་ provident care of the Almighty, when he established the laws of the universe. specifically heavier by the loss of its caloric. In winter, when the atmosphere became reduced to 32°, the water on the surface of our rivers would have sunk as it froze; another sheet of water would have froze immediately, and sunk also; the ultimate consequence of which would have been, that the beds of our rivers would have become repositories of immense masses of ice, which no subsequent summer could unbind; and the world would shortly have been converted into a frozen chaos. How admirable the wisdom, how skilful the contrivance, that, by subjecting water to a law contrary to what is observed by other fluids, the water as it freezes becomes specifically lighter, and, swimming upon the surface, performs an important service by preserving a vast body of caloric in the subjacent fluid from the effects of the surrounding cold, ready to receive its own accustomed quantity upon the first change of the atmosphere! I shall not regret having subjoined these remarks, should they but afford "One ray of light in this terrene abode, To prove to man the goodness of his God." In how many states do we find water? In four solid or ice; liquid or water; vapour or steam; and in a state of composition with other bodies. Which is the most simple state of water? That of ice. What is the essential difference between liquid water and ice? Water contains a larger portion of caloric.* * Ice at 32" must absorb 140° of caloric before it can become fluid; or such a quantity as would raise a body of water of equal bulk with itself from 32° to 172°. This may be made very evident to a youth who has been taught the use of a thermometer, by the following directions: "Take any quantity by weight of ice or snow at 32o, and mix it with an equal weight of water heated exactly to 172°. The snow instantly melts, and the temperature of the mixture is still only at thirty-two degrees. Here the water is cooled 140°, while the temperature of the snow is not increased at all; so that 140° of caloric have disappeared. They must have combined with the snow; but they have only melted it, without increasing its temperature. Hence, it follows irresistibly that ice, when converted into water, absorbs and combines with 140° of caloric. Water then, after being cooled down to 32°, cannot freeze till it has parted with 140° of caloric; and ice, after being heated to 32° (which is the exact freezing How do you define vapour? Vapour is water, combined with a still greater quantity of caloric.* point,) cannot melt till it has absorbed 140° more of caloric. This is the cause of the extreme slowness of these operations. There can be no doubt, then, but water owes its fluidity to its latent caloric, and that its caloric of fluidity is 140°." Thomson's Chemistry, vol. i. 365. The advantages which we derive from the slowness of these operations, and the inconveniences we should have suffered had it been otherwise, are numerous and obvious. See notes page 83 and 93; and Additional Notes, No. 5. * However long we boil a fluid, in an open vessel, we cannot make it in the smallest degree hotter than its boiling point. When arrived at this point, the vapour absorbs the heat, and carries it off as fast as it is generated. Yet, by continued heat, united with additional compression, both the expansibility and temperature of steam may be greatly increased; and some constructors of steam-engines have lately availed themselves of this property, to augment the power and diminish the expense. See note page 49; also Additional Notes, No. 3 and 4. Those who have an air pump may easily see that water requires a vast portion of caloric to convert it into steam; for, if a cup of hot water be put under the receiver, and the pump be set to work, the water will soon begin to boil furiously, and the receiver will be covered with vapour. If the receiver be now taken off, the water will be found barely lukewarm, owing to the vapour having carried off the greatest part of its heat. Water, in being converted into vapour, combines with more than five times the quantity of caloric that is required to bring icecold water to a boiling heat, and occupies a space 800 times greater than it does when in the form of water. Owing to the quantity of caloric that liquids require to convert them into vapour, all evaporation produces cold. It has been remarked before, that an animal might be frozen to death in the midst of summer, by repeatedly sprinkling ether upon him. Its evaporation would shortly carry off the whole of his vital heat. Water thrown on hot bodies acts in the same way; it becomes, in an instant, converted into vapour, and thus deprives these bodies of a great portion of the caloric they contain. The most striking example, that I have seen, of the production of cold by rarefaction, is given by Dr. Wolfe in his account of the fountain of Hiero, at the mines of Chemnitz in Hungary. In this curious machine, of which he has given a plate, the air is What are the properties of vapour? Vapour, owing to the large quantity of caloric which is combined with it, takes a gaseous form, acquires great expansive force,* and a capability of supporting enormous weights;† whence it has become a useful and powerful agent for raising compressed by a ponderous column of water, 260 feet high; it therefore happens, that whenever the stop cock is opened, this compressed air rushes out with great vehemence, becoming immediately much expanded. The consequence of this sudden rarefaction is, that the moisture the air contained is not only precipitated, but congealed; a part of which falls down in a shower of snow, and the other part forms icicles, which adhere to the nosle of the cock. Philosophical Transactions, vol, iii. * The expansive force of steam is found by experiment to be much greater than that of gunpowder. Some volcanic eruptions and earthquakes, it is supposed, owe their terrible effects to this power of steam; the water of the sea finding its way to subterraneous fires. See an account of the dreadful effects of the earthquake at Catania, in the notes to Madame de Genlis's Tales of the Castle, vol. ii. 241; or in Sir William Hamilton's splendid Survey of the two Sicilies. In boiling oil, the workmen are very careful to prevent any water coming near it; for a single drop coming among it would instantly, by the excessive heat of the oil, be converted into vapour, and would force part of the oil over the sides of the boiler. It is to the expansive force of steam that the well-known motion in water called boiling, is to be ascribed. The vapour is first formed at the bottom of the vessel, and, passing through the water, causes that motion in it which we call ebullition. The invention of the steam-engine was a vast acquisition to the arts. There is reason to believe that, in time, steam may be applied to many useful purposes, of which at present we have no idea. In America vessels are already navigated by steam. "Soon shall thy arm, unconquer'd steam! afar Or on wide waving wings expanded bear The flying chariot through the fields of air."-DARWIN The steam-engine, approaching to the nature of a perpetuum mobile, or rather an animal, is incapable of lassitude; it procures water from deep pits, and for other important purposes.* for us coals; it works metals; moves machines; and is certainly the noblest drudge that was ever employed by the hand of art. Thus we put a hook in the nose of the leviathan ; play with him as with a child; and take him for a servant for ever" thus we subdue nature, and derive aid from the ele ments of earthquakes. Analytical Review. The steam-engine is brought to such perfection, that one bushel of coals will raise 6,000 hogsheads of water ten feet high, and do the work of ten horses. Where there is no waste of steam, this work may be performed continually with the consumption of only one bushel of coals per hour. Some of the engine chambers in London are now fitted up with great taste, and are kept with the utmost neatness; in these one may spend hours without being annoyed by the escape of the most minute portion of steam. Dr. Black calls the steam-engine, the master-piece of human skill, and the most valuable present that was ever made by philosophy to the arts. *Steam is now employed in a vast variety of ways in the different manufactories of this kingdom. It is used with great economy of fuel in the dye-house of Mr. Desange, in Wheelerstreet, Spital-fields. It should however be remembered that whenever it is intended to heat water by means of steam, the steam must not be thrown in upon its surface, but must be conducted to the bottom of the cold liquor before it be disengaged, or the effect will not be produced, water not having the power of conducting heat downwards. Hence some of the deepest recesses of the sea, even in the torrid zone, are perpefually covered with ice. Messrs. Gott and Co. of Leeds, boil 30 large coppers by the steam of one boiler. It is employed elsewhere in drying malt, linen, coffee, paper, &c. and might be used with peculiar advantage in drying gunpowder. Dr. Black remarks, that steam is the most faithful carrier of heat that can be conceived, as it will deposite it only on such bodies as are colder than 212o. Water heated to 220 degrees or upwards is found to be very effectual in bleaching linen goods. This method is coming into practice in the North of England. I am told that the necessary pressure is given by means of large chambers constructed of massy stone; and that in these chambers the linen is submitted to the action of the condensed steam. 876791 |