GRENET CELLS
Into a pint gem-jar put water 10 parts, sulphuric acid 1 part, pota.s.s, bichromate 1 part. Have jar three quarters full. Cut a piece of board 4 in. square, bore two holes in it, and through the holes thrust two pieces of electric light carbon, 5 in. or 6 in. long. The outer edges of the carbons should not be more than two inches apart. With a saw, cut a slit in the board between the holes and insert a strip of zinc 2 in. by 7 in. previously rubbed over with mercury. Set the three elements in the jar, connect the two carbons to one wire, and the zinc to another.
One cell of this kind will run a small motor, operate a telegraph sounder, make a simple electro-magnet, or ring an electric bell; two cells will decompose water: three will heat a piece of fine iron wire red-hot.
DECOMPOSITION APPARATUS
1. Cut the neck end from a pickle bottle. Get a No. 1 stopper, (rubber) with two holes in it and insert a piece of platinum foil 2 in. by 1/8 in. into each hole so that 1/2 in. projects above and below. Insert a tight plug beside each strip, thus holding it fast and making the stopper watertight. Insert the stopper into the neck of the jar. Pour into the vessel thus formed enough water to cover the platinums, and add a few drops of sulphuric acid. Touch the wires from the battery to the lower ends of the strips. Note bubbles of gas arise from the platinums.
These may be collected in test-tubes and found by test to be oxygen and hydrogen.
2. Fasten a strip of platinum 1 in. by 1/8 in. to each wire from the battery and dip these into some acidulated water contained in a tumbler.
The decomposition of the water into two gases can be seen, but the gases cannot be collected so readily as in 1 above. Bits of electric light carbon will do instead of platinum if the current is not too weak.
PNEUMATIC TROUGH
When oxygen or other gas is to be collected over water, use a milk pan or similarly shaped vessel.
SPIRIT-LAMP
Use an ink-bottle to contain the alcohol and several strands of string for the wick; make a hole in a piece of tin and draw the wick through; then let the tin rest on the neck of the bottle to support the wick.
BAROMETER
A siphon barometer takes less mercury than a cistern barometer. To the open end of the barometer tube attach a piece of strong rubber tubing 4 in. long and to this a piece of gla.s.s tubing 3 in. long. Fill the tube thus formed with mercury to within 3 in. from the top. Holding the short gla.s.s tube open end up, turn the long tube closed end up. (A tube of 1/8 in. bore needs only one quarter of the mercury required to fill a tube 1/4 in. bore.)
HYGROMETER
For a hygrometer, suspend two dairy thermometers side by side against the wall, cover the bulb of one with thin muslin, and let the muslin hang down and dip into water in some small vessel placed about three inches below the bulb on a little shelf.
HINTS
To avoid explosions, a spirit-lamp should be kept filled.
Toy rubber balloons answer well for sheet rubber.
Red ink makes good colouring matter.
Make touch-paper by soaking any porous paper in a solution of saltpetre, and drying it.
Instead of bending gla.s.s tubes, join them with rubber tubing.
To make a test-tube holder, fold a sheet of paper until it is about half an inch wide and wrap this around the tube.
To bend gla.s.s tubing, hold in the flame of the spirit-lamp and rotate between the fingers till it becomes soft and flexible, remove from the flame, and bend.
To break gla.s.s tubing, first scratch with a file.
To break gla.s.s bottles, make neatly a deep cut with a file, then touch the gla.s.s near the cut with a red-hot wire. When a crack appears, move the hot wire and the crack will follow. Several heatings may be necessary.
In the case of a heavy gla.s.s bottle, file the cut as before, wrap the bottle with string dipped in alcohol, light it, and after it has burned, plunge the bottle vertically into cold water.
Melted paraffin is good for closing small leaks.
TIME APPORTIONED TO NATURE STUDY
The Nature Study lesson should be given a definite place on the time-table. It is recommended that each cla.s.s should have at least one lesson of fifteen minutes in length, a week. In addition to this, about five minutes a week should be spent in a.s.signing problems for out-of-door work and in discussing the observations which the pupils have made on problems previously a.s.signed.
CHAPTER III
FORM I
AUTUMN
GARDEN WORK
On the re-opening of school after the summer holidays, the pupils should see that their plots are put into good order without delay. If they have been neglected during the holidays, a good deal of attention will be needed, and in some cases it may not be possible to reclaim them because of prolonged neglect. If such plots are found, they should be cleaned off completely, spaded up, and left in readiness for planting the following spring. All plots should be cultivated throughout the month of September to keep the soil mellow and prevent the growth of weeds. The pupils should be allowed to pick flowers from their own plots, but should always leave a few in bloom for the sake of the general appearance of the garden. Paths should be kept clean, and all rubbish, weeds, dead plants, etc., removed to the compost heap, which should be in the least conspicuous part of the garden. Hoes, rakes, and claw-hand weeders should be used in cleaning up and cultivating the plots. The soil should be kept fine and loose on top to prevent drying out.
LESSONS ON A GARDEN PLANT
PANSY
LESSON I
~Materials.~--A flower for each pupil A plant set into a flower-pot A leaf for each pupil A pile of leaves containing a few pansy leaves and several of other kinds.
~Introduction.~--A conversation with the pupils about their favourite flowers.
~Observations.~--The pansy flowers are now distributed and the general form of the flower is first noted. The resemblance to the face of an animal will be discovered. The name _corolla_ is given, but no other botanical terms are to be introduced in this lesson.
The details of colours, perfumes, velvety feeling of the corolla, and the number of leaflets in it are next _discovered_ and described by the _pupils_. Lastly, in a withering flower they discover the seed cases and the little seeds.
LESSON II
The conception of the relationship between the flower, root, and stem is developed by a method similar to the following:
What soon happens to a pansy flower after it is broken from the plant?
Are the flowers that you have in your hands withering?
How can you keep them from withering?
Hence, what must the flower get from the stem?
Where does the stem get the moisture?