« PreviousContinue »
succeeded in bringing to light some most curious facts; so contrary, indeed, are some of his results to our preconceived ideas, that he confessed he should hardly have believed them possible, if he had not witnessed them. Some of these experiments he described, showing one or two of the most remarkable by way of illustration, and noti. cing the important consequences of this property of water, in being the frequent cause of steam-boiler explosions.
It is generally stated in books, that a red or white heat is necessary in order to throw the water into this globular form. Far lower temperatures, however, are sufficient. This may be proved by throwing some water into a saucer of melted lead, a metal which melts long before it becomes luminous in the dark: the water shows no appearance of boiling, but rolls about like a little crystal ball for a consider. able time.
M. Boutigny, indeed, succeeded in forming a spheroid of water in a capsule floating on oil, heated to not more than 340°, which is about 600° below what is usually called “red heat.”
Liquids more volatile than water become spheroidal at still lower temperatures. Alcohol, for instance, requires to be heated to 273°, ether not higher than about 140°; and it is found in general that those liquids which require the highest temperature for boiling, require also the highest to make them assume the spheroidal form.
Water and other liquids, when in the spheroidal state, slowly and gradually disappear, though no appearance of boiling is even observed. This is, of course, owing to slow evaporation, which goes on from every part of its surface, thus enveloping it with a film of vapor.
of the extreme slowness of the evaporation, some opinion may be formed from the fact, which has been proved by direct experiment, that a quantity of water, which would, under ordinary circumstances, boil a way at a temperature of 212° in one minute, will, if thrown into a vessel heated nearly to redness, require little less than an hour for its total dispersion.
[The lecturer here illustrated this property by dropping, from a glass tube, three or four drops of water into a red hot capsule of platinum, which he kept hot, and at the same time boiled about the same quantity in another capsule. The drops of water in the latter evaporated very rapidly, while those in the former became one spheriod, diminishing slowly in size, and rotating for a considerable time after the boiling water had entirely evaporated.]
We have seen, he continued, that when water is thrown upon a surface of red-hot platinum, it does not, as we might have expected, explode violently into steam; but, on the contrary, rolls calmly on its axis like a little world in space, and continues in the liquid state for a a considerable space of time. Let us then endeavor to ascertain what is the temperature of the globule of water, and what relation it bears to that of the heated vessel, as well as to that of its own thin coating of vapor.
[Having again formed a spheriod in the same manner as before mentioned, he plunged into it the bulb of a delicate thermometer,
taking care that it did not come in contact with the heated metal. The temperature thus indicated was invariably 2050.]
Perhaps one of the most curious facts which have been established in connexion with this subject is, that any variation in the temperature of a vessel containing a spheroid, does not affect the temperature of the spheroid itself. Thus, it is found that a spheroid of water, when contained in a crucible heated considerably below redness, is just as hot as one contained in a crucible intensely heated to whiteness in the most powerful blast furnace!
From numerous experiments, indeed, with water, alcohol, ether, and many other liquids, the following law may be deduced:
That bodies in the spheroidal state remain constunt ai a temperature below that of boiling, however high the temperature of the containing vessel may be.
Pure alcohol, which, under ordinary circumstances, boils at a temperature of 1730, never rises, when in the spheroidal state, higher than about 170°; and ether, whose usual boiling point is about 100°, and which almost boils with the heat of the hand, cannot be induced, when thrown into a crucible, heated to whiteness in a smith's forge, to rise above 95°! The same remarkable results are obtained, if, instead of pouring the liquids while cold, into the red-hot vessels, they be absolutely boiling at the moment; strange and almost incredible as it may appear, the instant they reach their fiery resting place, they absolutely become cooler, and, as it were, shaking off the trammels of all known laws of nature, cease to boil. Liquids, then, when in that peculiar physical condition, which I have called spheroidal, always remain at one definite temperature; and this temperature is invariably, in the case of every liquid, lower than that at which, under ordinary circumstances, that liquid boils. Let us inquire a little
. more narrowly into the consequences of this law. Dr. Faraday, by a simple and ingenious contrivance, succeeded, some years ago, in condensing into the liquid state, several of the gases, which had, up to that time, resisted all such attempts, and had consequently been considered permanent
gases, such as the air we breathe. This was the case with carbonic acid, chlorine, ammonia, sulphurous acid, and a few others. So great is the elastic force of these liquified gases, or, in other words, so prone are they to boil, and to pass again into the gaseous form, that a very great pressure is necessary to prevent their doing so, and unless the tube or other vessel containing them were very strong, it would probably be burst with a violent explosion. Now, it will readily be understood how it happens that these condensed liquids, unlike water and other fluids, do not require the application of artificial heat to make them boil, but, on the contrary, continue to boil, even when cooled far below the usual temperature of the air. Let us then inquire whether any of these liquids, whose boiling points are far below that at which water freezes, be subject to the same laws to which water is subject when they are thrown into a vessel sufficiently hot to cause them to pass into the speroidal state.
The gas which is the most easily liquified of those alluded to, is
sulphurous acid, which requires at a temperature of 45o a pressure equal to two atmospheres (or about 30 lbs. to the square inch of surface) to prevent its boiling. If this pressure be removed, violent ebullition takes place; and it has been found that, even when cooled as low as 14° of Fahrenheit's thermometer, or, in other words, 18° below the melting point of ice, it boils in precisely the same way as water boils when heated to 212°. Fourteen degrees, then, is the boiling point of sulphurous acid.
But we have found that when liquids, even while boiling, are thrown into a heated crucible they become cooler, and remain constantly at a temperature a few degrees below their boiling point. What, then, will be the effect of pouring into a red-hot crucible a few drops of liquid sulphurous acid? The experiment which was selected for the purpose of furnishing an answer to this question is, perhaps, one of the most striking and apparently paradoxical in the whole range of physical science. Liquid sulphurous acid is subject to the same remarkable law as water and other liquids, in being invariably, when in the spheroidal state, at a temperature lower than its boiling point, which is 14° of Fahrenheit, so that if a spheroid of sulphurous acid be formed, it remains constant at a temperature of about 12°, even though the crucible containing it be at a red or white heat. If a little water, contained in a small bulb, one-eighth or onetenth of an inch in diameter, be immersed in the spheroid of acid, it is almost instantly frozen, thus affording incontestible evidence of the remarkably low temperature of the spheroid. Most persons have seen the well-known lecture-table experiment of causing water and other liquids to boil in vacuo at temperatures considerably below their ordinary boiling points, a result depending upon the diminished pressure on their surface.
When liquids in the spheroidal state, however, are placed under the receiver of the air-pump, and the air removed, no sign of boiling is even perceived. We may therefore suppose that the temperature of the spheroid in vacuo, is lower than when exposed to the atmo spheric pressure, as otherwise ebullition would inevitably take place. The lecturer was not aware, however, that the temperature had ever been examined with a thermometer under these circumstances, and thought it would be by no means easily done.
He should, probably, scarcely be believed, when he stated that even liquid sulphurous acid does not, when contained in a red-hot crucible, and in the speroidal state, boil in vacuo.
If a thermometer is held in the atmosphere of vapor which surrounds a spheroid of water, it will give a far different result from that ensuing from its immersion in the globe itself.
Instead of indicating, as before, 205°, however hot the crucible may be, the degree at which it stands will now be found to depend entirely on the temperature of the latter. If it be heated to 400°, the thermometer will rise to that point; or if the crucible be raised to a red heat, a mercurial thermometer, graduated to 600°, is burst instantly, showing a temperature considerably higher. We have shown, experimentally, that when water is thrown into a red-hot crucible, it
does not, as common sense would have foretold, begin to boil, but remains constant at the temperature of 205°, so long as it retains the spheroidal form, however high the temperature of the crucible may be, but that the vapor surrounding it is, on the contrary, always about the same temperature as the crucible.
This comparatively low temperature of liquids in the spheroida! state, is generally attributed to the coating of vapor round the spheroid being incapable, as it is conceived, like all other gaseous bodies, of conducting heat. This explanation, however, though ingenious, does not meet all the difficulties of the case: for, besides the heat which would be conducted by the coating of vapor, if the vapor had the power of conducting it, (which is possible,) there is the enormous quantity of radiant heat, emanating from all parts of the heated erucible. If a vessel containing water be placed near a fire, it is well known that it gradually becomes warm, and if the fire be a good one, and the distance not too great, the water will shortly boil. The heat which causes the water to boil in this case, is not conducted by the fire to the water through the intervention of the air, since we know that air has no such power; but it is a portion of that which, like light from a candle, radiates from the fire in all directions, and is absorbed more or less completely by any substance which stands in its way, and intercepts its passage. Why, then, does not the spheroid of water, surrounded as it almost always is, by intensely heated metal, absorb the rays of heat, which dart towards it from every side, become intensely heated to the boiling point, and dispersed in vapor with explosive violence? In order to answer this question, some philosophers have stated that the radiant heat, when it meets with any liquid in the spheroidal state, passes through it without experiencing any interruption, and consequently does not impart any heat to it. A simple experiment is sufficient to show the fallacy of this hypothesis.
İf a crucible be made red hot, and a small bulb of glass, containing water, be brought near to its inner surface, the water boils violently, owing to the absorption of radiant heat, and notwithstanding the presence of a quantity of non-conducting air between the heated metal and the water. This shows that heat does radiate from the sides of the crucible, and, too, in sufficient quantity to cause water to boil with considerable violence. If now the crucible be again heated to an equal degree, and a few drops of water poured in, they at once assume the spheroidal state. Things being in this condition, let the little glass bulb containing water be immersed in the spheriod, and it is found that the water does not show the slightest tendency to boil. The spheroid of water has consequently, in some way or other, prevented the rays of heat from reaching the glass bulb, and the water which it contained.
But if, according to this hypothesis, the radiant heat passed through the substance of the spheroid, without being to any extent absorbed or arrested by it, it would obviously reach the bulb containing the water, and cause it to boil with as much violence almost as it does when no spheroid is interposed between it and the source of heat.
Another mode of explaining the low temperature of liquids in the spheroidal state, is clearly pointed out by the result of this experiment, which proves, beyond all doubt, that bodies in the spheroidal state have, when they have attained their maximum temperature, (which we have found to be always lower than their boiling point,) the remarkable property of reflecting, almost completely, radiant heat.
A curious variation of the last experiment, tending to the same conclusion, may be made by putting a piece of ice into the red-hot crucible. It instantly absorbs sufficient heat to cause a portion of it to become spheriodal, after which it continues at a temperature of 205°, even though a portion of the ice remain unmelted within the globule. Thus the ice, and afterwards the water, which has an almost perfect reflecting power at 2050, absorbs, instantaneously, as it were, all the heat necessary to raise it to that temperature, and above which it does not become heated! Why and how is this? are questions which, in the present state of our knowledge, cannot be answered; and we have here one of those deep mysteries, so frequently met with in our researches into the hidden laws of nature, which baffle and confound the reason, and set at nought, for a time, at least, the power of the human mind.
We have seen that not only water, but also alcohol, ether, and liquid sulphurous acid, may be obtained in the peculiar condition, which he had, on account of the external form which always attends it, called the spheroidul state. It becomes interesting to inquire, whether so remarkable a change may be produced in other liquids. A great number of experiments have been made with almost every kind of liquid; solutions of acids, alkalies, and salts; compressed gases and melted solids; fats and oils of every kind, both volatile and fixed; and they tend to show that all liquids, with scarcely an exception, pass, under favorable circumstances, into the spheroidal state. The temperature necessary to produce this effect, appears to bear some relation to the boiling point; those wbich boil most readily requiring a lower temperature than the less volatile substances. That a drop of water, or other fluid, when in the spheroidal state, is poised, as it were, without support, at some sensible distance from the surface of the vessel containing it, may be proved in many ways. spheroid of some opaque substance be formed on a nearly flat surface, and then interposed between a lighted candle and the eye, the image of the flame is distinctly seen between the hot surface and the globule. This effect might be produced if the spheroid were in a state of rapid motion up and down, since the image of the candle, seen during the ascent, will remain visible till the next ascent; just as an ignited point in rapid revolution appears as a circle of light. That this is not the case, however, may be shown in another way. If silver be touched with nitric acid, it is rapidly corroded, and in a short time dissolved; but if a quantity of nitric acid be poured into a crucible or dish of silver, sufficiently hot to induce the spheroidal state, no corrosion whatever will take place-clearly proving that the acid is at no time in absolute contact with the metal. That this is not owing to any