Boiling point

“ But a much larger quantity of heat enters into vapours than into liquids—into steam than into water. If over a steady fire a certain quantity of ice-cold water requires one hour to bring it to the boiling point, it will require a continuance of the same heat for five hours more to boil it off entirely. Yet liquids do not become hotter after they begin to boil, however long or with whatever violence the boiling is continued. ”

“ While water is below its boiling point its evaporation occurs at its surface only; but when its mass is heated to boiling point, and additional heat is imparted to it, evaporation occurs from the water lying against the surface from which it receives the heat, and an ebullition is caused by the vaporized water passing through the mass, the ebullition being what is known as boiling. ”

“ But to drive out all the dissolved air, the water should be subjected to a prolonged boiling, and this causes a wonderful increase in its cohesion after it is cooled; and water which has been treated thus will not boil except at temperatures considerably higher than the normal boiling point. Every engineer knows that the water from which he generates steam in his boilers must be aerated, if he would have the machine work regularly and avoid the danger of explosion. ”

“ To evaporate water into steam, it must first be heated to the boiling point, and then sufficient heat still further added to change it from the liquid to the gaseous state, or steam. Take one pound of water at 32 degrees and heat it to the boiling point, it will have received 212° - 32° = 180 heat units. A heat unit being the amount of heat necessary to raise one pound of water through one degree at its greatest density. ”

“ For measuring large quantities of heat, such as those produced by the combustion of fuel in a boiler, the most convenient method is the evaporation of water, which is commonly employed by engineers for the purpose. The natural unit in this case is the quantity of heat required to evaporate unit mass of water at the boiling point under atmospheric pressure. In boilers working at a higher pressure, or supplied with water at a lower temperature, appropriate corrections are applied to deduce the quantity evaporated in terms of this unit. ”

“ The decrease of pressure with altitude lowers the boiling point, the amount being approximately one degree for each 555 feet of ascent. The best results may be secured by having a person at the base of the mountain, where the elevation above sea level is known, determine the boiling point at the same time that a person on the mountain top does. ”

“ We may now understand what happens when something humid—say a sole—is put into a frying-pan which contains fat heated above 212°. Water, when suddenly heated above its boiling-point, is a powerful explosive, and may be very dangerous, simply because it expands to 1,728 times its original bulk when converted into steam. Steam engine boilers and the boilers of kitchen-stoves sometimes explode simply by becoming red-hot while dry, and then receiving a little water which suddenly expands to steam. ”

“ So low a boiling-point would make it impossible to cook anything in the open air. Boiled eggs could be prepared only under cover, and such people as liked their meat boiled would probably find it convenient to prefer it done differently. Fortunately, roasts would still remain possible. The lowering of the boiling-point would raise the relative amount of aqueous vapor held in suspension by the air at any temperature. ”

“ First, the boiler may be full and the water clean and clear; or, secondly, the boiler may not only be full but the water may be hot, very hot, hot enough to scald you, almost boiling; thirdly, it may be just one degree hotter and at the boiling point, giving forth its vapor in clouds of steam, pressing through the valves and driving the mighty piston which turns the wheels and propels the train of cars across the country. ”

“ Now as I was saying the harder you boil water the more steam it gives off and the heating and cooling processes are so exactly balanced that boiling water stands always at a uniform temperature no matter whether it is boiling hard as we say, or only just barely boiling. ”

“ And experiment teaches that this is the case; water boils at a temperature of 82° or 65°, as the pressure is reduced to one half or a quarter of an atmosphere, it boils at zero, and even below, in a vacuum. And we reach this remarkable result, that the boiling and freezing points unite, and that ice is formed while vapor is set free. ”

“ The heavier, also, the air is, from the quantity of moisture in it, the hotter water becomes before it boils. If the atmosphere were carbonic acid gas, water would get much hotter without boiling than it can under—"
"Present arrangements," interposed Mr. Badges. [248]
"Consisting of a mixture of nitrogen and oxygen," continued Harry. "Water requires only a very low heat to make it boil in an exhausted receiver, out of which the air has been pumped, so as to leave none to press upon its surface. Owing to boiling depending upon pressure, you can actually make water boil by means of cold." ”

“ Why would you apply the heat at the top, in this experiment?
Because in heating water it expands and rises. The boiling of water is caused by the heated water ascending from the bottom, and the colder water descending to occupy its place. If the heat were not applied at the top, it would be distributed quickly by convection, but not by conduction. ”

“ Nearly all foreign matter held in solution in water, on first becoming separated by boiling, rises to the top in the form of what is commonly called scum, in which condition much of it may be removed by the surface blow-off. If not removed, however, the heavier particles will be attracted to each other until they have become sufficiently dense to fall to the bottom, where they will be deposited in the form of scale, covering the whole internal surface of the boiler below the water line, with a more or less perfect non-conductor of heat. ”

“ And what is boiling?"
"Bubbling," suggested the young philosopher's mamma.
"Yes; but ginger-beer bubbles," said Harry, "but you wouldn't exactly call that boiling. Boiling is the escaping of steam. That causes the bubbling; so the bubbling of water over the fire is only the sign that the water boils. But what occasions the escape of the steam?"
"The heat, of course—the—what is the right word?—the caloric," answered Mr. Bagges. ”

“ If the internal heat is as great as is claimed, it ought to be enough to set every drop of water in the oceans into a boiling condition inside of fifteen minutes, but there does not seem to be heat enough to warm the bottom of the kettle. ”

“ The boiler is to be filled with straw and alkaline solution and then closed fluid and steam-tight. The boiler is made to revolve slowly, say about one or two revolutions per minute, and the steam is to be admitted. I find it desirable to keep up the heat and pressure during about three hours after the pressure above mentioned has been obtained, when the process of boiling is complete. A steam-gauge proper y fixed upon the boiler will enable one to ascertain when the pressure has attained the required degree. ”

“ If the flame is long, the gas pressure is greater than necessary. Regulate the gas pressure by adjusting the valve in the supply pipe. A short flame will save gas and produce satisfactory results, provided the cooking surface is the proper distance above the burner.
(4) After the contents of a cooking utensil boils, turn the gas cock so that only "gentle" boiling takes place. A food becomes no hotter in rapidly boiling than in gently boiling water. ”

“ All boilers are, or should be, provided with ample accommodation for removing the incrustated deposit, which forms with moderate rapidity, as the water is continually boiling, and as evaporation in a steam boiler is very rapid, the supply of water is constantly being renewed, and each successive charge of water brings its proportion of lime to be deposited. ”

“ The water is white, and exhibits truly the appearance of a lake of milk, boiling with a perpetual discharge of large bubbles, which rise with greatest force from the eastern side. The heat is 112° of Fahrenheit's scale: the apparent boiling arises from a constant development of fixed air. ”

“ But, although the boiling is advanced, although it takes place at zero instead of at 100 degrees, although the vapor is cold instead of hot, and the change takes place in a vacuum instead of in the air, it is a general law that a large quantity of heat is used, becomes latent, and enters into the formation of vapor. ”

“ Let it be remembered that the boiling spoken of so often is really caused by the formation of the steam particles, and that without the boiling there can be but a very slight quantity of steam produced. ”

“ This increase in the efficiency of the boiler alone with the decrease in the rate at which it is operated, will hold to a point where the radiation of heat from the boiler setting is proportionately large enough to be a governing factor in the total amount of heat absorbed. ”

“ As all the excess air has to be raised to the same temperature as that of the really burnt gases, it follows that an excess of air passing through the fire lowers the temperature in the fire and flues, and therefore lessens the heat transmission; and as it leaves the boiler at a high temperature it carries off some of the heat produced. ”

“ If the boiling is continued under constant pressure, the temperature will rise as the liquids approach each other in composition, and the curve will rise relatively to the curve , until the curves are tangent to each other, when the two liquids become identical in nature, as also the vapors which they yield. In composition, and in the value of per unit of mass, the vapor will then agree with the liquid. ”

“ Leaven consists in, or at least causes, fermentation. The name suggests the mechanical process of boiling. The most sublime and awful scenes which nature has ever presented have been produced in this way. When great masses are affected, a boiling becomes unspeakably grand and terrible. This earth, now so solid beneath, and so green on the surface, seems to have been once a boiling mass. ”