Why heat changes everything about a carrot

and cooked water may appear pedantic, but as I shall presently show, it is considerable,

very practical, and important. The best way to study any physical subject is to examine it

experimentally, but this is not always possible with everyday means. In this case, however,

there is no difficulty. Take a thin glass vessel such as a flask, or better, one of the beakers,

or thin tumbler-shaped vessels, so largely used in laboratories. Partially fill it with

ordinary household water, and then place it over the flame of a spirit lamp or Bunsen's,

or other smokeless gas burner. Carefully watch the result, and the following will be observed.

First of all, little bubbles will be formed, adhering to the sides of the glass, but ultimately,

rising to the surface, and they are becoming dissipated by diffusion in the air.

This is not boiling, as may be proved by trying the temperature with the finger. What then is it?

It is the yielding back of the atmospheric gases which the water has dissolved, or condensed within

itself. These bubbles have been collected, and by analysis proved, to consist of oxygen, nitrogen,

and carbonic acid, obtained from the air. But in the water they exist by no means in the same

proportions, as originally in the air, nor in constant proportions in different samples of water.

I need not, here, go into the quantitative details of these proportions, nor the reasons for their

variation, though they are very interesting subjects. Proceeding with our investigation,

we shall find that the bubbles continue to form and rise until the water becomes too hot for the

finger to bear immersion. At about this stage, something else begins to occur. Much larger

bubbles, or rather blisters, are now formed on the bottom of the vessel, immediately over the flame,

and they continually collapse into apparent nothingness. Even at this stage, a thermometer

immersed in the water will show that the boiling point is not reached. As the temperature rises,

these blisters rise higher and higher, become more and more nearly spherical. Finally, quite so,

then detach themselves and rise towards the surface. But, the first that make this venture perish in

the attempt, they gradually collapse as they rise, and vanish before reaching the surface. The thermometer

now shows that the boiling point is nearly reached, but not quite. Presently, the bubbles rise completely

to the surface and break there. Now, the water is boiling, and the thermometer stands at 212 degrees

Fahrenheit or 100 degrees centigrade. With the aid of suitable apparatus, it can be shown

that the atmospheric gases above named continue to be given off along with the steam for a

considerable time after the boiling has commenced. The complete removal of their traces being a very

difficult, if not impossible, physical problem.