As animal respiration seems to be a kind of slow combustion, in which it is probable that phosphoric acid is produced by the union of phosphorus with the vital air, so it is also probable that phosphoric acid is produced in the excretory or respiratory vessels of luminous insects, as the glow-worm and fire-fly, and some marine insects. From the same principle I suppose the light from putrid fish, as from the heads of hadocks, and from putrid veal, and from rotten wood in a certain state of their putrefaction, is produced, and phosphorus thus slowly combined with air is changed into phosphoric acid. The light from the Bolognian stone, and from calcined shells, and from white paper, and linen after having been exposed for a time to the sun's light, seem to produce either the phosphoric or some other kind of acid from the sulphurous or phlogistic matter which they contain. See note on Beccari's shells. l. 180.
There is another process seems similar to this slow combustion, and that is bleaching. By the warmth and light of the sun the water sprinkled upon linen or cotton cloth seems to be decomposed, (if we credit the theory of M. Lavoisier,) and a part of the vital air thus set at liberty and uncombined and not being in its elastic form, more easily dissolves the colouring or phlogistic matter of the cloth, and produces a new acid, which is itself colourless, or is washed out of the cloth by water. The new process of bleaching confirms a part of this theory, for by uniting much vital air to marine acid by distilling it from manganese, on dipping the cloth to be bleached in water repleat with this super-aerated marine acid, the colouring matter disappears immediately, sooner indeed in cotton than in linen. See note XXXIV.
There is another process which I suspect bears analogy to these above- mentioned, and that is the rancidity of animal fat, as of bacon; if bacon be hung up in a warm kitchen, with much salt adhering on the outside of it, the fat part of it soon becomes yellow and rancid; if it be washed with much cold water after it has imbibed the salt, and just before it is hung up, I am well informed, that it will not become rancid, or in very slight degrees. In the former case I imagine the salt on the surface of the bacon attracts water during the cold of the night, which is evaporated during the day, and that in this evaporation a part of the water becomes decomposed, as in bleaching, and its vital air uniting with greater facility in its unelastic state with the animal fat, produces an acid, perhaps of the phosphoric kind, which being of a fixed nature lies upon the bacon, giving it the yellow colour and rancid taste. It is remarkable that the super-aerated marine acid does not bleach living animal substances, at least it did not whiten a part of my hand which I for some minutes exposed to it.
NOTE XI.—STEAM-ENGINE.
Quick moves the balanced beam, of giant-birth, Wields his large limbs, and nodding shakes the earth.
CANTO I. l. 261.
The expansive force of steam was known in some degree to the antients, Hero of Alexandria describes an application of it to produce a rotative motion by the re-action of steam issuing from a sphere mounted upon an axis, through two small tubes bent into tangents, and issuing from the opposite sides of the equatorial diameter of the sphere, the sphere was supplied with steam by a pipe communicating with a pan of boiling water, and entering the sphere at one of its poles.
A french writer about the year 1630 describes a method of raising water to the upper part of a house by filling a chamber with steam, and suffering it to condense of itself, but it seems to have been mere theory, as his method was scarcely practicable as he describes it. In 1655 the Marquis of Worcester mentions a method of raising water by fire in his Century of Inventions, but he seems only to have availed himself of the expansive force and not to have known the advantages arising from condensing the steam by an injection of cold water. This latter and most important improvement seems to have been made by Capt. Savery sometime prior to 1698, for in that year his patent for the use of that invention was confirmed by act of parliament. This gentleman appears to have been the first who reduced the machine to practice and exhibited it in an useful form. This method consisted only in expelling the air from a vessel by steam and condensing the steam by an injection of cold water, which making a vacuum, the pressure of the atmosphere forced the water to ascend into the steam-vessel through a pipe of 24 to 26 feet high, and by the admission of dense steam from the boiler, forcing the water in the steam-vessel to ascend to the height desired. This construction was defective because it required very strong vessels to resist the force of the steam, and because an enormous quantity of steam was condensed by coming in contact with the cold water in the steam-vessel.
About or soon after that time M. Papin attempted a steam-engine on similar principles but rather more defective in its construction.
The next improvement was made very soon afterwards by Messrs. Newcomen and Cawley of Dartmouth, it consisted in employing for the steam-vessel a hollow cylinder, shut at bottom and open at top, furnished with a piston sliding easily up and down in it, and made tight by oakum or hemp, and covered with water. This piston is suspended by chains from one end of a beam, moveable upon an axis in the middle of its length, to the other end of this beam are suspended the pump-rods.