Full text of "The boy's playbook of science : including the various manipulations and arrangements of chemical and philosophical apparatus required for the successful performance of scientific experiments : in illustration of the elementary branches of chemistry and natural philosophy"

No.

Division ...

Received ...187^.

Wheatstone's telephonic concert at the Polytechnic, in which the sounds and vibra-
tions pass inaudible through an intermediate hall, and are reproduced in the lecture-
room unchanged in their qualities and intensities. Frontitpiece.

THE

BOY'S PLAYBOOK OF SCIENCE:

THE

anfo ^rrattgemen; i$

INCLUDING THE

CHEMICAL AND PHILOSOPHICAL APPARATUS REQUIRED

FOR THE SUCCESSFUL PERFORMANCE OF

SCIENTIFIC EXPERIMENTS.

IN ILLUSTRATION OF THE ELEMENTARY BRANCHES OF
CHEMISTRY AND NATURAL PHILOSOPHY.

JOHN HENRY PEPPER,

P.C.S., A. INST. C.E.; LATE PROFESSOR OF CHEMISTRY AT THE ROYAL POLYTECHNIC,

ETC. ETC.
AUTHOR OF "THE PLAYBOOK OF METALS."

NEW EDITION.

. Illustrated foitjj 47

CHIEFLY EXECUTED FROM THE AUTHOR'S SKETCHE S,
BY H. G. HIKE.

LONDON :
GEORGE EOUTLEDGE AND SONS,

THE BROADWAY, LUDGATE.
NEW YOEK: 416, BROOME STREET.

1869.

Z.OND01T.

BDWARDS AND CO., PRINTERS, CSABDOS 8TRBET.
COYBlfT GAEDES.

PROFESSOR LYON PLAYFAIR, C.B., F.R.S,

PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF
EDINBURGH,

DEAE SIR,

I DEDICATE these pages to your Children, whom I
often had the pleasure of seeing at the Polytechnic during
my direction of that Institution. I do so as a mark of
respect and appreciation of your talent and zeal, and of
your public-spirited advocacy of the Claims of Science in
this great and commercial country.

Without making you responsible in any way for the
shortcomings of this humble work on Elementary Science,,
allow me to subscribe myself,

Dear Sir,

Yours most respectfully,

JOHN HENRY PEPPER.

CONTENTS.

PAGB

INTRODUCTION 1

CHAPTER I.

THE PROPERTIES OF MATTER IMPENETRABILITY 3

CHAPTER II.

CENTRIFUGAL FORCE 17

CHAPTER III.

THE SCIENCE OF ASTRONOMY 19

CHAPTER IV.

CENTRE OF GRAVITY 32

CHAPTER V.

SPECIFIC GRAVITY 48

CHAPTER VI.

ATTRACTION OF COHESION , 59

CHAPTER VII.

ADHESIVE ATTRACTION 67

CHAPTER VIII.

CAPILLARY ATTRACTION , 69

V 1 CONTEXTS.

CHAPTER IX.

PAGB
CRYSTALLIZATION 73

CHAPTER X.

CHEMISTRY 81

CHAPTER XL

CHLORINE, IODINE, BROMINE, .FLUORINE 129

CHAPTER XII.

CARBON, BORON, SILICON, SELENIUM, SULPHUR, PHOSPHORUS . .151

CHAPTER XIII.

FRICTIONAL ELECTRICITY 173

CHAPTER XIV.

VOLTAIC ELECTRICITY 193

CHAPTER XV.

MAGNETISM AND ELECTRO-MAGNETISM 206

CHAPTER XVI.

ELECTRO-MAGNETIC MACHINES 211

CHAPTER XVII.

THE ELECTRIC TELEGRAPH 21S

CHAPTER XVIII.

RUHMKORFF'S, HEARDER'S, AND BENTLEY'S COIL APPARATUS . .230

CHAPTER XIX.

MAGNETO-ELECTRICITY 241

CHAPTER XX.

DIA-MAGNETISM , .247

CONTENTS. <VU

CHAPTER XXI.

PAGB
LIGHT, OPTICS, AND OPTICAL INSTRUMENTS . . 255

CHAPTER XXII.

THE REFRACTION OF LIGHT 298

CHAPTER XXIII.

REFRACTING OPTICAL INSTRUMENTS 303

CHAPTER XXIV.

THE ABSORPTION OF LIGHT 327

CHAPTER XXV.

THE INFLECTION OR DIFFRACTION OF LIGHT 328

CHAPTER XXVI.

THE POLARIZATION OF LIGHT 335

CHAPTER XXVII.

HEAT 352

CHAPTER XXVIII.

THE STEAM-ENGINE 406

CHAPTER XXIX.

THE STEAM-ENGINE continued . 4J

INTRODUCTION.

ALTHOUGH "The South Kensington Museum" now takes the lead, and
surpasses all former scientific institutions by its vastly superior collec-
tion of models and works of art, there will be doubtless many thousand
young people who may remember (it is hoped) with some pleasure the
numerous popular lectures, illustrated with an abundance of interesting
and brilliant experiments, which have been delivered within the walls of
the Royal Polytechnic Institution during the last twenty years.

On many occasions the author has received from his young friends
letters, containing all sorts of inquiries respecting the mode of performing
experiments, and it has frequently occurred that even some years
after a lecture had been discontinued, the youth, now become the young
man, and anxious to impart knowledge to some "home circle" or
country scientific institution, would write a special letter referring to a
particular experiment, and wish to know how it was performed.

The following illustrated pages must be regarded as a series of philo-
sophical experiments detailed in such a manner that any young person
may perform them with the greatest facility. The author has endea-
voured to arrange the manipulations in a methodical, simple, and popular
form, and will indeed be rewarded if these experiments should arouse
dormant talent in any of the rising generation, and lead them on
gradually from the easy reading of the present "Boy's Book," to the
study of the complete and perfect philosophical works of Leopold
Gmelin, Faraday, Brande, Graham, Turner, and Pownes.

Every boy should ride " a hobby-horse" of some kind ; and whilst
play, and plenty of it, must be his daily right in holiday time, he ought
not to forget that the cultivation of some branch of the useful Arts and
Sciences will afford him a delightful and profitable recreation when

2 IXTKODUCTION.

satiated with mere play, or imprisoned by bad weather, or gloomy with
the unamused tediousness of a long winter's evening.

The author recollects with pleasure the half-holidays he used to devote
to Chemistry, with some other King's College lads, and in spite of
terrible pecuniary losses in retorts, bottles, and jars, the most delightful
amusement was enjoyed by all who attended and assisted at these
juvenile philosophical meetings.

It has been well remarked by a clever author, that bees are geome-
tricians. The cells are so constructed as, with the least quantity of
material, to have the largest sized spaces and the least possible interstices.
The mole is a meteorologist. The bird called the nine-killer is an arith-
metician, also the crow, the wild turkey, and some other birds. The
torpedo, the ray, and the electric eel are electricians. The nautilus is
a navigator. Ea raises and lowers his sails, casts and weighs anchor,
and performs nautical feats. Whole tribes of birds are musicians. The
beaver is an architect, builder, and wood-cutter. He cuts down trees
and erects houses and dams. The marmot is a civil engineer. He does
not only build houses, but constructs aqueducts, and drains to keep
them dry. The ant maintains a regular standing army. Wasps are
paper manufacturers. Caterpillars are silk-spinners. The squirrel is a
ferryman. With a chip or a piece of bark for a boat, and his tail for a
sail, he crosses a stream. Dogs, wolves, jackals, and many others, are
hunters. The black bear and heron are fishermen. The ants are day-
labourers. The monkey is & rope dancer. Shall it, then, be said that any
boy possessing the Godlike attributes of Mind and Thought with Free-
will can only eat, drink, sleep, and play, and is therefore lower in the
scale of usefulness than these poor birds, beasts, fishes, and insects ?
No ! no ! Let " Young England" enjoy his manly sports and pastimes,
but let him not forget the mental race he has to run with the educated
of his own and of other nations ; let him nourish the desire for the
acquisition of " scientific knowledge," not as a mere school lesson, but
as a treasure, a useful ally which may some day help him in a greater or
lesser degree to fight " The Battle of Life."

THE

BOY'S PLAYBOOK OF SCIENCE.

CHAPTER I.

THE PROPERTIES OP MATTER IMPENETRABILITY.

IN the present state of our knowledge it seems to be universally agreed,
that we cannot properly commence even popular discussions on astro-
nomy, mechanics, and chemistry, or on the imponderables, heat, light,
electricity, and magnetism, without a definition of the general term
" matter ;" which is an expression applied by philosophers to every
species of substance capable of occupying space, and, therefore, to
everything which can be seen and felt.

The sun, the moon, the earth, and other planets, rocks, earths, metals,
glass, wool, oils, water, alcohol, air, steam, and hosts of things, both
great and small, all solids, liquids and gases, are included under the
comprehensive term matter. Such a numerous and varied collection of
bodies must necessarily have certain qualities, peculiarities, or properties;
and hence we come in the first place to consider " The general powers
or properties of matter." Thus, if we place a block of wood or stone in
any position, we cannot take another substance and put it in the space
filled by the wood or stone, until the latter be removed. Now this is
one of the first and most simple of the properties of matter, and is called
impenetrability, being the property possessed by all solid, liquid, and
gaseous bodies, of filling a space to the exclusion of others until they be
removed, and it admits of many amusing illustrations, both as regards
the proof and modification of the property.

Thus, a block of wood fills a certain space: how is it (if impenetrable)
that we can drive a nail into it ? A few experiments will enable us to
answer this question.

Into a glass (as depicted at fig. 1) filled with spirits of wine, a quantity
of cotton wool many times the bulk of the alcohol may (if the experiment
is carefully performed) be pushed without causing a drop to overflow
the sides of the vessel.

Here we seem to have a direct contradiction of the simple and indis-

BOY'S PLAYBOOK OF SCIENCE.

Fig. 1.

putable truth, that " two things cannot occupy the same space at once."
But let us proceed with our experiments :

We have now a flask full of water,
and taking some very finely-powdered
sugar, it is easy to introduce a not-
able quantity of that substance with-
out increasing the bulk of the water ;
the only precaution necessary, is not
to allow the sugar to fall into the
flask in a mass, but to drop it in
grain by grain, and very slowly, al-
lowing time for the air-bubbles (which
will cling to the particles of sugar)
to pass off, and for the sugar to dis-
solve. Matter, in the experiments
adduced, appears to be penetrable,
and the property of impenetrability
seems only to be a creation of fancy :
reason, however, enables us to say
that the latter is not the case.
A nail may certainly be hammered into wood, but the particles are
thrust aside to allow it to enter. Cotton wool may be placed m spirits
of wine because it is simply greatly extended and bulky matter, which
if compressed, might only occupy the space of the kernel of a nut, and

Fig. 2.

THE PROPERTIES OP MATTER IMPENETRABILITY. 5

if this were dropped into a half-pint measure full of alcohol, the increase
of bulk would not cause the spirit to overflow. The cotton-wool expe-
riment is therefore no contradiction of impenetrability. The experi
ment with the sugar is the most troublesome opponent to our term, and
obliges us to amend and qualify the original definition, and say, that the
ultimate or smallest particles or atoms of bodies only are impenetrable ;
and we may believe they are not in close contact with each other, because
certain bulks of sugar and water occupy more space separately than
when mixed.

If we compare the flask of water to a flask full of marbles, and the
sugar to some rape-seed, it will be evident that we may almost pour
another flask full of the latter amongst the marbles, because they are not
in close contact with each other, but have spaces between them ; and
after pouring in the rape-seed, we might still find room for some fine
sand.

The particles of one body may thus enter into the spaces left between
those of another without? increasing its volume ; and hence, as has been
before stated, " The atoms only of bodies are truly impenetrable."

This spreading, as it were, of matter through matter assumes a very
important function when we come to examine the constitution of the
air we breathe, which is chiefly a mechanical mixture of gases : seventy-
nine parts by volume or measure f of nitrogen gas, twenty-one parts of
oxygen gas, and four parts of carbonic acid vapour in every ten thousand
parts of air having the following relations as to weight :

Specific gravity.

Nitrogen 972

Oxygen 1105

Carbonic acid 1524

It might be expected that these gases would arrange themselves in
our atmosphere in the above order, and if that were the case, we should
have the carbonic-acid gas (a most poisonous one) at the bottom, and
touching the earth, then the oxygen, and, last of all, the nitrogen ; a

BOY S PLAYBOOK OF SCIENCE.

state of things in which oraanizedMfe could not exist. The gases do not,
however, separate : indeed, they seem to act as it were like vacuums to

one another, and " the diffusion of gases" has become a

recognised fact, governed by fixed laws. This fact is

curiously illustrated, as shown in our cut, by filling a

bottle with carbonic acid, and another with hydrogen ;

and having previously fitted corks to the bottles, perfo-

rated so as to admit a tube, place the bottle containing

the carbonic acid on the table, then take the other full

of hydrogen, keeping the mouth downwards, and fit in

the cork and tube : place this finally into the cork of

the carbonic-acid bottle, which may be a little larger than

the other, in order to make the arrangement stand firmer ;

and after leaving them for an hour or so, the carbonic

acid, which is twenty-two times heavier than the hydro-

gen, will ascend to the latter, whilst the hydrogen will

descend to the carbonic acid. The presence of the car-

bonic acid in the hydrogen

bottle is easily proved by

pouring in a wineglassful

of clear lime-water, which

speedily becomes milky,

owing to the production of

carbonate of lime; whilst

the proof of the hydrogen

being present in the car-

bonic acid is established

by absorbing the latter

with a little cream of lime

i.e., slacked lime mixed

to the consistence of cream

with some water and set-

ting fire to the hydrogen

that remains, which burns

quietly with a yellowish

flame if unmixed with air ;

but if air be admitted to

the bottle, the mixture of

air and hydrogen inflames

rapidly, and with some

noise. One of the most

elegant modes of showing
the diffusion of gases is by taking a large
round dry porous cell, such as would be
employe/ in a voltaic battery, and having

Cemented a brass cap With a glass tube di

attached to its open extremity, it may then

be supported by a small tnpod of iron porous ceU and tube in tumbler.

{Carbonic:

Fig. 4.

Fig. 5.
The porous cell.

B. The jar

ips into the tumbler containing

THE PROPEKTIES OF MATTER IMPENETRABILITY. 7

wire, and the end of the glass tube placed in a tumbler containing a
small quantity of water coloured blue with sulphate of indigo, if a
tolerably large jar containing hydrogen is now placed over the porous
cell, bubbles ot gas make their escape at the end of the tube, because
the hydrogen diffuses itself more rapidly into the porous cell than the
air which it already contains passes out. When the jar is removed, the
reverse occurs, hydrogen diffuses out of the porous cell, and the blue
liquid rises in the tube.

This diffusive force prevents the accumulation of the various noxious
gases on the earth, and spreads them rapidly through the great bulk of
the atmosphere surrounding the globe.

Although air and other gases are invisible, they possess the property
of impenetrability, as may be easily proved by various experiments.
Having opened a pair of common bellows, stop up the nozzle securely,
and it is then impossible to shut them ; or, fill a bladder with air by
blowing into it, and tie a string fast round the neck ; you then find that
you cannot, without breaking the bladder, press the sides together.

It is customary to say that a vessel is empty when we have poured out
the water which it contained. Having provided two glass vessels full
of water, place each of them in an empty white pan, to receive the over-

Fig. 6 represents the water overflow-
ing, as the glass, with the orifice closed, Fig. 7. The orange has entered the
is pressed down, proving the impene- glass vessel, and the air having passed
trability of air. from the orifice, no water overflows.

flow, then lay an orange upon the surface of the water of one of them,
and being provided with a cylindrical glass, open at one end, with a
hole in the centre of the closed end, place your finger firmly over the
orifice, and endeavour, by inverting the glass over the orange, and
pressing upon the surface of the water, to make it enter the interior
of the glass cylinder ; the resistance of the air will now cause the water
to overflow into the white pan, whilst the orange will not enter. The

BOY'S PLAYBOOK OF SCIENCE.

orange may now be transferred to the other vessel of wa-ter, and on
removing the finger from the orifice of the cylindrical glass, and in-
verting it as before over the orange, the air will rush out and the orange
and water will enter, whilst there will be no overflow as in the preceding
experiment. The comparison of the two is very striking, and at once
teaches the fact desired.

Whilst the vessels of water are still in use, another pretty experiment
may be made with the metal potassium. First throw a small piece of
the metal on the surface of the water, to show that it takes fire on con-
tact with that fluid; then, having provided a gas-jar, fitted with a cap

Fig. 8. Gas-jar with stop-stock closed,
and potassium in ladle ; air prevents the
entrance of the water.

Fig. 9. Gas-jar; stop-cock open ;
the air passes, the water enters, and
the potassium is inflamed.

and stop-cock, and a little spoon screwed into the bottom of the stop-
cock inside the gas-jar, place another piece of potassium in the little
spoon, and, after closing the stop-cock, push the jar into one of the
vessels of water : as before, the impenetrability of the air prevents the
water flowing up to the potassium ; but, on opening the stop-cock, the
air escapes, the water rushes up, and directly it touches the potassium,
combustion ensues.

^ Having sufficiently indicated the nature and meaning of impenetra-
bility, we may proceed to discuss experimentally three other marked
and special qualities of matter viz., inertia, gravity, and weight.

INERTIA, OR PASSIVENESS.

Inertia is a rjower which (according to Sir Isaac Newton) is implanted
in all matter ot resisting any change from a state of rest. It is sometimes
called vis inertia, and is that property possessed by all matter, of re-
maining at rest till set in motion, and vice versa; and it expresses, in
brief terms, resistance to motion or rest.

A pendulum clock wound up and ready to go, does not commence its
movements, until the inertia of the pendulum is overcome, and motion
imparted to it. On the other hand, when seated in a carriage, should
any obstruction cause the horse to stop suddenly, it is only perhaps by
a violent effort, if at all, that we can resist the onward movement of our

Fig. 10. Tin tray, with glass bottom, full of water; candle placed underneath.

bodies. To illustrate inertia, construct a metal tray, about three feet
long, two feet wide, and two inches deep, with a glass bottom, and
arrange it on a framework supported by legs, like a table, and having
filled it with water, let the room be darkened, and then place under the
tank a lighted candle, at a sufficient distance from the glass to prevent
the heat cracking it. If a piece of calico or paper, stretched on a frame-
work, be now held over the water at an angle of about thirty degrees,
all that occurs on the surface of the water will be rendered visible on
such screen. Attention may now be directed to the quiescence, or the
inertia of the water, while the opposite condition of movement and
formation of the waves may be beautifully shown by touching the sur-
face of the water with the finger ; the miniature waves being depicted
on the screen, and continuing their motion till set at rest by striking
against the sides of the tin tray.

BOYS PLAYBOOK OF SCIENCE.

Fig. 11.

Same tray, with calico screen ; showing the waves as they are produced by
touching the surface of the water with the finger.

Should the above experiment be thought too troublesome or expen-
sive to prepare, inertia may be demonstrated by filling a tea-cup or other
convenient vessel with water, and after moving rapidly with it in any
direction, if we stop suddenly, the rigidity of all parts of the cup we
hold brings them simultaneously to a state of rest ; but the mobility of
the liquid particles allows of their continuing in motion in their original
direction, and the liquid is spilled. Thus, carelessness in handing and
spilling a cup of tea (though not to be recommended) serves to illustrate
an important principle. The inertia of bodies in motion is further and
lamentably illustrated by the accidents caused from the sudden stoppage
of a railway train whilst in rapid motion, when heads and knees come in
contact with frightful results. It is more especially demonstrated by
the earth, the moon, and the other planets continuing their motion for
ever in the absence of any friction or resistance to oppose their onward
progress. It is the friction arising from the roughness of the ground,
the resistance of the air, and the force of the earth's attraction, which
puts a stop to bodies set in motion about the surface of the earth.

GRAVITATION.

Inertia represents a passive force, gravitation, an active condition of
matter ; and this latter may truly be termed a force of attraction, because
it acts between masses at sensible or insensible distances : it is illus-
trated by a stone, unsupported, falling to the ground ; by the stone
pressing with force on the earth, and requiring power to raise it from the
ground : indeed, it is commonly reported that it was by an accident
" an apple falling from a tree" that the great Newton was led to reflect
on the universal law of gravitation, and to pronounce upon it in the
following memorable words :

" Every particle of matter in the universe attracts every other particle
of matter with a force or power directly proportional to the quantity oj
matter in each, and decreasing as the squares of the distances which sepa-
rate the particles increase"

These words may appear very obscure to our juvenile readers ; but
when dissected and examined properly, they clearly define the property
of gravitation. For instance, " every particle attracts every other with
a force proportional to the quantity of matter in
each." This statement was verified some years
back by Maskelyne, who, having sought out and
discovered a steep, precipitous rock in the
Schichallion mountains, in Scotland, suspended
from it a metal weight by a cord, and going to
a convenient distance with a telescope, and ob-
serving the weight, he found that it did not
hang perpendicularly, like an ordinary plumb-
line, but was attracted, or impelled, to the sides
of the rock by some kind of attraction, which, of
course, could be no other than that indicated
by Newton as the attraction of gravitation.

This truly wonderful power of attraction per-
vades all masses; and being, as before stated,
proportional to the quantity of matter, if a man
could be transported to the surface of the sun,
he would become about thirty times heavier : he
would be attracted, or impelled, to the sun with
thirty times more gravitating force than on the
surface of the earth, and would weigh about two
tons. Of course, nursing a baby on the sun's
surface would be a very serious affair with our
ordinary strength ; whilst on some of the smaller

planets, such as Ceres and Pallas, we should pro- line, whilst the line "of the
bably gravitate with a force of a few pounds eight ?..

i i j i 1 1 i coursG, witn some t?xn.c >fT e-

only, and with the same muscular power now ration) the attractive power
possessed, we should quite emulate the exploits f t] ? e mass of "
of those domestic little creatures sometimes d ns " tfromt

Pig. 12. The Schichallion
Bocks. The dotted line and

rock

BOY'S PLAYBOOK OP SCIENCE.

called " the industrious fleas," and our jumping would be something
marvellous.

There is no very good lecture-table experiment that will illustrate
gravitation, although attention may be directed to the fact of a piece of
potassium thrown on the surface of water in a plate generally rushing
to the sides, and, as if attracted, attaching itself with great force to the
substance of the pottery or porcelain ; or, if a model ship, or lump of
wood, be allowed to float at rest in a large tank of water, and a number
of light chips of wood or bits of straw be thrown in, they generally col-
lect and remain around the larger floating mass.

A very good idea, however, may be afforded of the universal action of
gravity maintaining all things in their natural position on the earth by

Fig. is.

A. The centre ball, representing the earth's centre of gravity.

w w w w. Four wires fixed into centre ball, and passing through and secured ir. the
hoop, projecting about one foot from the circumference.

B B B B. Two balls a model ship and toy working on the wires like beads, with vul-
canized India-rubber straps attached to them and the circumference of the hoop.

GRAVITATION.

taking a hoop and arranging in and upon it balls, or a model ship, or
other toy, and wires, as depicted in our diagram.

With this simple apparatus we may illustrate the upward, downward,
and sideway movement of bodies from the earth, and the counteraction
by the force of gravitation of any tendency of matter to fall away from
the globe, which is represented in the model by the india-rubber springs
pulling the balls and toys back again to the circumference of the hoop.

The attraction of gravitation decreases (quoting the remainder of
Newton's definition) as the squares of the distances which separate
the particles increase i.e., it obeys the principle called "inverse pro-
portion" viz., the greater the distance, the less gravitating power ; the
less the distance, the greater the power of gravitation. Gravitation is
like the distribution of light and other radiant forces, and may be thus
illustrated.

Fig. 14. Place a lighted candle, marked A, at a certain distance from No. 1, a board one
foot square ; at double the distance the latter will shadow another board, No. 2, four feet
square ; at three times, No. 3, nine feet square ; at four, No. 4, sixteen feet ; and so on.

To make the comparison between the propagation of light and the
attraction of gravitation, we have only to imagine the candle, a, to
represent the point where the force of gravity exists in the highest
degree of intensity ; suppose it to be the sun the great centre of this
power in pur planetary system. A body, as at No. 1, at any given
distance will be attracted (like iron-filings to a magnet) wiih a certain
force ; at twice the distance, the square of two being four, and by in-
verse proportion, the attraction will be four times ( less; at thrice
the distance, nine times less ; at the fourth distance, sixteen times less ;
and so on. "With the assistance of this law, we may calculate,
roughly, the depth of a well, or a precipice, or a column, by ascer-
taining the time occupied in the fall of a stone or other heavy sub-
stance. A falling body descends about 16 feet in one second, 64 feet
in two seconds, 144 feet in three seconds, 256 feet in four seconds,
400 feet in five seconds, 576 feet in six seconds ; the spaces passed over
being as the squares of the times.

Suppose a stone takes three seconds in falling to the surface of the
_water in a well, then 3 X 3 = 9 x 16 = 144 feet would be a rough
estimate of the depth. The calculation will exceed the truth ia con-
sequence of the stone being retarded in its passage by the resistance of
the air.

BOY'S PLAYBOOK OF SCIENCE.

All bodies gravitate equally to the earth : for instance, if an open box,
sav one foot m length, two inches broad, and two inches deep, be pro-
vided with a nicely-fitted bottom, attached by a hinge, a number of
substances, such as wood, cork, marble, iron, lead, copper, may be
arr:;n^cd in a row ; and directly the hand is withdrawn, tne moveable
flap flies open, and if the manipulation with the disengagement of the
trap-door is good, the whole of the substances are seen to proceed to the
earth in a straight line, as shown in our drawing.

Fig. 15.

Fig. 16.

If a heavy substance, like gold, be greatly extended by hammering
and beating into thin leaves, and then dropped from the hand, the re-
sistance of the air becomes very apparent ; and a gold coin and a piece
of gold-leaf would not reach the earth at the same time if allowed to
fall from any given height. This fact is easily displayed by the assis-
tance of a long glass cylindrical vessel placed on the air-pump, with suit-
able apparatus arranged with little stages to carry the different sub-
stances ; upon two of them may be placed a feather and a gold coin, and
on the third, another gold coin and a piece of gold-leaf.

In arranging the experiment, great care ought to be taken that the
little stages are all nicely cleaned, and free from any oil, grease, or other
matter which might cause the feathers or the cold-leaf to cling to the
stages when they are disengaged, by moving the brass stop round that
works in the cottar of leathers. Sometimes these leathers are oiled, and

GRAVITATION.

in that case, when the vacuum is made, the oil, by the pressure, is

squeezed out, and, passing down, may reach the stages and spoil the

experiment, by causing the feathers and gold-
leal to stick to the brass, producing great dis-
appointment, as the illustration, usually called

the "guinea and feather glass experiment"

takes some time to prepare. The air-pump

being in good order, the long glass is first

greased on the lower welt or edge, and then

placed firmly on the air-pump plate. The top

edge, or welt, may now be greased, and the

gold coins, feathers, and gold-leaf arranged in

the drop-apparatus ; this is carefully placed on

the top of the glass, and firmly squeezed down.

The author has always found a tallow candle,

rolled in a sheet of paper (so as to leave about

half the candle exposed), the best grease to

smear the glass
with for air-
pump experi-
ments; if the

weather is cold, Fig. 17.

the caudle may

be placed for a few minutes before an
ordinary fire to soften the tallow. Po-
matum answers perfectly well when the
surfaces of glass and brass are all nicely
ground; but as air-pumps and glasses
by use get scratched and rubbed, the
tallow seems to fill up better all ordi-
nary channels by which air may enter
to spoil a vacuum.

The apparatus being now arranged,
the air is pumped out ; and here, again,
care must be taken not to shake the
gold off the stages. When a proper
vacuum has been obtained, which will
be shown by the pump-gauge, the stop
is withdrawn from one of the stages,
and the gold and feather are seen to
fall simultaneously to the air-pump

Elate. Another stage, with the gold-
;af and coin, may now be detached;
both showing distinctly, that when the
resistance of the air is withdrawn, all
bodies, whether called light or heavy,
gravitate equally to the earth. Then,
Fig. is. the screw at the bottom of the pump-

16 BOY'S PLAYBOOK OF SCIENCE.

barrels being opened, attention may be directed to the whizzing noise
the air makes on entering the vacuum, and when the air is once more
restored to the long glass vessel, the last stage may be allowed to fall ;
and now, the gold coin reaches the pump-plate first, and the feather,
lingering behind, loses (as it were) the race, and touches the plate after
the gold coin ; thus demonstrating clearly the resistance of the air to
falling bodies.

Another, and perhaps less troublesome, mode of showing the same fact,
is to use a long glass tube closed at each end with brass caps cemented
on. One cap should have the largest possible aperture closed by a
brass screw, and the other may fit a small hand-pump.

If a piece of gold and a small feather are placed in the tube, it may
be shown that the former reaches the bottom of the tube first, whilst it
is full of air, and when the air is withdrawn by means of the pump, and
the tube again inverted, both the gold and the feather fall in the same
time.

Fig. 19. A B. Glass tube containing a piece of gold and a feather, which are placed in at
the large aperture A. c. Small hand-pump.

For this reason, all attempts to measure heights or depths by observing
the time occupied by a falling body in reaching the earth must be in-
correct, and can only be rough approximations. An experiment tried at
St. Paul's Cathedral, with a stone, which was allowed to fall from the
cupola, indicated the time occupied in the descent to be four and a half
seconds : now, if we square this time, and multiply by 16, a height of
324 feet is denoted ; whereas the actual height is only 272 feet, and the
difference of 52 fee.t shows how the stone was retarded in its passage
through the air; for, had there been no obstacle, it would have reached
the ground in 4^ths seconds.

The force of gravitation is further demonstrated by the action of the
sun and moon raising the waters of the ocean, and producing the tides ;
and also by the earth and moon, and other planets and satellites, being
prevented from flying from their natural paths or orbits around the sun.
It is also very clearly proved that there must be some kind of attractive
force resident in the earth, or else all moveable things, the water, the
air, the living and dead matters, would fly away from
the surface of the earth in obedience to what is called
" centrifugal force." Our earth is twenty-four hours
in performing one rotation on its axis, which is an ima-
ginary line drawn from pole to pole, and represented
by the wire round which we cause a sphere to rotate.
All objects, therefore, on the earth are moving with
the planet at an enormous velocity ; and this movement
Fig. 20. is called the earth's diurnal, or daily rotation. Now,

CENTEIFUGAL FORCE.

it will be remembered, that mud or other fluid matter flies off, and is
not retained by the circumference of a wheel in motion : when a mop is
trundled, or a dog or sheep, after exposure to rain, shake themselves,
the water is thrown off by what is called centrifugal force (centrum, a
centre, fogio, to fly from).

CHAPTER II.

CENTRIFUGAL FORCE.

THAT power which drives a revolving body from a centre, and it
may be illustrated by turning a closed parasol, or umbrella, rapidly-
round on its centre, the stick being the axis the ribs fly out, and if
there is much friction in the parts, the illustration is more certain by
attaching a bullet to the end of each rib, as shown in our drawing.

Fig. 23.

Fig. 21.

The same fact may be illustrated by a square mahogany rod, say one
inch square and three feet long, with two flaps eighteen inches in length,
hanging bv hinges, and parallel to the sides of the centre rod, which
immediately fly out on the rotation of the long centre piece.

The toy called the centrifugal railway is also a very pretty illustration
of the same fact. A glass of water, or a coin, may be placed in the
little carriage, and although it must be twice hanging perpendicular in a
line with tne earth, the carriage does not tumble away from its ap-
pointed track, and the centrifugal force binds it firmly to tne interior of
the circle round which it revolves.

BOY'S PLAYBOOK OF SCIENCE.

Fig. 23.

Another striking and very simple illustration is to suspend a hemi-
spherical cup by three cords, and having twisted them, by turning round
the cup, it may be filled with water, and directly the hand is withdrawn,
the torsion of the cord causes the cup to rotate, and the water describes
a circle on the floor, flying off at a tangent from the cup, as may be
noticed in the accompanying cut.

Fig. 24

A hoop when trundled would tumble on its side if the force ot gravi-
tation was not overcome by the centrifugal force which imparts to it a
motion in the direction of a tangent (tango, to touch) to a circle. The
same principle applies to the spinning-top^ this toy cannot be made to
stand upon its point until set in rapid motion.

Returning again to the subject of gravitation, we may now consider
it in relation to other and more magnificent examples which we dis-
cover by studying the science of astronomy.

19
CHAPTER III.

THE SCIENCE OF ASTKONOMY.

IN a work of this kind, professedly devoted to a very brief and popular
view of the different scientific subjects, much cannot be said on any
special branch of science ; it will be better, therefore, to take up one
subject in astronomy, and by discussing it in a simple manner, our young
friends may be stimulated to learn more of those glorious truths which
are to be found in the published works of many eminent astronomers,
and especially in that of Mr. Hind, called "The Illustrated London
Astronomy." One of the most interesting subjects is the phenomenon
of the eclipse of the sun; and as 1858 is likely to be long remembered
for its " annular eclipse," we shall devote some pages and illustrations
to this subject.

Eclipses of the sun are of three kinds partial, annular, and total.
Many persons have probably seen large partial eclipses of the sun, and
may possibly suppose that a total eclipse is merely an intensified form of
a partial one ; but astronomers assert that no degree of partial eclipse,
even when the very smallest portion of the sun remains visible, gives
the slightest idea of a total one, either in the solemnity and overpower-
ing influence of the spectacle, or the curious appearances which accom-
pany it.

The late Mr. Baily said of an eclipse (usually called that of Thales),
which caused the suspension of a battle between the Lydians and Medes,
that only a total eclipse could have produced the effect ascribed to it.
Even educated astronomers, when viewing with the naked eye the sun
nearly obscured by the moon in an annular eclipse, could not tell that
any part of the sun was hidden, and this was remarkably verified in the
annular eclipse of the 15th March of this year.

During the continuance of a total eclipse of the sun, we are permitted
a hasty glance at some of those secrets of Nature which are not revealed
at any other time glories that hold in tremulous amazement even
veteran explorers of the heavens and its starry worlds.

The general meaning of an eclipse may be shown very nicely by light-
ing a common oil, or oxy-hydrogen lantern in a darkened room, and
throwing the rays which proceed from it on a three-feet globe. The
lantern may be called the sun, and, of course, it is understood that cor-
rect comparative sizes are not attempted in this arrangement ; if it were
so, the globe representing the earth would have to be a mere speck, for
if we make the model of the sun in proportion to a three-feet globe, no
ordinary lecture hall would contain it. This being premised, attention
is directed to the lantern, which, like the sun, is self-luminous, and is
giving out its own rays ; these fall upon the globe we have designated
the earth, and illuminate one -half, whilst the other is shrouded in dark-
ness, reminding us of the opacity of the earth, and teaching, in a familiar

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^.-"-"A ? .". "-.-:. 1 - ^.^-l..":" ? ' 5 --' ' r "

T-:

-J?-.l*

to he

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BOY'S PLAYBOOK OF SCIENCE.

With respect to' an annular eclipse, it must be remembered, that the
'paths of all bodies revolving round others are elliptical ; i.e., they take
place in the form of an ellipse, which is a figure easily demonstrated ;
and is, in fact, one of the conic sections.

If a slice be taken off a cone, parallel with the base, we have a circle
thus

Fig. 29.

If it be cut obliquely, or slanting, we see at once the figure spoken of,
and have the ellipse as shown in this picture.

Fig. 30.

Now, the ellipse has two points within it, called " the foci," and these
are easily indicated by drawing an ellipse on a diagram-board, in which
two nails have been placedina straight line, and about twelve inches apart.
Having tied a string so as to make a loop, or endless cord, a circle
may first be drawn by putting the cord round one of the nails, and
holding a piece of chalk in the loop of the string, it may be extended
to its full distance, and a circle described ; here a figure is produced
round one point, and to show the difference between a circle and an
ellipse, the endless cord is now placed on the two nails, and the chalk
being carried round inside the string, no longer produces the circle, but
that familiar form called the oval. As a gardener would say, an oval
has been struck ; and the two points round which it has been described,

THE SCIENCE OP ASTRONOMY.

Fig. 31.

are called fheftci. This explanation enables us to understand the next
diagram, showing the motion of the earth round the sun ; the latter
being placed in one of the foci of a very moderate ellipse, and the
various points of the earth's orbit designated by the little round globes
marked A, B, c, D, where it is evident that the earth is nearer to the sun
at B than at D. In this diagram the ellipse is exaggerated, as it ought,
in fact, to be very nearly a circle.

Bf)l-

Fig. 32.

We are about three millions of miles nearer to the sun in the winter
than we are in the summer ; but from the more oblique or slanting
direction of the rays of the sun during the winter season, we do not
derive any increased heat from the greater proximity. The sun, there-
fore, apparently varies in size ; but this seeming difference is so trifling
that it is of no importance in the discussion : and here we may ask, why

BOY'S PLAYBOOK OF SCIENCE.

does the earth move round the sun ? Because it is impelled by two
forces, one of which has already been fully explained, and is called the
centrifugal power, and the other, although termed the centripetal force,
is only another name for the " attraction of gravitation."

cr"

Fig. 33.

To show their mutual relations, let us suppose that, at the creation of
the universe, the earth, marked A, was hurled from the hand of its
Maker ; according to the law of inertia, it would continue in a straight
line, A c, for ever through space, provided it met with no resistance or
obstruction. Let us now suppose the earth to have arrived at the
point B, and to come within the sphere of the attraction of the sun s ;

Fig. 34.

THE SCIENCE OF ASTRONOMY.

here we have at once contending forces acting at right angles to eact
other ; either the earth must continue in its original direction, A c, or
fall gradually to the sun. But, mark the beauty and harmony of the
arrangement : like a billiard-ball, struck with equal force at two points
at right angles to each other, it takes the mean between the two, or
what is termed the diagonal of the parallelogram (as shown in our
drawing of a billiard-table), and passes in the direction of the curved
line, B D ; having reached D, it is again ready to fly off at a tangent ;
the centrifugal force would carry it to
E, but again the gravitating force con-
trols the centripetal, and the earth
pursues its elliptical path, or orbit, till
the Almighty Author who bade it move
shall please to reverse the command.

The mutual relations of the centri-
petal and centrifugal forces may be
illustrated by suspending a tin cylin-
drical vessel by two strings, and
having filled it with water, the vessel
may be swung round without spilling
a single drop ; of course, the movement
must be commenced carefully, by mak-
ing it oscillate like a pendulum.

The cord which binds it to the finger
may be compared to the centripetal
force, whilst the centrifugal power is
illustrated by the water pressing against the sides and remaining in the
vessel. Upon the like principles the moon revolves about the earth,

but her orbit is more ellip-
tical than that of the earth
around the sun ; and it is
evident from our diagram
that the moon is much fur-
ther from the earth at A
than at B. As a natural
consequence, the moon ap-
pears sometimes a little
larger and sometimes
smaller than the sun ; the
apparent mean diameter of
the latter being thirty-two
minutes, whilst the moon's

Fig. 36. apparent diameter varies

from twenty-nine and a

half to thirty-three and a half minutes. Now, if the moon passes exactly
between us and the sun when she is apparently largest, then a total eclipse
takes place ; whereas, if she glides between the sun and ourselves when
smallest i.e., when furthest off from the earth then she is not suffi-

Fig. 35.

26 BOY'S PLAYBOOK OF SCIENCE.

ciently large to cover the sun entirely, but a ring of sunlight remains
visible around her, and what is called an annular eclipse of the sun
occurs. This fact may be shown in an effective manner by placing the
oxy-hydrogen lantern before a sheet, or other white surface, and throw-

Fig. 37.

ing a bright circle of light upon it, which may be called the sun ; then,
if a round disc of wood be passed between the lantern and the sheet, at
a certain distance from the nozzle of the lantern, all the light is cut off,
the circle of light is no longer apparent, and we have a resemblance to
a total eclipse.

By taking the round disc of wood further from the lantern, and re-
peating the experiment, it will be found that the whole circle of light
is not obscured, but a ring of light appears around the dark centre, cor-
responding with the phenomenon called the annular (ring-shaped)
eclipse.

If a bullet be placed very near to one eye whilst the other remains
closed, a large target may be wholly shut out from vision; but if the
bullet be adjusted at a greater distance from the eve, then the centre
only will be obscured, and the outer edge or ring of the target remains
visible.

When the advancing edge, or first limb, as it is termed, of the moon
approaches very near to the second limb of the sun, the two are joined
together for a time by alternations of black and white points, called
Bailv's beads.

This phenomenon is supposed to be caused partly by the uneven and
mountainous edge of the moon, and partly by that inevitable fault of
telescopes, and of the nervous system of the eye, which tends to enlarge
the images of luminous objects, producing what is called irradiation. It
is exceedingly interesting to know that, although the clouds obscured
the annular eclipse of 1858, in many parts of England, we are yet

THE SCIENCE OF ASTRONOMY.

Fig. 38.

left the recorded observations of one fortunate astronomer, Mr. John
Yeats, who states that

" All the phenomena of an annular eclipse were clearly and beautifully
visible on the Fotheringay- Castle-mound, which is a locality easily iden-
tified. Baily's beads were perfectly plain on the completion of the
annulm, which occurrence took place, according to my observation, at
about seventy seconds after 1 o'clock ; it lasted about eighty seconds.
The 'beads/ like drops of water, appeared on the upper and under sides
of the moon, occupying fully three-fourths of her circumference.

" Prior to this, the upper edge of the moon seemed dark and rough,
and there were no other changes of colour. At 12'4<3, the cusps, for a
few moments, bore a very black aspect.

" There was nothing like intense darkness during the eclipse, and less
gloom than during a thunderstorm. Bystanders prognosticated rain;
but it was the shadow of a rapidly-declimn; day. At 12 o'clock, a lady
living on the farm suddenly exclaimed, 'The cows are coming home
to be milked!' and they came, all but one; that followed, however,
within the hour. Cocks crowed, birds flew low or fluttered about
uneasily, but every object far and near was well defined to the eye.

".A singular broadway of light stretched north and south for upwards
of a quarter of an hour ; from about 12'54 to I'lO P.M.

If the annular eclipse of the sun be a matter for wonderment, the total
eclipse of the same is much more surprising ; no other expression than
that of awfully grand, can give an idea of the effects of totality, and of
the suddenness with which it obscures the light of heaven. The dark-
ness, it is said, comes dropping down like a mantle, and as the moment
of full obscuration approaches, people's countenances become livid, the
horizon is indistinct and sometimes invisible, and there is a general
appearance of horror on all sides. These are not simply the inventions

28 BOY'S PLAYBOOK OF SCIENCE.

of active human imaginations, for they produce equal, if not greater
effects, upon the brute creation. M. Arago quotes an instance of a half-
starved dx)g, who was voraciously devouring some food, but dropped it
the instant the darkness came on. A swarm of ants, busily engaged,
stopped when the darkness commenced, and remained motionless till
the fight reappeared. A herd of oxen collected themselves into a circle
and stood still, with their horns outward, as if to resist a common
enemy ; certain plants, such as the convolvulus and silk-tree acacia,
closed their leaves. The latter statement was corroborated during the
annular eclipse of the 15th of March, 1858, by Mr. E. S. Lane, who
states, that crocuses at the Observatory, Beeston, had their blossoms
expanded before the eclipse ; they commenced closing, and were quite
shut at about one minute previous to the greatest darkness ; and the
flowers opened partially about twenty minutes afterwards. A " total
eclipse" of the sun has always impressed the human mind with terror
and wonder in every age : it was always supposed to be the forerunner
of evil ; and not only is the mind powerfully impressed, as darkness
gradually shuts out the face of the sun, but at the moment of totality,
a magnificent corona, or glory of light, is visible, and prominences, or
flames, as they are often termed, make their appearance at different-
points round the circle of the dark mass. This glory does not flash
suddenly on the eye; but commencing at the first limb of the sun,
passes quickly from one limb to the' other. Our illustration shows

Fig. 39.

"the corona" and the "rose-coloured prominences," whose nature we
shall next endeavour to explain. Professor Airy describes the change
from the last narrow crescent of light to the entire dark moon, sur-
rounded by a ring of faint light, as most curious, striking, and magical
in effect. The progress of the formation of the corona was seen dis-

THE SCIENCE OF ASTKONOMY. 29

tinctly. It commenced on the side of the moon opposite to that at
which the sun disappeared, and in the general decay and disease which
seemed to oppress all nature, the moon and the corona appeared almost
like a local sore in that part of the sky, and in some places were seen
double. Its texture appeared as if fibrous, or composed of entangled
threads ; in other places brushes, or feathers of light proceeded from
it, and one estimate calculated the light at about one-seventh part of a
full moon light. The question, whether the corona is concentric with
the sun and moon, was specially mooted by M. Arago, and Professor
Baden Powell has produced such excellent imitations of the " corona"
by making opaque bodies occult, or conceal, very bright points, that it
cannot be considered as material or real, although it ought to be re-
membered that the best theory of the zodiacal light represents it to be
a nebulous mass, increasing in density towards the sun, and yet no
portion of this nebulous mass was seen during the totality. But by far
the most remarkable of all the appearances connected with a " total
eclipse" are the rose-coloured prominences, mountains, or flames, pro-
jecting from the circumference of the moon to the inner ring of the
corona; and, although they had been observed by Vaserius (a Swedish
astronomer) in 1733, they took the modern astronomers entirely by
surprise in 1842, and they were not prepared with instruments to ascer-
tain the nature of these strange and almost portentous forms. In 1851,
however, great preparations were made to throw further light on the
subject. Professor Airy went to make his observations, and he says,
"That the suddenness of the darkness in 1851 appeared much more
striking than in 1842, and the forms of the rose-coloured mountains were
most curious. One reminded him of a boomerang (that curious weapon
thrown so skilfully by the aborigines of Australia) ; this same figure has
been spoken of by others as resembling a Turkish scimitar, strongly
coloured with rose-red at the borders, but paler in the centre. Another
form was a pale-white semicircle based on the moon's limbs ; a third
figure was a red detached cloud, or balloon, of nearly circular form,
separated from the moon by nearly its own breadth ; a fourth appeared
like a small triangle, or conical red mountain, perhaps a little white in
the interior ;" and the Professor proceeds to say, " I employed myself
in an attempt to draw roughly the figures, and it was impossible, after
witnessing the increase in height of some, and the disappearance of
another, and the arrival of new forms, not to feel convinced that the
phenomena belonged to the sun, and not to the moon."

Still the question remains unanswered, what are these "rose-
coloured prominences ?" If they belong to the sun, and are moun-
tains in that luminary, they must be some thirty or forty thousand miles
in height.

M. Faye has formally propounded the theory, that they are caused by
refraction, or a kind of mirage, or the distortion of objects caused by
heated air. This phenomenon is not peculiar to any country, though
most frequently observed near the margin of lakes and rivers, and on
hot sandy plains. M. Monge, who accompanied Buonaparte in his

30 BOY'S PLAYBOOK OF SCIENCE.

expedition to Egypt, witnessed a remarkable example between Alex-
andria and Cairo, where, in all directions, green islands appeared sur-
rounded by extensive lakes of pure, transparent water. M. Monge
states that " Nothing could be conceived more lovely or picturesque
than the landscape. In the tranquil surface of the lake, the trees and
houses with which the islands are covered were strongly reflected with
vivid and varied hues, and the party hastened forward to enjoy the
refreshment apparently proffered them ; but when they arrived, the lake,
on whose bosom the images had floated the trees, amongst whose
foliage they arose, and the people who stood on the shore, as if in-
viting their approach, had all vanished, and nothing remained but the
uniform and irksome desert of sand and sky, with a few naked and
ragged Arabs."

If M. Monge and his party had not been undeceived, by actually
going to the spot, they would, one and all, have been firmly convinced
that these visionary trees, lakes, and buildings had a real existence.
This kind of mirage is known in Persia and Arabia by the name of
" serab" or miraculous water, and in the western districts of India by
that of " scheram." This illusion is the effect of unusual refraction, and
M. Faye attempts to account for the rose-coloured mountains by some-
thing of a similar nature.

It is right, however, to mention, that learned astronomers do not con-
sider this theory of any value.

Lieutenant Patterson, one of the observers of the eclipse of 1851,
says, that " It is very remarkable that the flames or prominences cor-
respond exactly (at least as far as he could judge) with the spots on the
sun's surface." Taking this statement with that of M. Faye, it may
be assumed, as a new idea, and nothing more, that these prominences
are, after all, mere aerial pictures of these openings in the sun's atmo-
sphere, or what are called " sun spots." In the " Edinburgh Philoso-
phical Journal," it is said, that although it has lately been shown in the
Edinburgh Observatory that it is possible to produce, by certain optical
experiments, red flames on the sun's limb of precisely the rose-coloured
tint described, yet, on weighing the whole of the evidence, there does
seem a great preponderance in favour of the eclipse flames being real
appendages of the sun, and in that case they must be masses of such
vast size as to play no unimportant part in the economy of that stupen-
dous orb.

During the last eclipse great disappointment was felt that the dark-
ness was so insignificant, although, when we consider the enormous
light-giving power of the sun, and know that it was not wholly
obscured, we could hardly have expected any other result. There can
be no doubt that a decided change in the amount of light is only to
be observed during a total eclipse of the sun, one of wnich occurred
on the 7th of September, 1858 ; but, unfortunately, it was only visible
in South America ; we must therefore content ourselves with the de-
scriptions of those astronomers who can be fully relied on. From
the graphic account given by Professor Piazzi Smyth, the astronomer-

THE SCIENCE OP ASTRONOMY. 31

royal for Scotland, of a total eclipse as seen by him on the western
coast of Norway, we may form some notion of the imposing appearance
of the surrounding country wlien obscured during the occurrence of this
rare astronomical phenomenon.

The Professor remarks, " To understand the scene more fully, the
reader must fancy himself on a small, rocky island on a mountainous
coast, the weather calm, and the sky at the beginning of the eclipse
seven-tenths covered with thin and bright cirro-strati clouds. As the
eclipse approaches, the clouds gradually darken, the rays of the sun are
no longer able to penetrate them through and through, and drench
them with living light as before, but they become darker than the sky
against which they are seen. The air becomes sensibly colder, the clouds
still darker, and the whole atmosphere murkier.

" From moment to moment as the totality approaches, the cold and
darkness advance apace ; and there is something peculiarly and terribly
convincing in the two different senses, so entirely coinciding in their
indications of an unprecedented fact being in course of accomplishment.
Suddenly, and apparently without any warning (so immensely greater
were its effects tnan those of anything else which had occurred), the
totality supervenes, and darkness comes down. Then came into view
lurid lights and forms, as on the extinction of candles. This was the
most striking point of the whole phenomenon, and made the Norse
peasants about us flee with precipitation, and hide themselves for their
lives.

" Darkness reigned everywhere in heaven and earth, except where,
along the north-eastern horizon, a narrow strip of unclouded sky pre-
sented a low burning tone of colour, and where some distant snow-
covered mountains, beyond the range of the moon's shadow, reflected
the faint mono-chromatic light of the partially eclipsed sun, and exhi-
bited all the detail of their structure, all the light, and shade, and
markings of their precipitous sides with an apparently supernatural
distinctness. After a little time, the eyes seemed to get accustomed to
the darkness, and the looming forms of objects close by could be dis-
cerned, all of them exhibiting a dull-green hue ; seeming to have exhaled
their natural colour, and to have taken this particular one, merely by
force of the red colour in the north.

"Life and animation seemed, indeed, to have now departed from
everything around, and we could hardly but fear, against our reason,
that if such a state of things was to last much longer, some dreadful
calamity must happen to us all ; while the lurid horizon, northward,
appeared so like the gleams of departing light in some of the grandest
paintings by Danby and Martin, tnat we could not but believe, in spite
of the alleged extravagances of these artists, that Nature had opened
up to the constant contemplation of their mind's -eye some of those
magnificent revelations of power and glory which others can only get a
glimpse of on occasions such as these."

It can be easily imagined, that under such peculiar and awful circum-
stances, the careful observation of these effects must be somewhat dif-

32 BOY'S PLAYBOOK OP SCIENCE.

ficult, and the only wonder is that the astronomical observations are
conducted with any certainty at all.

In the eclipse of 1842, it was not only the vivacious Frenchman who
was carried away in the impulse of the moment, and had afterwards to
plead that " he was no more than a man" as an excuse for his unfulfilled
part in the observations, but the same was the case with the grave
Englishman and the more stolid German. In 1851, much the same
failure in the observations occurred ; and on some person asking a worthy
American, who had come with his instruments from the other side of
the world expressly to observe the eclipse, what he had succeeded in
doing ? he merely answered, with much quiet impressiveness, " That if
it was to be observed over again, he hoped he would be able to do some-
thing ', but that^ as it was, he had done nothing : it had been too much
for him" This is not quite so bad as the fashionable lady who
Jbad been invited to look at an eclipse of the sun through a grand
telescope, but arriving too late, inquired whether " it could not be shown
over again"

With this brief glance at the science of astronomy, we once more
return to the term "gravity," which will introduce to us some new
and interesting facts, under the head of what is called " centre of
gravity."

CHAPTER IV.

CENTRE OP GRAVITY.

That point about which all the parts of a body do, in any situation,
exactly balance each other.

THE discovery of this fact is due to Archimedes, and it is a point in
every solid body (whatever the form may be) in which the forces of
gravity may be considered as united. In our globe, which is a sphere,
or rather an oblate spheroid, the centre of gravity will be the centre.
Thus, if a plummet be suspended on the surface of the earth, it points
directly to the centre of gravity, and, consequently, two plummet-lines
suspended side by side cannot, strictly speaking, be parallel to each
other.

If it were possible to bore or dig a gallery through the whole substance
of the earth from pole to pole, and then to allow a stone or the fabled
Mahomet's coffin to fall through it, the momentum i.e., the force of the
moving body, would carry it beyond the centre of gravity. This force, how-
ever, being exhausted, there would be a retrograde movement, and after
many oscillations it would gradually come to rest, and then, unsupported
by anything material, it would be suspended by the force of gravitation, and
now enter into and take part in the general attracting force; and being
equally attracted on every side, the stone or coffin must be totally without
weight. Momentum is prettily illustrated by a series of inclined planes

THE CENTRE OF GRAVITY.

Fig. 40. p. The centre. ABODE. Plummet-lines, all pointing to the centre, and
therefore diverging from each other.

cut in mahogany, with a grooved channel at the top, in imitation of the
famous Russian ice mountains : and if a marble is allowed to run down

Fig. 41. P r P. Inclined planes, gradually decreasing in height, cut out of inch mahogany,
with a groove at the top to carry an ordinary marble. BBS. Different positions of the
marble, which starts from B A.

BOY'S PLAYBOOK OF SCIENCE.

the first incline, the momentum will carry it up the second, from whicn
it will again descend and pass up and down the third and last miniature
mountain.

In a sphere of uniform density, the centre of gravity is easily dis-
covered, but not so in an irregular mass ; and here, perhaps, an explana-
tion of terms may not be altogether unacceptable.

Mass, is a term applied to solids, such as a mass of lead or stone.
Bulk, to liquids, such as a bulk of water or oil.
Volume, to gases, such as a volume of air or oxygen.
To find the centre of gravity of any mass, as, for example, an ordinary
school-slate, we must first of all suspend it from any part of the frame ;
then allow a plumb-line to drop from the point of suspension, and mark

its direction on the slate. Again,
suspend the slate at various other
points, always marking the line of
direction of the plummet, and at
the point where the lines intersect
each other, there will be the centre
of gravity.

If the slate be now placed (as
shown in Fig. 43) on a blunt

Fig. 42. A B D. The three points of sus-
pension, c, The point of intersection, and,
therefore, the centre of gravity, p, The line
of plummet.

Fig. 43.,

wooden point at the spot where the
lines cross each other, it will be
found to balance exactly, and this
place is called the centre of gravity >
oeinff the point with which all other
particles of the body would move with parallel and equable motion during
its fall. The equilibrium of bodies is therefore much affected by the
position of the centre of gravity. Thus, if we cut out an elliptical figure
from a board one inch in thickness, and rest it on a flat surface by one
of its edges (as at No. 1, fig. 44), this point of contact is called the point
of support, and the centre of gravity is immediately above it.

In this case, the body is in a state of secure equilibrium, for any
motion on either side will cause the centre of gravity to ascend in these
directions, and an oscillation will ensue. But if we place it upon the
smaller end, as shown at No. 2 (fig. 44), the position will be one of

THE CENTRE OF GRAVITY.

equilibrium, but not stable or secure; although the centre of gravity
is directly above the point of support, the slightest touch will displace

N92

Fig. 44. The point of support, o, The centre of gravity.

the oval and cause its overthrow. The famous story of Columbus and
the egg suggests a capital illustration of this fact ; and there are two
modes in which the egg may be poised on either of the ends.

The one usually attributed to the great discoverer, is that of scraping
or slightly breaking away a little of the shell, so as to flatten one of the
ends, thus

Fig. 45. A. Represents the egg in its natural state, and, therefore, in unstable equilibrium ;
B, another egg, with the surface, s, flattened, by which the centre of gravity is lowered, and
if not disturbed beyond the extent of the point of support the equilibrium is stable.

The most philosophical mode of making the egg stand on its end and
without disturbing the exterior shell is to alter the position of the yolk,
which has a greater density than the white, and is situated about the
centre. If the egg is now shaken so as to break the membrane enclosing
the yolk, and thus allow it to sink to the bottom of the smaller end, the
centre of gravity is lowered; there is a greater proportion of weight.

BOY'S PLAYBOOK OF SCIENCE.

IM-2

concentrated in the small end, and the egg stands erect, as depicted at

fig. 46.

It is this variable position of the centre of gravity in ivory balls (one

part of which may be more
dense than another) that so
frequently annoys even the
best billiard-players ; and on
this account a ball will de-
viate from the line in which
it is impelled, not from any
fault of the player, but in
consequence of the ivory
ball being of unequal den-
sity, and, therefore, not hav-
ing the centre correspond-
ing with the centre of gra-
vity. A go o d billiard-player
should, therefore, always try

i I

No.2c. anto* of gravity, much lowered. *. The the ball before he engages
yolk at the bottom of the egg. to play for any large sum.

The toy called the " tombola" reminds us of the egg-experiment, as
there is usually a lump of lead inserted in the lower part of the hemi-

N'-l

Fig. 47 No. 1. c. Centre of gravity in the lowest ]

No. 2. c. Centre of gravity raised as the figure is inclined on either side, but falling
again into the lowest place as the figure gradually conies to rest.

sphere, and when the toy is pushed down it rapidly assumes the upright
position because the centre of gravity is not in the lowest place to which
it can descend ; the latter position being only attained when the figure
is upright.

There is a popular paradox in mechanics viz., "a body haying a
tendency to fall by its own weight, may be prevented from falling by
adding to it a weight on the same side on which it tends to fall," and
the paradox is demonstrated by another well-known child's toy as de-
picted in the next cut.

THE CENTRE OF GRAVITY.

Fig. 48. The line of direction falling beyond the base; the bent wire and lead weight
throwing the centre of gravity under the table and near the leaden weight ; the hind legs
become the point of support, and the toy is perfectly balanced.

After what has been explained regarding the improvement of the
stability of the egg by lowering the situation of the centre of gravity, it
may at first appear singular that a stick loaded with a weight at its
upper extremity can be oalanced perpendicularly with greater ease and
precision than when the weight is lower down and nearer the hand ;
and that a sword can be balanced best when the hilt is uppermost ;

N'-l

N'-2

Fig. 49. No. 1. Sword balanced on handle : the arc from c to D is very small, and if the

centre, c, falls out of the line of direction it is not easily restored to the upright position.

No 2. Sword balanced on the point : the arc from c to D much larger, and therefore the

sword is more easily balanced.

BOYS PLAYBOOK OF SCIENCE.

but this is easily explained when it is understood that with the
handle downwards a much smaller arc is described as it falls than when
reversed, so that in the former case the balancer has not time to re-
adjust the centre, whilst in the latter position the arc described is so
large that before the sword falls the centre of gravity may be restored
within the line of direction of the base.

Por the same reason, a cliild tripping against a stone will fall
quickly; whereas, a man can recover himself; this fact can be very
nicely shown by fixing two square pieces if mahogany of different

Fig. 50. No. 1. The two pieces of mahogany, carved to represent a man and a boy. one
being 10 and the other 5 inches long, attached to board by hinges at H H.

N?2

IfJlW '' '

Fig. 51. No. 2. The board pushed forward, striking against a nail, when the
short piece falls first, and the long one second.

lengths, by hinges on a flat base or board, then if the board be pushed
rapidly forward and struck against a lead weight or a nail put in the

THE CENTRE OP GRAVITY.

table, tlie short piece is seen to fall first and the long one afterwards ;
the difference of time occupied in the fall of each piece of wood (which
may be carved to represent the human figure) being clearly denoted by
the sounds produced as they strike the board.

Boat-accidents frequently arise in consequence of ignorance on the
subject of the centre of gravity, and when persons are alarmed whilst
sitting in la boat, they generally rise suddenly, raise the centre of gravity,
which falling, by the oscillation of the frail bark, outside the line of direc-
tion of the base, cannot be restored, and the boat is upset ; if the boat were
fixed by the keel, raising the centre of gravity would be of little con-
sequence, but as the boat is perfectly free to move and roll to one side
or the other, the elevation of the centre of gravity is fatal, and it
operates just as the removal of the lead would do, if changed from the
base to the head of the " tombola" toj.

A very striking experiment, exhibiting the danger of rising in a boat,
maybe shown by the following model, as depicted at Nos. 1 and 2, figs.
52 and 53.

Fig. 52. No. 1. Sections of a toy-boat floating in water. B B B. Three brass wires placed
at regular distances and screwed into the bottom of the boat, with cuts or slits at the top
so that when the leaden bullets, ILL, which are perforated and slide upon them like
beads, are raised to the top, they are retained by the brass cuts springing out ; when the

bullets are at the bottom of the lines they represent persons sitting in a boat, as shown
in the lower cuts, and the centre of gravity will be wit" "

be within the vessel.

We thus perceive that the stability of a body placed on a base depends
upon the position of the line of direction and tne height of the centre
of gravity.

Security results when the line of direction falls within the base. In-
stability when just at the edge. Incapability of standing when falling
without the base.

BOY'S PLAYBOOK OF SCIENCE.
N2Z

Pig. 53. No. 2. The leaden bullets raised to the top now show the result of persons sud-
denly rising, when the boat immediately turns over, and either sinks or floats on the
surface with the keel upwards.

The leaning-tower of Pisa is one hundred and eighty-two feet in
height, and is swayed thirteen and a half feet from the perpendicular,

Pig. 54. P. Board cut and painted to represent the leaning-tower of Pisa. o. The centre
of gravity and plummet-line suspended from it. H. The hinge which attaches it to the
base board, i. The string, sufficiently long to unwind and allow the plummet to hang out-
side the base, so that, when cut, the model falls in the direction of the arrow.

but jet remains perfectly firm and secure, as the line of direction falls
considerably within the base. If it was of a greater altitude it could
no longer stand, because the centre of gravity would be so elevated
that the line of direction would fall outside the base. This fact may
be illustrated by taking a board several feet in length, and having cut

THE CENTRE OF GRAVITY.

it out to represent the architecture of the leaning-tower of Pisa, it may
then be painted in distemper, and fixed at the right angle with a hinge
to another board representing the ground, whilst a plumb-line may be
dropped from the centre of gravity ; and it may be shown that as long
as the plummet falls within the base, the tower is safe ; but directly the
model tower is brought a little further forward by a wedge so that the
plummet hangs outside, then, on removing the support, which may be a
piece of string to be cut at the right moment, the model falls, and the
fact is at once comprehended.

The leaning-towers of Bologna are likewise celebrated for their great
inclination ; so also (in England) is the hanging-tower, or, more cor-
rectly, the massive wall which has formed part of a tower at Bridge-
north, Salop ; it deviates from the perpendicular, but the centre of
gravity and the line of direction fall within the base, and it remains
secure ; indeed, so little fears are entertained of its tumbling down, that
a stable has been erected beneath it.

One of the most curious paradoxes is displayed in the ascent of a
billiard-ball from the thin to the thick ends of two billiard-cues placed

is a---0

Fig. 55. No. 1. Two billiard-cues arranged for the experiment and fixed to a board : the
ball is rolling up.

No. 2. Sections showing that the centre of gravity, c, is higher at A than at B, which
represents the thick end of the cues; it therefore, in effect, rolls down hill.

at an angle, as in our drawing above ; here the centre of gravity is
raised at starting, and the ball moves in consequence of its actually
falling from the high to the low level.

Much of the stability of a body depends on the height through which
the centre of gravity must be elevated before the body can De over-
thrown. The greater this height, the greater will be the immovability
of the mass. One of the grandest examples of this fact is shown in
the ancient Pyramids ; and whilst gigantic palaces, with vast columns,

BOY S PLAYBOOK OF SCIENCE.

and aU 4 the solid grandeur belonging to Egyptian architecture, have
succumbed to time and lie more or less prostrate upon the earth, the

Fig. 56. c. Centre of gravity, which must be raised to D before it can be overthrown.

Pyramids, in their simple form and solidity, remain almost as they were
built, and it mil be noticed, in the accompanying sketch, how difficult,
if not impossible, it would be to attempt to overthrow bodily one of these
great monuments of ancient times.

The principles already explained are directly applicable to the con-
struction or secure loading of vehicles ; and in proportion as the centre
of gravity is elevated above the point of support (that is, the wheels),
so is the insecurity of the carriage increased, and the contrary takes
place if the centre of gravity is lowered. Again, if a waggon be loaded

No.l.

No. 2.

Fig. 57. No. 1. The centre of gravity is near the ground, and falls within the wheels.
No. 2. The centre of gravity is much elevated, and the line of direction is outside the wh0els

THE CENTRE OP GKAVITY. 43

with a very heavy substance which does not occupy much space, such
as iron, lead, or copper, or bricks, it will be in much less danger of an
overthrow than if it carries an equal weight of a lighter body, such as
pockets of horjs, or bags of wool or bales of rags.

In the one instance, the centre of gravity is near the ground, and falls
well within the base, as at No. 1, fig. 57. In the other, the centre of gravity
is considerably elevated above the ground, and having met with an ob-
struction which has raised one side higher than the other, the line
of direction has fallen outside the wheels, and the waggon is over-
turning as at No. 2.

The various postures of the human body may be regarded as so many
experiments upon the position of the centre of gravity which we are
every moment unconsciously performing.

To maintain an erect position, a man must so place his body as to
cause the line of direction of his weight to fall within the base formed
by his feet.

The more the toes are turned outwards, the more contracted will be
the base, and the body will be more liable to fall backwards or forwards ;
and the closer the feet are drawn together, the more likely is the body
to fall on either side. The acrobats, and so-called "India-Rubber

Fig. 58.

Brothers," dancing dogs, &c., unconsciously acquire the habit of accu-
rately balancing themselves in all kinds of strange positions ; but as
these accomplishments are not to be recommended to young people,
some other marvels (such as balancing a pail of water on a stick laid
upon a table) may be adduced, as illustrated in fig. 59.

Let A B represent an ordinary table, upon which place a broomstick,
c D, so that one-half shall lay upon the table and the other extend from

BOYS PLAYBOOK OP SCIENCE.

it ; f lace over the stick the handle of an empty pail (which may possibly
require to be elongated for the experiment) so that the handle touches
or falls into a notch at H ; and in order to bring the pail well under the

Fig. 59.

table, another stick is placed in the notch E, and is arranged in the
line G P E, one end resting at G and the other at E. Having made these
preparations, the pail may now be filled with water ; and although it
appears to be a most marvellous result, to see the pail apparently
balanced on the end of a stick which may easily tilt up, the principles
already explained will enable the observer to understand that the centre
of gravity of the pail falls within the line of direction shown by the
dotted line ; and it amounts in effect to nothing more than carrying a pail
on the centre of a stick, one end of which is supported at E, and the
other^ through the medium of the table, AB.

This illustration may be modified by using a heavy weight, rope, and
stick, as shown in our sketch below.

Fig. 60.

Before we dismiss this subject it is advisable to explain a term re-
ferring to a very useful truth, called the centre of percussion ; a know-
ledge of which, gained instinctively or otherwise, enables the workman
to wield his tools with increased power, and gives greater force to the
cut of the swordsman, so that, with some physical strength, he may
perform the feat of cutting a sheep in half, cleaving a bar of lead, or

THE CENTRE OF GRAVITY.

neatljr dividing, a la Saladin, in ancient Saracen fashion, a silk hand-
kerchief floating in the air. There is a feat, however, which does not
require any very great strength, but is sufficiently startling to excite
much surprise and some inquiry viz., the one of cutting in half a broom-
stick supported at the ends on tumblers of water without spilling the
water or cracking or otherwise damaging the glass supports.

Fig. 61.

These and other feats are partly explained by reference to time : the
force is so quickly applied and expended on the centre of the stick that
it is not communicated to the supports ; just as a bullet from a pistol
may be sent through a pane of glass without shattering the whole square,
but making a clean hole through it, or a candle may be sent through a
plank, or a cannon-ball pass through a half opened door without causing
it to move on its hinges. But the success of the several feats depends
in a great measure on the attention that is paid to the delivery of the
blows at the centre of percussion of the weapon; this is a point in a
moving body where the percussion is the greatest, and about which the
impetus or force of all parts is balanced on every side. It may be better
understood by reference to our drawing below. Applying this principle
to a model sword made of wood, cut in half in the centre of the blade,
and then united with an elbow -joint, the handle being fixed to a board
by a wire passed through it and the two upright pieces of wood, the
fact is at once apparent, and is well shown in JNOS. 1, 2, 3, fig. 62.

BOY'S PLAYBOOK OF SCIENCE.

AB IMM

\ \ AB

N23

Fig. 62. No. 1, is the wooden sword, with an elbow-joint at c. No. 2. Sword attached to
board at x, and being allowed to fall from any angle shown by dotted-line, it strikes
the block, w, outside the centre of percussion, p, and as there is unequal motion in the
parts of the sword it bends down (or, as it were, breaks) at the elbow-joint, c.

No. 3 displays the same model ; but here the blow has fallen on the block, w, precisely
at the centre of percussion of the sword, p, and the elbow-joint remains perfectly firm.

When a blow is not delivered with a stick or sword at the centre of
percussion, a peculiar jar, or what is familiarly spoken of as a stinging
sensation, is apparent in the hand ; and the cause of this disagreeable
result is further elucidated by fig. 63, in which the post, A, corresponds
with the handle of the sword.

THE CENTRE OF GRAVITY.

Pig. 63. A. The post to which a rope is attached. B and c are two horses running round
in a circle, and it is plain that B will not move so quick as c, and that the latter will have
the greatest moving force ; consequently, if the rope was suddenly checked by striking
against an object at the centre of gravity, the horse c would proceed faster than B, and
would impart to B a backward motion, and thus make a great strain on the rope at A. But
if the obstacle were placed so as to be struck at a certain point nearer c, viz., at or about
the little star, the tendency of each horse to move on would balance and neutralize the other,
so that there would be no strain at A. The little star indicates the centre of percussion.

All military men, and especially those young gentlemen who are
intended for the army, should bear in mind this important truth during
their sword-practice and with one of Mr. Wilkinson's swords, made
only of the very best steel, they may conquer in a chance combat which
might otherwise have proved fatal to them. To Mr. Wilkinson, of Pall
Mall, the eminent sword-cutler, is due the great merit of improving the
quality of the steel employed in the manufacture of officers' swords ;
and with one of his weapons, the author has repeatedly thrust through
an iron plate about one-eighth of an inch in thickness without injuring
the point, and has also bent one nearly double without fracturing it, the
perfect elasticity of the steel bringing the sword straight again. These,
and other severe tests applied to Wilkinson's swords, show that there is
no reason why an officer should not possess a weapon that will bear
comparison with, nay, surpass, the far-famed Toledo weapon, instead of
submitting to mere army-tailor swords, which are often little better than
hoops of beer barrels ; and, in dire combat with Hindoo or Mussulman
fanatics' Tulwah, may show too late the folly of the owner.

Fijr. 64

BOYS PLAYBOOK OF SCIENCE.

CHAPTER V.

SPECIFIC GRAVITY.

IT is recorded of the great Dr. Wollaston, that when Sir Humphry
Davy placed in his hand, what was then considered to be the scientific
wonder of the day viz., a small bit of the metal potassium, he ex-
claimed at once, " How heavy it is," and was greatly surprised, when
Sir Humphry threw the metal on water, to see it not only take fire,
but actually float upon the surface ; here, then, was a philosopher
possessing the deepest learning, unable, by the sense of touch and by
ordinary handling, to state correctly whether the new substance (and
that a metal), was heavy or light ; hence it is apparent that the pro-
perty of specific gravity is one of importance, and being derived from
the Latin, means species, a particular sort or kind ; and gravis, heavy
or weight i.e., the particular weight of every substance compared with
a fixed standard of water.

We are so constantly in the habit of referring to a standard of perfec-
tion in music and the arts of painting and sculpture, that the youngest
will comprehend the office of water when told tnat it is the philosopher's
unit or starting-point for the estimation of the relative weights of solids
and liquids. A good idea of the scope and meaning of the term specific
gravity, is acquired by a few simple experiments, thus : if a cylindrical

Fig. 65. A. A large cylindrical vessel containing water, in which the egg sinks till it
reaches the bottom of the glass. B. A similar glass vessel containing half brine and half
water, in which the egg floats in the centre viz., just at the point where the brine and
water touch.

SPECIFIC GRAVITY.

glass, say eighteen inches long, and two and a half wide, is filled with
water, and another of the same size is also filled, one half with water
and the other half with a saturated solution of common salt, or what is
commonly termed brine, a most amusing comparison of the relative
weights of equal bulks of water and brine, can be made with the help
of two eggs ; when one of the eggs is placed in the glass containing
water, it immediately sinks to the bottom, showing that it has a greater
specific gravity than water ; but when the other egg is placed in the
second glass containing the brine, it sinks through the water till it
reaches the strong solution of salt, where it is suspended, and presents
a most curious and pretty appearance ; seeming to float like a balloon in
air, and apparently suspended upon nothing, it provokes the inquiry,
" whether magnetism has anything to do with it ?" The answer, of
course, is in the negative, it merely
floats in the centre, in obedience to
the common principle, that all bodies
float in others which are heavier than
themselves ; the brine has, therefore,
a greater weight than an equal bulk
of water, and is also heavier than the
egg. A pleasing sequel to this expe-
riment may be shown by demonstrat-
ing how the brine is placed in the
vessel without mixing with the water
above it ; this is done by using a glass
tube and funnel, and after pouring
away half the water contained in the
vessel (Fig. 65), the egg can be floated
from the bottom to the centre of the
glass, by pouring the brine down the
funnel and tube. The saturated solu-
tion of salt remains in the lower part
of the vessel and displaces the water,
which floats upon its surface like oil
on water, carrying the egg with it.

The water of the Dead Sea is said
to contain about twenty-six per cent,
of saline matter, which chiefly con-
sists of common salt. It is perfectly
clear and bright, and in consequence
of the great density, a person may
easily float on its surface, like the egg'graduallynses?
egg on the brine, so that if a ship
could be heavily laden whilst floating on the water of the Dead Sea,
it would most likely sink if transported to the Thames. This illus-
tration of specific gravity is also shown by a model ship, which being
first floated on the brine, will afterwards sink if conveyed to another
vessel containing water. One -of the tin model ships sold as a magnetic

BOYS PLAYBOOK OF SCIENCE.

toy answers nicely for this experiment, but it must be weighted or
adjusted so that it just floats in the brine, A ; then it will sink, when
placed, in another vessel containing only water.

Fig. 67. A. Vessel containing brine, upon which the little model floats.
B. Vessel containing water, in which the ship sinks.

Another amusing illustration of the same kind is displayed with gold
fish, which swim easily in water, floating on brine, but cannot dive to
the bottom of the vessel, owing to the density of the saturated solution
of salt. If the fish are taken out immediately after the experiment, and
placed in fresh water, they will not be hurt by contact with the strong
salt water.

These examples of the relative weights of equal bulks, enable the
youthful mind to grasp the more difficult problem of ascertaining the
specific gravity of anv solid or liquid substance; and here the strict
meaning of terms should not be passed by. Specific weight must not be
confounded with Absolute weight ; the latter means the entire amount
of ponderable matter in any body : thus, twenty-four cubic feet of sand
weigh about one ton, whilst specific weight means the relation that sub-
sists between the absolute weight and the volume or space which that
weight occupies. Thus a cubic foot of water weighs sixty-two and a half
pounds, or 1000 ounces avoirdupois, but changed to gold, the cubic
foot weighs more than half a ton, and would be equal to about 19,300
ounces 4ience the relation between the cubic foot of water and that of

SPECIFIC GRAVITY. 51

gold is nearly as 1 to 19' 3 ; the latter is therefore called the specific
gravity of gold.

Such a mode of taking the specific gravity of different substances
viz., by the weight of equal bulks, whether cubic feet or inches, could not
be employed in consequence of the difficulty of procuring exact cubic
inches or feet of the various substances which by their peculiar proper-
ties of brittleness or hardness would present insuperable obstacles to any
attempt to fashion or shape them into exact volumes. It is therefore
necessary to adopt the method first devised by Archimedes, 600 B.C.,
when he discovered the admixture of another metal with the gold of
King Hiero' s crown.

This amusing story, ending in the discovery of a philosophical truth,
may be thus described : King Hiero gave out from the royal treasury a
certain quantity of gold, which he required to be fashioned into a crown ;
when, however, the emblem of power was produced by the goldsmith,
it was not found deficient in weight, but had that appearance which
indicated to the monarch that a surreptitious addition of some other
metal must have been made.

It may be assumed that King Hiero consulted his friend and philoso-
pher Archimedes, and he might have said, " Tell me, Archimedes, without
pulling my crown to pieces, if it has been adulterated with anv other
metal ?" The philosopher asked time to solve the problem, and going
to take his accustomed bath, discovered then specially what he had never
particularly remarked before that, as he entered the vessel of water,
the liquid rose on each side of him that he, in fact, displaced a certain
quantity of liquid. Thus, supposing the bath to have been full of water,
directly Archimedes stepped in, it would overflow. Let it be assumed
that the water displaced was collected, and weighed 90 pounds, whilst
the philosopher had weighed, say 200 pounds. Now, the train of
reasoning in his mind might be of this kind : " My body displaces 90
pounds of water ; if I had an exact cast of it in lead, the same bulk and
weight of liquid would overflow ; but the weight of my body was, say
200 pounds, the cast in lead 1000 pounds ; these two sums divided by
90 would give very different results, and they would be the specific
gravities, because the rule is thus stated : ' Divide the gross weight by
the loss of weight in water, the water displaced, and the quotient gives
the specific gravity.' " The rule is soon tested with the help of an
ordinary pair of scales, and the experiment made more interesting by
taking a model crown of some metal, which may be nicely gilt and
burnished by Messrs. Elkington, the celebrated electro-platers of Bir-
mingham. For convenience, the pan of one scale is suspended by
shorter chains than the other, and should have a hook inserted in the
middle ; upon this is placed the crown, supported by very thin copper
wire. For the sake of argument, let it be supposed that the crown weighs
Yl\ ounces avoirdupois, which are duly placed in the other scale-pan,
and without touching these weights, the crown is now placed in a
vessel of water. It might be supposed that directly the crown enters
the water, it would gain weight, in consequence of being wetted,

E 2

BOY'S PLAYBOOK OF SCIENCE.

but the contrary is the case, and by thrusting the crown into the water,
it may be seen to rise with great buoyancy so long as the 17 ounces are
retained in the other scale-pan ; and it will be found necessary to place
at least two ounces in the scale-pan to which the crown is attached
before the latter sinks in the water ; and thus it is distinctly shown that
the crown weighs only about 15 ounces in the water, and has therefore
lost instead of gaining weight whilst immersed in the liquid. The rule
may now be worked out :

Ounces.

Weight of crown in air 17^

Ditto in water ] 5 J

Less in water . , . . . . 2

The quotient 8| demonstrates that the crown is manufactured of
copper, because it would have been about 19 if made of pure gold.

Fi?. 88. A. Ordinary pair of scales. B. Scale-pan, containing 17 ounces, being the
weisrht of the crown in air. c. Pan, with hook and crown attached, which is sunk in the
water contained in the vessel D ; this pan contains the two ounces, which must be placed
there to make the crown sink and exactly balance B.

SPECIFIC GRAVITY. 53

Table of the Specific Gravities of the Metals in common use.

Platinum 20 '98

Gold 19-26 to 19-3 and 19-64

Mercury 13'57

Lead 11-35

Silver 10'47 to 1O5

Bismuth 9'82

Copper 8-89

Iron 7-79

Tin 7-29

Zinc 6-5 to 7"'i .

The simple rule already explained may be applied to all metals of any
size or weight, and when the mass is of an irregular shape, having
various cavities on the surface, there may be some difficulty in taking
the specific gravity, in consequence of the adhesion of air-bubbles ; but
this may be obviated either by brushing them away with a feather, or,
what is frequently much better, by dipping the metal or mineral first
into alcohol, and then into water, before placing it in the vessel of
water, by which the actual specific gravity is to be taken.

The mode of taking the specific gravity of liquids is very simple, and
is usually performed in the laboratory by means of a thin globular bottle
which holds exactly 1000 grains of pure distilled water at 60 Fahrenheit.
A little counterpoise of lead is made of the exact weight of the dry
globular bottle, and the liquid under examination is poured into the
bottle and up to the graduated mark in the neck ; the bottle is then
placed in one scale-pan, the counterpoise and the 1000-grain weight in
the other ; if the liquid (such as oil of vitriol) is heavier than water,
then more weight will be required viz., 845 grains and these figures
added to the 1000 would indicate at once that the specific gravity of oil
of vitriol was 1*845 as compared with water, which is I'OOO. When the
liquid, such as alcohol, is lighter than water, the 1000-grain weight will
be found too much, and grain weights must be added to the same scale-
pan in which the bottle is standing, until the two are exactly balanced.
If ordinary alcohol is being examined, it will be found necessary to place
180 grains with the bottle, and these figures deducted from the 1000
grains in the other scale-pan, leave 820, which, marked with a dot before
the first figure (sic '820), indicates the specific gravity of alcohol to be
less than that of water.

The difference in the gravities of various liquids is displayed in a
very pleasing manner by an experiment devised by Professor Griffiths,
to whom chemical lecturers are especially indebted for some of the most
ingenious and beautiful illustrations which have ever been devised.
The experiment consists in the arrangement of five distinct liquids of
various densities and colours, the one resting on the other, and dis-
tinguished not only by the optical line of demarcation, but by little balls
of wax, which are adjusted by leaden shot inside, so as to sink through

BOY'S PLATBOOK OF SCIENCE.

the upper strata of liquids, and rest only upon the one that it is in-
tended to indicate.

The manipulation for this experiment is somewhat troublesome, and
is commenced by procuring some pure bright quicksilver, upon which an
iron bullet (black-leaded, or painted of any colour) is placed, or one of
those pretty glass balls which are sold in such quantities at the Crystal
Palace.

Secondly. Put as much white vitriol (sulphate of zinc) into a half
pint of boiling water as it will dissolve, and, when cold, pour off the
clear liquid, make up a ball of coloured wax (say red), and adjust it by
placing little shot inside, until it sinks in a solution of sulphate of
copper and floats on that of the white vitriol.

Thirdly. Make a solution of sulphate of copper in precisely the same
manner, and adjust another wax ball to sink in water, and float on this
solution.

Fourthly. Some clear distilled water must be provided.
Fifthly. A little cochineal is to be dissolved in some common spirits
of wine (alcohol), and a ball of cork painted white provided.

Finally. A long cylindrical glass, at least eighteen inches high, and
two and a half or three inches diameter, must be made to receive these

five liquids, which are ar-
ranged in their proper order
of specific gravity by means
of a long tube and funnel.
The four balls viz., the
iron, the two wax, and the
cork balls, are allowed to
slide down the long glass,
which is inclined at an angle;
and then, by means of the
tube and funnel, pour in the
Solution of white vitriol, tincture of cochineal, and
all the balls will remain at
the bottom of the glass.
The water is poured down
next, and now the cork ball
floats up on the water, and
marks the boundary line of
the alcohol and water. Then
Fig. 69. Long cylindrical glass, 18 x 3 inches, con- the solution of blue vitriol,
taining the five liquids. when a wax ball floats upon

it. Thirdly, the solution of

white vitriol, upon which the second wax ball takes its place ; and lastly,
the quicksilver is poured down the tube, and upon this heavy metallic
fluid the iron or glass ball floats like a cork on water.

The tube may now be carefully removed, pausing at each liquid, so
that no mixture take place between them ; and the result is the arrange-
ment of five liquids, giving the appearance of a cylindrical glass painted

Alcohol.

Water.

Solution of blue vitriol.

Quicksilver.

SPECIFIC GRAVITY. 55

with bands of crimson, blue, and silver ; and the liquids will not mingle
with each other for many days.

A more permanent arrangement can be devised by using liquids which
have no affinity, or will not mix with each other such as mercury,
water, and turpentine.

The specific weight or weights of an equal measure of air and other
gases is determined on the same principle as liquids, although a diffe-
rent apparatus is required. A light capped glass globe, with stop-cock,
from 50 to 100 cubic inches capacity, is weighed full of air, then
exhausted by an air-pump, and weighed empty, the loss being taken as
the weight of its volume of air ; these figures are carefully noted,
because air instead of water is the standard of comparison for all gases.
When the specific gravity of any other gas is to be taken, the glass
globe is again exhausted, and screwed on to a gas jar provided with a
proper stop-cock, in which the gas is contained; and when perfect
accuracy is required, the gas must be dried by passing it over some
asbestos moistened with oil of vitriol, and contained in a glass tube, and
the gas jar should stand in a mercurial trough. (Fig. 70.) The stop-

Fig. 70. A. Glass globe to contain the gas. B. Gas jar standing in the mercurial
trough, D. c. Tube containing asbestos moistened with oil of vitriol.

cocks are gradually turned, and the gas admitted to the exhausted globe
from the gas jar ; when full, the cocks are turned off, the globe unscrewed,
and again weighed, and by the common rule of proportion, as the weight
of the air first found is to the weight of the gas, so is unity (1*000, the
density of air) to a number which expresses the density of the gas
required. If oxygen had been the gas tried, the number would be I'lll,
being the specific gravity of that gaseous element. If chlorine, 2'470.
Carbonic acid, 1*5 00. Hydrogen being much less than air, the number
would only be 69, or decimally 0'069.

A very good approximation to the correct specific gravity (particularly
where a number of trials have to be made with the same gas, such as

BOY'S PLAYBOOK OF SCIENCE.

ordinary coal gas) is obtained by suspending a light paper box, with holes
at one end, on one arm of a balance, and a counterpoise on the other.
The box can be made carefully, and should have a capacity equal to a

FIgf. 71. A* The balance. B. The paper box, of a known capacity, c. Gas-pipe blowing
in coal-gas, the arrows showing entrance of gas and exit of the air.

half or quarter cubic foot ; it is suspended with the holes downward, and is
filled by blowing in the coal gas until it issues from the apertures, and can
be recognised by the smell. The rule in this case would be equally simple :
as the known weight of the half or quarter cubic foot of common air is
to the weight of the coal gas, so is I'OOO to the number required.

(Kg- 71.)

As an illustration of the different specific weights of the gases, a
small balloon, containing a mixture of hydrogen and air, may be so
adjusted that it will just sink in a tall glass shade inverted and sup-
ported on a pad made of a piece of oilcloth shaped round and bound
with list. On passing in quickly a large quantity of carbonic acid, the
little balloon will float on its surface ; and if another balloon, containing
only hydrogen, is held in the top part of the open shade, and a sheet of
glass carefully slid over the open end, the density of the gases (although
they are perfectly invisible) is perfectly indicated ; and, as a climax to
the experiment, a third balloon can be filled with laughing gas, and
>nay be placed in the glass shade, taking care that the one full of pure
hydrogen does not escape ; the last balloon will sink to the bottom of the

SPECIFIC GRAVITY.

3 5

jar, because laughing gas is
almost as heavy as carbonic
acid, and the weight of the
balloon will determine its
descent. (Sis. 72.)

A soap-bubble will rest
most perfectly on a surface
of carbonic acidgas,and the
aerial and elastic cushion
supports the bubble till it
bursts. The experiment is
best performed by taking a
class shade twelve inches
broad and deep in propor-
tion, and resting it on a
pad; half a pound of ses-
quicarbonate of soda is
then placed in the vessel,
and upon this is poured a mixture of half a pint of oil of vitriol and half
a pint of water, the latter being previously mixed and allowed to cool
before use. An enormous quantity of carbonic acid gas is suddenly gene-
rated, and rising to the edge, overflows at the top of the glass shade. A
well-formed soap-bubble, detached neatly from the end of a glass-tube,
oscillates gently on the surface of the heavy gas, and presents a most
curious and pleasing appearance. The soapy water is prepared by
cutting a few pieces of yellow soap, and placing them in a two-ounce

Balloon.
Pure hydrogen.

(Air.)

Balloon.
Hydrogen & air.

(Carbonic acid.)

Balloon.

Laughing gas.

Fig. 72. Inverted large glass shade, containing half
carbonic acid and half common air.

Fig. 73. A. Inverted glass shade, containing the material, B, for generating carbonic acid
gas. c. The soap-bubble. D D. The glass tube for blowing the bubbles. E. Small lantern, to
throw a bright beam of light from the oxy-hydrogen jet upon the thin soap-bubble, which
then displays the most beautiful iridescent colours.

bottle containing distilled water. (Fig. 73.) The specific gravity of the
gases, may therefore be either greater, or less than atmospheric air,

VQ BOYS PLAYBOOK OP SCIENCE.

which has been already mentioned as the standard of comparison, and
examined by this test the vapours of some of the compounds of carbon
and hydrogen are found to possess a remarkably high gravity ; in
proof of which, the vapour of ether may be adduced as an example,
although it does not consist only of the two elements mentioned, but
contains a certain quantity of oxygen. In a cylindrical tin vessel, two
feet high and one foot in diameter, place an ordinary hot-water plate,
of course full of boiling water ; upon this warm surface pour about half
an ounce of the best ether ; and, after waiting a few minutes until the
whole is converted into vapour, take a syphon made of half-inch pewter
tube, and warm it by pouring through it a little hot water, taking care
to allow the water to drain away from it before use. After placing the
syphon in the tin vessel, a light may be applied to the extremity of the
long leg outside the tin vessel, to show that no ether is passing over
-until the air is sucked out as with the water-syphon; and after this has
been done, several warm glass vessels may be filled with this heavy
vapour of ether, which burns on the application of flame. Finally, the
remainder of the vapour may be burnt at the end of the syphon tube,
demonstrating in the most satisfactory manner that the vapour is
flowing through the syphon just as spirit is removed by the distillers
from the casks into cellars of the public-houses. (Fig. 74.)

Fl. 74. A. Tin vessel containing the hot-water plate, B, upon which the ether is
poured, c. The syphon. D. Glass to receive the vaoour. z. Combustion of the ether
vapour in another vessel.

SPECIFIC GRAVITY. 59

Before dismissing the important subject of specific gravity (or, as it
is termed by the French savants, " density"), it may be as well to state
that astronomers have been enabled, by taking the density of the earth
and by astronomical observations, to calculate the gravity of the planets
belonging to our solar system ; and it is interesting to observe that the
density of the planet Venus is the only one approaching the gravity of
the earth :

The Earth TOOO

The Sun -254)

The Moon '742

Mercury 2*583

Venus 1-037

Mars -650

Jupiter -258

Saturn -104

Herschel '220

CHAPTER VI.

ATTRACTION OF COHESION.

IN previous chapters one kind of attraction viz., that of gravita-
tion, has been discussed and illustrated in a popular manner, and
pursuing the examination of the invisible, active, and real forces of
nature, the attraction of cohesion will next engage our attention.
There is a peculiar satisfaction in pursuing such investigations, because
every step is attended bv a reasonable proof; there is no ghostly
mystery in philosophic studies ; the mind is not suddenly startled at one
moment with that which seems more than natural ; it is not carried away
in an ecstasy of wonder and awe, as in the so-called spirit-rapping ex-
periments, to be again rudely brought back to the material by the disclo-
sure of trickeries of the most ludicrous kind, such as those lately ex-
posed by M. Jobert de Lamballe, at the Academy of Sciences at Paris.
This gentleman has unmasked the effrontery of the spirit-rappers by
merely stripping the stocking from the heel of a young girl of fourteen.
M. Velpeau declares that the rapping is produced by the muscles of the
heel and knee acting in concert, and quotes the case of a lady once
celebrated as a medium, who has the power of producing the most
curious and interesting music with the tendons of the thigh. This
music is said to be loud enough to be heard from one end of a long
room to the other, and has often played a conspicuous part in the reve-
lations made by the medium. M. Jules Clocquet also explained the
method by which the famous girl pendulum had so long abused the cre-
dulity of the Paris public. This girl, whose self-styled faculty is that
of striking the hour at any time of the day or night, was attended at
the Hospital St. Louis by M. Clocquet, who states that the vibrations in

BOY S PLAYBOOK OF SCIENCE.

this case were produced by a rotatory motion in tlie lumbar regions of
the vertebral column. The sound of these (a la rattlesnake) was so
powerful, that they might be distinctly heard at a distance of twenty-
five feet.

In studying the powers of nature, which the most sceptical mind
allows must exist, there is an abundant field for experiment without
attempting the exploits of Macbeth's witches, or the fanciful powers of
Manfred ; and, returning to the theme of our present chapter, it may be
asked, how is cohesion defined? and the answer may be given, by
directing attention to the three physical conditions of water, which
assumes the form of ice, water, or steam.

In the Polar regions, and also in the Alpine and other mountains
where glaciers exist, there the traveller speaks of ice twenty, thirty, forty,
nay, three hundred feet in thickness. Here the withdrawal of a certain
quantity of heat from the water evidently allows a new force to come
into full play. We may call it what we like ; but cohesion, from the Latin
cum, together, and hareo, I stick or cleave, appears to be the best and
most rational term for this power which tends to make the atoms or
particles of the same kind of matter move towards each other, and to
prevent them being separated or moved asunder. That it is not merely
hypothetical is shown by the following experiments.

If two pieces of lead are cast, and the ends nicely scraped, taking
care not to touch the surfaces with the fingers, they may by simple
pressure be made to cohere, and in that state of attraction may be lifted

from the table by the ring which is
usually inserted for convenience in
the upper piece of lead ; they may be
hung for some time from a proper
support, and the lower bit of lead
will not break away from the upper
one ; they may even be suspended, as
demonstrated by Morveau, in the va-
cuum of an air-pump, to show that the
cohesion is not mistaken for the pres-
sure of the atmosphere, and no se-
paration occurs. And when the union
is broken by physical force, it is sur-
prising to notice the limited number
of points, like pin points, where the
cohesion has occurred; whilst the
weight of the lump of lead upheld
against the force of gravitation re-
minds one forcibly of the attraction
of a mass of soft iron bv a powerful
magnet, and leads the philosophic in-

Fig. 75. A A. Two pieces of lead, scraped quirer to speculate on the principle
c. stand, sup- of co h es ion being only some masked
form of magnetic or electrical attrac-
tion. (Fig. 75.)

clean at the surfaces B B

porting the two pieces of lead attached

to each other by cohesion.

ATTRACTION OF COHESION.

A fine example of the same force is shown in the use of a pair of flat
iron surfaces, planed by the celebrated Whitworth, of Manchester.

Fig. 76. A. Whitworth'i planes, with film of air between them.
B. Film of air excluded when cohesion occurs.

These surfaces are so true, that when placed upon each other, the upper
one will freely rotate when pushed round, in consequence of the thin
film of air remaining between the surfaces, which acts like a cushion,
and prevents the metallic cohesion. When, however, the upper plate is
slid over the lower one gradually, so as to exclude the air, then the two
may be lifted together, because cohesion has taken place. (Fig. 76.)

A glass vessel is a good example of cohesion. The materials of which
it is composed have been soft and liquid when melted in the fire, and on
the removal of the excess of heat it has become hard and solid, in
consequence of the attractive force of cohesion binding the particles
together ; in the absence of such a power, of course, the material would
fall into the condition of dust, and a mere shapeless heap of silicates of
potash and lead would indicate the place where the moulded and co-
herent glass would otherwise stand.

A lump of lead, six inches long by four broad, and half an inch
thick, may be supported by dexterously taking off a thick shaving
with a proper plane, and after pressing an inch or more of the strip on
the planed surface of the large lump of lead, the cohesion is so powerful
that the latter may be lifted from the table by the strip of metal.

The bullets projected from Perkins' steam- gun, at the rate of three
hundred per minute, are thrown with such violence, that, when received
on a thick plate of lead backed up with sheet iron, a cold welding takes
place between the two surfaces of metal in the most perfect manner,
just as two soft pieces of the metal potassium may be squeezed and
welded together. The surfaces of an apple torn asunder will not readily
cohere, but if cut with a sharp knife, cohesion easily occurs ; so with a
wound produced by a jagged surface, it is difficult to make the parts

BOY'S PLAYBOOK OF SCIENCE.

heal, whereas some of the most desperate sabre-cuts have been healed,
the cohesion of the surfaces of cut flesh being very rapid ; hence, if the
top of a finger is cut off, it may be replaced, and will grow, in conse-
quence of the natural cohesion of the parts.

The art of plating copper with silver, which is afterwards gilt, and
then drawn out into flattened wire for the manufacture of gold lace and
epaulets, usually termed bullion, is another example of the wonderful
cohesion of the particles of gold, of which a single grain may be ex-
tended over the finest plate wire measuring 345 feet in length.

The process of making wax candles is a good illustration of the
attraction of cohesion ; they are not generally cast in moulds, as most
persons suppose, but are made by the successive applications of melted
wax around the central plaited wick. Other examples of cohesion are
shown by icicles, and also stalagmites ; which latter are produced by the
gradual dropping of water containing chalk (carbonate of lime) held in
solution by the excess of carbonic acid gas ; the solvent gradually
evaporates, and leaves a series of calcareous films, and these cohere in
succession, producing the most fantastic forms, as shown in various
remarkable caverns, and especially in the cave of Arta, in the island of
Majorca.

In metallic substances the cohesion of the particles assumes an im-
portant bearing in the question of relative toughness and power of
resisting a strain ; hence the term cohesion is modified into that of the
property of "tenacity."

The tenacity of the different metals is determined by ascertaining the
weight Tequired to break wires of the same length and guage. Iron

Fig. 77. B. Paa supported by leaden wire broken by a weight which the iron
wire at A easily supports.

appears to possess the property of tenacity in the greatest, and lead in
the least degree. (Eig. 77.)

ATTRACTION OP COHESION.

The tenacity of iron is taken advantage of in the most scientific
manner by the great engineers who have constructed the Britannia Tube,
and that eighth wonder of the world, the Leviathan, or Great Eastern,
steam-ship. In both of these sublime embodiments of the genius and
industrial skill of Great Britain the advantage of the cellular principle
is fully recognised. The magnitude of this colossal ship is better
realized when it is remembered that the Great Eastern is six times the
size of the Duke of Wellington line-of-battle ship, that her length is more
than three times that of the height of the Monument, while in breadth
it is equal to the width of Pall Mall, and that a promenade round the
deck will afford a walk of more than a quarter of a mile. Up to the
water-mark the hull is constructed with an inner and outer shell, two
feet ten inches apart, each of three-quarter-inch plate ; and between
them, at intervals of six feet, run horizontal webs of iron plates, which
convert the whole into a series of continuous cells or iron boxes. (Fig. 78.)

Fig. 78. Transverse section of Great 'Eastern, showing the cellular construction
from keel to water-line, A A.

This double ship is useful in various ways ; in the first place, the
ganger arising from collision is diminished, as it is supposed that the
jvuter web only would be broken through or damaged ; so that the water
ivould not then rush into the steam-ship, but merely fill the space
Between the shells. In the second place, if there should be any difficulty
in procuring ballast, the space can be filled with 2500 tons of water, or
again pumped out, according to the requirements of the vessel. The
strength of a continued cellular construction can be easily imagined, and
may be well illustrated by a thin sheet of common tin plate. If the ends
be rested on blocks of wood, so as to lap over the wood about one inch,
they are easily displaced, and the mimic bridge broken down from its

BOY S PLAYBOOK OF SCIENCE.

supports by the addition to the centre of a few ounce weights ; whilst
the same tin plate rolled up in the figure of a tube, and again rested on the
same blocks, will now support many pounds weight without bending or
breaking down. (Fig. 79.)

Fig. 79. A. Flat tin plate, breaking down with a few ounce weights.
u. Same tin plate rolled up supports a very heavy weight.

The deck of the ship is double or cellular, after the plan of Stephenson
in the Britannia Tubular Bridge, and is 692 feet in length. The ton-
nage register is 18,200 tons, and 22,500 tons builder's measure;
the hull of the Great Eastern is considered to be of such enormous
tenacity, that, if it were supported by massive blocks of stone six feet
square, placed at each end, at stem and stern, it would not deflect, curve,
or bend down in the middle more than six inches even with all her
machinery, coals, cargo, and living freight.

In adducing remarkable instances of the adhesive power and tenacity of
inorganic matter, it may not be altogether out of place to allude to the
strength and force of living matter, or muscular power. It is stated that
Dr. George B. Winship, of Roxbury in America, a young physician, twenty-
five years old, and weighing 143 pounds, is the strongest man alive ; m
fact, quite the Samson of the nineteenth century. He can raise a barrel of
flour from the floor to his shoulders ; can raise himself with either little
finger till his chin is half a foot above it ; can raise 200 pounds with
either little finger ; can put up a church bell of 141 pounds ; can lift with
his hands 926 pounds dead weight without the aid of straps or belts of
any kind. As compared with Topham, the Cornish strong man, who
could raise 800 pounds, or the Belgic one, his power is greater; and
as the use of straps and belts increases the power of lifting by about
four times, it is stated that Winship could lift at least 2500 pounds
weight.

With these illustrations of cohesion we may return again to the ab-
stract consideration of this power with reference to water, in which we
have noticed that the antagonist to this kind of attraction is the force or
power termed caloric or heat. The latter influence removes the frozen
bands of winter and converts the ice to the next condition, water. In
this state cohesion is almost concealed, although there is just a slight

ATTRACTION OF COHESION.

excess to hold even the particles of water in a state of unity, and

this fact is beautifully illustrated by the formation of the brilliant dia-

mond drops of dew on the surfaces of various leaves, as also in the force

and power exercised by great volumes of water, which exert their mighty

strength in the shape of breaker-waves, dashing against rocks and

lighthouses, and making them tremble to their very base by the violence

of the shock ; here there must be some unity of particles, or the col-

lective strength could not be exerted, it would be like throwing a hand-

ful of sand against a window a certain amount of noise is produced, but

the glass is not fractured ; whilst the same sand united by any glutinous

material, would break its way through, and soon fracture the brittle

glass. It is so usual to see the particles of water easily separated, that it

becomes difficult to recognise the presence of cohesion ; but this bond of

union is well illustrated in the experiment of the water hammer. The

little instrument is generally made of a glass tube with a bulb at one

end ; in this bulb the water which it contains is boiled, and as the steam

issues from the other extremity, drawn out to a capillary tube, the open-

ing is closed by fusion with the heat of a blowpipe flame. As the

water cools the steam condenses, and a

vacuum, so far as air is concerned, is

produced; if now the tube is suddenly

inverted, the whole of the water falls en

masse, collectively, and striking against

the bottom of the tube, produces a me-

tallic ring, just as if a piece of wood or

metal were contained within the tube.

If the end to which the water falls is

not well cushioned by the palm of the

hand, the water hammers itself through

and breaks away that part of the glass

tube. Hence it is better to construct the

water hammer of copper tube, about

three-quarters of an inch in diameter and

three feet long ; at one end a female screw-

piece is inserted, into which a stop-cock

is fitted ; when the tube is filled to the

height of about six inches with water, and

shaken, the air divides the descending

volume of water, and the ordinary splash-

ing sound is heard ; there is no unity or

cohesion of the parts ; if, however, the

end of the copper tube is thrust into

a fire and the water boiled so that steam

issues from the cock, which is then closed,

and the tube removed and cooled, a smart

blow is given, and distinctly heard when

the copper tube is rapidly inverted or

shaken so as to cause the water to rise the end to be placed in the fire at a

Pig 80> A ordinary glass water
hammer. B. Copper tube ditto,

and fall. The experiment may be rendered still more instructive by
turning the cock and admitting the air, which rushes in with a whizzing
sound, and on shaking the tube the metallic ring is no longer heard,
but it may be again restored by attaching a small air syringe or hand
pump, ancl removing the air by exhaustion. (Fig. 80.)

In the fluid condition water still possesses a surplus of cohesion over
the antagonistic force of heat ; when, however, the latter is applied in
excess, then the quasi-struggle terminates; the heat overpowers the
cohesive attraction, and converts the water into the most willing slave
which has ever lent itself to the caprices of man viz., into steam-
glorious, useful steam : and now the other end of the chain is reached,
where heat triumphs ; whilst in solids, such as ice, cohesion is the con-
queror, and the intermediate link is displayed in the fluid state of water.
If any fact could give an idea of the gigantic size of the Great Eastern,
it is the force of the steam which will be employed to move it at the
rate of about eighteen miles perhourwith a power estimated at the nominal
rate of 2600 horses, but absolutely of at least 12,000 horses. This
steam power, coupled with the fact that she has been enormously
strengthened in her sharp, powerful bows, by laying down three complete
iron decks forward, extending from the bows backward for 120 feet, will
demonstrate that in case of war the Great Eastern may prove to be a
powerful auxiliary to the Government. These decks will be occupied
by the crew of 300 or 400 men, and with this large increase of strength
forward, the Great Eastern, steaming full power, could overtake and cut
in two the largest wooden line-of-battle ship that ever floated. Should
war unhappily spread to peaceful England, and the enormous power of
this vessel be realized, her name would not inappropriately be changed
from the Great Eastern to the Great Terror of the ocean. The Times
very properly inquires, " What fleet could stand in the way of such a
mass, weighing some 30,000 tons, and driven through the water by
12,000 horse-power, at the rate of twenty-two or twenty-three miles per
hour. To produce the steam, 250 tons of coal per diem will be re-
quired, and great will be the honourable pride of the projectors when they
see her fairly afloat, and gliding through the ocean to the Far West."

A good and striking experiment, displaying the change from the
liquid to the vapour state, is shown by tying a piece of sheet caoutchouc
over a tin vessel containing an ounce or two of water. When this boils,
the india-rubber is distended, and breaks with a loud noise; or in
another illustration, by pouring some ether through a funnel carefully
into a flask placed in a ring stand. If flame is applied to the orifice,
no vapour issues that will ignite, provided the neck of the flask has not
been wetted with the ether. When, however, the heat of a spirit-lamp
is applied, the ether soon boils, and now on the application of a lighted
taper, a flame some feet in length is produced, which is regulated by the
spirit-lamp below, and when this is removed, the length of the flame
diminishes immediately, and is totally extinguished if the bottom of the
flask is plunged into cold water ; the withdrawal of the heat restores the
power of cohesion. Another illustration of the vast power of steam

ADHESIVE ATTRACTION. 67

will be shortly displayed in the Steam Ram ; and, " Supposing," says the
Times, "the new steam ram to prove a successful design, the finest
specimens of modern men-of-war will be reduced by comparison to the
helplessness of cock boats. Conceive a monstrous fabric floating in
mid-channel, fire proof and ball proof, capable of hurling broadsides of
100 shot to a distance of six miles ; or of clapping on steam at pleasure
and running down everything on the surface of the sea with a momentum
utterly irresistible.

" This terrible engine of destruction is expected to be itself indestruc*
tible. We are told that she may be riddled with shot (supposing any
shot could pierce her sides), that she may have her stem and her stern
cut to pieces, and be reduced apparently to a shapeless wreck, without
losing her buoyancy or power. Supposing that she relies upon the
shock of her impact instead of fighting her guns, it is calculated that
she would sink a line-of-battle ship in three minutes, so that a squadron
as large as our whole fleet now in commission would be destroyed in about
one hour and a quarter."

CHAPTER YH.

ADHESIVE ATTRACTION.

THE term cohesion must not be confounded with that of adhesion, which
refers to the clinging to or attraction of bodies of a dissimilar kind. The
late Professor Daniell defines cohesion to be an attraction of homogeneous
(6fjLos, like, and yevos, kind) or similar particles ; adhesion to be an at-
traction subsisting between particles of a heterogeneous, erepos, different,
and ycvos, kind.

There are numerous illustrations of adhesion, such as mending china,
and the use of glue, or paste, in uniting different surfaces, or mortar, in
building with bricks ; it is also well shown at the lecture table by means
of a pair of scales, one scale-pan of which being well cleaned with alkali at
the bottom, may then be rested on the surface of water contained in a
plate ; the adhesion between the water and the metal is so perfect, that
many grain weights may be placed in the other pan before the adhesion
is broken ; and after breakage, if the pan be again placed on the water,
and a few grains removed from the other, so as to adjust the two pans,
and make them nearly equal, a drop of oil of turpentine being added, in-
stantly spreads itself over the water, and breaking the adhesion between
the latter and the metal, the scale-pan is immediately and again broken
away, as the adhesion between the turpentine and the metal is not so great
as that of water and metal. The adhesion of air and water is well dis-
played in an apparatus recommended for ventilating mines, in which a
constant descending stream of water carries with it a quantity of air,
which being disengaged, is then forced out of a proper orifice. The same
kind of adliesion between air and water is displayed in the ancient

* 2

BOY'S PLAYBOOK OF SCIENCE.

Spanish Catalan forge, where the blast
is supplied to the iron furnace on a simi-
lar principle, only, a natural cascade is
taken advantage of instead of an artificial
fall of water through a pipe.

The adhesion of air and water be-
comes of some value when a river
flows through a large and crowded city,
because the water in its passage to and
fro, must necessarily drag with it, a
continuous column of air, and assist
in maintaining that constant agitation of
the air which is desirable as a preventive
to any accumulation of noxious air
charged with foetid odours, arising from
mud banks or from other causes. The
fact of adhesion, existing between water
and air, is readily shown, by resting one
end of a long glass tube, of at least one
inch diameter, on a block of wood one
foot high. If water is allowed to flow
down the tube, so as to leave a sufficient
space of air above it, the adhesion be-
tween the two ancient elements becomes
apparent, directly a little smoke is pro-
duced, near the top end of the glass tube
resting on the block of wood. The
smoke, which has a greater tendency to
rise than to fall, is dragged down the
glass tube, and accompanies the water

Fig. 81. Model of the apparatus f s it flows from the higher to the lower
r drawing down air. A, cistern of level. 1 he same truth is aJ so illustrated
in horizontal troughs or tubes through
wnich water IS Caused to HOW.

The adhesion between air and glass is
<> great, that it is absolutely necessary
There is another ball- to boil the mercury m the tubes of the
SKA^S best barometers; and if this is not
level; the end of the pipe always dips carefully attended to, the adhering ail-
some inches into this water, whilst between the glass and mercurv gra-
the air escapes from the jet,!,. ^^ ^^ ^ ^ d estrO/S/ the

Torricellian vacuum at the top of the barometer tube. Even after
the mercury is boiled, the air will creep up in course of years ; and
in order to prevent its passage between the glass and quicksilver, it
has been recommended, that a platinum ring should be welded on to the
end of the glass tube, because mercury has the power of wetting or en-
filming the metal platinum, and the two being in close contact, would, as it
were, shut the only door by which the air could enter the barometer tube.

for

runs down the sides of the tube, and
draws down the air in the centre, B

tube, T.

09
CHAPTER VIII.

CAPILLARY ATTRACTION.

THIS kind of attraction is termed capillary, in consequence of tubes, of
a calibre, or bore, as fine as hair, attracting and retaining fluids.

If water is poured into a glass, the surface is not level, but cupped
at the edges, where the solid glass exerts its adhesive attraction for the
liquid, and draws it from the level. If the glass be reduced to a very
narrow tube, having a hair-like bore, the attraction is so great that the
water is retained in the tube, contrary to the force of gravitation.
Two pieces of flat glass placed close together, and then opened like a
book, draw up water between them, on the same principle. A mass of
salt put on a plate containing a little water coloured with indigo displays
this kind of attraction most perfectly, and the water is quickly drawn up,
as shown by the blue colour on the salt. A little solution of the ammonio-
sulphate of copper imparts a finer and more distinct blue colour to the
salt. A piece of dry Honduras mahogany one inch square, placed in a
saucer containing a little turpentine, is soon found to be wet with the
oil at the top, which may then be set on fire.

Almost every kind of wood possesses capillary tubes, and will float, on
account of these minute vessels being filled with air ; if, however, the air is
withdrawn, then the wood sinks, and by boiling a ball made of beech wood
in water, and then placing it under the vacuum of an air pump in
other cold water, it becomes so saturated with water that it will no
longer float. A remarkable instance of the same kind is mentioned by
Scoresby, in which a boat was pulled down by a whale to a great depth
in the ocean, and after coming to the surface it was found that the wood
would neither swim nor burn, the capillary pores being entirely filled
with salt water.

A piece of ebony sinks in water on account of its density, closeness,
and freedom from air. A gauge made of a piece of oak, with a hole
bored in it of one inch diameter, accurately receives a dry plug of willow
wood which will not enter the orifice after it is wetted. Millstones are
split by inserting wedges of dry hard wood, which are afterwards wetted
and swelled, and burst the stone asunder. One of the most curious
instances of capillary attraction is shown in the currying of leather, a
process which is intended to impart a softness and suppleness to the
skin, in order that it may be rendered fit for the manufacture of boots,
harness, machine bands, &c. The object of the currier is to fill the
pores of the leather with oil, and as this cannot be done by merely
smearing the surface, he prepares the way for the oil by wetting the
leather thoroughly with water, and whilst the skin is damp, oil is
rubbed on, and it is then exposed to the air ; the water evaporates
at ordinary temperatures, but oil does not ; the consequence is that the

BOY'S PLAYBOOK OF SCIENCE.

pores of the leather give up the water, which disappears in evaporation,
and the oil bv capillary attraction is then drawn into the body of the
leather, the oil in fact takes the place vacated by the water, and renders
the material very supple, and to a considerable extent waterproof. In
paper making, the pores of this material, unless filled up or sized, cause
the ink to blot or spread by capillary attraction. The porosity of soils is
one of the great desideratums of the skilful agriculturist, and drainage
is intended to remove the excess of water which would fill the pores of
the earth, to the exclusion of the more valuable dews and' rains con-
veying nutritious matter derived from manures and the atmosphere.

A cane is an assemblage of small tubes, and if a piece of about six
inches in length (cut off, of course, from the joints) be placed in a bottle
of turpentine, the oil is drawn up and may be burnt at the top ; it is on
this principle that indestructible wicks of asbestos, and wire gauze
rolled round a centre core, are used in spirit lamps. Oil, wax, and
tallow, all rise by capillary attraction in the wicks to the flame, where
they are boiled, converted into gas, and burnt.

The capillary attraction of skeins of cotton for water was known
and appreciated by the old alchemists; and Geber, one of the most
ancient of these pioneers of science, and who lived about the seventh
century, describes a filter by which the liquid is separated from the
solid. This experiment is well displayed by putting a solution of
acetate of lead into a glass, which is placed on the highest block of a
series of three, arranged as steps. Into this glass is placed the short end

Fig. 82. Gcber's filter. A. The solu-
tion of acetate of lead. B. The dilute
sulphuric acid. c. The clear liquid, sepa-
rated from the sulphate oflead in B.

Fig. 83. Prawn syphon.

CAPILLAEY ATTRACTION. 71

of a skein of lamp cotton, previously wetted with distilled water ; the lon
.end dips into another glass below, containing dilute sulphuric acid, and
as the solution of lead passes into it, a solid white precipitate of sulphate
of lead is formed; then another skein of wetted cotton is placed in
this glass, the long end of which passes into the last glass, so that the
clear liquid is separated and the solid left behind. (Kg. 82.)

In this filter the lamp cotton acts as a syphon through the capillary
pores which it forms. On the same principle, a prawn may be washed
in the most elegant manner (as first shown by the late Duke of Sussex),
by placing the tail, after pulling off the fan part, in a tumbler of water,
and allowing the head to hang over, when the water is drawn up by
capillary attraction, and continues to run through the head. (Fig. 83.)
The threads of which linen, cotton, and woollen cloths are made are small
cords, and the shrinkage of such textile fabrics, is well known and
usually inquired about, when a purchase is made ; here again capillary
attraction is exerted, and the fabric contracts in the two directions _ of
the warp and woof threads ; thus, twenty-seven yards of common Irish
linen will permanently shrink to about twenty-six yards in cold water.
In these cases the water is attracted into the fibres of the textile
material, and causing them to swell, must necessarily shorten their
length, just as a dry rope strained between two walls for the purpose of
supporting clothes, has been known to draw the hooks after being sud-
denly wetted and shortened by a shower of rain.

In order to tighten a bandage, it is only necessary to wind the dry
linen round the limbs as close as possible, and then wet it with water,
when the necessary shrinkage takes place.

If a piece of dry cotton cloth is tied over one end of a lamp glass, the
other may be thrust into, or removed from the basin of water very easily,
but when the cotton is wetted, the fibres contract and prevent air from
entering, so that the glass retains water just as if it were an ordinary
gas jar closed with a glass stopper.

A Spanish proverb, expressing contempt, says, "go to the well ^ with
a sieve," but even this seeming impossibility is surmounted by using a
cylinder of wire gauze, which may be filled with water, and by means of
the capillary attraction
between the meshes of
the copper-wire gauze
and the water, the whole
is retained, and may be
carefully lifted from a
basin of water ; the ex-
periment only succeeds
when the air is com-
pletely driven out of the
interstices of the gauze,
and the little cylinder A . Basin of water. B. Cylinder of wire gauze

completely filled with do JJ at both ends ^ ih gauze- when fuU of water it may
water ; this may be done be lifted from the basin by the handle, c.

72 BOY'S PLAYBOOK OP SCIENCE.

by repeatedly sinking and drawing out the cylinder, or still more
effectually, by first wetting it with alcohol and then dipping the cy Under p
in water.

A balloon, made of cotton cloth, cannot be inflated by means of a pair
of bellows, but if the balloon is wetted with water, then it may be swelled
out with air just as if it had been made of some air-tight material ;
hence the principle of varnishing silk or filling the pores with boiled oil,
when it is required in the manufacture of balloons.

Biscuit ware, porous tubes for voltaic batteries, alcarrazas, or water
coolers, are all examples of the same principle.

Whilst speaking most favourably of the benevolent labours of many
gentlemen (beginning with Mr. Gurney) who have erected " Drinking
Fountains" in London's dusty atmosphere and crowded streets, it must
not be forgotten that pious Mohammedans have, in bygone times, already
set us the example in this respect ; and in the palmy days of many of
the Moorish cities, the thirsty citizen could always be refreshed by a
draught of cool water from the porous bottles provided and endowed bv
charitable Mussulmans, and placed in the pubUc streets.

Fig 85. Moorish niche and porous earthenware
bottle, containing water.

CHAPTER IX.

CRYSTALLIZATION.

Library

IT has been already stated that the force of cohesion binds the similar
particles of substances together, whether they be amorphous or shape-
less, crystalline or of a regular symmetrical and mathematical figure.

Fig. 86. Crystals of snow.

The term crystal was originally applied by the ancients to silica in the
form of what is usually termed rock crystal, or Brazilian pebble ; and
they supposed it to be water which had been solidified by a remarkable
intensity of cold, and could not be thawed by any ordinary or summer
heat. Indeed, this idea of the ancients has been embodied (to a certain
extent) in the shape of artificial ice made by crystallizing large quan-
tities of sulphate of soda, which was made as flat as possible, and upon

74 BOY'S PLAYBOOK OF SCIENCE.

which skaters were invited to describe the figure of eight, at the usual
admittance fee, representing twelve pence. A crystal is now defined to-
be an inorganic body, which, by the operation of affinity, has assumed
the form of a regular solid terminated by a certain number of planes or
smooth surfaces.

Thousands of minerals are discovered in the crystallized state such as
cubes of iron pyrites (sulphuret of iron) and of fluor spar (fluoride of
calcium), whilst numerous saline bodies called salts are sold only in the
form of crystals. Of these salts we have excellent examples in Epsom
salts (sulphate of magnesia), nitre (nitrate of potash), alum (sulphate of
alumina), and potash ; the term salt being applied specially to all sub-
stances composed of an acid and a base, as also to other combinations
of elements which may or may not take .a crystalline form. Thus, nitre
is composed of nitric acid and potash; the first, even when much
diluted, rapidly changes paper, dipped in tincture of litmus and stained
blue, to a red colour, whilst potash shows its alkaline nature, by changing
paper, stained yellow with tincture of turmeric, to a reddish-brown. The
latter paper is restored to its original yellow by dipping it into the
dilute nitric acid, whilst the litmus paper regains its delicate blue colour
by being passed into the alkaline solution. An acid and an alkali com-
bine and form a neutral salt, such as nitre, which has no action whatever
on litmus or turmeric; whilst the element iodine, which is not an acid,
unites with the metallic element potassium, and therefore not an
alkali, and forms a salt that crystallizes in cubes called iodide of
potassium. Again, cane sugar, which is composed of charcoal, oxygen,
and hydrogen, crystallizes in hard transparent four-sided and irregular
six-sided prisms, but is not called a salt. Silica or sand is found crystal-
lized most perfectly in nature in six-sided pyramids, but is not a salt ;
it is an acid termed silicic-acid. Sand has no acid taste, because it is
insoluble in water, but when melted in a crucible with an alkali, such as
potash, it forms a salt called silicate of potash. Magnesia, from being
insoluble, or nearly so, in water, is all but tasteless, and has barely any
alkaline reaction, yet it is a very strong alkaline base ; 20'7 parts of it
neutralize as much sulphuric acid as 47 of potash. A salt is not always a
crystallizable substance, and vice versa. The progress of our chemical
knowledge has therefore demanded a wider extension and application of
the term salt, and it is not now confined merely to a combination of an
acid and an alkali, but is conferred even on compounds consisting only
of sulphur and a metal, which are termed sulphur salts.

So also in combinations of chlorine, iodine, bromine, and fluorine,
with metallic bodies, neither of which are acid or alkaline, the term
haloid salts has been applied by Berzelius, from the Greek (a\s, sea salt,
and fl8os form), because they are analogous in constitution to sea salt ;
and the mention of sea salt again reminds us of the wide signification of
the term salt, originally confined to this substance, but now extended
into four great orders, as defined by Turner :

ORDER I. The oxy-mlts. This order includes no salt the acid or
base of wliich is not an oxidised body (ex., nitrate of potash).

CRYSTALLIZATION. 75

ORDER II. The hydro-salts. This order includes no salt the acid or
base of which does not contain hydrogen (ex., chloride of ammonium).

ORDER III. The sulphur salts. This order includes no salt the
electro-positive or negative ingredient of which is not a sulphuret (ex.,
hydrosulphuret of potassium).

ORDER IV. The haloid salts. This order includes no salt the electr^-
positive or negative ingredient of which is not haloidal (Exs., iodide of
potassium and sea salt). To fix the idea of salt still better in the youthful
mind, it should be remembered that alabaster, of which works of art are
constructed, or marble, or lime-stone, or chalk, are all salts, because they
consist of an acid and a base.

In order to cause a substance to crystallize it is first necessary to
endow the particles with freedom of motion. There are many methods
of doing this chemically or by the application of heat, but we cannot by
any mechanical process of concentration, compression, or division, per-
suade a substance to crystallize, unless perhaps we except that remark-
able change in wrought or fibrous iron into crystalline or brittle iron,
by constant vibration, as in the axles of a carriage, or by attaching a
piece of fibrous iron to a tilt hammer.

If we powder some alum crystals they will not again assume their
crystalline form ; if brought in contact there is no freedom of motion. It
is like placing some globules of mercury on a plate. They have no
power to create motion ; their inertia keeps them separated by certain
distances, and they do not coalesce ; but incline the plate, give them
motion, and bring them in contact, they soon unite and form one
globule. The particles of alum are not in close contact, and they have
no freedom of motion unless they are dissolved in water, when they
become invisible; the water by its chemical power destroys the
mechanical aggregation of the solid alum far beyond any operation of
levigation. The solid alum has become liquid, like water ; the particles
are now free to move without let or hindrance from friction. A solution,
(from the Latin solvo, to loosen) is obtained. The alum must indeed be
reduced to minute particles, as they are alike invisible to the eye
whether assisted by the microscope or not. No repose will cause the
alum to separate ; the solvent power of the water opposes gravitation ;
every part of the solution is equally impregnated with alum, and the
particles are diffused at equal distances through the water ; the heavy
alum is actually drawn up against gravity by the water.

How, then, is the alum to be brought back again to the solid state ?
The answer is simple enough. By evaporating away the excess of
water, either by the application of heat or by long exposure to the
atmosphere in a very shallow vessel, the minute atoms of the alum are
brought closer together, and crystallization takes place. The assumption
of the solid state is indicated by the formation of a thin film (called a
pellicle) of crystals, and is further and still more satisfactorily proved by
taking out a drop of the solution and placing it on a bit of glass, which
rapidly becomes filled with crystals if the evaporation has been carried
sufficiently far (Fig. 87).

BOYS PLAYBOOK OF SCIENCE.

After evaporating away sufficient water, the dish is placed on one
bide and allowed to cool, when crystals of the utmost regularity of form

fig. 87. E E. Ring-stand, s s. Spirit-lamps. Fij. 88.

A. FJask containing boiling solution of alum.
Solution. B. Funnel, with a bit of lamp-cotton
stuffed in the bottom. Filtration, c. Evapo-
rating dish. Evaporation. D. Drop on glass.
Crystallization.

are produced, and, denoted by a geometrical term, are called octphedral
or eight-sided crystals, when in the utmost state of perfection (Fig. 88).

The science of crystallography is too elaborate to be discussed at
length in a work of this kind ; the various terms connected with crystals
will therefore only be explained, and experiments given in illustration of
the formation of various crystals.

When the apices i.e., the tips or points of crystals are cut off, they
are said to be truncated ; and the same change occurs on the edges of
numerous crystals.

If some of the salt called chloride of calcium in the dry and amor-
phous state is exposed to the air, it soon absorbs water, or what is termed
deliquesces: the same thing occurs with the crystals of carbonate
of potash, and if four ounces are weighed out in an evaporating dish,
and then exposed for about half an hour to the air, a very perceptible
increase in weight is observed by the assistance of the scales and grain
weights. Deliquescence is a term from the Latin deliyueo, to melt, and
is in fact a gradual melting, caused by the absorption of water from
the atmosphere. The reverse of this is illustrated with various crystals,
such as Glauber's salt (sulphate of soda), or common washing soda
(carbonate of soda) ; if a fine clear crystal is taken out of the solution,
called the mother liquor, in which it has been crystallized, wiped dry,
and placed under a glass shade, this salt may remain for a long period

CRYSTALLIZATION. 7 <

without change, but if it receive one scratch from a pin, the door is
opened apparently for the escape of the water which it contains, chemi-
cally united with the salt, and called water of crystallization; the
white crystal gradually swells out, the little quasi sore from the pin-
scratch spreads over the whole, which becomes opaque, and crumbling
down falls into a shapeless mass of white dust ; this change is called
efflorescence, from effloresce, to blow as a flower caused by the
abstraction from them of chemically-combined water by the atmosphere.
With reference to the preservation of crystals, Professor Griffiths re-
commends them to be oiled and wiped, and placed under a glass shade,
if of a deliquescent nature ; or if efflorescent, they are perfectly pre-
served by placing them under a glass shade with a little water in a cup
to keep the air charged with moisture and prevent any drying up of the
crystal.

Deliquescent crystals may be preserved by placing them, when dry,
in naphtha, or any liquor in which they are perfectly insoluble. Some
salts, like Glauber's salts, contain so much water of crystallization that
when subjected to heat they melt and dissolve in it, and this liquefac-
tion of the solid crystal is called " watery fusion." Other salts, such as
bay salt, chlorate of potash, &c., when heated, fly to pieces, with a
sharp crackling noise, which is due sometimes, to the unequal expansion
of the crystalline surface, or the sudden conversion of the water (retained
in the crystal by capillary attraction) into steam ; thus nitre behaves in
this manner, and frequently retains water in capillary fissures, although
it is an anhydrous salt, or salt perfectly free from combined water. The
crackling sound is called decrepitation, and is well illustrated by
throwing a handful of bay salt on a clear fire ; but this property is
destroyed by powdering the crystals.

Many substances when melted and slowly cooled concrete into the most
perfect crystals ; in these cases heat alone, the antagonist to cohesion,
is the solvent power. Thus, if bismuth be melted in a crucible, and
when cooling, and just as the pellicle (frompellis, a skin or crust) is
forming on the surface, if two small holes are instantly made by a
rod of iron and the liquid metal poured out from the inside (one of the
holes being the entrance for the air, the other the exit for the metal) ; on
carefully breaking the crucible, the bismuth is found to be crystallized
in the most lovely cubes. Sulphur, again, may be crystallized in pris-
matic crystals by pursuing a similar plan; and the great blocks of
spermaceti exhibited by wax chandlers in their windows, are crys-
tallized in the interior and prepared on the same principle.

There are other modes of conferring the crystalline state upon sub-
stances viz., by elevating them into a state of vapour by the process
called sublimation (from sublimis, high or exalted), the lifting up and
condensation of the vapour in the upper part of a vessel ; a process
perfectly distinct from that of distillation, which means to separate
drop by drop. Both of these processes are very ancient, and were in-
vented by the Arabian alchemists long antecedent to the seventh century.
Examples of sublimation are shown by heating iodine, and especially

BOY'S PLAYEOOK OP SCIENCE.

benzoic acid ; with the latter, a very elegant imitation of snow is pro-
duced, by receiving the vapour, on some sprigs of holly or other ever-

green, or imitation paper snow-
drops and crocuses, placed in a
tasteful manner under a glass
vessel. The benzoic acid should
first be sublimed over the sprigs
or artificial flowers in a gas jar,
which may be removed when the
whole is cold, and a clear glass
shade substituted for it. (Fig. 89.)
All electro deposits on metals
are more or less crystalline ; and
copper or silver may be deposited
in a crystalline form by placing
a scraped stick of phosphorus in
a solution of sulphate of copper
or of nitrate of silver. The phos-

Ehorus takes away the oxygen
:om the metal, or deoxidizes the
solution, and the copper or silver
reappears in the metallic form.
The surface of the phosphorus
must not be scraped in the air,
but under water, when the opera-

tion is perfectly safe

A Singular and almost mstan-
taneous crystallization can be
Prdaced * saturating boiling
water With Glaubers salt, of

which one ounce and a half of
water will usually dissolve about two ounces ; having done this, pour
the solution, whilst boiling hot, into clean oil flasks, or vials of any
kind, previously warmed in the oven, and immediately cork them, or tie
strips of wetted bladder, over the orifices of the flasks or vials, or pour
into the neck a small quantity of olive oil, or close the neck with a
cork through which a thermometer tube has been passed. When cold,
no crystallization occurs until atmospheric air is admitted ; and it was
formerly believed that the pressure of the air effected this object, until
some one thought of the oil, and now the theory is modified, and crystal-
lization is supposed to occur in consequence of the water dissolving
some air which causes the deposit of a minute crystal, and this being
the turning point, the whole oecomes solid. However the fact may be
explained, it is certain that when the liquid refuses to crystallize on the
admission of air, the solidification occurs directly a minute crystal of
sulphate of soda, or Glauber's salt, is dropped into the vessel.

"When the crystallization is accomplished, the whole mass is usually
so completely solidified, that on inverting the vessel, not a drop of liquid
falls out.

Fig. 89. A. Gas-jarwith stopper open at

first, to be shut when the lamp is withdrawn.

Wooden stand, with hole to carry the cup c,

M.
ranged on pieces of rock or mineral.

CRYSTALLIZATION.

It may be observed that the same mass of salt will answer any
number of times the same purpose. All that is necessary to be done, is
to place the vial or flask, in a saucepan of warm water, and gradually
raise it to the boiling point till the salt is completely liquefied, when the
vessel must be corked and secured from the air as before. When the
solidification is produced much heat is generated, which is rendered
apparent by means of a thermometer, or by the insertion of a copper
wire into the pasty mass of crystal in the flask, and then touching an
extremely thin shaving or cutting of phosphorus, dried and placed on
cotton wool. Solidification in all cases produces heat. Liquefaction
produces cold.

In Masters's freezing apparatus certain measured quantities of crystal-
lized sal-ammoniac, nitre, and nitrate of ammonia, are placed in a
metallic cylinder, sur-
rounded with a small
quantity of spring water
contained in an outer
vessel. Directly the
crystals are liquefied by
the addition of water, in-
tense cold is produced,
which freezes the water
and forms an exact cast
of the inner cylinder in
ice, and this may after-
wards be removed, by

nring away the lique-
salts, and filling the
inner cylinder, with water
of the same temperature
as the air, which rapidly

Fi - 90 - A - The inner cylinder which contains the

freezing mixtur e. B B. The outer one containing spring
ice, and allows it to slip water, oc. The ice slipping away from the inner cylinder.
off into any convenient
vessel ready to receive it. (Pig. 90.) ^

For an ingenious method of obtaining large and perfect crystals of
almost any size, experimentalists are indebted to Le Blanc. His method
consists in first procuring small and perfect crystals say, octohedra of
alum and then placing them in a broad flat-bottomed pan, he pours
over the crystals a quantity of saturated solution of alum, obtained
by evaporating a solution of alum until a drop taken out crystallizes on
cooling. The positions of the crystals are altered at least once a day
with a glass rod, so that all the faces may be alternately exposed to the
action of the solution, for the side on which the crystal rests, or is in
contact with the vessel, never receives any increment. The crystals
will thus gradually grow or increase in size, and when they have done so
for some time, the best and most symmetrical, may be removed and
placed separately, in vessels containing some of the same saturated

BOYS PLAYBOOK OF SCIENCE.

solution of alum, and being constantly turned they may be obtained of
almost any size desired.

Unless the crystals are removed to fresh solutions, a reaction takes
place, in consequence of the exhaustion of the alum from the water, and
the crystal is attacked and dissolved. This action is first perceptible on
the edges and angles of the crystal ; they become blunted and gradually
/ose their shape altogether. By this method crystals may be made to
grow in length or breadth the former when they are placed upon their
sides, the latter if they be made to stand upon their bases.

On Le Blanc's principle, beautiful crystal baskets are made with alum,
sulphate of copper, and bichromate of potash. The baskets are usually
.made of covered copper wire, and when the salts crystallize on them as a
nucleus or centre, they are constantly removed to fresh solutions, so
that the whole is completely covered, and red, white, and blue sparkling
crystal baskets formed. They will retain their brilliancy for any time,
by placing them under a glass shade, with a cup containing a little
water.

The sketch below affords an excellent illustration of some of Nature's
remarkable concretions in the peculiar columnar structure of basalt.

Fig. 91. The Giant's Causeway,

Fig. 92. Alchemists at work.

CHAPTER X.

CHEMISTKY.

THERE is hardly any kind of knowledge which has been so slowly
acquired as that of chemistry, and perhaps no other science has offered
snch fascinating rewards to the labour of its votaries as the philosopher's
stone, which was to produce an unfailing supply of gold ; or the elixir
of life, that was to give the discoverer of the gold-making art the time,
the prolonged life, in which he might spend and enjoy it.

Hundreds of years ago Egypt was the great depository of all learning,
art, and science, and it was to this ancient country that the most cele-
brated sages of antiquity travelled.

Hermes, or Mercurius Trismegistus, the favourite minister of the
Egyptian king Osiris, has been celebrated as the inventor of the art of
alchemy, and the first treatise upon it has been attributed to Zosymus,
of Chemnis or Panopolis. The Moors who conquered Spain were re-

82 BOY'S PLAYBOOK OF SCIENCE.

markable for their learning, and the taste and elegance with which they
designed and carried out a new style of architecture, with its love
Arabesque ornamentation. They were likewise great followers of the
art of alchemy, when they ceased to be conquerors, and became more
reconciled to the arts of peace. Strange that such a people, thirsting
as they did in after years for all kinds of knowledge, should have
destroyed, in the persons of their ancestors, the most numerous collection
of books that the world had ever seen : the magnificent library of
Alexandria, collected by the Ptolemies with great diligence and at an
enormous expense, was burned by the orders of Caliph Omar ; whilst it
is stated that the alchemical works had been previously destroyed by
Diocletian in the fourth century, lest the Egyptians should acquire by
such means sufficient wealth to withstand the Roman power, for gold
was then, as it is now, " the sinews of war."

Eastern historians relate the trouble and expense incurred by the suc-
ceeding Caliphs, who, resigning the Saracenic barbarism of their an-
cestors, were glad to collect from all parts the books which were to
furnish forth a princely library at Bagdad. How the learned scholar
sighs when he reads of seven hundred thousand books being consigned
to the ignominious office of heating forty thousand baths in the capital
of Egypt, and of the magnificent Alexandrian Library, a mental fuel for
the lamp of learning in all ages, consumed in bath furnaces, and affording
six months' fuel for that purpose. The Arabians, however, made amends
for these barbarous deeds in succeeding centuries, and when all Europe
was laid waste under the iron rule of the Goths, they became the pro-
tectors of philosophy and the promoters of its pursuits ; and thus we
come to the seventh century, in which Geber, an Arabian prince lived, and
is stated to be the earliest of the true alchemists whose name has reached
posterity.

Without attempting to fill up the alchemical history of the intervening
centuries, we leap forward six hundred years, and now find ourselves in
imagination in England, with the learned friar, Roger Bacon, a native of
Somersetshire, who lived about the middle of the thirteenth century : and
although the continual study of alchemy had not yet produced the
" stone," it bore fruit in other discoveries, and Roger Bacon is said,
with great appearance of truth, to have discovered gunpowder, for he
says in one of his works : " From saltpetre and other ingredients we
are able to form a fire which will burn to any distance ;" and again
alluding to its effects, " a small portion of matter, about the size of the
thumb, properly disposed, will make a tremendous sound and corusca-
tion, by which cities and armies might be destroyed." The exaggerated
style seems to have been a favourite one with all philosophers, from the
time of Roger Bacon to that of Muschenbroek of the University of Ley den,
who accidentally discovered the Leyden jar in the year 1746, and re-
ceiving the first shock, from a vial containing a little water, into which
a cork and nail had been fitted, states that " he felt himself struck in
his arms, shoulders, and breast, so that he lost his breath, and was
two days before he recovered from the effects of the blow and the

CHEMISTHY. 83

terror ;" adding, that " he would not take a second shock for the kingdom
of France." Disregarding the numerous alchemical events occurring
from the time of Roger Bacon, we again advance four hundred years
viz., to the year 1662, when, on the 15th of July, King Charles II.
granted a royal charter to the Philosophical Society of Oxford, who
had removed to London, under the name of the Royal Society of London
for Promoting Natural Knowledge, and in the year 1665 was published
the first number of the Philosophical Transactions ; this work contains
the successive discoveries of Mayow, Hales, Black, Leslie, Cavendish,
Lavoisier, Priestley, Davy, Faraday; and since the year 1762 lias been
regularly published at the rate of one volume per annum. With this
preface proceed we now to discuss some of the varied phenomena of
chemical attraction, or what is more correctly termed

CHEMICAL AFFINITY.

The above title refers to an endless series of changes brought about
by chemical combinations, all of which can be reduced to certain fixed
laws, and admit of a simple classification and arrangement. A me-
chanical aggregation, however well arranged, can be always distinguished
from a chemical one. Thus, a grain of gunpowder consists of nitre,
which can be washed away with boiling water, of sulphur, which can be
sublimed and made to pass away as vapour, of charcoal, which remains
behind after the previous processes are complete; this mixture has
been perfected by a careful proportion of the respective ingredients, it
has been wetted, and ground, and pressed, granulated, and finally
dried; all these mechanical processes have been so well carried out
that each grain, if analysed, would be similar to the other ; and yet it
is, after all, only a mechanical aggregation, because the sulphur, the
charcoal, and the nitre are unchanged. _ A grain of gunpowder mois-
tened, crushed, and examined by a high microscopic power, would
indicate the yellow particles of sulphur, the black parts of charcoal,
whilst the water filtered from the grain of powder and dried, would
show the nitre by the form of the crvstal. On the other hand,
if some nitre is fused at a dull red heat in a little crucible, and two
or three grains of sulphur are added, they are rapidly oxidized, and
combine with the potash, forming sulphate of potash ; and after this
change a few grains of charcoal may be added in a similar manner, when
they burn brightly, and are oxidized and converted into carbonic acid,
which also unites in like manner with the potash, forming carbonate of
potash ; so that when the fused nitre is cooled and a few particles
examined by the microscope, the charcoal and sulphur are no longer
distinguishable, they have undergone a chemical combination with
portions of the nitre, and have produced two new salts, perfectly dif-
ferent in taste, gravity, and appearance from the original substances
employed to produce them. Hence chemical combination is defined
to be "*that property which is possessed by one or more substances,
of uniting together and producing a third or other body perfectly dif-

a 9

84 BOY'S PLAYBOOK OF SCIENCE.

ferent in its nature from either of the two or more generating the new
compound"

To return to our first experiment with the gunpowder : take sulphur,
place some in an iron ladle, heat it over a gas flame till it catches fire, then
ascend a ladder, and pour it gently, from the greatest height you can
reach, into a pail of warm water : if this experiment is performed in a
darkened room a magnificent and continuous stream of fire is obtained,
of a blue colour, without a single break in its whole length, provided
the ladle is gradually inclined and emptied. The substance that drops
into the warm water is no longer yellow and hard, but is red, soft, and
plastic ; it is still sulphur, though it has taken a new form, because that
element is dimorphous (fiig twice, and \iop$T] a form), and, Proteus-like,
can assume two forms. Take another ladle, and melt some nitre in it at
a dull red heat, then add a small quantity of sulphur, which will burn as
before ; and now, after waiting a few minutes, repeat the same experiment
by pouring the liquid from the steps through the air into water ; observe
it no longer flames, and the substance received into the water is not
red and soft and plastic, but is white, or nearly so, and rapidly dis-
solves away in the water. The sulphur has united with the oxygen of
the nitre and formed sulphuric acid, which combines with the potash
and forms sulphate of potash ; here, then, oxygen, sulphur, and potas-
sium, have united and formed a salt in which the separate properties
of the three bodies have completely disappeared ; to prove this, it is
only necessary to dissolve the sulphate of potash in water, and after
filtering the solution, or allowing it to settle, till it becomes quite clear
and bright, some solution of baryta may now be added, when a white
precipitate is thrown down, consisting of sulphate of baryta, which is in-
soluble in nitric or other strong acids. The behaviour of a solution of
sulphate of potash with a nitrate of baryta may now be contrasted with
that of the elements it contains ; oh the addition of sulphur to a solu-
tion of nitrate of baryta no change whatever takes place, because the
sulphur is perfectly insoluble. If a stream of oxygen gas is passed from
a bladder and jet through the same test, no effect is produced ; the nitrate
of baryta has already acquired its full proportion of oxygen, and no
further addition has any power to change its nature ; finally, if a bit of
the metal potassium is placed in the solution of nitrate of baryta it does
not sink, being lighter than water, and it takes fire ; but this is not in
any way connected with the presence of the test, as the same thing will
happen if another bit of the metal is placed in water it is the oxygen
of the latter which unites rapidly with the potassium, and causes it to
become so hot that the hydrogen, escaping around the little red-hot
globules, takes fire ; moreover, the fact of the combustion of the potas-
sium under such circumstances is another striking proof of the opposite
qualities of the three elements sulphur, oxygen, and potassium as
compared with the three chemically combined and forming sulphate of
potash. The same kind of experiment may be repeated with charcoal ;
if some powdered charcoal is made red-hot, and then puffed into the air
with a blowing machine, numbers of sparks are produced, and the char

CHEMISTRY. 85

coal burns away and forms carbonic acid gas, a little ash being left
behind; but if some more nitre be heated in a ladle, and charcoal
added, a brilliant deflagration (deflayro, to burn) occurs, and the charcoal,
instead of passing away in the air as carbonic acid, is now retained in
the same shape, but firmly and chemically united with the potash of the
nitre, forming carbonate of potash, or pearl-ash, which is not black and
insoluble in water and acids like charcoal, but is white, and not only
soluble in water, but is most rapidly attacked by acids with effer-
vescence, and the carbon escapes in the form of carbonic acid gas. Thus
we have traced out the distinction between mechanical aggregation and
chemical affinity, taking for an example the difference between gun-
powder as a whole (in which the ingredients are so nicely balanced that
it is almost a chemical combination), and its constituents, sulphur,
charcoal, and nitre, when they are chemically combined ; or, in briefer
language, we have noticed the difference between the mechanical mix-
ture, and some of the chemical combinations, of three important elements.
Our very slight and partial examination of three simple bodies does not,
however, afford us any deep insight into the principles of chemistry ; we
have, as it were, only mastered the signification of a few words in a lan-
guage ; we might know that chien was the French for dog, or cheval
horse, or homme man ; but that knowledge would not be the acquisition of
the French language, because we must first know the alphabet, and
then the combination of these letters into words ; we must also acquire
a knowledge of the proper arrangement of these words into sentences,
or grammar, both syntax and prosody, before we can claim to be a
French scholar : so it is with chemistry any number of isolated experi-
ments with various chemical substances would be comparatively useless,
and therefore the " alphabet of chemistry," or " table of simple ele-
ments/' must first be acquired. These bodies are understood to be
solids, fluids, and gases, which have hitherto defied the most elaborate
means employed to reduce them into more than one kind of matter.
Even pure light is separable into seven parts viz., red, orange,
yellow, green, blue, inaigo, and violet ; but the elements we shall
now enumerate are not of a compound, but, so far as we know, of an
absolutely simple or single nature ; they represent the boundaries, not
the finality, of the knowledge that may be acquired respecting them.

The elements are sixty-four in number, of which about forty are
tolerably plentiful, and therefore common; whilst the remainder, twenty-
four, are rare, and for that reason of a lesser utility : whenever
Nature employs an element on a grand scale it may certainly be called
common, but it generally works for the common good of all, and fulfils
the most important offices.

BOY'S PLAYBOOK OF SCIENCE.

CLASSIFICATION OF THE ALPHABET OF CHEMISTRY.

13 Non-Metallic Bodies.

Combining

Coi

nbining

Name.

ymbol

pro

portion
nt.nmift

Name. i

3ymbo

prc

' nr

(portion,
fitnmio.

weight.

Oxygen . .

Carbon . .

Hydrogen

Boron . . .

10-9

Nitrogen . .

10.

Sulphur . .

;

Chlorine . .

35-5

11.

Phosphorus .

Iodine . . .

127-1

12.

Silicon . .

21-3

Bromine . .

80-

13.

Selenium . .

39-5

Fluorine . .

18-9

51 Metals.

Aluminum .

13-7

27.

Nickel. . .

29-6

Antimony

129

28.

Norium . .

Arsenic . .

29.

Niobium . .

Barium . .

68-5

30.

Osmium . .

99-6

Bismuth . .

213

31.

Platinum . .

987

Cadmium . .

32.

Potassium .

39-2

Calcium . .

33.

Palladium

53-3

Cerium . .

34.

Pelopium . .

Chromium

B-

26-7

35.

Rhodium . .

52-2

10.

Cobalt. . .

29-5

36.

Rhuthenium .

52-2

11.
12.

Copper . .
Donarium . .

"~~

31-7

37.

38.

Silver . . .
Sodium . .

108-1
23

13.

Didymium. .

39.

Strontium

43-8

14.

Erbium . .

40.

Tin. . . .

15,

Gold . . .

197

41.

Tantalum . .

184

16.

Glucinum . .

42.

Tellurium . .

64-2

17.

Iron . . .

43.

Terbium . .

18.

Ilmenium . .

44.

Thorium . .

59-6

19.

Iridium .

45.

Titanium . .

20.

Lead . . .

103-7

46.

Tungsten . .

21.

Lanthanium .

47.

Uranium . .

22.

Lithium . .

6-5

48.

Vanadium

68-6

23.

Magnesium .

12-2

49.

Yttrium . .

24.

Manganese .

27-6

50.

Zinc- . . .

32-6

25.

Mercury . .

100

51.

Zirconium

22-4

26.

Molybdenum .

(N.B. The elements printed in italics are at present unimportant.

A few words will suffice to explain the meaning of the terms which
head the names, letters, and numbers of the Table of Elements. The

* From the mineral Wolfran, and now exceedingly valuable, as when alloyed with iron
it is harder than, and will bore through steel.

CHEMISTEY. 87

names of the elements have very interesting derivations, which it is not
the object of this work to go into; the symbols are abbreviations,
ciphers of the simplest kind, to save time and trouble in the frequent re-
petition of long words, just as the signs -|- plus, and minus, are used
in algebraic formulae. For instance the constant recurrence of water
in chemical combinations must be named, and would involve the most
tedious repetition; water consists of oxygen and hydrogen, and by taking
the first letter of each word we have an instructive symbol, which not
only gives us an abbreviated term for water, but also imparts at once a
knowledge of its composition by the use of the letters, HO.

Again, to take a more complex example, such as would occur in the
study of organic chemistry a sentence such as the hydrated oxide of
acetule,^ is written at once by C 4 H 4 2 , the figures referring to the number
of equivalents of each element viz., 4 equivalents of C, the symbol for
carbon, 4 of H (hydrogen), and 2 of (oxygen).

The long word paranaphthaline, a substance contained in coal tar, is
disposed of at once with the symbols and figures C 30 H 12 .

The figures in the third column are, however, the most interesting
to the precise and mathematically exact chemist. They represent the
united labours of the most painstaking and learned chemists, and are
the exact quantities in which the various elements unite. To quote one
example : if 8 parts by weight of oxygen viz., the combining propor-
tions of that element are united with 1 part by weight of hydrogen, also
its combining number, the result will be 9 parts by weight of water ;
but if 8 parts of oxvgen and 2 parts of hydrogen were used, one only of
the latter could unite with the former, and the result would be the
formation again of 9 parts of water, with an overplus of 1 equivalent of
hydrogen.

It is useless to multiply examples, and it is sufiicient to know that
with this table of numbers the figures of analysis are obtained. Sup-
posing a substance contained 27 parts of water, and the oxygen in
this had to be determined, the rule of proportion would give it at once,
9 : 27 : : 8 : 24. 9 parts of water are to 27 parts as 8 of oxygen (the
quantity contained in 9 parts of water) are to the answer required
viz., 24 of oxygen. The names, symbols, and combining proportions
being understood, we may now proceed with the performance of many
interesting

CHEMICAL EXPERIMENTS.

As the permanent gases head the list, they will first engage our
attention, beginning with the element oxvgen Symbol 0, combining
proportion 8. There is nothing can give a better idea of the enormous
quantity of oxygen present in the animal, vegetable, and mineral king-
doms, than the statement that it represents one-third of the weight of
the whole crust of the globe. Silica, or flint, contains about half its
weight of oxygen ; lime contains forty per cent. ; alumina about thirty-
three per cent. In these substances the element oxygen remains inactive
and powerless, chained by the strong fetters of chemical affinity to the

BOY'S PLAYB00K OF SCIENCE.

silicium of the flint, the calcium of the lime, and the aluminum of the
alumina. If these substances are heated by themselves they will not
yield up the large quantity of oxygen they contain.

Nature, however, is prodigal in her creation, and hence we have but
to pursue our search diligently to find a substance or mineral containing
an abundance of oxygen, and part of which it will relinquish by what
used to be called by the " old alchemists" the torture of heat. Such a
mineral is the black oxide of manganese, or more correctly the binoxide
of njjhganese, which consists of one combining proportion of the metal
manganese viz., 27'6, and two of oxygen viz., 8 X 2 = 16. If three
proportions of the binoxide of manganese are heated to redness in an
iron retort, they yield one proportion (equal to 8) of oxygen, and all
that has just been explained by so many words is comprehended in the
symbols and figures below :

3 Mn0 2 = Mn 3 O 4 + 0.

Thus the 3 Mn0 2 represent the three proportions of the binoxide of
manganese before heat is applied, whilst the sign =, the sign of equation
(equal to), is intended to show that the elements or compounds placed
before it produce those which follow it ; hence the sequel Mn 3 4 -f(?
shows that another compound of the metal and oxygen is produced,
whilst the + indicates the liberated oxygen gas. The iron retort
employed to hold the mineral should be made of cast iron in preference
to wrought iron, as the latter is very soon worn out by contact with
oxygen at a red heat. A gun-barrel will answer the purpose for an
experiment on the small scale, to which must be adapted a cock and
piece of pewter tubing. Such a make-shift arrangement may do very
well when nothing better offers ; but as a question of expense, it is
probably cheaper in the end to order of Messrs. Simpson and Maule, or
of Messrs. Griffin, or of Messrs. Bolton, a cast-iron bottle, or cast-iron
retort, as it is termed, of a size sufficient to prepare two gallons of

Pig. 93. A. The iron bottle, containing the black oxide of manganese, with pipe passing to
the pneumatic trough, B B, in which is fixed a shelf, c, perforated with a hole, under which
the end of the pipe is adjusted, and the gas passes into the gas-jar, D.

oxygen from the binoxide of manganese, which, with four feet of iron
conducting-pipe, and connected to the bottle with a screw, does not

PREPARATION OF OXYGEN GAS.

cost more than six shillings an enormous dip, perhaps, in the juvenile
pocket, and therefore we shall indicate presently a still cheaper appa-
ratus for the same purpose. (Eig. 93.)

The oxygen is conveyed to a square tin box provided with a shelf at
one end, perforated with several holes at least one inch in diameter,
called the pneumatic trough ; any wooden trough, butter or wash-tub,
foot-pan or bath, provided with a shelf, may be raised by the same
title to the dignity of a piece of chemical apparatus. The gas jar rn^t
be filled with water by withdrawing the stopper and pressing it down
into the trough, and when the neck is below the level of the water, the
stopper is again inserted, and the jar with the water therein contained

A D

Fig. 94. A A. Pneumatic trough, with gas jar raised to shelf; bubbles of air are rushing
in at B, as the level of the water is below the shelf viz., at c c. D D. Same trough and
gas jar with water kept over the shelf by the introduction of the stone pitchers, full of
water.

lifted steadily on to the shelf, the entry of atmospheric air being prevented
by keeping the lower part of the gas jar, called the welt, under the water.
Sometimes the pneumatic trough contains so small a quantity of water
that on raising the gas jar to the shelf the liquid does not coyer the bottom,
and the air rushes up in large bubbles. Under these circumstances it
is better to provide a galWstone jug full of water, so that when the
jar is being raised to the shelf it may be thrust into the trough (on the
same principle as the crow and the pitcher in the fable), and thus by its
bulk (as the stones in the pitcher) raise the water to the proper level.
When the gas jar is about half filled with gas the jug may be withdrawn.
This arrangement saves the trouble of constantly adding and baling out
water from the pneumatic trough. (Fig. 94.)

There are other solid oxygenized bodies in which the affinities are less
powerful, and hence a lower degree of heat suffices to liberate the
oxygen gas, and one of the most useful in this respect is the salt termed
chlorate of potash. If the substance is heated by itself, the temperature
required to expel the oxygen is almost as high as that demanded for
the black oxide of manganese ; but, strange to say, if the two substances
are reduced to powder, and mixed in equal quantities by weight, then a
very moderate increase of heat is sufficient to cause the chlorate of

BOY'S PLAYBOOK OF SCIENCE.

potash to give up its oxygen, whilst the oxide of manganese undergoes
no change whatever. It seems to fulfil only a mechanical office possibly
that of separating each particle of chlorate of potash from the other, so

Fig. 95. Preparation of oxygen from

KO.C10 5 ={ a

that the heat attacks the substance in detail, just as a solid square of
infantry might repel almost any attack, whilst the same body dispersed
over a large space might be of little use ; so with the chlorate of potash,
which undergoes rapid decomposition when mixed with and divided
amongst the particles of the oxide of manganese ; less so with the red
oxide of iron, and still less with sand or brick-dust. (Fig. 95.)

This curious fact is explained usually by reference to what is called
catalytic action, or decomposition by contact (Kara, downwards, and \va>, I
unloosen), being a power possessed by a body of resolving another into a new
compound without undergoing any change itself. To make this term still
clearer, we may notice another example in linen rags, which may be
exposed for any length of time to the action of water without fear of
conversion into sugar ; if, however, oil of vitriol is first added to the
linen rags, and they are subsequently digested at a proper temperature
with water, then the rags are converted into sugar (the author has seen
a specimen made of an " old shirt") ; but, curious to relate, the oil of
vitriol is unchanged in the process, and if the process be commenced with a
pound of acid, the same quantity is discoverable at the end of the chemical
decomposition of the linen rags, and their conversion into sugar.

If a mixture of equal parts of oxide of manganese and chlorate of
potash is placed in a clean Florence flask, with a cork, and pewter, or
glass tube attached, great quantities of oxygen are quickly liberated, on
the application of the heat of a spirit lamp. Such a retort would cost
about fourpence, and if the flask is broken in the operation it can be
easily replaced by another, value one penny, as the same cork and tube
will generally suit a number of these cheap glass vessels. Corks may

PREPARATION OP OXYGEN GAS.

always be softened by using either a proper cork squeezer, or by placing
them under a piece of board or a flat surface, and rolling and pressing
the cork till cpite elastic.

Whilst fitting the latter into the neck of a flask, it is perhaps safer
to hold the thin and fragile vessel in a cloth, so that if the flask breaks
the chemical experiment may not be arrested for many days by the
severe cutting and wounding of the fingers. After the cork is fitted, it
is to be removed from the flask and bored wifti a cork borer. This
useful tool is sold in complete sets to suit all sizes of glass tubes, and
the pewter or glass being inserted, the flask and tube will be ready for
use, provided the tube is bent to the proper curve. This is easy enough
to perform with the pewter, but not quite so easy with the glass tube,
which must be held over the flame of a spirit lamp till soft, and then

Fig. -96. A. The cork squeezer. B. The cork borers, c. The operation of bending the
glass tube over the flame of the spirit-lamp. D. The neck of the flask, with cork and tube
bent and fitted complete for use.

bent very gradually to the proper curve. If a short length of the glass
tube is heated, it bends too sharply, and the convexity of the glass is
flattened, whilst the internal diameter of the tube is lessened, so that at
least three inches in length should be warmed, and the heat must not
be continued in one place only, but should be maintained in the direc-
tion of the bend, the whole manipulation being conducted without any
hurry. (Fig. 96.)

Having filled a gas jar with oxygen, it may be removed from the
pneumatic trough by sliding it into a plate under the surface of the
water, and to prevent the stopper being thrust out accidentally from the
jar by the upward pressure of the gas, whilst a little compressed, during
the act of passing it into the plate, it is advisable to hold the stopper
of the jar firmly but gently, so that it cannot slip out of its place. A
number of jars of oxygen may be prepared and arranged in plates, all of
which of course must contain a little water, and enough to cover the
welt of the jar.

BOY'S PLAYBOOK OF SCIENCE.

EXPERIMENTS WITH OXYGEN GAS.

This gas was originally discovered by Priestley, in August, 1 774, and
was first obtained by heating red precipitate i.e., the red oxide ot
mercury.

HgO=Hg + 0.

We leave these symbols and figures to be deciphered by the youthful
philosopher with the aid of the table of elements, &c., and return to the
experiments.

There are certain thin wax tapers like waxed cord, called bougies,
which can be bent to any shape, and are very convenient for experiments
with the gases. If one of these tapers is bent as
in Tig. 97, then lighted and allowed to burn for
some minutes, a long snuff is gradually formed,
which remains in a state of ignition when the flame
of the taper is blown out. On plunging this into
a jar of oxygen, it instantly re-lights with a sort
of report, and burns with greatly-increased bril-
liancy, as described by Dr. Priestley in his first
experiment with this gas, and so elegantly repeated
by Professor Brande in his refined dissertation on
the progress of chemical science.

"The 1st of August, 1774, is a red-letter day in
the annals of chemical philosophy, for it was then
that Dr. Priestley discovered dephlogisticated air.
Some, sporting in the sunshine of rhetoric, have
called this the birthday of pneumatic chemistry ;
but it was even a more marked and memorable
period ; it was then (to pursue the metaphor) that
this branch of science, having eked out a sickly and infirm infancy in
the ill-managed nursery of the early chemists, began to display symp-
toms of an improving constitution, and to exhibit the most hopeful
and unexpected marks of future importance. The first experiment,
which led to a very satisfactory result, was concluded as follows:
A glass jar was filled with quicksilver, and inserted in a basin of the
same; some red precipitate of quicksilver was then introduced, and
floated upon the quicksilver in the jar; heat was applied to it in this
situation with a burning-lens, and to use Priestley's own words, I pre-
sently found that air teas expelled from it very readily. Having got
about three or four times as much as the bulk of my materials, 1 ad-
mitted wetter into it, and found that it was not imbibed by it. But
what surprised me more than I can well express was, that a candle
burned in this air with a remarkably vigorous flame, very much like that
enlarged flame with which a candle burns in nitrous air exposed to iron
or lime of sulphur (i.e., laughing gas) ; but as I had got nothing like
this remarkable appearance from any kind of air besides this peculiar

Fig. 97.

EXPERIMENTS WITH OXYGEtf GAS.

Fig. 98. A. Glass vessel full of mercury, con-
taining the red precipitate at the top, and stand-

modification of nitrous air, and
I kneio no nitrous acid was used
in the preparation of mercurius
calcinatus, I was utterly at a loss
how to account for it" (Fig. 98.)

Second Experiment.

The term oxygen is derived
from the Greek \ofrar, acid, and
yevvao), I give rise to), and was
originally given to this element
by Lavoisier, who also claimed
its discovery ; and if this honour
is denied him, surely he has de-
served equal scientific glory inhis

masterly experiments, through ing in the dish B^lso'containing mercury, c. The
if ,J j ',, , ,? burning-glass concentrating the sun's rays on the

Which he discovered that the re d precipitate, being Priestley's original experi-
mixture of forty-two parts by ment.

measure of azote, with eight parts by measure of oxygen, produced a
compound precisely resembling our atmosphere. The name given to
oxygen was founded on a series of experiments, one of which will now
be mentioned.

Place some sulphur in a little copper ladle
attached to a wire, and called a deflagrating
spoon, passed through a round piece of zinc
or brass plate and cork, so that the latter
acts as an adjusting arrangement to fix the
wire at any point required. The combus-
tion of the" sulphur, previously feeble, now
assumes a remarkable intensity, and a pecu-
liar coloured light is generated, whilst the
sulphur unites with the oxygen, and forms
sulphurous acid gas. It produces, in fact,
the same gas which is formed by burning an
ordinary sulphur match. This compound is
valuable as a disinfectant, and is a very im-
portant bleaching agent, being most exten-
sively employed in the whitening of straw
employed in the manufacture of straw bon-
nets. It is an acid gas, as Lavoisier found,
and this property may be detected by pour-
ing a little tincture of litmus into the bot-
tom of the plate in which the gas jar stands. The'gasjarT
The blue colour of the litmus is rapidly
changed to red, and it might be thought that no further argument
could possibly be required to prove that oxygen was the acidifying
agent, themore particularly as the result is thesameinthe next illustration.

Fig. 99. A. The deflagrating

9i BOY'S PLAYBOOK OF SCIENCE.

Third Experiment.

Cut a small piece from an ordinary stick of phosphorus under
water, take care to dry it properly with a cloth, and after placing it
in a deflagrating spoon, remove the stopper from the gas-jar, as there
is no fear of the oxygen rushing away, because it is somewhat heavier
than atmospheric air ; and then, after placing the spoon with the phos-
phorus in the neck of the jar, apply a heated wire and pass the spoon
at once into the middle of the oxygen; in a few seconds a most
brilliant light is obtained, and the jar is filled with a white smoke ;
as this subsides, being phosphoric acid, and perfectly soluble in water,
the same litmus test may be applied, when it is in like manner
changed to red. The acid obtained is one of the most important con-
stituents of bone.

Fourth Experiment.

A. bit of bark-charcoal bound round with wire is set on fire either
by holding it in the flame of a spirit-lamp, or by attaching a small piece
of waxed cotton to the lower part, and igniting this ; the charcoal may then
be inserted into a bottle of oxygen, when the most brilliant scintilla-
tions occur. After the combustion has ceased and the whole is cool,
a little tincture of litmus may also be poured in and shaken about,
when it likewise turns red, proving for the third time the generation
of an acid body, called carbonic acid an acid, like the others already
mentioned, of great value, and one which Nature employs on a stu-
pendous scale as a means of providing plants, &c., with solid char-
coal. Carbonic acid, a virulent poison to animal life, is, when properly
diluted, and as contained in atmospheric air, one of the chief alimen-
tary bodies required by growing and healthy plants.

In three experiments acid bodies have been obtained ; can we specu-
late on the result of the next ?

Fifth Experiment.

Into a deflagrating spoon place a bit of potassium, set this on fire
by holding it in the spoon in the flame of a spirit-lamp, and then rapidly
plunge the burning metal into a bottle of oxygen. A brilliant ignition
occurs in the deflagrating spoon for a few seconds, and there is little or no
smoke in the jar. The product this time is a solid, called potash,
and if this be dissolved in water and -filtered, it is found to be clear
and bright, and now on the addition of a little tincture of litmus to
one half of the solution, it is wholly unaffected, and remains blue ;
but if with the other half a small quantity of tincture of turmeric is
mixed, it immediately changes from a bright yellow solution to a
reddish-brown, because turmeric is one of the tests for an alkali ; and
thus is ascertained by the help of this and other tests that the result
of the combustion is not an acid, but an alkali. The experiment
is made still more satisfactory by burning another bit of potassium
in oxygen and dissolving the product in water, and if any portion of

EXPEIUMENTS WITH OXYGEN GAS. 05

the reddened liquid derived from the sulphurous, phosphoric, and car-
bonic acids taken from the previous experiments, be added to separate
portions of the alkaline solution, they are all restored to their original blue
colour, because an acid is neutralized by an alkali ; and the experiment is
made quite conclusive by the restoration of the reddened turmeric to a
bright yellow on the addition of a solution of either of the three acids
already named. Moreover, an acid need not contain a fraction of
oxygen, as there is a numerous class of %dracids, in which the acidi-
fying principle is hydrogen instead of oxygen, such as the hydrochloric,
hydriodic, hydro-bromic, and hydrofluoric acids.

Sixth Experiment.

A. piece of watch-spring is softened at one end, by holding it in the
flame of a spirit-lamp, and allowing it to cool. A bit of waxed cotton,
is then bound round the softened end, and after being set on fire, is
plunged into a gas jar containing oxygen ; the cotton first burns away,
and then the heat communicates to the steel, which gradually takes fire,
and being once well ignited, continues toburn with amazing rapidity, form-
ing drops of liquid dross, which fall to the bottom of the plate and also
a reddish smoke, which condenses on the sides of the jar ; neither the
dross which has dropped into the plate, nor the reddish matter condensed
on the jar, will affect either tincture of litmus or turmeric; they are
neither acid nor alkaline, but neutral compounds of iron, called the
sesquioxide of iron (Ee^), and the magnetic oxide (Fe 3 4 =EeO.

Some oxygen gas contained in a bladder provided with a proper
jet may be squeezed out, and upon, some liquid phosphorus con-

Fig. 100. A. Bladder containing- oxygen, provided with a stop-cock and jet leading to,
B, B. Finger glass containing boiling water, c. The cup of melted phosphorus under the
water. The gas escapes from the bladder when pressed.

tained in a cup at the bottom of a finger glass full of boiling water,
when a most brilliant combustion occurs, proving that so long as the
principle is complied with viz., that of furnishing oxygen to a com-
bustible substance it will burn under water, provided it is insoluble,
and possesses the remarkable affinity for oxygen which belongs to
phosphorus. The experiment should be performed with boiling water,
to keep the phosphorus in the liquid state j and it is quite as well to hold

BOY'S PLAYBOOK OF SCIENCE.

a square foot of wire gauze over the finger glass whilst the experiment
is being performed. (Eig. 100.)

Eighth Experiment.

Oxygen is available from many substances when they are mixed with
combustible substances, and hence the brilliant effects produced by
burning a mixture of nitre, meal powder, sulphur, and iron or steel
filings ; the metal burns with great brilliancy, and is projected from the
case in most beautiful sparks, which are long and needle-shaped with
steel, and in the form of miniature rosettes with iron filings ; it is the
oxygen from the nitre that causes the combustion of the metal, the
other ingredients only accelerate the heat and rate of ignition of the
brilliant iron, which is usually termed a gerb.

Ninth Experiment.

A mixture of nitrate of potash, powdered
charcoal, sulphur, and nitrate of strontium,
driven into a strong paper case about two
inches long, and well closed at the end with
varnish, being quite waterproof, may be set on
fire, and will continue to burn under water
until the whole is consumed ; the only precau-
tion necessary being to burn the composition
from the case with the mouth downward, and
if the experiment is tried in a deep glass jar it
has a very pleasing effect. (Fig. 101.)

The red-fire composition is made by mixing
nitrate of strontia 40 parts by weight, flowers
of sulphur 13 parts, chlorate of potash 5 parts,
sulphuret of antimony 4 parts. These ingre-
dients must first be well powdered separately,
and then mixed carefully on a sheet of paper
with a paper-knife. They are liable to explode
if rubbed together in a mortar, on account of
^he presence of sulphur and chlorate of potash,
and the composition, if kept for any time, is
liable to take fire spontaneously.

Fig.'ioi. A. Case of red fire
downwards, and at-

?f* s?nk a

U. c c. Jar containing water.

Tenth Experiment.

Some zinc is melted in an iron ladle, and made quite red hot ; if a
kittle dry nitre is thrown upon the surface, and gently stirred into the
metal, it takes fire with the production of an intense white light, whilst
large quantities of white flakes ascend, and again descend when cold,
being the oxide of zinc, and called by the alchemists the " Philosopher's
Wool" (ZnO). In this experiment the oxygen from the nitre effects
the oxidation of the metal zinc.

THE BUDE LIGHT.

Eleventh Experiment.

A mixture of four pounds of nitre with two of sulphur and one and
a half of lamp black produces a most beautiful and curious fire, con-
tinually projected into the air as sparks having the shape of the rowel
of a spur, and one that may be burnt with perfect safety in a room, as
the sparks consume away so rapidly, in consequence of the finely divided
condition of the charcoal, that they may be received on a handkerchief
or the hand without burning them. The difficulty consists in effecting the
complete mixture of the charcoal. The other two ingredients must
first be thoroughly powdered separately, and again triturated when
mixed, and finally the charcoal must be rubbed in carefully, till the
whole is of a uniform tint of grey and very nearly black, and as the
mixture proceeds portions must be rammed into a paper case, and set
on fire ; if the stars or pinks come out in clusters, and spread well
without other and duller sparks, it is a sign that the whole is well
mixed; but if the sparks are accompanied with dross, and are pro-
jected out sluggishly, and take some time to burn, the mixture and
rubbing in the mortar must be continued ; and even that must not be
carried too far, or the sparks will be too small. N.B. If the lamp-black
was heated red hot in a close vessel, it would probably answer better
when cold and powdered.

Twelfth Experiment.

Into a tall gas jar with a wide neck project some red-hot lamp-black
through a tin funnel, when a most brilliant flame-like fire is obtained,
showing that finely divided charcoal with pure oxygen would be suf-
ficient to afford light; but as the atmosphere consists of oxygen
diluted with nitrogen, compounds of charcoal with hydrogen, are the
proper bodies to burn, to produce artificial light.

Thirteenth Experiment. The Bude
Light.

This pretty light is obtained by pass -
ing a steady current of oxygen gas (es-
caping at a very low pressure) through
and up the centre pipe of an argand oil
lamp, which must be supplied with a
highly carbonized oil and a very thick
wick, as the oxygen has a tendency to
burn away the cotton unless the oil is
well supplied, and allowed to overflow
the wick, as it does in the lamps of the
lighthouses. The best whale oil is
usually employed, though it would be
worth while to test the value of Price's
"Belmontine Oil" for the same pur-
pose. (Fig. 102.) fl F !f- 10 . 2 - A - Reservoir of oil. B. The
v flexible pipe conveying oxygen to centre

of the argand lamp.

BOY S PLAYBOOK OP SCIENCE.

Fourteenth Experiment. A Red Light.

Clear out the oil thoroughly from the Bude light apparatus ; or, what
is better, have two lamps, one for oil, and the other for spirit ; fill the
apparatus with a solution of nitrate of strontia and chloride of calcium
in spirits of wine, and let it burn from the cotton in the same way as
the oil, and supply it with oxygen gas.

Fifteenth Experiment. A Green Light.

Dissolve boracic acid and nitrate of baryta in spirits of wine, and
supply the Bude lamp with this solution.

Sixteenth Experiment. A Yellow Light.

Dissolve common salt in spirits of wine, and burn it as already de-
scribed in the Bude light apparatus.

Seventeenth Experiment. The Oxy -calcium Light.

This very convenient light is obtained in a simple manner, either by
using a jet of oxygen as a blowpipe to project the flame of a spirit
lamp on to a ball of lime ; or common coal-gas is employed instead of the

No.l.

No. 2.

Pig. 103. No. 1. A. Oxygen jet. B. The ball of lime, suspended by a wire. c. Spirit
lamp.

No. 2. i>. Oxygen jet. E. Gas (jet connected with the gas-pipe in the rear by flexible
pipe) projected on to ball of lime, r.

spirit lamp, being likewise urged against a ball of lime. By this plan
one bag containing oxygen suffices lor the production of a brilliant light,
not equal, however, to the oxy-hydrogen light, which will be explained in
the article on hydrogen. (Fig. 103.)

Eighteenth Experiment.

To show the weight of oxygen gas, and that it is heavier than air,
the stoppers from two bottles containing it may be removed, one bottle
may be left open for some time and then tested by a lighted taper, when

EXPERIMENTS WITH OXYGEN GAS. 99

it will still indicate the presence of the gas, whilst the other may be
suddenly inverted over a little cup in whicli some ether, mixed with a
few drops of turpentine, may be burning the flame burns with much
greater brilliancy at the moment when, the oxygen comes in contact
with it.

The theory of the effect of oxygen upon the system when inhaled
would be an increase in the work of the respiratory organs ; and it is
stated that after inhaling a gallon or so of this gas, the pulse is raised
forty or fifty beats per second : the gas is easily inhaled from a large
indiarubber bag through an amber mouthpiece ; it must of course be
quite pure, and if made from the mixture of chlorate of potash and
oxide of manganese, should be purified by being passed through lime
and water, or cream of lime.

There are certain colouring matters that are weakened or destroyed
by the action of light and other causes, which deprive them of oxygen
gas or deoxidize them. A weak tincture of litmus, if long kept, often
becomes colourless, but if this colourless fluid is shaken in a bottle
with oxygen gas it is gradually restored ; and if either litmus, turmeric,
indigo, orchil, or madder, paper, or certain ribbons dyed with the same
colouring matters, have become faded, they may be partially restored by
damping and placing them in a bottle of oxygen gas. The effect of the
oxygen is to reverse the deoxidizing process, and to impart oxygen to
the colouring matters. By a peculiar process indigo may be obtained
quite white, and again restored to its usual blue colour, either by ex-
posure to the air or by passing a stream of oxygen through it.

Twenty-first Experiment.

Messrs. Matheson, of Torrington- street, Russell-square, prepare
in the form of wire some of the rarest metals, such as magnesium,
lithium, &c. A wire of the metal magnesium burns magnificently in
oxygen gas, and forms the alkaline earth magnesia. The metal lithium,
to which such a very low combining proportion belongs viz., 6'5, can
also be procured in the state of wire, and burns in oxygen gas with an
intense white light into the alkaline lithia, which dissolved in alcohol
with a little acetic acid, and burnt, affords a red flame, making a curious
contrast between the effects of colour produced by the metallic and oxi-
dized state of lithium.

THE ALLOTROPIC CONDITION OF OXYGEN GAS.

The term allotropy (from aXXorpoTro?, of a different nature) was
first used by the renowned chemist Berzelius. Dimorphism, or diver-
sity in crystalline form, is therefore a special case of allotropy,
and is most amusingly illustrated with the iodide of mercury (Hgt),
which is made either by rubbing together equal combining proper-

IT I

100 BOYS PLAYBOOK OF SCIENCE.

tions of mercury and iodine (both of which are to be found in the
Table of Elements, page 86), or by carefully precipitating a solution of
corrosive sublimate (chloride of mercury (HgCl) ) with one of iodide of
potassium, just enough and no more of the latter being added to pre-
cipitate the metal, or else the iodide of mercury is redissolved by the
excess of the precipitant. It is first of a dirty yellow, and then gradually
changes when stirred to a scarlet ; if this be collected on a filter, and
washed and drained, it is a beautiful scarlet, and when some of this
substance is rubbed across a sheet of paper, a bright scarlet is apparent,
which may be rapidly changed to a lemon-yellow by heating the paper
over the flame of a spirit lamp ; and the iodide of mercury is again brought
back to a scarlet colour by rubbing down the yellow crystals with the
fingers. This experiment may be repeated over and over again with
the like results. If some of the scarlet iodide of mercury is sublimed from
one bit of glass to another, it forms crystals, derived from the right
rhombic prism ; when these are scratched with a pin they change again to
the scarlet state, the latter when crystallized being in the form of the
square-based octohedron.

Other cases of dimorphism may be mentioned viz., with sulphur,
carbonate of lime, and lead, and many others, whilst allotropy is
curiously illustrated in the various conditions of charcoal, which, in
the more numerous examples, is black and opaque, and in another instance
transparent like water. Lamp-black is soft, but the diamond is the
hardest natural substance. The allotropic state of sulphur has been
already alluded to ; phosphorus, again, exists in three modifications : 1st,
Common phosphorus, which shines in the dark and emits a white smoke.
2nd, White pnosphorus. 3rd, Red or amorphous phosphorus, which
does not shine or emit white smoke when exposed to the air, and is so
altered in its properties that it may be safely carried in the pocket.

Enough evidence has therefore been offered to show that the allo-
tropic property is not confined to one element or compound, but is dis-
coverable in many bodies, and in no one more so than in the allotropic
state of the element oxygen called

OZONE.

The Greek language has again been selected by the discoverer, Schon-
bein, of Basle, for the title or name of this curious modification of
oxygen, and it is so termed from ogeiv, to smell. The name at once
suggests a ^narked difference between ozone and oxygen, because the
latter is pe/fectly free from odour, whilst the former has that peculiar
smell which is called electric, and is distinguishable whenever an
electrical machine is at work, or if a Ley den jar is charged by the

Sowerful Rhumkoff, or Hearder coil; it is also apparent when water is
ecomposed by a current of electricity and resolved into its elements,
oxygen and hydrogen. When highly concentrated it smells like chlorine ;
and the author recollects seeing the first experiments by Schonbein, in
England, at Mr. Cooper's laboratory in the Blackfriars-road. Ozone
is prepared by taking a clean empty bottle, and pouring therein a very

EXPERIMENTS WITH OZONE.

101

little distilled water, into
which a piece of clean
scraped phosphorus is
introduced, so as to ex-
pose about one-half of
its diameter to the air in
the bottle, whilst the
other is in contact with
the water. (Fig. 104.)

Tor the sake of pre-
caution, the bottle may
stand in a basin or soup
plate, so that if the
phosphorus should take
fire, it may be instantly
extinguished by pour-
ing cold water into the
bottle, and should this

crack and break, the

phosphorus is received

into the plate. D D . A soup-plate.

When the ozone is
formed the phospho i s can be withdrawn, and the phosphorous-acid
smoke washed out by shaking the bottle ; it is distinguishable by its
smell, and also by its action on test paper, prepared by painting with
starch containing iodide of potassium on some .Bath post paper ; when
this is placed in the bottle containing ozone, it changes the test blue,
or rather a purplish blue.

Ozone is a most energetic body, and a powerful bleaching agent ; if
a point is attached to the prime conductor of an electrical machine,
and the electrified air is received into a bottle, it will be found to smell,
and has the power of bleaching a very dilute solution of indigo. Ozone

quart bottle, with the stopper loosely

Fig. 105. v. A small voltaic battery standing on the stool with glass legs, a s, and
capable of heating a thin length of platinum wire about two inches long, and bent to form
a point between the conducting wires, ww. N.B. The voltaic current can be cut off at
pleasure, so as to cool the wire when necessary. A is the prime conductor of an ordinary
cylinder electrical machine. B is the wire conveying the frictional electricity to the
conducting wires of the voltaic battery, where the point P being the sharpest point in the
sirrangement, delivers the electrified and ozonized air.

102 BOY'S PLAYBOOK OP SCIENCE.

is not a mere creation of fancy, as it can not only be produced by certain
methods, but may be destroyed by a red heat. If a point is prepared
with a loop of platinum wire, and this latter, after being connected with
a voltaic cattery, made red hot, and the whole placed on an insulating
stool, and connected with the prime conductor of an electrical machine,
it is found that the electrified air no longer smells, the ozone is destroyed;
on the other hand, if the voltaic battery is disconnected, and the electri-
fied air again allowed to pass from the cold platinum wire, the smell is again
apparent, the air will bleach, and if caused to impinge at once upon
the iodide of starch test, changes it in the manner already described.
(Eig. 105.)

Ozone is insoluble in water, and oxidizes silver and lead leaf, finely
powdered arsenic and antimony ; it is a poison when inhaled in a con-
centrated state, whilst diluted, and generated by natural processes, it is a
beneficent and beautiful provision against those numerous smells originat-
ing from the decay of animal and vegetable matter, which might produce
disease or death : ozone is therefore a powerful disinfectant. The test for
ozone is made by boiling together ten parts by weight of starch, one of iodide
of potassium, and two hundred of water ; it may either be painted on
Bath post paper, and used at once, or blotting paper may be saturated
with the test and dried, and when required lor use it must be damped,
either before or after testing for ozone, as it remains colourless when
dry, but becomes blue after being moistened with water.

Paper prepared with sulphate of manganese is an excellent test for
ozone, and changes brown rapidly by the oxidation of the proto-salt of
manganese, and its conversion into the binoxide of the metal.

Ozone is also prepared by pouring a little sulphuric ether into a
quart bottle, and then, after heating a glass rod in the flame of the spirit
lamp, it may be plunged into the bottle, and after remaining there a few
minutes ozone may be detected by the ordinary tests.

NITROGEN, OB AZOTE.

Nirpov, nitre ; ye vvam, I form ; a, privative ; far), life. Symbol, N >
combining proportion, 14. Also termed by Priestley, phlogisticated air.

In the year 1772, Dr. Rutherford, Professor of Botany in the Uni-
versity of Edinburgh, published a thesis in Latin on fixed air, in which
he says : " By the respiration of animals healthy air is not merely
rendered mephitic (i.e., charged with carbonic acid gas), but also suffers
another change. For after the mephitic portion is absorbed by a caustic
alkaline lixivium, the remaining portion is not rendered salubrious ; and
although it occasions no precipitate in lime-water, it nevertheless extin-
guishes flame and destroys life'' Such is the doctor's account of the
discovery of nitrogen, which may be separated from the oxygen in the
air in a very simple manner. The atmosphere is the great storehouse
of nitrogen, and four-fifths of its prodigious volume consist of this
element

PREPARATION OF NITROGEN GAS.

103

Oxygen .
Nitrogen

Composition of Atmospheric Air.

Bulk. Weight.

20 22-3

80 777

100 100-

The usual mode of procuring nitrogen gas is to abstract or remove
the oxygen from a given portion of atmospheric air, "and the only point
to be attended to, is to select some substance which will continue to
burn as long as there is any oxygen left. Thus, if a lighted taper is
placed in a bottle of air, it will only burn for a certain period, and is
gradually and at last extinguished ; not that the whole of the oxygen is
removed or changed, because after the taper has gone out, some burning
sulphur may be placed in the vessel, and will continue to burn for a
limited period ; and even after these two combustibles have, as it were,
taken their fill of the oxygen, there is yet a little left, which is snapped
up by burning phosphorus, whose voracious appetite for oxygen is only
appeased by taking the whole. It is for this reason that phosphorus is
employed for the purpose of removing the oxygen, and also because the
product (phosphoric acid) is perfectly soluble in water, and thus the
oxygen is first combined, and then washed out of a given volume of air,
leaving the nitrogen behind.

First Experiment.

To prepare nitrogen gas, it is only
necessary to place a little dry phos-
phorus in a Berlin porcelain cup on a
wine glass, and to stand them in a
soup plate containing water. The
phosphorus is set on fire with a hot
wire, and a gas jar or cylindrical jar
is then carefully placed over it, so that
the welt of the jar stands in the water
in the soup plate. At first, expansion
takes ])lace in consequence of the heat,
but this effect is soon reversed, as the
oxygen is converted into a solid by
union with the phosphorus, forming a
white smoke, which gradually disap-
pears. (Fig. 106.)

Supposing two grains of phospho-
rus had been placed in a platinum
tube, and just enough atmospheric air
passed over it to convert the whole

into phosphoric acid, the weight Of glass, supporting c, the cup containing

the phosphorus would be increased to the burning phosphorus, and the whole
4* grains by the addition of 2| grains S ngm a soup - plate ' D D ' contaaiuns

104

BOY'S PLAYBOOK OF SCIENCE.

of oxygen ; now one cubic inch of oxygen weighs 0'3419, or about |rd
of a grain, hence 7 '3 cubic inches of oxygen disappear, which weigh
as nearly as possible 2?r grains, so that as 36 - 5 cubic inches of air con-
tain 7'3 cubic inches of oxygen, that quantity of air must have passed
over the 2 grains of phosphorus to convert it into 4 grains of phos-
phoric acid.

For very delicate purposes, nitrogen is best prepared by passing air
over finely-divided metallic copper heated to redness ; this metal absorbs
the whole of the oxygen and leaves the nitrogen. The finely-divided copper
is procured by passing hydrogen gas over pure black oxide of copper.

A very instructive experiment is performed by heating a good mass of
tartrate of lead in a glass tube which is herme cally sealed, and being

placed on an iron sup-
port, is then covered
by a capped air jar
with a sliding rod and
stamper, the whole
being arranged in
a plate containing
water. When the
stamper is pushed
down upon the glass
the latter is broken
(Fig. 107), and the air
gradually penetrates
to the finely divided
lead, when ignition oc-
curs, and the oxygen
is absorbed, as demon-
strated by the rise
of the water in the
jar. On the same
principle, if a bottle
is filled about one-
third full with a liquid
amalgam of lead and
mercury, and then
stopped and shaken
for two hours or
more, the finely di-
vided lead absorbs
the oxygen and

Fig. 107. A. Glass jar, with collar of leather, through which
the stamper, c, works. B B. The tube containing the finely-
divided lead, part of which falls out, and is ignited, and
retained by the little tray just below, being part of the iron
stand, D D, with crutches supporting the ends of the glass
tube, and the whole stands in the dish of water, B E.

leaves pure nitrogen. Or if a mixture of equal weights of sulphur
and iron filings, is made into a paste with water in a thin iron cup,
and then warmed and placed under a gas jar full of air standing on the

EXPERIMENTS WITH NITROGEN GAS. 105

shelf of the pneumatic trough, or in a dish full of water, the water
gradually rises in the jar in about forty-eight hours, in consequence of
the absorption of the oxygen gas.

Third Experiment.

Nitrogen is devoid of colour, taste, smell, of alkaline or acid qualities ;
and, as we shall have occasion to notice presently, it forms an acid
when chemically united with oxygen, and an alkali in union with hydro-
gen. A lighted taper plunged into this gas is immediately extinguished,
while its specific gravity, which is lighter than that of oxygen or air,
is demonstrated by the rule of proportion.

Weight of 100 cubic
inches of air at 60
Fahr., bar. 29'92 in.

30-829

Unity.

Weight of 100 cubic
inches of nitrogen at
60 Fahr., bar. 29'92 in

: 29-952 :

Specific
gravity of
nitrogen.

971

And its levity may be shown very prettily by a
simple experiment. Select two gas jars of the
same size, and after filling one with oxygen gas
and the other with nitrogen gas, slide glass
plates over the bottoms of thej ars, and proceed
to invert the one containing oxygen, placing
the neck in a stand formed of al)ox open at
the top; then place the jar containing nitro-
gen over the mouth of the first, withdrawing
the glass plates carefully ; and if the table
is steady the top gas jar will stand nicely
on the lower one. Then (having previously
lighted a taper so as to have a long snuff)
remove the stopper from the nitrogen jar
and insert the lighted taper, which is im-
mediately extinguished, and as quickly re-
lighted by pushing it down to the lower
jar containing the oxygen. This experi-
ment may be repeated several times, and is
a good illustration of the relative specific
gravities of the two gases, and of the im-
portance of the law of universal diffusion
already explained at p. 6, by which these
gases mix, not combine together, and the
atmosphereremains in one uniform state of
composition in spite of the changes going
on at the surface of the earth. Omitting ^^ IL> ai
the aqueous vapour, or steam, ever present jar Ml of c
in variable quantities in the atmosphere, ten ghted X at n8 o
thousand volumes of dry air contain, ac- porting the jars,
cording to Graham :

The taper,
Stan? ^iT"

106

BOY S PLAYBOOK. OF SCIENCE.

Nitrogen 7912

Oxygen . t 2080

Carbonic acid 4

Carburetted hydrogen (CH 2 ) ... 4
Ammonia a trace

Fourth Experiment.

10,000

It was the elegant, the accomplished, but ill-fated Lavoisier who dis-
covered, by experimenting with quicksilver and air, the compound
nature of the atmosphere ; and it was the same chemist who gave the
name of azote to nitrogen ; it should, however, be borne in mind that it

does not necessarily
follow because a gas
extinguishes flame
that it is a poison.
Nitrogen extinguishes
flame, but we inhale
enormous quantities
of air without any ill
effects from the nitro-
gen or azote that it
contains ; on the other
hand, many gases that
extinguish flame are
specific poisons, such as
carbonic acid, carbonic
oxide, cyanogen, &c.

Lavoisier's experi-
ment may be repeated
by passing into a mea-
sured jar, graduated
into five equal vo-
lumes, four measures
Fig. 109. A. Gas jar divided into five equal parts. B B. of nitrogen and one
Section of pneumatic trough, to show the decantation of gas measure of OXVffen a
from one vessel to another. The gas is being passed from c , , , J f i ,J

to A, through the water. glass plate should then

be slid over the mouth

of the vessel, and it may be turned up and down gently for. some little
time to mix the two gases, and when the mixture is tested with a lighted
taper, it is found neither to increase nor diminish the illuminating power
and the taper burns as it would do in atmospheric air. (Fig. 109.1

PREPARATION OF HYDROGEN GAS.

107

HYDROGEN.

Hydrogen (vSoop, water; yewaa), I give rise to), so termed by Lavoisier
called by other chemists inflammable air, and phlogiston. Symbol, H ;
combining properties, 1. The lightest known form of matter.

Every 100 parts by weight of water contain 11 parts of hydrogen
gas ; and as the quantity of water on the surface of the earth represents
at least two-thirds of the whole area, the source of this gas, like that of
oxygen or nitrogen, is inexhaustible. Van Helmont, Mayow, and
Hales had shown that certain inflammable and peculiar gases could be
obtained, but it was reserved for the rigidly philosophic mind of Cavendish
to determine the nature of the elements contained in, and giving a spe-
ciality to, the inflammable gases of the older chemists. By acting with
dilute acids upon iron, zinc, and tin, Cavendish liberated an inflammable
elastic gas ; and he discovered nearly all the properties we shall notice
in the succeeding experiments, and especially demonstrated the compo-
sition of water in his paper read before the lloyal Society in the year
1784.

Hydrogen is prepared in a very simple manner, by placing some zinc
cuttings in a bottle, to which is attached a cork and pewter or bent
glass tube, and pouring upon the metal
some dilute sulphuric or hydrochloric
acid. Effervescence and ebullition take
place, and the gas escapes in large quanti-
ties, water being decomposed ; the oxygen
passes to the zinc, and forms oxide of
zinc, and this uniting with the sulphuric
acid forms sulphate of zinc, which may
be obtained after the escape of the hy-
drogen by evaporation and crystallization.
(Fig. 110.)

Zn + HO.S0 3 = ZnO.S0 3 + H;

or,
Zn + HC1 = ZnCl + H.

In nearly all the processes employed
for the generation of hydrogen gas, a
metal is usually employed, and this fact
has suggested the notion that hydrogen
may possibly be a metal, although it is
the lightest known form of matter ; and it
will be observed in all the succeeding expe-

rimeilts that a metallic substance Will be marked B, containing a funnel,

employed to take away the oxygen and ^ ae^nip^c add
displace the hydrogen. through the pipe c.

108

BOY'S PLAYBOOK OF SCIENCE.

Whenever hydrogen is prepared it should be allowed to escape from
the generating vessel for a few minutes before any flame is applied, in
order that the atmospheric air may be expelled. The most serious acci-
dents have occurred from carelessness in this respect, as a mixture of
hydrogen and air is explosive, and the more dangerous when it takes
fire in any close glass bottle.

Second Experiment.

If a piece of potassium is confined in a little coarse wire gauze cage,
attached to a rod, and thrust under a small jar full of water, placed
on the shelf of the pneumatic trough, hydrogen gas is produced with
great rapidity, and is received into the gas jar. The bit of potassium
being surrounded with water, is kept cool, whilst the hydrogen escaping
under the water is not of course burnt away, as it is whenever the metal
is thrown on the surface of water.

Third Experiment.

Across a small iron table-furnace is placed about eighteen inches of
1-inch gas-pipe containing iron borings, the whole being red-hot ; and
attached to one end is a pipe conveying steam from a boiler, or flask, or
retort, whilst another pipe is fitted to the opposite end, and passes to
the pneumatic trough. Directly the steam passes over the red hot iron
borings it is deprived of oxygen, which remains with the iron, forming
the rust or oxide of iron, whilst the hydrogen, called in this case water
gas, escapes with great rapidity. When steam is passed over red-hot
charcoal, hydrogen is also produced with carbonic oxide gas, and this in
fact is the ordinary process of making water gas, which being puri-
fied is afterwards saturated with some volatile hydrocarbon and burnt.
At first sight, such a mode of making gas would be thought extremely
profitable, and in spite of the numerous failures the discovery (so called)
of water gas is reproduced as a sort of chronic wonder; but experience
and practice have clearly demonstrated that water gas is a fallacy, and
as long at we can get coal it is not worth while going through the
round-about processes of first burning coal to produce steam ; secondly,

Fig. 111. A. Flask containing water, and producing steam, which passes to the iron
tube, B B, containing the iron borings heated red hot in the charcoal stove c. The
hydrogen passes to the jar D, standing on the shelf of the pneumatic trough.

EXPERIMENTS WITH HYDROGEN GAS.

109

of burning coal to heat charcoal, over which the steam is passed to be
converted into gas, which has then to be purified and saturated with a
cheap hydrocarbon obtained from coal or mineral naphtha ; whilst ordi-
nary coal gas is obtained at once by heating coal in iron retorts.
(Fig. 111.)

Thus, by the metals zinc, tin, potassium, red-hot iron (and we might
add several others), the oxygen of water is removed and hydrogen gas
liberated.

Fourth Experiment.

If bottles of hydrogen gas
are prepared by all the processes
described, they will present the
same properties when tested un-
der similar circumstances. A
lighted taper applied to the
mouths of the bottles of hydro-
gen, which should be inverted,
causes the gas to take fire with a
slight noise, in consequence of
the mixture of air and hydrogen
that invariably takes place when
the stopper is removed; on
thrusting the lighted taper into
the bulk of the gas it is extin-
guished, showing that hydrogen
possesses the opposite quality to
oxygen viz., tnat it takes fire,
but does not support combustion.
By keeping the bottles contain-
ing the hydrogen upright, when
the stopper is removed the gas
escapes with great rapidity, and
atmospheric air takes its place,
so much so that by the time a
lighted taper is applied, instead
of the gas burning quietly, it fre-
quently astonishes the operator
with a loud pop. This sudden
attack on the nerves may be pre-
vented by always experimenting
with inverted bottles. (Eig. 112.)

Fifth Experiment.

Hydrogen is 14'4 lighter than air, and for that reason may be passed
into bottles and jars without the assistance of the pneumatic trough.
One of the most amusing proofs of its levity is that of filling paper bags
or balloons with this gas ; and we read, in the accounts of the fetes at

110

BOY'S PLAYBOOK OF SCIENCE.

Paris, of the use of balloons ingeniously constructed to represent animals,
so that a regular aerial hunt was exhibited, with this drawback only,
that nearly all the animals preferred ascending with their legs upwards,
a circumstance which provoked intense mirth amongst the volatile
Frenchmen. The lightness of hydrogen may be shown in two ways
first, by filling a little goldbeater's-skin balloon with' pure hydrogen
(prepared by passing the gas made from zinc and dilute pure sulphuric
acid through a strong solution of potash, and afterwards through one
of nitrate of silver), and allowing the balloon to ascend; and then
afterwards, having of course secured the balloon by a thin twine or strong
thread, it may be pulled down and the gas inhaled, when a most curious
effect is produced on the voice, which is suddenly changed from a manly
bass to a ludicrous nasal squeaking sound. The only precaution's
necessary are to make the gas quite pure, and to avoid flarne whilst
inhaling the gas. It is related by Chaptal that the intrepid (quaere, foolish)
but unfortunate aeronaut, Mons. Pilate de Rosio, having on one occasion
inhaled hydrogen gas, was rash enough, to approach a lighted candle,
when an explosion took place in his mouth, which he says " was so
violent that he fancied all his teeth were driven out" Of course, if it
were possible to change by some extraordinary power the condition of
the atmosphere in a concert-room or theatre, all the bass voices would
become extremely nasal and highly comic,
whilst the sopranos would emulate railway
whistles and screech fearfully ; and supposing
the specific gravity of the air was continu-
ally and materially changing, our voices
would never be the same, but alter day by day,
according to the state of the air, so that the
" familiar voice" would be an impossibility.
A bell rung in a gas jar containing air
emits a very different sound from that which
is produced in one full of hydrogen a simple
experiment is easily performed by passing a jar
containing hydrogen over a self-acting bell,
such as is used for telegraphic purposes.
(Fig. 113.)

Sixth Experiment.

Some of the small pipes from an organ
may be made to emit the most curious sounds
by passing heavy and light gases through
them ; in these experiments bags containing
Fig. 113. A. stand and bell, the gases should be employed, which may

*^d^i^4a5 * t> f ygen ' carb?nic ac f idj or hyd r^ n '

depressed at pleasure, by lifting through the organ pipes at precisely tne

it with the knob at the top, same pressure,
when the curious changes in the
sound of the bell are audible.

BALLOONS AND AEROSTATION.

Ill

Seventh Experiment.

One of those toys called " The Squeak-
ing Toy" affords another and ridiculous
example of the effect of hydrogen on sound,
when it is used in a jar containing this
gas. (Eig. 114.)

Eighth Experiment.

An accordion played in a large receptacle
containing hydrogen gas demonstrates still
more clearly what would be the effect of
an orchestra shut up in a room containing
a mixture of a considerable portion of
hydrogen with air, as the former, like
nitrogen, is not a poison, and only kills in
the absence of oxygen gas.

Ninth Experiment.
Some very amusing experiments with .,,,,., , ^

in i i i 11 -\ir T\ i I iff. 114. The squeaking toy. used

balloons have been devised by Mr. Darby, in ajar of hydrogen.

the eminent firework manufacturer, oy

which they are made to carry signals of three kinds, and thus the
motive or ascending power may be utilized to a certain extent.

Mr. Darby's attention was first directed to the manufacture of a
good, serviceable, and cheap balloon, which he made of paper, cut with
mathematical precision; the gores or divisions being made equal,
and when pasted together, strengthened by the insertion of a string
at the juncture; so that the skeleton of the balloon was made of
string, the whole terminating in the neck, which was further stif-
fened with calico, and completed when required by a good coating
of boiled oil. These balloons are about nine feet high and five feet in
diameter in the widest part, exactly like a pear, and tapering to the
neck in the most graceful and elegant manner. They retain the hydrogen
gas remarkably well for many hours, and do not leak, in consequence of
the paper of which they are made being well selected and all holes
stopped, and also from the circumstance of the pressure being so well
distributed over the interior by the almost mathematical precision with
which they are cut, and the careful preparation of the paper with proper
varnish. One of their greatest recommendations is cheapness ; for
whilst a gold-beater's skin balloon of the same size would cost about 51.,
these can be furnished at 5s. each in large quantities.

A balloon required to carry one or more persons must be constructed
of the best materials, and cannot be too carefully made ; it is therefore
a somewhat costly affair, and as much as 200/., 500/., and even 1000/.
have been expended in the construction of these aerial chariots.

The chief points requiring attention are : first, the quality of the
silk ; secondly, the precision and scrupulous nicety required in cutting

112 BOY'S PLAYBOOK OF SCIENCE.

out and joining the gores ; thirdly, the application of a good varnish to
fill up the pores of the silk, which must be insoluble in water, and suf-
ficiently elastic not to crack.

The usual material is Indian silk (termed Corah silk), at from 2.?. to
2s. 6d. per yard.

The gores or parts with which the balloon is constructed require, as
before stated, great attention; it being a common saying amongst
aeronauts, "that a cobweb will hold the gas if properly shaped," the
object being to diffuse the pressure equally over the whole bag or
balloon.

The varnish with which the silk is rendered air-tight can be made
according to the private recipe of Mr. Graham, an aeronaut, who states
that he uses for this purpose two gallons of linseed oil (boiled), two
ditto (raw), and four ounces of beeswax ; the whole being simmered
together for one hour, answers remarkably well, and the varnish is
tough and not liable to crack.

For repairing holes in a balloon, Mr. Graham recommends a cement
composed of two pounds of black resin and one pound of tallow,
melted together, and applied on pieces of varnished silk to the apertures.
The actual cost of a balloon will be understood from information also
derived from Mr. Graham. His celebrated " Victoria Balloon," which
has passed through so many hairbreadth escapes, was sixty-five feet
hih, and thirtv-eight feet in diameter in the broadest part ; and the
following articles were used in its constructiou

s. d.
1400 yards of Corah silk, at 2*. bd. per yard . . 175

The netting weighed 70 Ibs 20

Extra ropes weighed 20 Ibs. at 2*. per Ib. ... 200

The car weighed 25 Ibs 700

Varnish, wages, &c 16

220

Thirty-eight thousand cubic feet of coal gas were required to fill this
balloon, charged by one company 20/., by others from 9/. to 10/. ; and
eight men were required to hold the inflated baggy monster.

Such a balloon as described above is a mere soap bubble when com-
pared with the " New Aerial Ship" now building in the vicinity of New
York ; the details are so practical and interesting, that we quote nearly
the whole account of this mammoth or Great Eastern amongst balloons,
as given in the New York Times.

" An experiment in scientific ballooning, greater than has yet been
undertaken, is about to be tried in this city. The project of crossing
the Atlantic Ocean with an air-ship, long talked of, but never accom-
plished, has taken a shape so definite that the apparatus is already pre-
pared and the aeronaut ready to undertake his task.

" The work has been conducted quietly, in the immediate vicinity of
New York, since the opening of spring. The new air-ship, which has

AEROSTATION. 113

been christened the City of New York, is so nearly completed, that but
few essentials of detail are wanting to enable the projectors to bring it
visibly before the public.

" The aeronaut in charge is Mr. T. S. C. Lowe, a New Hampshire
man, who has made thirty-six balloon ascensions.

" The dimensions of the City of New York so far exceed those of
any balloon previously constructed, that the bare fact of its existence is
notable. Briefly, for so large a subject, the following are the di-
mensions : Greatest diameter, 130 feet ; transverse diameter, 104 feet ;
height, from valve to boat, 350 feet ; weight, with outfit, 3 tons ;
lifting power (aggregate), 22^ tons ; capacity of gas envelope, 725,000
cubic feet.

" The City of New York, therefore, is nearly five times larger than
the largest balloon ever before built. Its form is that of the usual
perpendicular gas-receiver, with basket and lifeboat attached.

" Six thousand yards of twilled cloth have been used in the con-
struction of the envelope. Reduced to feet, the actual measurement of
this material is 54,000 feet or nearly 11 miles. Seventeen of Wheeler
and Wilson's sewing machines have been employed to connect the
pieces, and the u^per extremity of the envelope, intended to receive the
gas-valve, is of triple thickness, strengthened with heavy brown linen,
and sewed in triple seams. The pressure being greatest at this point,
extraordinary power of resistance is requisite. It is asserted that 100
women, sewing constantly for two years, could not have accomplished
this work, which measures by miles. The material is stout and the
stitching stouter.

" The varnish applied to this envelope is a composition the secret of
which rests with Mr. Lowe. Three or four coatings are applied, in
order to prevent leakage of the gas.

" The netting which surrounds the envelope is a stout cord, manu-
factured from flax expressly for the purpose. Its aggregate strength is
equal to a resistance of 160 tons, each cord being capable of sustaining
a weight of 400 Ibs. or 500 Ibs.

" The basket which is to be suspended immediately below the balloon
is made of rattan, is 20 feet in circumference and 4 feet deep. Its form
is circular, and it is surrounded by canvas. This car will carry the
aeronauts. It is warmed by a lime-stove, an invention of Mr. 0. A.
Gager, by whom it was presented to Mr. Lowe. A lime-stove is a new
feature in air voyages. It is claimed that it will furnish heat without
fire, and is intended for a warming apparatus only. The stove is 1| feet
high, and 2 feet square. Mr. Lowe states that he is so well convinced
of the utility of this contrivance, that he conceives it to be possible to
ascend to a region where water will freeze, and yet keep himself from
freezing. This is to be tested.

" Dropping below the basket is a metallic lifeboat, in which is placed
an Ericsson engine. Captain Ericsson's invention is therefore to be
tried in mid-air. Its particular purpose is the control of a propeller,
rigged upon the principle of the screw, by which it is proposed to obtain

114 BOY'S PLAYBOOK OF SCIENCE.

a regulating power. The application of the mechanical power is in-
geniously devised. The propeller is fixed in the bow of the lifeboat,
projecting at an angle of about forty-five degrees. From a wheel at
the extremity twenty fans radiate. Each of these fans is 5 feet in
length, widening gradually from the point of contact with the screw to
the extremity, where the width of each is 1^ feet. Mr. Lowe claims
that by the application of these mechanical contrivances his air-ship
can be readily raised or lowered, to seek different currents of air ; that
they will give him ample steerage way, and that they^ will prevent the
rotatory motion of the machine. In applying the principle of the fan, he
does not claim any new discovery, but simply a practical development
of the theory advanced by other aeronauts, and partially reduced to
practice by Charles Green, the celebrated English aeronaut.

"Mr. Lowe contends that the application of machinery to aerial
navigation has been long enough a mere theory. He proposes to
reduce the theory to practice, and see what will come of it. It is
estimated that the raising and lowering power of the machinery will be
<jqual to a weight of 300 Ibs., the fans being so adjusted as to admit of
very rapid motion upward or downward. As the loss of three or four
pounds only is sufficient to enable a balloon to rise rapidly, and as the
escape of a very small portion of the gas suffices to reduce its altitude,
Mr. Lowe regards this systematic regulator as quite sufficient to enable
him to control his movements and to keep at any altitude he desires.
It is his intention to ascend to a height of three or four miles at the
start, but this altitude will not be permanently sustained. He prefers,
he says, to keep within a respectable distance of mundane things, where
* he can see folks.' It is to be hoped his machinery will perform all
that he anticipates from it. It is a novel affair throughout, and a
variety of new applications remain to be tested. Mr. Lowe, expressing
the utmost confidence in all the appointments of his apparatus, assured
us that he would certainly go, and, as certainly, would go into the ocean,
or deliver a copy of Monday's Times in London on the following
Wednesday. He" proposes to effect a landing in England or France,
and will take a course north of east. A due easterly course would
land him in Spain, but to that course he objects. He hopes to make
the trip from this city to London in forty-eight hours, certainly in sixty-
four hours. He scouts the idea of danger, goes about his preparations
deliberately, and promises himself a good time. As the upper currents,
setting due east, will not permit his return by the same route, he pro-
poses to pack up the City of New York, and take the first steamer for
home.

" The air-ship will carry weight. Its cubical contents of 725,000
feet of gas suffice to lift a weight of 22| tons. "With outfit complete
its own weight will be Batons." With this weight 39 tons of lifting
power remain, and there is accordingly room for as many passengers as
will care to take the venture. We understand, however, that the
company is limited to eight or ten. Mr. Lowe provides sand for
ballast, regards his chances of salvation as exceedingly favourable,

AEROSTATION. 115

places implicit faith in the strength of his netting, the power of his
machinery, and the buoyancy of his lifeboat, and altogether considers
himself secure from the hazard of disaster. If he accomplish his voyage
in safety, he will have done more than any air navigator has yet ventured
to undertake. If he fail, the enterprise sinks the snug sum of 20,000
dollars. Wealthy men who are his backers, sharing his own enthusiasm,
declare failure impossible, and invite a patient public to wait and see."
A night ascent witnessed at any of the public gardens is certainly a
stirring scene, particularly if the wind is rather high. On approaching
the balloon, swayed to and fro by the breeze, it seems almost capable of
crushing the bold individual who would venture beneath it ; seen as a
large dark mass in the yet dimly-lighted square, it appears to be inca-
pable of control ; when the inflation is completed, the aeronaut, all im-
portance, seats himself in the car, and blue lights, with other fire-
works, display the victim who is to make a " last ascent," or perhaps
descent. Finally the word is given, the ropes are cast off, and the bulky
chariot rises majestically to the sound of the National Anthem. The
crowd see no more, but the next day's Times reports the end of the aerial
journey.

Balloons can never be of any permanent value as means of locomotion
until they can be steered ; and this is a problem, the solution of which is
something like perpetual motion. In the first place, a balloon of any size
exposes an enormous surface to the pressure and force of the winds ;
and when we consider that they move at the rate of from three to eighty
miles per hour, it will be understood that the fabric of the balloon itself
must give way in any attempt to tear, work, or pull it against such a
force. Secondly and lastly, the power has not yet been created which
will do all this without the inconvenience of being so heavy that the
steering engine fixes the balloon steadily to the earth by its obstinate
gravity. When engines of power are constructed without the aeronaut's
obstacle of weight when balloons are made of thin copper or sheet-iron,
then we may possibly hear of the voyage of the good ship Aerial, bound
for any place, and quite independent of dock, port, and the host of dues
(quere), which the sea-going ships have to disburse. It is, however, gratify-
ing to the zeal and perseverance of those who dream of aerial navigation, to
know that a balloon is not quite useless ; and here we may return to the
consideration of Mr. Darby's signals, which are of various kinds, and in-
tended to appeal to the senses by night as well as by day ; and first, by
audible sounds. Such means have long been recognised, from the ancient
float and bell of the " Inchcape Rock," to the painful minute-gun at sea, or
the shrill railway whistle and detonating signals employed to prevent the
horrors of a collision between two trains. The signal sounds are pro-
duced by the explosion of shells capable of yielding a report equal to
that of a six-pounder cannon, and they are constructed in a very simple
manner. A ball, composed of wood or copper, and made up by screwing
together the two hemispheres, is attached to a shaft or tail of cane or
lance-wood, properly feathered like an arrow ; at the side opposite to
that of the arrow viz., at its antipodes, is placed a slight protuberance

I 2

116

BOY'S PLAYBOOK OF SCIENCE.

containing a minute bulb of glass filled with oil of vitriol, and sur-
rounded with a mixture of chlorate of potash and sugar, the whole being
protected with gutta-percha, and communicating by a touch-hole with
the interior, which is of course filled with gunpowder. These shells are
attached to a circular framework by a strong whipcord, which passes
to a central fuse, and are detached one after the other as the slow fuse
(made hollow on the principle of the argand lamp) burns steadily away.
Directly a shell falls to the ground, the little bulb containing the oil of
vitriol breaks, and the acid coming in contact with the chlorate of
potash and sugar, causes the mixture to take fire, when the gunpowder
explodes. During the siege of Sebastopol many similar mines were
prepared by the Russians in the earth, so that when an unfortunate
soldier trod upon the spot, the concealed mine blew up and seriously
injured him ; such petty warfare is as bad as shooting sentries, and a
cruel application of science, that unnecessarily increases the miseries of
war without producing those grand results for which the truly great
captains, Wellington and Napoleon, only warred. (Fig. 115.)
The bill distributor consists of a long piece of wood, to which are

Fig. 115. A. King attached to balloon, ,.

carrying an hexagonal framework with six \^

shells. B. Hollow fuse, which burns slowly

up to the strings, and detaches each shell in Fig. 116. The bill distributor, consisting

succession, c. Section of shell. The shaded of three hollow fuses, with bills attached in

portion represents the gunpowder. packets.

BALLOON SIGNALS.

117

attached a number of hollow fuses, with packets of bills, protected from
being burned or singed by a thin tin plate; 10,000 or 20,000 bills can
thus be delivered, and the wind assists in scattering them, whilst the bal-
loon travels over a distance of many miles. It must be recollected that
in each case the shells and the bills are detached by the string burning
away as the fire creeps up from the fuse. (Fig. 116,)

Another most ingenious arrangement, also prepared by Mr. Darby,
is termed by the inventor, the " Land and Water Signal," and may be
thus described : A short hollow ball of gutta-percha, or other con-
venient material, five or six
inches in diameter, and filled
with printed bills, or the in-
formation, whatever it may
be, that is required to be
sent, is attached to a cap to
which a red flag, having the
words " Open the shell" and
four cross sticks, canes, or
whalebones with bits of cork
at equal distances, are fitted.
The whole is connected by
a string to the fuse as before
described. These signals
are adapted for land and
water : in either case they
fall upright, and in conse-
c[uence of the sticks pro-
jecting out they float well
in the water, and can be
seen by a telescope at a dis-
tance of three miles. (Fig.
117.) Many of these sig-
nals were sent away by Mr. w

Darby from Vauxhall; one

was nirlfprl nr> at Harwirh F *%' 117 ' The land and water signal, which re-

as picKea up at narwicn, mains upright on land> or floats On 8 the gurface of

another at Brighton, a third water. A. The water-tight gutta-percha shell, con-
at Crovdon : in the latter tuning th e message or information. B B B. Sticks

case it was found by a cot- tL^l^t^fg^^^ P siti n; at
tager, who, fearing gunpow-
der and combustibles, did not examine the shell, but having mentioned
the circumstance to a gentleman living near him, they agreed to cut it
open ; and intelligence of their arrival, in this and the other cases, was
politely forwarded to Mr. Darbv at Vauxhall Gardens.

Balloons, like a great many other clever inventions, have been despised
by military men as new-fangled expedients, toys, which may do very well
to please the gaping public, but are and must be useless in the field.
Over and over again it has been suggested that a balloon corps for
observation should be attached to the British army, but the scheme has

118 BOY'S PLAYBOOK OF SCIENCE.

been rejected, although the expense of a few yards of silk and the gene-
ration of hydrogen gas would be a mere bagatelle as compared with the
transport and use of a single 32-pounder cannon. The antiquated notions
of octogenarian generals have, however, received a great shock in the
fact that the Emperor Napoleon III. was enabled, by the assistance of
a captive balloon, to watch the movements and dispositions of the
Austrian troops ; and with the aid of the information so obtained, he
made his preparations, and was rewarded by the victory of Solferino ;
and as soon as the battle was over Napoleon III. occupied at Cavriana
the very room and ate the dinner prepared for his adversary, the Emperor
IVancis Joseph.

Over and over again the most excellent histories have been written of
aerostation, but they all tend to one truth, and that is, the great danger
and risk of such excursions ; and to enable our readers to form their
own judgment, a chronological list of some of the most celebrated
aeronauts, &c., is appended.

1675. Bernair attempted to fly killed.

1678. Besnier attempted to fly.

1772. I/ Abbe Desforges announced an aerial chariot.

1783. Montgolfier constructed the first air balloon.

Roberts freres, first gas balloon, destroyed by the peasantry of
Geneva, who imagined it to be an evil spirit or the moon.

1784. Madame Thible, the first lady who was ever up in the clouds ;

she ascended 13,500 feet.
Duke de Chartres, afterwards Egalite Orleans, travelled 135

miles in five hours in a balloon.
Testu de Brissy, equestrian ascent.

D'Achille, Desgranges, and Chalfour Montgolfier balloon.
Bacqueville attempted a flight with wings.
Lunardi gas balloon.

Rambaud Montgolfier balloon, which was burnt.
Andreani Montgolfier balloon.

1785. General Money gas balloon, fell into the water, and not rescued

for six. hours.

Thompson, in crossing the Irish Channel, was run into with the
bowsprit of a ship whilst going at the rate of twenty miles
per hour.
Brioschi gas balloon ascended too high and burst the balloon ;

the hurt he received ultimately caused his death.
A Venetian nobleman and his wife gas balloon killed.
Pilatre de Rozier and M. Romain gas balloon took fire botli

killed.
1806. Mosment gas balloon killed.

Olivari Montgolfier balloon killed.
1808. Degher attempted a flight with wings.
1812. Bittorf Montgolfier balloon killed.
1819. Blanchard, Madame gas balloon killed.

BALLOON ACCIDENTS.

119

1819. Gay Lussac gas balloon, ascended 23,040 feet above the level of

the sea. Barometer 12'95 inches ; thermometer 14*9 Eah.
Gay Lussac and Biot gas balloon for the benefit of science.

Both philosophers returned safely to the earth.
1824. Sadler gas balloon killed.
Sheldon gas balloon.
Harris gas balloon killed.
1836. Cocking parachute from gas balloon killed.
1847. Godard Montgolfier balloon fell into and extricated from the

Seine.

1850. Poitevin, a successful French aeronaut.
Gale, Lieut. gas balloon killed.
Bixio and Barral gas balloon.
Graham, Mr. and Mrs. gas balloon. Serious accident ascending

near the Great Exhibition in Hyde Park.
Green, the most successful living aeronaut of the present time.

Of the 41 persons enumerated, 14 were killed, and nearly all the
aeronauts met with accidents which might have proved fatal.

Fig. 118. Flying machine (theoretical).

120 BOY'S PLAYBOOK OF SCIENCE.

Tenth Experiment.

Soap bubbles blown with hydrogen gas ascend with great rapidity,
and break against the ceiling ; if interrupted in their course with a
lighted taper they burn with a slight yellow colour and dull report.

Eleventh Experiment.

By constructing a pewter mould in two halves, of the shape of a
tolerably large flask, a balloon of collodion may be made by pouring the
collodion inside the pewter vessel, and taking care that "every part is
properly covered ; the pewter mould may be warmed by the external
application of hot water, so as to drive off the ether of the collodion,
and when quite dry the mould is opened and the balloon taken out.
Such balloons may be made and inflated with hydrogen by attaching to
them a strip of paper, dipped in a solution of wax and phosphorus, and
sulphuret of carbon ; as the latter evaporates, the phosphorus takes fire
and spreads to the balloon ; which burns with a slight report. The pewter
moulo must be very perfectly made, and should be bright inside ; and if
the balloons are filled with oxygen and hydrogen, allowing a sufficient
excess of the latter to give an ascending power, they explode with a
loud noise directly the fire reaches the mixed gases.

Twelfth Experiment.

In a soup-plate place some strong soap and water ; then blow out
a number of bubbles with a mixture of oxygen and hydrogen ; a loud
report occurs on the application of flame, and if the room is small the
window should be placed open, as the concussion of the air is likely to
break the glass.

Thirteenth Experiment.

Any noise repeated at least thirty-two times in a second produces a
musical sound, and bv producing a number of small explosions of
hydrogen gas inside glass tubes of various sizes, the most peculiar
sounds are obtained. The hydrogen flame should be extremely small,
and the glass tubes held over it may be of all lengths and diameters ;
a trial only will determine whether they are fit for the purpose or not.

Fourteenth Experiment.

Flowers, figures, or other designs, may be drawn upon silk with a
solution of nitrate of silver, and the whole being moistened with water,
is exposed to the action of hydrogen gas, which removes the oxygen
from the silver, and reduces it to the metallic state.

In like manner designs drawn with a solution of chloride of gold are
produced in the metallic state by exposure to the action of hydrogen
gas. Chloride of tin, usually termed muriate of tin, may also be
reduced in a similar manne care being taken in these experiments that

EXPERIMENTS WITH HYDROGEN.

121

the fabric upoii which the letters, figures, or designs are painted with
the metallic solution be kept quite damp whilst exposed to the
hydrogen gas.

Fifteenth Experiment.

A mixture of two volumes of hydrogen with one volume of oxygen
explodes with great violence, and produces two volumes of steam, which
condense against the sides of the strong glass vessel, in which the
experiment may be made, in the form of water. As the apparatus
called the Cavendish bottle, by which this experiment only may be
safely performed, is somewhat expensive, and requires the use of an
air-pump, gas jars with stop-cocks, and an electrical machine and Leyden
jar, other and more simple means may be adopted to show the combi-
nation of oxygen and hydrogen, and formation of water.

If a little alcohol is placed in a cup and set on fire, whilst an empty
cold gas jar is held over the flame, an abundant deposition of moisture
takes place from the combustion of the hydrogen of the spirits of wine.
Alcohol contains six combining properties of hydrogen, with four of
charcoal and two of oxygen. If a lighted candle, or an oil, camphine,
Belmontine, or gas flame, is placed under a proper condenser, large
quantities of water are obtained by the combustion of these substances
(Fig. 119).

Fig. 119. A. A burning candle, or oil or gas lamp. Copper head and long pipe fitting
into B c, the receiver from which the condensed water drops into D. E E. Two corka
fitted, between which is folded some wet rag.

122 BOY'S PLAYBOOK OF SCIENCE.

Sixteenth Experiment.

During the combustion of a mixture of two volumes of hydrogen with
one of oxygen, an enormous amount of heat is produced, which is use-
fully applied in the arrangement of the oxy-hydrogen blowpipe. The
flame of the mixed gases produces little or no light, but when directed
on various metals contained in a small hole made in a fire brick, a most
intense light is obtained from the combustion of the metals, which is
variously coloured, according to the nature of the substances employed.
With cast-iron the most vivid scintillations are obtained, particularly if
after having fused and boiled the cast-iron with the jet of the two gases,
one of them, viz., the hydrogen, is turned off, and the oxygen only
directed upon the fused ball of iron, then the carbon of the iron burns
with great rapidity, the little globule is enveloped in a shower of sparks,
and the whole affords an excellent notion of the principle of Bessemer's
patent method of converting cast-iron at once into pure malleable iron,
or by stopping short of the full combustion of carbon, into cast-steel.

The apparatus for conducting these experiments is of various kinds,
and different jets have been from time to time recommended on account
of their alleged safety. It may be asserted that all arrangements pro-
posed for burning any quantity of the mixed gases are extremely aan-

gerous : if an explosion takes place
it is almost as destructive as gun-
powder, and should no particular
damage be done to the room, there
is stiff the risk of the sudden vibra-
tion of the air producing permanent
deafness. If it is desired to burn
the mixed gases, perhaps the safest
apparatus is that of Gurney ; in this
arrangement the mixed gases bubble
up through a little reservoir of water,

and thus the gasholder viz., a

Fig. 120. Gurney's jet. A. Pipe with bladder, is cut off from the jet when

stop-cock leading from the gas-holder, the Combustion takes place, (.rig.

"V?^ 6 *?** 16 . res f voir of , w K a * er thr 3 Q 120 ) This let is much recom-

which the mixed gases bubble, c. The ^ f/ ^ J -) j-f-rj ^ , ,, ,. ,,

jet where the gases burn. D. Cork, which mended by Mr. Woodward, thehighly
is blown out if the flame recedes in the respected President of the Islington
pipe ' c * Literary and Scientific Institution,

and may be fitted np to show the phenomena of polarized light, the
microscope, and other interesting optical phenomena.

Mr. Woodward states, that a series of experiments, continued during
many years, has proved, that while the bladder containing the mixed
gases is under pressure, the flame cannot be made to pass the safety
chambers, and consequently an explosion is impossible; and even if
through extreme carelessness or design, as by the removal of pressure or
the contact of a spark with the bladder, an explosion occurs, it can
produce no other than the momentary effect of the alarm occasioned by

THE OXY-HYDROGEN OR LIME LIGHT.

123

Pig. 121. A. The bladder of mixed gases, pressed by the board, B B, attached by wire
supports to another board, c c, which carries the weights, D D. BE. Pipe to which the
bladder, A, is screwed, and when A is emptied, it is re-filled from the other bladder, B.
p p p. Pipe conveying mixed gases to the lantern, G G, where they are burnt from a
Gurney's jet, H.

the report ; whereas, when the gases are used in separate bags under a
pressure of two or three half hundredweights, if the pressure on one of
the bags be accidentally removed or suspended, the gas from the other
will be forced into it, and if not discovered in time, will occasion an ex-
plosion of a very dangerous character ; or if through carelessness one
of the partially emp-
tied bags should be
filled up with the
wrong gas, effects of
an equally perilous
nature would ensue.

In the oxy-hydro-
gen blowpipe usually
employed, the gases
are kept quite sepa-
rate, either in gas-
ometers or gas bags,
and are conveyed oy

distinct pipes to a rig< 122 ^^ jet
jet of very simple
construction, devised
by the late Professor
Daniell, where they
mix in very small volumes, and are burnt at once at the mouth of the
jet. (Fig. 122.)

The gases are stored either in copper gasometers or in air-tight bags
of Macintosh cloth, capable of containing from four to six cubic feet of
gas, and provided with pressure boards. The boards are loaded with
two or three fifty-six pound weights to force out the gas with sufficient

Fig. 122. DanielTs jet. o o. The stop-cock and pipe con-
veying oxygen, and fitting inside the larger tube H H, to which
is attached a stop-cock, H, connected with the hydrogen re-
ceiver. A. The orifice near which the gases mix, and
they are burnt.

irhere

BOY'S PLAYBOOK OF SCIENCE.

pressure, and of course must be equally weighted ; if any change of
weight is made, the stop-cocks should be turned off and the light put out,
as the most disastrous results have occurred from carelessness in this
respect. (Fig. 123.)

Fig. 123. Gas bag and pressure boards.

The oxy-hydrogen jet is further varied in construction by receiving
the gases from separate reservoirs, and allowing them to mix in the
upper part of the jet, which is provided with a safety tube filled with

Fig. 124. A A. Board to which B B is fixed, o. Oxygen pipe. H. Hydrogen pipe.
c c. Space filled with wire gauze. D. Lime cylinder.

circular pieces of wire gauze. (Fig. 124.) With this arrangement a
most intense light is produced, called the Drummond or lime light, and
coal gas is now usually substituted for hydrogen.

ANALYSIS AND SYNTHESIS OF WATER. 125

There are many circumstances that will cause the union of oxygen and
hydrogen, which, if confined by themselves in a glass vessel, may be pre-
served for any length of time without change ; but if some powdered glass,
or any other finely-divided substance with sharp points, is introduced
into the mixed gases at a temperature not exceeding 660 Fahrenheit,
then the gases silently unite and form water.

This curious mode of effecting their combination is shown in a still
more interesting manner by perfectly clear platinum foil, which if intro-
duced into the mixed gases gradually begins to glow, and becoming red-
hot causes the gases to explode. Or still better, by the method first
devised by Dobereiner, in 1824, by which finely prepared spongy pla-
tinum i.e., platinum in a porous state, and exposing a large metallic
surface is almost instantaneously heated red-hot by contact with the
mixed gases. When this fact became known, it was further applied to
the construction of an instantaneous light, in which hydrogen was made
to play upon a little ball of spongy platinum, and immediately kindled.
These Dobereiner lamps were possessed by a few of the curious, and
would no doubt be extensively used if the discovery of phosphorus had
not supplied a cheaper and more convenient fire-giving agent. When
the spongy platinum is mixed with some fine pipeclay, and made into
little pills, they may (after being slightly warmed) be introduced into
a mixture of the two gases, and will silently effect their union. The
theory of the combination is somewhat obscure, and perhaps the simplest
one is that which supposes the platinum sponge to act as a conductor of
electric influences between the two sets of gaseous particles ; although,
again, it is difficult to reconcile this theory with the fact that powdered
glass at 660, a bad conductor of electricity, should effect the same
object. The result appears to be due to some effects of surface by
which the gases seem to be condensed and brought into a condition
that enables them to abandon their gaseous state and assume that of
water.

When Sir H. Davy invented the safety-lamp, he was aware that, in
certain explosive conditions of the air in coal mines, the flame of the
lamp was extinguished, and in order that the miner should not be left
in the dreary darkness and intricacies of the galleries without some
means of seeing the way out, he devised an ingenious arrangement with
thin platinum wire, which was coiled round the flame of the lamp, and
fixed properly, so that it could not be moved from its proper place by
any accidental shaking. When the flame of the safety -lamp, having the
platinum wire attached, was accidentally extinguished by the explosive
atmosphere in which it was burning, the platinum commenced glowing
with an intense heat, and continued to emit light as long as it remained
in the dangerous part of the mine. Sir H. Davy warned those
who might use the platinum to take care that no portion of the
thin wire passed outside the wire gauze, for the obvious reason
that, if ignited outside the wire gauze protector, it would inflame the
fire-damp.

126

BOYS PLAYBOOK OP SCIENCE.

Eighteenth Experiment.

Water is decomposed
by passing a current
of voltaic electricity
through it by means of
two platinum plates,
which may be connected
with a ten-cell Grove's
battery. The gases are
collected in separate
tubes, and the experi-
ment offers one of the
most instructive illus-
trations of the composi-
tion of water. (Fig. 125.)
There is a current of
electricity passing from
and between two plati-
num plates decomposing
water, offering the con-
verse of the Dobereiner
Fig. 125. p P. Two platinum plates connected with experiment, and highly
wires to the cups. The wires are passed through holes suffffestive of the proba-
in the finger-glass, B B, and are fixed perfectly steady by viV ~f -t-l, 1,
pouring in cement composed of resin and tallow to the blllt y ot tne theory al-
line i L. Two glass tubes filled with water acidulated with ready advanced in CX-
sulphuric acid, and placed over the platinum plates in nln-nnfinn r>f HIP cinmi
finger-glass, which ako contains dilute sulphuric acid to P lanatlon . ottne sm g u -
improve the conducting power of the water. The wires of lar combination or oxy-
the battery are placed in the cups, and the arrows show the ran and hvdrogen in the
direction of the current of electricity. ^^ $ ^ ^

num foil, and more especially when we consider the operation of Grove's
gas battery, in which a current of electricity is produced by pieces of
platinum foil covered with finely-divided platinum, called platinum black ;
each piece is contained in a separate glass tube filled alternately with
oxygen and hydrogen, and by connecting a great number of these tubes
a current of electricity is obtained, whilst the oxygen and hydrogen are
slowly absorbed and disappear, having combined and formed water,
although placed in separate glass tubes. (Fig. 126.)

The analysis of water is shown very perfectly on the screen by fitting
up some very small tubes and platinum wires in the same manner as
shown in fig. 125. The vessel in which the tubes and wires are con-
tained with the dilute sulphuric acid must be small, and arranged so as to
pass nicely into the space usually filled by the picture in an ordinary
magic lantern, or, still better, m one lighted by the oxy-hydrogen or
lime light. If the dilute acid is coloured with a little solution of indigo,
the gradual displacement of the fluid by the production of the two gases
is very perfectly developed on the screen when the small voltaic battery
is attached to the apparatus ; and of course a large number of persons
may watch the experiment at the same time.

With respect to the application of the light produced from a jet 01

THE SYNTHESIS OF OXYGEN AND HYDBOGSX.

12'

Fig. 126. Grove's gas battery consists of tubes containing oxygen and hydrogen alternately,
and haying a thin piece of platinum foil, f, inserted by the blowpipe in each glass tube.
The foil hangs down the full length of the interior of the glass. Each pair of tubes is
contained in a little glass tumbler containing some dilute sulphuric acid, and the
hydrogen tube, H, of one pair, is connected with the oxygen tube, Oj of the next, w w.
The terminal wires of the series.

the mixed gases thrown upon a ball of lime, it may be stated that for
many years the dissolving view lanterns and other optical effects have
been produced with the assistance of this light ; and more lately Major
Titzmaurice has condensed the mixed gases in the old-fashioned oil
gas receivers, and projected them on a ball of lime; and it was this
light thrown from many similar arrangements that illuminated the
British men-of-war when Napoleon III. left her Majesty's yacht at night
in the docks at Cherbourg.

Mr. Sykes Ward, of Leeds, has also proposed a most simple and excel-
lent application of the oxy-hydrogen light for illumination under the

Fig. 127. Cherbourg.

128

BOY S PLAYBOOK OF SCIENCE.

Fig. 128. A A. Tube re-
servoir to hold the mixed
gases. B. The jet and lime
ball. 3>. The first glass
shade, held down by a cap
and screw, c. The second
glass shade. E E. The
handle by which it is low-
ered into the water.

surface of water, and for the convenience of
divers, who are frequently obliged to cease their
operations in consequence of the want of light.
Mr. Ward's submarine lamp consists of a series
of very strong copper tubes, which are filled
with the mixed gases by means of a force-pump ;
and in order to prevent the lamp being extin-
guished, it burns under double glass shades,
which are desirable in order to prevent the glass
immediately next to the light cracking by con-
tact with the cold water.

The author tried this lamp at Hyde, and
although the coast-guards objected to the pro-
duction of a brilliant light at night, which they
stated might be mistaken for a signal and
would cause some confusion amongst the war
vessels in the immediate neighbourhood, enough
experiments were made, to show that the Ward
lamp would burn for a considerable time under
water, and could be kept charged with the gas
by means of a process that was easily work-
able in the boat. The gases were taken out
mixed in gas bags, and pumped into the reser-
voir when required. With a much larger reser-
voir greater results could be obtained; and if
nautilus diving bells are to be used in modern
warfare, they will require a powerful light to
show them their prey, so that they may attach
the explosives which are to blow great holes in
the men-of-war.

Fig. 129. Submarine lamp.

129

CHLORINE, IODINE, BROMINE, FLUORINE.

The four Halogens, or Producers of Substances like Sea Salt.

Chlorine (^Xwpos, green). Symbol, Cl. Combining proportion, 35 '5.
Specific 'gravity, 2'l4. Scheele termed it dephlogisticated muriatic
acid; Lavoisier, oxymuriatic acid; Davy, chlorine.

The consideration of the nature of this important element introduces
to our notice one of the most original chemists of the eighteenth
century viz., the illustrious Scheele, who was born at Stralsund, in 1742,
and in spite of every obstacle, fighting his " battle of life" with sickness
and sorrow, he succeeded in making some of the most valuable dis-
coveries in science, and amongst them that of chlorine gas. It was in
the examination of a mineral solid viz., of manganese that Scheele
made the acquaintance of a new gaseous element; and in a highly
original dissertation on manganese, m 1774, he describes the mode of
procuring what he termed dephlogisticated muriatic acid a name which
is certainly to be regretted, from its absurd length, but a title which

was strictly in accordance with the then established theory of phlogiston ;
and if the latter is considered synonymous with hydrogen, quite in
accordance with our present views of the nature of this element.

Scheele discovered the leading characteristics of chlorine, and especially
its power of bleaching, which is alone sufficient to place this gas in a
hign commercial position, when it is considered that all our linen used
formerly to be sent to Holland, where they had acquired great dexterity
in the ancient mode of bleaching viz., by exposure of the fabric to
atmospheric air or the action of the damps or dews, assisted greatly by
the agency of light. Some idea may be formed of the present value
of chlorine, when it is stated that the linen goods were retained by the
Dutch bleachers for nine months ; and if the spring and summer hap-
pened to be favourable, the operation was well conducted ; on the other
hand, if cold and wet, the goods might be more or less injured by con-
tinual exposure to unfavourable atmospheric changes. At the present
time, as much bleaching can be done in nine weeks as might formerly
have been conducted in the same number of months ; and the whole of
the process of chlorine bleaching is carried on independent of external
atmospheric caprices, whilst the money paid for the process no longer
passes to Holland, but remains in the hands of our own diligent
bleachers and manufacturers.

First Experiment.

As Scheele first indicated, chlorine is obtained by the action of the
black oxide of manganese, on "the Spirit of Salt," or hydrochloric
acid ; and the most elementary and instructive experiment snowing its
preparation can be made in the following manner :

130

BOY S PLAYBOOK OF SCIENCE.

Fig. 130.

Place in a clear Florence oil-flask, to which a cork and bent tube have
been first fitted, some strong fuming hydrochloric acid. Arrange the
flask on a ring-stand, and then pass the bent tube either to a Wolfe's
bottle containing some pumice stone moistened with oil of vitriol, or to

a glass tube containing
either pumice or as-
bestos wetted with the
same acid. , Another
glass tube, bent at
right angles, passes
away from the Wolfe's
bottle into a receiving
bottle. (Fig. 130). On
the application of heat,
the hydrochloric gas is
driven off from its so-
lution in water, and
any aqueous vapour
carried up is retained
by the asbestos or pu-
mice stone wetted

A. Flask containing the fuming hydrochloric .ui, ^i n t ^f^Cryl 4V,a
acid,"which is gently boiled by the heat of the spirit lamp. W11J A O 11 . 01 vlinoi , me
B. Tube passing to the Wolfe's bottle, containing pumice- application of the lat-
stone or asbestos moistened with sulphuric acid. c. f pr jc nallprl dniinn f}>/>
Second tube passing into a dry empty bottle, which receives lb .~^J ^F? 9

the hydrochloric acid gas. gas i.e., depriving it

of all moisture ; some-
times the salt called chloride of calcium is used for the same purpose, and
it must be understood by the juvenile chemist that gases are not dried
like towels, by exposure to heat, or by putting them in bladders before the
fire, as we once heard was actually recommended, but by causing the gas
charged with invisible steam to pass over some substance having a great
affinity for water. The dry hydrochloric gas falls into the bottle, and dis-
places the air, beinj* about one-fourth heavier than the latter, and gradu-
ally, overflowing from the mouth of the vessel, produces a white smoke,
which is found to be acid by litmus paper, but has no power to bleach,
and is not green ; it is, in fact, a combination of one combining pro-
portion of chlorine with one of hydrogen, and to detach the latter, and
set the chlorine free, it is necessary to convey the hydrochloric gas to
some body which has an affinity for hydrogen. Such a substance is
provided in the use of the black oxide of manganese, which is placed
either in a small flask or in a tube provided with two bulbs, and when
heated with the lamp it separates the hydrogen from the hydrochloric
gas, and forms water, which partly condenses in the second bulb. And
now the gas that escapes is no longer acid and fuming with a white
smoke on contact with the air; but is green, has a strong odour,
bleaches, and is so powerful in its action on all living tissues, that it
must be carefully avoided and not inhaled ; if a small quantity is acci-
dentally inhaled, it produces a violent fit of coughing, which lasts a

THE PREPARATION OF CHLORINE GAS.

131

-considerable time, and is only abated by inhaling the diluted vapour of
ammonia, or ether, or alcohol, and swallowing milk and other softening
drinks. (Kg. 131).

Fig. 131. A. The flask containing the fuming hydrochloric acid, heated by spirit lamp.
B. Tube passing to Wolfe's bottle, containing the pumice-stone or asbestos wetted with
oil of vitriol, c. Second tube, which passes into a wide-mouthed small flask containing
black oxide of manganese, partly in powder and partly in lump ; and the third tube
conveys the chlorine to any convenient vessel. The double bulb tube, E E, may be substi-
tuted for the flask, the oxide of manganese being contained hi the bulb M. N.B. Any tube
may be joined on to another by a bit of india-rubber tubing, which is tied by string.

C B

Tube A is joined to tube B by the caoutchouc pipe c, tied with packthread.

The mode of preparing chlorine, as already given, though very in-
structive, is troublesome to perform ; a more simple process may there-
fore be described :

Pour some strong hydrochloric acid upon powdered black oxide of
manganese contained in a Florence oil-flask, taking care that the whole
of the black powder is wetted with the acid so that none of it clings to the
bottom of the flask in the dry state to cause the glass to crack on the
application of heat. A cork and bent glass tube is now attached, and
conveyed to the pneumatic trough ; on the application of heat to the
mixture in the flask the chlorine is evolved, and may be collected in
stoppered bottles, the first portion that escapes, although it contains
atmospheric air, should be carefully collected in order to prevent any

132

BOY S PLAYBOOK OF SCIENCE.

accident from inhaling the gas, and it will do very well to illustrate the
bleaching power of the gas, and therefore need not be wasted. The
above process may be described in symbols, all of which are easily deci-
phered by reference to the table of elements, page 86.

Mn0 3 +2 HCl=MnCl+2 IIO+C1.

Third Experiment.

Another and still more expeditious mode of preparing a little chlorine,'
is by placing a small beaker glass, containing half an ounce of chlorinated

lime, usually termed chloride of
lime or bleaching powder, care-
fully at the bottom of a deep and
large beaker glass, and then, by
means of a tube and funnel, con-
veying to the chloride of lime
some dilute oil of vitriol, com-
posed of half acid and half
water ; effervescence immedi-
ately occurs from the escape of
chlorine gas, and as it is pro-
duced it falls over the sides of
the small beaker glass into the
large one, when it may be dis-
tinguished by its green colour.
If a little gas be dipped out with
a very small beaker glass ar-
ranged as a bucket, and poured
into a cylindrical glass contain-
ing some dilute solution of in-
digo, and shaken therewith, the
colour disappears almost instan-
taneously; and if a piece of
Dutch metal is thrown into the
beaker glass it will take fire if

Fig. 132. ^ The large beaker glass. B. enough chlorine has been gene-
The small one, containing the chloride of lime, rated, Or some very nnely-pow-
c. The tube and funnel down which the dilute d erec l antimony will demonstrate
sulphuric acid is poured. D D. Sheet of paper , ^, rpv.no f],

over top of large glass, with hole in centre to the same result. Ihus, With a
admit the tube. u. The little beaker used as a f ew beaker glasses, some chlo-
ride of lime, sulphuric acid, a

solution of indigo, and a little Dutch metal, the chief properties of
chlorine may be displayed. (Eig. 132.)

Fourth Experiment.

Into a little platinum spoon place a small pellet of the metal sodium
aud after heating it in the flame of a spirit lamp, introduce the metal

EXPERIMENTS WITH CHLORINE GAS. 133

into a bottle of chlorine, when a most intense and brilliant combustion
occurs, throwing out a vivid yellow light, and the heat is frequently so
great that the bottle is cracked. After the combustion, and when the
bottle is cool, it is usually lined with a white powder, which will be
found to taste exactly the same as salt, and, in fact, is that substance,
produced by the combination of chlorine, a virulent poison, with the
metal sodium, which takes fire on contact with a small quantity of
water ; and hence the use of salt for the preparation of chlorine gas
when it is required on the large scale.

Parts.

Common salt 4

Black oxide of manganese .... 1

Sulphuric acid 2

Water 2

'Fifth Experiment.

Some Dutch metal, or powdered antimony, or a bit of phosphorus,
immediately takes fire when introduced into a bottle containing chlorine

fas, forming a series of compounds termed chlorides, and demonstrating
y the evolution of heat and light, the energetic character of chlorine,
and that oxygen is not the only supporter of combustion ; chlorine
gas has even, in some cases, greater chemical power, because some
time elapses before phosphorus will ignite in oxygen gas, whilst it takes
fire directly when placed in a bottle of chlorine.

Sixth Experiment.

The weight and bleaching power of chlorine are well shown by placing
a solution of indigo in a tall cylindrical glass, leaving a space at the
top of about five inches in depth. By inverting a bottle of chlorine
over the mouth of the cylindrical glass, it pours out like water, being
about two and a half times heavier than atmospheric air, and then, after
placing a ground glass plate over the top of the glass, the chlorine
is recognised by its colour, whilst the bleaching power is demonstrated
immediately the gas is shaken with the indigo solution.

As a good contrast to the last experiment, another cylindrical jar of
the same size may be provided, containing a solution of iodide of potas-
sium with some starch, obtained by boiling a teaspoonful of arrowroot
with some water ; any chlorine left in the bottle (sixth experiment) may
be inverted into the top of this glass and shaken, when it turns a beautiful
purple blue in consequence of the liberation of iodine by the chlorine,
whose greater affinity for the base produces this result. The colour is
caused by the union of the iodine and the starch, which form together a
beautiful purple compound, and thus the apparent anomaly of destroying
and producing colour with the same agent is explained.

134

BOY S PLAYBOOK OF SCIENCE.

Eighth Experiment.

Dry chlorine does not bleach, and this fact is easily proved by taking
a perfectly dry bottle, and putting into it two or three ounces of fused

chloride of calcium broken
in small lumps, then if a
bottle full of chlorine is
inverted over the one con-
taining the chloride of cal-
cium, taking the precau-
tion to arrange a few
folds of blotting paper
with a hole in the centre
on the top of the latter to
catch any water that may
run out of the chlorine
bottle at the moment it is
inverted, the gas will be
dried by contact with the
chloride of calcium, and
if a piece of paper, with
the word chlorine written

Fig. 133. A A. Dry bottle, containing chloride of On $ th indi ?> \

calcium. B. Bottle of chlorine. The arrow indicates the previously made not and

gas. c c. The blotting-paper, to catch any water from dry, is placed in the chlo-

the bottle, B. . The bottle closed, and containing the ^ no change ^^

but directly the paper is

removed, dipped in water, and placed in a bottle of damp chlorine, the
colour immediately disappears. (Fig. 133.)

This experiment shows that chlorine is only the means to the end,
and that it decomposes water, setting free oxygen, which is supposed to
exert a high bleaching power it its nascent state, a condition which many
gases are imagined to assume just before they take the gaseous state, a
sort of intermediate link between the solid or fluid and the gaseous con-
dition of matter. The nascent state may possibly be that of ozone, to
which we have already alluded as a powerful bleaching agent.

Ninth Experiment.

A piece of paper dipped in oil of turpentine emits a dense black
smoke, and frequently a flash of fire is perceptible, 'directly it is plunged
into a bottle containing chlorine gas ; here the gas combines only with
the hydrogen of the turpentine, and the carbon is deposited as soot.

Tenth Experiment.

If a lighted taper is plunged into a bottle of chlorine it continues to
burn, emitting an enormous quantity of smoke, for the reason already
explained > and demonstrating the perfection of the atmosphere in which.

EXPEKIMENTS WITH CHLORINE GAS.

135

we live and breath, and showing that had oxygen gas possessed the
same properties as chlorine, the combustion of compounds of hydrogen
and carbon would have been impossible, in consequence of the enormous
quantity of soot which would have been produced, so that some other
element that would freely enter into combination with it must have
been provided to produce both artificial light and heat. Chlorine is a
gas which cannot be inhaled, and ozone presents the same features, as a
mouse confined for a short time with an excess of ozone soon died ; but
ozone is the extraordinary condition of
oxygen ; the element in the ordinary state
is harmless, and is the one which enters
so largely into the composition of the air
we breathe.

When one volume of olefiant gas (pre-
pared by boiling one measure of alcohol
and three of sulphuric acid) is mixed
with two volumes of chlorine, and the two
gases agitated together in a long glass ves-
sel for a few seconds, with a glass plate
over the top, which should have a welt
ground perfectly flat, they unite on the ap-
plication of flame, with the production of a
great cloud of black smoke, arising from
the deposited carbon, whilst a sort of
roaring noise is heard during the time
that the flame passes from the top to the
foot of the glass. (Fig. 134.)

Twelfth Experiment.

Formerly Bandannah handkerchiefs
were in the highest estimation, and no
gentleman's toilet was thought complete
without one. The pattern was of the
simplest kind, consisting only of white
spots on a red or other coloured ground.
These spots were produced in a very in-
genious manner by Messrs. Monteith, of
Glasgow, by pressing together many
layers of silk with leaden plates perforated
with holes ; a solution of chlorine was
then poured upon the upper plate and
pressure being applied it penetrated the O f chlorine,
whole mass in the direction of the holes,
bleaching out the colour in its passage. This important commercial
result may be imitated on the small scale by placing a piece of calico
dyed with Turkey red between two thick pieces of board, each of which

Fig. 134. Eemarkable deposition

136 BOY'S PLAYBOOK OF SCIENCE.

is perforated with a hole two inches in diameter, and corresponding
accurately when one is placed upon the other. The pieces of board
may be squeezed together in any convenient way, either by weights,
strong vulcanized india-rubber bands or screws, and when a strong

solution of chlorine
gas or of chloride of
lime is poured into
the hole and perco-
lates through the
cloth, the colour is
removed, and the
part is bleached al-
most instantaneously
by first wetting the
_ calico with a little
weak acid, and then
pouring on the solu-
Fig. 135. A. Circular hole in the upper piece of wood, a 4-; nn n f phlnrirlp nf
similar one being perforated in the lower one. B B. The strong P. 1013 le . Ot

india-rubber bands. The bleaching solution is poured into A. lime. Un removing

and washing the fol-
ded red calico it is found to be bleached in all the places exposed to the
solution, and is now covered with white spots. (Fig. 135.)

IODINE.

Iodine (la>8rjs, violet coloured). Symbol, I; combining proportion,
127'1 ; specific gravity, 4*948. Specific gravity of iodine vapour, 8716.

In the previous chapter, devoted to the element chlorine, little or
nothing has been said of that inexhaustible storehouse of chlorine,
iodine, and bromine viz., the boundless ocean. Some one has remarked
that, as it is possible the air may contain a little of everything capable
of assuming the gaseous form, so the ocean may hold in a state of solu-
tion a modicum of every soluble substance, in proof of which we have
lately read of some very important experiments resulting in the separa-
tion of the metal silver from sea water, not certainly in any profitable
quantity, but quite enough to prove its presence in the ocean.

No elaborate research is necessary to ascertain the presence of chlorine,
when it is remembered that Schafhautl has calculated, that all the oceans
on the globe contain three millions fifty-one thousand three hundred and
forty-two cubic geographical miles of salt, or about five times more than
the mass of the Alps.

Now, salt contains about 60 per cent, of chlorine gas, and therefore
the bleachers can never stand still for want of it ; but iodine is not so
plentiful, and was discovered by M. Courtois, of Paris, in kelp, a sub-
stance from which he prepared carbonate of soda, or washing soda ; but
as this is now more cheaply prepared from common salt, the kelp is at
present required only for the iodine salts it contains, as also for the
chloride of potassium. Kelp is obtained by burning dried sea-weeds in a

EXPERIMENTS WITH IODINE.

137

shallow pit ; the ashes accumulate and melt together, and this fused mass
broken into lumps forms kelp. The ocean bed no doubt has its fertile and
barren plains and mountains, and amongst the so-called "oceanic
meadows" are to be mentioned the two immense groups and bands of
sea-weed called the Sargasso Sea, which occupy altogether a space
exceeding six or seven times the area of Germany.

The iodine is contained in the largest proportion in the deep sea
plants, such as the long elastic stems of the fucus palmatus, &c. The
kelp is lixiviated with water, and after separating all the crystallizable
salts, there remains behind a dense oily -looking fluid, called "iodine
ley," to which sulphuric acid is added, and after standing a day or two
the acid "ley" is placed in a large leaden retort, and heated gently
with black oxide of manganese. The chlorine being produced very
slowly, liberates the iodine, as already de-
monstrated in experiment seven, p. 133,
and it is collected in glass receivers.

Iodine, when quite pure and well crys-
tallized, has a most beautiful metallic lustre,
and presents a bluish-black colour, afford-
ing an odour which reminds one at once
of the " sea smell."

First Experiment.

A few grains of iodine placed in a flask
may be sublimed at a very gentle heat, and
afford a magnificent violet vapour, which
can be poured out of the flask into a warm
bottle. If the bottle is cold the iodine
condenses in minute and brilliant crystals.
(Fig. 136.)

Second Experiment.

Upon a thin slice of phosphorus place a
few small particles of ioSine ; the heat pro-
duced by the combination or the two ele- Cold flask above to receive the
ments soon causes the phosphorus to take y a P r - op. Sheet of cardboard

to cut off the heat from the spirit
"*. lamp.

Third Experiment.

Heat a brick, and then throw upon it a few grains of iodine ; by
holding a. sheet of white paper behind, the spleadid violet colour of the
vapour is seen to great advantage. It was by the discovery of iodine in
the ashes of sponge which had long been used as a remedy for goitre, a
remarkable glandular swelling that this element began to be used for
medical purposes, and the important salt called iodide of potassium is
now used in large quantities, not only in medicine, bat likewise for that
most fascinating art, which has made its way steadily, and is now
practised so extensively, under the name of photography.

138 BOY'S PLAYBOOK OF SCIENCE.

THE ART 01 PHOTOGRAPHY.

It was the great George Stephenson who asked the late Dean Buckland
the posing question, " Can you tell me what is the power that is driving
that train ?" alluding to a train which happened to be passing at the
moment. The learned dean answered, "1 suppose it is one of your
big engines." "But what drives the engine?" "Oh, very likely a
canny Newcastle driver." " What do you say to the light of the sun ?"
"How can that be?" asked Buckland. "It is nothing else," said
Stephenson. " It is light bottled up in the earth for tens of thousands
of years ; light, absorbed by plants and vegetables, being necessary for
the condensation of carbon during the process of their growth, if "it be
not carbon in another form ; and now, after being buried in the earth
for long ages in fields of coal, that latent light is again brought forth
and liberated, made to work as in that locomotive for great human
purposes."

Such was the opinion of the most original and practical man that
ever reasoned on philosophy ; and could he have lived to realize the
thorough adaptation and business use of light in the art of photography,
he would have said, man is only imitating nature, and in producing
photographs he must employ the same agent which in ages past assisted
to produce the coal.

In another part of this elementary work we shall have to consider
the nature of light; here, however, the chemical part only of the
process of photography will be discussed.

Many years ago (in the year 1777) Jenny Lind's most learned
countryman, Scheele, discovered that a substance termed chloride of
silver, obtained by precipitating a solution of chloride of silver with
one of salt, blackened much sooner in the violet rays than in any other
part of the spectrum. He says, " Fix a glass prism at the window,
and let the refracted sunbeams fall on the floor ; in this coloured light
put a paper strewed with luna cornua (horn silver or chloride of silver),
and you will observe that this horn silver grows sooner black in the
violet ray than in any of the other rays."

In 1779, Priestley directed especial attention to the action of light on
plants ; and the famous Saussure, following up these and other experi-
ments, determined that the carbonic acid of plants was more generally
decomposed into carbon and oxygen in the blue rays of the spectrum ;
these facts probably suggested the bold theory of Stephenson already
alluded to. Passing by the intermediate steps of photography, we
come to the second year of the present century, and find in the Journal of
the Royal Institution a paper by Wedgwood, entitled " An Account of
a Method of Copying Paintings upon Glass, and of making Profiles, by
the Agency of Light upon Nitrate of Silver ; with observations, by
H. Davy." Such a paper would lead the reader to suppose that very
little remained to be effected, and that mere details would quickly
establish the art ; but in this case the experimentalists were doomed to

THE ART OP PHOTOGRAPHY. 130

disappointment, as, after producing their photographs, they could not
make them permanent ; they had not yet discovered the means of fixing
the pictures. Nearly fourteen years elapsed, when the subject was
again taken up by Niepce, of Chalons, with little success, so far as the
fixing was concerned ; and twenty-seven years had passed away since
the experiments of Wedgwood and Davy, when, in 1829, Niepce and
Daguerre executed a deed of co-partnership for mutually investigating
the matter. These names would suggest a rapid progress ; but, strange
to relate, ten years again rolled away, the father Niepce had in the
meantime died, and a new contract was made between the son and M.
Daguerre, when, in January, 1839, the famous discovery was made
known to the world, and in July of the same year the French Govern-
ment granted a pension for life of six thousand francs to Daguerre,
and four thousand to the son of Niepce, who had so worthily continued
the experiments commenced by his father. The triumph of the indus-
trious French experimentalists was not, however, to be unique ; across
the Channel another patient and laborious philosopher had completed on
paper precisely the same kind of results as those obtained by Daguerre
on silver plates. Mr. Fox Talbot, in England, had immortalized himself
by a discovery which was at once called the Talbotvpe, and for which a
patent was secured in 1841. Having thus hastily sketched a brief
history of the art, we may now proceed to the details of the process.

First Experiment.

A. photogenic drawing, so called, but now termed a positive copy, is
prepared by placing some carefully selected paper, which is free from
spots or inequalities (good paper is now made by several English manu-
facturers, although some kinds of French paper, such as Cansan's, are
in high repute), in a square white hard porcelain dish containing a
solution of common salt in distilled water, 109 grains of salt to the pint.
The paper is steeped in this solution for ten minutes, and then taken
out and pressed in a clean wooden press, or it should be dabbed dry on a
clean flat surface with a clean piece of white calico, which may be kept
specially for this duty and not used for anything else, and it is well that
all would-be photographers should understand that neatness and cleanli-
ness are perfectly indispensable in conducting these processes. If a
design were required for the armorial bearings of the art of photo-
graphy, it might certainly be most fanciful, but the motto must be
cleanliness and neatness, and in preparing paper it should not be unne-
cessarily handled, but lifted by the corners only. The object of dabbing
the paper is to prevent the salt accumulating in large quantities in one
part of the paper and the reverse in another, and to distribute the salt
equally through the whole. The paper being now dried, is called salted
paper, and is rendered sensitive when required by laying it down on a
solution of ammpnio-nitrate of silver, prepared by adding ammonia to a
solution containing sixty grains of nitrate of silver to the ounce of dis-
tilled water, until the whole of the oxide of silver is re-dissolved, except

140 BOY'S PLAYBOOK OF SCIENCE.

a very small portion. A few drops of nitric acid are also recom-
mended to be added, and after allowing the solution to stand, it may be
poured off quite clear, and is ready for use either in the bath, or if
economy must be rigidly adhered to, the salted paper may be laid flat
on a board, and held in its place with four pins at the corners, and then
just enough to wet the surface of the paper may be run along the side
of a glass spreader, and the liquid gently drawn over the surface of the

Fig. 137. A. The glass spreader with cork handle. B. The silver solution clinging to
rod and paper by capillary attraction, c c c c. Four pins holding down the paper on a
board. N.B. The spreader is made of glass rod three-eighths thick.

salted paper, which is allowed to dry on a flat surface for a few minutes,
and afterwards hung up by one corner to a piece of tape stretched
across the room, until quite dry, and then placed in a blotting-book
fitting into a case which completely excludes the light. Copying-paper
should be made at night, as the day is then free for all photographic
operations requiring an abundance of light. It will not keep long, and
should be used the next day.

A piece of lace, a skeleton leaf, a sharp engraving on thin paper, and
above all things, a negative photograph on glass or paper, is easily copied
by placing the prepared paper with the prepared side (carefully protected
from the light) upwards on any flat surface, such as plate glass; upon
this is arranged the bit of lace or the negative photograph with the face
or picture downwards, another bit of plate glass is then placed over it,
and weights arranged at the corners ; after exposure to the sun's rays for
thirty minutes, more or less (according to the dullness or bright aspect of
the day), the picture is brought into a dark room and examined oy the
light of a candle or by the light from a window covered with yellow
calico, and after placing a paper weight on one corner of the lace, or

PHOTOGRAPHIC MANIPULATIONS.

141

negative picture, or copying paper, it may be carefully lifted in one
part, and if the copy is sufficiently dark, is ready for fixing, but if it
is faint the lifted corner is carefully replaced, the upper glass is laid
on, and the picture again exposed to the light. Should the position of the
lace or negative be changed during the examination, re-exposure is use-
less, and would only produce a double and confused picture, as it would
be impossible to lay the lace or the negative exactly in the same place
again on the copying paper.

The manipulations just de-
scribed are much facilitated by
using a copying-frame or press,
which consists of a square
woodenframe with a thick plate-
glass window; upon this are
placed the negative picture and
the copying paper, and the two
are brought in close contact by-
means of a board at the back
Pressed by a hand-screw. (Fig.
38.) After the photogenic
drawing or positive copy is
taken, it is fixed by being placed

in a solution of hyposulphite

of soda consisting of one fluid

Ounce ot saturated solution to and is of course the part exposed to the light.

eight of water. The saturated

solution of hyposulphite of soda is conveniently kept in a large bottle

for use, and in order to improve the colour a very little chloride of

gold is added to the fixing solution, the picture must now be thoroughly

washed, dried, and pressed.

Another mode of preparing the copying paper, called albumen paper,
is to take the whites of four eggs, and four ounces of distilled water
containing one hundred and sixty grains of chloride of ammonium;
these are beaten up with a fork or a bundle of feathers, and as the froth
is produced it is skimmed off by a silver spoon into another basin,
or a beaker glass, and being allowed to settle for twelve hours it is
strained through fine muslin, and is ready for use. The best paper is
floated on the surface of this liquid for three minutes, taken out, and
dried at once on a hot plate.

In floating paper one corner is first laid down, and care taken not to
enclose any air bubbles, which would prevent the fluid wetting the
paper, whilst the remainder of the paper is slowly laid upon the surface
of the fluid.

The albumen paper is excited by laying it for five minutes on a
solution of nitrate of silver, seventy-two grains to the ounce of water,

142 BOY'S PLAYBOOK OF SCIENCE.

and when dry it will keep for three days. This copying paper is used
in the same manner as the last, and fresh eggs only must be used in
its preparation, because stale ones soon cause the copy to change and
blacken all over from the liberation of sulphur, which unites with the
silver. The colour of the copy is sometimes improved by a solution of
hot potash, and by dipping the well-washed picture, after the use of the
hyposulphite of soda, in a very dilute solution of hydrosulphuret of
ammonia.

Third Experiment.

In the Daguerreotype process, a silver plate, after being thoroughly
cleaned and polished, is exposed to the vapour of iodine, and is thus
rendered so sensitive that it may be at once exposed in the camera.
In the Talbotype process, the same principle is apparent, and paper is
prepared by first covering its surface with iodide of silver, which is
afterwards rendered sensitive to the action of light by means of au
excess of nitrate of silver, as follows :

One side of a sheet of selected Cansan's paper is first covered
(by means of a spreader) with a solution of nitrate of silver (thirty
grains to the ounce of water), hung up in a dark room and dried;
it is then immersed in a solution of iodide of potassium of five
hundred grains to a pint of distilled water, for five or ten minutes,
and immediately changes, to a yellow colour in consequence of the pre-
cipitation of the yellow iodide of silver ; it is then well washed with
plenty of water, and being dried, may be kept for any length of time,
and is called " iodized paper." Light has no action whatever upon it.
To render the paper sensitive, three solutions are prepared in separate
bottles, and marked 1, 2, 3.

No. 1, contains a solution of nitrate of silver, fifty grains to the ounce
of water.

No. 2, glacial acetic acid.

No. 3, a saturated solution of gallic acid.

With respect to No. 3, Mr. William Crookes has shown, that when
a saturated solution of gallic acid is required in large quantities, that
it is better to dissolve at once two ounces of gallic aciu in six ounces
of alcohol (60 over proof) ; to hasten solution, the flask may be con-
veniently heated by immersion in hot water ; when cold it should be
filtered, mixed with half a drachm of glacial acetic acid, and preserved
in a stoppered bottle for use ; so prepared it will keep unaltered for
a considerable length of time. The gallic acid is not precipitated from
this solution by the addition of water ; consequently, if in any case
desirable, the development of a picture may be effected with a much
stronger bath than the one usually employed. To obtain a solution
of about the same strength as a saturated aqueous solution, such as
No. 3, half a drachm of the alcoholic solution is mixed with two ounces
of water ; but for my particular purpose, says Mr. Crookes, referring
to the wax-paper process, " I prefer a weaker bath, which is prepared
by mixing half a drachm with ten ounces of water." In either case it

PHOTOGRAPHIC MANIPULATIONS. 143

will be found necessary to add solution of nitrate of silver in small
quantities, as the developing picture seems to require it.

Returning again to the solutions marked 1, 2, 3, the numbers will
assist the memory in mixing the proportions of each. If the paper
is required to be used at once, a drachm of each may be mixed to-
gether and spread over the iodized paper (of course, in a dark room),
which is then transferred to a clean blotting-book of white bibulous
paper, and being placed in the paper-holder may be taken to the camera
ami exposed at once. If the paper is not required to be used imme-
diately, the solutions are mixed in the proportions of the numbers viz.,
one of No. 1, two of No. 2, three of No. 3 ; and in making the mixture, it
is advisable to keep a measure specially for No. 3, the gallic acid, or
else the measure, if used for the three solutions, will have to be washed
out every time, which is very troublesome, particularly where water is
not plentiful.

If the excited paper is required to be kept some hours before use,
No. 3 must be added in still larger proportion, as much as ten or even
twenty measures of No. 3 to two of No. 2, and one of No. 1, being used,
and even this large dilution is frequently insufficient to prevent the
paper spoiling in hot weather; therefore if the temperature is high,
too much reliance must not be placed on this paper, as it is peculiarly
disappointing, after walking some miles to romantic and beautiful
scenery, to find, when developing the pictures in the evening, that the
paper used was all spoilt before exposure ; and it will be seen presently
that when the excited paper is to be carried about for use, it is better
to adopt the wax-paper process.

After the excited iodized paper is exposed in the camera and the
time of exposure cannot be taught, as that speciality is only acquired by
experience, and may vary from five to thirty minutes, or even more
the invisible picture is developed and rendered visible, not by exposure
to the vapour of mercury, as in Daguerre's process with silver plates,
but by a mixture of one of No. 1 with four of No. 3. The development
is carefully watched by looking through the negative placed before a
lighted candle, and the time of development may vary from ten to thirty
minutes, and all the time the picture must be kept wet with the
solution, so that it is better perhaps to make a bath of the solution
and lay the picture on its surface than to pour the liquid over the
picture. After the development is matured, the picture is now washed
in clean water, and fixed temporarily, if required, by immersion in a
bath containing 200 grains of bromide of potassium in one pint of water,
or permanently by the hyposulphite of soda, made by mixing one part
of a saturated solution with five or ten of water, or one ounce of the
salt to six or twelve of water ; but, as before mentioned, it is better to
keep a Winchester quart full of a saturated solution of hyposulphite
of soda, and then it is always ready for use instead of employing the
weights and scales, and continually weighing out portions of the salt.
The picture after fixing is thoroughly washed with water, and being

144 BOY'S PLAYBOOK OF SCIENCE.

dried is now placed between the folds of a wax book i.e., some leaves
of blotting-paper are kept saturated with white wax, and when a
picture is placed between them, and a hot iron passed over the outside
sheet, the wax enters the pores of the paper, and after removing any
excess of wax by passing the picture through a book of bibulous paper,
over which the hot flat iron is passed, the negative picture at last is
ready for use, and any number of positive copies may be taken from it,
as already described in the first experiment, page 139.

This mode of manipulation is called the Talbotype, and before
dismissing the subject another process of iodizing the paper may be
explained.

To a solution of nitrate of silver of twenty, thirty, or fifty grains
to the ounce of water, a sufficient number of the crystals of iodide of
potassium is added, first to produce the yellow iodide of silver, and
then to dissolve it, so that the yellow precipitate appears with a
small quantity, and disappears with an excess of the iodide. If this
solution is spread over sheets of paper, and these latter then placed
in a bath of water, the iodide of silver is precipitated on the surface,
and after plenty of washing to remove the excess of iodide of
potassium, the paper may be dried, and will keep for any length of time
without change. This paper may be excited, exposed, developed, fixed,
and waxed, as already explained.

Fourth Experiment. The Wax-paper Process.

This mode of taking negative photographs begins where the talbo-
type ends viz., by first waxing the paper perfectly and evenly, as
already explained, Cansan's negative paper being preferred. The wax
paper is now well soaked in a bath, made by dissolving one hundred
grains of iodide of potassium, six grains of cyanide of potassium,
four grains of fluoride of potassium, ten grains of bromide of potassium,
ten grains of chloride of sodium, in one pint of fresh whey, with the
addition of a little alcohol and a few grains of iodine. When soaked
in this solution for about one hour, the paper is taken out and hung up
to dry.

N.B. With respect to iodizing the wax paper, it is almost better to
obtain it ready prepared, and then every sheet may be relied on. Mr.
Melhuish, of Blackheath and Holborn, supplies it in any quantity, and
his paper never fails; the operator has then only to perform the sensi-
tizing and developing processes. To render the iodized paper sensitive it
is immersed for about six minutes in a bath containing a solution of
nitrate of silver (thirty-five grains to the ounce of water, with forty
drops of glacial acetic acid); the paper is now removed, and washed in
two trays of common clear rain-water or distilled water, and is then
dried off between folds of blotting-paper.

This process may be performed on the previous evening by the light
of a candle, or by day in a room lit by one window covered with four
thicknesses of yellow calico, and after the paper is dry it will keep for three

PHOTOGRAPHIC MANIPULATIONS.

145

weeks or a month, and may be exposed in a camera with a three-inch
lens of eighteen-inch focus, with the inch diaphragm, on a bright day
from five to fifteen minutes ; in bad weather the exposure must be longer.
The picture may be carried home and rendered visible or developed
by immersion in a bath containing a saturated solution of gallic acid,
and as the developing continues, a few drops of the sensitizing solution
of nitrate of silver and glacial acetic acid may be added. Finally, the

Eicture is fixed by immersion for a quarter of an hour in a solution of
yposulphite of soda (four ounces of the crystal to one pint of water, or
one part of the saturated solution to eight of water), and being well
washed, is then dried, hung before the fire to melt the wax, and is now
ready to print from.

Fifth Experiment. Albumen on Glass Process.

Albumen is the scientific name for the white of egg, of which four
ounces by measure are mixed with one ounce and a half of distilled
water, and after being whisked to a
froth, are removed by a spoon into
another basin or a beaker glass, and
allowed to stand for several hours
and then filtered. Mr. Crookes has
recommended a very ingenious, simple,
and useful ^ filter. (Fig. 139.) He
says : " This simple and inexpensive
piece of apparatus, which any instru-
ment maker or glass-blower can supply
at a few hours' notice, will be found in-
valuable in almost every photographic
process on glass. The sponge has this
great advantage over all other kinds of
filters, that thick gelatinous liquids
phoney, albumen,gelatme,meta-gela-

tine, or the various preservative syrups squeezed into the head of the tube,
flow through it with the utmost readi- ny liquid poured in at B will flow

i ., , & , ., ,. i , . through the sponge until it has at-

ness ; whilst at the same time dust, air tained the same level in A.
bubbles, or froth, and dried particles

floating iii the liquid, are effectually kept back, and if fitted with stop-
pers, collodion might be filtered in it ; or if the ends were fitted together
with a bit of flexible pipe, the stoppers might be dispensed with altogether.
Having poured the albumen on a perfectly clean glass plate, taking
care to have sufficient to run freely over the surface of the glass,
the excess is then gently drained off and the plate turned so as to
have the coated side downwards ; it is then fixed in a sline^ made by
taking a stout bit of string about three feet long, which is doubled
and knotted at the fold, leaving the two ends free ; two small triangles
or stirrups of silver wire looped at one corner are now tied on to the
ends of the string, and these form a support for the opposite edges of
the glass plate to rest on ; the two strings are knotted together at a

BOY'S PLAYBOOK OF SCIENCE.

Fig. 140. A. Loop for finger. B. The knot
which prevents the stirrups of silver wire, c c,
slipping off the corners of the glass plate.
D D. The opposite corners of the glass plate
on which the stirrups are placed.

Fig. 141. A A. Tin box, with partitions to
hold glass plates. B B. The outer jacket, be-
tween which and the boz, A, the lid or cover,
c, slides.

convenient distance from the
stirrups to prevent the glass slip-
ping out, and the plate is now
rotated rapidly over a heated me-
tallic surface, such as an iron
box containing some burning
charcoal or the warming pan,
care being taken to avoid dust as
much as possible, and to use only
the whites of new-laid eggs.
(Tig. 140.) The glass plate, co-
vered with dry albumen, is now
iodized to a straw colour by ex-
posure over a box containing
iodine, as in the Daguerreotype
process, and is sensitized by im-
mersion for three or four minutes
in a bath containing a solution
of nitrate of silver (twenty -five
grains to an ounce of water) ;
the plate is afterwards washed in
distilled water and left to dry
spontaneously, of course in a
darkened room. The plates may
then be placed ready for use in a
very ingenious tin box devised by
Mr. Crookes, which keeps them
perfectly light-tight even in the
sun, and at the same time is less
bulky than the ordinary wooden
ones. It is made of tin plate,
the cover sliding tight over the
top, and more than half way down
the sides; light is further ex-
cluded by means of an outer
jacket of tin, which is soldered
to the box a little below the
centre. The cover thus slides
between the case and the jacket,
and renders injury to the plates
by the entrance of light an im-
possibility. (Tig. 141.)

The sensitive albumenized
glass plate is exposed in the
camera from fifteen to thirty
minutes, and developed (much in
the same way as the paper pic-
tures) with one ounce oi a satu-

PHOTOGRAPHIC MANIPULATIONS. 14.7

rated solution of gallic acid containing ten or fifteen drops of the sen-
sitizing solntion. The plate is usually placed on a levelling stand, and
the solution poured on the glass plate ; the development is slow, and may
be quickened sometimes by the application of heat.

The picture is fixed by immersion for a short time in a bath con-
taining one part of a saturated solution of hyposulphite of soda in
eight of water. The pictures produced by this process are exquisitely
denned, provided always the camera is well focussed, and to assist .this
operation a magnifying glass may be employed. After removal from the
hyposulphite of soda the plate is well washed with water, and being
allowed to dry spontaneously, is now ready to print from.

Sixth Experiment. Tfie Collodion on Glass Process.

The glass plates for this, as well as the albumen on glass process,
should be cleaned by rubbing them over first with a mixture of Tripoli
powder and ammonia, which is washed off under a tap, and the glass
being drained is rubbed dry and polished with a clean calico duster kept
exclusively for this purpose.

The iodized collodion is now poured on, and the excess re-
turned to the bottle. Collodion can be made very easily, but if prepared
without due precautions, it cannot be used afterwards, and reminds one
of the old story of the enthusiastic son, who, when asking his father's
permission to espouse the beloved, enumerated amongst her other ac-
complishments, the fact that she could make a pudding, and was
answered by the bluff question, " But can you eat it afterwards ?"
So it is with collodion : a great deal of messing and loss of time
is saved by purchasing it of the various makers, amongst whom
may be specially noticed Mr. Richard Thomas, of 10, rail Mall,
who has devoted the whole of his attention to the preparation of this
important photographic chemical, and with a success which his numerous
patrons can well testify. The collodion is sold either mixed with the
iodizing solution, or the two can be obtained separately, with direc-
tions on the bottles as to the quantities to be mixed together.

The plate covered with the iodized collodion is quickly transferred to
a bath containing a solution prepared in the following manner :
Dissolve four ounces of nitrate of silver in eight ounces of water, and to
this add twenty grains of iodide of potassium in one ounce of water ;
shake them together, and then pour the whole into fifty-six ounces of
distilled water, and in half an hour add one ounce of alcohol and half an
ounce of ether ; agitate the whole and filter the next morning. The
collodion plate is kept in this solution for ?, certain period, only learnt
by experience, and should be occasionally lifted out to see if a uniform
transparency is obtained ; say that the immersion may be continued for
five minutes, it is now ready for the camera, and may be exposed from
about one to two minutes, or more if the light is deficient ; the time of
exposure is also a matter of practice, mere directions can be of no use
in this stage of the process.

The picture is developed on a levelled stand, with a solution of three

148

BOY'S PLAYBOOK OF SCIENCE.

Fig. 142. A. Glass or gutta-percha bath to
hold the sensitizing solution. B. Glass, with
piece cemented on the end to hold the prepared
glass plate, c, whilst dipped in the bath, A.
The plate c has a cross in one corner to show
prepared side.

grains of pyrogallic acid in three
ounces of water, to which sixty
drops of glacial acetic acid have
been added. When fully deve-
loped the plate is washed with
water and fixed with a solution
of hyposulphite of soda, consist-
ing of one part of the saturated
solution to eight of water, again
thoroughly but gently washed,
so as not to endanger the sepa-
ration of the film from the glass ;
it is allowed to dry spontaneously,
and being coated with amber var-
nish (a solution of amber in chlo-
roform) is now ready to print
from. (Fig. 123.) It is, perhaps,
hardly necessary to add, that the
sensitizing and developing pro-
ared cesses must be performed in a
dark room.

Fig. 143. First effect of peripatetic photography on the rural population.

CHEMISTRY. 149

BUOMINE.

Bromine Opoofio?, a bad odour). Symbol, Br. Combining propor-
tion, 80. Specific gravity, 2'966.

In a previous portion of this work, the connexion between chlorine,
iodine, and bromine has been pointed out ; and as we have to notice the
colour of the element bromine, the chromatic union of the triad may
be alluded to. These elements present very nearly all the colours of
the spectrum :

Bromine red to orange.

Chlorine yellow to green.

Iodine blue, indigo, violet.

These three elements also furnish examples of the three conditions of
matter; iodine being a solid, bromine a. fluid, chlorine a gas; the
relation of their combining proportions is also curious : as might be ex-
pected, the fluid bromine takes an intermediate position, and (according
to the axiom that half the sum of the extremes is equal to the mean)
by dividing the combining proportions of iodine and chlorine, and
adding them together, we nave, as nearly as possible, the combining
proportion of bromine :

Chlorine 35 ~ 2 = 17'75

Iodine 126 ~ 2 = 63

80-75

The combining proportion of bromine is 80, but 80'75 is so near,
that it may reasonably be conjectured future experiments will reduce the
number of the three elements, and may prove that they are only modifi-
cations of a single one. This is the only kind of alchemy which is
tolerated in the nineteenth century, and any philosopher who will reduce
the number of elements, and prove that some of them are only modi-
fications of others, will achieve a renown that must transcend the eclat
of all previous discoverers.

Bromine was discovered by Balard, in 1826, and, like chlorine and
iodine, is a constituent of sea water. The chief source of bromine is
a mineral spring at Kreutznach, in Germany. The process by which it
is obtained offers a good example of chemical affinity ; the water of the
mineral spring is evaporated, alt crvstallizable salts removed, and a current
of chlorine gas passed through the remaining solution, which changes
to a yellow colour, in consequence of the liberation of the bromine by
the combinations of chlorine with the bases previously united with the
former ; the liquid is then shaken with ether, which dissolves out the
bromine. In the next place, the etherial solution is agitated with
strong solution of potassa, and is thus obliged to part with the bromine^
which is converted into bromate of potassa ; this is ultimately changed
by fusion to bromide of potassium ; and by distillation with black oxide
of manganese and sulphuric acid, the bromine is finally obtained. Six

150 BOY'S PLAYBOOK OF SCIENCE.

processes are therefore necessary before the small quantity of bromine
contained in the mineral spring-water, is separated.

First Experiment.

Bromine is a very heavy fluid, which should be preserved by keeping
it in a bottle covered with water ; when required, a few drops may be
removed by means of a small tube, and dropped into a warm bottle,
which is quickly filled with the orange-red vapour. If some phosphorus
is placed in a deflagrating spoon, and exposed to the action of bromine
vapour, it takes fire spontaneously.

Second Experiment.

Powdered antimony sprinkled into the vapour of bromine immediately
takes fire.

Third Experiment.

A burning taper immersed in a bottle containing the vapour of bromine
is gradually extinguished.

Fourth Experiment.

Liquid bromine exposed to a freezing mixture of ice and salt, or
reduced to a temperature of about eight degrees below zero, solidifies
into a yellowish-brown, brittle, crystalline mass.

Fifth Experiment.

A solution of indigo shaken' with a small quantity of the vapour of
bromine is quicklv bleached. Many substances, when brought in contact
with liquid bromine, combine with explosive violence, and therefore
experiments with liquid bromine are not recommended, as all the most
instructive and conclusive results can be obtained by the use of the
vapour of bromine, which is easily procured by allowing a few drops to
fall' into a warm, dry bottle.

Bromine, as already mentioned, is used in the art of photography.

FLTJOEINE.

Symbol, F. Combining proportion, 19.

This singular element seems almost to embody the ancient idea of
the alchemists, being a sort of alkahest, or universal solvent ; or in
plainer language, its affinities for other bodies are so powerful, that it
attacks every substance (not even excepting gold), at the moment of
its liberation, and combines therewith, so that its isolation has not
yet been effected. Chemists who assert that they have been able to
obtain fluorine in the elementary condition, pronounce it to be a gas
which possesses the colour of chlorine ; but the experiments, as hitherto
conducted, render that statement extremely doubtful.

ETCHING ON GLASS. 151

The only interesting fact connected with fluorine, is the remarkable
property of attacking glass and other silicious bodies, belonging to its
combination with hydrogen gas, called hydrofluoric acid. This acid is
easily obtained and used by placing some powdered fluorspar in a leaden
tray six inches square and two inches deep. If sulphuric acid is now mixed
with the powdered spar, so as to form a thin paste, and heat applied,
the vapour of the hydrofluoric acid quickly rises, and can be employed
to etch a glass plate upon which a drawing may have been previously
traced by scratching away the wax, with which it is first coated. By
heating the glass plate before a fire, a sufficient quantity of wax is soon
melted on to it by merely rubbing the wax against the glass j>late ; any
excess should be avoided, if a well-executed drawing is required to be
etched on its surface. (Fig.' 144.)

Fig. 144. A A A. The glass plate, with the waxed side downwards, placed on the
leaden tray containing the fluorspar and sulphuric acid. u. Spirit lamp.

The wax plate must not remain too long over the leaden tray, as the
heat is apt to melt the wax, when the acid not only attacks those parts
from which the wax has been removed by the etching needle, but also
the surface of the glass generally, and thus the clearness of the design
is spoilt. After exposure and it is as well to prepare two or three
glass plates for the experiment the wax is quickly removed by rubbing
and washing with oil of turpentine, and the design (beautifully etched
into the glass) is then apparent.

CHAPTER XII.

CARBON, BORON, SILICON, SELENIUM, SULPHUR, PHOSPHORUS.

THIS group of non-metallic elements has been frequently styled
" Metalloids," meaning substances allied to, but not possessing, all the
properties belonging to a metallic substance; and therefore perhaps
the expression, non-metallic solids, is the best that can be adopted. They
may be subdivided into two classes of three each, which have properties
more or less allied to each other viz.,

Carbon, Boron, Silicon; and

Selenium, Sulphur, Phosphorus.

152 BOY'S PLAYBOOK OF SCIENCE.

CARBON.

Symbol, C ; Combining Proportion, 6.

This element has almost the property of ubiquity, and is to be found
not only in all animal and vegetable substances, in common air, sea, and
fresh water, but also in various stones and minerals, and especially in
chalk and limestone.

There is, perhaps, no element which oifers a greater variety of amusing
experiments and elementary facts than carbon, whether it be considered
either in its simple or combined state.

A piece of carbon, in the shape of the Koh-i-Noor, was one of the
chief attractions at the first Exhibition in Hyde Park. The diamond is
the hardest and most beautiful form of charcoal ; how it was made in
the great laboratory of nature, or how its particles came together, seems
to be a mystery which up to the present time has not yet been solved,
at all events no artificial process has yet produced the diamond.

Sir D. Brewster, speaking of the Koh-i-Noor, remarks that on placing
it under a microscope, he observed several minute cavities surrounded
with sectors of polarized light, which could only have been produced
by the expansive action of a compressed gas or fluid, that had existed in
the cavities when the diamond was in the soft state.

Now it is known that bamboo, which is of a highly silicious nature,
has the property of depositing in its joints a peculiar form of silica,
called tabasheer. Silicon is one of the triad with carbon i.e., it is allied
to carbon on account of certain analogies ; may it not then be supposed
that, in times gone by, ages past, when the atmosphere was known to
be highly charged with carbonic acid gas, there might possibly have
existed some peculiar tree which had not only the power of decomposing
carbonic acid (possessed by all plants at the present period), but was
enabled, like the bamboo, to deposit, not silica, which is the oxide of,
silicium, but carbon, the purest form of charcoal viz., the diamond ?
Speculation in these matters is ever more rife than stern proof, and it
may be stated, that all attempts to manufacture this precious gem
(like those of the alchemists with gold and silver) have most signally
failed.

First Experiment.

Box and various woods, dried bones, and different organic matters,
placed in a nearly close iron or other vessel, and heated red hot, so that all
volatile matter may escape, leave behind a solid black substance called
charcoal. If that kind obtained from bones, and termed bone black or
ivory black, is roughly powdered, and placed in a flask with some solu-
tion of indigo or some vinegar, or syrup obtained by dissolving common
moist sugar in water, and boiled for a short period, the colour is re-
moved, and on filtering the liquid it is found to be as clear and colour-
less as water, provided sufficient ivory black has been employed.

COMBUSTION OP THE DIAMOND.

153

Second Experiment.

Charcoal is a disinfectant, and is used for respirators ; it has even been
recommended medically, and charcoal lozenges can be bought at various
chemists' shops. If a few drops of a strong solution of hydrosulphuret
of ammonia (which has the agreeable odour belonging to putrid eggs)
is mixed with half a pint of water, it will of course smell strongly, and
likewise precipitate Goulard water, or a solution of acetate ol lead
black ; but on shaking the water with a few ounces of charcoal, it no
longer smells of sulphuretted hydrogen, and if filtered and poured into
a solution of lead does not turn it black. This chemical action of
charcoal, independent of its seeming mechanical attraction for colouriog
matter, would appear to show that the pores of charcoal contain oxygen,
which in that peculiar condensed state destroys colouring matter, and
oxidizes other bodies.

Third Experiment.

A very satisfactory experiment, proving that the diamond and plum-
bago or black lead are identical with charcoal, although differing in
outward form and purity, can be made at a little cost,
by purchasing a fragment of refuse diamond, called
"boart," of Mr. Tennant of the Strand. A small
piece costs about five shillings. The fragment should
be carefully supported by winding some thin platinum
wire round it, as, if the wire is too thick, it cools
down the heat of the bit of diamond and prevents it
kindling in the oxygen gas. A difficulty may arise in
preparing the fragment, in consequence of the wire
continually slipping off. The " boart" should there-
fore be grasped by the thumb and first finger, and the
wire wound round ; then it must be carefully turned
and again wound across with the platinum wire, as
in the sketch below. (Fig. 145.)

A piece of black lead (so called) may now be taken
from a lead pencil and also supported by platinum
wire ; likewise a bit of common bark charcoal or hard
coke. Three bottles of oxygen should now be pre-
pared from chlorate of potash and oxide of manga-
nese, an extra bottle being provided for the diamond or^B^amondT
in case there should be any failure in its ignition.
The bark charcoal can be first ignited by holding a corner in the spirit
lamp for a few seconds ; when plunged into oxygen it immediately
kindles and burns with rapidity, and if the cork is well fitted, the
product of combustion viz., carbonic acid gas is retained for future
examination. The small piece of black lead is next heated red hot in
the flame of the spirit lamp, and being attached by its platinum sup-
port to a stiff copper wire thrust through a cork, which fits the bottle
of oxygen, is placed whilst red hot in the gas, and continues to glow
until consumed. The fragment of diamond is by no means, however so

Pig. 146. i. The

154

BOY S PLAYBOOK OF SCIENCE.

easily ignited, the flame of the spirit lamp must be urged upon it with
the blowpipe ; when quite red hot, an assistant may remove the stopper
from the bottle of oxygen, and the person heating the diamond should
plunge it instantly into the gas ; if this is dexterously managed, the
fragment of boart glows like a little star, and the combustion frequently
continues till the piece diminishes so much that it falls out of its platinum
support.

Sometimes the diamond cools down without igniting, the same pro-
cess must therefore be repeated, and a few extra bottles of oxygen
will prevent disappointment, as every failure destroys the purity of the

'as by admixture with atmospheric air when the stopper is removed.

Fig. 146.)

Fig. 146.

Bottle containing bark charcoal. B. Ditto the plumbago or
black lead. c. Ditto the diamond.

The combustion having ceased in the three bottles, the corks are
removed, and the glass stoppers again fitted for the purpose of testing
the products, which offer no apparent indication of any change, as oxygen
and carbonic acid gas are both invisible. In each bottle a new com-
bination has been produced ; the charcoal, the black lead, the diamond
have united with the oxygen, in the proportion of six parts of carbon to
sixteen parts of oxygen, to form twenty-two parts of carbonic acid gas,
which may be easily detected by pouring into each bottle a small quan-
tity of a solution of slacked lime in water, called lime water. This
test is easily made by shaking up common slacked lime with rain or
distilled water for about an hour, and then passing it through a calico
or paper filter. The test, though perfectly clear when poured in, be-
comes immediately clouded with a white precipitate, usually termed a
milkiness, no doubt in allusion to the London milk, which is supposed to
contain a notable proportion of chalk and water, for in this case the
precipitate is chalk, the carbonic acid from the diamond and the charcoal
having united with the lime held in solution by the water and formed
carbonate of lime, or chalk, a substance similar in composition to
marble, limestone, Iceland or double refracting spar, these three being
la early similar in composition, and differing only, like carbon and the
diamond, in external appearance.

PREPARATION OF CARBONIC ACID GA.S. 155

The milkiness, however, must not be held as conclusive of the pre-
sence of carbonic acid gas until a little vinegar or other acid, such as
hydrochloric or nitric, has been finally added; if it now disappears
with effervescence (like the admixture of tartaric acid, water, and car-
bonate of soda), the little bubbles of carbonic acid gas again escaping
slowly upwards, leaving the liquid in the three bottles quite clear, then
the experimentalist may sum up his labours with these effects, which
prove in the most decisive manner that common charcoal, black lead,
and the diamond, are formed of one and the same element viz.,
carbon.

Fourth Experiment.

Having effected the synthesis (or combining together) of the diamond
and oxygen, it is no longer possible to recover it in its brilliant and
beautiful form. If the product of combustion is retained in a flask
made of thin, hard glass, and two or three pellets of the metal potassium
are placed in directly after the diamond has ceased to burn, and the
flame of a spirit lamp applied till the potassium ignites, then the metal,
by its great affinity for oxygen, takes away and separates it again from
that which was formerly the diamond ; but instead of the jewel being
deposited, there is nothing but black, shapeless, and minute particles of
carbon obtained, if the potash produced is dissolved in water, and the
charcoal separated by a filter.

Fifth Experiment.

Chalk is made by uniting carbonic acid gas with lime ; it may there-
fore be employed as a source of the gas, by placing a few lumps of
chalk, or marble, or limestone, in a bottle such as was used in the gene-
ration of hydrogen gas ; on the addition of some water and hydrochloric
acid, effervescence takes place from the escape of carbonic acid gas, and
the cork and pewter pipe being adapted, it may be conveyed by its own
gravity into glasses, jugs, or any other vessels, and a pneumatic trough
will not be required. Carbonic acid gas has a specific gravity of 1'529,
and is therefore rather more than half as heavy again as atmospheric air.

Sixth Experiment.

In order to satisfy the mind of the operator that the gas obtained
from chalk is similar to the product of combustion from the diamond, some
lime-water may be placed in a glass, and the gas from the bottle allowed
to bubble through it ; instantly the same milkiness is apparent, which
again vanishes on the addition of acid. And this experiment is rendered
still more striking if a lighted taper be placed in the glass just after the
addition of the acid, when it will be immediately extinguished.

Seventh Experiment.

If a lady's muff-box, supported by threads or chains, is hung on one end
of a scale-beam, and counterbalanced by a scale pan and a few shot, it is

156

BOY'S PLAYBOOK OF SCIENCE.

immediately depressed on pouring into the muff-box a quantity of car-
bonic acid gas, which may have been previously collected in a large tin
vessel. After showing the weight of the gas, the box is detached
from the scale-beam, and the contents poured upon a series of lighted
candles, which are all extinguished in succession. (Fig. 147.)

Fig. 147. A. Carbonic acid gas poured out of the tin box into B, the muff-box.
B B. Detached muff-box, and candles extinguished by the carbonic acid gas poured from it.

Eighth Experiment.

The property of carbonic acid gas of extinguishing flame, as com-
pared with the contrary property of oxygen, is nicely shown by first
passing into a large and tall gas jar one half of its volume of oxygen
gas; a large cork perforated with holes may be introduced, so as
to float upon the surface of the water in the gas jar, and is usefully
employed to break the violence with which the carbonic acid enters the
gas jar, as it is passed in to fill up the remaining half volume of the gas
lar, which now contains oxygen at the top, and carbonic acid gas at the
bottom. On testing the, contents of the jar with a lighted taper, it
burns fiercely in the oxygen, but is immediately extinguished in the

EXPERIMENTS WITH CAEBONIC ACID GAS. 157

carbonic acid gas, being alternately lighted and put out as it is raised or
depressed in the gas jar.

Ninth Experiment.

A little treacle, water, and a minute portion of size, may be placed
with some yea,st in a quart bottle, to which a cork and pewter or glass
pipe is attached; directly the fermentation begins, quantities of car-
oonic acid gas may be collected, and tested either with lime-water or the
lighted taper.

Tenth Experiment.

Some clear lime-water placed in a convenient glass is quickly rendered
milky on passing through it the air from the lungs by means of a glass
tube; thus proving that respiration and (as shown by the ninth ex-
periment) fermentation, as well as the combustion of charcoal, produce
carbonic acid gas.

Eleventh Experiment.

Qarbonic acid gas is not only generated by the above processes, but
is liberated naturally in enormous quantities from volcanoes, and from
certain soils : hence the peculiar nature of the air in the Grotto del
Cane. Dogs thrust into this cave drop down immediately, and are
immediately revived by the tender mercies of the guides, who throw
them into the adjoining lake. This natural phenomenon is well imitated
by taking a box, open at the top, and nailing on to it a frame of card-

Fig. 148. A A. The box model of the Grotto del Cane. B B. Cardboard fixed in front
of box, and painted to imitate rocks, c. Carbonic acid gas bottle, with bent tube passing
through hole in the side of the box. A taper introduced at D burns in the upper, and ia
extinguished in the lower, part of the model.

158 BOY'S PLAYBOOK OF SCIENCE.

board, which may be painted to represent rocks, taking care that a portion
(about three inches deep) at the lower part is well pasted to the box at
the edges, so that the gas may be retained ; a hole is perforated at the
top side to admit a lighted taper, and another at the side for the pipe
from the carbonic acid bottle ; when the bottom is filled with gas, a
taper is applied, which is found to burn in the upper part, but is imme-
diately extinguished when it reaches the lower division, where the three
inches of pasteboard prevent it falling out : thus showing in a simple
manner why a guide may enter the cave with impunity, whilst the dog-
is rendered insensible because immersed in the gas. (Fig. 148.)

Twelfth Experiment.

Many fatal accidents have occurred in consequence of the air in deep
pits, graves, &c., becoming unfit for respiration by the accumulation of
carbonic acid gas, which may arise either from cavities in the soil, where
animal matter has undergone decomposition, or it may happen from Jhe
depth and narrowness of the hole or well preventing a proper draught
or current of air, so that it becomes foul by the breathing of the man
who is digging the pit. Air which contains one or two per cent, of
carbonic acid will support the respiration of man, or maintain the flame
of a candle ; but it produces the most serious results if inhaled for
any length of time ; a lighted candle let down into a well (suspected
to contain foul air) before the descent of the person who is to work
in it, may burn, but does not indicate the presence of the small
percentage of the poison, carbonic acid. Frequently no trouble is taken
to test the air with a lighted candle ; a man is lowered by his com-
panions, who see him suddenly become insensible, another is then lowered
quickly to rescue him, and he shares the same fate ; and indeed cases
have occurred where even a third and a fourth have blindly and igno-
rantly rushed to their death in the humane attempt to rescue their fellow
creatures. What is to be done in these cases? Are the living to
remain idle whilst the unfortunate man is suffocating rapidly at the
bottom of the pit ? No ; provided they do not venture themselves into
the pit, they may try every known expedient to alter the condition of
the foul air, so as to enable them to descend to the rescue. One should
be despatched to any neighbouring house or cottage for a pan of burning
coals; if any slacked lime is to be had, it may be rapidlv mixed with
water, and poured down the side of the pit ; a bundle of shavings set
on fire and let down, keeping it to one side, so as to establish a current ;
or even the empty buckets constantly let down empty and pulled up full
of the noxious air, may appear a somewhat absurd step to take, but
under the circumstances any plan that will change the air sufficiently to
enable another person to descend must be adopted ; in proof of which
the following experiments may be adduced :

Fill a deep glass jar with carbonic acid, and ascertain its presence
with a lighted taper ; if a beaker glass to which a string is attached is
jet down into the vessel and drawn up, and then inverted over a lighted

EXPERIMENTS WITH CARBONIC ACID GAS.

taper, the utility of
this simple plan is at
once rendered appa-
rent ; the beaker glass
represents the empty
bucket, and can be let
down and pulled up
full of carbonic acid
until a sensible change
in the condition of the
atmosphere is pro-
duced. The best plan,
however, is to set the
air in motion by heat
obtained from burning
matter, or even a kettle
of boiling water, low-
ered by a cord, and
this fact is well shown
by putting a small flask
full of boiling water,
and corked, at the bot-
tom of the deep glass
iar containing the car

Fig. 149. A. Deep jar containing carbonic acid gas, which
is being removed by the little glass bucket. B. Jar con-
taining corked flask of boiling water on a pad; the heated
gas rises and the cold air descends to take its place.

bonic acid gas, which rises like other gases when sufficiently heated, and
passing away, mixes with the surrounding air. (Fig. 149.)

Thirteenth Experiment.

Carbonic acid gas dissolved in water under considerable pressure,,
forms that most agreeable drink called soda-water ; the gas is not only
useful in this respect, but has been applied most successfully by Mr.
Gurney to extinguish a fire on a gigantic scale, which had been burning
for years in the waste of a coal mine in Scotland. The same gas, gene-
rated suddenly by the combustion of a mixture of nitre, coke dust, and
clay, or plaster of Paris, in vessels of a peculiar construction, has
formed the subject of a patent by Phillips, since merged into the Fire
Annihilator Company. The instrument is peculiarly adapted for ship-
ping, and might, if properly used, be the means of saving many ships and
valuable lives. (Fig. 150.)

Its practical value is established by the test of actual use : in the
streets, by the Leeds Fire Brigade, and by firemen of the Fire Anni-
hilator Company, temporarily stationed at Liverpool and Manchester.

The Fire Anninilator has been formally recognised by the Government
Emigration Commissioners, who introduced into the Passengers' Act,
1852, in 24, the alternative, " Or other apparatus for extinguishing fire"
with distinct reference to this invention, and subsequently by formal
order authorized their officers to pass ships carrying Fire Annihilators.

160

BOY S PLAYBOOK OP SCIENCE.
A

Fig. 150. A. A carriage with six fire annihilators, No. 5 size, fitted with moveable pipes.
The body of the carriage forms a tank for forty gallons of water ; the tank is filled at a
bunghole in the platform ; a patent tap is fitted to the rear of the carriage; a spigot is
placed near the end upright of the rail ; a hand-pump is placed in the box at rear ol
carriage ; a leather bucket with foot-holds and three canvas buckets are hung on the
carriage ; a hammer for removing and driving on the cover of the fire annihilator, and a
nut wrench for the No. 10 truck, are placed in the box. B. A fire annihilator, No. 10 size,
with moveable pipe, on a spring truck, is attached to the carriage.

The battery is fitted with shafts for one horse. A pole is also provided to fix across the
shafts, so that the battery may be drawn by hand.

Monsieur Adolphe Girard has proposed that all houses should be
provided with an apparatus for the generation of carbonic acid gas,

Pig. 151. A. Tank containing acid, communicating by a pipe with B, half filled with
chalk and water, c c c c. Pipes conveying carbonic acid from the generator B, to the
ceiling, where it is discharged from numerous holes on the fire beneath.

CHEMISTRY. 161

placed outside the building, which is to be conveyed along the ceiling
by means of pipes perforated with numerous holes, and to be put in
operation directly a fire breaks out. This plan, however ingenious,
could hardly supply the carbonic acid gas with sufficient rapidity, and
it is to be feared would utterly fail in practice. (Fig. 151.)

BORON.
Symbol, B ; combining proportion, 10'9.

Discovered by Homberg, in 1702, in borax, which is a biborate of
soda (NaO,2B0 3 ), and is used very extensively in the manufacture of
glass ; also for glazing stoneware and soldering metals ; it is also a
valuable flux in various crucible operations, whilst in testing minerals
with the blowpipe it is invaluable. Borax is made either from tincal, a
substance that occurs naturally in some parts of India, China, and
Persia, or by the addition of carbonate of soda to boracic acid, a sub-
stance obtained from the volcanic districts of Tuscany, whence it is
imported to this country, and used in the manufacture of borax.

The element boron may be obtained by placing some pure boracic
acid and some small bits of potassium in a tube together, and applying
the flame of a spirit-lamp, a glow of heat takes place, and when the tube
is cold the potash may be washed away, and the boron remains as a
dark brownish powder somewhat resembling carbon. M. -St. Claire
Deville and Wohler have lately made some important discoveries with
respect to this element, and disproved the statement that it is uncrystal-
lizable. Their researches prove it to be producible under three forms
and of various colours, such as honey -yellow and garnet-red, the crystals
in some cases being like diamonds of the purest water /.<?., limpid
and transparent. A new combination of aluminium and boron is
stated to possess the most remarkable properties. It is harder than
the diamond, and in the state of powder will cut and drill rubies, and
even the diamond itself, with more facility than diamond powder.
Deville and Wohler incline to the belief that the diamond is dimorphous,
and capable (in conditions yet to be described) of assuming the same forms
as boron. At a high temperature, boron, like titanium, absorbs nitrogen
only from the atmosphere, and rejects the oxygen. (Query, may not
some of those remarkably hard black diamonds prove to be boron ?)

SILICON.
Symbol, Si ; combining proportion, 21' 3.

The great Berzelius was the first to obtain this element in 1823.
Silicon in the pure state is a dark brown powder ; if ignited at a very
high temperature it assumes a chocolate colour, which is supposed to
be the allotropic condition, because it no longer burns when heated
moderately in oxygen or air, and is not attacked by hydrofluoric acid.

162 BOY'S PLAYBOOK OF SCIEXCE.

The most interesting combination of silicon is the teroxide called
silicic acid, silica (SiO 3 ). Silicon is next to oxygen so far as regards
its plentifulness, and is found in the state of silica in nearly every
mineral, but especially in rock crystal, quartz, flint, sand, jasper, agate,
and tripoli. It is largely used in the manufacture of glass, and a most
useful " soluble glass" is obtained by melting together in a crucible
fifteen parts of sand, ten parts of carbonate of potash, and one part of
charcoal.

Cold water merely washes away the excess of alkali, and after this is
done the powdered soluble glass may be boiled with water in the pro-
portion of one of the former with five of the latter, when it gradually
dissolves ; the solution may be evaporated to a thick pasty fluid, which
looks like jelly when cool, and on exposure to the air in thin films
changes to a transparent, colourless, brittle, but not hard glass. Wood,
cotton, and linen fabrics are rendered less combustible when coated
with this glass, which excludes the oxygen of the air, and it has lately
been employed to fill up the porous and capillary openings in stone
exposed to the atmosphere, and is stated to be very efficacious as a
preservative of the stone in some cases.

SULPHUR.
Symbol, S ; combining proportion, 16.

Sulphur, like charcoal, is of common occurrence in nature, and is
chiefly supplied from the volcanic districts of Tuscany and Sicily : there
is an abundance of this element in the United Kingdom, but then it is
locked up in combination with iron, copper, and lead, under the name
of iron pyrites, copper pyrites, galena ; and whilst Sicily and Tuscany
supply thousands of tons weight in the uncombined state, it is not, of
course, worth while to go through expensive operations at home for the
separation of sulphur from the ores. During the dispute between Sicily
and England, several patents were secured for new and economical pro-
cesses by which sulphur was obtained from various minerals ; and had
this country been excluded from a supply of native sulphur, no doubt
some of these patents would now be in active operation.

It is almost possible to estimate the commercial prosperity of a country
by the sulphur it consumes, not, happily, by their warlike operations, but
in the manufacture of oil of vitriol or sulphuric acid, which is the starting
point of a great number of useful arts and manufactures.

First Experiment.

Some very curious results may be obtained by heating sulphur at cer-
tain temperatures ; in the ordinary state it is a pale yellow solid, and
when subjected to a temperature of 226 Fahr. it melts to a brownish-
yellow, transparent, thin fluid ; according to all preconceived notions of
the properties of substances which liquify by an increase of heat, it
might oe imagined that every additional degree of heat would onlv

EXPERIMENTS WITH SULPHUR. 163

render the melted sulphur still more liquid, but strange to say, when it
reaches a temperature of about 320 Fahr. it changes red, and thick
like treacle ; and as the heat rises it becomes so tenacious, that the ladle
in which it is contained may be inverted, and the sulphur will hardly
flow out : at about 482 Fahr. it again becomes liquid, but not so fluid
as at the lower temperature. If allowed to cool from 482 Fahr., the
above results are simply inverted; the sulphur becomes thick, again
liquid, and finally crystallizes in long, thin, rhombic prisms, which are
seen most perfectly by first allowing a crust of sulphur to form on the
liquid portion, and then having made two holes in this crust, the sulphur
is poured out, when the remainder is found in the interior of the crucible
crystallized in the form already mentioned. Sulphur takes fire in the
air when exposed to a heat of about 560 Fahr., and burns with a pale
blue flame ; and, as already stated, it may be poured from a considerable
height on a still dark night, and produces a continuous column of blue
fire, just like an unbroken current of electricity. If the melted and
burning sulphur is received into a vessel containing boiling water, it is
no longer yellow, but assumes a curious allotropic state, in which it is a
reddish-brown, transparent, shapeless mass, that may be easily kneaded
and used for the purpose of taking casts of seals, which become yellow
in a few days, and are found then to be hard and crystallized.

Second Experiment.

Sulphur vapour, in one sense, may be regarded as a supporter of com-
bustion : if a clean Florence oil-flask is filled with copper turnings, and a
little roughly-powdered sulphur sprinkled in, and heat applied, the copper
glows with an intense heat, and burning in the vapour of the sulphur, pro-
duces a sulphuret of copper ; from this compound the sulphur maybe again
obtained by boiling the powdered sulphuret with weak nitric acid, which
oxidizes and dissolves the copper, leaving the greater part of the sul-
phur behind, which may be collected, melted, and burnt, and will be
found to display all the properties belonging to that element. This
experiment is a very good example of simple analysis; and if the
copper is weighed and likewise the combined sulphur, a good notion may
be formed of the principles of combining proportions.

Third Experiment.

A little sulphur burnt under a gas jar, or in any convenient box (a
hat-box, for instance), produces sulphurous acid (S0 2 ), which will bleach
a wetted red rose or dahlia, and many other flowers. This gas is em-
ployed most extensively in bleaching straw, and sundry woollen goods,
such as blankets and flannel, and likewise silk, and is perhaps one of the
best disinfectants that can be employed ; when fever has been raging in
the dwellings of the poor, as in cottages, &c., all metaDic substances
should be removed, the doors and windows closed, the bedding, &c., well
exposed, and then a quantity of sulphur should be burnt in an old fry-

1 BOY'S PLAYBOOK OF SCIENCE.

ing-pan placed on a brick, taking care to avoid the chance of setting the
place on fire ; after a few hours the doors and windows may be opened, and
the disinfectant will be found to have done its work cheaply and surely.

Fourth Experiment.

The presence of sulphur in various organic substances, such as hair,
the white of egg, and fibrine, is easily detected by heating them in a
solution of potash, and adding acetate of lead as long as the precipi-
tate formed is redissolved ; finally the solution must be heated to the
boiling point, when it instantly becomes black by the separation of sul-
phuret of lead.

Fifth Experiment.

Sulphuric acid, HO,S0 3 , or oil of vitriol, is made in such enormous
quantities that it is never worth while to attempt its preparation on a small
scale. In consequence of its great affinity for water, many energetic
changes are produced by its action. Oil of vitriol poured on some loaf
sugar placed in a breakfast-cup with the addition of a dessert-spoonful of
boiling water, rapidly boils and deposits an enormous quantity of black
charcoal. If a word be "written on a piece of white calico with dilute
sulphuric acid, and then rapidly and thoroughly washed out, no visible
change occurs ; but if the calico is exposed to heat, so that the excess
of water is driven off, the remaining and now concentrated oil of vitriol
attacks the calico, and the word is indelibly printed in black by the
decomposition of the fabric of cotton. A very remarkable process has
lately been introduced by Mr. Warren de la Rue, by which paper is con-
verted into a sort of tough parchment-like material, called ametastine, by
the action of oil of vitriol and water of a certain fixed strength ; and any
departure from the exact proportions destroys the toughness of the paper.
After the paper has been acted upon by the acid, it oecomes extremely
tenacious, and will support a considerable weight without breaking. Mr.
Smee has used this ametastine in the construction of an hygrometer, and
states that it may save many a traveller from catching a severe rheu-
matism in a damp bed.

Sixth Experiment.

When the vapour of sulphur is passed over red-hot charcoal and the
product carefully condensed, a peculiar liquid is obtained, called bisul-
phide of carbon (CS 2 ), which possesses a peculiar odour, is extremely
transparent and brilliant-looking, and enjoys a high refractive power.
This liquid is used as a solvent for phosphorus and other substances, and
is extremely volatile and combustible, and burns silently with a pale
blue flame. The combustion of its vapour, mixed with certain gases,
offers a good example of the fact that slow burning may be a peaceful
experiment, whilst very rapid combustion often resolves itself into an
explosion. Thus, if a few drops of bisulphide of carbon are dropped into
a narrow-mouthed dry quart bottle containing common air, and flame
applied, the combustion takes place with rapidity, a rushing or

EXPERIMENTS WITH SULPHUR.

165

roaring sound being audible, in consequence of the diffused vapour being
supplied with more oxygen, and burning more rapidly than it would do
if simply consumed from a stick or glass rod wetted with the fluid. A
still greater rapidity of combustion is ensured by dropping some bisul-
phide of carbon into a long stout cylindrical jar, fifteen inches long
and three inches in diameter, containing nitric oxide gas (N0 2 ) ; when
flame is applied the mixture burns with a bright flash and some noise,
and if burnt in a narrow mouthed bottle would most likely blow it to
atoms.

The greatest rapidity of combustion, and of course the loudest noise,
is obtained by shaking some bisulphide of carbon in a similar stout and
strong cylindrical jar filled with oxygen gas, but in this case the jar
must DC protected with a double cylinder of stout wire gauze; it does
not always break, but if it is blown to fragments each particle becomes
a lancet-shaped piece of glass, which is capable of producing the most
dangerous wounds. (Fig. 152.)

Fig. 152. A. Air and bisulphide of carbon. B. Nitric oxide and ditto, c. Oxygen and
ditto. D D. Stout cylinder of double wire gauze, open top and bottom.

SELENIUM.

Selenium (o-eAqin/, the Moon*) ; symbol, Se ; combining
proportion, 39 '5.

This new metallic element is allied to sulphur, and is a species 01
chemical curiosity, being found in minute quantities in various minerals ;
it may be melted and cast into any form. Medallions of the discoverer
(Berzelius) of selenium, in little cases, are imported from Germany,
for the cabinets of the curious.

* Called selenium on account of its strong analogy to the metal tellurium (tellus, the

earth).

166 BOY'S PLAYBOOK OF SCIENCE.

PHOSPHORUS.

Phosphorus ((f)S)s, light ; typeiv, to bear ; symbol, P ; combining
proportion, 32.)

Monsieur Salverte, in his work on the Occult Sciences of the
Ancients, quotes a remarkable story respecting the probable discovery
of the nature of phosphorus in 1761 : " A Prince San Severe, at
Naples, cultivated chemistry with some success ; he had, for example,
the secret of penetrating marble with colour, so that each slab sawed
from the block presented a repetition of the figure imprinted on its
external surface. In 1761, he exposed some human skulls to the action
of different reagents, and then to the heat of a glass furnace, but paying
so little attention to his manner of proceeding, that he acknowledged
he did not expect to arrive a second time at the same result. From the
product he obtained a vapour, or rather a gas was evolved, which
kindling at the approach of a light, burned for several months
without the matter appearing to die or diminish in weight. San
Severo thought he had found the impossible secret of the inextin-
guishable lamp, but he would not divulge his process, for fear that
the vault in which were interred the princes of his family should
lose the unique privilege with which he expected to enrich it, of being
illuminated with a perpetual lamp" Had he acted like a philosopher of
the present day, San Severo would have attached his name to the im-
portant discovery of the existence of phosphorus in the dones, and made
public the process by which it might be obtained.

This element, formerly sold at four or five shillings the ounce, has now
fallen so much in price, from the greater demand and larger production,
that it may be bought for a few shillings the pound, and is imported in
tin cases in large quantities from Germany. It was discovered about
two hundred years ago by Brandt, a merchant of Hamburg, and may
be prepared on a small scale by distilling at a red heat phosphoric
acid previously fused with one-fourth, of its weight of powdered
charcoal.

First Experiment.

Phosphorus, when pure, is without taste or colour, but generally of a
very pale buff-colour, and semi-transparent ; it is extremely combus-
tible, and is usually preserved under the surface of water ; when per-
fectly dry, a thin slice will take fire at 60 Fah., and burns with
great brilliancy. Considering the heat produced during the com-
bustion of phosphorus, it might be thought that it would infallibly set
fire to any ordinary combustible, such as paper or wood, but this is not
the case when phosphorus is employed by itself, as may be proved by
the following experiment.

Cut five very small pieces of phosphorus, and place them like the
five of diamonds on a sneet of cartridge-paper laid upon the table, set
the bits of phosphorus on fire, when they will be rapidly burnt away

EXPERIMENTS WITH PHOSPHORUS. 167

leaving only five black spots, but not firing the paper, as would be the
case if some red-hot coals or charcoal were placed in the same position.
The cause is very simple. Phosphorus in burning produces phosphoric
acid, which is an anti-combustible, and coats the surface of the paper
round the spot where the combustion occurs, and acting as a kind of
glaze or glass, excludes the oxygen of the air, and prevents the fire
spreading.

If some powdered sulphur is sprinkled round the spot where the bit
of phosphorus is to be burnt, the case is very different ; the heat melts
and sets fire to the sulphur, which being uncoated with the phosphoric
acid, communicates to the paper ; and it is on this principle that lucifer-
matches can be used as instantaneous lights. The tip of the wood of
which they are composed is first dipped in sulphur, and then the phos-
phorus composition made of gum, chlorate of potash, vermilion, and
phosphorus, is placed over it ; and if the latter were used alone without
the sulphur, not one match in a hundred would take fire properly.

Common phosphorus is perfectly and rapidly dissolved by bisulphide
of carbon. The solution must be carefully preserved, as it is a liquid
combustible, which takes fire spontaneously after the bisulphide of
carbon evaporates ; so that wherever it is dropped, a flame, arising from
the spontaneous combustion of the finely-divided phosphorus, is sure to
be produced. This liquid was recommended many years ago to the
Government for the purpose of setting sails of ships or other combus-
tible matter on fire. The solution of phosphorus alone did not answer
the purpose, as already explained in the first experiment ; but when wax
was dissolved with the phosphorus, it then became a most dangerous
fluid, which it was recommended should be used in shells, and discharged
from a mortar or howitzer in the ordinary manner. Dr. Lypn Playfair
.was the first to make this proposed application of the solution, and it
has since, we believe, been recommended by Captain Norton in his liquid-
fire shells.

Third Experiment.

One of the most curious facts in connexion with phosphorus,
is its assumption of the allotropic state in what is termed amorphous
(shapeless) or red phosphorus. This substance, when handled for the
first time, might be mistaken for a lump of badly-made Venetian red.
There is no risk of its taking fire like the common phosphorus, and it
does not (according to Schrotter, of Berlin, who discovered this peculiar
condition) exhale those fumes which are so prejudicial to the lucifer-
match makers. When the vapour of common phosphorus is continually
inhaled, it is said to cause a peculiar and disgusting disease, which,
terminates in the destruction of the jaw-bone ; whilst the bones in other
parts of the body become brittle, and arm-bones thus affected are
fractured with the slightest blow.

The difference between common and red phosphorus is well shown

163 BOY'S PLAYBOOK OF SCIENCE.

first, by placing a few small pieces of both kinds in separate bottles or
vials containing bisulphide of carbon; the common phosphorus, as
already explained, quickly dissolves in the liquid, and if poured on a
sheet of paper, and hung up, is soon on fire ; whilst the red variety is
wholly unaffected, and if the bisulphide of carbon is poured off on to
paper, it merely evaporates, and no combustion occurs.

The similarity in composition, though not in outward form, is further
shown by filling two jars with oxygen gas. and having provided two
deflagrating spoons, some common phosphorus is placed in one, and red
phosphorus in the other; a wire, gently heated by dipping it into
some boiling water, is now applied to the former, which immediately
takes fire, and may be plunged into the jar of oxygen gas, when it burns
with the usual brilliancy. The red phosphorus, however, must be brought
to a much higher temperature (500 Fah.) before it will even shine in
the dark, and then with a still further increase of heat it takes fire, and on
being placed in the other jar of oxygen burns up much more slowly than
the yellow phosphorus, but at last exhibits that brilliant flash of light
which is so characteristic of the combustion of phosphorus in oxygen.

The amorphous or red phosphorus is employed in the manufacture of
safety chemical matches, and M. A. Meunons has secured a patent in
England for an improvement in lucifer matches, with a view to obviate
the risks of accidental ignition. To attain this end the matches are first
cut by a machine from cubes of wood, the cut being stopped at a
short distance from the end of each cube, so as to leave the lower ex-
tremities adherent. The upper or free extremity of each packet of
splints thus formed being coated with wax or sulphur, is dipped in one
of the following preparations : Chlorate of potash, two parts; pul-
verized charcoal, one part ; umber, one part ; or, chlorate of potash,
sulphur, and umber, in equal parts, thoroughly mixed with glue. The
opposite extremity or " cut" of each packet is then painted over with
amorphous phosphorus blended with size, so that on separating the
matches the phosphorus is only found en the top of each. The matches
thus prepared are ignited by breaking off a small piece of the phos-
phorised end and rubbing it on the opposite extremity covered with the
inflammable preparation.

Loud exploding and dangerous lucifers were formerly made by dipping
bundles of matches, previously coated with sulphur at the tips, into a
thick solution of gum, at a temperature of 104 Fahr., coloured with
smalt or red lead, in which was dissolved a certain proportion of chlorate
of potash, and also containing finely divided particles of phosphorus ob-
tained by the constant stirring and rubbing of the materials in a mortar.
When dry the matches exploded if rubbed against a gritty surface, and
there was always a risk of a fragment flying off and entering the eye.
To obviate this danger, silent or noiseless lucifer matches were invented,
and the composition used (according to Bottger) is as follows : Gum
arabic, 16 parts by weight ; phosphorus, 9 parts ; nitre, 14 parts ; pow-
dered black oxide of manganese, 16 parts. The above ingredients are
worked up in a mortar with water, at 104 Fahr., and the matches pre-
viously tipped with sulphur are dipped therein and afterwards dried.

EXPERIMENTS WITH PHOSPHORUS.

169

Fourth Experiment.

The combustion of
phosphorus under
water is easily de-
monstrated by plac-
ing some ordinary
stick phosphorus in
a metallic cup, and
then plunging it ra-
pidly under the sur-
face of boiling water.
If a jet of oxygen
gas is now directed
upon the liquid phos-
phorus, it burns
with great brilliancy.

Fig. 153. A A. Fin
a metallic cup with.

gas. D D. Sheet of wire gauze.

lass of boiling water containing
phosphorus, c. J et of oxygen

When the oxygen escapes too rapidly from the jet, it causes some small
particles to be thrown out of the water, so that it is advisable to defend
the face with a sheet of wire gauze held a few inches above the glass
whilst the experiment is being conducted. (Eig. 153.)

Fifth Experiment.

Phosphorus burns and emits beautiful
flashes of light in the presence of the
gas called peroxide of chlorine (C10 4 ),
which must be very carefully generated
under the surface of water by first placing
some cut phosphorus and chlorate of pot-
ash at the bottom of a long and stout
cylindrical glass nearly full of water ;
sulphuric acid is then conveyed to the
chlorate, of potash by means of a syphon,
the end of which must be drawn out to a
small opening, or else the oil of vitriol
will descend too rapidly, and the glass
will be cracked by the heat. Immediately
the peroxide of chlorine comes in contact
with the phosphorus it explodes, and
passes again to its original elements,
oxygen and chlorine. These bubbles en-
velope minute particles of phosphorus,
which rapidly ascend, like water-spiders,
to the surface, and burn as they pass up-
wards, producing a continual series of
sparks of fire, which have an extremely
pretty effect. (Fig. 154.) The syphon is of
course first filled with water, and as that is
displaced, the oil of vitriol takes its place.

Fig. 154. A A. Tall glass nearly
full of water ; at the bottom are the
chlorate of potash and phosphorus.
B. Wolfe's bottle and syphon, con-
veying the oil of vitriol to bottom
of A A.

170

BOY'S PLAYBOOK OF SCIENCE.

Sixth Experiment.

If a little phosphorus is placed in a small copper boiler, and tho
steam allowed to escape from a jet, it is observed to be luminous, in
consequence of a minute portion of phosphorus being carried up mecha-
nically with the steam. The same fact is shown very prettily by boiling
water in a flask containing some phosphorus.

Seventh Experiment.

Phosphorus explodes violently when
rubbed with a little chlorate of potash,
and in order to perform this experi-
ment safely, it should be made in a
strong iron mortar, the pestle of which
must oe surrounded with a large circle
of cardboard and wire gauze ; so that
when it is brought down upon the
phosphorus and chlorate of potash,
any particles that may fly out are de-
tained by the shield. "Without this
precaution the experiment is one of
the most dangerous that can be made.
155.)

Eighth Experiment.

Phosphuretted hy-
drogen owes its pro-
perty of spontaneous
combustion to the
presence of the va-
pour of a liquid,
phosphide of hydro-
gen (PH 2 ), which
may be prepared by
placing some phos-
phide of calcium into
a flask with water
heated to a tempera-
ture of 140 JFah.,
and conveying the

tube surrounded with
a mixture of ice and
salt. The liquid obtained is colourless, and must be preserved from
contact with air, as it takes fire spontaneously directly it is exposed
to the atmosphere. (Fig- 156.)

Fig. 155. A. The iron mortar con-
taining the phosphorusav.il chlorate of
potash. B. The pestle, with the shield,
c c, composed of a circle of wire gauze,
covered with one of cardboard.

rig. 156. A. The flask containing the phosphide of calcium
and water, and placed in a water-bath heated to 140 Fan.
B. Bent tube conveying the gas to c c, the U-shaped tube,
to which it is attached by india-rubber tubing, c c. The U-
shaped tube, surrounded with a freezing mixture. D D. Bent
tube, passing into a cup of water to prevent contact with air.

EXPERIMENTS WITH PHOSPHORUS. 171

Ninth Experiment.

Phosphide of calcium is quickly prepared by placing some small
pieces of lime in a crucible and making them red-hot ; if lumps of dry
phosphorus are thrown into the crucible, and the cover placed on
quickly, and immediately after the phosphorus, the latter unites with
the calcium, and forms a brown substance which produces gaseous
phosphide of hydrogen (PH 3 ) when placed in water, and the gas takes
fire spontaneously when it comes in contact with the air.

Tenth Experiment.

Phosphorus placed in a retort with a tolerably strong solution of
potash, and a small quantity of ether, affords a large quantity of phos-
phide of hydrogen (commonly called phosphuretted hydrogen) when
boiled. The neck of the retort must dip into a basin of water, and the
object of the ether is to prevent the combustion of the first bubbles of
gas inside the retort, which by their explosion would probably break the
glass. If the neck of the retort is kept under water in which potash is
dissolved, the gas may be generated for many days at pleasure, although
it is not a desirable experiment to renew too often, on account of the
disagreeable odour produced. (Eig. 157.)

Fig. 157. A retort containing the phosphorus, water, potash, and ether, u. Neck dipping
into a basin of water, c. The gas burning, and producing beautiful rings of smoke.

Eleventh Experiment.

When ajar of oxygen is held over the neck of the retort generating the
phosphuretted hydrogen, a bright flash of light and explosion are ob-
served ; and if the experiment is performed in a darkened room, it is just
like a sudden flash of lightning. A bottle of chlorine held over the neck

172 BOY'S PLAYBOOK OF SCIENCE.

of the retort, and dipping of course in the water of the basin, produces
a green flame every time the bubble of gas passes into it. That curious
appearance of light, sometimes seen in marshy districts, called will-o'-the-
wisp, is supposed to be due to the escape, from decomposing matter, of
bubbles of hydrogen, nitrogen, &c., through which the spontaneously
inflammable phosphide of hydrogen is diffused.

At a place called Dead Man's Island, near Sheerness, magnificent
effects of this kind are sometimes apparent when the rnud banks are
accidentally stirred at night by a boat-hook. A credible observer says,
he once saw there a flash of yellowish-green light, accompanied with
noise, about thirty feet in height. The apparent height might be due to
the duration of the impression of the flash on the eye, as the light from
the burning phosphuretted hydrogen ascended rapidly upwards. The
source of this gas appears to be due to the fact, that during the time some
Russian ships were watched by the Brest fleet, a number of the sailors
died of cholera, and were buried in the banks ; the decomposition of the
bone containing phosphorus would account for the appearance of light
already described.

With the discussion of some of the most interesting properties of the
thirteen non-metallic elements we take leave of the subject of chemistry,
reserving the consideration of the metals for another popular juvenile
work, of which they will form the subject.

In answer to the oft-repeated question, " Where can I get the things
for the experiments P" it may be stated that every kind of glass vessel
and the chemicals mentioned in this chapter, can be procured either of
Messrs. Simpson, Maule, and Co., Kennington, or of Griffin and Co.,
Bunhill-row, or Bolton and Co., High Holborn.

Fig. 153. Will-o'-the-wisp.

173

Fig. 159. Franklin and his kite.

CHAPTER XIII.

PBICTIONAL ELECTRICITY.

OP all the agents with which man is acquainted, not one can afford a
greater source of wonderment to the ignorant, of meditation to the
learned, than the effects of that marvellous force pervading all matter
called electricity. We look at matter endowed with life, and matter
wanting this divine gift, with some degree of interest, depending on our
various tastes and occupations ; we know at a glance a bird, a beast, or
a fish ; we observe with pleasure and admiration the wonderful changes
of nature, and know that a few seeds thrown into the broken clods and
well-tilled earth may become either the waving, golden corn-field or in
time may grow from the tender little shrub . to the stately forest-tree ;
we know all these things because they belong to the visible world, and
are continually passing before our eyes : but in looking at the visible,
we must not forget and ignore the invisible. It may with truth be

BOYS PLAYBOOK OP SCIENCE.

stated that the greatest powers of nature are all concealed, and if any
truth would leacl us from Nature to Nature's God, it is the fact that
no visible, solid, tangible agent can work with so much force and
power as invisible electricity. Many centuries passed away since the
commencement of the Christian era, before the human mind was pre-
pared to appreciate this great power of nature ; other forces had claimed
attention, and the difference in the presence or absence of two of the
imponderable agents, heat and light, as derived from the sun, in the
effects of the change of the seasons, and other common facts, had led
philosophers to speculate early upon their nature ; but electricity, from
its peculiar properties, long escaped observation, and it was not until
the beginning of the eighteenth century (about 1730) that any material
facts had been discovered in this science, when Mr. Stephen Grey, a
pensioner of the Charterhouse, discovered what he termed electrics
and non-electrics, and also the use of insulating materials, such as silk,
resin, glass, hair, &c. ; and it is obvious that, until the latter fact was
discovered, the science would remain in abeyance, because there would
be no mode of preserving the electrical excitement in the absence of
non-conductors of this force.

The year 1750 was remarkable for Volta's discoveries and Dr. Frank-
lin's identification of the electricity of the machine with the stupendous
effects of the thunderstorm. Sir Humphry Davy, in 1800, with his
commanding genius, threw fresh light upon the already numerous
electrical effects discovered. In 1821, Faraday commenced his studies
in this branch of philosophy ; which he has since so diligently followed
up, that he has been for some years, and is still the first electrician of
the age. From the commencement of the present century, discoveries
have succeeded each other in regular order and with the most amazing
results ; and now electricity is regularly employed as a money-getting
agent in the process of the electrotype and electro-silvering and gilding ;
also in the electric telegraph ; and in a few years we may possibly see
it commonly employed as a source of artificial light.

The nature of electricity, says Turner, like that of heat, is at present
involved in obscurity. Both these principles, if really material, are so
light, subtle, and diffuse, that it lias hitherto been found impossible to
recognise in them the ordinary characteristics of matter ; and therefore
electric phenomena may be referred, not to the agency of a specific sub-
stance, but to some property or state of common matter, just as sound
and light are produced by a vibrating medium. But the effects of
electricity are so similar to those of a mechanical agent, it appears so
distinctly to emanate from substances which contain it in excess, and
rends asunder all obstacles in its course so exactly like a body in rapid
motion, that the impression of its existence as a distinct material sub-
stance sui generis forces itself irresistibly on the mind. All nations,
accordingly, have spontaneously concurred in regarding electricity as a
material principle ; and scientific men give a preference to the same
view, because it offers an easy explanation of phenomena, and suggests
a natural language intelligible to all.

SOURCES OF ELECTRICITY.

175

There are five well-ascertained sources of electricity, and three which
are considered to be uncertain. The five sources are friction, chemical
action, heat, magnetism, peculiar animal organisms. The three uncertain
sources are contact, evaporation, and the solar rays.

First Experiment.

A stick of sealing-wax or a bit of glass tube, perfectly dry, rubbed
against a warm piece of flannel, has
elicited upon its surface a new power,
which will attract bits of paper, straw, or
other light materials; and after these sub-
stances are endowed with the same force,
a repellent action takes place, and they
fly off. One of the most convenient ar-
rangements for making experiments with
the attractive and repellent powers of
electricity is to fix with shell-lac varnish
round discs of gilt paper, of the size of
a half-crown, at each end of a long straw
that is supported about the centre with
a silk thread, which may hang from the
ceiling or any other convenient support.
(Kg. 160.)

The varnish is easily prepared by
placing four or eight ounces of shell-
lac in a bottle, and pouring enough
pyroxylic spirit (commonly termed wood
naphtha) upon the lac to cover it. After
a short time, and by agitation, solu-
tion takes place. In a variety of ways
friction is proved to be a source of jjj&- 16 2; A * T v lass iP iUa ? SU ,P*
electricity, and forms a distinct branch ^thread? ' ^ *

of the science, under the name of /fic-
tional electricity.

The nature of chemical action has been already explained, and is
alluded to here as a source of electricity of which the proof is very
simple. Apiece of copper and a similar-sized plate of zinc have attached
to them copper wires ; these plates are placed opposite to, but do not
touch each other, in a vessel containing water acidulated with a small
quantity of sulphuric acid. When the wires are brought in contact, a
current of electricity circulates through the arrangement, but has no
power to attract bits of paper, straw, &c. In order to ascertain whether
the current of electricity passes or not, a piece of covered copper wire
is bent several times round a magnetic needle, so that it has freedom of
motion inside the core or hollow formed by twisting the copper wire.
This arrangement, properly constructed, is called the galvanometer

176

BOY S PLAYBOOK OF SCIENCE.

needle, and is invaluable as a means of ascertaining the passage of
electricity derived from chemical action. (Fig. 161.)

Fig. 161. A. The galvanometer needle, u. Vessel containing weak acid and the zinc and
copper plates. The arrows show the path of the electric current.

When the wires leading from the metal plates are connected with the
extremities of the coil in the galvanometer, the needle is deflected or
pushed aside to the right hand or to the left, according to the direction
of the current.

Third Experiment.

The third source of electricity is heat, and the effect of this agent is
well shown by twisting together a piece of platinum and silver wire, so
as to form one length. If the silver end is attached to any screw of the
galvanometer, and the platinum end to the second screw, no movement
of the magnetic needle takes place until the heat of a spirit-lamp is
applied for a moment to the point of juncture between the silver and
platinum wires, when the magnetic needle is immediately deflected.

Fig. 162. A. The galvanometer needle, with wires attached, s, s. Silver wire joined
to P, P, the platinum wire. The heat of the spirit-lamp is applied at the point of
juncture, +.

Fourth Experiment.

The fourth source of electricity viz., magnetism requires a some-
what more complicated arrangement ; and a most delicate galvanometer
needle must be provided, to which is attached the extremities of a long
spiral coil of copper wire covered with cotton or silk. Every time a
bar magnet is introduced inside the coil, so that the conducting wire cuts
the magnetic curves, a deflection of the galvanometer needle takes place,

SOURCES OF ELECTRICITY. 177

and the same effect is produced on the withdrawal of the magnet, the
needle being deflected in the opposite direction.

The magnetic spark can be obtained by employing a magnet of suffi-
cient power ; and the arrangement for this purpose is very simple. A
cylinder of soft iron is provided, and round its centre are wound a few
feet of covered thin copper wire, one end of which is terminated with a
copper disc well amalgamated, and the other end, after being properly
cleaned and coated with mercury, is brought into contact with the disc.
Directly this cylinder is laid across the poles of the magnet, and as
quickly removed, the point and disc, from the elasticity of the former,
separate for the moment, the contact is broken between the point and
disc, and a brilliant but tiny spark is apparent.

Pig. 163. A B. Horse-shoe magnet, c. Cylinder of soft iron. D. Coil of copper
wire and contact breaker.

Fifth Experiment.

The fifth mode of procuring electricity would require the assistance
of an electrical eel, a fine specimen of which (forty inches in length) was
exhibited at the Adelaide Gallery some years ago. Various experiments
were made with this animal, and the author had the pleasure of wit-
nessing all the ordinary phenomena of frictional electricity, illustrated
by Dr. Faraday, with the assistance of the animal electricity derived
from this curious creature. Recent experiments have, however, proved
that the electric current is induced through the agency of the nervous

178 BOY'S PLAYBOOK OF SCIENCE.

system. This important fact has been communicated by M. Dubois-
llaymond, whose experiment is thus recorded: A cylinder of wood is
firinly fixed against the edge of a table ; two vessels filled with salt and
water are placed on the table, in sucli a position that a person grasping
the cylinder may, at the same time, insert the fore-finger of each hand
in the water. Each vessel contains a metallic plate, and communicates,
by two wires, with an extremely sensitive galvanometer. In the instru-
ment employed by M. Dubois-Raymond, the wire is about 3|- miles in
length. The apparatus being thus arranged, the experimenter grasps
the cylinder of wood firmly with both hands, at the same time dipping
the fore-finger of each hand in the saline water. The needle of the
galvanometer remains undisturbed ; the electric currents passing by the
nerves of each arm, and being of the same force, neutralize eacn other.
Now, if the experimenter grasp with energy the cylinder of wood with
the right hand, the left hand remaining relaxed and free, immediately the
needle will move from west to south, and describe an angle of 30, 40,
and even 50; on relaxing the grasp, the needle will return to its original
position. The experiment may be reversed by employing the left arm,
and leaving the right arm free : the needle will, in this case, be deflected
from west to north. The reversing of the action of the needle proves the
influence of the nervous force. The conditions, it may be added,
essential to the success of the experiment are : 1st, Great muscular and
nervous energy ; 2nd, The contraction of only one arm at a time ; 3rd,
Dryness and cleanliness of skin ; and 4th, Freedom from any kind of
wound on the immersed part.

Sixth Experiment.

In making electrical experiments of the simplest kind, it soon becomes
apparent that certain substances, such as glass, sealing-wax, &c., retain
the condition of electrical excitement ; whilst other bodies, and especially
the metals, seem wholly incapable of electrical excitation : hence the
classification of bodies into conductors and non-conductors of electricity.
This arrangement is not strictly correct, because no substance can be
regarded as absolutely a conductor, or vice versa. It is better to con-
sider these terms as meaning the two extremes of a long chain of inter-
mediate links, which pass by insensible gradations the one into the other.
In the manufacture of electrical apparatus, glass is of course largely
employed, and this substance, with brass and wood, constitute the usual
materials. One of the most instructive pieces of apparatus is the elec-
troscope, which can be made with a gas jar, a cork, a piece of glass
tube, brass wire and ball, or a flat disc of brass, with some Dutch metal,
or still better, gold leaf. The latter is first cut into strips by retaining
the leaf between a sheet of well-glazed paper and cutting through the
paper and the copper or gold leaf, otherwise it would be impossible to
cut the metal, on account of its excessive thinness, except with a guder's
knife and cushion. The cork is next fitted to the gas jar, and perforated
with a hole to admit the glass tube, which must be thoroughly dry, and

THE ELECTROSCOPE.

179

is best coated both inside and out with the shell-lac varnish described
at page 175. Some dry silk is wound round the
brass wire, so that it remains fixed and upright in
the glass tube, the end outside the jar having a
ball, or still better, a flat disc of brass attached,
and the other extremity being split so as to act
like a pair of forceps, to retain a piece of card to
which the gold leaves are attached. By removing
the cork, tube, and brass wire bodily from the neck
of the gas jar, and then in a perfectly still atmo-
sphere carefully bringing the card, slightly wetted
with gum. at the extremity, on two of the cut
gold leaves, they may be stuck on, and the whole
is again arranged inside the dry gas jar, and forms
the important instrument called the electroscope.
(Fig. 164.) With the help of this arrangement,
a number of highly instructive experiments are
performed.

First, the difference between conductors and
non-conductors is admirably shown by rubbing a
bit of sealing-wax against a piece of woollen cloth Fig. 164. A. The brass
or flannel : on bringing the wax to the brass disc of wire, with flat disc out-
the electroscope the gold leaves no longer hang ^d'TeafTSd^thf
quietly side by side, but stand out and repel each jar. c c. The glass
other, in obedience to the law " that bodies simi- tube -
larly electrified repel each other." If the brass cap is touched whilst the
leaves are in this electrical state, they fall again to their original posi-
tion, showing that sealing-wax, after being excited, retains its electrical
condition, as also the gold leaves, because they are supported on glass,
or what is termed insulated i.e., cut off from conducting communica-
tion with surrounding objects. When, however, the sealing-wax is
passed through a damp hand, or the brass disc of the electroscope
touched, the electricity is conveyed away to the earth, because the human
body is a conductor of electricity.

Eighth Experiment.

When a brass wire is rubbed and brought to the electroscope, the
leaves do not move, in consequence of the electricity passing away to the
earth through the body as fast as it is generated : it is just like pouring
water into a leaky cistern ; but if the brass wire is tied to a long stick
of sealing-wax, and this latter held in the hand whilst the wire is rubbed
with a bit of flannel, then the gold leaves of the electroscope are affected,
on account of the insulation of the metal, as everj substance which can
be rubbed (even fluids, as water) produces electricity.

180

BOY'S PLAYBOOK OF SCIENCE.

Ninth Experiment.

An insulating stool is merely a piece of strong square board, supported
on glass legs, which should be well varnished. If the assistant stands
on this stool and touches the disc of the electroscope, no movement of
the leaves takes place until his coat is briskly struck with a piece of dry
silk or skin, when the usual repulsion occurs.

Fig. 165. Assistant standing on the insulating stool and touching the disc of the
electroscope whilst being struck with a dry handkerchief.

Tenth Experiment.

If a little powdered chalk is placed inside a pair of bellows, and then
forcibly ejected on to the disc of the electroscope, the friction of the
particles of chalk against the inside of the nozzle of the bellows and
against the disc of the instrument soon liberates sufficient electricity to
cause the gold leaves to stand out and repel each other.

Eleventh Experiment.

Whilst the leaves of the electroscope aie repelled from each other by
the application of a bit of rubbed sealing-wax, they may be again caused
to approach each other on bringing a dry glass tube previously rubbed
with a silk-handkerchief ; because the electricity obtained from sealing-
wax is different from that procured from glass : the former is called
resinous or negative electricity, the latter positive or vitreous electricity.
Either, separately, is repulsive of its own particles, but attractive of the

ELECTKICAL EXPERIMENTS. 181

other. No electrical excitation can occur without the separation of
these two curious states of electricity, and electrical quiescence takes
place when the two electricities are brought together ; hence the fall of
the gold leaves repelled by rubbed wax when the excited glass is brought
towards the disc of the electroscope. This experiment may be reversed
by repelling the leaves first with the excited glass, and then bringing the
rubbed wax, when the same effect takes place.

Twelfth Experiment.

To show the important elementary truth, that in all cases of electrical
excitation the two kinds of electricity are generated, take a dry roll of
flannel, and holding it as lightly as possible, rub it against a bit of wax.
If the flannel is brought to the electroscope, the leaves repel each other,
and they immediately fall when the wax is now approached, because the
flannel is in the positive or vitreous state of electricity, whilst the
sealing-wax is in the negative or resinous condition.

Thirteenth Experiment.

Any kind of friction generates electricity. A little roll brimstone
placed in a dry mortar and powdered, and then thrown on to the electro-
scope, quickly causes the repulsion of the leaves.

Fourteenth Experiment.

A sheet of dry brown paper laid on a flat surface, and vigorously
rubbed with a piece of india-rubber, produces so much electricity
that sparks and flashes of light are apparent in a dark room when it
is lifted from the table ; and it affects the leaves of the electroscope
very powerfully, so much so that care must be taken to apply it very
carefully to the disc, or the violence of the repulsion may cause the
fracture of the gold leaves, and then a great deal of time is wasted
before they can be put on again.

A dry wig or bunch of horse- hair when combed becomes electrical,
and likewise affects the leaves of the electroscope.

Sixteenth Experiment.

Two dry silk ribbons, the one white and the other black, passed
rapidly together through the fingers, exhibit sparks and flashes of
light when drawn asunder, and also cause the gold leaves to repel each
other.

Seventeenth Experiment.

Much instructive amusement is afforded by testing the gold leaves
when separated from each other during either of the former experiments.

183 BOY'S PLAYBOOK OF SCIENCE.

with an excited piece of sealing-wax. If the electricity produced is
negative, they repel each other further when the excited wax is ap-
proached ; if positive, they fall when the excited wax is brought near
them.

'Eighteenth Experiment.

When fresh, dry, ground coffee is received on to the disc of the elec-
troscope, as it falls from the mill, powerful electrical excitation is
displayed, and this is sometimes so apparent, that the particles cling
around the lower part of the mill or to the sides of the cup or basin
held to catch it.

Nineteenth Experiment.

After playing a tune on a violin, hold the bow (well rosined) to the
electroscope, when the usual divergence of the leaves will be apparent.

Twentieth Experiment.

Cut some chips from a piece of wood with a knife attached to a glass
handle, and as they fall on to the electroscope the leaves are repelled.

Twenty-first Experiment.

Warm a piece of bombazine by the fire and then draw out some of the
threads (which are of two kinds viz., silk and wool), and place them
on the electroscope, when divergence of the leaves immediately takes
place.

Twenty-second Experiment.

Put upon the same leg a worsted stocking and over that a silk one,
if the latter is now quickly rubbed all over with a dry hand and near
the fire, and then suddenly slipped off, the sides repel each other, and
the silk stocking retains very much the same shape as if the leg still
remained in it, and of course collapses as the electricity passes away.

Twenty-third Experiment.

Electrical machines consist only in the better arrangement of larger
pieces of glass and a more convenient mechanical contrivance for rubbing
them, and are of two kinds viz., the cylinder and plate machines ; it is
usual to give directions for the manufacture of an electrical machine
from a common bottle, and doubtless such rude instruments have been
made, but as Messrs. Elliott Brothers, of 30, Strand, now supply excel-
lent small machines at a very low cost, it is hardly worth while to incur
even a small expense for an instrument that must at the best be a very
imperfect one and frequently out of order. (Fig. 166.)

ELECTRICAL MACHINES.

Fig. 166. A cylinder electrical machine.

Plate machines are somewhat more expensive than cylinder ones, but
at the same time are more quickly prepared for experiments, and Mr.
Hearder, of Plymouth, states, that the secret in obtaining the greatest
amount of electricity from a cylinder machine, is to keep the inside of
the glass absolutely clean, dry, and free from dust. Sometimes the
glass of which electrical machines are made is wholly unfit for elec-

Fig. 167. The ordinary plate electrical machine.

184

BOY'S PLAYBOOK OF SCIENCE.

trical purposes, in consequence of the decomposition of the surface
from imperfect manufacture and the liberation of the alkali. (Figs.
167, 168.)

Fig. 168. Woodward's double plate electrical machine, giving a much la "src
quantity of electricity than Fig. 167.

Cylinder and plate machines are furnished with proper rubbers, and
before using the instrument it is usual to remove them, and after care-
fully cleaning the glass with a dry silk handkerchief before a fire,
the rubbers are scraped with a paper-knife to remove the old amalgam,
and fresh applied by first melting the end of a tallow candle slightly,
and after passing this over the rubber, the finely powdered amalgam is
now dusted on to it. Electrical amalgam is prepared by fusing one part
of zinc with one of tin, and then agitating the liquid mass with two
parts of hot mercury placed in a wooden box; when cold it should
be carefully powdered and kept in a well-stoppered bottle for use.
When the amalgam has been applied, the rubbers are again screwed
in their places, and the machine when turned (if the atmosphere is
tolerably dry) will emit an abundance of bright sparks.

Twenty-fifth Experiment.

Attraction and repulsion are shown on a larger scale, with the as-
sistance of electrical machines, by placing a fishing rod (the last joint of

ATTRACTION AND REPULSION.

185

which is made of glass) in an erect position, and attaching to the ex-
tremity a long tassel of paper from
which a thhrwire passes to me prime
conductor of the electrical machine ;
on turning the instrument, the
strips of paper all stand out and
repel each other. (Fig. 169.)

Twenty -sixth Experiment.
Suspend from the prime conductor
by a chain a circular brass plats

Fig. 170. A. Prime conductor.
B. Upper brass-plate. c. Lower
ditto. The figures are seen between
B and c.

Fig. 169. A A. The glass joint of the
fishing-rod, from which the last joint,
carrying the paper tassel, B, projects, c.
The electrical machine.

and under this place another supported by a brass adjusting stand.
If pith figures of men and women are placed on the lower plate, they rise
directly the machine is turned, although sometimes, in consequence of
irregularity in the adjustment of the centre of gravity, they perversely
dance on their heads instead of the usual position ; out of half a dozen
figures, one only perhaps will be found to dance well, by alternately
jumping to the upper plate and falling to the lower one to discharge the
excess ^of electricity ; and indeed the experiment will be found to
succeed better with one or two only on the plate instead of a number,
as they cling together and impede each other's movements. (Fig. 170.)

186

BOY S PLAYBOOK OF SCIENCE.

Twenty-seventh Experiment.

An assistant provided with a wig of well-combed hair presents a
most ridiculous appearance when standing on the insulating stool and
connected by a wire with the prime conductor of the electrical
machine, every hair, when not matted together, standing out in the most
absurd manner, when the machine is put in motion.

Twenty-eighth Experiment.

Whilst standing on the stool, sparks may be obtained from his body,
and if some tow is tied over a brass ball, and moistened with a little
ether, and presented to the tip of his finger, a spark flies off which
quickly sets fire to the inflammable liquid.

Twenty-ninth Experiment.

If small discs of tinfoil, cut out with a proper stamp, are pasted in
continuous lines over plate glass, or spirally round glass tubes, a very

171 A A A. A ring: of brass wire supported on a glass pillar inside which the spiral
tube"B, revolves, and produces beautiful and ever-changing circles of light, when connected
'

ueB, revov,
with' the conductor, c, of the electrical machine.

EFFECTS OF INDUCTION.

187

pretty effect is produced when they receive the sparks from the electrical
machine, and the passage of the electricity from one disc to the other
produces a vivid spiral or other line of light. When the tube is
mounted in a proper apparatus, so as to revolve whilst the sparks pass
down the spiral tube, the effect of the continuous electric sparks is much
heightened. (Fig. 171.)

Thirtieth Experiment.

A great variety of experiments, depending on the proper arrangement
of discs of tinfoil on various tubes of coloured glass are manufactured,
and some in the form of windmills, the sails being made luminous by the
passage of the electricity. The names of illustrious electricians, beautiful
crescents, stars, and even profile portraits, have been produced in con-
tinuous streams of electric sparks.

Thirty-first Experiment.

When an electrified body is brought towards another which is not
electrical, the latter is thrown into the opposite state of electricity as
long as the excited body remains in its neighbourhood ; and this con-
dition of electrical disturbance, set up without any contact or supply of
electricity, is called induction, and involves a vast number of interesting
facts, which are thoroughly discussed in Dr. Noad's excellent work on
electricity, but can only be briefly alluded to here.

If a number of lengths of brass wire, supplied with balls at the ex-
tremities, are supported on glass legs and arranged in a line, with a
little pith ball attached to a thread hanging from each end of the length
of brass wire, the effect of induction is shown very nicely ; and when an
excited glass rod is brought towards one end of the series, the rising of
the pith balls to each other betrays the change which has occurred in

Fig. 172. The lengths of brass wire supported on glass rod pillars indented by blowpipe,
so as to retain the brass wires with the pith balls hanging from each series, the letters
p and N mean Positive and Negative, and the signs for these terms are placed above.
The letters p and N are painted on the blocks which support the glass rods.

the electrical state of the brass wires by the mere neighbourhood of the
excited glass tube. The glass tube is electrified positively, and attracts
the negative electricity from the brass wire towards the end nearest to

188 BOl'S PLAYBOOK OF SCIENCE.

it ; the other extremity of the brass wire is found to be in the positive
state, and this re-acting on the next, and so on throughout the lengths,
completes the electrical disturbance in the whole series. (Pig. 172.)

Tli irty -second Experiment.

If an insulated brass rod (such as has been described in the last
experiment) is touched by the finger whilst under induction, it remains
permanently electrified on the removal of the disturbing electrified body ;
and it is on this principle that the useful electrical machine called the
Electrophorus is constructed. This constant electrical machine for it
will remain in action during weeks and months if kept sufficiently dry
was invented by Volta in the year 1774, and has been brought to great
perfection by Mr. Lewis M. Stuart, of the City of London School ; so that
with a little additional apparatus the whole of the fundamental prin-
ciples of electricity can be demonstrated. It consists of a flat brass or
tin circular dish about two feet in diameter and half an inch deep, which
is filled with a composition of equal parts of black rosin, shell-lac, and
Venice turpentine ; the rosin and the Venice turpentine being first
melted together, and the shell-lac added afterwards, care of course being
taken that the materials do not boil over and catch fire, in which case
the pot must be removed from the heat, and a piece of wet baize or other
woollen material thrown over it. Another tin or brass circular plate of
twelve inches diameter, and supported in the centre with a varnished
glass handle nine inches long, is also provided, and the resinous plate
being first excited by several smart blows with a warm roll of flannel,
the plate held by the glass handle is now laid upon the centre of the
resinous one, and if removed directly afterwards, does not afford the
electric spark ; but if, whilst standing upon the excited resinous plate,
it is touched, and then removed by the glass handle, a powerful electric
spark is obtained ; and this may be repeated over and over again with
the like results, provided the plate with the glass handle is touched with
the finger just before lifting it from the resinous plate. (Fig. 173.)

Fig. 173. A A. Large circular tin or brass disc with turned-up edge half an inch deep,
and containing the resinous mixture B, which is rubbed with the warm flannel, c c. The
upper plate supported by the glass handle D, a pith ball attached to a wire shows the
electrical excitation, and the spark is supposed to be passing to the hand B.

THE ELECTROPHORUS. 189

The electricity excited on the resinous plate is not lost, and by induc-
tion sets up the opposite condition in the plate with the glass handle.
The resinous plate, being excited with negative electricity, disturbs the
electrical quiescence of the upper plate, and positive electricity is found
on the surface touching the resinous plate, and negative electricity on
the upper one, so that when it is removed without being touched, the
two electricities come togeth&r again, and no spark is obtained ; but if,
as already described, the upper plate is touched whilst under induction,
then positive electricity appears to pass from the finger to the negative
electricity on the upper side of the plate, when the two temporarily
neutralize each other, and then, when the plate is removed, the excess
of electricity derived from the earth through the finger becomes appa-
rent. Induction requires no sensible thickness in the conductors, and
can be just as well produced on a leaf of gold as on the thickest plate of
metal ; and it should be remembered that non-conductors do not retain
their state of electrical excitation when the disturbing cause is removed,
whereas conductors possess this power, and this fact brings us to the
consideration of the Ley den jar.

Thirty-third Experiment.

If one side of a dry glass plate is held before and touches a brass ball
proceeding from the prime conductor of an electrical machine whilst in
action, the other side is soon found to be electrical ; this does not arise
from the conduction of the electricity through the particles of the glass,
but is produced by induction, the side nearest the ball being in the
positive state, and the other side negative : as glass is a non-conductor
of electricity, the effect is much increased by coating each side with tin-
foil, leaving a margin of about two inches of uncovered glass round the
covered portion, then, if one side of such a plate is held to the prime
conductor of the electrical machine, and the other connected with the
ground, a powerful charge is accumulated ; and if the opposite sides
are brought in contact with a bent brass wire, a loud snapping noise is
heard, and the two electricities resident on either side of the glass come
together with the production of a brilliant spark, or if the hands are
substituted for the bent brass wire, that most disagreeable result is
obtained viz., an electric shock ; hence these glass plates are some-
times fitted up as pictures, and when charged and handed to the
unsuspecting recipient, he or she receives the electric discharge to the
great discomfort of their nervous system.

Mica is sometimes substituted for glass, and the late Mr. Crosse, the
celebrated electrician, constructed a powerful combination of coated
plates of this mineral. It consisted ot seventeen plates of thin mica,
each five inches by four, coated on both sides with tinfoil within half
an inch of the edge. They were arranged in a box with a glass plate
between each mica plate, all the upper sides were connected by strips
of tinfoil to one side of the box, and all the under surfaces in the same
manner with the opposite extremity of the box. They were charged like
an ordinary Leyden battery.

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BOYS PLAYBOOK OF SCIENCE.

Fig. 174. A A. Glass plate or stand coated
with tinfoil on each side, B. c. Wire
with pith balls oscillating during the
discharge of the glass plate.

Thirty-fourth Experiment.

If the glass plate coated with tin-
foil is charged, and then placed up-
right on a stand, it may be slowly dis-
charged by placing a bent wire on the
edge with the extremities covered with
pith balls. The wire balances itself,
and continues to oscillate \dth noise
until the electricities of the two sur-
faces neutralize each other. (Fig. 174.)

Thirty-fifth Experiment.

It is easy to imagine the glass
plate of the last experiment rolled up
into the more convenient form of the
Leyden jar, which consists of a glass
vessel lined both inside and out with tinfoil, leaving some two or three
inches of the glass round the mouth uncovered and varnished with

shell-lac ; a piece of dry wood is fitted
into the mouth of the jar, through
which a brass wire and chain are
passed, and the end outside is fitted
with a ball. The Leyden jar is
charged by holding the ball to the
prime conductor of the electrical
machine until a sort of whizzing
noise is heard, caused by the excess
of electricity passing round the un-
covered part of the jar and not
through it, as the smallest crack in
the glass of the Leyden jar would
render it useless. Electricity is
sometimes called a fluid, and the fact
of collecting it like water in a jar,
helps us to understand this analogy.
The noise, the bright spark, or the
shock are obtained by grasping the outside with one hand and touching
the ball with a brass wire held in the other. (Fig. 175.)

Fig. 175. The Leyden jar and brass
wire discharger.

Thirty -sixth Experiment.

The jar is silently discharged if the balls are removed from the dis-
charger and points used instead ; so, also, the whole of the electricity
produced by an electrical machine in full action may be readily drawn
off by a pointed conductor, such as a needle, placed at the end of a brass
wire. Electricity passes much more rapidly through points than rounded
surfaces, hence the reason why all parts of electrical apparatus are free
from sharp points and rough asperities.

THE LEYDEN BATTERY.

191

Thirty -seventh Experiment.

Extremely thin wires may be burnt by passing the charge of a large
Leyden jar through them. The show jars, called specie jars, usually
decorated and placed in the windows of chemists' shops, make excel-
lent Leyden jars, when not too thick; and with two of the largest, all

Fig. 176. A. Mahogany board with a sheet of white paper and three pairs of brass wire*
and balls fixed in the wire, three on each side. The thin wires are stretched between the
balls, and the lower one is in course of deflagration. B u. Charged large Leyden battery
of two jars; the arrows indicate the path of the electricity.

the interesting effects produced by accumulated electricity may be dis-
played. To pass the discharge through wires, nothing more is required
than to strain them across a dry mahogany board, between two brass
wires and balls, and if a sheet of white paper is placed under them, most
curious markings are produced by the fine particles of the deflagrated
metal blown into the surface of the paper. An arrangement of two or
more Leyden jars is usually called a Leyden Battery, just as a single
cannon is spoken of as a gun, whilst two or more constitute a battery.
(Kg. 176.)

Thirty -eighth ^Experiment .

Little models of houses, masts of ships, trees, and towers are sold by
the instrument makers, and by placing a long balanced wire on the top
of the pointed wire of a large Leyden jar, having one end furnished
with wool to represent a cloud, a most excellent imitation of the eifects
of a charged thunder-cloud is produced. The mechanical effect of a
flash of lightning has been analysed, and it has been stated, in one
instance, that the power developed through fifty feet was equal to a
12,220 horse-power engine, or about the power of^c-' engines of the
Great "Eastern, and that the explosive power was <<5qufll' 'to a pressure of -^
three hundred millions of tons. (Fig. 177.) //'<& -- '^. -*V

Oftltforni*v

192

BOY'S PLAYBOOK OF SCIENCE.

r. 177. A. Charged Leyden jar with balanced wire and wool at B, representing a thunder-
cloud, c. The obelisk overturned with the discharge. . Another model of the gable
end of a house ; the square pieces of wood fly out when the continuity of the conductor is
broken.

It was the learned but humble minded Dr. Franklin who established
the identity between the mimic effects of the electrical machines (such
as have been described), and the awe-inspiring thunder and lightning of
nature. A copper rod, half an inch thick, pointed and gilt at the ex-
tremity, and carried to the highest point of a building, will protect a
circle with a radius of twice its length. The bottom of the rod must be
passed into the earth till it touches a damp stratum.

Fig. 178. A storm.

193
CHAPTER XIV.

VOLTAIC ELECTRICITY.

IN describing the various means by which electricity may be obtained,
it was stated that " Chemical Action" was a most important source of
this remarkable agent ; at the same time it must be understood that it
is not every kind of chemical action which is adapted for the purpose ;
there are certain principles to be rigidly adhered to first, in the
generation of the force ; and secondly, in carrying it by wires so as to
be applicable either for telegraphic purposes, or for the highly valuable
processes of electrotyping and electro-silvering, plating, and gilding.

A lighted candle, or an intense combustion of coal, coke, or charcoal,
no doubt involves the production of electricity, but there are no means at
present known by which it may be collected and conducted ; when that
problem is solved, the cheapest voltaic battery will have been constructed,
m which the element decomposed is charcoal, and not a metal, such as iron
or zinc. The first and most simple experiment that can be adduced in
proof of electrical excitation by chemical means, is to take a bit of clean
zinc and a clean half-crown, and placing one on the tongue and the other
below it, as long as they remain separate no effect is observed, but
directly they are made to touch each other, whilst in that position, a
peculiar thrill is rendered evident by the nerves of the tongue, which in
this case answers the same purpose as the electroscope already de-
scribed, and in a short time a peculiar metallic taste is perceptible.

It has been stated over and over again that it was to a somewhat
similar circumstance we owe the discovery of voltaic electricity, and
the story of the skinned frogs agitated and convulsed by an accfdental
communication with two different metals, or, as some say, with the
electricity from an ordinary machine, has been repeated in nearly every
work on the science. Professor Silliman, however, asserts that the gal-
vanic story is doubtful, and is a fabrication of Alibert, an Italian writer
of no repute, and that greater merit is due to Galvani than that of being
merely the accidental discoverer of tliis kind of electricity, because he had
been engaged for eleven years in electro-physiological experiments, using
frogs' legs as electroscopes. It was whilst experimenting on animal
irritability, Galvani noticed the important fact that when the nerve of a
dead frog, recently killed, was touched with a steel needle, and the muscle
with a silver one, no convulsions of the limb were produced until the two
different metals were brought in contact, and he explained the cause of
these singular after-death contortions by supposing that the nerves and
muscles of all animals were in opposite states of electricity, and that
these nervous contractions were caused by the annihilation, for the time,
of this condition, by the interposition of a good conductor between them.

This theory of Galvani had several opponents, one of whom, the cele-

194

BOY S PLAYBOOK OF SCIENCE.

brated Volta, succeeded in pointing out its fallacy ; lie maintained that
the electrical excitement was due entirely to the metals, and that the
muscular contractions were caused by the electricity thus developed
passing along the nerves and muscles of the dead animal.

To Volta we are indebted for the first voltaic battery, and the distin-
guished philosopher may truly be said to have laid the foundation of this
now commercially valuable branch of science.

First Experiment. ,

If a plate of clean bright zinc is placed in a vessel containing some
dilute sulphuric acid, energetic action occurs from the oxidation of the
metal, and its union as an oxide with the acid, and the escape of a mul-
titude of bubbles of hydrogen gas. After the action has proceeded some
time, the zinc may be removed, and if a little quicksilver is now rubbed
over the surface with a woollen rag tied on the end of a stick, it unites

with the metal, and the sur-
face of the zinc assumes a
brilliant silvery appearance,
and is said to be amalga-
mated. In that condition it
is no longer acted upon by
dilute sulpnuric acid, and for
the sake of economy this is
the only form in which zinc
should be employed in the
construction of voltaic batte-
ries or single circles. If a
clean plate of copper, with a
^ wire attached, is now placed

in the dilute acid opposite to

Fig. 179. A single voltaic circle, consisting of a and not touching the amal-

^&F^^&$FF& gamated zinc plate, which may
current. also be furnished with a con-

ducting wire, no bubbles of

hydrogen escape until the wires from the two metals are brought in
contact, and then, singular to relate, the hydrogen escapes from the
copper plate, whilst the oxygen is rapidly absorbed by the zinc, and a
current of electricity will now be found to pass from the zinc through
the fluid to the copper, and back again through the wire to the starting-
point, and if the wires are disconnected, the chemical action ceases, and
no more electricity is produced. (Fig. 179.)

The passage of the current of electricity is not discoverable by the
electroscope, because it is adapted only to indicate electricity of high
tension or intensity, such as that produced from the electrical machine,
which will pass rapidly through a certain thickness of air, and cause
pith balls to stand out and repel each other ; such effects are not pro-
ducible by a single voltaic circle, or even an ordinary voltaic battery,
although one comprising some hundreds of alternations would produce

THE GALVANOMETER. 195

an effect on a delicate electrometer ; hence voltaic electricity is said to
be of low intensity, and this property makes it much more useful to
mankind, because it has no desire to leave a metallic path prepared for
it, and does not seize the first opportunity, like the electricity from the
electrical machine, to run away to the' earth through the best and
shortest conductor offered for it. If electricity had only been producible
by friction, we should never have heard of electrotyping, and the other
useful applications of electrical force of low intensity.

Second Experiment.

To ascertain the
passage of a current
of voltaic. electricity,
the instrument called
the galvanometer
needle IS provided, Fig m A ga i va nometer needle, consisting of a coil of
which consists OI a covered copper wire, the ends of which terminate at the
nnil nf pnrmpr wirp binding screws. The magnetic needle is suspended on a

)i copper wire, point in the centre) aQd the coil ia surrounded writh a gradu .
surrounding a mag- ated circle,
netic needle, so as to

leave the latter freedom of motion from right to left, or vice versa.
When this coil is made part of the voltaic circle it becomes magnetic,
and reacting on the magnetized needle, deflects it to one side or the
other, according to the direction of the current. (Fig. 180.)

Third Experiment.

If a number of simple voltaic circles, such as the one described in the
first experiment, are connected together, they form a voltaic battery,
in which of course the quantity of electricity is greatly increased.
Batteries of all kinds, from the original Volta's pile, consisting of round
zinc and copper plates soldered together with interposed cloth moistened
with dilute sulphuric acid, or his couronne des tosses, consisting of zinc
and silver wires soldered together in pairs, and placed in glass cups
containing dilute acid, to the improved batteries of Cruikshank, Wil-
kinson, Babington, Wollaston, and the still more perfect arrangements
of Daniell, Mullins, Shillibeer, and Grove, have been from time to time
recommended for their own peculiar features.

Amongst these several inventions, none will be found more useful
than the constant battery of Daniell for electrotyping, silvering, gilding,
and other purposes, and Grove's battery for all the more brilliant results,
such as the deflagration of the metals or the production of the electric
light. The construction of the Daniell and Grove batteries will there-
fore be described. The former consists of a cylindrical vessel made of
copper, in which is suspended or placed (as it is open at the top) a
membranous, brown-paper, canvas, or porous earthenware tube, con-
taining an amalgamated rod of zinc. To charge this arrangement, a
strong solution of sulphate of copper, with some sulphuric acid, is
poured into the copper vessel, which is provided usually with a sort of

106

BOYS PLAYBOOK OF SCIENCE.

colander at the top to hold crystals of sulphate of copper, and in the
porous tube containing the zinc rod is poured dilute sulphuric acid. A
number of these cylinders of copper, twenty inches high and three inches
and a half in diameter, arranged in wooden frames to the number of

Fig. 181. A A. Copper cylindrical vessel with colander to hold the crystals of sulphate
of copper. B. The amalgamated zinc rod inside the porous cell c c. D. A series of single
cells forming a DanielFs battery.

twenty, afford a quantity of electricity sufficient to demonstrate all the
usual phenomena. (Fig. 181.)

Protessor Grove's battery consists of a flat glazed earthenware vessel
containing a flat porous cell. An amalgamated zinc plate is placed
outside the porous cell, and a platinum plate inside the latter. The
arrangement is put in action by pouring dilute sulphuric acid round the
zinc and strong nitric acid inside the porous cell. A set of Grove's
nitric acid battery, as manufactured by Messrs. Elliott, Brothers, of
30, Strand, with fifty pairs of sheet platinum, five inches by two inches
and a quarter, and double amalgamated zinc plates, flat porous cells, and
separate earthenware troughs for each pair, and stout mahogany stand,
arranged '
one
sition

arranged as a single series of fifty pairs of plates. Even thirty pairs
exhibit the most splendid effects, whilst forty may be regarded as the
happy medium, giving all the results that can be desired. (-Fig. 182.)

The advantage of employing amalgamated zinc is very prominently
illustrated whilst using any powerful arrangements of either Daniell's or
Grove's batteries, as they will remain for hours quiescent, like a giant
asleep, until the terminal wires of the series are brought in contact

BATTERIES OF DANIELL AND GROVE.

197

C C A.

Fig. 182. A A. Amalgamated zinc plate in flat earthenware trough. Attached to a bind-
ing screw is the platinum plate in porous cell, c c. D. A series of single cells forming a
Grove's battery.

either through the intervention of some fluid under decomposition or by
means of charcoal points. The author had the pleasure of witnessing
at King's College some of the effects of an enormous battery, prepared
by the late Professor Daniell, and consisting of seventy of his cells.

A continuous arch of flame was produced between two charcoal points,
when distant from each other three quarters of an inch, and the light
and heat were so intense that the professor's face became scorched and
inflamed, as if it had been exposed to a summer heat. The rays col-
lected by a lens quickly fired paper held in the focus.*

Fourth Experiment.

It is bv " chemical action" the electricity is produced, and as action
and reaction are always equal, but contrary, we are not surprised to find
that the electricity from the voltaic battery will in its turn decompose
chemically many compound bodies, of which water is one of the most
interesting examples. It was in the year 1800, and immediately after
Volta's announcement -to Sir Joseph Banks of his discovery of the pile,
that Messrs. Nicholson and Carlisle constructed the first pile in England,
consisting of thirty-six half-crowns, with as many discs of zinc and paste-
board soaked in salt water. These gentlemen, whilst experimenting
with the pile, observed that bubbles of gas escaped from the platinum
wires immersed in water and connected with the extremities of the
Volta's pile, and covering the wires with a glass tube full of water, on
the 2nd of May, 1800, they completed the splendid discovery of the
fact that the Volta's current had the power to decompose water and
other chemical compounds.

* By the light from the same battery photogenic drawings were taken, and the heating
power was so great as to fuse with the utmost readiness a bar of platinum one-eighth of an
inch square ; and all the more infusible metals, such as rhodium, iridium, titanium, &c.,
were melted like wax when placed in small cavities in hard graphite and exposed to ths
current of electricity.

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BOYS PLAYBOOK OF SCIENCE.

Fig. 183. A A. A finger glass with two holes drilled
to pass the wires through, which are imbedded in
cement up to the platinum plates. B B. Glass tubes,
closed at one end and open at the other, which are
placed over the platinum plates to receive the liberated
oxygen and hydrogen. The scale at the side shows
the respective volumes of two of H to one of 0.

In 1801, Davy had sue-
ceeded to a vacant post in
the Royal Institution, and
on Oct. 6th, 1807, made
his transcendent discovery
of potassium with the aid
of the voltaic battery, and
from that and other expe-
riments inferred that the
whole crust of the globe
was composed of the oxides
of metals. To exhibit the
decomposition of water,
two platinum plates with
proper connecting wires,
passing to small metallic
cups full of mercury, are
cemented inside a glass
vessel, which is then filled
with dilute sulphuric acid.
Just above the platinum
plates and over them, stand
two glass tubes also con-
taining the same fluid in
contact with the battery.
Two measures of hydrogen
are found in one tube, and
one of oxygen in the other.
(Fig. 183.)

To measure the quan-
tity power of the voltaic
battery, an important in-
strument invented by Fa-
raday is used. It consists
of separate platinum plates
cemented in a wooden
stand, and over which a
capped air-jar with a bent
pipe is also cemented. Tin's
apparatus contains dilute
sulphuric acid of the same

Fig. 184. A. Gas jar with cap and bent tube passing , ' ,1 f i , ,

to the graduated tube c; the jar is cemented in the f?*^*" l j 1 T

same stand which carries the connecting cups, wires, the battery under exami-
and platinum plates, which are bent round each other Cation ancl bv takin " the
to improve the action of the voltameter. .. '-, '*.*. *J J.-L

time, tne quantity 01 tne

mixed oxygen and hydrogen gases producible by a battery per minute is
accurately determined, the gases of course being collected in a gra-
duated jar. (Fig. 184.)

ELECTRO-CHEMISTRY.

199

Fifth Experiment.

By grouping the simple circles forming a voltaic battery in various
numerical relations, the quantity and intensity effects are modified.

Thus, if a series of thirty pairs of Grove's battery are all connected
together in consecutive order, the smallest quantity and the largest
intensity effect is produced.

If changed to two groups of fifteen each, the quantity is doubled
that is to say, it will produce double the quantity of the mixed gases
from the voltameter with half the intensity.

If arranged in three groups of ten each, it is trebled with a propor-
tional loss of intensity, until the grouping reaches six series of five each,
when a maximum supply of the mixed gases is obtained from the
voltameter.

In arranging the groups, all the zinc ends of each series are con-
nected, and all the platinum ends are likewise joined by proper wires.

Sixth Experiment.

A plate-glass trough, con-
taining a few grains of iodide
of potassium dissolved in
water with some starch, is
quickly decomposed into its
elements by placing in two
platinum plates and connect-
ing them with the wires of
the voltaic battery. If the
glass trough is divided in the
centre with a bit of cardboard,
the purple colour of the iodine
and starch is shown very beau-
tifully on one side, but not on
the other, as iodine is libe-
rated at one pole and the al-
kali at the other. (Fig. 185.)

Seventh, Experiment.

Some solution of common salt coloured with sulphate of indigo and
placed in the trough is decomposed into chlorine, which bleaches one
side of the indigo solution, and the alkali liberated on the other does
not affect it.

Eighth Experiment.

Some nitrate of potash dissolved in water and coloured with litmus
placed in the glass trough, changes red on one side of the cardboard by
the liberation of acid, and is not affected on the other.

In these experiments the oxygen, iodine, chlorine, and nitric acid are
liberated at the electro-positive pole, and are hence termed electro-
negative bodies, whilst hydrogen and the alkalies are set free at the
electro-negative pole, and are therefore called electro-positive bodies.

Fig 1 . 185. A A. A glass trough containing the
salt dissolved in water, and divided temporarily
with a bit of cardboard, B. c c are the two platinum
plates connected with the battery, and the shaded
side is supposed to represent the liberation of the
iodine.

200

BOY'S PLAYBOOK OF SCIENCE.

Faraday has modified these terms, and calls the two classes "unions"
and " cathions" and the two poles "anodes" and "cathodes."

Anode, from az/a, up, and 686s, a way : the way which the sun rises.
Anions, from ai/a, up, ei/w, to go : that which goes up ; a substance
which passes to the anode during the passage of a current of elec-
tricity. Cathode, from /caret, down, and 6S6s, a way : the way which
the sun sets. Cathion, from Kara, down, and el/j.1, to go : that which
goes down ; a substance which passes to the cathode during the passage
of electricity from the anode to the cathode.

Ninth Experiment.

In the process of the electrotype is presented a valuable application
of the chemical power of the voltaic circle or battery, and it may be
conducted either as a single cell operation or by distinct batteries. In
the former case the most simple arrangement will suffice; the only
articles necessary are a large mug or tumbler ; some brown paper and
a ruler ; a bit of amalgamated zinc, four inches long and half an inch
wide ; a short length of copper wire ; some black lead, blue vitriol, and
oil of vitriol.

The mould from which the electrotype is to be taken can be made
of common sealing wax, plaster of Paris, white wax, gutta percha,
or fusible alloy. Supposing the first to be selected viz., a common

seal, it is first thoroughly black-leaded,*
then one end of the copper wire is bent
round the top of the amalgamated zinc,
and the other is gently warmed and
melted into the side of the seal, leaving
a small portion uncovered by the wax,
which is then well black-leaded. A few
ounces of blue vitriol are dissolved in
boiling water, and when cold the solu-
tion is poured into the tumbler, and the
porous cell to contain the mixture of
eight parts water to one of sulphuric
acid is made by rolling the brown paper
three or four times round the ruler and
closing the end, and fixing the side with
a little sealing wax. The porous cell of
brown paper is now filled with the di-
lute acid, and placed in the tumbler
containing the solution of blue vitriol,
the amalgamated zinc being arranged in
the paper cell, and the attached seal in
Fig. 186. A A The tumbler con- th solution; in about twelve

tamine the solution of sulphate ot . rr '

copper B B. The brown paper cell hours a good deposit of copper IS pro-
containing the dilute sulphuric acid, duced, and a perfect cast in metal of
inside which is the amalgamated zinc ,, , Ju*. _il /ENo- 1 QA "\

with wire attached to the seal D. the seal obtained. (* ig. 1 SO.)

* The application of plumbago, or black lead, for electrotype purposes, was first nude
by the late lamented Mr. Robert Murray.

THE ELECTROTYPE.

201

Messrs. Elliott provide every kind of convenient vessel for the pur-
pose, and in the picture below it will be noticed that the single cell appa-
ratus, though not so economical as the simple tumbler arrangement already
described, is perhaps more convenient for electrotyping. (Fig. 187.)

Fig. 187. A. Single cell apparatus with proper vessel, porous tube, and binding screws.
B. A large trough divided by a diaphragm of biscuit-ware or very thin porous wood.

Tenth Experiment.

A single cell apparatus is only adapted to produce small electrotypes,
but when larger ones are required, a separate battery of three or four

Fitr. 188. A. A single cell, Darnell's, attached to B, the trough containing the mould
and the plate of copper. Below is a Smee's battery ready to be attached to a larger trough
for the purpose of electrotyping a great number of moulds at the same time.

202

BOY S PLAYBOOK OF SCIENCE.

Dnuirll's or Smcc's cells is required; and it is usual to place the mould
to be copied in a separate wooden trough, ul.ladiing it to the cathode
wire, whilst a copper plate is connected with the anode, so that as the
solution of sulphate pi copper undergoes decomposition by the passage
of the electricity, it is kept almost in a normal state, in consequence of
the oxygen of the water and the acid passing to the copper plate, which
they attack and dissolve as fast as the oxide of copper and hydrogen
are liberated at the cathode, where the latter deoxidizes the oxide of
copper, and by a secondary action deposits metallic copper; the object
being to dissolve fresh metal as the copper is deposited on the mould.
(Fig? 188.)

Eleventh Experiment.

To silver electrotypes or other brass and copper articles, the first
attention must be paid to the cleanness of them ; and when an electrotype
is just removed from the copper solution, and washed in clean water,
it is at once ready to receive the coating of silver ; otherwise, if it has
been handled, or is slightly greasy, it should be first boiled in a solution
of common washing soda, and then the oxide removed by passing it
rapidly in and out of some "Dipping Acid," which is prepared by
mixing together equal parts of oil of vitriol and nitric acid; when
removed from the "Dipping Acid," it must be well washed in water,
and may remain under the surface of the water until the silvering
solution is ready. A silver solution may be prepared by dissolving a
sixpence in some nitric acid contained in a flask ; it is then poured into
a solution of common salt, which precipitates the chloride of silver, and
leaves the copper in solution the latter is poured off when the chloride
has subsided, and after being well washed in some boiling water, is
dissolved in a solution of cyanide of potassium. If a clean electrotype
is plunged into this solution, it is imme-
diately covered with a very thin coating of
silver, which of course would soon wear off,
and in order to increase the thickness of
the silver deposit, a single cell arrangement
may be constructed of a large gallipot con-
taining a wide porous cell and a circle of
amalgamated zinc around it; the arrange-
ment is set in action by pouring a solution
of salt (or, still better, sal ammoniac) into
and around the porous vessel, and the sil-
vering solution into the latter ; a connect-
ing wire passes from the zinc, and the ar-
ticlc being attached to it, is now plunged
into the porous cell, when a current of
electricity slowly passes and deposits the
screw to which tho medal is silver on the copper article, (l<ig.

attached, and contained in the
porous vessel holding the silvering
solution and mcdul.

Fig. 189. The gallipot con-
ining tho solution of sal ammo-

ELECTRO-SILVERING AND GILDING. 203

Twelfth Experiment.

Separate batteries and large troughs containing a solution of cyanide
of silver in cyanide of potassium are used on a grand scale in the electro-
plating establishment of Messrs. Elkin^ton ot Birmingham, where the
finest specimens of the art are to be obtained; a plate of silver being
attached to the anode to supply the loss of silver in these troughs.

Thirteenth Experiment.

The art of gildingr by the agency of electricity is quite as simple as
the processes already described, although greater care is necessary to
avoia any loss of the precious metal. A small bit of gold is dissolved
in a mixture of three parts muriatic acid and one of nitric acid, which
forms the chloride of gold. This is then digested with an excess of
calcined magnesia, and the gold is precipitated as an oxide of the metal;
the latter is collected and washed, and then boiled in strong nitric acid
to remove the magnesia clinging to it, and being again thoroughly washed
with water, is dissolved in a solution of cyanide of potassium, forming
a solution of cyanide of gold and potassium, which may be placed in
the* porous cell of the single cell arrangement already described in
the Eleventh Experiment.

Fourteenth Experiment.

The safest and surest mode of making a gilding solution is to dissolve
some cyanide of potassium in water in a gallipot, and having placed a
porous vessel therein containing the same solution, put a plate of copper
into the porous cell, and some thin foil of pure gold into the gallipot ;
connect the gold with the anode of a single cell of Daniell, and the
copper in the porous cell with the cathode, and in a few hours sufficient
gold will be dissolved for the purpose of gilding.

It is usually recommended to warm the gilding solution till it reaches
a temperature of about 150 Fahr., and a very moderate battery power
is employed in Electro Gilding. Indeed the same arrangement, shown
in the Eleventh Experiment, Eig. 189, will also answer tor the gilding
solution. After being gilt, the articles may be rubbed with a little
tripoli, or burnished (with taste) by the handle of a key.

Fifteenth Experiment.

Passing on to the more brilliant results obtainable from a powerful
voltaic battery (of at least thirty pairs of Grove), the beautiful incan-
descence of platinum wire may first be noticed. If a wire of this metal
is stretched oetweeii the brass standards of two ring stands, the length
must be proportioned to the power of the battery; the adjustment can
be made verv conveniently by twisting the platinum wire on one ring
stand, and tlien leaving the other end loose, the second ring stand may
be brought nearer and nearer to the first, until the desired intensity of

204

BOY S PLAYBOOK OF SCIEXCE.

light from the incandescent
wire is obtained. (Fig. 190.)
If the wire is contained in
a glass tube the cooling
effect of currents of air is
prevented, and a much
greater length of wire can
be made hot.

Sixteenth Experiment.

With the same arrange-
ment, a chain composed of
alternate links of silver and
platinum wire presents a
very pretty effect, every

. Two ring stands with the battery alternate link of platinum

being incandescent, whilst
the silver, from its excellent
conducting power, remains

comparatively cool.

Fig. 190,

wires B B (which should be a convenient length) at
tached. c. Platinum wire, fixed end. D. The other
end held in one hand and shortened as the stand is
moved by the other hand.

Fireworks or gunpowder, arranged
in proper cases, are fired at a great
distance from the voltaic battery by
heating a thin iron or platinum wire
contained within them by the pas-
sage of the electricity; and sub-
marine and other explosions of gun-
powder by the same agency have
become a common engineering ope-
ration. (Fig. 19].)

During the operation of blasting
the hard marl rocks in the River
Severn by Mr. Edwards, C.E., a
number of holes were made side by
side in the bed of the river, and
rSuncfthe cartridges formed of strong duck or

battery wires tied to the outside of the case. Canvas, tapered at the bottom,
c. A gut bladder containing the thin wire were fiU e( J w ith charges of powder
and powder for a miniature submarine f , f ,

explosion. f rom two to f ur pounds, accord-

ing to the depth of the marl;

thus, two pounds for four feet, three pounds for four feet six inches, and
four pounds for five feet. Into the bag were conveyed the wires of the
voltaic battery, or Bickford's fuse, and being then coated with pitch and
tallow, and finally greased all over and dusted with whitening, thev
rarely failed, and were all fired simultaneously under water. The pitcu
and tallow first, and afterwards the simple tallow, effectually excluded
the water from the gunpowder contained in the canvas bag.

THE ELECTRIC LIGHT.

205

Eighteenth Experiment.

The burning of various
metals by the battery is
displayed with great effect
by De la Rue's discharger,
as also the incandescence
of the charcoal points pro-
ducing the electric light.
The illuminating power
derived from a forty-cell
Grove's battery of the or-
dinary size is about equal
to the light of 500 candles.

Fizeau and Foucault
have made a careful com-
parison of the light ob-

Fig. 192. De la Rue discharger, containing a series
of six pairs of difl'crent substances, such as charcoal,
iron, lead, zinc, copper, antimony, in six pair of crayon
holders, and turning on a centre, so as to be charged at
pleasure.

tained from 92 carbon couples as arranged in a Bunsen's battery, and
of the oxy-hydrogen, or Drummond Light, as compared with that of
the sun, and they state that " On a clear August day, with the sun two
hours high, the electric light (assuming the sun as unity) bore to it the
ratio of one to two and a half i.e., the s-un was two and a half times
more powerful, while the Drummond Light was only T^th that of the
sun." Bunsen found the light from 48 carbons equal to 572 candles.
In Bunsen's battery carbon is substituted for the platinum in Grove's
arrangement; and simultaneously witli Bunsen, Cooper (in England)
had applied charcoal for the same purpose.

At night the giant ship (Polyphemus like) is to have an electric light
at the masthead whilst steaming across the Atlantic.

Fig. 193. Gnat: Lantern, with electric light.

206

BOY S PLAYBOOK OF SCIENCE.

CHAPTER XV.

MAGNETISM AND ELECTRO-MAGNETISM.

IF a small helix, or coil of covered wire, is arranged with an unmag-
netized steel needle within it, so that the discharge of a large Leyden

jar may take place
through the coil, the
needle will be found
strongly magnetic af-
ter the discharge of
the electricity. "(Fig.
194.) Many years
before this was
known, it had been
noticed that when a
ship was struck by
lightning, the com-
passes were generally
reversed; and in a
special case, where a
house was struck, the
electricity entered a

Fig. 194. A A. A plass tube supported on two uprights of h nx n f Vnivpq fnsi no-
wood, with coil of copper wire passing round it, terminating in D l Kmve . s > IU& i n g
the balls B B. c. Needle to place inside glass tube. some, tearing the

handles off others,

but leaving' them strongly magnetic. Electricians tried to repeat the
effect by sending the discharge of powerful Leyden batteries through
bars of steel without any important result; and it was not until
Oersted, in the year 1819, made his important discovery that the copper
lire conveying the electricity possessed peculiar magnetic power, that

the principle began
to be understood, and
then the electricians
succeeded in imitat-
ing the effects of
lightning on steel, as
already described in
the beginning of this
chapter. (Fig. 194.)
When the electri-
city has passed away
from the Leyden jar
Fig. 105. through the coil of

THE LOADSTONE. 207

copper wire, it no longer possesses any power to affect a piece of steel
or iron, but if the wires of the voltaic battery are now connected with
the coil of copper wire, which should be covered with cotton or silk,
and many yards in length, then a bar of steel or soft iron is not only
rendered magnetic, but remains permanently so, as long as the current
of electricity continues to pass along the coil of wire, so that if some
nails or iron filings are brought to the bar of iron, one end of which
projects from the coil, they cling to it with great force, and a great
number of nails may be hung on in this manner, but they imme-
diately fall off when the contact is broken with the battery. (Pig. 195.)

Electricity thus becomes a source of magnetism, and the discoverer,
Oersted, found that only needles or bars of steel or iron were thus
affected, and not those of brass, shell-lac, sulphur, and other substances ;
he termed the conducting wire " a conjunctive wire," and described the
effect of the electric current or " electric conflict" as he called it, as
resembling a Helix (from eXiVo-o), to turn round; a screw or spiral), and
that it is not confined to the conducting wire, but radiates an influence
at some distance. This latter statement is exactly in accordance with
our present notions, and hence the coil conveying the current is said to
induce magnetism in the iron or steel, just as the phenomena of induction
are produced with frictional electricity. The effect of Oersted's disco-
very-, says Silliman, was truly electric; the scientific world was ripe
for it, and the truth he thus struck out was instantly seized upon by
Arago, Ampere, Davy, Faraday, and a crowd of philosophers in all coun-
tries. The activity with which this new field of research has been cul-
tivated, has never relaxed even to this hour, while it has borne fruit in
a multitude of theoretical and practical truths, and above all, in the
electro-magnetic telegraph, truly called, and especially in connexion
with the Atlantic telegraph wire, " the great international nerve of
sensation"

Magnetism is not only the result of a current of electricity through
any good conductor, but there are certain
oxides of iron, called magnetic iron ores,
which have the property of attracting iron
filings, and are mostly found in primitive
rocks, being abundant at Roslagen, in
Sweden, and called the loadstone, from its
always pointing, when freely suspended, to
the Polar, North, or Load Star. If a tole-
rably large specimen of this mineral is exa-
mined, there will be found usually two points
where the iron filings are attracted in larger
quantities than in other parts of the same
specimen. These attractive points are called
poles, and the loadstone being properly F} 196 A
mounted with soft iron bars, termed cheeks, mounted in brass or sliver,
bound round it (in old-fashioned loadstones) with the iron cheeks B B at-
silver plate and dulv ornamented with ' S ft

208

BOY S PLAYBOOK OF SCIENCE.

engraving, has its magnetic power greatly increased, and is then said to
be endowed with magnetic polarity; and to prevent the loss of power, a
soft piece of iron, called the armature, is placed across and attracted
to the poles of the loadstone. (Fig. 196.)

Second Experiment.

If a needle of tempered steel (fitted with a little brass cup in the
centre to work upon a point) is rubbed with the loadstone iu one direc-
tion only, it is rendered permanently magnetic, and will now be found
to take a certain fixed position, pointing always in a direction due north
and south. The end which points towards the north is called the north
pole, and the other extremity the south pole, and it is usual to mark
the north pole with an indent or scratch to distinguish it at all times.

Third Experiment.

If another bar of steel is magnetized, and the north pole duly marked,
and then brought towards the same pole of the suspended magnet, in-
stant repulsion takes
place; the magnet, of
course, grasped in
the hand is not free
to move, but the
small magnet imme-
diately shows the
same fact noticed
with electricity, viz.,
Pig. 197. A magnetic needle, the north pole v being at- " th a similar maqne-
tracted to the south pole of the bar magnet s, and repelled from , . ; m__

the north end. tttmt repel. Iwo

n>i th poles repel each

other, but when the bar of steel is reversed, the opposite effect occurs,
and the suspended magnet is attracted, showing that dissimilar mag-
netisms attract, and a north will attract a south pole. (Fig. 197.)

Fourth Experiment.

By contact, the magnetic power is transferred from the magnet to a

piece of unmagnetized
steel, and it is stated
that the highest magnet-
izing effect is that pro-
duced by the simple me-
thod of Jacobi. A horse-
shoe magnet has its poles
brought in contact with
the intended poles of an-
tagnet, and another one other bar of steel, like-
snd; the one shaded and w i se bent in the torm

Fig. 198. The horse-shoe m
nnmagnetized, placed end to en

nnmagnetized, placed end to end; the one shaded and wlse bent in tne lorm
lettered K and s is the magnet. A A. The piece of soft f horseshoe, and by
iron moved in the direction of the arrow.

ELECTRO-MAGNETS.

209

drawing the feeder over the unmagnetized horse-shoe in the direction of
the arrow in the cut, and when it reaches the curve, bringing it back
again to the same place, say at least twelve times, and after turning
the whole over without separating the poles, and repeating the same
operati<~yn on the other side likewise twelve times, the steel is then
powerfully magnetized ; and it is said that a horse-shoe of one pound
weight may be thus charged so as to sustain twenty-six and a half
pounds, and that by the old method of magnetizing it would only have
sustained about twenty -two pounds. (Fig. 198.)

Fifth Experiment.

If the horse-shoe magnet is placed on a sheet of paper, and some iron
filings are dusted between the poles, a very beautiful series of curves are
formed, called the magnetic curves, which indicate the constant passage
of the magnetic power from pole to pole.

The magnetic force
exerted by a horse-
shoe-shaped piece of
soft iron, surrounded
with many strands of
covered copper wire
in short lengths, is
extremely powerful
(Fig. 199), and enor-
mous weights have
been supported by an
electro-magnet when
connected with a vol-
taic battery. Sup-
posing a man were
dressed in complete
armour, he might be
held by an electro-
magnet, without the

limself, thus realiz-
ing the fairy story of
the bold knight who
was caught by a rock
of loadstone, and,
in full armour, de-
tained by the un-
friendly magician.

Sixth Experiment.

Fig. 199. A. Powerful electro-magnet supporting a great
weight. B. The battery.

210

EOT S PLAYBOOK OF SCIENCE.

Seventh Experiment.

When a piece of soft iron is held sufficiently near one of the poles
of a powerful magnet, it becomes by induction endowed with magnetic
poles, and will support another bit of soft iron, such as a nail, brought,
in contact with it. When the magnet is removed, the inductive action
ceases, and the soft iron loses its magnetic power. Tliis experiment
aifords another example of the connexion between the phenomena of
electricity and magnetism. It is in consequence of the inductive action
of the magnetism of the earth that all masses of iron, especially
when they are perpendicular, are fcTind to be endowed with magnetic
polarity ; hence the reaction of the iron in ships upon the compasses,
which have to be corrected and adjusted before a voyage, or else serious
errors in steering the vessel would occur, and there is no doubt that many
shipwrecks are due to this cause. No other metals beside iron, steel,
nickel, cobalt, and possibly manganese, can receive or retain magnetism
after contact with a magnet.

The remarkable effect of magnetism upon all matter, so ably investi-
gated by Faraday and others, will be explained in another part of this
book viz., in the article on Dia-Magnetism.

I":;,'. 200. JIagiciaii and bis loadstone-rock. Vide Fairy Talt.

211

CHAPTER XVI.

ELECTRO-MAGNETIC MACHINES.

THE experiments already described in illustration of some of the phe-
nomena of electro-magnetism are of such a simple nature that they
may be comprehended without difficulty ; but it is not such an easy
task to appreciate the curious fact of an invisible power producing
motion. It has already been explained that a copper or other metallic
wire conveying a current of electricity becomes for the time endowed
with a magnetic power, and if held
above, or below, or close to, a sus-
pended magnetized steel needle,
affects it in a very marked degree,
causing it to move to the right or
left, according to the direction of
the electric current ; and in order
to form some notion of the con-
dition of a metallic wire whilst the
electricity is passing through it,

v * Fig. 201. Portion of a square copper con-

the annexed diagrams may DC re- ductor, in which A B represents the direction

of the electricity, and the small arrows, c c c c,
the magnetic current or whirl at right angles

ferred to. (Figs. 201, 202.)

Dr. Rpget says: "The magnetic to^h^eiectricai' current, and exercising a
force which emanates from the elec- tangential action,
trical conducting wire is entirely
different in its mode of operation
from all other forces in nature with
which we are acquainted. It does
not act in a direction parallel to
that of the current which is pass-
ing along .the wire ,nor many plane
passing through that direction. It f orce .
is evidently exerted in a plane per-
pendicular to the wire, but still it has no tendency to move the poles of
the magnet in a right or radial line, either directly towards, or directly
from, the wire, as in every other case of attractive or repulsive agency.
The peculiarity of its action is that it produces motion in a circular
direction all round the wire that is, in a direction at right angles to
the radius, or in the direction of the tangent to* a circle described round
the wire in a plane perpendicular to it ; hence the electro-magnetic force
exerts a tangential action, or that which Dr. Wollaston called a vertigi-
nous or whirling motion.

513

BOY'S PLAYBOOK OF SCIENCE.

Dr. Faraday concluded that there is no real attraction or repulsion
between the wire and either pole of a magnet, the action which imitates
these effects being of a compound nature ; and he also inferred that the
wire ought to revolve round a magnetic pole of a bar magnet, and a

magnetic pole round a wire,
if proper means could be de-
vised for giving effect to
these tendencies, and for
isolating the operations of a
single pole. For the first
idea of electro-magnetic ro-
tation the world is indebted to
Dr. Wollaston; but Dr. Fara-
day, with his usual ingenuity,
was the first who carried out
the theory practically. The
rotation of a wire (conveying
a current of voltaic electri-
city) round one of the poles
of a magnet is well displayed
with the simple contrivance
devised by him. (Fig. 203.)
By a careful observation of
the complex action of an
electrified wire upon a mag-
netic needle, Dr. Faraday was
enabled to analyse the phe-
nomena with his usual pene-
Fig. 203. IT. A small bar magnet cemented into , i i , n .K;i:*.

a wineglass, the north pole being at K. A is a tration and exhaustive ability,
moyeable wire looped over the hook, which is the and he found, as Daniell
positive (+) pole of the battery; the free extremity
rotates round the pole of the magnet when the cur-
rent of electricity passes. The dotted line repre- _,, , . ,, , , .,, ,
sents the level of the mercury which the glass con- * lf the electrified wire is
tains. The electricity passes in at A, and out at P laced * perpendicular position,
the wire B, as shown by the arrows, c is connected an ? mad to approach towards one
with the negative, and with the positive, pole of P ole . of the needle the pole wi 11 not
the batterv ' be simply attracted or repelled, but

will make an effort to pass off on
one side in a direction dependent

upon the attractive or repulsive power of the pole ; but if the wire be continually made to
approach the centre of motion by either the one or the other side of the needle, the ten-
dency to move in the former direction will first diminish, then become null, and ulti-
mately the motion will be reversed, and the needle will principally endeavour to pass in
the opposite direction. The opposite extremity of the needle will present similar phe-
nomena in the opposite direction ; hence Dr. Faraday drew the conclusion that the direc-
tion of the forces was tangential to the circumference of the wire, that the pole of the
needle is drawn by one force, not in the direction of a radius to its centre, but in that of
a line touching its circumference, and that it is repelled by the other force in the opposite
direction. In this manner the northern force acted all round the wire in one direction,
and the southern in the opposite one. Each pole of the needle, in short, appeared to have
a tendency to revolve round the wire in a direction opposite to the other, and, conse-
quently, the wire round the poles. Each pole has the power of acting upon the wire by
itself, and not as connected with the opposite pole, and the apparent attractions and
repulsions are merely exhibitions of the revolving motions in different parts of their
circles."

FARADAY S EXPERIMENTS.

213

The same fact il-
lustrated at Fig. 203,
is also demonstratedin
a still more striking
manner by means of
wire bent into a
rectangular form, and
so arranged that whilst
the current of electri-
city passes, it is free
to move in a circle ;
and when the poles of
a magnet are brought
towards the electrified
wire, it may be at-
tracted or repelled at
pleasure, and in fact

Fig. 204 A A A A. The rectangular wire covered with silk becomes a magnetic

and varnished, one end of which being pointed, rests on the indicator and places

little cup B, connected with a covered wire passing down the ,-f 00 if f\c nnva e^\^

centre of the brass support to the binding screw c let into ltse V (" Carelully SUS-

ivory. D. The other extremity of the rectangular wire; this peilded) at right angles

being covered and varnished, is not in metallic contact with '
the end B, but is likewise pointed, and dips into the mercury -, ,-. - Q

contained in the large cup E E. The upper and lower cups Qian. (1: Ig. 2
do not touch, and are separated by ivory, marked by the
shaded portion, and the cup E E is in metallic communication <?

with the brass pillar, and is connected with the negative pole menlS 01 a magnetized

of the battery at r, whilst c is connected with the positive needle, and rotations

pole of the battery, and the electricity circulates round the ^f T T 7 ; T .po onrl msn-ripfc

wire in the direction of the arrows. When a bar magnet, N, is ?* wir nd ueib,

brought towards the wire, the latter is immediately set in brought about by the

motion, and by alternately presenting the opposite poles of agency of ail active
the magnet, the rectangular wire rotates freely round the J , e i , ,

CU p B> current or electricity,

have induced Sir David

Brewster to advance his admirable theory, which supposes the affection
of the mariner's compass needle, and all other suspended pieces of
steel, to be due to the agency of electrical currents continually circu-
lating around the globe ; and Mr. Barlow contrived the following expe-
riment in illustration of Brewster's theory. A wooden globe, sixteen
inches in diameter, was made hollow, for the purpose of reducing its
weight, and while still in the lathe, grooves one-eighth of an inch deep
and broad were cut to represent an equator, and parallels of latitude
at every four and a half degrees each way from the equator to the poles.
A groove of double depth was also cut like a meridian from pole to pole,
but only half round. The grooves were cut to receive the copper wire
covered with silk, and the laying on was commenced by taking the
middle of a length of ninety feet of wire one-sixteenth of an inch in
diameter, which was applied to the equatorial groove so as to meet in the
transverse meridian ; it was then made to pass round this parallel, re-
turned again along the meridian to the next parallel, and then passedround
this again, and so on, till the wire was thus led in continuation from pole

These Curious mOVC-

BOY'S PLAYBOOK OF SCIENCE.

to pole. The length of wire still remaining at each pole was returned
from each pole along the meridian groove to the equator, and at this
point, each wire being fastened down with small staples, the wires from
the remaining five feet were bound together near their common ex-
tremity, when they opened to form separate connexions for the poles of
a voltaic battery. When the battery was connected, and magnetic
needles placed m different positions, they behaved precisely as they
would do on the surface of the earth, the induction set up by the elec
trified wire being a perfect imitation of that which exists on the globe.

The opposite effect to that
already described viz., the
rotation of one pole of a
magnet round the electri-
fied wire, was also arranged
by Faraday in the following
manner. (Fig. 205.)

In the examination of the
magnetic phenomena ob-
tained from wires trans-
mitting a current of elec-
tricity, it should be borne
in mind that any conducting
medium which forms part of
a closed circuit i.e., any
conductor, such as charcoal,
saline fluids, acidulated
water, which form a link
in the endless chain re-
quired for the path of the
electricity, will cause a
magnetic needle placed near
it to deviate from its natu-
ral position.

These positions of the
electrified wire and the
magnetic needle are of
course almost unlimited,
and in order to assist the
memory with respect to the
fixed laws that govern these

Fig. 205. IT s. A little magnet floating in mercury
contained in the glass A A; the north pole is allowed
to float above the surface of the quicksilver, and the
south pole is attached to the wire passing through
the bottom of the glass vessel. The electricity passes
in at B, and taking the course indicated by the arrows
travels through the glass of quicksilver to the other
pole of the battery at c. Directly contact is made
with the battery, the little magnet rotates round the
electrified wire, w. The dotted line shows the level of
the mercury in glass.

relative movements, Monsieur Ampere has suggested a most useful
mechanical aid, and he says : " Let the observer regard himself as the
conductor, and suppose a positive electric current to pass from his head
towards his feet, in a direction parallel to a magnet ; then its north
pole in front of him will move to his right side, and its south pole to
his left.

" The plane in which the magnet moves is always parallel to the plane
in which the observer supposes liimself to be placed. If the plane of his

ELECTRO-MAGNETIC ROTATION.

215

chest is horizontal, the plane of the magnet's motion will be horizontal,
but if he lie on either side of the horizontally-suspended magnet, his
face being towards it, the plane of his chest will be vertical, and the
magnet will tend to move in a vertical plane."

This very lucid comparison will be seen to apply perfectly to the
direction of the rotations in Tigs. 203 and 205.

The whole of this apparatus is
made in the most elegant and
finished manner by Messrs.Elliott,
of 30, Strand; and by a modi-
fication of the latter arrangement
(Fig. 206), the opposite rotations
of the opposite poles of the mag-
nets round the electrified wire, are
shown in the most instructive
manner. The apparatus (Fig.
206) was devised oy the late Mr.
Francis Watkins, and consists of
two flat bar magnets doubly bent
in the middle, and having agate
cups fixed at the under part of
the bend (by which they are sup-
ported) upon upright" pointed
wires, the latter being fixed
upright on the wooden base of
the apparatus, and the magnets
turn round them as upon an axis.

Two circular boxwood cisterns,
to contain quicksilver, are sup-
ported upon the stage or shelf
above the base. A bent_ pointed wire is directed into the cup of each
magnet, the ends of which dip into the mercury contained in the box-
wood circular troughs on the stage. By using a battery to each magnet,
and taking care that the currents of electricity flow precisely alike, they
will then rotate in opposite directions.

Directly after the ingenious experiments of Faraday became known, a
great number of electro- magnetic engine models were constructed, and
many thought that the time was fast approaching when steam would
be superseded by electricity; and really, to see the pretty electro-
magnetic models work with such amazing rapidity, it might be supposed
that if they were constructed on a larger scale, a great amount of hard work
could be obtained from them. This idea, however, has been proved to be a
fallacy, for reasons that will be presently explained. The figure on p. 216
displays two of these engines, one of which represents the rotation
of electro-magnets within fovrjixed steel magnets, and the other the
rotation of steel magnets by the fixed electro-magnets. The latter
(No. 2) moves with such o;reat velocity, that unless the strength of the
battery is carefully adjusted, the connexions are soon destroyed. (Fig. 207.)

Fig. 206. A. Wire conveying the current
of electricity. B B. The magnets balanced on
points rotating round the wires.

21G

OY'S PLAYBOOK OF SCIENCE.

Fig. 207. No. 1 consists of vertical permanent steel magnets and horizontal soft-iron
electro-magnets which rotate.

No. 2 consists of two fixed soft-iron electro-magnets, and four bent permanent steel
magnets, which rotate, in both cases of course, only when connected with the battery.

Considering the prodigious power or pull of a soft-iron electro-
magnet, and its capability of supporting considerable weight, the most
reasonable expectations of success might be entertained with machines
acting by the direct pull. It was, however, discovered that they soon
became inefficient, from the circumstance that the repeated blows re-
ceived by the iron so altered its character, that it eventually assumed
the quality of steel, and had a tendency to retain a certain amount of
permanent magnetism, and thus to interfere with the principle of making
and unmaking a magnet. It was this fact that induced Professor Jacobi,
of St. Petersburg, after a large expenditure of money, to abandon
arrangements of this kind, and to employ such as would at once produce
a rotatory motion. The engine thus arranged was tried upon a tolerably
large scale on the Neva, and by it a boat containing ten or twelve
people was propelled at the rate of three miles an hour.

Various engines have been constructed bv Watkins, Botta, Jacobi,
Armstrong, Page, Hjorth ; the engine made by the latter (Hjorth) ex-
cited much attention in 1851-52, and consisted of an electro-magnetic
piston drawn within or repelled from an electro-magnetic cylinder ; and
by this motion it was thought that a much greater length of stroke
could be secured than by the revolving wheels or discs, but the loss of
power (not only in this engine, but in others) through space is very
great, and the lifting power of any magnet is greatly reduced and

ELECTRO-MAGNETIC MACHINES. 217

altered at the smallest possible distance from its poles. This loss of
power is therefore a great obstacle in the way of the useful application
of electro-magnetic force, and can be appreciated even with the little
models, all of which may be stopped with the slightest friction, although
they may be moving at the time with great velocity.

In the second place, supposing the reduced force exerted by the two
magnets, a few lines apart, was considered available for driving
machinery, the moment the magnets begin to move in front of one
another there is again a great loss of power, and as the speed increases,
there is curiously a corresponding diminution of available mechanical
power, a falling-off in the duty of the engine as the rotations become
more rapid. In the third place, the cost of the voltaic battery, as com-
pared with the consumption of coal in the steam-engine, is very startling,
and extremely unfavourable to electro-magnetic engines.

Mr. J. P. Joule found that the economical duty of an electro-magnetic
engine at a given velocity and for a given resistance of the battery is
proportioned to the mean intensity of the several pairs of the battery.
With his apparatus, every pound of zinc consumed in a Grove's battery
produced a mechanical force (friction included) equal to raise a weight
of 331,400 pounds to the height of one foot, when the revolving magnets
were moving at the velocity of eight feet per second. Now, the duty of
the best Cornish steam-engine is about one million five hundred thousand
pounds raised to the height of one foot by the combustion of each pound
of coal, or nearly five times the extreme duty that could be obtained
from an electro-magnetic engine by the consumption of one pound of
zinc. This comparison is therefore so very unfavourable, that the idea
of a successful application of electricity as an economic source of power,
is almost, if not entirely abandoned.

By instituting a comparison between the different means of producing
power, it has been shown that for every shilling expended there might be
raised by

Pounds.

Manual power . . . 600,000 one foot high in a day.

Horse 3,600,000

Steam 56,000,000

Electro-magnetism . 900,000

A powerful magnet has been compared to a steam-engine with an
enormous piston but with an exceedingly short stroke. Although
motive power cannot be produced from electricity and applied success-
fully to commercial purposes, like the steam-engine, yet the achievements
of the electric telegraph as an application of a small motive power must
not be lost sight of, whilst the fall of the ball at Deal and other places,
by which the chronometers of the mercantile navy are regulated, as also
the means of regulating the time at the General Post Office and various
railway stations, are all useful applications of the power which fails to
compete in other ways with steam.

218

CHAPTER XVII.

THE ELECTRIC TELEGRAPH.

THE engineering and philosophical details of this important instrument
have grown to such formidable dimensions, that any attempt (short of
devoting the whole of these pages to the subject) to give a full account
of the history and application of the instrument, the failures and successes
of novel inventions, and the continued onward progress of this mode
of communication, must be regarded as simply impossible, and there-
fore a very brief account of the principle only will be attempted in these
pa^es.

For the complete history of the discovery and introduction of the
principle of the Electric Telegraph the reader is referred to the Society
of Arts Journal (Nos. 348-9, vol. viii.), where it is stated that it is half
a century, dating from August, 1859, since the first galvanic telegraph
was made. "It was the Russian Baron Schilling's electro-magnetic
telegraph which, without its being known to be his, was brought to
London, and caused the establishment of the first practically useful
telegraph lines, not only in Great Britain, but in the world." Dr.
Hamel says : " The small sprout nursed on the Neva, which had been
exhibited on the Rhine, and thence brought to the Thames, grew up
here to a mighty tree, the fruit-laden brandies of which, along with
those from trees grown up since, extend more and more over the lands
and seas of the Eastern hemisphere, whilst kindred trees planted in the
Western hemisphere have covered that part of the world with their
branches, some of which will, ere long, be interwoven with those in our
hemisphere."

The first telegraph line in England was constructed by Mr. Cooke
from Paddington along the Great Western Railroad to West Drayton
in 1S38-39 ; and it must be remembered that it was in February, 1837,
that Mr. Cooke first consulted Professor Charles Wheatstoue, having
previously visited Dr. Faraday and Dr. Roget, and on the 19th
November, 1837, a partnership contract was concluded between Messrs.
Cooke and Wheatstone.

To the distinguished philosopher, Professor Wlieatstone, the merit of
the ingenious construction of the vertical-needle telegraph is due;
whilst Mr. Cooke's name will always be associated with the practical
establishment of the first telegraph lines in England. The first line in
the United States, from Washington to Baltimore, was completed in
1844, being arranged and worked by Professor Morse.

In British India, in April and "May, 1839, the first long line of
telegraph, twenty-one miles in length, and embracing 7000 feet of
river surface, was constructed by Dr. (now Sir William) Q'Shaughnessy

THE ELECTRIC TELEGRAPH. 219

The construction of the electric telegraph may be considered under
three heads :

1st. The Battery, the motive power.
2nd. The Wires, the carriers of the force.
3rd. The Instruments to be worked the bell and the needle telegraph.

THE BATTERY.

The construction and rationale of the batteries generally in use have
been explained in another part of this work ; those used for telegraphic
purposes consist of one or more couples, of which zinc is one, the second
being copper, silver, platinum, or carbon. Each couple is termed an
element, and a series of such couples a battery.

The batteries employed chiefly on the English lines consist of a plate
of cast-zinc four inches square and T 3 6-ths of an inch thick, attached by a
copper strap one inch broad to a thin copper plate four inches square.
The zinc is well amalgamated with mercury. Twelve of these couples
are arranged in a trough of wood, porcelain, or gutta-percha, divided by
partitions into twelve water-tight cells, 1 men wide. The zinc and
copper preserve the same order and direction throughout, and when
arranged, the trough is filled with the finest white sand, and then
moistened with water previously mixed with five per cent, by measure of
pure sulphuric acid. This mode of applying the acid is the clever prac-
tical improvement of Mr. Cooke, and prevents any inconvenience from
the spilling of the acid, and at the same time renders the battery quite
portable. The voltaic arrangement thus prepared is found to remain
in action for several weeks, or even months, with the occasional addition
of small quantities of acid, and answers well for working needle tele-
graphs in fine and dry weather. In fogs and rains, at distances ex-
ceeding 200 miles at most, their action is not so perfect, and a vast
number of couples must be employed, 144 to 288 being frequently in
use. In Erance, Prussia, and America, sand batteries do not appear to
answer, and Daniell's arrangement is preferred. Sixty couples suffice in
France for some of the long lines viz., from Paris to Bordeaux, 284
miles ; Paris to Brussels, 231^ miles ; and in fact, the advantages of
the Daniell's battery have become so apparent, that they are now being
used on English lines. In Prussia, Bunsen's carbon battery is much
used ; in India, a modification of Grove's battery is preferred, the zinc
being acted upon by a solution of common salt in water. Two of these
elements were found sufficient to work a line of forty miles totally un-
insulated, and including the sub-aqueous crossing of the Hooghly River,
6200 feet wide.

The continual energy of the battery, whatever may be its construc-
tion, depends on the circulation of the electricity, the object being to
pass the force from the positive end of the series through the wires,
back again to the negative extremity of the voltaic series.

The wire (the carrier of the force) must be continuous throughout,
unless, of course, water or earth forms a part of the endless conducting
chain.

220

BOY'S PLAYBOOK OF SCIENCE.

THE CONDUCTING WIRES.

These roads for the electricity may be of any convenient metal, and
the one preferred and used is iron, which is well calculated from its
great tenacity (being the most tenacious metal known) and cheapness

to convey the electricity, al-
though it is not such a good
conductor as copper, and
offers about six times more
resistance to the flow of the
current than the latter metal.
The wire does not appear to
be made of iron, because
it is galvanized or passed
through melted zinc, which
coats the surface anddefends
it from destructive rust,
at the same time does not
destroy its valuable property
of tenacity or power of re-
sisting a strain. About one
ton of wire is required for
every five miles, and to sup-
port this weight, stout posts
of fir or larch are erected
about fifty yards apart, and
from ten to twenty-five feet
high . At e verv quarter
mile, on many lines, are
straining - posts with
ratchet wheel winders,
for tightening the
wires. On some of the
lines the wires are at-
tached to the posts by
side brackets carrying
the insulators invented
by Mr. C. V. Walker,
which are composed
of brown salt-glazed
stoneware of the hour-
glass shape, as shown
in the drawing. (Fig.
208.)

There are some ob-
jections to the hour-
glass .insulators, and
they have been modi-
Fig. 209. Clark's insulator. fied by Mr. Edwin

Fig. 208. Walker's insulator.

THE ELECTKIC TELEGKAPH.

221

Clark, who employs a very strong stone-ware hook open at the side,
so that the wire can be placed on the hook without threading, and the
hooks can be replaced in case of breaking, without cutting the tele-
graph wire, which is securely fastened to each insulator by turns of
thinner wire. An inverted cap of zinc is used to keep the insulator
dry. (Fig. 209.)

In India the conductor is rather a rod than a wire, and weighs about
half a ton per mile ; it is erected in the most substantial manner, and
many miles of the rod are supported on granite columns, other portions
on posts of the iron-wood of Arracan, or of teak.

The number of wires required by the electric telegraph often puzzles
the railway traveller, and people ask why so many wires are used on
some lines and so few on others ? The answer is very simple : they are
for convenience. Two wires only are required for the double needle
telegraph, and one for the single needle instrument. But as so many
instruments are required at the terminal stations, an increased number
of wires, like rails for locomotives, must be provided; thus, on the
Eastern Counties, seven wires are visible, and are thus employed. The
two upper wires pass direct from London to Norwich ; the next pair
connect London, Broxbourne, Cambridge, Brandon, Chesterfield, Ely;
the third pair all the small stations between London and Brandon ; and
the seventh wire is entirely devoted to the bell.

If the earth was not a conductor of electricity, and employed in the
telegraphic circuit, four wires would be required for the double needle
telegraph, and two for the single instrument. To understand this, let
us suppose a battery circuit extending from Paddington to the instru-
ment at Slough, and the wire returning from Slough to Paddington, it
is evident that one wire would take the electricity to Slough, and the
other return it to London, as in the diagram below. (Fig. 210.)

LONDON

SLOUGH

Fi#. 210. A. The battery. B. The instrument. The arrows show the passage of the
electricity to the single needle telegraph instrument by one wire, and the return current
fly the other.

If the whole of the return wire is cut away except a few feet at each
end, which are connected by plates of copper with the damp earth, the
current not only passes as before, but actually has increased m intensity,
and will cause a much more energetic movement of the needle in the
telegraph instrument. (Fig. 211.) These plates are called "Earth
Plates ;" and Steinheil, in 1837, was the first who proved that the earth
might perform the function of a wire.

222 BOY'S PLAYBOOK OF SCIENCE.

Fig. 211. A. The battery. B. The instrument, c. Earth plate at Slough. D. Earth
plate at London. The arrows show the direction of the electric current.

It must be obvious that a message may be received at any station
without a battery, but in order to be able to return an answer, every
station must have its own battery.

Ingeniously-constructed lightning-conductors are attached to the posts
which carrv the wires, so that in case of a storm, the natural electricity
is conveyed to the earth, whilst the voltaic electricity artificially pro-
duced pursues its own course without deviation. Protectors are also
required for the instruments at the stations, and the plan devised by
Mr. Highton is thus described by the inventor :

" A portion of the wire circuit say for six or eight inches is enve-
loped in blotting-paper or silk, and a mass of metallic filings, in con-
nexion with the earth, is made to surround it. This arrangement is
placed on each side of the telegraph instrument at a station. When a
flash of lightning happens to be intercepted by the wires of the tele-
graph, the myriads of infinitesimally fine points of metal in the filings
surrounding the wire at the station, on having connexion with the
earth, at once draw off nearly the whole charge of lightning, and carry
it safely to the earth."

THE INSTRUMENTS TO BE WORKED THE BELL AND THE TELEGRAPH.

The bell or alarum resembles in construction that of an ordinary
clock, and is in fact a piece of clockwork wound up and ready to ring
a bell, when the detent or preventive is removed. The detent is con-
nected with a piece of soft iron placed before an electro-magnet, and
directly the current passes, the electro-magnet attracts the soft piece of
iron attached to a perpendicular lever which the bell-crank lever rests
upon ; the detent is removed, and the bell rings, and again stops when
the current of elsctricity ceases to pass.

One of the most simple alarum clocks is a common American clock,
wound up daily. A small electro-magnet surrounded with thick wire
is placed below a moveable piece of tinned iron, so that when this is
attracted, the fly of the clock is released, and its bell tolls unceasingly

THE BELL OE ALARU:

223

the magnet is excited. This
arrangement is employed by Sir W.
O'Shaughnessy in the Indian tele-
graph system. (Fig. 212.)

It will readily be comprehended
from this description that the alarum
is sounded by ordinary mechanism,
and that the duty of the current of
the electricity is simply comprised in
the act of removing the lever and
liberating machinery, which may be
large or small; and if it were
thought necessary, the bells of the
great clock-tower of the Houses of
Parliament, which chime the quar-
ters, or even "Big Ben" himself
(when his constitution is restored),
could be rung by a person at York
or Edinburgh, supposing wires, bat-
teries, and a powerful electro-
magnet with a detent mechanism
for the bells, were properly arranged
and connected with the. clock-
work.

la certam cases, Mr. Charles V. *
vy alker states that a single and dis- liberates the detent,
tinct wire is used for the bell only,
with his special mechanism, called the ringing key. If the bell was al-
ways on the same wire as the needle-coil, the bell would not only call the
attention of, but seriously annoy the clerk (unless, of course, he hap-
pened to be a very deaf person) by its ringing whilst he was reading
the signals of the needle. The nuisance is prevented by what is termed
joining over or making the short circuit in fact, by providing for the
current a shorter and much more capacious road to the needle coil than
by going through that of the bell-magnet, which is made with very
fine wire; and the control of the short circuit is put in the hand's
of the clerk.

COOKE AND WHEATSTONE'S DOUBLE NEEDLE TELEGRAPH.

The principle of this instrument, as already explained, is involved in
the elementary experiment of Oersted viz., the deflection of a mag-
netic needle from the inside of a coil of wire conveying a
current of electricity, and as it is difficult to give a good de-
scription and drawing of the interior of the instrument that can
really be understood, it may be sufficient to state that the handles
give the operator the power of reversing the current of electricity,
so that the needles are deflected with, the utmost certainty to

224:

BOY'S PLAYBOOK OF SCIENCE.

one side or the other, cither separately or simultaneously. (Eig.
2] 3.)

Fig. 213. The letters of the alphabet, figures, and a variety of conventional signals, are
indicated by the single and combined movements of the needles on the dial. The left-
halid needle moving once to the left indicates the +, which is given at the end of a word.
Twice in the same way, A ; thrice, B ; first right, then left, c ; the reverse, D. Once direct
to the right, E ; twice, F ; thrice, G. In the same order with the other needle for H, i, K,
t, M, H, o, P. The signals below the centre of the dial are indicated by the parallel move-
ments of both needles simultaneously. Both needles moving once to the left indicate E ;
twice, s ; thrice, T. First right, then left with both, u ; the reverse, v. Both moving once
to the right, \v ; twice, x ; thrice, T. The figures are indicated in the same way as the
letters nearest to which they are respectively placed. To change from letters to figures the
operator gives H, followed by the +, which the recipient returns to signify that he under-
stands. If, after the above signs (H and +) were given, c B H L were received, 1845 would
be understood. A change from figures to letters is notified by giving i, followed by the + ,
which the recipient also returns. Each word is acknowledged. If the recipient under-
stand, he gives B ; if not, the +, in which case the word is repeated. Attention to a com-
munication by this instrument is called by the ringing of a bell (of any size), which is
effected through the agency of an electric current. The upper case contains the bell.

Sir "W. O'Shaughnessy, in his excellent work on the electric telegraph
in British India, gives a description of a telegraphic instrument of re-
markable simplicity, which is successfully employed in India, and is

O'SHAUGHNESSY'S SIMPLE TELEGRAPH INSTRUMENT. 225

highly spoken of by Mr. E. V. Walker and other gentlemen practically
acquainted with the working of telegraphs. It consists of a coil of fine
wire on a card or ivory frame, a magnetic needle with a li^ht index of
paper pasted across it ; two stops of thin sheet lead to limit the vibra-
tions of the index ; a supporting board eight inches square, and a square
of glass in a frame of wood, or a common glass tumbler placed over it as
a shade, to prevent the index being moved by currents of air. It is
stated that the office boys, with the assistance of a native Indian
carpenter, make up these telegraphs at a price not exceeding two
shillings each.

In England of course they would be more expensive; but the
simplicity and perfection of the arrangement are so much to be com-
mended that we give the details for the benefit of those boys who might
wish to establish a telegraph on a small scale for amusement.

THE FRAME.

This is a piece of mahogany eight inches square and one inch thick,
with a hollow groove cut in its centre two inches and a half long, half an
inch wide, and a quarter of an inch deep ; a ledge of the same wood
one inch wide and half an inch deep surrounds the frame, leaving the
inner surface seven inches square ; this is stained black with ink to
make the motions of the index more conspicuous.

THE COIL.

This consists of fifty feet of the finest silk-covered copper wire wound
on a frame of card two inches long, half an inch broad, three-eighths
deep in the open part.

An edge or flange of card, three-eighths of an inch wide, is attached
to it at each side to keep the wire in its place. The frame may be of
thin wood or ivory, and the winding of the wire commences at the
lower left corner, and it is coiled from left to right, as the hands of a
watch would move in the same plane. (Fig. 214.)

Fig. 214 ThecoiL

Two inches of each end of the coil wire are now stripped of their silk
covering by being rubbed with sand-paper. The coil is mounted in the
frame by inserting its lower edge or flange in the groove, so that the
lower part or floor of the inside of the coil is level with that of the

226

BOYS PLAYBOOK OF SCIENCE.

frame, as shown below, and it is now ready to receive the magnetized
needle. (Fig. 215.)

Fig. 215. The coil fitted into frame.
THE NEEDLE.

This is one inch long, one-twelfth of an inch wide, of the thinnest
steel, and fitted with a little brass cap turned to a true cone to receive
the point on which it is balanced. These needles are of hard tempered
steel, and are magnetized by a single contact with the poles of an
electro-magnet or other ordinary powerful magnet.

The magnet is now to be balanced on a steel point one-eighth of an
inch high ; these are nipped oif with cutting pliers from common sewing
needles, and soldered into a slip of thin copper three inches long, half
an inch wide. (Fig. 216.)

Fig. 216. A. The needle. B. The point on the slip of copper.

As the north end of the needle will be found to dip, it is advisable to

counteract this by touching the south end with a little shell-lac varnish,

which dries rapidly, and soon restores the needle to a perfect equilibrium.

The needle is completed for use by fixing to it an index of paper (cut

from glazed letter paper) two inches long, tapering from one-eighth of

an inch to a point, and
fastened at rignt angles
on to the needle with
lac varnish, so as to
be truly balanced, and
pointing the sharp end

to the east, when the

J needle placed on the
point settles due north
and south, its north
pole being opposite the
observer's right hand,
the observer facing west.
Fig. 217. The needle with the paper index. (Fig- 217.)

O'SHAUGHNESSY'S SIMPLE TELEGRAPH INSTRUMENT. 227

The coil frame is placed north and south, and the needle is now intro-
duced by sliding the end of the slip of copper into the opening in the
frame.

To limit the vibrations of the pap_er index a stop is placed at each
side. The stops are made of a strip of thin sheet-lead or copper, a
quarter of an inch broad, one inch and a half long, and turned up at a
right angle, so that one inch rests on the board and half an inch is
vertical. For ordinary practice these stops are placed each at half an
inch from the index.

The telegraph is placed in a box, which may have a piece of looking-
glass in the lid, so that the readings can be taken with the needle in the
vertical instead of the horizontal position, if required. (Fig. 218.)

A /

B //

M \\

!C" HI

N \\\

D ////

\\\

E V

P A

'K W

Q AV

e MII

R A\\

H W/

S. M

U \!\

T N

K W

U V /A\

W W

Y W/

X IV

zv////

Fig. 218. Box containing the telegraph, with the looking-glass hi the lid. A small
steel magnet is placed on or near the frame, if required, the south pole of this magnet
oeing opposite to the north pole of the needle in the telegraph coil. The bar is four inches
long, half an inch broad, three-sixteenths of an inch thick, and it is only used to counteract
any local deviation which may arise in using the instrument with miles of wire. It would
not be required under ordinary circumstances. The alphabet used is shown to the left.

The ends of the fine wire of the telegraph coil are joined on to the
wires from the reversing instrument, and this is connected with a voltaic
series of one or more elements, so that by the employment of the
reverser the needle is caused to move right or left at pleasure. The

228 BOY'S PLAYBOOK OF SCIENCE.

white paper index on the black ground can be followed with the greatest
certainty, and Sir W. O'Shaughnessy states that with this instrument a
telegraph clerk may read at the rate of twenty words per minute with a
double needle wire, being equal to forty words per minute.

THE EEVERSEB,

consists of a block of wood, two inches and a half square, in which
four hollows, half an inch deep, are cut, and these hollows are joined
diagonally by copper wires let into the substance of the wood, and most
carefully insulated from each other by melted cement, but exposing
a clean metallic surface in each cell, which is filled with mercury.
(Tig. 219.)

Pig. 219. Block of wood with four holes ; the positive terminal is connected with the
holes A and B, the negative with c and u ; the hollows are filled with mercury. T T are the
wires from the telegraph box, and it is obvious that by dipping them alternately into c B
and A D the current is reversed, and the needle deflected right or left at pleasure.

In practice a more elaborate reverser is employed, but to demonstrate
the principle the simple block above described is quite sufficient.

With the telegraph placed at the top of a house, or in a distant
cottage, and a single cell of Grove's battery, or at most two, for any
short distances, with the reverser, messages may be passed with great
rapidity from the bottom of the house to the top, or from a mansion to
the lodge, it being understood that a battery, reverser, and telegraph,
are required at both places where messages are received and answered;
but if no answers are required, the battery and reverser are placed at
one end of the wire in the house, and the telegraph at the other ex-
tremity in the cottage, and earth plates may be arranged to return the
current, or another wire used for that purpose. *

Whilst lauding to the utmost the invention of the electric telegraph,
we must remember " there is nothing new under the sun," and that
after all Nature claims the principle of telegraphing, and with the silent
gesture, the speaking eye, interpreted and answered by others, she pro-
claims herself to be the originator of communication by signs. Whilst

THE ELECTRIC TELEGRAPH.

229

the language of flowers, and the mournful requirements of the deaf and
dumb in the use of the finger alphabet, show how readily man has
adopted the important principle, till he has brought it to the highest
state of perfection in the electric telegraph.

When the telegraph was first adopted on the Great "Western Railway,
the most ridiculous ideas were formed of its capabilities, and many persons
firmly believed that the wires were used for the purpose of dragging
letters and different articles from station to station. " Wife," said a man,
looking at the telegraph wires, " I don't see, for my part, how they send
letters on them wires, without tearin' 'em all to bits." "Oh, you
stupid!" exclaimed his intellectual spouse ; "why, they don't send the
paper: they just send the writin' in a fluid state."

Fig. 220. One of the ideas of telegraphic communication.

230 BOY'S PLAYBOOK OF SCIENCE.

CHAPTER XVIII.

RUHMKORFF'S, HEARDER'S, AND BENTLEY'S COIL APPARATUS.

IN the course of the popular articles on frictional and voltaic electricity,
it has already been mentioned that whilst the intensity effects such as
the capability of the spark to pass through a certain thickness of air,
or the production of the peculiar physiological effect of the shock
belong especially to the phenomena of frictional electricity, they are
not apparent with the quantity effects, such as may be produced oy an
ordinary voltaic battery, unless the latter consists of an immense
number of elements, such as the famous water battery of the late
respected Mr. Crosse, which consisted of two thousand five hundred
pairs of copper and zinc cylinders, well insulated on glass stands, and
protected from dust and light. If, however, the feeble intensity current
of voltaic electricity, from four or five elements, is permitted to pass into
a coil of a peculiar construction, fitted with a condenser, and manu-
factured either by Ruhmkorff of Paris, or Mr. Hearder of Plymouth, then
the most remarkable effects are producible, which have created quite a
new and distinct series of phenomena, and further established in the
most satisfactory manner the connexion between the electricities derived
from friction and chemical action.

The construction of these coils does not differ very materially, and
great merit is due to Messrs. Ruhmkorff, Hearder, and Bentley, who
have separately and independently worked out the construction of the
most formidable machines of this class. In a letter to the author
Mr. Bentley says :

" I commence the formation of my coil by using as an axis an iron
tube ten inches long and half an inch diameter ; around this is placed a
considerable number of insulated iron wires the same length as the tube,
and sufficiently numerous to form a bundle one inch and three quarters
diameter. This core is wrapped carefully in eight or nine layers of
waxed silk, the necessity of which will be obvious presently.

" My primary helix, which is formed of thirty yards of No. 14 cotton-
covered copper wire, is wound carefully on this core, and consists of
two layers, each layer being carefully insulated one from the other by
waxed silk, for I find that if a wet string or fine