SECTION

XXI.

XXII.

XXIV.

XXV.

XXVI.

EXPANSION OF A GAS.

A tube of 1 cm. bore and about 25 cms. long is suitable. The divisions etched on it may be rendered more distinct by rubbing a little rouge into them. A strip of white enamelled glass should be placed between the tube and frame.

PRESSURE AND BOILING POINT.

An ordinary boiling flask with the delivery tube bent upwards at the point where it joins the neck of the flask is suitable. A condenser 40 cms. long is necessary

LAWS OF COOLING.

The calorimeter of copper 3 mm. thick is 6.5 cms. diameter and 8 cms. high. It stands on cork legs within a water-jacket, the inside diameter of which is 8.5, the outside 12.5, and the height 12 cms. CALORIMETRIC MEASUREMENTS.

A piece of rubber 1 × 3 × 3 cms. is convenient. SPECIFIC HEAT OF QUARTZ.

The steam heater is 40 cms. long, has an internal diameter of 6.5 and an external of 9.5 cms. The internal cavity is closed at the top by a cork, and at the bottom by a metal door which can be moved aside so that the substance may be lowered into the calorimeter.

XXVIII. LATENT HEAT OF STEAM.

XXIX.

XXX.

The condenser is of copper 3 mm. thick. The box is 4 × 3 × 1.5 cm., so that it can pass freely into the calorimeter.

HEAT OF SOLUTION.

A calorimeter of thin copper 3.5 cms. diameter and 4 cms. high is used to hold the salt. MECHANICAL EQUIVALENT OF HEAT.

The apparatus used is that of Puluj, with the arrangement for measuring the frictional couple improved.

S. P.

24

SECTION

XXXI.

XXXIII.

XXXV.

XXXVI.

XXXVII.

XXXVIII.

XXXIX.

XLI.

XLII.

FREQUENCY BY THE SYREN.

It is convenient to apply part of the pressure on the top of the bellows by hand, as this enables the note of the syren to be readily varied by a slight change of the force used.

LISSAJOUS' FIGURES.

Large forks of frequencies 128 and 256 are suitable.

SEXTANT.

The objects viewed should be at a considerable distance from the observer, and their angular distance apart should not be greater than about 20°.

CURVATURE Of Lenses.

The optic bench is 1 metre long and 14 cms. wide. The lens is an ordinary reading lens of 11 cms. diameter.

TOTAL REFLECTION.

The cube has an edge of 4·5 cms., and the slit is 22 cms. above the table.

MAGNIFYING POWERS.

A board painted white, with a black scale painted on it with divisions about cms. apart, and each fifth numbered, makes a suitable object for the first exercise.

USE OF SPECTROSCOPE.

The salts are contained in 2 inch corked sample bottles placed in holes in a block of wood 20 cms. by 7 cms. The crayons are the ordinary coloured crayons sold in sixpenny boxes.

THE SPECTROMETER AND ITS ADJUSTMENTS.

The model of the vernier is about 30 cms. long. The graduations are on paper gummed to wooden blocks and varnished.

REFRACTIVE INDEX OF A SOLID.

The small piece of mirror is provided to enable light to be reflected down on to the verniers when the readings are being taken.

SECTION

XLIV. PHOTOMETRY.

XLVI.

The standard sperm candle weighs of a pound.

DIFFRACTION GRATING.

One of Thorp's replicas answers the purpose admirably.

XLVIII. ROTATION OF PLANE OF POLARISATION.

XLIX.

L.

LII.

LIII.

II.

The tubes containing the sugar solution should be of glass or be glass-lined, to prevent the acid used in inverting the sugar acting on them.

There are other means of producing the half shadow field, as effective as the plate of quartz described on p. 229.

MAGNETIC Fields.

The horizontal graduated scales are about 3 mms. thick and 80 cms. long. A deflecting magnet about 6 x 5 x 6 cms. is suitable.

MAGNETIC SURVEY.

The apparatus consists of a circular scale of 15-20 cms. diameter, over which a magnetic needle 4 cms. long with a cross section of 04-06 sq. cm., is suspended by a fine untwisted silk fibre about 20 cms. long. The needle should have a light aluminium pointer attached to it.

COMPARISON OF CURRENT METERS.

The resistance coils are of No. 16 platinoid wire, and are arranged parallel to each other between terminals which may be connected together in desired way by means of strips of copper.

APPLICATION OF OHM'S LAW.

any

The wires are stretched along graduated metre scales screwed to rods of wood 1.5 cms. thick and 6 cms. broad.

SECTION

LIV.

LVI.

LVIII.

LIX.

LX.

LXII.

LXIII.

LXIV.

LXV.

ARRANGEMENT OF CELLS.

The outer jars of the cells are 13 cms. high and 10 cms. diameter outside, and the porous pots 12 cms. high and 5.5 cms. diameter.

COPPER VOLTAMETER.

The copper plates used are about 6 cms. square, and each has a lug about 3 cms. long, which fits into and makes good electrical contact with a spring clip.

MEASUREMENT OF RESISTANCE.

Coils of about 4, 20, 100, 500, and 2000 ohms give sufficient practice to the student.

HIGH RESISTANCE.

Strips of insulating material clamped between binding screws answer for the last portion of the

exercise.

Low RESISTANCE.

A coil of about 30 cms. of No. 14 platinoid wire, with connections made to it at several points of its length, is convenient.

RESISTANCE OF A CELL.

A condenser of to 1 microfarad capacity is suitable.

CAREY FOSTER'S METHOD.

The two equal coils may conveniently be made of bare platinoid or manganin wire wound on glass and kept in the same bath of petroleum.

TEMPERATURE CHANGE OF RESISTANCE.

About 4 metres of No. 38 copper, and 2 metres of No. 29 platinoid or manganin wire wound on strips of insulating fibre, form suitable coils. RESISTANCE OF ELECTROLYTES.

A tube about 16 cms. long and 4 cm. internal diameter enables all the solutions to be tested by means of one Post Office box of 11,000 ohms.

SECTION

LXVI.

LXVIII.

LXX.

LXXI.

LXXII.

LXXIII.

STANDARD CELL.

The vertical limbs of the H tube are 8 cms. long and 1.6 cms. diameter.

POTENTIOMETER METHOD OF Measuring CurreNTS.

The wire used for the standard low resistance should be capable of carrying the current without the increase of temperature produced altering its resistance appreciably.

EQUIVALENT OF HEAT BY THE ELECTRICAL METHOD. The heating coil consists of 90 cms. of No. 14 platinoid wire.

INDUCTION OF ELECTRIC CURRENTS.

The 3 inner coils each consist of one layer of 50 turns of No. 20 copper wire, and are wound in parallel. The 3 outer coils are similar but have 40 turns. Short lengths of platinoid wire are interposed between the ends of the coils and the terminals, so that whether one coil, or two in series, or three in series are in circuit the resistance is the same.

INDUCTANCE OF A COIL.

The coil consists of 575 turns of No. 20 copper wire, the mean radius of a turn being 25.3 cms. LEAKAGE AND ABSORPTION OF CONDENSERS.

The dielectric of the condenser used consists of paraffined paper, one side of which is shellac varnished.