Knight's cyclopædia of the industry of all nations, 1851 / [edited by George Dodd].

Date:
[1851]
Catalogue details

Licence: Public Domain Mark

Credit: Knight's cyclopædia of the industry of all nations, 1851 / [edited by George Dodd]. Source: Wellcome Collection.

    64/1000
    69 outside of the bladder can be exhausted; the interior air will expand so soon as the exhaus- tion begins, mil presently distend the bladder to its fullest dimensions, and in some cases will even burst it. On the re- (^d^iiss^on of he air into the space suiTOunding thebladdei, the latter wU gradually resume its former dimen 2ons, and its withered or flaccid appearance. Is we ascend the atmosphere, the superui- cumbent column of ah: becomes of less weight and the density becomes less; that is a cubic foot at the height of (say) 1000 foet above the ground is not so heavy, or does not contam o much ah-, as a cubic foot at the surface o. the earth The pressure and density ot the air ai-e rec'ulated by the follo^ving law : at the same temperature, the elastic forces of two portions of ah- (or, which is the same thmg, the weights of mercury they will balance) are m du-ect proportion to the densities, or in inverse pro- portion to the spaces, occupied by these por- tions. The human body would he crushed by the pressure of the air on it, were there not a counter pressure from within- _ The temperature of air influences its elastic force. It is probable that air would become fii-st liq-aid, and then sohd, if it could be made sufficiently cold. Like all other substances, ah gives out heat when it is compressed; a property strikingly illustrated by the fact that tinder can be set on fire when the ah in which it is contamed is suddenly and violently com- Ah-, hke gases and vapom-s generally, en- larges its bulk with every increase of tempera- tm°e, or increases its elastic force if enlarge- ment of bulk be prevented. The quantity of this expansion, when the temperature passes from the freezing to the boihng point of ;ater (that is, from 32° to 212° of Fahren- Lt's thermometer, from 0° to 80° of Reau- mur's, and from 0° to 100° of the Centigrade), is 375 parts out of a thousand of the bulk which it had at the freezing point. And this enlargement is uniform; that is, whatever ex- pansion arises from an increase of 12 ol tem- perature, half as much arises from an in- crease of 6, twice as much from one ol 24° and so on. Trom the different sys- tem's on which the Fahrenheit, Reaumur, and Centigrade themometers axe graduated, Slows that the increase of bulk, coiTes- ponLg to a rise of one degree of temperature fnCair (the bulk of 32° F. bemg taken as ft standai-d) i« ^V^^^ *° ^espec^ tively In some fow cases this regulaanty of expansion is not quite certam, bn^ it is known holies wf-ay notice that probably tJaere . a slight adhesion of air to many, if not to all surfaces. A small needle may be made to swim on water, and in this state the water evidently retires from around it, leaving it, as it were, suspended over a hollow in the fluid. This is attributed to the adhesion of a coat of air, which, vrith the iron, makes the whole specifically Ughter than the water. Recent experiments on the pendulum have led some to suspect, that, hi addition to the resistance of the ah, a shght coating of this substance travels vnih. the pendulum, and thereby causes an irregular addition to its weight, These few details concerning the general properties of air will meet mth various illus- trations under Air-gun; Aib-pump; Atijos- PHEnE ; Ralloqk; Combustion; Pneumatics; Stove ; Ventilation, &c. AIR-BEDS and CUSHIONS. [Water- PROOF Compositions.] AII^^BLAUDER. Cod-sounds, which are brought in great quantities fr-om Newfoundland, are nothmg more than the salted air-bladdei-s of these fishes. The Iceland fishermen, as well as those of America, prepai-e isinglass of a very excellent quality from cod-sounds; though they are not acquainted wth the method of clarifying it, which the Russians practise in preparing that article from the sound of the sturgeon, [Isinglass.] AIR ENGINES, Many attempts have been made withhi 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 afr, brought about in some one of many difi'erent ways, is the agentrelied upon for producing amoving force. In 1840 Mr. Stfrhng patented such a machine, and read a description of it before the Institute of Civil Engineers in 1846. In this engine two strong ah--tight vessels ai-e connected with the opposite ends of a cylmder, in which a piston works in the usual manner. About four-fifths of the interior space in these vessels is occupied by two sunilar 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 pressm-e increased, whereas its heat and pressiure are diminished when it is forced to the cold end. Now as the interior vessels necessarily move m opposite du-ections, it follows that the prassiu-e of the enclosed air in the one vessel is increased,