islands in the West Indies and the Pacific, settlements on the West Coast of Africa, on the east side of the Bay of Bengal, and in other places.

The British Empire is the largest in the world, except Russia, and the most populous, except China.

2. How did our forefathers look upon barracks and a standing army? How do you explain the change in popular feeling on this subject?

The foundation of a standing army and barracks was looked upon by the people of this country with a feeling of distrust, and met with considerable opposition. They saw in the one only a means of interference and meddling abroad and an increase of the power of the king, and in the other a means of oppression and taxation at home.

The change has come about since the growth of the power of Parliament, the limitation of the power of the king, the extension of our colonial empire, the increase of population and manufactures, and the spread of education and popular power by the extension of the franchise to almost all classes of people.

3. When did the House of Hanover come to the throne? Show the names and relationship of all our sovereigns of that House, with their dates.

The Act of Settlement passed after the accession of William III. provided that the crown should pass to his children if he left any, then to Anne or her heirs, and in default of either to the descendants of Elizabeth, daughter of James I. Elizabeth married the Elector Palatine, and had issue Sophia, who married Ernest Augustus, the Elector of Hanover. On the death of Queen Anne, George, the son of the Electress Sophia, became King of England.

The sovereigns of the House of Hanover are:

4. Who sit in the House of Peers? Explain the name, and discuss the constitutional advantages of a Second Chamber.

The House of Peers consists of the Lords Spiritual and Temporal of England, and the Representative Peers of Ireland and Scotland. Twenty-six Bishops of the Church of England occupy their seats for life, or till the resignation of their bishopric. The Lords Temporal are of five orders, Dukes, Marquises, Earls, Viscounts, and Barons. Their title is hereditary. The repre sentative peers of Ireland are elected for life, the Scottish peers for a single Parliament only.

The word means an equal, and is derived from the Latin par, equal, and the persons sitting in the House of Lords sit there as equals.

Perhaps the chief advantages of a Second Chamber are, that it provides for the reconsideration of measures which may have been hurriedly passed, or only imperfectly and partially considered by a body of men who are not subject to the capricious changes of opinion which often occur among a numerous and partially-educated population.

Teaching.

Write notes of a lesson on one of these subjects:

The four seasons. Gold.

Cause of Seasons.-The inclination of the earth's axis to the plane of its orbit. Illustration. Place lamp on table, and move globe round it with axis perpendicular. From this derive, that half of the earth receives light and heat at once; that if the earth's axis were perpendicular there would never be any change of season, each place on the earth would have always 12 hours day and 12 hours night.

Inclination of Axis, and its Effects.-23 degrees. Now show the effects of inclining the axis, and keeping the inclination always parallel to itself. Place the globe with north pole turned towards lamp. Make it revolve, and show that parts round

about the North Pole never lose sight of the sun during the revolution; then draw attention to the South Pole, and elicit that the people there never see the sun during that revolution. Changes places, and observe change of season. These give winter and summer clearly.

Next move globe slowly, till it occupies place midway between former positions. Show that North Pole and South Pole are then equally distant from sun, and that each place will have twelve hours day and night in the revolution.

From this derive, that the North Pole and the district 23 degrees around it passes from all day gradually to all night during the revolution, that the amount of heat received varies according to length of day; that this variation we name the seasons.

The Seasons.-Spring, Summer, Autumn, Winter. Name the months for each in this country, and show that the further a place is from the North or South Pole the less difference there is in the seasons.

Benefits of the Seasons.-Nearly all parts of the earth are rendered habitable; greater variety of climate; greater diversity of products; temperate zones produce fruits which would never ripen but for this change.

Chemistry of the Non-Metallics.

BY EDWARD AVELING, D.Sc. LONDON.

[This series of articles, whilst dealing with the subjects required by the University of London for the Matriculation Examination and with those required at the Elementary Stage of the Inorganic Chemistry (Branch X.) Science and Art Department, is intended as a practical guide to the philosophical and systematic study of the non-metallics.]

CHAPTER IV.-HYDROGEN-(continued).

PROPERTIES. DIFFUSION OF GASES.

D. The Properties of Hydrogen.-If the student has carefully observed the behaviour of the gas prepared in any one of the four experiments given above he will be able to make out its properties.

(1) Condition. A gas at ordinary temperatures. Until recently all efforts to liquefy hydrogen had failed. The two chief agents in liquefying gases are reduction of temperature and increase of pressure. Each of these helps to bring the particles of the gas closer to each other. Cohesion between these particles triumphs over the repulsion of them one by the other, and a liquid results. A pressure of 3,000 atmospheres, i.e., 3,000 times as great as the pressure of the air at the earth's surface, or 3,000 times 1,033 grams on the square centimetre has been applied to hydrogen without liquefying it. Hence hydrogen was for a long time spoken of as a permanent gas, i.e., one that could not be reduced to the liquid state. In 1878-9, however, two Frenchmen, MM. Cailletet and Pictet, working quite independently one of the other, succeeded by the use of very ingenious methods in liquefying hydrogen and all the other gases said to be permanent.

The method employed by M. Pictet is as follows. The tube of glass containing the gas to be liquefied (5 metres long, 14 mm. in external diameter, 4 in internal, and therefore 5 mm. in thickness) is placed in a tube containing solid carbon dioxide. The latter is frozen by being placed in a tube containing liquid sulphur dioxide. The vapour of this last is constantly drawn off from the surface of the liquid by means of a vacuum-pump. The evaporating sulphur dioxide, producing a temperature of -65° to 70°, cools the carbon dioxide. The solid carbon dioxide has a temperature of -140°. The gas within the innermost tube is, at the same time as it is cooled by the frozen carbon dioxide, subjected to great pressure (500 atmospheres, e.g.). On turning a stop-cock at the free projecting end of the tube containing the gas to be liquefied, the latter escapes as a liquid.

The method employed by M. Cailletet is as follows. The gas to be liquefied is placed in a small tube of glass, surrounded by a freezing mixture, and so arranged that the gas may at a certain moment be put into connection with the air. This glass tube opens below into a cylinder of steel, containing mercury. This mercury, pressed on by water that is forced into the cylinder from a massive steel cylinder, presses on the gas. When the latter, lowered in temperature by the freezing mixture and compressed by the mercury that is under pressure from the forced-in water, is suddenly allowed to escape into the air its expansion causes a very great reduction of temperature and the gas is liquefied.

(2) Effect on the Senses.-Without taste or odour; invisible and colourless.

(3) Specific Gravity.—The lightest terrestrial body known. It is indeed the standard of comparison for all gases as to weight. The specific gravity of a body is its weight in reference to the weight of an equal volume of some standard body. Its density is the amount of matter, or the mass, of a certain volume of any substance, as compared with the mass of an equal volume of the standard. The student is warned not to confuse specific gravity with density, or weight with mass. A body may have no weight. It must have mass. As hydrogen is the lightest substance known, it is taken as the standard for gases. Its specific gravity and its density alike are represented by

the number 1. The air is sometimes taken as the standard for gases. There are two reasons why it is not a good standard. It is a mixture, not an element, and it is, compared with hydrogen, a heavy gas. Air is 14'47 times as heavy as hydrogen. Hence the specific gravity of any gas can be expressed upon the air-scale by dividing its specific gravity upon the hydrogen scale by 14'47. The specific gravity of hydrogen on the air-scale is 1÷14'47069.

II 2

By the law explained on page 259, 112 litres of hydrogen at o° and 760 mm. weigh 1 gram, therefore I litre weighs - grams=0896 grams. This number 0896, much used in chemical arithmetic, is called the crith, κριθη (crithe) = a barleycorn. The weight of a litre of any other gas may be calculated by multiplying the crith by the number representing specific gravity of the gas. (4) Solubility.-Very little soluble in water. 100 cc. of water at normal temperature and pressure dissolve 193 cc. of hydrogen.

(5) Relation to Combustion.-Inflammable, but not a supporter of combustion. If a lighted taper is plunged into the gas, the taper goes out, and the hydrogen burns, uniting with the oxygen of the air to form hydrogen oxide, or steam. Hydrogen and oxygen mixed together burn on application of a light with explosive violence. If mixed in the proportion of 2 and 1, their combining proportions by volume, the explosion is dangerously violent. Symbols of the combustion of hydrogen : + O2 = 2H2O 36

2H

4 + 32 = 4 vols. 2 vols. 4 vols.

It will be seen that the two gases unite in the proportion of 4 and 32 by weight to form 36 by weight of water, or (dividing by 4) in the proportion of 1 to 8 to form 9 by weight of water.

The volume-relationship demands close attention. 4 vols. of hydrogen with 2 of oxygen only form 4 vols. of steam. To understand this we must turn to the law explained on page 259, and see how the weights and volumes of compound gases are related.

I gram hydrogen at o°C. and under 760 mm. 16 grams oxygen

nitrogen

occupy each 11.2 litres.

And, generally, the number of grams of any element gas represented by the weight-number of the element occupy at normal temperature and under normal pressure 11.2 litres.

The weight-number of the compound gas, steam (HO)=18.

18 grams steam (H3O) at normal temperature and pressure occupy 22°4 litres, and generally the number of grams of any compound gas represented by the weightnumber of the compound, occupy at normal temperature and under normal pressure 22.4 litres or 2 volumes.

In the special case under consideration, therefore, the 4 vols. of hydrogen and the 2 vols. of oxygen are condensed into 4 vols. of steam.

EXERCISES ON THE BURNING OF HYDROGEN (solved).

39. 20 grams hydrogen are burnt. What weight of oxygen is required and what weight of steam is formed?

4 grams H require 32 O and form with them 36H2 O 1 gram,, requires a O and forms 32 x 20, PO and form 36 x 20 20 grams,, requires

4

4

EXAMPLES ON THE BURNING OF HYDROGEN (for solution).

33. How much oxygen by weight and by volume is necessary for the combustion ofgram of hydrogen?...4 grams, 2.8 litres. 34. 224 grams water are required. What weight hydrogen and oxygen must be taken ?.......... .24 and 1991.

35. What weight of hydrogen must be mixed with 1 gram of oxygen, that upon explosion nothing but steam may be left ? ... gram.

36. A mixture of equal weights of oxygen and hydrogen is exploded. What gas will be left after the explosion, and what proportion by weight of the original mixture will it equal?..

Oxygen; .

37. 12cc. of hydrogen and 15cc. of oxygen are exploded. What gases are left after the explosion, supposing that no condensation takes place? 12cc. steam, 9cc. oxygen.

38. What volume of hydrogen must be mixed with 8 grams oxygen that after the explosion 5c0cc. of hydrogen may be left? 11700CC.

(6) Specialties.-Hydrogen by its extreme tenuity renders sounds very weak. A bell rung in a jar of hydrogen can scarcely be heard. Hydrogen is a great reducing agent, i.e., it readily takes away oxygen from compounds containing that element, and uniting with it forms water If the gas is driven over the magnetic iron oxide formed in the experiment described on page 378, water is formed and iron is left.

The rapidity of its diffusion is another special point. Diffusion is the passage of one gas into the space occupied by another. Take some plaster of Paris, mix it with water, spread the mixture on filter paper. Take a glass tube

of an inch in diameter, and some two or three feet long. Press one end of the tube into the moistened plaster of Paris, and let the plaster set. The tube will be closed at one end by a porous plug of plaster of Paris. Fill the tube with hydrogen, and place its open end in a vessel

Fig. 14.

containing any coloured liquid. (Fig. 14.) The liquid is seen to rise within the tube. The hydrogen is diffusing out through the plug more rapidly than air is passing in through the plug.

Another method of showing the diffusion of hydrogen is to join the tube with its porous plug to a U-shaped tube containing water, and to place over the plug-end a beaker (B, Fig. 15.) Pass hydrogen into this beaker, and

B

Fig. 15.

the hydrogen in the beaker B will pass through the porous plaster more quickly than the air passes out, and will force the water below up and out of the free limb of the bent tube.

It is found that the lighter a gas is, the more rapidly it diffuses. Experiments with various gases show that the power of diffusion of gases varies inversely as the square roots of their densities. Oxygen is 16 times as heavy as hydrogen. The square root of 16 is 4, of 1 is 1. Hydrogen diffuses 4 times as rapidly as oxygen.