Boiling point of water

“ 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. ”

“ 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. ”

“ Water is at the boiling point when it is jumping or rolling all over. Water is not boiling when bubbles merely form on the bottom or when they begin to rise to the top. The water must be kept boiling all during the period of sterilization. ”

“ The same evaporation which thus affects the hands, renders the land cold, when filled with water, every gallon of which thus carried off requires, and actually carries off, as much heat as would raise five and a half gallons of water from the freezing to the boiling point. ”

“ 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 by becoming red-hot while dry, and then receiving a little water which suddenly expands to steam. ”

“ If a bubble of steam is surrounded by water maintained at the boiling temperature, it will not condense at all, because any effort of condensation would be accompanied with an evolution of heat exactly sufficient to evaporate its own result. If, however, the surrounding water is slowly radiating, or otherwise losing its heat, the enclosed bubble of steam will condense proportionately, by giving off to its envelope an amount of its latent heat just sufficient to maintain the water at the boiling-point. ”

“ However long we boil a fluid, in an open vessel, we cannot make it in the smallest degree hotter than the boiling point.93 When arrived at this point, the vapor absorbs the heat, and carries it off as fast as it is generated. When water is received into the atmosphere, if the air be warm, it becomes so far changed by its union with the matter of heat as to be perfectly invisible. ”

“ Whether the water be heated or cooled at this temperature, it expands to the boiling or freezing point when it becomes steam or ice, as the case may be.
Water, when heated, is lighter than cold water. You can prove this in filling a bath from two taps of hot and cold water at the same time. The cold falls to the bottom, and if you do not stir up the water when mixed you will have a hot surface and a cold foundation. The heat increases the volume of water, it becomes lighter, and comes uppermost. ”

“ By this means we are able to maintain a constant body temperature of almost one hundred degrees.
The average human body produces enough heat every hour to raise two and one-half pounds of water from the freezing point to the boiling point. This is equivalent to boiling about seven gallons of ice-water every twenty-four hours. Differently expressed, the body gives off each hour the same amount of heat as a foot and a half of two-inch steam coil. ”

“ Suppose a geyser-tube filled with water, and heated at its lower end. As the water is heated below, convection tends to distribute the heat throughout the column of water above. If convection were free, and the tube short, the result would be a boiling spring; but if the tube is long, and especially if convection is impeded, the water at some level below the surface may be brought to the boiling-point earlier than that at the top. ”

“ It is a well-known fact that when water is brought up to a certain degree of heat, called the boiling-point, that it sends forth a vapour, the elastic properties of which, when in an open vessel, are not perceived—as, for instance, in a common pan—yet if the vessel is closed or shut up at the top, you will find that the vapour acquires such a degree of elastic force, that, if not allowed to escape by fair means, it would soon make a way or vent for itself by bursting whatever vessel it was contained in. ”

“ 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. ”

“ 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." ”

“ 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. ”

“ 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. ”

“ 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. ”

“ It is not generally understood, or at least it is not borne in mind with sufficient care, that “after water is just boiling, all the fuel which is needed to make it boil violently is just so much wasted, without in the smallest degree expediting or shortening the process of cooking. It is by the heat, its intensity and the time of its duration, not by the boiling or bubbling up of the water, that the food is cooked.” ”

“ 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. ”

“ Now, every one knows that no amount of heat can raise the temperature of boiling-water if it is unconfined. Where, then, does the heat go to? Plainly it is carried off by the vapor in an insensible or latent condition. It is a demonstrated fact that it requires as much heat to convert a quantity of water into steam as it takes to raise the same quantity 1,000° of temperature. The same amount is required to evaporate water without boiling it. Consequently, when the sun's rays evaporate water, a vast amount of heat becomes insensible to our thermometers. ”

“ 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. ”

“ 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. ”

“ The boiling motion is from volumes of steam working its way through the waters from the bowels of the earth and spreading upon the breeze. Boiling water elsewhere wastes itself away, but these pools boil and boil from year to year, and scarcely vary perceptibly in height. Our untutored tourist turns his eye upon the mountain bordering the valley, whose sides are so encrusted with geyserite deposit that it appears to have been formed of this material, and to have been erected by boiling springs ”

“ Boiling effects partial destruction or removal of organic and mineral impurities found in water, hence the importance of boiling the water where such impurities exist. Boiling also expels all the air and the gases which give fresh water its sparkle and vitality. ”