Page:The New International Encyclopædia 1st ed. v. 04.djvu/74

* calophyllum:. 52 CALORIC ENGINE. them are some of the substances known by the name of Tacamahaea. Calophi/Uum inophyUum is a very large and beautiful umbrageous tree, often planted for its shade and the fragrance of its (lowers, which are white and in louse axillary racemes. It is one of the most valuable timber- trees of the South Sea Islands. The timber re- sembles mahogany, being of equally close texture, although of lighter color, and very durable. The leaves are obkmg and obtuse; the fruit is a globose drupe or stone-fruit, aboxit the size of a w-aluut, and a fixed oil is ex])ressed from its kernel, which is used for lamps, etc. In the Hawaiian Islands this oil is extensively applied to bruises and in rheumatism. A similar oil is expressed from the seed of CalophjjUum cahiba, a native of Ceylon, which also has white sweet- scented flowers, and whose timber is used for various purposes, particularly for staves, cask- headings, and house-building. Considerable dif- ference of opinion exists as to the species pro- ducing the Tacamahaea resin and the Poon spars. The more recent authors state that Caloi/hyllum calaba yields the true Tacamahaea and Calophyl- lum inophyllum a resin quite similar. Doubtless several species furnish the Poon Spars. There are a number of other species, some of which yield heavy, durable timber that is valuable for engineering purposes. CALOR'IC (Fr. calori(iue, from Lat. color, heat). An early term for heat, when it was con- sidered an invisible, imponderable fluid. See Heat. CALORIC ENGINE, or Hot-Aib Engine. An engine in which the pressure acting on the piston is produced by increasing the tem- perature of air through the application to it of heat by transfer through a separating metal wall. This definition distinguishes the hot-air engine from the compressed-air engine (see Compre.ssed- AlB Engine) on one hand, and the internal com- bustion engine (see Gas-Engike) on the other hand. There are, however, hot-air engines which employ both previous compression, and internal combustion. The action of hot-air engines, like that of all other heat-engines, consists in admit- ting the air at a high temperature and pressure, am? by allowing it to perform work on the piston Teducinir its pressure and temiicrature, after which it is cither exhausted into the atmosphere and a fresh supply is introchiccd, or else it is again heated for a" repetition of the former process. In their principal working parts hot-air engines are very similar to ordinary steam-engines. The heated air is introduced into a cylinder in which works a tightly fitting piston, which is thiis c(nn- pelled to move up and down and transfer its mo- tion to a revolving shaft by means of piston and connecting rods and the other usual mechanisms of steam-engines. (See Steam-Engine.) Hot- air engines are of several types, which may l)e described and explained as follows: Closed-cyele engines are those which operate continuously with the same mass or weight of air, only taking in a fresh charge to replace leakage or to in- crease the mass in use. Open-cycle engines are those in which at each stroke a new charge is drawn in from the atmosi^here, and after being heated and expanded is exhausted again into the atmosphere. Regenerative and non-regenerative engines are those which, respectively, use or do not use a regenerator to absorb the heat of the exhaust air and to restore it to the incoming cooler air. Finalh', closed-cycle engines may be divided into two sub-classes, which differ by hav- ing the temperature change take i)lace in the air at constant pressure or at constant volume. Each of these types is identified with the name of some designer or engineer. Hot-air engines have been designed in great numbers, but the limited e.xtcnt to which they have been used makes most of them but little more than names. The hot-air engine as defined at the beginning of this article seems to have been invented by the Rev. Robert Stirling, an Englishman, in 1816. His first successful engine was built in 1827, and one afterwards was used in a foimdry in Dun- dee, Scotland, developing 20 brake horse-power im the consumption of .50 pounds of coal per hour. In this engine, shown diagrammatieally in Fig. 1, the same volume of air was alternately heated ' I ' l' i' i' l ' l ' I I I I I I T I I I I I I ' ' ' I I I' FIG. 1. STIBLINO HOT-AIH ENGINE. and cooled, producing a variation of pressure which actuated a working pist(m. The heating and cooling were ell'ected by changing the air by means of a ])lunger, D, from end to end of a cyl- inder, A, one end of which was kept hot by a fire and the other cool by a coil of water-pipe, C. On its way from end to end the air passed through a passage partly filled with thin plates of metal, E, which alternately absorbed the heat from the air and gave it back on the return. This was the first application of the economizer or regenerator, and its invention is said to be due to .Tames Stir- ling, a civil engineer. This engine failed through the giving out of the heaters, which required to be kept red-hot. In 1844 Franchot. a Frenchman, patented an arrangement of the Stirling engine with large and efficient heating and cooling sur- faces. Further attempts at improvement were made by Rankine and Napier, and by Professor Jenkin in England, and also by Lauberau in France. The Stirling engine belongs to the type of hot-air engines with temperature changes at constant volumes. Another hot-air engine which has much the same classic and historical interest as the Stirling engine is that invented by John