Quick-lime is a strong alkali and does the work of such substances. It is used in tanneries in taking hair from hides and also in decomposing fats for mak ing candles. When dead animal substance is buried in lime, the process of decomposition is greatly hastened, probably because the lime unites with all water present while the strong alkali acts upon the fats reducing them to soaps of different kinds.

Whitewash is simple slaked lime mixed with water. It is very cleansing in its effects and also gives the appearance of freshness and cleanness. When newly applied, it is nearly colorless, for the calcium hydrate is colorless; this in the air soon changes to calcium carbonate which is white and opaque.

CHEMISTRY AND ELECTRICITY.

In most houses electricity is used for operating the door bell, table bell and perhaps the electric gas lighters. We have learned how stored up chemical energy is changed into heat and force in the stove and in the human body; but in the electric cell, chemical energy is changed into electrical energy.

If a strip of pure zinc be placed in a weak solution of acid, no chemical action takes place. Place in the same solution a strip of sheet copper and again no action takes place; but let the copper and the zinc be brought in contact, or connected by a copper wire, and immediately vigorous chemical action will begin at the surface of the copper plate; bubbles of hydrogen collecting there. This action is as follows: the zinc dis

Whitewash

A Voltaic
Cell

solves in the acid and hydrogen is set free. This hydrogen travels with an electric current set up in the liquid, passing from particle to particle through the liquid until it reaches the copper. Here the hydrogen stops, but the electric current passes up the copper plate and over the wire to the zinc and down that to

Leclanche

Cell

Voltaic Cell.

the liquid and so on. This arrangement of acid an-1 metals is called a simple voltaic cell. Fig. 27.

Other cells are arranged with different liquids and solids to gain various ends, and several cells may be united by wires between the plates to gain additional strength of current. The form of cell often employed to work electric bells is the Leclanche cell. Fig. 28. This consists of a plate of carbon (or a porous cell containing carbon), in place of the copper, a strip or rod of zinc, and a solution of ammonium chloride.

which takes the place of the acid. The zinc is not affected by the ammonium chloride unless it is connected with the carbon, but when there is a circuit for the electricity, a current is generated. The common conductors of the electric current are the metals and carbons.

Fig. 29. A Battery of Cells Connected in Series.

The zinc is gradually changed to zinc chloride, at the expense of the ammonium chloride, and after a time both the zinc and the ammonium chloride must be renewed. In renewing the battery, the jars should be cleaned out carefully and the zincs renewed if they are completely eaten through. A quarter of a pound of pure ammonium chloride (sal-ammoniac) is dissolved in enough water to about half fill a jar. When the carbon and the zinc are replaced, this will bring the liquid up to two inches from the top. The jar should not be filled too full. The wires which have . been disconnected should be reconnected as before.

For bell work the cells are usually connected up "in series," that is, the zinc of one cell is connected to

Renewing
Batteries

Cells in
Series

Plant Foods

the carbon of the next, the outside circuit being established between the end carbon and end zinc. Fig. 29. If there is a short circuit anywhere

in the line, that is, if the current has a chance in any way to flow from one wire to the other without going through the bell or other apparatus, the batteries are very quickly exhausted.

A modification of this cell has been made in which the spaces inside it are filled with some spongy mass in the pores of which the ammonium chlorFig. 30. A Dry Cell. ide is held. These may easily be carried about without danger of spilling solutions. They are called dry cells and when exhausted cannot readily be renewed.

PLANTS.

Most housekeepers have at least a few house plants and many have gardens which occupy part of the time each day. All foods are directly or indirectly produced by plants and it is well to consider also what food these living things require in their turn.

Plants are able to take from the materials forming the crust of the earth and from the air surrounding them all that they need for their life. The leaves of the plants, because of the green substance called

chlorophyl, have the power of decomposing carbon dioxide gas in a such a way that plants make use of the carbon and breathe out oxygen. Fig. 31. This separation is very difficult to

make in the laboratory. The energy of sunlight is utilized by the plant for this work, for the action does not take place in darkness. In this way plants return to the air the oxygen so necessary for animal life and are themselves fed in part by the useless and even harmful gas exhaled by animals.

Breathing Pores

Fig. 31. Section Through
a Leaf.

The soil on which the plant grows furnishes the mineral matter needed. When plant tissues are burned, these mineral substances remain as ashes. When the ashes of plants are analyzed, they are found to consist of potash, soda, iron, and lime in the form of phosphates, sulphates, and silicates. Some of these substances are present in the soil in inexhaustible quantities, but others are less abundant and unless the soil be fertilized from time to time, the plant soon. uses them up. These less abundant substances are phosphates, potash, and nitrogen.

The lover of house plants has long resorted to various expedients for feeding them, and many plant. foods are now sold and in common use. In using these for manuring potted plants, care must be taken not to

Chlorophyl

Fertilizers