The morning bath will introduce us agreeably to the wonderful chemical substance, water, and with this substance we will begin our study of a day's chemistry. The water for the house may come from the town supply, from wells, cisterns, or springs. It may be "surface water," from pond, lake, or stream, or it may be "ground water," from wells or deep springs. Cistern water is, of course, rain water. Water is present in many substances where we might not suspect it. All living things contain a large percentage of water. Of an athlete weighing 150 pounds, all but about 42 pounds is water. Wood, meat, vegetables, fruit, when dried, weigh from 50 to 98 per cent less. Many natural and artificial substances owe their crystalline form to water and when heated, give off this "water of crystallization" and crumble to powder. Common washing soda shows this effect, when exposed to the air, and soon gives off so much water that its crystalline character is lost.
All water found in nature is more or less impure, that is, it contains substances in solution. It dissolves air and takes substances from the soil and rocks over which it runs. Often it comes in contact with animal and vegetable substances and dissolves something from them. Near dwellings the water in streams, ponds, and wells is very likely to become contaminated. Decaying substances give rise to materials easily dissolved in water, which may travel for a considerable distance under ground, so that the drainage from the house or barn is frequently carried to near-by streams or wells, making their waters quite unfit to drink. Fig. I.
The following experiment will illustrate that air is dissolved in water.
Experiment. Place a tumbler of fresh well-water or tap-water in a warm place. After a time, bubbles will be seen collecting on the sides of the glass. This is air which was dissolved in the water. As the water grows warm, it cannot hold so much air in solution and some of it separates.
Most of the impurities in water are less easily converted into vapor than the water itself; hence, when the water is boiled, they stay behind while the water "boils away". Water from almost any source can be made pure and clear by distillation. Distilled water is prepared in an apparatus known as a still. See Fig. 2. A still consists of a boiler, A, and a condenser. In the condenser, a coil of tube, D, usually made of pure tin, is surrounded by cold water which continually runs through the apparatus. The steam, admitted at the upper end of the coil, is condensed by the low temperature and distilled water is collected at the lower end. In the laboratory, distilled water is often made in the glass apparatus shown in Fig. 3.
Distilled water has a flat taste, because air and other dissolved substances which give water its taste have been removed. It will again dissolve the air on being poured several times from one vessel into another.
Rain is water which has been evaporated from the surfaces of natural bodies of water, oceans, lakes, and from the land, and is practically free from mineral matter, but contains dissolved gases.
The vapor, cooled at the low temperatures of the upper levels of air, falls as rain. The first fall of any shower is mixed with impurities which have been washed from the air. Among these may be carbon dioxide, ammonia, and carbon in the form of soot and creosote. It is these last impurities which cause the almost indelible stain left when rain water stands upon window-sills or other finished woods.
Water is a nearly universal solvent. It dissolves more substances and these in larger quantities than any other liquid. At a given temperature, water will dissolve only a certain proportion of the various salts and other soluble substances. When the water will take up no more, the solution is said to be saturated. Increasing the temperature generally increases the dissolving power of water for solids and liquids. The reverse is usually true for gases.
When a saturated solution of a solid is cooled, crystals are frequently formed, many having beautiful shapes. Examples are shown in Fig. 4.
Experiment. In an earthen-ware or enameled dish dissolve as much alum as possible in a little boiling water. Pour the solution into a shallow dish or saucer, and set it away for a day or more where it will be undisturbed. Beautiful, clear, six-sided crystals will form in the dish. If strings are hung in the solution,the crystals will form upon them. Rock candy crystals are made from cane sugar syrup in this way.
The experiment may be repeated, using washing soda instead of alum.
Fig. 1. Well, Contaminated By House Drainage
FIG. 2. A STILL. A, Gooseneck; B, Boiler; D, Condensing Coil
Fig. 3. Making Distilled Water in the Laboratory
Silver, copper, and tin are not perceptibly dissolved in pure water, but when combined with acid substances, the compounds formed are soluble. These compounds of a metal with an acid are called salts. The salts of copper, zinc, and lead are poisonous. Copper, brass, (an alloy of copper with zinc) tin, solder, and iron are metals easily affected by acids, so that cooking utensils made of these materials should not be used with acid substances like lemon and vinegar.