonic acid gas assumes a liquid form un der a pressure of about 540 lbs. to the inch, at a temperature of 32'; and the project con sists in an attempt to make the sudden vapo risation of this liquid a source of power. Car bonate of ammonia is made by one of the usual chemical processes ; and this being separated into its proximate elements of car bonic acid gas and ammoniacal gas, these two gases are brought to the liquid state, either by the chemical method of Mr. Faraday
or the mechanical method of Sir M. I. Brunel. The locomotive or other engine is charged with the condensed or liquefied gases, which are contained in very strong wrought iron tubes ; and on opening certain valves, the liquids suddenly flash into the vaporic form, mix and combine together, and are condensed into carbonate of ammonia in an adjoining condenser. This carbonate of ammonia can be again used as a source whence to ob. twin the two gases. The sudden force gene. rated when the liquids expand into vapour becomes a moving power for the machine Apparatus must be provided at suitable sta. tions, for making the two gases, and con densing them into the liquid form.—Such is the rationale of this singular scheme ; bu we are not aware that it has proceeded beyond the specification of the patent.
Mr. H. Pratt published a pamphlet, abou 1845, with a view of sheaving that the ascen sive force of a lofty current of air, when aides by heat, may he applied to the moving of ma chincry. The common smoke-jack, and man, other machines long in use, illustrate th force of an ascending column of heated air but Mr. Pratt's object is to show that there i n ascensive power in a tall current of air lore than equal to the result produced by the eating of the air to a temperature beyond bat of the external atmosphere. A large akery has been established on this principle t New York, the machinery being worked by he ascensive force of a current of air heated iy the baking ovens. At a certain height cithin a lofty vertical shaft is a horizontal wheel, with wings or vanes attached at an angle 4 10° ; the ascending air causes this wheel to evolve horizontally ; drums are fixed on the pindle of the wheel, and straps or bands 'rom these drums drive the machinery for ;rinding the flour and kneading the dough. [he dimensions of the various parts are so alculated as to produce about 200 horse mwer.
Baron Von Rathen made trial of an air ocomotive on a common road, in 1848. It ravelled from Putney College (where it was !onstructed) to Wandsworth, at the rate of 10 n. 12 miles an hour. The air-reservoir (sub ;fitute for a steam boiler) had a capacity of 75 cubic feet; it was capable of being charged with air to a pressure of fifty atmospheres, by a 0-horse power engine.