Although it is impossible to raise ice even one degree above 32° without thawing, it is not difficult to reduce water many degrees below that point without freezing it.
In order to obtain both the constituents of water in a separate state, it must be decomposed by galvanism, each pole of a battery terminating in a separate tube containing water, when the result will be that at the positive pole oxygen gas will be evolved, and hydrogen at the negative, the latter being double the quantity of the former. Now, if you mix the gases thus obtained, introduce them into a vessel called a “Eudiometer,” and pass an electric spark through them from a Leyden phial, a sudden flash will be seen, and the gases will entirely disappear, being again converted into water. If you have a mercurial trough, and perform this experiment over mercury, the inside of the eudiometer will exhibit minute drops of water. Thus you have proved both by analysis and synthesis, that water consists of oxygen and hydrogen, in the proportion of one volume of the former to two of the latter.
EXPERIMENT.
Take some perfectly pure distilled water, filter it, surround it with a mixture of light snow, or powdered ice, and salt, taking care to keep it perfectly still, a thermometer having been previously placed in it. The mercury will gradually sink many degrees below the freezing point 32° (it has been reduced as low as 4°), the water still remaining fluid; when all at once, either from shaking the table, or simply because the reduction can be carried no further, it suddenly starts into ice, and the thermometer jumps up at once to 32°, where it remains until the whole is frozen, when the temperature gradually sinks to that of the surrounding medium.
Now if you remove the glass of ice from the freezing mixture into the apartment, and watch the thermometer, you will find it gradually rise to 32°, and there remain until all the ice is melted, when it will gradually acquire the temperature of the room. The reason of this is, that the water in passing from the solid to the fluid form absorbs, and in passing from the fluid to the solid form gives out caloric, so maintaining the temperature at 32°, the point at which the change of form takes place, until it is completed.
Between the temperature of 32° and 212°, water exists in a fluid form, under ordinary circumstances; but at the latter point it assumes the form of vapour or steam, and acquires many of the properties of gases, being indefinitely expansible by heat, the force increasing as the temperature is raised, provided the steam be confined, until it becomes irresistible,—witness the frequent explosions of steam-engines even in this country; and in America, where the engines are worked at a high pressure, accidents are of daily occurrence.
The temperature at which water boils is modified by the pressure applied to it. Thus, as you ascend a mountain, and so pass through a portion of the atmosphere, water boils at a lower temperature, until at great heights it boils at so low a heat, that good tea cannot be made because it is impossible to heat the water sufficiently. Under the exhausted receiver of an air-pump, water boils at about 140°.
CHLORINE.
Another gaseous element, sometimes called a supporter of combustion, is named chlorine, from a Greek word signifying yellowish green.