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CHEMICAL LECTURE
EXPERIMENTS

FRANCIS GANO BENEDICT, Ph.D.

INSTRUCTOR IN CHEMISTRY IN WESLEYAN UNIVERSITY

Neto gotfe
THE MACMILLAN COMPANY

LONDON: MACMILLAN & CO., Ltd.
1901

Nortooorj $«m

J. S. Cuihing & Co. — Berwick & Smith
Norwood Mass. U.S.A.

3Co tfje iWemorg of
JOSIAH PARSONS COOKE

FOR FORTY-THREE YEARS ERVING PROFESSOR OF CHEMISTRY
AND MINERALOGY IN HARVARD UNIVERSITY

THIS BOOK IS DEDICATED

AS A TRIBUTE TO AN INSPIRING TEACHER

THE A UTHOR

PREFACE

The demonstration of chemical phenomena on the lecture
table, though originally strongly imbued with an element
of mysticism inherited from the hermetic art, has always
been considered an essential phase of chemical instruction.
After chemistry was placed on a broader basis by Lavoisier,
and the black art converted to a science, experimental lec-
tures still remained a legitimate factor in presenting the
subject. Soon text-books and class recitations and later
laboratory exercises for the student supplemented the lec-
ture, and with the introduction of the latter a tendency to
neglect the experimental lecture developed. Laboratory
exercises, however great their influence in developing the
experimental side of teaching the science, have their limita-
tions, experimentally and educationally, and cannot sup-
plant the experimental lecture, for it is in the lecture,
and there only, where each experiment stands out clearly
defined and unattended by the distractions necessarily
accompanying laboratory exercises, that the first accurate
observations of chemical phenomena can be made by
students.

The late Professor Josiah P. Cooke, though one of the first
to introduce laboratory exercises into the educational insti-
tutions of this country, said, nevertheless, "Experimental
lectures are, I am convinced, much the best way of pre-
senting these subjects [Chemistry and Physics] as syste-
matic portions of knowledge." His belief in the method
gave rise to that grand series of experimental lectures

vii

Vlll PREFACE

delivered for more than forty years at Harvard College;
a course of lectures whose stimulus to chemical study and
research has influenced so many of the prominent teachers
of chemistry in this country.

The most versatile and fluent chemical lecturer of his
day, the late Professor Victor Meyer, was another great
advocate of the experimental lecture. The breadth and
scope of his lectures gave unusual opportunities for experi-
ments, and his contributions to experimental science were
of so brilliant and striking a character as to infuse new life
into the chemistry of the lecture room.

Constant attendance on Professor Cooke's lectures for
five successive years gave the first impulse to the prepara-
tion of this book, an impulse which wTas, through my inter-
course with Professor Meyer, stimulated into a purpose.

The object of this book is primarily to furnish teachers
with a large number of reliable lecture experiments. That
these experiments require in many cases different treat-
ment from those performed in the laboratory will be obvi-
ous when it is considered that the demonstrations on a
lecture table must be of sufficient magnitude and of a
character marked enough to enable the phenomena to be
observed at as great a distance as possible.

The two or three previous works treating of this branch
of experimental science are remarkably complete and ex-
haustive, but there is one serious hindrance to their ready
adoption in most colleges and schools, i.e., the requirement
of elaborate and costly apparatus and the assumption of
great proficiency on the part of the teacher in glass-blowing
and general manipulation. To overcome this difficulty all
experiments requiring especially elaborate apparatus have
here been rigorously excluded. By adhering to this rule
some familiar experiments have doubtless been omitted,
but it has been possible in many cases to substitute an

PREFACE IX

equivalent experiment. As most of the apparatus required
is that commonly used by students, it is considered that
the large majority of experiments here presented may be
easily performed with an ordinary laboratory equipment.

As an aid to the inexperienced the descriptions of the
apparatus and the manipulations are given in considerable
detail together with many suggestions regarding the prepa-
ration and care of apparatus. Experimental manipulation
is not, however, merely a matter of rules, and, while the
suggestions given will, it is hoped, prove of value to the
inexpert, the fullest confidence so essential to successful
experimenting must be obtained by experience.

With but few exceptions the elements are treated in the
order of their arrangement in the periodic classification.
An attempt has been made to have the cross-references in
the index so complete that a list of experiments on any
subject may be readily obtained.

The material here presented has been prepared with
reference also to its use by students desiring collateral
reading in connection with experimental lectures. As an
elaboration of the laboratory manual, the book may also be
used by students for the preparation of many compounds
not considered in elementary text-books.

The great number of contributors to the evolution of the
phase of experimental chemistry treated in this book ren-
ders it impossible to designate with any degree of justice
the originators of the very large majority of experiments
of this class, and rather than encumber the book with mul-
titudinous references I prefer personally to make no espe-
cial claim to originality. My indebtedness to the former
works pertaining to this subject, all of which have been
freely drawn upon, is inadequately expressed by enumera-
tion in the list on p. 419.

In performing the experiments, which have all had my

X PREFACE

personal supervision, I have enjoyed the skilful assistance
of Drs. H. M. Smith and J. F. Snell and Mr. W. S. Baker.
I am deeply indebted to Professor W. P. Bradley, who has
rendered me signal service in the many suggestions born of
his long experience in chemical manipulation. I would
also express my thanks to Professor W. 0. Atwater, who
generously placed his magnificent chemical library at my
disposal. The index was prepared by Mrs. Cornelia Golay
Benedict, whose assistance in this and in many other ways
has made the writing of this book possible.

The object of this book will have been attained if it sup-
plements to some extent the admirable works of Arendt,
Heumann, and JSTewth in their task of stimulating the
demonstration of chemical phenomena.

F. G. B.

Wesleyan University,

mlddletown, connecticut.

TABLE OF CONTENTS

PAGB

Introduction 1

Oxygen 8

Ozone 31

Hydrogen 39

oxyhydrogen gas and water 62

Hydrogen Peroxide 74

Chlorine 80

Hydrochloric Acid 89

Chlorine Monoxide . .98

Hypochlorous Acid 99

Chlorine Peroxide ......... 101

Chloric Acid 104

Perchloric Acid 104

Bromine 106

Hydrobromic Acid 108

Iodine . 112

Hydriodic Acid 117

Iodic Acid 124

Hydrofluoric Acid 127

Sulphur 130

Hydrogen Sulphide 135

Hydrogen Persulphide ........ 147

Sulphur Monochloride 148

Sulphur Dioxide and Sulphurous Acid .... 149

Hydrosulphurous Acid 157

Xll TABLE OF CONTENTS

PAGE

Sulphur Trioxide 158

Sulphuric Acid 164

Selenium 177

Nitrogen 180

Atmospheric Air 186

Ammonia . 189

Nitrogen Chloride 204

Nitrogen Iodide 205

Hydroxylamine 207

Nitrous Oxide 208

Nitric Oxide 211

Nitrous Anhydride and Nitrous Acid 218

Nitrogen Peroxide 219

Nitric Acid 222

Hydrazine 228

Hydrazoic Acid 229

Phosphorus 232

Hydrogen Phosphide 249

Phosphonium Iodide 258

Phosphorus Trichloride 259

Phosphorus Pentachloride 261

Phosphorus Bromides 263

Phosphorous Acid 264

Hypophosphorous Acid . . . . . * 266

Phosphorus Pentoxide and Phosphoric Acids . . . 266

Arsenic 268

Antimony 273

Boron 278

Silicon 283

Carbon 291

Carbon Monoxide 296

Carbon Dioxide . 303

Carbon Disulphide 317

TABLE OF CONTENTS xiii

PAGE

Methane 319

Ethylene 320

Acetylene 323

Illuminating Gas 324

Structure of Flame 328

Reciprocal Combustion 339

Sodium 349

Potassium 354

Ammonium Compounds 358

Calcium 363

Strontium and Barium 367

Magnesium 371

Zinc and Cadmium 377

Mercury 381

Copper 384

Silver 388

Aluminium 391

Tin 396

Lead 400

Bismuth 404

Chromium • 405

Iron 409

Cobalt and Nickel 413

Appendix 419

Index 423

CHEMICAL LECTURE EXPERIMENTS

INTRODUCTION

Owing to the independent nature of each experiment the
description is in most instances prefaced with a short state-
ment of the nature of the reaction under consideration.
The equations have been given as far as practicable, and
where the reaction is not regular and the product is of a
complex nature, the fact that the equation represents the
general reaction only is indicated by its being followed by
an interrogation mark enclosed in brackets.

To facilitate the preparation of experiments, a list of the
apparatus and the chemicals required has been appended to
experiments demanding anything not ordinarily found on a
lecture table. Just how extensive such a list should be has
been a matter of considerable question, and to avoid undue
repetition it is assumed that burners, test-tubes, retort
stands, pneumatic trough, and such general apparatus, as
well as the common reagents, are either on the lecture table
or within reach.

Where approximate quantities of solid substances are
required, it has been the custom hitherto to make reference
to the size of a "pea," "walnut," "'hazelnut," (ieggf^ and
so forth. The latitude thereby allowed in the selection of
the quantity of material is often much greater than that
intended by the writer, owing to the variations in the con-
ceptions of the different sizes by individual experimenters.
Believing that this phraseology is unsatisfactory, the

2 CHEMICAL LECTURE EXPERIMENTS

approximate diameter of an equivalent spherical mass is
here used. A " 7 mm. piece" of sodium would mean a mass
whose general form if spherical would have an approximate
diameter of 7 mm. As a matter of fact a piece of this
dimension would ordinarily be designated as being the
" size of a pea." A paper millimeter scale pasted to the
table or wall will materially aid in estimating the various
sizes.

Under the various subjoined heads suggestions are made
regarding the general apparatus required.

Weights and measures. — The metric system of weights
and measures alone is used. A meter stick and some cheap
scales with a set of metric weights should be at hand.
Sheets of paper of convenient size to place on the scale
pans should be cut ready for use in weighing out solids.
Corrosive solids should be weighed in previously tared watch-
glasses. Liquids are best measured in the several sizes of
graduated cylinders.

Glassware. — All glassware except test-tubes should be
made of Jena glass. The use of this glassware is deemed
of such importance that it is especially emphasized in the
descriptions of many experiments. By thus including it in
the specifications of apparatus, it must not be thought that
other forms of glass will not serve the purpose, though the
advantage always lies with the apparatus constructed with
Jena glass.

It will be observed that all glassware required is of the
nature ordinarily used in the laboratory. The Erlenmeyer
form of flask is especially recommended, and in general is
to be substituted for the older form, as it is much easier to
clean, and the greater area of the bottom renders it more
stable and results in a more even distribution of heat.
Bulb-tubes are especially advantageous, but may in most

INTRODUCTION 3

cases be replaced by short pieces of combustion-tube, though
in this case if the substance to be acted upon is a liquid or
an easily melted solid, it should be placed in a porcelain
boat.

Test-tubes and ignition-tubes. — A rack should be filled
with clean, dry test-tubes of different sizes, and an assort-
ment of hard-glass test-tubes or ignition-tubes should be
provided. A plate containing clean white sand is useful to
lay ignition-tubes on, and to place under heated tubes to
catch anything that might fall.

Kipp gas generators. — Though faulty in principle, the
Kipp generator, or one of its various modifications, remains
to-day the only portable gas generator for the lecture table.
At least two generators are necessary, — one for hydrogen,
and the other for carbon dioxide. A large quantity of dilute
hydrochloric acid (1 : 1) should be made up ready for use in
these generators. As a rule, the simpler and less expensive
the form of Kipp used, the better. A tubulature in the lower
chamber is desirable. Especial care should be exercised to
have all joints and connections tight.

Batteries. — An open circuit battery, preferably of the
"dry" form, and a "bichromate" battery of six cells are
necessary. The expensive windlass form of bichromate
battery may be replaced by simpler though less convenient
forms at a much lower cost. The zincs should be amalga-
mated. An excellent battery solution is made as follows : —

600 g. potassium dichromate.
1000 cc. concentrated sulphuric acid.
4800 cc. water.

Splinters, tapers, and candles. — Splinters of wood are used
frequently in testing for oxygen, and should accordingly be
of a material that will retain a spark for some time. The

4 CHEMICAL LECTURE EXPERIMENTS

best splinters for this purpose are made from cigar-box
wood. A supply should always be kept in a place where
they cannot become wet. An assortment of candles con-
sisting of short pieces of the ordinary household size, and
especially the small candles so often used for decorative
purposes, should be at hand. The latter will be found
particularly convenient, as they can be readily thrust into a
small-necked vessel. Suitable wires and supports for low-
ering the candles into a vessel or thrusting them up into an
inverted jar are desirable.

Asbestos paper. — The free use of this paper, which should
be about the thickness of ordinary blotting-paper, is espe-
cially recommended. Asa protection to the table, as a heat
distributor under a flask or beaker to be heated, and as a
valuable accessory in many experiments, it is almost indis-
pensable on the lecture table.

Compressed gases. — Cylinders of compressed or liquefied
gases, if not of an unwieldy size, are an invaluable adjunct
to a lecture table. Their high price prohibits their ever
being universally used, but cylinders of liquefied carbon
dioxide are found in many drug stores and confectionery
shops. Liquefied nitrous oxide is used by many dentists,
and may be borrowed, the gas used being determined by the
loss in weight. Liquefied anhydrous ammonia is an essen-
tial in most refrigerating plants where a partially filled
cylinder may often be borrowed. Compressed oxygen is of
such importance that it has received special treatment in
the text. All of these gases, together with hydrogen and
sulphur dioxide, may be obtained in compressed or liquefied
form from the regular dealers in chemical supplies. Where
it is possible to obtain them near home, however, the ex-
pense of the express or freight, as well as rental on the
cylinders, is saved.

INTRODUCTION 5

Shields, gauntlets, and eyeglasses. — Experiments of a
dangerously explosive nature are not to be recommended to
the inexperienced. It is true, however, that experiments
with explosive mixtures can be made on a small scale with
practically no danger to experimenter or observers, by
using small quantities of material and placing the apparatus
between glass screens. In this way all flying particles of
glass or chemicals are confined to the area between the
shields, and no harm can possibly come. The simplest
screen is represented in Fig. 50, p. 102, and can be cheaply
constructed by any carpenter. Two such screens will serve
as a protection in nearly all experiments, though in a
few cases four may be used to advantage. One screen is
placed between the apparatus and the audience, and the
other between the experimenter and the apparatus. This
leaves two danger zones lengthwise of the table, but if no
inflammable materials are carelessly exposed on the table,
no danger need be feared.

For many experiments a protection to the hand is indis-
pensable. The driving glove or gauntlet (Fig. 7, p. 19) is
especially well adapted to this work, as the coat sleeve may
be thrust into the sleeve of the gauntlet, and thereby the
possibility of bits flying up the open sleeve may be avoided.

In experiments where there is an evolution of intense
light it is advisable to cover the eyes with colored glasses.
Glasses of smoked or colored mica are furthermore useful
as a protection in many operations of an explosive nature.
With proper use of the glass screens, however, protection
to the eyes except from the effect of bright light is seldom
necessary.

Reagents and test papers. — A full set of the common
qualitative reagents, together with the various test papers,
such as red and blue litmus, turmeric and iodo-starch, as
well as touch-paper, should be provided.

6 CHEMICAL LECTUKE EXPERIMENTS

Precipitations may be made in glass cylinders or conical
wine-glasses. If the precipitation is to be made in a hot
solution, the test-tube on foot (Fig. 51, p. 103), made of
thin glass which will stand heat, is the vessel best adapted.
A supply of long and short glass rods whose ends have
been rounded in the flame should be provided.

Aspirators, water pumps, and water blast. — The sim-
plest form of aspirator is made by fitting a two-holed cork
to a large bottle and inserting in one hole a glass tube ex-
tending to the bottom of the bottle, while a glass elbow is
thrust into the second hole in the cork. By attaching a
rubber tube to the long glass tube and starting the siphon
thus formed, the water in the bottle will be siphoned off and
air drawn in to take its place. If the bottle has a tubula-
ture at the bottom, the siphon is dispensed with and water
simply drawn off at the bottom, the air entering at the top.
A water suction pump will practically replace the aspi-
rator, and in addition is invaluable in many other operations,

such as rapid filtration, etc. The
glass forms are less liable to corro-
sion, and if wound with several
thicknesses of wire gauze, are not
easily broken.

A combined suction pump and
water blast with suitable cocks for
regulating the suction and the
strength of blast is of great value.
The expensive metallic forms may
be replaced by the less convenient
apparatus (Fig. 1) constructed by at-
taching a metal or glass filter-pump
to one neck of a three-necked one-liter Wolff bottle. The
middle neck is fitted with a rubber stopper and a glass elbow,

Fig. 1

INTRODUCTION 7

through which the blast of air is discharged. The third
neck carries a cork through which a large glass tube extend-
ing to the bottom of the Wolff bottle is thrust. The upper
part of the glass tube, which must be about twice as high
as the Wolff bottle, is bent downward in the form of a U,
and its opening so directed as to deliver the water into a
sink or overflow. On allowing water to flow through the
filter-pump, the air is drawn in, and the air and the water
delivered into the bottle, the water collecting in the bot-
tom of the bottle. If the air exit tube in the middle neck
is not opened, the air is compressed sufficiently to force the
water out of the bottle through the tube in the third neck.
Soon the water will have been so far removed that water
mixed with air is forced over. By opening the air-blast
tube, air may be withdrawn at the rate desired, provided the
level of the water in the bottle does not rise enough to flow
out of the air-tube. With a good strong filter-pump suffi-
cient air may be obtained to operate a blast-lamp.

Pneumatic troughs. — The pneumatic trough is indispen-
sable in experimenting with many gases. When only small
quantities of a gas are to be collected, a glass crystallizing
dish is used, as the operation is then entirely visible.
When larger quantities are to be operated with, a zinc,
galvanized iron or copper trough is used. The metal should
be well coated with asphalt varnish to resist the action of
acids. Sinks and troughs set in the lecture table are a
great convenience, but by no means indispensable.

OXYGEN

PREPARATION

1. From mercuric oxide. — Owing to its historical interest,
this experiment is almost invariably used in introducing the
subject of oxygen.

A one-centimeter layer of dry mercuric oxide is placed in
a hard-glass test-tube, and heated in a Bunsen burner pro-

Fig. 2

vided with a chimney. The tube is clamped in an inclined
position nearly horizontal, and the burner with its chimney
so arranged (Fig. 2) that only the mercuric oxide is heated,
that portion of the test-tube above the oxide remaining as
cool as possible.

OXYGEN 9

By using a somewhat larger portion of mercuric oxide,
and fitting a cork with a delivery-tube into the mouth of the
test-tube, sufficient oxygen may be obtained to fill several
small jars at the pneumatic trough.

2HgO=2Hg + 02.
Bunsen burner and chimney ; crystallizing dish and cylinders ; HgO.

2. From silver oxide. — Another compound of oxygen that
is easily decomposed by heat is silver oxide. The decompo-
sition is attended by a characteristic change in color from
the brown of the oxide to the silver- white of the metal.

The oxygen is evolved in such considerable quantities
that when the test-tube is fitted with a delivery-tube, several
small jars of oxygen may be collected at the pneumatic
trough. The change in color above referred to especially
recommends the method for lecture use, as the metallic sil-
ver is easily seen at a distance. If the heat is not high
enough to fuse the glass, metallic silver in a semi-porous
lump may be shaken out of the test-tube and allowed to fall
on a plate, thus further showing its metallic character.

On dissolving the residue in nitric acid and precipitating
with an excess of sodium hydroxide, hydrated silver oxide
is obtained, which, on being filtered and dried, yields the
original product ready for a repetition of the experiment.

2 Ag20 = 4 Ag + 02.

Test-tube and delivery-tube ; several 50 cc. cylinders ; porcelain
plate ; dry Ag20.

3. By heating potassium chlorate in the presence of small
quantities of other oxides. — The catalytic action of manga-
nese dioxide and ferric oxide on molten potassium chlorate,
causing the rapid evolution of oxygen, illustrates the aclvan-

10 CHEMICAL LECTURE EXPERIMENTS

tage of using these oxides with potassium chlorate in the
preparation of oxygen.

Potassium chlorate is melted at a low temperature in a
hard-glass tube, and the absence of oxygen shown by a
glowing taper. The salt must not be heated much above
its melting point. On removing the lamp and immediately
dropping in a small pinch of powdered manganese dioxide,
a vigorous evolution of oxygen ensues. The experiment
may be repeated with another tube of molten potassium
chlorate, using ferric oxide instead of manganese dioxide.
The demonstration of the unchanged nature of the oxides is
not adapted to lecture-table experimentation.

KCIO3 ; Mn02 ; Fe203.

4. By heating a mixture of potassium chlorate and man-
ganese dioxide. — As was seen in the preceding experiment,
the presence of manganese dioxide influences the liberation
of oxygen from potassium chlorate in two ways: first, the
temperature at which oxygen is evolved is much lower
when a mixture of the two compounds is heated, than
when the potassium chlorate is heated by itself; second,
the evolution of oxygen from the mixture is much more
regular. Accordingly, in the preparation of large quanti-
ties of oxygen, the mixture is almost invariably used. The
two ingredients must be pulverized and thoroughly dried.

Twenty grams of each are intimately mixed and placed in a
250 cc. Jena glass Erlenmeyer flask fitted with a cork and a
rather wide glass elbow, and clamped on a ring-stand. To
the elbow is attached a rubber tube fitted with a glass elbow
at the other end, which permits of a free movement of the
tube in the pneumatic trough. On gradually increasing the
heat, a rapid, though steady, evolution of oxygen ensues.
The gas may be collected in several glass cylinders for
special experiments, or may be transferred to one of the

OXYGEN

many forms of gas holders. At the end of the reaction,
the tube must be removed from the pneumatic trough to
prevent the back suction of the water. The purity of the
manganese dioxide is of considerable importance, as an
admixture of carbonaceous matter of any nature is likely to
cause an explosion. It is advisable to test a small portion
of the mixture by heating it in a test-tube. If glass other
than Jena is used, the flask should be protected in heating
by a piece of asbestos paper.

2KC103=2KCl + 3 02.

250 cc. Erlenmeyer flask (Jena) ; 1-holed rubber cork and two wide
(7 mm.) glass elbows ; dry Mn02 ; KC103.

5. From sodium peroxide. — Water decomposes sodium
peroxide with the formation of sodium hydroxide and
oxygen.

If water in a dropping-funnel is allowed to fall, drop by
drop, on 5 g. of dry sodium peroxide in a dry 100 cc.
Erlenmeyer flask fitted with a delivery-tube (Fig 3), a

12 CHEMICAL LECTURE EXPERIMENTS

steady evolution of pure oxygen is secured. The yield
of oxygen is very good, 6.25 g. of the peroxide giving
1 1. of the gas. As the volume of the ingredients is
small, a small flask is used, and consequently there is no
great volume of air to displace before beginning to collect
the product.

The advantages of this method of preparing oxygen are
numerous. Peroxide of sodium, while but recently intro-
duced into the market, is obtainable at a very reasonable
price, ranging at this date (1901) from 75 cents per pound
in one-pound packages to 40 cents per pound in large
quantities. At the higher price the cost of 1 1. of oxygen
prepared in this manner is but a trifle over 1 cent ; there-
fore the method is in no sense expensive. However,
owing to its tendency to deteriorate in the air, sodium
peroxide must be preserved in tightly stoppered bottles,
preferably (in case of long standing) sealed with a little
melted paraffin. The apparatus necessary for the opera-
tion is extremely simple, and as no heat is necessary,
breakage seldom occurs.

The chemistry of the reaction is certainly no more com-
plex to the elementary student's mind than that of the
potassium chlorate reaction, especially when the introduc-
tion of manganese dioxide must be explained to the class.

The regulation of the flow of oxygen is nearly perfect, as
each drop of water generates a certain amount of oxygen ;
thus a few centimeters or an almost unlimited volume per
minute can be obtained by simple regulation of water sup-
ply. Only a small quantity of water, however, is necessary
to decompose the peroxide.

2 Na202 + 2 H20 = 4 NaOH + 02.

100 cc. Erlenraeyer flask ; 50 cc. dropping-funnel ; glass elbow ;
rubber stopper ; Na202.

OXYGEN

6. By the action of the chlorophyl of green leaves. — The

exhalation of oxygen by green ] eaves under the influence
of sunlight may be readily shown by
filling a 2 1. flask containing green
leaves (not too closely packed), with
water through which carbon dioxide
has been allowed to bubble (Fig. 4).
A large funnel is passed through a hole
in the cork, which is firmly pressed
down into the flask in such a manner
that the carbon dioxide water will rise,
thereby expelling the air in the stem
of the funnel. The funnel is two-
thirds filled with water, and a small cyl-
inder filled with water is inverted with
its mouth directly over the stem of the
funnel. The whole apparatus is placed
in bright sunlight, and in a few hours
sufficient oxygen will have risen and dis-
placed the water in the small cylinder to
give a good test. The apparatus may be
left, and the oxygen tested at the next
exercise. If the carbon dioxide water is
not too strongly charged with the gas, it will be unneces-
sary to remove the trace of the carbon dioxide from the
oxygen before testing.

Apparatus (Fig. 4) ; green leaves ; carbon dioxide water.

Fig. 4

7. From the electrolysis of copper sulphate. — In the elec-
trolysis of copper sulphate, where but one of the final
products of electrical decomposition is gaseous, that product,
oxygen, may be isolated and tested. (Compare with the
electrical decomposition of water, sodium sulphate solution,
etc., where two gaseous products are formed.)

CHEMTCAL LECTURE EXPERIMENTS

<- p

The glass bottle of the electrolytic apparatus (Fig. 5) is
completely filled with a saturated solution of copper sul-
phate, and the cork inserted
in such a manner as to drive
out all the air and fill the de-
livery-tube with the solution.
If a current from four cells of
a bichromate battery is passed
through the apparatus, a steady
stream of oxygen will be de-
livered. One of the platinum
electrodes, the negative one, will become coated almost in-
stantly with metallic copper; the other, from which the
bubbles of gas rise, will retain its original color.

Pieces of cardboard with the signs + and — are placed
in a proper position to show the electrical connection.

2 CuS04 + 2 H20 = 2 Cu + 2 H2S04 + 02.
Electrolytic apparatus (Fig. 5) ; battery ; saturated CuS04 solution.

Fig. 5

8. Compressed oxygen. — No gas is used as frequently as
oxygen on the lecture table. Uniting, as it does, with
almost every element, in most instances with brilliancy,
it is an essential factor in chemical experimenting. The
method of obtaining this gas, given in Ex. 5, is the most
advantageous of all methods involving the preparation of
the gas, but, as a ready supply of oxygen for lecture table
as well as for other laboratory purposes, there is nothing so
satisfactory and reliable as a cylinder of compressed oxygen
such as is obtainable in the market.

Oxygen as ordinarily used in the laboratory is delivered
from a gasometer either of metal, or of glass with metal
connections. These gasometers, owing to the corrosive action

OXYGEN 15

of acids and fumes in the laboratory, soon begin to leak, and
are repaired with great difficulty. Furthermore, their chief
use is to store either air or oxygen, as the Kipp form of
generator furnishes a steady, constant supply of many gases
such as hydrogen, carbon dioxide, hydrogen sulphide, hydro-
chloric acid gas, etc. Since by means of the water-blast a
steady current of air may be readily obtained, the gasometer
is necessary only as a holder of oxygen. The cost of a
Pepys or Mitscherlich gasometer is very considerable, and
for a much less sum a steel cylinder holding 10 cubic feet of
oxygen may be obtained. By simply opening the valve in
the top of the cylinder, the gas is allowed to flow out at any
desired rapidity from one bubble a second upward.

A so-called "commercial oxygen," which has slight traces
of carbon dioxide and nitrogen as impurities, may be ob-
tained from the S. S. White Dental Mfg. Co., Princess Bay,
K.Y., at the very reasonable rate of ten cents per cubic foot.
(One cubic foot equals 28.3 1.) This gas is sufficiently
pure to be used in elementary organic analysis after being
freed from the small amount of carbon dioxide. A less
pure, though for experimental purposes equally good, oxygen
may be obtained from the dealers in calcium light supplies.

A pressure regulator, while by no means indis- , ,

pensable, is of great advantage in using a cyl-
inder of compressed gas. Owing to its cost,
however, its use is not likely to be universal,
and recourse must be had to a simpler device
which, with a little care, gives equally satisfac-
tory results. The stem of a long T-tube is
thrust through a two-holed rubber stopper which
is fitted into the mouth of a 50 cc. cylinder
(Fig. 6) . The tube should extend nearly to the
bottom of the cylinder, which should be covered with a
2 cm. layer of mercury. One arm of the T is connected with

1 "

v////////>

16 CHEMICAL LECTURE EXPERIMENTS

the oxygen cylinder, and the other arm is connected with
the apparatus to be filled by means of a rubber tube provided
with a screw pinch-cock.

When the pinch-cock is open, the oxygen flows directly
from the cylinder through the T into the vessel. If the
pinch-cock is closed, the oxygen flows down through the
stem of the T and bubbles through the mercury.

In many cylinders the rate of the issuing gas may be very
accurately controlled by the operation of the valve in the
cylinder. In some, however, it is difficult to open the valve
slowly enough to prevent a sudden rush of gas, which might
prove a serious difficulty in many operations. With such
cylinders the gas is conducted through the T-tube, one arm
of which is closed. The rushing gas bubbles through the
mercury and, by closing the valve on the cylinder, the cur-
rent may be so regulated that the gas slowly bubbles through
the mercury. By means of the screw pinch-cock oxygen
may now be withdrawn at any rate desired. It is always
possible so to regulate the pinch-cock and the valve on the
cylinder that no gas escapes through the mercury.

This mercury safety-bottle serves the additional purpose
of furnishing a vent for the gas in case the tubes of the
apparatus used for the experiment become clogged. Soon
the pressure would rise sufficiently to cause the gas to
bubble through the mercury, where from its sound it would
immediately attract attention. It is unnecessary, however,
to use the regulator if the cylinder is provided with easily
controlled valves, as the danger resulting from the stoppage
of tubes is very slight.

The gas may be collected in cylinders over water or, owing
to the greater density of oxygen, it may be collected more
conveniently by displacement in dry jars. A glass tube
leading to the bottom of the jar to be filled is connected
with a rubber tube to a cylinder. On opening the valve the

OXYGEN 17

gas is slowly allowed to enter the jar and, as it rises, push
out the air at the top. A glass plate is slipped over the
mouth of the jar, and a glowing splinter held at the opening
beside the glass tube. When the jar is filled, the glowing
taper will be ignited. The gas should not be shut off until
the tube is withdrawn. The moment the end of the glass
tube is drawn out of the jar, the glass plate is slipped on to
seal the mouth of the cylinder. One great difficulty in fill-
ing jars by this method is the fact that the gas is often
allowed to flow at too rapid a rate, thus causing air currents
inside the cylinder and a consequent test for oxygen before
the jar is really filled. It is well to dip the end of the
delivery-tube into water for an instant to see how rapid
the flow of gas is, before lowering it into the jar to
be filled. The rate of flow may also be determined by
inserting a gas washing-bottle between the cylinder and
the jar.

Some manufacturers give the net weight of the cylinder
as well as the weight of the oxygen it contains. In such
cases, by keeping a record of the weight of the cylinder, it
is easy to determine how much oxygen remains at any
given time.

PROPERTIES

9. Combustion of wood. — The increased brilliancy of
combustion, as well as the rekindling of a glowing taper,
may be shown by thrusting a splinter, the end of which is
glowing, into a cylinder of oxygen. The experiment may
be repeated a number of times, and, if care is taken not to
thrust the taper too deeply into the jar, and not to let it re-
main there too long to consume the oxygen, it will be seen
that at each repetition the splinter must be thrust a little
deeper to effect rekindling.

It is somewhat difficult to get a wood that will retain a
c

18 CHEMICAL LECTURE EXPERIMENTS

spark, though splinters made from cigar-box wood give satis-
factory results. It is best, in extinguishing the flame from
the burning taper, not to blow it out, but to shake it out by
a sudden twist of the hand, as in this way the spark is more
likely to be retained.

10. Combustion of a candle. — Owing to the fact that
there are considerable quantities of gas generated in the
combustion of a candle, its burning in oxygen presents a
condition slightly different from that where a splinter is
used. If the candle is lowered immediately after being
blown out, the gas generated by the still hot wick will
cause a slight explosion when the wick is rekindled, espe-
cially noticeable if the oxygen is in a rather tall jar.

Small candle on wire ; jar of oxygen.

11. Combustion of charcoal. — Charcoal, when burning
in the air, gives no flame, but simply glows. In oxygen no
flame is obtained, though the glowing may approach vivid
incandescence.

A glass cylinder of 1 1. capacity is filled with oxygen
and covered with a glass plate. A 3 cm. piece of char-
coal, preferably of bark, is supported in a loop on one
end of a stout copper or iron wire some 40 cm. in length.
On heating the charcoal in a Bunsen burner until it be-
gins to glow and then quickly introducing it into the jar
of oxygen, the increased brilliancy of combustion is very
marked. If the copper or iron wire is too fine, it is likely
to melt or burn and allow the charcoal to fall to the bottom
of the jar. When the charcoal ceases to glow, the wire is
withdrawn, and some clear lime water poured into the jar,
the glass plate replaced, and the cylinder shaken, after
which the contents may be poured into a glass. The

OXYGEN

limewater is cloudy, with a white precipitate of calcium
carbonate.

c+o2 = co2.

3 cm. piece of charcoal on wire ; 1 1. cylinder of oxygen ; lime-
water.

12. Combustion of powdered charcoal. — (a) While the
combustion of a solid lump of charcoal gave no apprecia-
ble flame, the combustion of hot finely powdered charcoal
in oxygen is attended with a flame of intense brilliancy.
An ordinary iron saucer, such as is used for a sand bath, is
one-third filled with finely powdered charcoal (willow char-
coal is the best) and heated until the charcoal just begins
to glow in spots. A grocer's sugar
funnel or an ordinary glass funnel,
cut so as to make the frustum of
a cone, is quickly slipped into the
mouth of a cylinder of oxygen of
not less than 1 1. capacity. The red-
hot charcoal is immediately poured
from the iron dish into the funnel,
care being taken to use the crucible
tongs and to protect the hands
with gauntlets. The face should
not be held too near the jar, as the flame reaches a consid-
erable height. When the hot charcoal falls through the
oxygen, the combustion is of almost explosive violence and
dazzling brilliancy (Fig. 7).

Large wide-mouthed bottle or jar of oxygen (Fig. 7) ; grocer's
tin sugar funnel ; powdered willow charcoal ; iron dish ; crucible
tongs ; gauntlets.

(b) A stream of oxygen, when allowed to play on glowing,
powdered charcoal, produces a most vivid combustion.
Finely powdered willow charcoal is placed in a small iron

Fig. 7

CHEMICAL LECTURE EXPERIMENTS

dish (sand bath) and heated until the surface begins to glow.

The flame is then removed, and a stream of oxygen is passed

through a long glass tube with a
bend at the end and allowed to
- play over the surface of the glow-
ing charcoal. The combustion be-
comes very vivid, and if the stream
of oxygen is of sufficient force to
blow the dust out of the dish, the
brilliancy of the combustion is
almost blinding (Fig. 8).

Fig. 8

Iron dish (sand bath) ; powdered wil-
low charcoal : current of O.

13. Combustion of sulphur. — A porcelain crucible about
the size of a thimble is so suspended in a loop of stout iron
wire that it may be lowered into a jar of oxygen. The
crucible is three-fourths rilled with small bits of lump sul-
phur which are heated to boiling. On lowering the burning
sulphur into a 500 cc. jar of oxygen, the combustion is con-
tinued with great brilliancy, resulting in the production
of a blue flame. That the product of combustion differs
materially from oxygen may be shown either by bleaching
moistened blue litmus paper or by thrusting a piece of
filter-paper moistened with potassium dichromate solution
into the jar. In the latter case the red color of the dichro-
mate is turned deep green by reduction.

s + o2 = so2.

Small porcelain crucible and stout iron wire ; 500 cc. jar of
oxygen ; lump sulphur ; K2Cr207 solution.

14. Combustion of phosphorus. — (a) The brilliancy of
the combustion of phosphorus in oxygen is so great that this
experiment has frequently been termed the " mock sun."

OXYGEN 21

A 5 mm. piece of phosphorus, which has been carefully
dried between filter-paper/ is placed in a small deflagrating
spoon and a short piece of cotton twine laid beside it in
such a manner that when a spark is started at the end of
the twine it will serve as tinder to light the phosphorus
on its introduction into the oxygen. The oxygen is held in
a large flask or bottle, the bottom of which is covered with
a little water. The deflagrating-spoon is previously arranged
to allow the phosphorus to burn near the bottom of the
vessel. On lowering the deflagrating-spoon into the jar, the
glowing bit of twine bursts into a flame, which is immedi-
ately communicated to the phosphorus, and the combustion
continues with dazzling brilliancy. White clouds of phos-
phorus pentoxide fill the whole jar, and by reflection of the
light make the interior of the vessel luminous. If the flask
was filled with oxygen by the displacement of air and the
interior is dry, the phosphorus pentoxide wrill settle as a
white hygroscopic powder all over the interior of the flask.
In this case, however, it is advisable to place a layer of
sand in the bottom of the vessel. A very small flame
should be used to start a spark on the twine, and care taken
to prevent a premature ignition of the phosphorus.

P4 + 5 02 = 2 PA.

Large flask or jar of oxygen ; deflagrating-spoon ; cotton twine ; P.

(b) The diminution in volume of the gas by the com-
bustion of phosphorus in oxygen is shown by using an
apparatus similar to that of Fig. 78, p. 182. The liter
bell-jar used in this experiment should be tubulated. A
crucible cover containing .5 g. of red phosphorus is placed
on a large cork floating on the surface of water in a
pneumatic trough. The bell-jar is then placed over the
float, and by removing the stopper oxygen is conducted

1 For precautions in handling phosphorus, see p. 232.

CHEMICAL LECTURE EXPERIMENTS

into the jar, thereby driving out the air. When all the air
has been removed and a good test for oxygen obtained at
the mouth of the bell-jar, a bit of string or paper which has
previously been ignited is dropped upon the crucible lid,
which has been brought under the opening in the bell-jar
by means of a long wire. The cork is then immediately
inserted. As the phosphorus burns, the water rises in the
jar, and it will thus be seen that a considerable quantity of
oxygen will be consumed.

Cork ; crucible lid ; tubulated liter bell-jar ; string ; red P.

15. Quantitative combustion of phos-
phorus in oxygen. — Phosphorus burning
in oxygen forms phosphorus pentoxide,
a white powder, which weighs consider-
ably more than the phosphorus used.
The increase in weight is shown by
burning the phosphorus in a confined
volume of oxygen in such a manner that
the product of combustion is retained.

A dry two-liter flask is filled with
oxygen and fitted with a one-holed rub-
ber stopper carrying a 20 cm. length of
glass tubing, 7 mm. in diameter, which
is loosely filled with coarse glass wool
or asbestos (Fig. 9). A stout copper
wire is fastened to the stopper with the
lower end, which is provided with a
loop in which a small crucible is placed,
near the bottom of the flask. The cru-
cible should not contain more than 1 or
2 cc, and should be about two-thirds
filled with red phosphorus. One end of a 2 cm. length
of string is inserted in the phosphorus in such a man-

Fig. 9

OXYGEN 23

ner that the other end may be ignited in the air. The
system is then brought into equilibrium on the lecture-
balance. The stopper is removed, care being taken not to
disturb the crucible or contents, the string ignited, and the
stopper again thrust into the flask, where the string com-
municates the fire to the phosphorus, which in turn burns
with a bright flame. The glass wool prevents the exit of
the phosphorus pentoxide, which remains as a dry white
powder covering the bottom and a portion of the sides of
the flask. After a few minutes the increase in weight of
the system, amounting to about .5 g., will be very apparent.

Lecture-balance ; cork and tube with glass wool ; copper wire ;
small crucible ; string ; 0 supply ; red P.

16. Combustion of " steel wool" in oxygen. — Of the

numerous forms of finely divided iron, that best adapted
for combustion in oxygen is the so-called " steel wool " or
steel fibre, which, as the name indicates, is a mass of fine
shreds of steel. This product is used extensively for polish-
ing hardwood, and is accordingly obtainable from most
dealers in hardware or painters' supplies. A German prod-
uct, which is sold only in pound packages, is but very little,
if any, better than the American product, which can be ob-
tained in quantities as small as desired.

A bit of the wool heated in the air will continue to burn
for a few moments.

It is in pure oxygen, however, that the brilliancy of the
combustion is best observed. A tuft of the wool is fastened
on the end of a stout iron wire, heated in the Bunsen flame
to incipient combustion, and then thrust into a jar of oxygen,
on the bottom of which a layer of water, sand, or asbestos
paper is provided. The wool burns with beautiful scintilla-
tions, the iron oxide falling to the bottom in fused globules.

Jar of 0 with H20, sand, or asbestos ; " steel wool."

24 CHEMICAL LECTURE EXPERIMENTS

17. Combustion of aluminium. — Aluminium in the form
of thin leaf is as combustible in oxygen as magnesium or
any of the other finely divided metals, while in air it is
not easily ignited.

Three or four leaves of aluminium are loosely bound
with a stout iron wire and lowered into a jar of oxygen.
A centimeter piece of twine fastened to the loop of the iron
wire and ignited an instant before being thrust into the jar
serves to kindle the aluminium leaf. The combustion is
instantaneous and accompanied by a bright flash. If the
iron wire is too fine, it also will burn in the oxygen.

Aluminium leaf ; 300 cc. cylinder of 0.

18. Combustion of finely divided magnesium, aluminium,
zinc, or iron in oxygen. — The brilliancy of the combustion
of these metals in oxygen is shown by causing each of
them to be blown lengthwise through the Bunsen flame by
a sudden puff of oxygen. Each powder is placed in the
bend of a glass elbow, of 5 or 6 mm. internal diameter, in
such a way that it does not quite obstruct the passage of
the gas through the tube. A very gentle stream of oxygen
is allowed to flow through the elbow over the metal till all
the air is driven out. On directing the open end of the
elbow toward the Bunsen flame, and suddenly admitting a
puff of oxygen or air, the greater portion of the powdered
metal will be shot across or through the flame and there be
burnt with a blinding flash. The elbow should be so directed
that the powder will be blown through the length of the
flame. As considerable care is necessary to secure the
proper introduction of the metal into the glass elbow, it is
advisable to have prepared four elbows, all properly filled
with the respective powders.

Four glass elbows (6 mm. diameter) ; Mg, Al, and Fe powders ;
Zn dust.

OXYGEN

19. Explosion of a mixture of powdered charcoal and
oxygen. — Oxygen ladened with charcoal dust forms an ex-
plosive mixture which varies in violence with the amount
of dust suspended in the gas. Variations in the rapidity of
combustion may be easily studied by means of the following
experiment : —

A 5 mm. layer of finely powdered willow charcoal is
placed in the bottom of a dry 500 cc. cylinder. A stream
of oxygen is directed through a glass tube which extends
to the bottom of the glass cylinder and is
bent at right angles 3 cm. above the mouth
of the cylinder (Fig. 10) in such a manner -^
that the current of gas stirs up the char-
coal powder in the bottom of the cylinder
and fills it with a dust-ladened atmosphere
of oxygen. The oxygen is then cut off
and a flame instantly applied at the mouth
of the cylinder. By varying the rapidity
of the current of oxygen, and consequently
the proportion of the dust in the gas, the
flame may be made to travel down the
cylinder with varying degrees of velocity,
affording an interesting study of the rate
of propagation of an explosion. This and the following
experiment are striking illustrations of the explosion of
a solid in a gas.

500 cc. cylinder ; powdered willow charcoal ; current of O.

Fig. 10

20. Explosive combustion of powdered iron, aluminium, or
zinc in oxygen. — An atmosphere of oxygen ladened with
the dust of iron, aluminium, or zinc, possesses explosive
properties.

Oxygen is conducted through a bent glass tube to the
bottom of a glass cylinder, o cm. in diameter and 15 cm.

26 CHEMICAL LECTURE EXPERIMENTS

high. A 5 mm. layer of powdered iron or aluminium or zinc
dust is placed on the bottom of the jar. The stream of
oxygen is so directed as to blow the dust up into the cyl-
inder and produce an atmosphere of oxygen ladened with
the metallic dust. On applying a flame at the mouth of the
cylinder the mixture explodes. The brilliancy of the com-
bustion renders the use of colored glasses necessary.

100 cc. glass cylinder ; colored glasses ; current of 0 ; powdered Fe,
Al ; Zn dust.

21. Absorption of oxygen by potassium pyrogallate. —

Oxygen is collected in a eudiometer (Fig. 11), and potassium

pyrogallate solution is allowed to flow down through

O the stopcock into the gas. The absorption of the

oxygen is almost immediate, the water rising to

take the place of the absorbed gas.

Potassium pyrogallate solution is best made by
dissolving 10 g. of pyrogallic acid in a solution of
100 g. of stick potassium hydroxide in 500 cc. of
water. Made with these proportions the solution
absorbs oxygen readily and, if tightly corked, keeps

Fig. 11 well.

Eudiometer (Fig. 11) ; pyrogallic acid ; stick KOH ; O.

22. Combustion of zinc in air. — At the ordinary temper-
ature it is extremely difficult to ignite zinc, though, when at
or near its boiling point, combination with the oxygen of
the air takes place easily.

Three or four grains of zinc (not granulated) are heated
in a small porcelain crucible with a blast-lamp. After a few
minutes the zinc boils and catches fire on the surface. The
zinc oxide formed collects in white flocks around the edge of
the crucible, which, on cutting off the blast, ascend with the

OXYGEN 27

hot current of air in white clouds. On cooling, the floccu-
lent nature of the zinc oxide may be observed.

2 Zn + 02 = 2 ZnO.

Crucible ; blast-lamp ; Zn.

23. Combustion of iron in air (quantitative experiment). —

A small magnet to which a considerable quantity of iron
powder is hanging is suspended from one arm of a lecture-
balance which is brought into equilibrium. The iron is
then ignited by gently playing a Bunsen flame upon it, care
being taken not to disturb the balance. In a few moments
sufficient oxygen will have combined with the iron to pro-
duce a very considerable change in the equilibrium of the
balance.

A much larger amount of iron, consequently showing a
greater deflection, can be burned by placing the iron powder
on a square of sheet asbestos that has previously been
ignited. The asbestos is placed on a square of wire gauze,
and so laid on the balance pan as to prevent undue heating
and consequent unsoldering of its supports. The balance is
then brought into equilibrium, and the iron ignited by means
of a small gas-jet. The combustion continues of itself, and
soon a large deflection of the balance is noticeable.

Magnet ; lecture-balance ; ignited asbestos paper ; square of wire
gauze ; iron powder.

24. Combustion of magnesium in air (quantitative exper-
iment). — Magnesium powder burns quietly in the air, form-
ing white magnesium oxide.

Five grains of magnesium powder are heaped on a 12 cm.
square of previously ignited asbestos paper, which is in turn
placed on the pan of a lecture-balance, with all the pre-
cautions of the preceding experiment. After bringing the

CHEMICAL LECTURE EXPERIMENTS

system to equilibrium, the magnesium is ignited with a
match or gas-jet. The combustion soon proceeds through
the whole mass, which increases in volume considerably,
and a small portion of the magnesium oxide formed
escapes as a white smoke. After the mass has become
cool, approximately 2 g. will be required to restore the
equilibrium.

Lecture-balance ; wire gauze ; asbestos paper ; Mg powder.

25. Increase in weight by the combustion of a candle in
air. — In burning a candle, if provision is made to collect
the products of combustion, i.e., carbon di-
oxide and water, it will be found that they
weigh more than the candle consumed.

A cylindrical Argand lamp chimney, 21
cm. high, 5.5 cm. in diameter, is provided
with a false, wire gauze bottom, as is shown
in Fig. 12. A circular piece of rather
coarse wire gauze is cut of such a size as to
readily pass through the chimney. Three
pieces of fine copper wrire, 50 cm. long, are
fastened at three equidistant points in the
circumference of the gauze by tying a knot
in the middle of each of the three strands.
The gauze bottom is placed inside the
chimney 6 cm. from one end, and fastened
in this position, by bringing the wires up
on the outside as well as the inside of the
chimney and twisting the ends of each wire
together at the top. One end of each strand
is left long enough to twist all three to-
gether and form a suspension for the chim-
ney. A few lumps of quicklime are placed on top of the
wire gauze and the rest of the space nearly filled with stick

Fig. 12

OXYGEN 29

sodium hydroxide. A large cork is fitted to the lower part
of the chimney. Several good-sized holes are made through
the cork to allow for the draft, and the ring of a crucible
lid is pressed into a slit in the centre of the cork, forming a
pan on which a candle is placed. The whole apparatus is
suspended on the arm of a lecture-balance and brought into
equilibrium. The cork is removed, the candle lighted, and
the cork quickly replaced. If the holes in the cork are of
sufficient size, there will be a good draft and the candle will
burn freely. The candle is of ordinary size and rather
short, about 15 mm. high. Any wax dropping from the
candle is caught in the crucible cover. The holes in
the cork can be made by cutting V-shaped sections out of
the edge. After burning a few minutes a very perceptible
increase in weight will be obtained.

Argand lamp chimney ; wire gauze ; lecture-balance ; Cu wire
(fine) ; quicklime ; stick NaOH.

26. Quantitative combustion of phosphorus in air. — The

apparatus of Ex. 15 may be used to demonstrate the in-
crease in weight of phosphorus burning in air.

It is better to substitute yellow for red phosphorus and
to induce the ignition by a strip of touch-paper (p. 355).
A 7 mm. piece of well-dried phosphorus is placed in the
crucible on top of a piece of touch-paper which protrudes
some 2 or 3 cm. above the top of the crucible. The
apparatus is then carefully tared, as before, the cork re-
moved, and the touch-paper ignited. The time required for
the touch-paper to communicate the flame to the phosphorus
is generally sufficient to permit the insertion of the cork
and the adjusting of the balance.

The phosphorus pentoxide formed settles to the bottom
and sides of the flask as a dry, white powder.

After the combustion is complete, and the system has

30 CHEMICAL LECTURE EXPERIMENTS

reached the room temperature, an increase in weight of
.5 g. will be obtained.

Apparatus (Ex. 15.) ; O supply ; yellow P ; touch-paper.

27. Increase in weight by burning sulphur in the air.

— If the sulphur dioxide formed by burning sulphur could
be collected, its weight would be exactly twice that of the
sulphur used. By means of a slight modification of the
apparatus of Fig. 12, p. 28, the increase in weight by burn-
ing sulphur in the air may be easily demonstrated, though
it is impossible to make the experiment so far quantitative
as to show any mathematical relation between the weight of
the sulphur and the weight of the product.

The Argand lamp chimney, prepared and filled with
quicklime and sodium hydroxide, as described in Ex. 25, is
provided with a perforated cork carrying a crucible cover, a
small disk of asbestos paper being placed between the cork
and the crucible cover. A few bits of sulphur are placed in
the crucible lid, the cork inserted in the chimney, and the
whole brought to equilibrium on the lecture-balance. The
cork is then removed, the sulphur ignited, and the cork
replaced in the chimney. It is advisable to let the sulphur
burn in the air for a moment or two to insure its thorough
iguition. The sulphur burned by so waiting interferes in
no way with the experiment. A few minutes after the
cork is replaced in the chimney a marked increase in weight
is observed.

Lamp chimney rilled with lime and NaOH ; cork with asbestos disk
and crucible cover ; S.

28. Absorption of oxygen by rusting iron. — The absorp-
tion of oxygen from the air by rusting iron can be readily
effected by inserting a wad of steel wool (Ex. 16) into a
eudiometer tube containing 100 cc. of air, inverted over

-—

■=r—

=_-=

OZONE 31

a crystallizing dish of water (Fig. 13). The eudiometer
should first be rilled with water and then enough of the
water allowed to flow out of the tube to confine
about 100 cc. of air. The plug of steel wool is
then thrust under water and inserted in the tube
by means of a long copper wire.

The apparatus thus prepared is allowed to
stand twenty-four hours, when it will be seen
that the iron has rusted considerably and that
the volume of the enclosed gas has materially
diminished.

Eudiometer tube ; steel wool ; Cu wire. Fig. 13

OZONE

FORMATION AND PREPARATION

29. By heating potassium chlorate or mercuric oxide. —

If a small quantity of potassium chlorate or mercuric oxide
is heated in a hard-glass tube until oxygen is evolved, a
piece of moistened iodo-starch paper held at the mouth of
the tube will be turned a deep blue.

KC103 = KCl+03. [?]
3HgO = 3Hg+03. [?]
KCIO3 ; HgO ; Kl-starch paper.

30. From barium peroxide and sulphuric acid. — By act-
ing on a peroxide with a strong acid, ozone is formed in
very appreciable quantities.

Three or four grams of powdered barium peroxide are
carefully and gradually shaken into a small beaker containing
10 cc. of concentrated sulphuric acid externally cooled by
ice. The air immediately above the beaker is very rich in
ozone and will give any of the usual tests.

32 CHEMICAL LECTURE EXPERIMENTS

In this experiment the process may be reversed by drop-
ping the cooled sulphuric acid upon the barium peroxide in
the bottom of the externally cooled beaker.

3 Ba02 + 3 H2S04 = 3 BaS04 + 3 H20 + 08. [?]
Ba02; ice.

31. By the action of sulphuric acid on potassium perman-
ganate. — As the action of concentrated sulphuric acid
liberates chromic anhydride from potassium dichromate
(Ex. 2, p. 405), in like manner permanganic anhydride is
liberated from potassium permanganate.

Permanganic anhydride, owing to its unstable nature, im-
mediately decomposes into manganese dioxide and ozone,
the latter being obtained in considerable quantities. This
reaction is very violent, and consequently must be performed
on a small scale only. It may be safely carried out, how-
ever, by placing 1 g. of powdered potassium permanganate
in each of six small beakers standing in a large crystallizing
dish, the bottom of which is covered with a centimeter layer
of water. The potassium permanganate in the beakers is
moistened with a few drops of water.

Into one of the beakers 2 cc. of concentrated sulphuric
acid are poured. A vigorous reaction takes place, accom-
panied by a smoke consisting chiefly of brown manganese
dioxide. A pinch of sulphur flowers dropped into the
beaker is instantly ignited.

The second beaker is likewise treated with 2 cc. of con-
centrated sulphuric acid, and a small piece of phosphorus
thrown into it. The combustion is instantaneous.

Into the third beaker, after the addition of sulphuric acid,
1 cc. of alcohol is poured from a test-tube fastened to the
end of a. long stick. The combustion is of almost explosive
violence.

OZONE 33

A polished silver coin, held by tongs above the mixture in
the fourth beaker, is rapidly turned black, giving the char-
acteristic ozone test. Then a slow stream of illuminating
gas is allowed to pass through a glass tube held at the mouth
of the beaker. It is ignited, and, by pinching the rubber
tube, the flame may be extinguished and relighted a number
of times.

A glass rod is dipped in the mixture in the fifth beaker,
and then touched to the wick of an alcohol lamp. The
oxidizing mixture adhering to the glass rod lights the lamp.

Four cubic centimeters of ether are poured from a test-
tube along the floor, and one end of the moistened strip
touched with a glass rod dipped in the fresh mixture pre-
pared in the sixth beaker. The ether is ignited, and the
flame travels along the floor. As but a few cubic centimeters
of ether are used, the combustion is of short duration and
harmless. As the ether burns, it will be seen that the vapor
has rolled out on either side of the moistened strip.

In all these experiments, protection is necessary from fly-
ing drops of concentrated sulphuric acid that might spurt
from the beakers in such vigorous reactions. After use,
each beaker should be removed with crucible tongs, and
plunged into a dish of water kept at hand for that purposec

2 KMn04 + H2S04 = K2S04 + Mn207 + H20.
Mn207 = 2 Mn02 + 03.

Six 50 cc. beakers ; large evaporating dish rilled with water ; large
crystallizing dish ; test-tube on a long stick ; pulverized KMn04 ; S
flowers ; small piece of P ; alcohol and alcohol lamp ; ether.

32. By slow oxidization of phosphorus. — When moist
phosphorus is allowed to remain in contact with air, it is
slowly oxidized, and a portion of the oxygen of the air
is converted to ozone.

CHEMICAL LECTURE EXPERIMENTS

A few sticks of freshly scraped phosphorus, about 4 cm.
in length, are placed on the bottom of a 2 or 3 1. flask, and
half covered with water. The mouth of the flask is then
loosely closed with a watch-glass, and the whole allowed to
stand at the room temperature. In a few minutes the air
inside the flask will be found to be rich in ozone, which

instantly turns blue a moistened piece
of potassium iodide starch paper. As
it is desirable to pass the ozonized air
through certain tubes, the flask should
be selected with a neck small enough
to be fitted with a two-holed rubber
stopper which has two glass elbows
thrust through it, the end of one of
the elbows extending 10 or 12 cm. be-
low the bottom of the stopper. When
water from the faucet is allowed to
run slowly through the shorter elbow,
it gradually fills the flask, driving the
ozone out through the elbow whose
end is nearest the bottom. As rubber
rapidly destroys ozone, the ozonized air must be drawn
from below the rubber stopper (Fig. 14). The formation
of ozone in this manner is dependent on the temperature,
and at 20° it is not uncommon to have very strongly
ozonized air in the flask at the end of half an hour.
A large bottle can be used instead of the flask.

Flask, 2 or more 1. ; cork and tubes (Fig. 14) ; sticks of P 4 cm.
long ; Kl-starch paper.

Fig. 14

33. From the slow combustion of ether in air. — When
ether is burned in air under certain conditions, a product is
formed giving the ozone reactions, and is commonly called
ozone, though its nature is not thoroughly understood.

OZONE 35

Two cubic .centimeters of ether are poured into a 200 cc.
cylinder and well shaken. When a platinum wire, which has
been heated in a Bunsen flame and allowed to cool until the
glow has disappeared, is lowered into the jar containing
the mixture of ether vapor and air, a partial combustion
takes place. A glass rod heated till the flame begins to be
colored may be substituted for the platinum wire. The
gaseous contents of the cylinder will give a decided ozone
reaction when a strip of iodo-starch paper is introduced.

200 cc. cylinder ; platinum wire ; iodo-starch paper ; ether.

PROPERTIES

34. Iodo-starch paper (potassium iodide and starch). —

Ozone acts upon potassium iodide and liberates iodine. The
free iodine immediately unites with the starch, forming the
blue compound, and accordingly potassium iodide, in the
presence of starch, gives an excellent test for ozone.

One gram of starch is suspended in 100 cc. of water
which is brought to a boil. After the starch has been com-
pletely emulsified, .5 gram of potassium iodide is dissolved
in the solution. Strips of filter or other bibulous paper are
dipped in the solution and dried. When testing for ozone,
a strip of the dried paper is moistened and held in the gas.
The blue coloration immediately appears.

6 KI + 03 + 3 H20 = 6 KOH + 3 I2.

35. Preparation of ozone paper (potassium iodide and red
litmus). — In the experiment with iodo-starch paper, in
which the free iodine liberated combines with the starch to
form the blue compound, the potassium hydroxide formed
can be utilized to turn red litmus paper blue, and thus serve
as a delicate test for ozone.

Strips of blue litmus paper are dipped in a solution com-

36 CHEMICAL LECTURE EXPERIMENTS

posed of 100 cc. of water, 1 drop of sulphuric acid, and .5 g.
of potassium iodide. Red litmus paper may be used and
the sulphuric acid omitted. For preservation, the strips are
dried, and require moistening before using. When the moist
paper is held in the presence of ozone, the color rapidly
turns blue.

36. Action on mercury. — Ozone acts on pure mercury,
destroying its lustre and its mobility.

Two 100 cc. stoppered cylinders, each containing 5 cc. of
pure dry mercury, are tilled, the one with oxygen and the
other with ozonized air, from the apparatus, Fig. 14. A
strip of iodo-starch paper is held in the mouth of each
cylinder, and while it is unacted upon by the oxygen, it will
be immediately turned blue by the ozonized air. Each cyl-
inder is then closed and vigorously shaken, when it will be
found that the mercury in the oxygen cylinder is unacted
upon, while the mercury in contact with the ozonized air
will be tarnished and will stick to the walls of the vessel
when shaken. That the ozone has been destroyed is shown
by holding a strip of iodo-starch paper in the mouth of the
cylinder. Its color will not be changed.

Two 100 cc. stoppered cylinders ; ozonized air apparatus (Fig, 14) ;
O supply ; pure Hg.

37. Oxidation of lead sulphide by ozone. — The oxidizing
action of ozone is shown by its conversion of the black
sulphide of lead to the white sulphate. Lead sulphide is
formed by moistening a strip of filter-paper with lead
acetate and exposing it an instant to the fumes of hydrogen
sulphide. On suspending the blackened paper in a jar of
ozone, the black rapidly disappears.

38. Decomposition by copper oxide. — At the room tern
perature copper oxide decomposes the ozone molecule, funn-
ing ordinary oxygen.

OZONE 37

A stream of ozonized air from the flask (Fig. 14) is
passed through a 20 cm. piece of combustion tubing fitted
with a cork at each end. A glass elbow dipping into a
beaker containing potassium iodide starch solution is in-
serted in the cork at the farther end of the combustion
tube. A slow stream of the ozonized air is now passed
through the system, and its action on the potassium iodide
starch mixture shown. A spiral of copper, made by winding
some copper wire around a glass rod until the spiral has
reached the length of 10 cm., is then heated until the sur-
face of the copper is entirely oxidized. The cork containing
the glass elbow is removed, and the copper oxide spiral,
after becoming cold, is introduced into the combustion
tube and the cork replaced. After allowing the ozonized
air to pass through the system a few minutes, it will be
seen that a fresh iodo-starch solution will not be acted upon
by the gas bubbling through it. If the spiral is removed
and the cork reinserted, the ozonized air will again change
the color of the solution in the beaker.

To insure non-contamination of the iodo-starch solution,
two corks carrying elbows should be provided, that they, as
well as the beakers, may be changed.

Ozonized air in flask (Fig. 14, p. 34) ; 20 cm. length combustion
tubing ; two corks carrying glass elbows ; two 50 cc. beakers ; iodo-
starch solution ; copper spiral.

39. Decomposition by heat. — Any appreciable increase of
temperature destroys the ozone molecule and consequently
its property of setting free iodine from potassium iodide.

A gentle stream of ozonized air from the flask (Fig. 14,
p. 34) is directed through a 5 mm. glass tube connected
at one end with an elbow which dips into a small beaker
containing potassium iodide-starch solution. On heating
the glass tube with a Bunsen burner, the ozone is destroyed

38 CHEMICAL LECTURE EXPERIMENTS

and a fresh beaker of potassium iodide-starch solution is
unacted upon by the gas that bubbles through. A fresh
elbow must be connected to the tube.

All connections should be made with glass touching glass,
the rubber only serving to hold the tubes together.

2 03 = 3 02.

Ozonized air in flask (Fig. 14, p. 34) ; two glass elbows (5 mm.) ;
Kl-starch solution.

40. Decomposition by rubber. — The decomposition of
ozone by rubber and the consequent necessity of avoiding
rubber connections in all ozone apparatus is shown by con-
ducting a rapid stream of ozonized air through a 1.5 m.
length of rubber tubing and testing the issuing gas with
iodo-starch paper. The ozonized air is best obtained from
the apparatus. Fig. 14, p. 34, and the water should flow
into the flask at the rate of about 40 cc. in 10 seconds.
The ozonized air should be tested just as it leaves the glass
elbow, and then the rubber tube should be connected.
After a few moments the gas issuing from the other end of
the tube will be found to be free from ozone.

Ozonized air in apparatus (Fig. 14, p. 34) ; 1.5 m. length of
rubber tubing.

HYDROGEN

PREPARATION

1. By the action of sodium on water. — Sodium reacts
vigorously with water, liberating hydrogen and forming
sodium hydroxide. The preparation of hydrogen by this
reaction is only of theoretical interest, and should be carried
out on a very small scale only.

A 5 mm. piece of sodium is cut from a large piece of the
fresh metal whose crust has been removed, the whole
operation being performed under petroleum, ether, or ben-
zine. The small piece is then freed from petroleum by
being carefully dried on a piece of filter-paper. It is neces-
sary that the hands should be dry, as even small quantities
of perspiration are liable to ignite the sodium and cause a
bad burn. In case a bit of sodium becomes ignited, it can
be extinguished readily by covering it with a handful of
dry sand (water must never be used).

The sodium is now wrapped in a piece of thin sheet lead
(the leaf lining to tea chests, obtainable at any grocer's,
serves the purpose admirably), one end of the sodium being
left uncovered. The lead should be pressed down on all
sides closely, and the end opposite the exposed end tightly
pinched together. On dropping the sodium prepared in
this way into water in a crystallizing dish, the action is

40 CHEMICAL LECTURE EXPERIMENTS

very gentle, and hydrogen is steadily evolved (Fig. 15).

By covering the sodium with an inverted jar full of water,

the hydrogen may be collected. If the

sodium is overlapped at its exposed end

by the lead, a bubble of air often prevents

the water from* coming in contact with the

sodium. The lead should be trimmed off

just flush with the exposed surface of the

sodium. When tea lead is used, it should

be doubled, as one thickness is liable to be

melted through by the intense heat of the
Fig. 15 ° J

reaction. Three or four pieces of sodium
may be wrapped in separate bits of sheet lead, and when
the gas evolution from one has ceased another may be
thrown into the water and thus sufficient gas collected.

The wire gauze baskets so often used in this experiment
are liable to introduce a considerable quantity of air into
the gas, with the possible formation of an explosive mix-
ture. Furthermore, when a second piece of sodium is to be
introduced in order to fill a jar with the gas, a second dry
basket must be nsed. The introduction of bits of sodium
on the end of a needle is not to be recommended, as the
metal often becomes disengaged from the needle before it is
under the jar, and rises to the surface of the water outside,
and thereby causes annoyance.

Sodium, even under naphtha, oxidizes slowly, and while
a number of pieces of sodium can be wrapped in lead and
preserved in naphtha, the facility with which they can be
prepared leaves very little to be gained by having a stock
on hand. Freshly prepared, they will never fail to give a
steady evolution of hydrogen.

2 H20 + 2 Na = 2 NaOH + H2.

Metallic sodium (5 mm. pieces) ; tea lead ; crystallizing dish and
cylinder.

HYDROGEN

2. From the reduction of water vapor by iron. — Iron acts
upon water at the ordinary temperatures very slowly. If,
however, a current of steam is conducted over red-hot
metallic iron, the reduction is very rapid, hydrogen being
liberated.

A 60 cm. length of iron gas pipe is filled with nails and
heated to redness in a small furnace or over a four-tube
burner (Fig. 16). One end of the iron tube is connected with
a steam generator and the other end fitted with a cork and a
delivery-tube leading to the pneumatic trough. The steam
generator consists of a 300 cc. Erlenmeyer flask fitted with a

•a r^e

Fig. 16

two-holed rubber stopper, carrying a long thistle- tube and a
glass elbow extending to the combustion-tube. The thistle-
tube must extend to the bottom of the flask in which 100
cc. of water are brought to a boil. On passing a current of
steam through the hot tube, a regular flow of hydrogen may
be obtained at the pneumatic trough. Owing to the conduc-
tion of heat by the iron, care should be taken that the corks
in the ends of the tube are protected from the heat. This
can be accomplished either by having a rather long iron
tube and heating only the middle portion, or by using red
rubber stoppers, which stand a much higher temperature
than ordinary cork or rubber stoppers. A still further pro-

42 CHEMICAL LECTURE EXPERIMENTS

tection may be secured by wrapping a thin sheet of asbestos
around the corks before inserting them in the tube. By
forcing the corks into the tube, a tight joint may be obtained.

60 cm. length gas pipe (1 cm. inter, diam.) ; iron nails ; 300 cc.
Erlenmeyer flask ;'long thistle-tube ; elbow ; 4-tube burner.

3. From the reduction of water vapor by zinc. — Finely
divided zinc reduces water vapor, forming zinc oxide and
liberating hydrogen. The temperature at which the reduc-
tion is effected by means of zinc is, however, very much
lower than that required when using iron, and it is only
necessary to heat the tube, which is of glass rather than
of iron, a little above the boiling point of water. The
apparatus is similar to that used in the preceding experi-
ment. The combustion-tube is filled with zinc dust and
gently heated with a four-tube burner. As the zinc becomes
converted to zinc oxide, a marked color-change in the con-
tents of the tube is noticed, and at times the rapidity of
the reduction is such as to cause the zinc to glow.

Zn + H20 = ZnO + H2.

Glass combustion -tube ; apparatus of preceding experiment ; Zn
dust.

4. From the reduction of water vapor by magnesium. —
See Ex. 1, p. 371.

5. From the ignition of sodium hydroxide and iron
powder. — One gram of powdered sodium hydroxide and 20 g.
of iron powder are intimately mixed and heated in a
hard-glass test-tube fitted with a cork and a delivery-tube,
the upper part of the mixture being heated first. A rapid
stream of hydrogen is obtained, and the gas may be
collected at the pneumatic trough.

Powdered NaOH ; Ee powder.

HYDROGEN 43

6. By heating calcium hydroxide and zinc dust or iron
powder. — To illustrate a technical process for the prepara-
tion of hydrogen, a mixture of equal parts by volume of
zinc dust and dry calcium hydroxide is heated in a hard-
glass test-tube, provided with a cork and a delivery-tube,
the end of which dips into a pneumatic trough. On apply-
ing heat, the liberation of hydrogen is very regular, and the
gas may be collected in bottles for testing. It is important
that the calcium hydroxide be dry, as otherwise an excess
of moisture is likely to collect on the tube and run back,
causing it to break.

Iron powder may be substituted for the zinc dust in the
above experiment with equally satisfactory results.

Ca(OH)2 + Zn = CaO + ZnO + H2.

Dry Ca(OH)2 ; Zn dust ; Fe powder.

7. From aluminium and sodium hydroxide solution. —

Fifty cubic centimeters of dilute sodium hydroxide solution
and a few grams of scrap aluminium are placed in a 300 cc.
Erlenmeyer flask fitted with a thistle-tube and a delivery-
tube. In the cold the action is at first very slow, soon
warming up of itself and becoming very vigorous. As some
time is required for the reaction to take place in the cold,
it can be hastened by warming slightly. When once started
the flame must be extinguished. A large quantity of pure
hydrogen may be obtained in this manner from a very small
weight of the metal.

6 NaOH + 2 Al = 2 Na3A103 + 3 H2.

300 cc. flask ; thistle-tube ; delivery -tube ; aluminium scrap.

8. From zinc and sulphuric or hydrochloric acid. — This
method for the preparation of hydrogen is almost univer-

44 CHEMICAL LECTURE EXPERIMENTS

sally used in the laboratory, by reason of its economy and
simplicity.

Owing to its great importance, large quantities of hydro-
gen are used on the lecture table, and it is necessary to have
one or more forms of apparatus that will yield considerable
quantities of the gas.

A ready supply of hydrogen may be obtained from the
apparatus of the preceding experiment. Granulated zinc is
placed in the flask, covered with water, and a few cubic
centimeters of concentrated sulphuric acid are then added
through the thistle-tube, which should extend to the bottom
of the flask. After the addition of acid, the flask and its
contents are gently shaken. Instead of adding concentrated
acid to the water in the flask, the acid may be previously
diluted, and the cold dilute acid added. In this case the
reaction is not as rapid at first. Dilute hydrochloric acid
(1 : 1) is also used to prepare hydrogen in this manner, this
dilution of acid producing a rapid gas evolution.

On account of the large surface which is presented to the
action of the acid, the so-called granulated or feathered zinc
(Ex. 1, p. 377) is preferred for making hydrogen. The
diffusibility of hydrogen renders it absolutely essential
that all apparatus used in its preparation should be gas-
tight. Ground glass joints, if any, should be well lubricated
with vaseline ; rubber stoppers should be crowded into place,
and, if necessary, all connections with rubber tube should be
bound with wire.

After the generation of the gas has begun, it is necessary
to allow the gas to escape till the air in the apparatus has
been completely expelled by the hydrogen, as otherwise con-
siderable danger may result from the ignition of an explosive
mixture of hydrogen and air if the issuing jet of hydrogen
is lighted too soon. According to the amount of air space
in the generator and the purifying apparatus, the gas is

HYDROGEN 45

allowed to escape into the air for some time, and then it is
better to test it before applying a match directly to the
issuing gas. A simple method of testing the gas is to allow
it to bubble through a soap solution contained in an evap-
orating dish and, after removing the delivery-tube, to light the
bubbles and see if they give an explosion. If not, it will be
safe to ignite the gas. Another method is to lead the gas,
by means of a rubber tube, to the bottom of an inverted
test-tube, the lighter hydrogen rising and pushing down the
air in the test-tube. The delivery-tube is slowly withdrawn
and the thumb placed over the mouth of the test-tube, which
is then carried to the Bun sen flame and ignited. When the
gas is perfectly pure, it should burn quietly and give a flame
of sufficient duration to serve in igniting the hydrogen
issuing from the generator. On the danger of premature
ignition of a hydrogen jet, see Exs. 29 and 30.

Commercial zinc ordinarily has sufficient impurity to give
a rapid action with dilute acid. At times, however, the
zinc may be so pure as to give a rather slow action. In
such cases, use is made of the electrolytic action between
zinc and copper or platinum to accelerate a liberation of the
gas, and a few cubic centimeters of copper sulphate solution,
or a few drops of platinic chloride solution, are added to the
acid in the generator. The zinc becomes coated with a fine
deposit of copper or platinum, and the increased gas evolu-
tion is very marked.

Hydrogen may be collected either by displacement of air
or at the pneumatic trough, the second of these methods
being used when a dry cylinder of the gas is not required.
In collecting the gas by displacement (the operation on a
small scale has been described above), it is essential that
a rather rapid stream of gas be used, to prevent the diffusion
of air into the vessel to be filled.

The gas is dried by passing it through a gas washing-

CHEMICAL LECTUKE EXPERIMENTS

bottle containing concentrated sulphuric acid. When the
issuing gas is to be lighted, it should be dried by passing
through a U-tube containing calcium chloride, or pumice-
stone drenched with sulphuric acid. In either case the gas
must have a clear passageway through the drier, that the
flame may not be affected by the irregular bubbling through
a liquid.

If a special purification is necessary, the gas may be con-
ducted through a gas washing-bottle containing acidulated
potassium permanganate solution.

The Kipp generator furnishes, at the same time, the most
convenient, as well as the most satisfactory, apparatus for
maintaining a constant supply of hydrogen. The simpler
form of apparatus (Fig. 17) consists practically of two

pieces, the base being a glass bottle
constricted in the middle, forming two
chambers, the upper chamber being
fitted with a side tubulature in which
a stop-cock is inserted, and the lower
chamber tubulated for the removal of
spent acid. The upper chamber con-
tains the zinc, and the lower chamber
serves as a reservoir for gas generated
in excess of that wanted for immediate
use. In the neck of the upper chamber
is fitted a long funnel, the lower end of
which extends down through the con-
striction to the bottom of the vessel.
The funnel is made in the shape of a
large bulb and serves as an acid reser-
voir. To charge the apparatus, gran-
ulated zinc is introduced through the opening in the upper
chamber, and the stop-cock replaced. Dilute hydrochloric
acid (1 : 1) is poured into the funnel. On opening the

Fig. 17

HYDROGEN 47

stop-cock the acid will rise in the lower chamber, pass
through the constriction, and come in contact with the zinc.
The hydrogen generated will escape through the stop-cock.
When the stop-cock is closed, the hydrogen presses down-
ward on the acid, which is forced back into the funnel, the
lowest chamber serving as a gas reservoir. In order to
obtain a steady flow of hydrogen, it is only necessary to open
the stop-cock.

Zn + H2S04 = ZnS04 + H2.

Zn + 2 HC1 = ZnCl2 + H2.

300 cc. flask ; thistle and delivery tubes ; Kipp generator ; HC1
(1:1); granulated Zn.

PROPERTIES

9. Lighter than air. — (a) All. beaker is suspended in
an inverted position on the arm of a lecture-balance. The
system is then brought into equilibrium. If a liter cylinder
of hydrogen is inverted under the mouth of the beaker and
the hydrogen allowed to ascend, the equilibrium of the
balance will be destroyed and a deflection of the pointer
be obtained. Instead of allowing the hydrogen to rise from
the cylinder, it may be passed through a glass tube, the
mouth of which will reach up to the bottom of the beaker.
In either case, however, the balance must not be touched
with the cylinder or the glass tube.

If the system be allowed to stand for a few moments, the
hydrogen will rapidly diffuse out, and the balance come
again to equilibrium. The removal of the hydrogen may be
facilitated either by unhanging and inverting the beaker a
moment, or, what is perhaps more striking, by sucking out
the hydrogen through the tube used to introduce it, care
being taken, of course, not to touch the beaker or the
balance. If a strong suction by means of the water-pump

CHEMICAL LECTURE EXPERIMENTS

is maintained, the hydrogen will be rapidly withdrawn and
the balance assume a state of equilibrium.

Lecture-balance ; liter beaker ; suction pump ; liter cylinder of H.

(b) The ascending current of hydrogen, flowing from an
inverted cylinder of the gas, may be made to rotate a wheel
such as is described in Ex. 36, p. 313.

A liter cylinder of the gas inverted under the buckets
will cause the wheel to rotate.

Paper wheel (Pig 125, p. 313) ; liter cylinder of H.

10. Determination of the specific gravity. — By means of a
balance weighing two centigrams a very satisfactory demon-
stration of the fact that hydrogen is approximately 14.4
times lighter than an equal volume of air may be made.

On one arm of a lecture-balance a clean, dry, graduated
liter flask is suspended mouth downwards (Fig. 18) by means
of a harness of fine wire. After bringing the balance into
equilibrium hydrogen, dried by passing through a gas wash-
ing-bottle containing sul-
phuric acid, is allowed to
pass through a fine tube
into the inverted flask.
After a few minutes the
air will have been en-
tirely replaced by the
hydrogen, and it will be
found necessary to place
1.14 g. on the flat bottom
of the inverted flask in
order to bring the sys-
tern to equilibrium again.
Taking the weight of a liter of air at the laboratory tem-
perature and standard barometric pressure as 1.225 g., it

HYDROGEN 49

will be seen that the weight of a liter of hydrogen is the
difference between 1.225 and 1.14 or .085 g. On dividing
the weight of air under these conditions, i.e., 1.225 g. by the
weight of an equal volume of hydrogen, i.e., .085 g., the
quotient is 14.4, or the air is 14.4 times heavier than
hydrogen.

In filling the flask with hydrogen the tube should lead
clear up to the bottom and should be withdrawn while the
gas is still flowing through it. If the graduated flask has a
long narrow neck, the rate of diffusion is so slow that there
is no appreciable change of weight in bringing the balance
into equilibrium. In fact, it will be some time before enough
air will have diffused into the flask to disturb the equilibrium
materially. If desirable, a rubber stopper can be balanced
with the flask and inserted after withdrawing the tube
delivering the hydrogen.

Current of dry H ; liter graduated flask ; lecture-balance and
weights.

11. Use in balloons. — The use of hydrogen in balloons
is shown by filling a small collodion balloon with the
gas.

If a collodion balloon is obtainable, it is only necessary to
fasten the mouth of the balloon to a glass tube through which
hydrogen is passing, and after the balloon is completely filled
to tie the mouth with a string. The glass tube connected
with the hydrogen generator should be bent vertically up-
ward, contain a loose 2 cm. plug of cotton wool, and be
drawn down to a jet of 2 mm. diameter. The end of the jet
is rounded a little in the flame to avoid cutting the thin
tissue with sharp edges of glass. The collodion balloon,
which should be flattened as much as possible to expel all
air, is fastened well up on the shoulder of the jet so that by
tightening the string and pushing the balloon down to the

50 CHEMICAL LECTURE EXPERIMENTS

point of the jet, it can be easily sealed. A balloon so filled
with hydrogen rises in the air and will support a con-
siderable length of string or thread which may be used
to recover it.

H generator ; collodion balloon ; glass jet with cotton thread.

12. Filling a balloon under pressure. — (a) The collodion
balloons used in the preceding experiment are short lived
and somewhat expensive. The small thin rubber bags so
often used on toy whistles or in games1 are admirably
adapted for experimenting with hydrogen, if provision is
made to fill them with the gas under pressure, since it is
necessary to fill not only the small volume of the rubber
bag, but to cause its distension and thereby enclose a con-
siderable quantity of gas. The apparatus for conducting
the hydrogen into the rubber bag consists of a 1 or 2 1.
bottle having a two-holed rubber stopper carrying an elbow
and a jet such as is described in the preced-
ing experiment (Fig. 19). The bottle is first
filled with hydrogen either over water or by
displacement, and the stopper inserted, care
being taken to allow no hydrogen to escape.
A rubber tube connects the water tap with
the glass elbow. The rubber bag is securely
fastened on the shoulder of the jet as de-
scribed in the preceding experiment. By

allowing the water to flow into the bottle,
Fig. 19

the gas is forced under considerable pressure

out through the jet into the rubber bag, which may be dis-
tended and form a balloon some 15 cm. in diameter.

H generator ; 2 1. bottle ; 2-holed stopper ; elbow ; jet ; thin
rubber bag.

1 Rubber bags of this form may be obtained at any toy store.

HYDROGEN

(b) If the hydrogen generator is so constructed as to
permit of considerable pressure, the gas may be drawn
directly from the generator into the rubber balloon. A thick-
walled flask is provided with a two-holed cork carrying a
small long-stemmed dropping-funnel and one arm of a three-
way stop-cock (Fig. 20). The zinc is placed in the flask and
dilute hydrochloric acid (1 : 1) al-
lowed to flow through the drop-
ping-funnel into the flask. The
three-way stop-cock should be so
arranged that the gas escapes
through the open arm of the T.
The rubber balloon is tied to a
jet (such as is described in the
preceding experiments) which is
connected by means of a short
piece of rubber tubing to the
stem of the T-tube. When all
the air has been driven out of
the generator, the three-way stop-
cock should be turned so as to

deliver hydrogen through the stem of the T into the balloon.
It is necessary to close the stop-cock on the dropping-funnel
immediately, as otherwise the gas will push up through the
column of liquid and out through the funnel. When the
rubber has been distended to a sufficient size, the three-way
cock may be so turned as to seal the stem of the T-tube and
open both arms, allowing a vent for the compressed gas
inside the generator. The balloon may then be tied and
drawn off the jet as described in the preceding experiment.
If proper care is used in opening and closing the stop-cock,
this method of filling a rubber balloon leaves very little to
be desired.

Stout-walled flask ; dropping-funnel ; three-way cock ; rubber
balloon.

Fig. 20

52 CHEMICAL LECTURE EXPERIMENTS

13. Soap-bubbles blown with hydrogen. — If soap-bub-
bles are tilled with hydrogen, they will rise rapidly and, if
touched with a lighted taper, burn.

Hydrogen from a Kipp generator is first passed through
a U-tube containing soda-lime slightly moistened, i.e., not
dry enough to have any dust, and then through a rubber
tube connected with an ordinary thistle-tnbe. The soda-
lime tube completely removes any hydrochloric acid vapor,
which is quite destructive to the soap film. After dipping
the mouth of the thistle-tube in the soap solution 1 and
shaking off the excess of water, the bubble is started with
the mouth of the thistle-tube downwards. When the
bubble has attained the size of the thistle, the mouth may
be pointed upwards and the hydrogen admitted as fast as
desired. By means of the glass stop-cock in" the Kipp gener-
ator the supply of hydrogen may be easily regulated. On
giving the tube a little side shake, the bubble is released
and immediately ascends. A small taper or candle fastened
on the end of a long stick may be used to ignite the bubble,
and it is better to hold the flame above the
bubble, bringing it down so as to meet it, rather
than to try to follow the bubbles and catch them
as they ascend.

A glass or preferably tin funnel 15 cm. across
^ the top (Fig. 21) may be clamped mouth down-
wards to the gas pipe or other fixture over the
lecture-table, and a small gas-jet burning at the
\J end of a glass tip may be so arranged that it
r^^^t . will burn horizontally across the mouth of the
Fig. 21 funnel. If the hydrogen bubbles are allowed

1 Preparation of soap solution. — The presence of glycerine in soap
solution used in blowing soap-bubbles materially increases the dura-
bility of the film.

One hundred grams of white castile (or any other pure soap) are

HYDROGEN

to rise beneath this funnel, they will ascend and come in
contact with the gas flame, insuring ignition. The mouth
of the funnel should be about 1.5 m. from* the point of
liberation of the bubble.

H generator (Kipp) ; candle at the end of a long stick ; thistle-
tube ; soap solution ; soda-lime ; U-tube.

14. Conductivity for heat. — Hydrogen, in contrast to
the other gases, is a good conductor of heat, and this prop-
erty, which it shares in common with the metals, is well
shown by lowering a jar of hydrogen over a piece of platinum
wire which has been heated by means of the electric current.

A 20 mm. piece of fine platinum wire is connected with
two upright copper wires fastened to a small block of wood.
The copper wires should be 30 cm. long
and so arranged that about a 20 cm.
length stands upright from the board.
They are fastened about 25 mm. apart,
thus permitting the lowering of the cyl-
inder of hydrogen over them (Fig. 22).
The copper wires are connected with a
battery of sufficient strength to just raise
the platinum wire to incandescence. On
lowering the jar of hydrogen over the
glowing wire the gas will be ignited at
the mouth of the jar, and the glow will
nearly if not entirely disappear from the
wire. On removing the jar, the glow
will again appear.

~" —

Fig. 22

cut in thin shavings and placed in a bottle with 1 1. of water. The
mixture should be well shaken until a saturated solution of soap is
obtained. After allowing the liquid to stand for some time the clear
supernatant solution is decanted and mixed with half its volume of
glycerine.

54 CHEMICAL LECTURE EXPERIMENTS

The strength of the current may be previously determined
and the jar lowered before the connections are made. On
switching on the current, the wire will undergo no apparent
change, but on withdrawing the jar, it will become heated
and ignite the hydrogen at the mouth of the cylinder. The
platinum wire should be as fine as possible (such as that
used in suspending Welsbach mantles), and care should be
taken not to have the current strong enough to melt it.

Fine iron wire may be used in place of platinum, though
it cannot be raised to as high a degree of incandescence
without danger of oxidation and combustion in air. In this
case it is better to lower the jar and then close the circuit
and allow the iron wire to become heated on removing the
jar containing hydrogen.

Fine platinum or iron wire ; stout copper wire ; battery ; jar of
hydrogen.

15. Non-conductivity for sound. — Hydrogen is a poor
conductor of sound, and consequently when a bell is thrust
into an atmosphere of hydrogen and then struck, very little
if any sound is heard.

A small bell is fastened on the end of a stick or wire and
then thrust up into a liter bell-jar of hydrogen. If the bell
is then struck with a second piece of wire or
a hie, the sound is very much diminished.

The effect is more striking if an electric bell
(Fig. 23) is used. A switch should be placed in
the circuit, which is closed after the bell is thrust
into the jar. The box which usually covers the
magnets of the bell should be removed, as it is
possible to have an explosive mixture of hydro-

Fig 23

gen and air formed inside the box which might
be ignited by the feeble spark produced at the contact.

Two 1 liter bell-jars ; bell and wire ; electric bell ; battery and
switch ; H generator.

HYDROGEN

16. Diffusibility. — The great diffusibility of hydrogen
through the walls of a porous cell may be shown by a
number of striking experiments in which the variations in
pressure caused by the hydrogen enter-
ing or leaving the cell are utilized.

A porous cell, approximately 12 cm.
long and 5 cm. in diameter, is provided
with a two-holed rubber stopper tightly
fitted into its mouth. Through one hole
a 5 cm. length of glass tubing of 6 mm.
internal diameter is thrust, and through
the other a short piece of small glass
tubing about 3 mm. internal diameter.
The smaller glass tube is plugged with
a short piece of rubber tubing and a bit
of glass rod. The larger tube is con-
nected by means of a rubber tube with a
long glass U-tube half filled with colored
water. If a jar of hydrogen is now
brought down over the porous cell, the
pressure inside is increased and the level of the water in
the U-tube will be disturbed, that in the arm connected
with the porous cell falling, that in the other arm rising an
equal distance.

Porous cup ; long glass U-tube ; ink water ; jar of H.

Fig. 24

17. Diffusion out of a porous cup. — When the interior of
the porous cup is filled with hydrogen, the diffusion out-
ward is so rapid as to cause an internal diminution of
pressure.

The jet tube is removed from the Wolff bottle in Fig. 25
and a rapid stream of hydrogen is sent into the porous cup
through a small glass tube which is provided with a rubber
connector and a pinch-cock. On suddenly stopping the

CHEMICAL LECTURE EXPERIMENTS

flow of the gas by closing the pinch-cock, the hydrogen will
diffuse out of the porous cup into the air, diminishing the
internal pressure inside the cup. The colored water will
rise immediately in the pipette, nearly filling the bulb.
Apparatus (Fig. 25) ; II generator (Kipp).

18. Diffusion producing a fountain. — One neck of a
small two-necked Wolff bottle is fitted with a glass tube

whose lower end nearly touches the bot-
tom of the bottle, the upper end reach-
ing a few centimeters through the cork
and being drawn down to a fine jet
(Fig. 25). The Wolff bottle is then
nearly filled with water colored with
ink. The stem of a 100 cc. pipette is
thrust through a rubber stopper in the
second neck, extending nearly to the
bottom of the bottle. The upper end
of the pipette is connected with the
II porous cell described in Ex. 16. On

M_ Si lowering a bell-jar of hydrogen over

the- porous cell, the internal pressure
becomes so great that the water is
forced out of the Wolff bottle in a
fine jet to a considerable height.

Apparatus (Fig. 25) ; 2-necked 500 cc. Wolfl bottle; 100 cc,
pipette ; porous cup used in Ex, 16 ; glass jet to fit second neck of
the Wolff bottle; bell-jar of II.

19. Diffusion and its application to the fire-damp indi-
cator.— The porous cup in Kx. 16 is connected with one
limb of a U-tnbe which is half filled with mercury. Through

the open end of the U-tube two insulated annunciator wires
twisted together are thrust, the ends of which arc made
bare so as to give good electrical contact. One of the wires

Fia. 25

HYDROGEN

dips some distance into the mercury, and the bare end of
the other wire is held a millimeter above the mercury menis-
cus. On lowering the bell-jar of hydro-
gen over the porous cup, the internal
pressure will cause the mercury in the
open end of the U-tube to rise, thereby
closing

an electric circuit, which coil-

Fig. 26

sists of a battery and a bell * or buzzer.

The practical application of the indi-
cator in mines may be better shown by
having the bell at some distance from
the lecture table ; in the back part of the
room, for example. A further realism
may be added by covering the apparatus
with a large box or closet and admitting illuminating gas
into its interior, thereby creating an artificial fire-damp.

vy/ , 1 1 , i L t _ , 1 L Z p Porous cup used in Ex. 10 ; insulated annun-

ciator wire ; battery ; bell or buzzer ; U-tube ; Hg.

20. Diffusion through rubber. — That
hydrogen also readily diffuses through a
material such as rubber may be shown
by means of the following apparatus (Fig.
27): —

A tubulated bell-jar is fitted with a cork
and a wide glass tube 20 cm. long. A piece
of thin dentist's rubber is tightly stretched
over the mouth of the jar, and tightly tied
on with a string passing under the rim of
glass around the mouth of the jar. After
clamping the apparatus in an upright posi-
tion, hydrogen is conducted through a fine

Fig. 27

1 Dry batteries and bells or annunciators or buzzers are readily ob-
tainable at almost any electrical supply store, at a very low price.

CHEMICAL LECTURE EXPERIMENTS

tube small enough to be pushed up through the larger tube
into the bell-jar. When all the air is displaced, the small
glass tube is withdrawn without stopping the flow of hydro-
gen, and a vessel of colored water is so placed that the large
glass tube will dip under the surface of the water. Soon
the hydrogen will begin to diffuse out through the rubber,
and the colored water will rise in the glass tube.

Apparatus (Fig. 27) ; small tubulated bell-jar; sheet of dentist's
rubber 15 cm. square ; ink water.

21. Separation of hydrogen and oxygen by diffusion. —
The elements of oxyhydrogen gas may be separated by

diffusion by passing a slow stream of the gas through a
long porous tube and testing the gas issuing at the other
end after collecting it over water. The hydrogen being
much more diffusible than oxygen, rapidly passes out
through the walls of the porous tube, leaving the oxygen
behind.

A simple apparatus for demonstrating this principle may
be made by connecting the tips of two clay pipes with

extra long stems by a
short piece of rubber tub-
ing. The bowl of each
pipe is closed with a one-
holed rubber stopper. One
pipe is connected with a
supply of oxyhydrogen

gas.

and the other with

a pneumal lc t rough | Fig.

28). The rate at which
FlG 28 the, gaseous mixture is

passed through the pipes
will influence in a marked degree the composition of the
gas collected at the pneumatic trough. If the rate is too

HYDROGEN 59

rapid, the hydrogen will not have time to diffuse out,
and the collected gas will still retain its explosive char-
acter. If the rate is too slow, sufficient air to dilute the
oxygen will have diffused into the tube, and the collected
gas will not relight a glowing splinter. A preliminary test
should be made to determine the rate of bubbling in the
pneumatic trough that will give the most satisfactory
results. For preliminary testing not more than 30 cc.
should be collected at one time. The so-called church-
warden pipes serve this purpose admirably, and they may
be mounted in a double burette clamp. The oxyhydrogen
gas is best held in a tubulated bell-jar fitted with a cork
and a stop-cock, immersed in a pail of water. The jar is
filled one-third with oxygen and two-thirds with hydrogen.
The effect of increasing and diminishing the rate of flow
of the gases should be noticed after the experiment is
ended. Increasing the flow causes the collected gas to
explode; diminishing the flow contaminates the collected
gas with air to such an extent that a glowing splinter is
not rekindled.

Oxyhydrogen gas in a tubulated bell-jar ; 2 churchwarden pipes ;
double burette clamp.

22. Combustion in air. — (a) The characteristic colorless
hydrogen flame is best obtained by allowing gas from a
Kipp generator (free from air) to burn at the tip of an
ordinary blowpipe. The flame is so nearly colorless that it
cannot be seen at a distance, so its presence is shown by
igniting a piece of paper with it or by holding in it a fine piece
of platinum wire, which will be heated to incandescence.

In case a glass jet is used, the flame will be colored yel-
low from the sodium in the glass. A platinum tip (Ex.
5, p. 182) may be substituted for the glass or blowpipe jet.

Blowpipe jet ; fine platinum wire.

CHEMICAL LECTURE EXPERIMENTS

Fig. 29

(6) Owing to its low specific gravity, hydrogen may be
siphoned out of a glass bell- jar by means of a glass siphon
tube, 8 to 10 mm. in diameter. A large bell-jar is clamped
mouth downwards and the shorter limb of a glass siphon
thrust up into it (Fig. 29). A rapid stream
of hydrogen from a generator enters the bell-
jar through the siphon tube, pushing the air
down until the jar is completely filled with
hydrogen. The rubber tube Leading from the
generator is disconnected, and the hydrogen
begins to flow upwards out of the longer arm
of the siphon. After the siphon is started,
the gas may be lighted at the upper end. and
will burn quietly until the mixture of air and
hydrogen reaches the flame, when the latter

will be seen to run slowly back through the siphon, igniting

the explosive gaseous mixture inside the bell-jar,
producing a loud though harmless report.

Apparatus (Fig. 20) ; large bell-jar ; siphon tube (1 cm.
inter, diam.).

23. Chemical harmonica. — Hydrogen is ig-
nited at the end of a metal blowpipe tip, whieh
is straightened out ami clamped in a vertical
position, and glass tubes of varying diameters
are lowered in turn some 15 cm. over the burn-
ing jet (Fig. 30). As the flame bums in the
glass tubes, it produces wave mot ions resulting
in different tones. By varying the diameters of J

the -lass tubes and the distance that they are
lowered over the burning jet, great diversity in
tone may be produced. The glass tidies should
not be too small in diameter. As a general rule tin
mum diameter giving satisfactory results is equal

Fio. SO

maxi-

to the

HYDROGEN 61

length of the hydrogen flame; so a flame 2 cm. long would
give a tone with a glass tube 2 cm. in diameter.
Straight metal blowpipe ; glass tubes, different sizes.

24. Ignition of hydrogen by platinized asbestos. — (a) A

stream of hydrogen impinging on finely divided platinum is
ignited.

A small bundle of asbestos fibre is wound in a loop at the
end of a stout copper wire and moistened with a few drops
of platinum chloride solution. On ignition in a Bunsen
flame the platinum chloride is decomposed and the asbestos
coated with a fine deposit of metallic platinum. On cooling
and holding the platinized asbestos in a stream of hydrogen,
it is first seen to glow, and then almost instantaneously the
hydrogen is ignited. This is the principle of the self-
lighting lamp of Dorbereiner.

Asbestos ; copper wire ; platinum chloride solution.

(b) A dry jar is filled with hydrogen by displacement and
held in a slightly inclined position mouth downwards. On
carefully introducing the bundle of platinized asbestos near
the mouth of the jar, it will be seen that the asbestos will
glow, causing a combustion of the hydrogen. If now the
asbestos is carefully inserted into another dry jar of hydro-
gen, its introduction can be so regulated that the combustion
of the hydrogen and. the air will not be produced on the
asbestos to such an extent as to cause the ignition of the
hydrogen. The water formed by this slow combustion will
be seen as white clouds at the mouth of the jar, which finally
condense as moisture on the walls of the cylinder. If the
bundle of asbestos is suddenly thrust up the jar into the
hydrogen atmosphere, it will no longer glow, and the action
ceases. On withdrawing it till it comes in contact with the
zone between the hydrogen and the air, the combustion again
proceeds.

Two 200 cc. dry cylinders of hydrogen ; platinized asbestos.

62 CHEMICAL LECTURE EXPERIMENTS

25. Reduction of cupric oxide by hydrogen. — A small
quantity of powdered cupric oxide is placed on a porcelain
crucible lid, the ring of which is pressed into a slit in a
cork fastened on the end of a long iron wire. This arrange-
ment permits of thrusting the crucible lid up into an atmos-
phere of hydrogen in a dry liter cylinder. The cylinder is
first filled with hydrogen and clamped in a vertical position
with the mouth downwards, the mouth being kept closed by
holding a glass plate against it. The cupric oxide is heated
from above with a small Bunsen flame till quite hot and
then thrust rapidly up into the hydrogen. Soon moisture
condenses on the side of the jar, and on allowing the cupric
oxide to cool in the atmosphere of hydrogen for a few
minutes and then withdrawing it, it will be seen to have the
characteristic red color of metallic copper.

Crucible lid ; cork ; stout iron wire ; liter cylinder of H ; CuO
powder.

OXYHYDROGEN GAS AND WATER

26. Formation of water by the combustion of hydrogen in
air. — (a) By passing the products of combustion of hydrogen
in air through a U-tube, a considerable quantity of water is

condensed in a short time. In the
apparatus (Fig. 31) one limb of
the U-tube is fitted with a rubber
stopper and a glass elbow con-
nected with the suction-pnnip.
The other limb is fitted with a
cork containing the small end of
a bent thistle-tube. Hydrogen,
dried by passing through a U-tube
containing calcium chloride, is allowed to burn from a blow-
pipe jet held immediately under the bulb of the thistle-tube.
The rate of suction must not be such as to cause the first

OXYHYDROGEN GAS AND WATER 63

limb of the U-tube to become warm enough to vaporize any
water that may have condensed.

Apparatus (Fig. 31); U-tube; bent thistle-tube ; metallic blowpipe
jet ; CaCl2 drying tube.

(b) Dry hydrogen is allowed to escape through a blow-
pipe jet and a dry liter bell-jar is held over the tip to show
that no moisture is deposited inside the jar. On lighting
the hydrogen jet and bringing the bell-jar again over the
flame, moisture will soon be deposited all over the inside of
the jar. The hydrogen flame should not be high enough to
generate sufficient heat to break the jar.

H generator ; drying tube ; blowpipe jet ; liter bell-jar (dry).

27, Synthesis of water by reduction of cupric oxide by
hydrogen. — A hard-glass bulb-tube maybe packed full of
cupric oxide, such as is used in elementary organic analysis,
and weighed. After reduction and cooling in a current of
hydrogen, the loss in weight may very readily be noted.
The water formed may be collected in a U-tube containing
glass beads or bits of pumice-stone drenched with concen-
trated sulphuric acid. A U-tube containing 10 g. of sulphuric
acid will take up approximately 1 g. of water, though, if a
U-tube having a bulb blown on one arm is used, the greater
portion of the water will condense in the bulb and the sul-
phuric acid will absorb the uncondensed moisture. In this
way several grams of water may be collected with quantita-
tive accuracy. With careful manipulation it is not a dif-
ficult matter to make the whole experiment quantitative, i.e.,
to determine the loss of weight of the cupric oxide and the
weight of water formed. With these data a simple calculation
will show that 8 parts of oxygen require 1 part of hydrogen

to form water.

CuO + H2 = Cu + H20.

Hard-glass bulb-tube ; H2S04 and pumice-stone U-tube ; current
of purified H ; granular CuO.

64 CHEMICAL LECTURE EXPERIMENTS

28. The oxyhydrogen flame. — The intense heat of hy-
drogen burning in air may be still more increased by
introducing a jet of burning oxygen in the centre of the
hydrogen flame. The hydrogen burning under these condi-
tions is furnished with a supply of oxygen from the air on
the outside and pure oxygen for the interior, giving rise to
the intensely hot oxyhydrogen flame. In burning these two
gases a special form of burner is required, consisting essen-
tially of a tube in the centre of which a fine jet is longi-
tudinally placed. Hydrogen is admitted to the larger tube
and ignited at its mouth. A gentle current of oxygen is
then directed through the fine jet into the centre of the
hydrogen flame. Burners specially adapted for this form
of flame are much used in producing the so-called calcium
or Drummond light.

In case such a burner is not obtainable the phenomenon
may be studied, though less advantageously, with an ordi-
nary gas blast-lamp. Unless a large hydrogen generator is
at hand, it is more satisfactory to use illuminating gas
in place of hydrogen. Oxygen may be obtained from a
gasometer or from a steel cylinder. In using the lamp,
illuminating gas is first admitted to the larger tube and
ignited at the mouth of the hurnor, where it will burn with
a flickering, smoky flame, Oxygen is then gradually admit-
ted through the central air tube. As the result of the
increase in temperature, the illuminating gas burns with
almost dazzling brilliancy, which gradually diminishes as
more oxygen is admitted. The heat is so great that only a
small flame, some 5 or 6 cm. in length, can be used. Hydro-
gen or coal gas under considerable pressure, when used witli
a regular oxyhydrogen burner, will, however, give flames of
any desired length. The small colorless pointed flame is
extremely hot, and may be used in any of the following
experiments to show its intense heat.

OXVMVDKOGKN GAS AND WATER 65

A bundle of iron wires or a small rat-tail file, when held
in the flame, burns with great brilliancy, sending out show-
ers of sparks. The molten globules of iron oxide fall to
the table, which should be protected with a sheet of asbestos
paper. The burner should be so placed that the flame is
horizontal. After the iron has become well ignited, the
illuminating gas may be cut off and the iron held in the jet
of oxygen, where it continues to burn.

A thick copper wire is immediately melted when held in
the flame.

Pieces of zinc, lead, and cadmium are readily oxidized,
while silver, though not oxidized, is soon melted to a bright
metallic globule, which by continued heating, may be made
to boil. The silver should be placed in a small bone-ash
cupel and the flame directed upon it from above. If after
the silver is melted it is allowed to cool in a current of
oxygen, a considerable quantity of the gas will be absorbed
by the metal, and just before solidification the gas will
be given off suddenly, causing a spurting out of the
metal.

A piece of thick platinum wire held in the flame is soon
melted to a globule, which may be shaken from the wire and
allowed to drop into a dish of water placed beneath the
flame.

A glass rod held in the flame is immediately melted, and
drops of molten glass are allowed to fall into a cylinder of
water.

Perhaps the most remarkable phenomenon that can be
produced with the oxyhydrogen flame is the so-called cal-
cium light. A piece of quicklime held in the flame is
immediately raised to a brilliant incandescence of almost
blinding intensity. Other highly refractory substances,
such as magnesium oxide, may also be raised to incandes-
cence when held in the flame.

66 CHEMICAL LECTURE EXPERIMENTS

In all experiments with the oxyhydrogen flame it is
advisable to protect the hands with gloves and the eyes
with colored glasses.

Oxyhydrogen blowpipe or burner ; gas blast-lamp ; cupel ; O and
H supply ; bundle of iron wires ; Cu and Pt wires ; pieces of Ag, Pb,
Cd ; quicklime.

29. Explosion of hydrogen and air. — (a) A round-
bottomed thick-walled "ginger-ale" bottle is marked in
sevenths. Two-sevenths of its volume arc filled with hydro-
gen over the pneumatic trough, and by lifting the mouth
of the bottle and allowing the water to run out, the re-
maining five-sevenths arc filled with air. On closing the
mouth of the bottle with the thumb, and inverting it once
or twice, the gases will rapidly mix, and when a taper is
applied to the mouth, a sharp explosion will result. A good
stout bottle should stand the force of the explosion, though,
unless previously tested, it is well to cover the bottle with
a towel.

Round-bottomed ginger-ale bottle ; H generator.

(b) A bulb-tube is filled with hydrogen by allowing the
gas to flow through the upper end of the tube, when held
vertically, and thereby to push out the air at the bottom.
When full, the rubber tube through which the hydrogen
flows is removed from the upper end of the bulb-tube and a
flame applied. The hydrogen, being lighter than air. rises
rapidly in the tube and burns at the top. In a few minutes
the air entering the bottom of the tube will have mixed
with the hydrogen in explosive proportions, and the flame
will strike downwards from the mouth of the tube, produc-
ing a sharp, though harmless, explosion. The internal
diameter of the arms of the bulb-tube should not be greater
than 5 or 6 mm. In case the tubing is larger than this, it is

OXYHYDROGEN GAS AND WATEB

advisable to choke the upward flow of the gas by inserting
in the upper arm of the bulb a small piece of glass tubing
thrust through a small cork, or through a short piece of
rubber tubing.

Bulb-tube ; H generator.

(c) The preceding experiment may be performed with an
equal degree of safety on a much larger scale by using a
tubulated liter bell-jar, the tubulature of which
is fitted with a cork containing a short piece
of tubing 0 nun. in diameter (Fig. 32). The
bell-jar is filled with hydrogen, either by
sending a slow stream of the gas in at the
top through the glass tube, thus forcing out
the air at the bottom, or at the pneumatic
trough, in which latter case it will be neces-
sary to plug the glass tube temporarily by a
short piece of rubber tubing and a bit of glass
rod. The hydrogen is lighted at the top of
the glass tube, and burns regularly, as it is
forced out by the air rising from the bottom.
In a few minutes the explosive mixture with air is formed,
and the flame strikes downwards through the glass tube,
causing an explosion in the bell-jar.

Tubulated liter bell-jar ; IT generator.

Fig.

30. Explosion of a hydrogen generator. — (a) To illus-
trate the explosive nature of a mixture of hydrogen and
air and the consequent danger of applying a lighted taper
to a hydrogen generator before all the air has been driven
out, a stout round-bottomed ginger-ale bottle is used for the
generator, as, owing to its strength, it will suffer no damage
by an internal explosion (Fig. oo). Ten grams of granulated
zinc are placed in the bottle, which is clamped in an up-

CHEMICAL LECTUKE EXPERIMENTS

right position, and 8 cc. of dilute sulphuric acid, made by-
adding 1 cc. of concentrated sulphuric acid to 7 cc. of
water in a test-tube are poured, while still warm
from the act of dilution, into the bottle. A
well-fitting one-holed cork, carrying a 10 cm.
length of oiled paper tube, such as is used in
drinking beverage8, is loosely placed in the mouth
of the bottle and the tip of the paper immedi-
ately ignited. The burning paper soon ignites
the explosive mixture of hydrogen and air which
strikes back into tin* bottle, producing a sharp
explosion and blowing out the cork. While care
should he taken not to direct the bottle toward
any one, the nature of the cork and the paper

Rio. 33

tube is such as to cause no dam

Ginger-ale bottle; 10 cm. paper tube (artificial bar Btra
granulated Zn.

(b) A more striking illustration of the danger of explosion
of a hydrogen generator by premature lighting is shown by
means of the following apparatus. A
250 cc, Krlenmeyer tlask, preferably of
very thin glass, is fitted with a two-
holed stopper carrying a thist le-tube
and a glass elbow. A tew scraps of
zinc are placed in the bottom of the
tlask and 5 cc. of concentrated hydro-
chloric acid poured into the thistle-
tube. A candle fastened on a wire is
placed with its flame at the end of the
glass elbow which serves as a delivery-
tube for the gas. To retard the action
of the hydrochloric acid on the zinc in order to afford time
for lighting the candle and properly covering the apparatus,

Fig. 34

OXYHYDROGEN GAS AND WATER 69

the lower end of the thistle-tube is drawn out into a fine point,
allowing the acid to fall drop by drop (Fig. 34). Soon the
mixture of hydrogen and air assumes the right proportion
for the mixture to strike back through the glass elbow into
the flask, producing an explosion which will destroy the
whole apparatus. In order to protect the audience, it is
necessary either to cover the entire apparatus with a small
wooden box, or better, to surround it with heavy glass
screens. Instead of a thistle-tube, a piece of glass tubing
may be used, of which the lower end is drawn out into a fine
point, and the upper end, extending but a short distance
above the cork, is joined with a small glass funnel by means
of a rubber connector. In this arrangement the glass
funnel is seldom broken.

250 cc. Erlenmeyer flask ; thistle-tube : glass elbow ; two-holed
rubber stopper ; wooden box or glass shields ; candle ; scrap Zn.

31. Explosion of hydrogen and oxygen. — (a) While the
explosion of hydrogen and diluted oxygen, i.e., atmospheric
air, is sharp, that produced by the ignition of a gaseous
mixture consisting of two parts hydrogen and one part
oxygen is very violent, necessitating considerable care in its
demonstration.

The round-bottomed bottle used in Ex. 29 is two-thirds
filled with hydrogen over the pneumatic trough, and the
remaining one-third with oxygen. On shaking the bottle
for a moment, the gases become sufficiently mixed to produce
a violent explosion when a taper is applied. It is advisable
to wrap the bottle in two or three layers of towel. As the
proportions in which the gases are mixed should be approx-
imately correct, the bottle is roughly graduated by pasting a
strip of paper on the outside indicating two-thirds of its
volume.

Round-bottomed ginger-ale bottle ; H and 0.

70 CHEMICAL LECTURE EXPERIMENTS

(b) The explosion of a half liter of oxyhydrogen gas may
be safely accomplished by placing a flask filled with the gas

under a box, and exploding the mix-
ture with an electric current (Fig. 35).
A 500 cc. flask is two-thirds filled
with hydrogen and the remaining
third with oxygen. A two-holed
Fig. 35 rubber stopper carrying stout rods

of brass, which extend to the centre
of the flask, is then inserted in the neck. The inner ends
of the brass rods should be electrically connected with a
piece of very fine platinum wire (Ex. 14). The flask is then
placed on a piece of asbestos paper on the table and covered
with a small wooden box, which is in turn covered with a
larger box. The larger box should be raised one inch from
the table by small blocks of wood at each corner. Two lead
wires are brought from the brass rods to the bichromate
battery, which may be placed at some distance from the
box. On making the connection, the platinum wire is heated
to redness and the gaseous mixture is exploded. While it
is not uncommon to have the small box destroyed by the
force of the explosion, the large box will not be damaged.
The glass flask will be reduced to a line powder.

500 cc. flask ; 2-boled rubber stopper ; two brass rods ; line I't wire ;
small and large wooden boxes ; asbestos paper ; bichromate battery ;

connecting wires ; II supply ; 0 supply.

32. Explosion of oxyhydrogen soap-bubbles. — (a) Soap-
bubbles are blown with the oxyhydrogen mixture in a
thistle-tube as described in Ex. 13. On being liberated

they rise slowly through the air, and are easily ignited
by touching with a small wax candle on the end of a stick.
It is of the utmost importance that no particles of burn-
ing paper or other material should be allowed to come

OXYHYDKOGEN GAS AND WATER ?1

in contact with the thistle-tube by which the bubbles are
blown, as a dangerous explosion would result by the striking
back of the explosive gaseous mixture into the holder. It is
advisable to use a non-sparking material for a taper, such as
a small wax candle firmly fastened on a long stick. The
glass funnel used in igniting bubbles filled with hydrogen
(Fig. 21, p. 52) may be used here to advantage.

Oxyhydrogen gas ; thistle-tube ; soap solution ; candle on stick.

(b) A small quantity of soap solution is placed in the
bottom of a large iron mortar or dish, and a handful of soap-
bubbles blown by directing a stream of mixed hydrogen and
oxygen through it. After removing the tube conducting the
mixed gases, the soap-bubbles are exploded by means of
a candle on the end of a long stick. The concussion is so
great that only a small volume of the mixed gases should
be exploded at one time.

33. Electrolysis of water and the preparation of oxy-
hydrogen gas. — A simple apparatus for the electrolysis of
water is shown in Fig. 5, p. 14, and consists of a small wide-
mouthed bottle with a three-holed rubber stopper. Glass
tubes carrying platinum electrodes are fitted into two of the
holes, and a delivery-tube thrust into the third hole leads to a
pneumatic trough. The end of the delivery-tube must not
be thrust clear through the cork. The bottle is filled to
overflowing with 10 per cent sulphuric acid, and the cork
pushed down into the flask in such a manner that the dilute
acid will fill the delivery -tube, expelling all air. Before turn-
ing on the electric current, care should be taken that the
platinum electrodes are as far apart as possible in the vessel.
On allowing the current from three or four bichromate cells
to pass through the solution, a rapid evolution of hydrogen
and oxygen takes place. The mixed gases may be collected

72 CHEMICAL LECTURE EXPERIMENTS

in a eudiometer (Fig. 11, p. 26) at the pneumatic trough.
The eudiometer is transferred to another dish by placing the
thumb on the bottom of the tube, and potassium pyrogallate
solution is allowed to flow through the mixed gases and
absorb the oxygen. When the absorption is complete, it will
be found that the residual gas, which will burn quietly, is
two-thirds of the original volume.

If the delivery-tube dips sufficiently beneath the surface
of the water in the pneumatic trough to disengage the
bubbles (to prevent the explosion from striking back into
the bottle) from the delivery-tube before reaching the surface
of the water, they may be exploded by holding a match or
gas-jet at the surface of the water.

Electrolytic apparatus (Fig. 5, p. 14) ; eudiometer (Fig. 11. p. 26) ;
four bichromate cells; 11 -S( )4 (lo per oeut) ; potassium pyrogallate

solution (Ex. 21, p. 20).

34. Electrolysis of water. — (a) The decomposition of
water by the electric current with the separation of the two
gases, hydrogen and oxygen, in their relative volumes two to
one, is shown by the use of the apparatus (Fig. 40, p. 95)
which, of the many forma of electrolytic apparatus described
by Hoffmann, is the one best adapted for many experiments.
The electrodes here used are made by passing small ^\:
tubes through one-holed rubber stoppers inserted in the two
lower openings of the apparatus. Through these glass tubes
platinum wires are passed and fused to prevent any escape
of the liquid through the glass tube. Small pieces of plat-
inum foil are fastened to the ends of the wire, thus giving
greater surface to the electrodes. The glass portion of the
apparatus is mounted on a specially devised iron stand.
After use the apparatus should be thoroughly rinsed with
water, the rubber stoppers carrying the electrodes removed,
and the glass stop-cocks either removed and tied with a

OXYHYDROGEN GAS AND WATER 73

piece of twine to their respective tubes, or wedged into their
openings with a piece of paper. When properly handled
such an apparatus should last for years.

For the electrolysis of water the stop-cocks are closed and
the open bulb filled with 10 per cent sulphuric acid, the elec-
trodes having been tightly inserted. On opening the stop-cock
the solution will rise, expelling the air, and in case it is de-
sired to ignite the hydrogen after electrolysis, care should be
taken to allow no water to enter the hole drilled through the
glass stop-cock, or the bit of tube extending beyond. In
case water should reach these portions, it should be removed
by a strip of filter-paper rolled into a fine point, as other-
wise on opening the cock drops of water will be forcibly
ejected, and. may easily extinguish a match or taper used to
test the gas. As at best there is not a large quantity of gas
to be experimented with, all precautions should be taken
that none is wasted. Having filled both arms of the tube,
the current from four or more cells of a bichromate battery
may be sent through the apparatus, and immediately bub-
bles will rise from both electrodes. After a few minutes it
will be observed that twice as much gas will have collected
in one tube as in the other.

On holding a glowing splinter over the tube containing
the smaller volume of gas, proof may be had of the presence
of oxygen. The gas issuing from the other jet when opened
may be ignited and shown to be hydrogen. If the tip of the
glass tube is moistened with strong sodium chloride solution,
the hydrogen flame will be sufficiently colored to be seen at
a distance. 2H20=2H2 + 02.

Hoffmann electrolytic apparatus (Fig. 46, p. 95); four cells bichro-
mate battery ; 10 per cent H2S04.

(b) The decomposition of acidulated water by the electric
current may be much more simply effected by using the

CHEMICAL LECTURE EXPERIMENTS

apparatus shown in Fig. 36. The electrodes of this appa-
ratus are prepared by sealing a short piece of platinum
wire fastened to a piece of platinum foil into a drawn-out

tube bent in the form of a
hook. The tube is then filled
with mercury, and the con-
nections are made by thrust-
ing the lead wires from a
battery into the mercury in
the tube. Two glass cylin-
ders of equal diameter are
filled with the acidulated
water and inverted over the
electrodes.
The electrodes may be still further simplified by fasten-
ing pieces of platinum foil to rubber-covered copper wire.
It is necessary in this case, however, to cover with paraffin
all parts of exposed copper.

Fig. 36

HYDROGEN PEROXIDE

FORMATION AND PREPARATION

35. By cooling a jet of burning hydrogen. — When a
flame of burning hydrogen is suddenly cooled, small quanti-
ties of hydrogen peroxide are formed.

Hydrogen obtained from the action of zinc on dilute sul-
phuric acid is allowed to burn from a glass jet, 3 or 4 mm.
in diameter, directed downwards upon
water in a porcelain evaporating dish,
which has a few pieces of ice floating
in it. Two or three drops of dilute
sulphuric acid should be added to
the water in the dish. The jet flame is so played on the
surface of the water as to cool about one-half of it, and ig

Fig. 37

HYDROGEN PEROXIDE 75

allowed to burn in this way for two or three minutes. The
jet should be clamped in the proper position.

The liquid is tested by adding some potassium iodide-
starch solution, to which a drop of ferrous sulphate solution
has been added. A blue color indicates the presence of
hydrogen peroxide.

H from Zn and H2S04 ; ice ; KI starch solution ; FeS04 solution.

36. By the action of sodium peroxide on water. — When
small quantities of water are added to sodium peroxide, oxy-
gen is liberated, sodium hydroxide being formed (Ex. 5,
p. 11). If small quantities of the peroxide are added to a
large quantity of water, the oxygen is not liberated but is
retained as hydrogen peroxide.

One hundred cubic centimeters of cold water, to which
5 cc. of sulphuric acid have been added, are placed in a
beaker into which 2 or 3 g. of sodium peroxide are allowed
to fall slowly. The liquid should be constantly stirred.
After the addition of the sodium peroxide the liquid, which
should still be strongly acid, will contain considerable quan-
tities of hydrogen peroxide.

Na202 + 2 H20 = 2 NaOH + H202.

37. From barium peroxide and sulphuric acid. — Concen-
trated sulphuric acid acts on barium peroxide to produce
oxygen which under 75° C. is rich in ozone (Ex. 30, p. 31).

When, however, dilute sulphuric acid and barium perox-
ide are allowed to interact under conditions which maintain
the mixture at a low temperature, considerable quantities
of hydrogen peroxide are formed.

A handful of crushed ice is placed in a beaker and a few
grams of barium peroxide stirred in with it. Enough dilute
sulphuric acid is added to cover the ice, and the liquid is fil-

76 CHEMICAL LECTURE EXPERIMENTS

terecl off from the insoluble barium sulphate formed. The
filtrate contains hydrogen peroxide, which may be used for
any of the following experiments.

With care the method with slight alterations will give a
chemically pure solution of hydrogen peroxide. Such a
solution is, however, readily obtained in the market.

Ba02 + H2S04 = H202 + BaS04.

Crushed ice ; Ba02.

PROPERTIES

38. Action on potassium dichromate. — In a dilute acidu-
lated solution, potassium dichromate reacts with hydrogen
peroxide, giving an intense blue color due to the formation
of perchromic acid. This reaction serves to identify small
quantities of hydrogen peroxide.

A very dilute solution of potassium dichromate, contain-
ing a few drops of sulphuric acid, is placed in a stoppered
glass cylinder and 1 cc. of hydrogen peroxide is added.
The liquid is colored intensely blue. If one-half of the
solution is poured into a small cylinder and allowed to stand
for a few moments, the color rapidly disappears.

A 1.5 cm. layer of ether is added to the remaining solu-
tion in the stoppered cylinder and the cylinder shaken. On
standing, the ether will separate and will acquire the deep
blue color, which will have disappeared from the liquid
beneath.

100 cc. stoppered cylinder ; IIo()2 ; K2Cro07 solution ; ether.

39. Action on lead sulphide. — The oxidizing action of
hydrogen peroxide in converting a sulphide to a sulphate is
shown by the conversion of black lead sulphide to white lead
sulphate. To a small quantity of freshly precipitated lead
sulphide suspended in water a few cubic centimeters of

HYDROGEN PEROXIDE 77

hydrogen peroxide are added. Immediately the black sul-
phide is oxidized to the white sulphate. By dipping filter-
paper in a solution of lead acetate and exposing it to the
fames of hydrogen sulphide, black lead sulphide is formed
on the paper. On immersing the blackened paper in hydro-
gen peroxide solution, the paper becomes colorless.

PbS + 4 H202 = PbS04 + 4 H20.
Freshly precipitated PbS suspended in water ; H202.

40. Oxidizing action on zinc and sulphuric acid. — A

small piece of zinc placed in a test-tube is covered with
about 10 cc. of water, and then 1 drop of concentrated sul-
phuric acid added. Almost immediately the evolution of
hydrogen takes place, and the liquid is seen to be opaque as
a result of the bubbles. On adding an equal volume of
acidulated hydrogen peroxide, the gas evolution immediately
ceases and the solution becomes clear.

That this cessation of the evolution of the gas may not
be the result of dilution, the hydrogen peroxide should con-
tain enough sulphuric acid to maintain the solution at or
above the original percentage of acid.

H202 + H2 = 2 H20.

Acidulated H202 solution ; granulated Zn.

41. Electrolysis of hydrogen peroxide. — The rapid oxi-
dation of nascent hydrogen by a solution of hydrogen per-
oxide is well shown when the electric current is used to
produce an evolution of hydrogen in an acidulated solution
of hydrogen peroxide.

A small cylinder is filled with a 10 per cent solution of sul-
phuric acid. A similar cylinder is filled with hydrogen per-
oxide which contains a few drops of concentrated sulphuric
acid. The solutions in the cylinders are electrically con-

CHEMICAL LECTURE EXPERIMENTS

Fig. 38

nected by means of a loop of platinum wire dipping into the
liquid in each cylinder (Fig. 38). Electrodes consisting of
small pieces of sheet platinum are dipped
^X rT\ into each cylinder and the circuit of a

^ ' bichromate battery thereby closed. If

the positive electrode is immersed in the
dilate sulphuric acid, a rapid evolution of
hydrogen will take place and the liquid
will become turbid from the ascending
bubbles. The negative electrode, i.e., the
one immersed in the peroxide of hydro-
gen solution, will also give rise to a gas evolution. If now
the current be reversed or the electrodes transposed, it will
be found that the electrode immersed in the hydrogen per-
oxide solution gives no gas evolution if the battery is not
too strong, while that immersed in the dilute sulphuric acid
acts as before. In this case the nascent hydrogen liberated
by the electrolytic action is oxidized by the hydrogen per-
oxide as fast as formed.

When acidulated hydrogen peroxide is electrolyzed with
platinum electrodes in the Hoffmann apparatus (Fig. 46,
p. 95), a gas collects only in one arm of the tube, the hydro-
gen being oxidized as fast as formed by the hydrogen
peroxide.

Bichromate battery, two or three cells ; Pt wires ; Pt electrodes ;
Hoffmann electrolytic apparatus (Fig. 46, p. 96); HsOs; 10 per
cent H2S04.

42. Bleaching action. — Hydrogen peroxide, when not
too acid, bleaches organic matter readily. This bleaching
action is best shown by adding to a solution of aniline red
a few cubic centimeters of hydrogen peroxide. If the
reagent is not too acid, the color will be discharged on
boiling.

HYDROGEN PEROXIDE 79

If acid is added to the hydrogen peroxide, the mixture of
aniline red and the reagent can be boiled with no appreci-
able change in color, as the acidulated solution of the per-
oxide is very stable. On adding a few drops of sodium
hydroxide to the hot solution, the color is instantly dis-
charged

If the hydrogen peroxide solution is made alkaline and
then added to the aniline red, the color is discharged instantly
even in the cold.

Aniline red ; H202.

CHLORINE

PREPARATION

1 . From manganese dioxide and hydrochloric acid. —

Concentrated hydrochloric acid when mixed with manga-
nese dioxide and gently heated yields chlorine.

A 2 1. flask is one-fourth filled with coarsely pulverized
(not powdered) manganese dioxide. Sufficient concentrated
hydrochloric acid is added to cover the solid and the mix-
ture is heated with a low flame. A two-holed rubber stopper
carrying a bulb safety-tube and a glass elbow is inserted in
the neck of the flask. The gas is first conducted through a
gas washing-bottle containing a small quantity of water, then
through a three-way cock into a second gas washing-bottle
containing sulphuric acid. The third arm of the three-way
cock (Fig. 39) is connected with a flue. The bend of the
safety-tube is filled with concentrated sulphuric acid # or
mercury. By means of the three-way cock the gas may be
conducted into the flue until desired and then by turning the
cock may be passed through the sulphuric acid into any
apparatus.

Though no difficulty should be experienced in properly
turning the three-way cock it is easy to note by the bubbling
in the sulphuric acid bottle whether or no the gas is properly

CHLORINE

directed. In case the cock should be so turned as to cut
the exit of the gas off entirely, the rise of the sulphuric acid
or mercury in the safety -funnel as well as the absence of
bubbles in the gas washing-bottle containing water will be
immediately noticed. The stopper used in the generating
flask should be of rubber, and both the safety-tube and

the glass elbow should fit snugly
into the respective holes. Chlo-
rine will in course of time attack
rubber and render it hard and
unsuited for use. By coating
the under side of the stopper
with collodion just before insert-
ing it in the flask, the action of

^=a=^a

Fig. 39

the chlorine may be very much lessened. The water in the
gas washing-bottle removes traces of hydrochloric acid car-
ried over, and the gas issuing from the sulphuric acid bottle
is, accordingly, quite pure. In case a flue is not at hand,
the warste gas issuing from the stem of the three-way cock
should be conducted through a glass tube into potassium or
sodium hydroxide solution.

Mn02 + 4 HC1 = MnCl2 + 2 H20 +C12.

Apparatus (Fig. 39) ; 2 1. flask ; two gas washing-bottles ; three-
way cock ; safety -tube ; 2-holed rubber stopper ; coarsely pulverized
Mn02.

82 CHEMICAL LECTURE EXPERIMENTS

2. By the action of sulphuric acid on a mixture of sodium
chloride and manganese dioxide. — Instead of acting directly
on manganese dioxide with hydrochloric acid, the acid may
be prepared in the presence of manganese dioxide, where it
is immediately oxidized with the liberation of chlorine.
The apparatus used is shown in Fig. 39.

One hundred grams of finely pulverized manganese dioxide
are mixed with an equal weight of sodium chloride, and the
mixture is placed in the generating flask. One hundred and
ten cubic centimeters of concentrated sulphuric acid are
poured slowly into 100 cc. of water in a beaker and the
mixture cooled. The dilute acid is then poured into the
generating flask upon the manganese dioxide and sodium
chloride. The flask is well shaken for a moment and the
cork immediately inserted. A rapid stream of chlorine,
which may be maintained by the application of a gentle
heat, is obtained.

4 NaCl + MnOa + 3 H2S04 = 2 NaHS04 + Na2S04 +
MnCl2 + 2 H20 + Cl2.

Apparatus (Fig. 39) ; finely pulverized Mn02 ; NaCl ; acid mixture
(110 cc. H2S04 + 100 cc. IIoO).

3. From hydrochloric acid and potassium dichromate. —

Potassium dichromate oxidizes hydrochloric acid, yielding
chlorine free from carbon dioxide. The apparatus (Fig. 39)
is used, and 500 cc. of concentrated hydrochloric acid are
poured upon 100 g. of coarsely pulverized potassium dichro-
mate in the generating flask. By gently heating over a wire
gauze a rapid stream of pure chlorine is obtained.

K2Cr207 + 14 HC1 = 2 KC1 + 2 CrCl8 + 7 H20 + 3 CI*

Apparatus (Fig. 39) ; K2Cr207.

4. By the action of a mixture of gaseous hydrochloric acid
and air on heated copper salts (Deacon's process). — An in-

CHLORINE 83

teres ting process for the technical manufacture of chlorine
is the so-called " Deacon's process/' in which a mixture of air
and hydrochloric acid is conducted over a heated copper salt.

Small fragments of pumice-stone, sufficient to fill a bulb-
tube, are heated in an evaporating dish with a strong solu-
tion of copper sulphate or copper chloride until all water of
crystallization is driven from the salt. The bulb is then
filled with the prepared pumice-stone. A mixture of air and
hydrochloric acid gas is obtained by allowing the gases to
enter a three-necked Wolff bottle (Fig. 69, p. 159) and bubble
through concentrated sulphuric acid. The mixed gases issue
through the third neck of the Wolff bottle, through a glass
elbow which is connected with one end of the bulb-tube. The
other end of the tube is fitted with a rubber stopper and an
elbow dipping into a beaker containing a solution of potas-
sium iodide and starch. The gaseous mixture is passed
through the system and no color is obtained in the beaker.
On heating the bulb with a Bunsen lamp the air and the
hydrochloric acid gas react in the presence of the copper
salt to form free chlorine, and a blue color immediately
appears in the beaker. It is necessary that the hydrochloric
acid gas used in this experiment should be perfectly free
from chlorine.

Instead of preparing gaseous hydrochloric acid the experi-
ment can be more simply carried out by conducting a gentle
current of air through a gas washing-bottle containing con-
centrated, chemically pure hydrochloric acid. In passing
through the bottle sufficient hydrochloric acid gas will be
taken up by the air current to react when passed through
the heated bulb and will give a blue coloration in the

beaker.

2 HC1 + 02 = H20 + Cl2 [?].

3-necked Wolff bottle ; bulb-tube containing pumice-stone and
CuS04 ; HC1 gas supply ; air-blast ; Kl-starch solution.

84 CHEMICAL LECTURE EXPERIMENTS

PROPERTIES

5. Chlorine water. — (a) Chlorine is readily absorbed by
water, imparting to it a greenish color and many of the

properties of the
gas.

A retort is com-
pletely filled with
FlG 40 ^^^E^^ water and inverted

as in Fig. 40. Chlo-
rine is conducted through a long delivery-tube in the neck
of the retort, and the body is about half filled with the gas.
The absorption is quite rapid, and in a short time the water
has a decided greenish color.
500 cc. retort ; CI supply.

(b) The preparation of any considerable quantity of chlo-
rine water is best effected by conducting the gas through a
series of Wolff bottles (Fig. 85, p, 196) half filled with
cold water. The tube through which the gas enters each
Wolff bottle should dip only a little below the surface of
the water. Provision should be made for absorbing any
gas escaping from the system in sodium hydroxide or for
conducting it to a flue.

Apparatus (Fig. 8-"), p 196) ; CI supply.

6. The crystalline hydrate of chlorine. — One molecule of
chlorine combines with ten molecules of water to form a
white crystalline hydrate (Cl2 + 10 ILAJ) which decom-
poses a little above zero.

A current of chlorine is conducted into 25 cc. of water in
a 100 cc. flask containing a few small pieces of ice. Soon
the hydrate is formed, and the liquid in the flask solidities
to a crystalline mass.

CI supply ; ice.

CHLORINE

Fig. 41

-T7

Fig. 42

7. Combustion of hydrogen in chlorine.— A jet of burning
hydrogen when lowered into an atmosphere of chlorine
continues to burn with a blue

flame, forming hydrochloric
acid.

Hydrogen is conducted
through the recurved jet, Fig.
41, and lowered into a liter
cylinder of chlorine. White
fumes of hydrochloric acid
gas rise from the mouth of
the cylinder, and a piece of
blue litmus paper is reddened
when held in the gas.

A jet of chlorine burns when thrust up into an inverted
cylinder of hydrogen (Fig. 42).

H2 + Cl2 = 2 HC1.

Recurved jet Fig. 41 ; H supply ; liter cylinder of CI ; litmus paper
(blue).

8. Explosion of a mixture of chlorine and hydrogen. —

A mixture of equal volumes of chlorine and hydrogen when
ignited explodes with considerable force.

A 100 cc. stout-walled cylinder is filled with chlorine and
placed mouth to mouth with a cylinder of the same size
filled with hydrogem The gases are mixed by shaking, and
the cylinders are then separated and covered with glass
plates. On removing the plates and applying a flame the
mixture explodes with a loud report. The greatest care
should be taken to keep the mixed gases away from all
direct sunlight, as under the influence of bright light the
gases combine with explosion.

100 cc. cylinder of CI ; 100 cc. cylinder of H.

86 CHEMICAL LECTURE EXPERIMENTS

9. Combustion of a candle. — The gaseous hydrocarbons
volatilized by a burning candle will burn in chlorine with
the liberation of carbon in the form of soot. A burning
candle when lowered into chlorine, which should be free
from any great amount of carbon dioxide, burns with a
lurid, smoky flame, large quantities of soot being deposited.
The flame is easily extinguished and at best burns only a
few moments.

A burning splinter thrust into chlorine is immediately
extinguished.

Candle on wire ; jar <>f CI.

10. Action on turpentine. — When slightly warmed tur-
pentine is introduced into chlorine, the reaction is BO great
that the turpentine is ignited.

Three or four cubic centimeters of turpentine are warmed
in a test-tube and poured on a piece of filter-paper or che<

cloth fastened on a wire. The doth is then quickly lowered
into a liter cylinder of chlorine. In a few moments the
turpentine will become ignited and deii>e clouds of soot will

pour out of the cylinder. Obviously the experiment should

be conducted only in a good draft

Liter cylinder <>t' CI ; turpentine ; filter-paper on wire.

11. Bleaching. — on Chlorine, combining, as it d
with the hydrogen of water and liberating nascent oxygen,
is a powerful bleaching agent.

A piece of cloth dyed with turkey red is dampened and
lowered into a cylinder of chlorine. Jn a lew moments the
color will have entirely disappeared.

The importance of having water in the operation of
bleaching with chlorine may be shown as follows: A piece
of turkey-red cloth which has been dried for half an
hour in an air-bath immediately before use is lowered into

CHLORINE 87

a cylinder of chlorine which has been especially dried by
shaking the gas with 25 cc. of concentrated sulphuric acid.
Care should be taken in drying the gas to have the cylinder
closed with a glass plate to avoid spattering the acid. If
the wire on which the piece of cloth is suspended is fastened
to a piece of cardboard large enough to cover the mouth of
the cylinder, the cloth may be left for some time in the gas
with no appreciable change of color. If the cloth is then
removed and held in steam for a few moments and again
introduced into the gas, the color is almost immediately dis-
charged.

Two cylinders of CI (one dried by shaking with con. II2S04) ; pieces
of turkey-red cloth ; boiling water in a beaker.

(b) Chlorine bleaches many organic dyes used in prepar-
ing writing-inks, though it is without action on carbon in
the graphite of the lead pencil and the lamp-black of print-
ing-ink.

A piece of white paper, upon which several characters in
printing-ink have been stamped, is marked with a lead
pencil, several kinds and colors of writing-ink, and with a
blue pencil. The paper is then moistened by dipping into
water and thrust into a cylinder of chlorine. The printing-
ink and lead-pencil marks will be unaffected by the chlorine.
The blue pencil is ordinarily turned green, and the writing-
inks will for the most part be entirely bleached.

Large cylinder of CI ; piece of paper ; colored inks ; blue and black
lead pencils.

12. Decomposition of chlorine water by sunlight. — In the

presence of sunlight chlorine combines with the hydrogen
of water, forming hydrochloric acid and liberating oxygen.

A eudiometer tube or plain glass tube sealed at one end
is completely filled with strong chlorine water, inverted in
a crystallizing dish containing the same liquid, and clamped

CHEMICAL LECTURE EXPERIMENTS

in a vertical position. If the apparatus is placed in direct
sunlight, the action will soon begin, and fine bubbles of gas
will collect in the top of the tube. The reaction requires
some time for completion, though on standing twenty-four
hours a sufficient quantity of gas will have collected in the
top of the tube to be tested. A glowing splinter thrust into
the gas will be rekindled. See also apparatus (Fig. 4, p. 13).

2 H20 + 2 Cl2 = 4 HC1 + 02
Eudiometer tube ; strong CI water.

13. Action on brass. — (a) Thin brass or so-called Dutch
metal leaf burns when thrust into a jar of chlorine. A
small piece of the leaf is fastened to a stout iron wire and
lowered into a 250 cc. cylinder of chlorine. On entering
the gas the leaf takes fire and burns brilliantly.
Dutch metal leaf ; jar of CI.

(b) A few leaves of Dutch metal are placed in a dry,
stout-walled filter-flask, which is fitted with a one-holed
rubber stopper carrying a short piece of rub-
ber tubing and a pinch-cock. In case the
filter-flask has a side tube it should be securely
plugged. The flask is then attached to a
filter-pump, and a good vacuum is obtained.
A glass tube is fastened to the free end of
the rubber tube and lowered into a 500 cc.
jar of chlorine (Fig 43). On opening the
pinch-cock the chlorine rushes up the tube
into the flask, and the Dutch metal is imme-
diately ignited.

A straight glass stop-cock may be advan-
tageously used in place of the rubber tube
and pinch-cock.

Filter-flask ; rubber stopper (1 -holed) ; £lass tube ; rubber tube
and piuch-cock ; Dutch metal leaves ; jar of CI.

J /

Fig. 43

HYDROCHLORIC ACID

PREPARATION

14. From the union of hydrogen and chlorine. — See Exs.

7 and 8.

15. By the combustion of chlorine in hydrogen. — The

combustion of chlorine in an atmosphere of hydrogen, form-
ing hydrochloric acid gas, may also be shown by means of
the apparatus (Fig. 44).

Hydrogen from a Kipp generator is conducted through
the cork in the top of the lamp chimney and ignited at the
bottom. A regular stream of chlorine, which should not be
allowed to bubble through a liquid, is conducted through
the glass tube which extends to the centre of the cylinder.
The tube is inserted in a two-holed rubber
stopper which fits the base of the chim-
ney. As the tube passes through the
hydrogen flame the chlorine takes fire
and may be seen to be burning at the
end of the tube in the atmosphere of
hydrogen. The cork is then inserted in
the base of the chimney. The hydro-
chloric acid gas together with the excess
of hydrogen issues through the open tube
(15 cm. long) in the second hole of the
cork. As the hydrochloric acid gas comes
in contact with the air it fumes strongly.
By dipping the open end of the tube a
few millimeters beneath the surface of water in a beaker
the hydrochloric acid will be absorbed and the excess of
hydrogen will bubble through the liquid. By carefully
regulating the flow of hydrogen the minimum quantity
may be caused to escape uncombined.

Fig. 44

90 CHEMICAL LECTURE EXPERIMENTS

It is of the utmost importance in carrying out this experi-
ment to avoid the formation of an explosive mixture of
hydrogen and chlorine inside the lamp chimney, and conse-
quently, if the flame of chlorine should be accidently
extinguished, the current of chlorine should be stopped and
the cork removed, and, after filling the lamp chimney again
with hydrogen, the experiment repeated.

Apparatus (Fig. 44) ; CI supply ; H generator (Kipp).

16. Explosion of a mixture of hydrogen and chlorine by
burning magnesium. — The explosion of a mixture of equal
volumes of hydrogen and chlorine may be effected by the
actinic rays of a magnesium light.

A 100 cc. cylinder is filled with chlorine and placed
mouth to mouth with a cylinder of equal size filled with
hydrogen. The mixture of the two gases must be made by
diffused daylight only or, better, by gaslight. The jars are
well shaken, separated by cardboard disks, and one of them
placed in front of a glass screen. The other should be
covered with a towel or box to cut out the light. A strong
magnesium flame is then producd in front of the screen,
either by allowing magnesium powder to fall through the
flame of a Bunsen burner, or by igniting one of the flash-
light cartridges (Ex. 5, p. 375). As a result of the brilliant
flash the mixture of gases in the cylinder on the other side
of the screen explodes.

It is important that the gaseous mixture should be
approximately correct as regards volume, and consequently
the chlorine should not be contaminated by too great a
proportion of carbon dioxide, which is likely to result from
impure manganese dioxide. The flash should be very strong
and a considerable quantity of magnesium must be used.
The eyes of the operator should be protected by colored
glasses.

HYDROCHLORIC ACID 91

An interesting addition to the experiment may be made
by interposing between the light and the gases red and blue
screens. When the red screen is interposed, no explosion
occurs, as the actinic rays are cut off by the red glass. If
the blue screen, which permits the passage of the actinic
rays, is used, the explosion is produced.

H2 + Cl2 = 2 HC1.

Glass screen ; colored spectacles ; Mg powder or flash-light car-
tridge ; 100 cc. cylinder of H ; 100 cc. cylinder of CI.

17. By the action of sulphuric acid on sodium chloride. —

Sulphuric acid reacts with sodium chloride, yielding hydro-
chloric acid gas.

A constant current of gas may be obtained by heating
120 g. of sodium chloride with a mixture of 100 cc. of con-
centrated sulphuric acid and 60 cc. of water. The diluted
acid must be cooled before being introduced in the generat-
ing flask. The apparatus shown in Fig. 39, p. 81, is well
adapted for this purpose. The safety-tube should be half
filled with concentrated sulphuric acid and the first gas
washing-bottle with concentrated hydrochloric acid. By
means of a three-way cock the gas can be directed at will
either into the flue or through the sulphuric acid in the second
wash-bottle into a piece of apparatus. By gently heating
the flask a regular current of hydrochloric acid gas, which
is regulated by increasing or diminishing the size of the
flame, may be obtained. The gas may be collected over
mercury or, owing to its great specific gravity, by displace-
ment.

NaCl + F2S04 = NaHS04 + HCL

Apparatus (Fig. 39, p. 81) ; NaCl ; 100 cc. H2S04 + 60 cc. H20
mixed and cooled.

CHEMICAL LECTURE EXPERIMENTS

Fig. 45

18. By the action of concentrated sulphuric acid on am-
monium chloride. — Concentrated sulphuric acid is allowed

to drop from the funnel of the apparatus
(Fig. 45) upon small lumps of sublimed
ammonium chloride in the flask. The
issuing gas is conducted through a glass
elbow in the second hole of the cork.

This method is readily adapted for
furnishing a large quantity of hydro-
chloric acid for a considerable period
of time. In that case it is desirable
to place the lumps of ammonium chlo-
ride in the middle chamber of a Kipp generator. The acid
reservoir is filled with concentrated sulphuric acid.

2 NH4C1 + 1LS04 = (NH4)fS04 + 2HCL

Apparatus (Fig. 45) ; Kipp generator (Fig. 17, p. 46) ; lumps of
sublimed NII4CI.

19. By heating commercial concentrated hydrochloric
acid. — Commercial concentrated hydrochloric acid consists
of an aqueous solution of the gas. The gas may be expelled
from the solution by gentle heat and, after being dried, used
for any of the experiments described beyond. The appa-
ratus (Fig. 39, p. 81) is suitable for this experiment when a
constant stream of the gas is desired. Two hundred cubic
centimeters of the strongest acid are placed in the generat-
ing flask, which is then gently heated. A rapid evolution of
gas is obtained

The gas may be made in smaller quantities by heating the
aqueous solution in a flask fitted with a thistle-tube and a
delivery-tube.

Apparatus (Fig. 30, p. 81); flask; thistle-tube; delivery-tube ;
con. IIC1.

HYDROCHLORIC ACID 93

20. By the action of concentrated sulphuric acid on con-
centrated hydrochloric acid. — When concentrated sulphuric
acid is allowed to fall upon concentrated hydrochloric acid,
large quantities of hydrochloric acid gas are liberated.

Two hundred cubic centimeters of concentrated commer-
cial hydrochloric acid are placed in a 500 cc. flask, fitted
with a two-holed rubber stopper carrying a large dropping-
funnel and a glass elbow (Fig. 45). Strong sulphuric acid is
allowed to enter, drop by drop, and after a few moments
hydrochloric acid gas will be given off.

500 cc. flask ; gas washing-bottle ; rubber stopper (2-holed) ; drop-
ping-funnel ; elbow.

PROPERTIES

21. Generation of heat by the absorption of the gas in
water. — The absorption of hydrochloric acid gas by water
is accompanied by a great evolution of heat.

The bulb of a thermometer is covered with a piece of
filter-paper moistened with water. If the thermometer is
thrust into a jar of the gas, the water on the filter-paper
absorbs sufficient gas with generation of heat to cause the
mercury to rise in the thermometer some 40 to 50 degrees.

The ether thermometer described in Ex. 73, p. 174, may
here be used to advantage. The bulb, which is about one-
third filled with ether, is wrapped with a wet filter-paper,
and the thermometer then thrust into a cylinder of the gas.
Sufficient heat is generated to boil the ether. The ether
vapor issuing from the end of the tube may be ignited.

Thermometer; ether thermometer (Ex. 73, p. 174); ether; 2 cyl-
inders of dry HC1.

22. Solubility in water. — Water dissolves 450 volumes
of hydrochloric acid gas at the ordinary temperature.

A dry cylinder filled with the gas is covered with a metal
plate and opened under water. As the plate is slipped to

94 CHEMICAL LECTURE EXPERIMENTS

one side, the water rushes with almost explosive violence
into the cylinder, filling the interior.

The absorption of the gas in water with the production of
a fountain may be shown by means of the apparatus (Fig.
84, p. 195). The large flask is filled with dry hydrochloric
acid gas by downward displacement, and after the cork
carrying the long glass tube and small pipette nearly filled
with water has been inserted, is firmly supported in an in-
verted position. The long glass tube is dipped under water
colored blue with litmus solution. On pinching the rubber
bulb of the pipette the operation is started, and the water
rushes with great force through the long tube into the flask.
The litmus solution is turned to a deep red by the acid.

Apparatus (Fig. 84, p. 195) ; large flask (dry) ; rubber bulb pipette
(medicine dropper or ink filler) ; HC1 supply; litmus solution.

23. Preparation of aqueous hydrochloric acid. — The prep-
aration of aqueous hydrochloric acid on a large scale may
be accomplished by conducting the gas through a series of
Wolff bottles (Fig. 85, p. 196), provided with safety-tubes.
The arrangement of the bottles is identical with that de-
scribed for preparing ammonium hydroxide, with the single
exception that the tubes conducting the gas into the differ-
ent bottles dip only a few millimeters beneath the surface
of the water.

As the absorption proceeds, currents of the heavy aqueous
hydrochloric acid may be seen to be settling in the liquid in
the Wolff bottles.

Series of Wolff bottles (Fig. 85, p. 190) ; HC1 supply.

24. Electrolysis of hydrochloric acid. — The decomposi-
tion of aqueous hydrochloric acid by the electric current into
equal volumes of chlorine and hydrogen is at best an unsatis-
factory experiment. While the products of the decompo-

HYDROCHLORIC ACID

sition of water, i.e., hydrogen and oxygen, are, relatively
speaking, insoluble in water, chlorine is very soluble, and
it becomes necessary to continue the electrolysis until the
liquid is saturated with chlorine.

The electrolytic apparatus (Fig.
46) is provided with carbon elec-
trodes, consisting of rods of elec-
tric-light carbon, preferably of a
small size, inserted in rubber stop-
pers. Platinum electrodes, when
used for this decomposition, are at-
tacked by the nascent chlorine.

The addition of small quantities
of sodium chloride to the hydro-
chloric acid used in the experiment
diminishes the capacity of the liquid
for the absorption of chlorine. Con-
centrated hydrochloric acid is satu-
rated with sodium chloride and the
saturated liquid used in the elec-
trolytic apparatus. Both stop-cocks
being open, sufficient acid is poured
into the bulb to rise in the two arms
to within 2 cm. of the stop-cocks.
The current from six cells of a bi-
chromate battery is then conducted
through the liquid for half an hour,
leaving the stop-cocks open. While
this operation as a rule should be be-
gun before the lecture, the difference

in the evolution of gases from the two poles forms an inter-
esting experiment for showing the solubility of chlorine.
At the end of half an hour the liquid in the arm of the
electrolytic apparatus over the positive electrode will have

Fig. 46

96 CHEMICAL LECTURE EXPERIMENTS

become saturated with chlorine, and by closing both stop-
cocks it will be found that the two tubes fill with gas at
nearly the same rate. The volume of hydrogen will proba-
bly be somewhat greater than that of chlorine, though if the
stop-cock is carefully opened and the liquid allowed to rise
in the hydrogen tube to the level of the liquid in the chlo-
rine tube, after 20 or 30 cc. of gas have collected, the vol-
umes of the gases will increase with much greater regularity.
Rubber rings are advantageously placed on the arms about
15cm. below the stop-cocks, and the actual measurement of
the evolution of the gases begun when the liquids have been
depressed to this level.

A piece of white paper held behind the tube containing
chlorine will show the green color of the gas. On Opening
the stop-cock the hydrogen may be ignited as it issues from
the tube, and a piece of iodo-starch paper is instantly turned
blue when held in the gas issuing from the other stop-cock.

2HC1 = H,+ CI*

Electrolytic apparatus (Fig 46) ; carbon electrodes; bichromate

battery; IIC1 saturated with Nad ; KI-staivh paper.

25. The electrolysis of hydrochloric acid and the collection
of the mixture of hydrogen and chlorine. — The explosive
mixture of hydrogen and chlorine is most satisfactorily
obtained from the electrolysis of hydrochloric acid, and the
mixture so formed is considerably more sensitive to tie1
actinic rays of light than the mechanical mixture made in
Ex. 16.

The hydrochloric acid is best decomposed in an electro-
lytic apparatus like that shown in Fig. 47. Owing t<>
the corrosive action of nascent chlorine on platinum, it is
necessary to use carbon electrodes. This may be done
either by thrusting small rods of electric light carbon

HYDROCHLORIC ACID

=^ —

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—

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V4i

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o e ",

y -

■i— ••<£-

PPfr

^-4£.

through the holes of a cork, or, in case rods of small
diameter are not available, pieces of carbon of the regular
size may be fastened to platinum wires sealed into the glass
tubes, which are filled with mercury as indicated. Inasmuch
as here again the liquid being electro-
lyzed should be completely saturated /^l(fn\^

with chlorine, the minimum quantity
of acid should be used and a bottle
should be selected just large enough
to take the cork conveniently and not
have the electrodes touch. Concen-
trated hydrochloric acid, saturated with
salt as described in the preceding ex- FlG# 47

periment, is poured into the bottle to
within 2 cm. of the cork. Owing to the rise in tempera-
ture attending the electrolysis, it is advisable to place the
bottle in a crystallizing dish containing cold water. The
room is darkened so as to have very diffused daylight, or
better only gaslight, and then the apparatus is connected
with six cells of the bichromate battery. The evolution of
gas begins almost immediately, though, as the major part
of the chlorine is absorbed by the acid in the bottle, the
first portions of the gas consist mainly of hydrogen. After
the apparatus has been running for half an hour the mixed
gases may be collected over salt brine. Several small cyl-
inders and the lecture eudiometer (Fig. 11, p. 26) should
be filled with the gas.

At the conclusion of the experiment the current is stopped,
and before exposing the apparatus to bright light, the excess
of the explosive gaseous mixture remaining in the bottle
above the liquid should be removed by taking out the
cork.

The cylinders of the mixed gases may be exploded either
by a match or by means of the magnesium light (Ex. 16).

CHEMICAL LECTURE EXPERIMENTS

The gas in the lecture eudiometer is reserved for use in
the following experiment.

Electrolytic apparatus consisting of small wide-mouthed bottle, 3-
holed cork, and carbon electrodes (Fig. 47) ; bichromate battery ;
eudiometer (Fig. 11, p. 26) ; salt brine ; HC1 saturated with NaCl.

26. Analysis of the mixture of hydrogen and chlorine
obtained by the electrolysis of hydrochloric acid. — That the
gas in the lecture eudiometer from the preceding experiment
consists of a mixture of equal volumes of hydrogen and
chlorine is shown by allowing a strong solution of potassium
iodide to flow through the stop-cock into the gas. The
solution immediately becomes dark-colored from the libera-
tion of iodine, and the liquid will rise inside the tube half-
way to the stop-cock. If the eudiometer is then inverted
and the residual gas tested, it will be found to burn quietly,
giving the hydrogen name.

Eudiometer filled with II and CI from the preceding experiment ;
KI solution.

CHLORINE MONOXIDE

27. Preparation. — AVhen chlorine is passed over yellow
mercuric oxide, the brownish oxychloride of mercury to-
gether with chlorine monoxide
is formed.

A slow stream of chlorine is
passed through a piece of glass
tubing, 50 cm. long and 8 to
10 mm. internal diameter, which
is bent at right angles at a dis-
tance of 10 cm. from one end
(Fig. 48). Dry mercuric oxide (the yellow amorphous
modification) is placed in the tube, which is clamped in a
horizontal position, the elbow dipping into a small cylin-

-*>=m

Fig. 48

HYPOCHLOROUS ACID 99

der. That portion of the tube containing the mercuric oxide
is kept cool by allowing ice-water to drop on a piece of filter-
paper laid upon it. In a few minutes the cylinder will be
filled with a brownish yellow gas. Several cylinders of the
same size should be filled.

A small quantity of chlorine monoxide is exploded by
thrusting a burning match or hot iron wire into the mouth
of a cylinder.

Sulphur flowers are sifted into a cylinder of chlorine mo-
noxide. The reaction follows with an explosion.

A 2 or 3 mm. piece of phosphorus placed in a small
deflagrating spoon is lowered into a jar of the gas. An ex-
plosion takes place.

Glass tube 50 cm. long, 8-10 mm. internal diameter; several small
cylinders ; ice-water ; CI generator; HgO (yellow) ; S flowers ; P.

HYPOCHLOROUS ACID

PREPARATION

28. By the action of chlorine on mercuric oxide. — Moist,
freshly precipitated mercuric oxide is covered with strong
chlorine water. The oxide soon dissolves, forming a solu-
tion of hypochlorous acid.

Yellow mercuric oxide may be suspended in water in a
200 cc. flask and chlorine conducted into the liquid. The
brown oxychloride is soon formed and a considerable quantity
of mercuric oxide goes into solution. The clear filtrate con-
tains hypochlorous acid.

HgO + H20 + 2C12 = HgCl2 + 2HC10 [?].

200 cc. flask ; CI water or CI generator; HgO (freshly precipitated) .

29. By the action of nitric acid on calcium hypochlorite. —

If a 5 per cent solution of nitric acid is carefully added to a
clear solution of calcium hypochlorite, a liquid containing

100

CHEMICAL LECTURE EXPERIMENTS

calcium nitrate, calcium chloride, and hypochlorous acid is
obtained which by distillation yields a colorless solution of
hypochlorous acid.

Bleaching powder solution ; 5 per cent HN03.

30. Preparation of chloride of lime. — (a) By conducting
chlorine over moistened calcium hydroxide a mixture of
calcium hypochlorite and calcium chloride, the so-called
chloride of lime, is formed.

A 40 cm. length of combustion tubing is filled with cal-
cium hydroxide which is slightly moistened. A current of
chlorine, passed through a gas washing-bottle containing
water, is conducted into one end of the tube and a cork

, -_"■=- I i , - . _--

33=^

Fig. 49

carrying a glass elbow dipping into a beaker of water is
thrust into the other end (Fig. 49). On account of the
absorption of the chlorine by the calcium hydroxide, very
little if any chlorine leaves the tube.

Apparatus (Fig. 49); 40 cm. length of combustion tubing; gas
washing-bottle ; CI generator ; Ca(OH)2.

(b) A 2 1. flask is filled with chlorine and about 20 cc.
of the milk of lime are introduced. On shaking the flask
the chlorine is entirely absorbed, as may be noticed by the

CHLORINE PEROXIDE 101

disappearance of the green color. On the addition of an
excess of concentrated hydrochloric acid, chlorine is liberated
and the flask again becomes filled with the green gas.

2 1. flask ; CI generator ; milk of lime.

31. Bleaching action of sodium hypochlorite. — - Sodium
hypochlorite bleaches colored cloth (turkey red). A small
piece of the cloth is dipped into a solution of sodium hypo-
chlorite in a beaker. In a few -moments the color will
disappear.

If hypochlorous acid is present, the bleaching is more
rapid, and consequently if a small quantity of hydrochloric
acid is added to the sodium hypochlorite in a second beaker,
a piece of cloth dipped in the liquid is almost immediately
bleached.

Sodium hypochlorite ; cloth dyed turkey red.

32. Action of hypochlorous acid on silver oxide. — Silver
oxide and hypochlorous acid interact, forming silver chloride
and liberating oxygen.

A few grams of the oxide are placed in a test-tube and
covered with a strong solution of hypochlorous acid. On
gently warming, a gas will be evolved which when tested is
seen to be oxygen.

The experiment may be repeated, using cupric oxide and
a solution of bleaching powder.

2 HCIO + Ag20 = 2 AgCl + H20 + 02.

HCIO solution ; Ag20 ; fresh bleaching powder ; CuO.

CHLORINE PEROXIDE

33. Preparation. — A few centigrams of finely powdered
potassium chlorate are placed in a crucible which rests on
the bottom of a 100 cc. cylinder. Five drops of concentrated

102

CHEMICAL LECTURE EXPERIMENTS

Fig. 50

sulphuric acid are allowed to fall, one at a time, upon the
potassium chlorate from a long glass tube bent at one end.
A yellowish gas is slowly evolved and displaces the air in

the cylinder. When a long iron
wire is heated at one end and
lowered into the gas, a sharp
explosion takes place, and care
should be taken to protect the
face and hands from flying drops
of acid (Fig. 50).

In preparing chlorine peroxide
the potassium chlorate may be
allowed to fall into sulphuric
acid. Two or three cubic centimeters of strong sulphuric
acid are placed in the bottom of a small thick-walled glass
cylinder and 2 g. of potassium chlorate are carefully sifted
into the acid, care being taken to protect the hand with a
gauntlet. The yellow gas rises in the cylinder and may be
exploded with an iron wire.

Two 100 cc. Rtout-walled cylinders ; crucible ; bent glass tube ; glass
shield ; gauntlets ; iron wire ; KCIO3.

34. Action of hydrochloric acid on potassium chlorate. —
A concentrated solution of potassium chlorate, when heated
with concentrated hydrochloric acid, turns yellow, and the
gas evolved bleaches litmus paper.

If a hot glass rod is held in the gas from the test-tube, a
slight explosion follows.

On the powdered salt the action of the acid is more
marked, producing the mixture of chlorine and chlorine
dioxide called " euchlorine."

35. Chlorine peroxide and sugar. — Equal weights of

finely pulverized potassium chlorate and cane sugar are

CHLORINE PEROXIDE 103

carefully mixed on paper, avoiding all friction, and placed
on an asbestos sheet or a brick in a hood. One drop of
sulphuric acid is allowed to come in contact with the mix-
ture, which is ignited and burns fiercely. The sulphuric
acid may be dropped from a long bent glass tube, or the
acid may be more satisfactorily added by dropping a small
piece of asbestos paper in concentrated sulphuric acid and
allowing the moistened paper to fall on the powdered mix-
ture. The combustion proceeds with great rapidity, giving
an intense blue potassium flame.

Asbestos sheet ; KC103; sugar.

36. Combustion of phosphorus. — Phosphorus burns in
chlorine peroxide, and the combustion may be
made to proceed under water.

Five grams of crystallized potassium chlorate
are placed on the bottom of a 100 cc. cylinder or,
better, of a test-tube on foot (Fig. 51). Fifty
cubic centimeters of water are then added and
two or three 2 mm. pieces of phosphorus are
thrown into the water.

A 10 cc. pipette is half filled with concentrated
sulphuric acid and the tip thrust into the cylinder
until it touches the potassium chlorate crystals.
As the acid comes in contact with the crystals, chlorine
peroxide is evolved and the phosphorus burns.

Test-tube on foot (Fig. 51) ; 10 cc. pipette ; crystallized KC103;
2 mm. pieces of P.

37. Explosive combustion of alcohol in chlorine per-
oxide. — A small quantity of chlorine peroxide is generated
in a 50 cc. cylinder according to the method in Ex. 33. The
cylinder is placed behind a glass screen and a few drops of
aleohol are allowed to fall from a test-tube into the gaseous

104

CHEMICAL LECTURE EXPERIMENTS

mixture. A sharp explosion occurs which is likely to blow
some of the acid out of the cylinder.

Glass screen ; alcohol ; C102 in cylinder.

CHLORIC ACID

38. Preparation. — Sulphuric acid, when added to a solu-
tion of barium chlorate, forms barium sulphate and chloric
acid.

Dilute sulphuric acid should be gradually added to a solu-
tion of barium chlorate nntil the barium is completely pre-
cipitated. On filtering off the liquid it will be found to
contain chloric acid and possess strong bleaching properties.

Ba(C108)2 + H2S04 = BaS04 + 2 HC10S.

Litmus; Ba(C103)2.

PERCHLORIC ACID

39. Preparation. — Sulphuric acid reacts with pure potas-
sium perchlorate, liberating perchloric acid.

Five grams of chemically pure
potassium perchlorate are heated
gently with 12 cc. of pure concen-
trated sulphuric acid in a 100 cc.
tubulated retort (Fig. 52). The
powder is placed in the flask and the
concentrated acid poured through
a funnel, the introduction of acid
into the neck of the retort being
thus avoided. The retort is then
gently heated by a low flame. A
high temperature is as undesirable as it is unnecessary,
since the perchloric acid distils at about 110°. A few drops

Fig. 52

PERCHLOKIC ACID 105

of an oily, strongly fuming distillate are obtained in the
test-tube used as a receiver.

2 KC104 + H2S04 = K2S04 + 2 HC104.
100 cc. tubulated retort ; c. p. KC104 ; c. p. con. H2S04.

40. Bleaching action. — One drop of the distillate ob-
tained in the preceding experiment is allowed to fall into a
test-tube containing 3 or 4 cc. of water. The diluted per-
chloric acid, when added to a solution of indigo, bleaches it
immediately.

Perchloric acid ; indigo solution.

41. Combustion of charcoal. — Perchloric acid is a strong
oxidizing agent, and when a small piece of charcoal, heated
to glowing, is dropped into a test-tube containing a few
drops of the acid, the charcoal burns.

Perchloric acid ; charcoal.

24. Action on organic matter. — A drop of perchloric acid
on the end of a glass rod is spread on a piece of filter-paper.
The acid destroys the paper completely, cutting a hole in it
and igniting it. By holding the paper high above the name
and gently warming it the ignition may be immediately ac-
complished.

A drop of the perchloric acid is spread on the stem of a
match held with pincers. The match is lighted, and when
the flame reaches the part covered with acid, the combustion
is much more rapid, and the flame sputters.

BROMINE

1. Preparation from potassium bromide. — Metallic bro-
mides, when heated with sulphuric acid in the presence of
an oxidizing agent such as manganese dioxide, give up all
their bromine. This reaction, used in the technical prepa-
ration of the element, is easily carried out on a small scale.

Three and one-half grains of powdered potassium bromide
are mixed with 7 g. of finely pulverized manganese dioxide
and introduced into a 500 cc. retort. Fifteen cubic centi-
meters of concentrated sulphuric acid and 90 cc. of water are
mixed and carefully introduced, care being taken to get none
of the acid into the neck of the retort. After the mixture is
thoroughly stirred the retort is placed on a ring-stand and its
neck thrust deep into a 500 cc. flask, which can be externally
cooled by immersion in water. On gently heating the con-
tents of the retort the bromine is liberated, filling the retort
with deep reddish brown fumes, which distil over and con-
dense in the flask to a heavy, dark fluid, bromine, covered
with a lighter layer of bromine water. Owing to the vola-
tility of the bromine the flask should be cooled with ice-
water. (Fig. 93, p. 223.)

2 KBr + Mn02 + 2 H2S04 = K2S04 + MnS04 + 2 H,0 + Br*

500 cc. retort ; 500 cc. flask ; ice-water ; KBr ; Mn02.

100

BROMINE 107

2. Solidification by cold. — Bromine readily freezes in a
mixture of salt and ice to a dark, crystalline mass which has
a dull metallic lustre. Five cubic centimeters of bromine
are placed in a thin-walled test-tube and immersed in a freez-
ing-mixture of salt and ice. After a few minutes the bro-
mine will have solidified. The tube is warmed a little in the
hand, and the solid lump of bromine still retaining the shape
of the test-tube shaken out upon a white platea

Ice and salt ; Br.

3. Vaporization. — Bromine is very volatile, giving rise
to a deep reddish brown vapor. This is best shown by pour-
ing 5 drops of liquid bromine into a dry 500 cc. flask, the
mouth of which is covered with a small watch-glass. On
gently warming, the vapor rises, displacing the air, and fills
the flask with deep-colored fumes.

500 cc. flask ; watch-glass ; Br.

4. Bromine water. — Five cubic centimeters of bromine
are poured into 200 cc. of water in a 250 cc. flask. The
bromine, by reason of its great specific gravity, sinks to the
bottom of the flask. On corking the flask and shaking, the
bromine is dissolved in the water.

5. Action on arsenic and antimony. — When either anti-
mony or arsenic is allowed to come in contact with liquid
bromine, a vigorous reaction occurs, the metal burning on top
of the bromine.

One cubic centimeter of liquid bromine is placed in a test-
tube which is inserted in the mouth of a wide-mouthed bot-
tle (Fig. 109, p. 262). A 2 or 3 mm. piece of antimony or
arsenic is dropped into the liquid. In case the heat is suf-
ficient to break the tube, the bromine will fall into the wide-
mouthed bottle and there do no harm.

Apparatus (Fig. 109, p. 262); As; Sb ; Br.

108

CHEMICAL LECTURE EXPERIMENTS

HYDROBROMIC ACID

FORMATION AND PREPARATION

6. By heating a mixture of hydrogen and bromine. — If
hydrogen is allowed to bubble through bromine and is then

ignited, sufficient bromine vapor will
'JP have been carried with the hydrogen

1 1 to combine with it and form hydro-

bromic acid.

A simple arrangement for this ex-
periment consists of a large test-tube
fitted with a two-holed rubber stopper.
Hydrogen is allowed to pass through a
glass elbow thrust through the stopper
down to the bottom of the test-tube in

which a few drops of bromine are placed.
An open glass tube is thrust through
the other hole in the cork and serves
as a jet. After sufficient hydrogen has
passed through the apparatus to drive
out all air, the gas is lighted at the
Fig. 53 Open tube. Clouds of h ydrobromie acid

vapor will appear, the quantity of which

may be increased by gently warming the bromine in the

test-tube (Fig. 53).
H generator ; Br.

7. By the action of bromine on hydrogen sulphide. — Bro-
mine unites with the hydrogen of hydrogen sulphide, form-
ing hydrobromic acid and setting free sulphur. By filtering

off the sulphur a dilute solution of hydrobromic acid may be
obtained.

Hydrogen sulphide gas is conducted into a 100 cc. Erlen-
meyer flask containing 20 cc. of strong bromine water. In a

HYDROBROMIC ACID

109

few minutes the solution will have become decolorized and
large quantities of sulphur will have separated. By adding
a few more drops of bromine from time to time, the reaction
may be continued.

H,S + Bra = 2 HBr + S.

100 cc. flask ; H2S generator ; Br water.

8. From sulphuric acid and potassium bromide. — Dilute
sulphuric acid liberates hydrobromic acid from bromides
in a pure form containing but small quantities of bromine
vapor or sulphur dioxide. This method is very satisfactory
for the preparation of gaseous hydrobromic acid.

Ten grams of potassium bromide are placed in a 300 cc.
Erlenmeyer flask fitted with a dropping-funnel and a glass
elbow (Fig. 54). A mixture is made
of 3 volumes of concentrated sul-
phuric acid and 1 volume of water
by pouring the acid gradually into
the water and cooling the mixture.
Sufficient of this mixture is added
to cover the potassium bromide
and the contents of the flask are
very gently warmed. The gas is
steadily evolved and may be col-
lected in cylinders by displace-
ment. The gas regulation is easily

controlled by varying the heat applied to the flask. If the gas
is not perfectly colorless, the small quantity of bromine vapor
may be removed by conducting the gas through a U-tube filled
either with red phosphorus or with glass beads or pumice-
stone drenched with concentrated hydrobromic acid solution.

2 KBr + H2S04 = K2S04 + 2 HBr.

300 cc. Erlenmeyer flask ; dropping-funnel ; KBr ; H2S04 (3 : 1) ;
U-tube ; red P ; con. HBr solution.

Fig. 54

110

CHEMICAL LECTURE EXPERIMENTS

9. From bromine and naphthaline. — Bromine reacts with
naphthaline, liberating hydrobromic acid gas. This reaction
is very satisfactory for preparing the gas.

Fifteen grams of naphthaline are covered with 20 cc. of
kerosene in a 500 cc. distilling flask. A small dropping-
funnel, the tip of which should dip beneath the liquid, is
inserted in a one-holed stopper in the neck of the flask (Fig.
55). Fifteen to 20 cc. of bromine are placed in the drop-
ping-funnel and allowed to flow very slowly into the flask.
The reaction begins almost immediately, and the hydro-

Fig. 55

bromic acid gas, which carries with it slight traces of bro-
mine vapor, should be purified by conducting it through
a gas washing-bottle containing not more than 10 cc. of a
strong aqueous solution of hydrobromic acid in which a
small quantity of red phosphorus is Buspended. The issu-
ing gas will be perfectly colorless. While the heat of the
reaction is often sufficient to liberate the hydrobromic acid
gas, the flask may advantageously be very gently warmed
with a low, smoky flame. The gas washing-bottle may be
replaced by a U-tube filled with red phosphorus. The puri-

HYDROBROMIC ACID 111

fied gas is dried by conducting it through a tube containing
calcium chloride.

500 cc. distilling flask ; 100 cc. dropping-funnel ; gas washing-bottle ;
CaCl2 drying-tube ; U-tube containing red P ; naphthaline ; Br ; kero-
sene ; red P ; con. HBr.

PROPERTIES

10. Hygroscopic nature. — On opening a cylinder of hydro-
bromic acid the gas fumes in the air.

11. Action with litmus. — A piece of moistened blue lit-
mus paper thrust into a jar of the gas will be reddened.

12. Action with ammonia. — A few drops of strong am-
monium hydroxide are poured on a test-tube brush, which is
then lowered into a jar of the gas. Dense white fumes of
ammonium bromide are formed.

13. Solubility in water. — A jar of gaseous hydrobromic
acid is opened under water. The solubility is so great that
the water rushes into the cylinder with considerable violence.

14. Decomposition by chlorine. — Two cylinders of equal
size are filled, one with hydrobromic acid gas, and the other
with chlorine. The cylinder containing chlorine is placed
mouth downwards on the top of the cylinder containing
hydrobromic acid. On slipping out the glass plates between
the cylinders, the gases mix and the brown vapors of bro-
mine are set free. After standing for a few minutes, or,
more rapidly by shaking, both jars become filled with bro-
mine vapor.

If a slow stream of chlorine is passed through the recurved
jet (Fig. 41, p. 85), and lowered into a jar of hydrobromic
acid gas, brown fumes will immediately appear.

Jar of HBr gas ; jar of CI ; CI supply ; recurved jet.

IODINE

■♦■

IODINE

PREPARATION

1. From potassium iodide, manganese dioxide and sul-
phuric acid. — Potassium iodide when acted upon by sul-
phuric acid in the presence of an oxidizing agent such as
manganese dioxide is completely decomposed, the iodine
being liberated.

Three and one-half grams of potassium iodide are mixed
with 7 g. of finely pulverized manganese dioxide, and placed
in a 500 cc. tubulated retort. One hundred cubic centimeters
of cold dilute sulphuric acid ('made by adding 17 cc. of the
concentrated acid to 86 cc. of water) are added, and the
mixture thoroughly stirred. The retort is gently heated,
and vapors of iodine soon appear and condense in crystals on
the neck of the retort and in a flask through the neck of
which the mouth of the retort is thrust. No external cool-
ing of the flask is necessary, and care should be taken not
to heat the mixture too much.

2 KI 4- Mn02 + 2 H,S04 = K2S04 + MnS04 + 2H20 + L.

500 cc. tubulated retort ; 500 cc. flask ; Mn02 ; KI ; mixture of 17
cc. cone. H2SO4 and 85 cc. water.

112

IODINE

118

PROPERTIES

2. Melting iodine. — Iodine melts at 114° to a brown
liquid which solidifies at ordinary temperatures to a heavy
metallic-appearing mass.

Three grams of iodine are carefully heated in a clean, dry
test-tube, until completely melted. On allowing it to cool,
it solidifies, and by carefully breaking the test-tube the solid
mass, which has taken the form of the interior of the tube,
may be placed on a plate, where its dark color and metallic
appearance are readily observed.

3. Distillation. — (a) A few grams of iodine are heated in
a small tubulated retort, the neck of which is thrust into
the mouth of a large glass cylinder.

On boiling the iodine, the vapors
partially condense in the neck of
the retort, which should, be as wide
as possible, and care should be taken
that it does not become clogged.
The vapor issuing from the neck
of the retort falls by reason of its
great weight into the cylinder. As
the vapors descend and become
cooled, the iodine solidifies in min-
ute particles, which fall as a shower of glistening crystals
to the bottom and sides of the cylinder (Fig. 56).

250 cc. tubulated retort ; 4 or 5 1. cylinder ; I.

(b) When iodine vapor is cooled in the air, the iodine
condenses in the form of minute crystals.

Two grams of iodine are heated in a test-tube to boiling,
and the dense violet vapor poured out on a sheet of white
paper. The iodine settles on the paper in the form of a
shower of fine crystals.

Fig. 56

114 CHEMICAL LECTURE EXPERIMENTS

4. Volatilization at ordinary temperatures. — Iodine vapor-
izes at ordinary temperatures, as may be seen by dropping
one or two small crystals of iodine into a 3 or 4 1. flask, in
the neck of which a piece of paper moistened with starch
solution is suspended. After a few minutes the paper will
be turned blue by the vaporized iodine.

3 or 4 1. flask ; I crystals ; starch solution.

5. Solubility in alcohol. — Alcohol dissolves iodine read-
ily, with the formation of a deep reddish brown solution,
the so-called tincture of iodine. Two and a half grams of
iodine crystals are placed in the bottom of a glass cylinder
and 25 cc. of alcohol poured over them. On stirring the
mixture with a rod, the iodine will be entirely dissolved.

6. Solubility in carbon disulphide and chloroform. — A few
crystals of iodine added to either of these reagents dissolve
readily, forming a violet color, in Btrong contrast to the
color iodine gives with ether or alcohol.

Iodine water is shaken in a stoppered cylinder with 5 CC
of carbon disulphide. The heavy solvent extracts the iodine
from the iodine water, which becomes dear, and settles to
the bottom of the cylinder as a violet-colored liquid.

100 cc. stoppered cylinder; CSj ; CHClfj I ; I water.

7. Iodine and starch. — (a) Iodine forms with starch
paste a deep bine color. The delicacy of this reaction is
such as to cause its use in many operations in analytical

chemistry.

A few drops of starch paste are added to a liter of water.

Iodine water which contains but a small amount of iodine
is allowed to fall drop by drop into the solution. A very
few drops will produce a deep blue color, thereby showing
the extreme delicacy of the reaction.

IODINE

115

The color is discharged by an excess of chlorine water,
by heat, and by alkalies.

Starch paste ; I water.

(b) Effect of heat. — A few cubic centimeters of the
blue liquid are vigorously boiled in a test-tube for three or
four minutes. Even before the liquid fairly boils, the
color is completely discharged. On allowing the test-tube
to stand it will be seen that the color does not return.

If the blue solution, containing a slight excess of iodine
rather than of starch, is heated gently until the color is just
discharged, and then allowed to cool, the blue color will
return. This moderate heating is best carried on by
immersing the test-tube containing the blue solution in a
beaker of water which has just been brought to a boil, and
removed from the flame. The color will shortly disappear,
and if the tube is then immediately immersed in a beaker
of cold water, the blue color will return.

On boiling, the iodine liberated from the starch compound
by heat is volatilized with the water vapor passing off into
the air. If the blue solu-
tion is heated in a distill-
ing flask, and the vapor
condensed in a long glass
tube, which acts as an air
condenser (Fig. 57), the
liquid dropping from the
end of the tube will pro-
duce a blue color in a
beaker of starch paste

placed beneath it. On cooling, it will be found that the
residue in the distilling flask will not regain its original
blue color, the iodine having been driven off by boiling.

Fig. 57

250 cc. distilling flask ; long glass tube ; starch solution ; I.

116 CHEMICAL LECTURE EXPERIMENTS

8. Union with potassium. — On gentle warming, potassium
and iodine unite with explosive violence.

A few crystals of iodine are placed in a dry test-tube,
and a 3 mm. piece of clean, dry, metallic potassium added.
When warmed, the elements unite with a slight explosion,
the flame possessing the characteristic violet color of the
potassium flame. Care should be taken to protect the face
and hands from the results of the reaction.

2 K + I2 = 2 KL

Screens ; gauntlets ; K ; I.

9. Union with zinc dust. — Zinc dust and iodine unite in
the presence- of moisture with the evolution of heat.

One gram of zinc dust is intimately mixed with 5 g. of
finely powdered iodine in a dry beaker. One or two
drops of water are allowed to fall into the beaker, when the
reaction begins, the heat generated vaporizing a large quan-
tity of iodine. A crystalline sublimate of iodine on the
walls of the beaker is obtained.

The reaction may be carried out with a similar result by
using iron powder in the place of zinc dust.

Zn + I, = Znl2.

Dry beaker ; Zn dust ; powdered I.

10. Union with mercury. — Mercury and iodine unite
with incandescence to form mercuric iodide.

A few globules of mercury are heated to boiling in a test-
tube clamped in a vertical position. The flame is then
removed and a few crystals of iodine dropped into the hot
mercury. A feeble flame is observed, and the iodide of mer-
cury sublimes in a crystalline mass on the sides of the tube.

If both elements are in the gaseous form, the union is
still more vigorous. The mercury is heated in a test-tube

HYDRIODIC ACID 117

as before, and the lamp turned down to give a flame just
sufficient to keep the mercury boiling. A few crystals of
iodine are brought to a boil in another test-tube and the
vapors poured upon the boiling mercury. The union is
accompanied with a flame, the product being deposited as a
colored crystalline sublimate.

Hg + I2 = HgL,
Dry test-tubes ; Hg ; I.

11. Union with phosphorus. — Iodine and phosphorus
unite, even in the cold, with sufficient energy to ignite the
phosphorus.

The reaction between iodine and phosphorus may be
readily shown by placing a few crystals of iodine on a brick
and carefully placing a small piece of dried yellow phos-
phorus on top of the crystals. The phosphorus is almost
immediately ignited.

Brick ; yellow P ; I crystals.

HYDRIODIC ACID

FORMATION AND PREPARATION

12. From hydrogen and iodine. — Hydrogen, mixed with
iodine vapor and passed through a heated tube, unites with
the iodine to form hydriodic acid.

A few crystals of iodine are placed in the bulb of an ordi-
nary bulb-tube with long arms through which hydrogen
from a Kipp generator is passed. A strip of blue litmus
paper held in the issuing gas is unacted upon, showing the
absence of acid fumes. The open arm of the bulb-tube is
heated to a low red heat by means of a Bun sen burner, and
the iodine in the bulb is then gently warmed, subliming

118 CHEMICAL LECTURE EXPERIMENTS

some of the vapors into the atmosphere of hydrogen. The
issuing gas will now form white fumes of hydriodic acid
and a strip of moistened blue litmus paper will be immedi-
ately reddened. A piece of paper moistened with potas-
sium dichromate solution is instantly changed in color by
the reducing action of the hydriodic acid. On igniting the
gas as it issues from the bulb-tube, the heat of the burning
hydrogen will be sufficient to decompose the hydriodic acid
with the liberation of free iodine, which will appear as a
violet vapor rising from the flame. A white paper may be
held behind the flame to serve as a background for the
violet vapor. If a piece of cold porcelain, such as an evapo-
rating dish, is held in the flame, the iodine liberated will
be deposited as a brownish yellow mass.

H2 + I2 = 2 HI.

Bulb-tube ; H generator ; I ; K2Cr207 solution.

13. From iodide of phosphorus and water. — Water re-
acts with iodide of phosphorus, liberating hydriodic acid
gas.

In preparing the iodide of phosphorus, 2 g. of yel-
low phosphorus are cut in pieces of approximately .5 g.
each, carefully dried between filter-paper and dropped one
at a time on top of 22 g. of iodine crystals placed in
the bottom of a 100 cc. Jena glass Erlenmeyer flask. The
phosphorus should be dropped as near the middle of the
flask as possible, and the second and succeeding pieces
should not be added until* the reaction has entirely ceased.
At the end of the reaction the flask will contain a lique-
fied mass of phosphorus iodide.

After the flask and its contents have become perfectly
cold, 6 cc. of water are added, afld a cork carrying a glass
elbow is inserted in the neck of the flask. A purifying

HYDRlODrC ACID

119

Fig. 58

U-tube containing red phosphorus should be connected with
the glass elbow, the issuing gas being collected in dry cylin-
ders (Fig. 58). The gas evolution in this operation is quite
rapid, and provision should be made
for filling several clean, dry jars.
As the evolution of gas diminishes
in rapidity, a very small flame may
be used to heat the contents of the
flask, which at the end of the oper-
ation will have become perfectly
clear. The rapidity of the reaction
after the addition of water is so

great that it is advisable to wait a moment before inserting
the cork in the neck of the flask.

100 cc. Jena glass Erlenmeyer flask ; U-tube with red P; I ; P
(yellow).

14. By the action of iodine on rosin. — In the complex
reaction obtained by heating a mixture of iodine and
rosin a considerable quantity of hydriodic acid gas is
formed.

Fifteen grams of finely powdered iodine are mixed with
an equal bulk of finely powdered rosin. To regulate the
reaction more satisfactorily, the mixture is intimately rubbed
with an equal volume of pulverized quartz or very fine sand.
The powder is then placed in a dry 100 cc. Jena glass Erlen-
meyer flask fitted with a one-holed cork and a glass tube,
7 mm. wide, bent so as to extend nearly to the bottom of a
vertically clamped test-tube (Fig. 59). The test-tube is
fitted with a two-holed stopper, in the second hole of which
a glass elbow is inserted. On heating the flask, hydriodic
acid gas is liberated, mixed with considerable quantities of
free iodine and an oily liquid, which condenses in the test-
tube. To purify the issuing gas it should first be conducted

120

CHEMICAL LECTURE EXPERIMENTS

through a U-tube filled with red phosphorus, and then
through a calcium chloride tube. This method gives a very

Fig. 59

good yield of hydriodic acid gas and is strongly to be recom-
mended.

100 cc. Jena glass Erlenmeyer flask ; U-tube filled with red P ;
CaCl2 drying-tube; powdered quartz or very fine sand; powdered
rosin ; I.

15. By dissolving the gas in water. — A very simple
method of obviating the difficulties attend-
ing the absorption of this gas in water is
that of conducting the gas through the
stem of an inverted funnel, the mouth of
which is thrust a few millimeters under
the surface of the water in a crystallizing
dish. If back suction occurs, air will be
drawn under the edge of the funnel before
the water has risen in the cone of the
funnel as far as the stem.
Fig. 00 The funnel may be replaced by a retort.

HYDRIODIC ACID 121

PROPERTIES

16. Decomposition by heat. — (a) The decomposition of
hydriodic acid gas by heat, its great specific gravity, and
the fact that it is a non-supporter of combustion, are shown
by pouring 500 cc. of the gas from a cylinder upon a Bunsen
flame about 2 cm. high. Iodine is set free in the form of a
violet vapor and the flame is extinguished. As the hydri-
odic acid gas comes in contact with the air, it fumes strongly
from the absorption of moisture.

500 cc. cylinder of III.

(b) If a glass rod is strongly heated and then suddenly
thrust into a jar of the gas, a combustion is observed and
iodine vapor is liberated.

17. Acidity. — On opening a jar of hydriodic acid, dense
fumes like those observed about the mouth of a concen-
trated hydrochloric acid bottle, are formed. If a piece of
moistened blue litmus paper is held over the mouth of the
jar, it will instantly be colored red.

A rod moistened with ammonium hydroxide gives heavy
white fumes of ammonium iodide which partially sink into
the cylinder and remain suspended in the heavy gas. A
strip of paper moistened with potassium dichromate solu-
tion is instantly turned black.

Cylinder of HI gas ; K2Cr207 solution.

18. Solubility in water. — When a cylinder of the dry
gas is opened under water, the gas is rapidly absorbed, the
water rising to take its place. It is advisable to use a
metal disk to cover the mouth of the cylinder, as the suction
is so great as to break a glass jolate.

Metal disk ; cylinder of HI gas.

122 CHEMICAL LECTURE EXPERIMENTS

19. Oxidation by nitric acid. — The oxidizing action of
nitric acid on gaseous hydriodic acid is so great as to pro-
duce a flame.

Three cubic centimeters of hot fuming nitric acid are
poured from a test-tube into a cylinder of hydriodic acid
gas. A red flame proceeds from the cylinder and large
quantities of violet iodine vapor are set free.

100 cc. cylinder of HI gas ; screen ; gauntlets ; fuming HN03.

20. Combustion of oxygen in hydriodic acid gas. — A

gentle stream of oxygen is passed through a rubber tube
which dips under water to determine the rate of flow of the
gas. The rubber tube is then quickly slipped over the end
of a bent glass tube whose end has been heated very hot.
On suddenly thrusting the tube into a jar of hydriodic acid
gas, the oxygen takes fire and burns, setting free large quan-
tities of iodine.

4 HI + 02 = 2 H20 + 2 I2.

0 supply ; cylinder of III gas.

21. Decomposition of gaseous hydriodic acid by means of
chlorine. — (a) Chlorine reacts with hydriodic acid gas,
forming hydrochloric acid gas and liberating iodine. In the
presence of an excess of chlorine, the liberated iodine com-
bines with the chlorine to form crystals of yellow iodine
trichloride.

A current of hydriodic acid gas, prepared as in Ex. 14,
is dried by being passed through a calcium chloride tube,
and is then conducted through the recurved jet (Fig. 41,
p. 85) into a 500 cc. cylinder of chlorine. If the end of
the jet has been warmed a little, the issuing gas becomes
ignited as it enters the chlorine, and burns, liberating iodine
as a violet vapor. The iodine immediately combines with

HYDRIODIC ACID 123

the excess of chlorine, and the walls of the cylinder become
covered with yellow iodine trichloride.

A current of chlorine, conducted through the recurved jet
into a cylinder of hydriodic acid gas, likewise becomes
ignited, liberating iodine. As chlorine continues to be
introduced, the iodine combines with it, and is deposited on
the walls of the cylinder in yellow crystals of iodine tri-
chloride.

2 HI + Cl2 = 2 HC1 + I2.

I2 + 3 Cl2 = 2 ICL,

HI supply ; CaCl2 tube ; recurved jet (Fig. 41, p. 85) ; 500 cc.
cylinder of CI ; CI generator ; 500 cc. cylinder^of HI.

(b) Two glass cylinders are filled, the one with chlorine,
the other with hydriodic acid gas, and the cylinder contain-
ing chlorine is placed mouth downwards on top of the
cylinder containing hydriodic acid gas. Glass plates sepa-
rate the two cylinders. On slipping out the glass plates,
and allowing the mouths of the cylinders to come together,
the chlorine and hydriodic acid gas interact, iodine being
liberated. A slight flame is noticed at first, though there
is not enough heat generated to force the gases out into
the room. As the hydriodic acid gas is the heavier, the
progress of its diffusion into the lighter chlorine may be
noted by the color change of the deposition on the walls of
the chlorine cylinder. At first in the upper cylinder, where
there is an excess of chlorine, the deposition consists chiefly
of iodine trichloride, a yellow crystalline compound. At
the end of the reaction, the walls of both cylinders are
covered with crystals of iodine or iodine monochloride.
This experiment illustrates beautifully the diffusion of
gases.

Cylinder of HI gas ; cylinder of CI.

124 CHEMICAL LECTURE EXPERIMENTS

IODIC ACID

22. Preparation by the action of nitric acid on iodine. —

When iodine is heated with fuming nitric acid, it is con-
verted into iodic acid, with the liberation of the oxides of
nitrogen.

Three grams of iodine are placed in a dry 200 cc. Erlen-
meyer flask with 40 cc. of fuming nitric acid. The mixture
is heated for a few minutes and the liquid poured off from
the undissolved residue. On diluting with an equal volume
of water and shaking with 10 cc. of carbon disulphide, the
iodine is dissolved out, the solution becoming colorless.
The carbon disulphide is drawn off in a separating-funnel,
and the upper layer of liquid tested for iodic acid. The
liquid is first filtered to free from drops of carbon disulphide.
Starch paste is added to a portion of the solution and then
a few drops of sulphur dioxide water. Iodine will be
liberated and form the blue compound with starch. An
excess of sulphurous acid causes the decolorization of the
liquid.

3 I2 + 10 HN03 = 6 HIO3 + 10 NO + 2 II ,< >.

Separating-funnel ; I ; fuming IIN03 ; CSo ; SOa-water ; starch paste.

23. Decomposition by heat (iodic anhydride). — Iodic acid
on heating in a porcelain evaporating dish loses water and
forms the anhydride, iodic pentoxide. The heating should
be regular and should cease at that point where iodine
vapors are liberated. The molten mass is allowed to solidify
and is then used in the following experiments on iodic
anhydride.

Iodic anhydride, when heated in a test-tube, gives off
oxygen, with the liberation of iodine. A glowing splinter
introduced in the test-tube is immediately relighted.

The oxidizing power of iodic anhydride may be shown

IODIC ACID 125

by heating a mixture of the powdered anhydride and char-
coal powder. The mixture on heating gives off violet
vapors, the carbon feebly burning inside the tube.

A small quantity of flowers of sulphur or pulverized
sugar is mixed with some powdered anhydride and heated
in a dry test-tube. The reaction is very vigorous, being
accompanied with a slight explosion.

2 HI03 = I A + H20.

2 I A = 2 I2 + 5 02.
HIO3 ; I0O5 ; powdered charcoal ; S flowers ; sugar.

24. Reduction by sulphurous acid. — Sulphurous acid
acts in the same manner as hydriodic acid in reducing
iodic acid. The reduction is first accompanied by a libera-
tion of iodine. If, however, an excess of sulphurous acid is
added, the iodine itself becomes converted to hydriodic acid.

If to a solution of iodic acid starch paste is added, no
color will appear, as the combined iodine of the iodic acid
does not produce the blue compound with starch. On the
addition of a few drops of sulphurous acid the blue color
will instantly appear. An excess of sulphurous acid dis-
charges the color.

By adjusting the concentrations of the two solutions a
most interesting experiment on the time required for a re-
action to be completed may be made. The interaction of
sulphurous acid and iodic acid appears to require some con-
siderable time to begin, but having once started it proceeds
instantaneously throughout the whole solution.

Ten grams of iodic acid are dissolved in a liter of dis-
tilled water and the solution bottled as a stock solution for
use in this experiment. The solution is very permanent.
Fifty cubic centimeters of water are saturated with sulphur
dioxide by allowing the gas to bubble through it for a few

126 CHEMICAL LECTURE EXPERIMENTS

minutes. Twenty-five cubic centimeters of this saturated
sulphurous acid solution are diluted to a liter and preserved
in a bottle as a stock solution. This solution, however, as
might be expected, is not so permanent as the iodic acid
solution, hence it is advisable to make it fresh for every
experiment. Two hundred and fifty cubic centimeters of
water are placed in each of two clean beakers and to one
50 cc. of the stock iodic acid solution, and to the other 50 cc.
of the stock sulphurous acid solution are added. A few
drops of starch paste are then added to the dilute iodic acid
solution. The contents of each beaker are then stirred to
insure thorough mixing and then rapidly poured together
in a large cylinder capable of holding 700 cc. The mixed
liquids should be immediately stirred with a long, clean
stirring rod. No apparent reaction will take place for about
half a minute, when instantly the contents of the whole
cylinder will be turned a deep blue. It is advisable to place
the cylinder before a background of white paper.

The experiment can be made still more striking by using
a metronome to indicate the seconds. By counting off the
strokes of the metronome it will be easy to state before-
hand on what stroke the color change will occur.

In determining before the lecture the length of time
required for this reaction, it is essential to observe that no
changes are made in the proportions of the ingredients,
dilution, and temperature, since the length of time required
for the reaction is greater at greater dilutions and with a
higher content of iodic acid, while an increase in tempera-
ture shortens the time required for the reaction.

2 HI03 + 5 SO, + 4 H20 = 5 H2S04 + I,.
Metronome ; HIO3 ; S02-water (saturated) ; starch paste.

FLUORINE

HYDROFLUORIC ACID

1. Preparation from calcium fluoride and sulphuric acid. —

Calcium fluoride, when warmed with concentrated sulphuric
acid, undergoes decomposition, with the formation of hydro-
fluoric acid gas and calcium sulphate. The corrosive action
of this gas on glass necessitates that the operation be carried
out in a lead dish or a platinum crucible.

A thin paste of powdered fluorspar and concentrated sul-
phuric acid is placed in a lead dish or a platinum crucible
and gently warmed. The gas is readily evolved and its
etching action on glass is shown as follows : —

A piece of glass is carefully cleaned and coated with a
thin layer of paraffin. By means of a sharp-pointed pin or
needle a few characters are cut in the wax coating, care
being taken to scratch clear through the wax down to the
glass. The plate is then placed, with the waxed surface
down, on top of the dish in which hydrofluoric acid is being
generated and allowed to remain there for from five to
twenty minutes. Care should be taken not to heat the dish
sufficiently to melt the wax on the surface of the glass and
thereby spoil the design.

In case a platinum crucible is used, it will be found diffi-
cult, owing to the small size of the opening, to etch a design
of any size. The gas may be generated in the crucible,

127

128 CHEMICAL LECTURE EXPERIMENTS

however, and retained in a paper box of sufficient size to
expose a much larger surface of glass to the action of the
gas. A round pill box, some 8 to 10 cm. in diameter, has a

hole cut in the bottom a little

smaller than the maximum di-
ameter of the platinum crucible
(Fig. 61). The crucible is then
crowded down into the hole un-
til its rim is but a few millime-
ters above the bottom of the box.
The paste of calcium fluoride and concentrated sulphuric
acid is very gently warmed in the platinum crucible, the
gaseous fumes ascending into the pill box. A large glass
plate may be prepared and etched as described above.

CaF2 + H2S04 = CaS04 + 2 HF.

Lead dish or platinum crucible ; large pill box ; waxed glass plates ;
CaF2.

2. Acidity. — The gas formed in the preceding experi-
ment will immediately redden a piece of moistened blue
litmus paper.

3. Etching glass with aqueous hydrofluoric acid. — Aque-
ous hydrofluoric acid is obtainable in the market in rubber
or paraffin bottles, and is much used in analytical operations.
This aqueous solution etches glass fully as well as the gas.

A glass plate is coated with wax, prepared as described in
Ex. 1, and a piece of filter-paper moistened with the aqueous
hydrofluoric acid laid on top of the wax. In a few minutes
the etching will be complete.

If a small rim of wax of sufficient height is made around
the design, the aqueous acid may be poured directly upon the
wax, and being retained by the rim will effect the etching as
before.

FLUORINE

129

In either of these experiments a paste of calcium fluoride
and concentrated sulphuric acid may be substituted for the
aqueous hydrofluoric acid.

Waxed glass plate ; aqueous HF ; CaF2 (powdered).

4. Corrosive action of hydrofluoric acid on glass. — The

corrosive action of aqueous hydrofluoric
acid on glass and the consequent necessity
of using bottles other than glass for hold-
ing this liquid may be shown by placing
50 cc. of the solution in a thin 200 cc.
Erlenmeyer flask and gently warming.
The flask should be set in an iron or,
better, a platinum evaporating dish which
is kept warm by a water-bath (Fig. 62).
A rubber stopper fitted with a short glass
elbow and a rubber tube conducts the
fumes into the flue. In a short time
(from one-half to three-quarters of an
hour) the acid will have eaten through
the bottom of the flask and run into the platinum evapo-
rating dish.

Thin flask ; iron or platinum dish ; aqueous HF.

Fig. 62

SULPHUR

PROPERTIES

1. Roll sulphur. — Sulphur is a very poor conductor of
both heat and electricity and. when gently warmed, a1 tunes
even by the warmth of the hand, the roll will break in pieces.

A roll of sulphur is laid on a piece of asbestos paper and
very gently wanned with a low flame. It will crackle and
fall in pieces, owing to the unequal expansion produced by
the heat.

Asbestos paper ; roll of 8,

2. Distillation of sulphur and preparation of sulphur
flowers. — The vapors of sulphur, when allowed to escape

into the air, condense in the
form of a line dust, the so-called

Bowers of sulphur.

A retort is one-third tilled

with roll sulphur, and the neek

of the retort, which should he

as short as possible, thrust in

the mouth of a bottle, which is

laid on its side and has a layer

Fl(J gj of asbestos paper, in cm. wide,

along its length (Pig. 63). The

sulphur is brought to a boil by means of a powerful burner

and large quantities of the vapor are driven into the bot-

190

SULPHUR 131

tie. An asbestos covering should be made for the mouth
of the bottle and provided with a hole through which the
neck of the retort may be thrust. A considerable portion
of the sulphur vapor will condense in the neck of the retort
and drop as a liquid upon the asbestos paper. The vapors
will fill the bottle and be deposited all over the sides as a
fine powder.

200 cc. retort ; asbestos paper ; bottle ; large burner ; roll S.

3. Preparation of plastic sulphur. — (a) Sulphur, when
heated above its melting point, is changed into a black vis-
cous mass having the properties of rubber.

Roll sulphur is gently heated in a 100 cc. Erlenmeyer
flask and very carefully melted. A clear, yellow liquid
results. If some of this light yellow liquid is poured into
water, it will solidify to a hard, light yellow, opaque mass.
On heating still further, however, the liquid becomes viscous
and turns black, and the sulphur will not flow out, even if
the flask is held mouth downwards.

If the liquid is heated still further, it again becomes more
fluid, and can then be poured into cold water in a beaker. A
funnel is placed mouth dowmvards in the beaker, and the thin
stream of melted sulphur is poured around the stem of the
funnel, forming a coil of solidified sulphur in the beaker
(Fig. 64). On removing the sulphur from the beaker it will
be found to be elastic and plastic.

(b) A 200 cc. glass-stoppered tubulated retort, preferably
with a wide neck, is one-third filled with lumps of sulphur
and clamped in such a position that it may be strongly
heated in a large Bunsen burner. A sheet of asbestos paper
is laid over the top of the retort, extending almost to the
mouth, and held in place by having the stopper of the retort
thrust through it. The contents of the retort are then
melted and the heat gradually increased until they are vig-

132

CHEMICAL LECTURE EXPERIMENTS

orously boiling. The vapor partially condenses in the neck
of the retort and falls in a thin stream into a large beaker
of water, in which is immersed an inverted funnel about the
diameter of the beaker (Fig. G4). The sulphur solidifies, and

the beaker should be slowly revolved
to allow the sulphur to collect in a
spiral form on the funnel. It is ad-
visable to ignite the sulphur vapor not
condensed in the neck of the retort, as
otherwise the flowers of sulphur will
settle on the surface of the water and
interfere with the proper cooling of
the sulphur. When the contents of
the retort are vigorously boiling, a
flame of sulphur vapor, some 10 to 15 cm. in length, issues
from the mouth of the retort. It is best to stop the heat
before all the sulphur has been distilled. On withdraw-
ing the funnel from the beaker the sulphur will be found
as a bundle of tine threads and will possess elastic
qualities.
200 cc. retort

Fig. G4

large burner

beaker and funnel ; S.

4. Crystallization from fusion (prismatic sulphur). — A
150 cc. Jena glass beaker is two-thirds filled with roll sul-
phur, which is then carefully melted, care being taken to
keep the temperature as low as possible. When the sulphur
is completely melted, the flame is removed and the beaker
imbedded in a dish of sand. As soon as it is cooled suf-
ficiently to form a crust on the surface, a hole is made
through the crust and the remaining melted sulphur poured
out into water. A fine network of yellowish, transparent
crystals will have formed all around the walls of tin1
beaker, the needles extending into the centre of the
mass.

SULPHUR 133

5. Crystallization from carbon disulphide (octahedral sul-
phur).— Sulphur is quite soluble in carbon disulphide, and
crystallizes from its solution in this solvent in octahedrons.

Twenty grams of pulverized roll sulphur are placed in a
100 cc. flask and covered with 50 cc. of carbon disulphide.
The flask is then tightly closed with a cork (a rubber stop-
per cannot be used) and vigorously shaken. After a few
moments the solution is allowed to stand, and the clear
supernatant liquid decanted into a glass evaporating dish.
As the liquid evaporates, the sulphur is deposited in octa-
hedral crystals.

Glass evaporating dish ; roll S ; CS2.

6. Union with iron powder. — Iron powder, when heated
with twice its volume of sulphur flowers, combines with the
latter with the evolution of heat and light to form ferrous
sulphide. The mixture is gently heated in a hard-glass
test-tube throughout the whole mass, and then the temper-
ature is materially increased at the bottom. The union of
the elements begins at this point and proceeds with a great
evolution of heat and light through the contents of the test-
tube.

A modification may be introduced by placing a small heap
of the mixture of iron powder and sulphur flowers on a plate
and touching it at one point with a hot glass rod. The
mixture ignites, and the whole mass is soon converted to
ferrous sulphide.

Fe + S = FeS.

~Fe powder ; S flowers.

7. Union with iron at ordinary temperatures. — Iron pow-
der and sulphur flowers unite at ordinary temperatures when
mixed with a small quantity of water.

Twenty-two grams of iron powder and 15 g. of sulphur

134 CHEMICAL LECTURE EXPERIMENTS

flowers are rubbed together in a mortar with 7 cc. of water.
After a thorough mixing the damp powder is placed on a
white plate and moulded into a conical heap. The mixture
is pressed firmly down with the fingers and allowed to stand
some 15 to 20 minutes. Soon the mixture heats, and the
cone cracks open and steam is seen to rise. The whole mass
becomes black in color. That iron sulphide is actually
formed is easily shown by adding some hydrochloric acid to
a small quantity of the black powder and testing the hydro-
gen sulphide evolved.
Fe powder ; S flowers.

8. Combustion of iron in sulphur vapor. — Red-hot iron,
when thrust into sulphur vapor, combines with the sulphur
with incandescence, forming ferrous sulphide.

Sulphur is brought to a boil in a hard-glass test-tube and
a piece of common iron wire gauze heated to redness in a
Bunsen burner. On thrusting the gauze into the boiling
sulphur the union takes place, the molten iron sulphide fall-
ing to the bottom of the test-tube.

9. Union with copper. — (a) Sulphur in a 100 cc. Jena
glass flask is heated to boiling and the sulphur vapor allowed
to burn at the mouth. A spiral of copper made by winding
fine copper wire around a rod, or a piece of fine copper gauze
is thrust into the neck of the flask through the flame of
burning sulphur. The two elements unite with an evolu-
tion of light and heat.

Cu + S = CuS.

Fine copper wire or fine copper gauze ; roll S.

(b) A space, 1 cm. square, in a piece of thin sheet copper
is heated strongly. When very hot a small bit of sulphur is
thrown upon it. The sulphur and copper unite, forming
cupric sulphide, which remains as a bright metallic black

HYDROGEN SULPHIDE 135

spot in the centre of the sheet. The brittle nature of the
product is shown by thrusting the point of a lead pencil
through the spot.
Cu sheet ; S.

10. Combustion of magnesium in sulphur vapor. — Burning
magnesium, when lowered into sulphur vapor, continues to
burn with the formation of magnesium sulphide.

Sulphur is brought to a boil in a 100 cc. flask and a 15 cm.
strip of magnesium ribbon is ignited in the air. When the
magnesium is burning freely, it is lowered through the mouth
of the flask into the sulphur vapor, where it continues to
burn with the formation of magnesium sulphide.

Mg + S = MgS.
Boiling S ; Mg ribbon.

11. Combustion of zinc and sulphur. — A mixture of two
parts of zinc and one part of sulphur flowers, when thrown
into a hot iron dish or saucer, burns violently, forming zinc
sulphide.

This mixture is also readily ignited by touching it with a
hot glass rod. A small heap of the mixed powders is placed
on a brick or a piece of asbestos paper and touched with a
glass rod which has been heated in the Bunsen flame.

Zn + S = ZnS.
Iron dish or crucible ; Zn dust ; S flowers.

HYDROGEN SULPHIDE

PREPARATION

12. By the union of hydrogen and sulphur. — Hydrogen,
when passed over sulphur in the cold, has no action on the
element, though, if the sulphur is heated, a portion of it
combines with the hydrogen to form hydrogen sulphide.

136 CHEMICAL LECTURE EXPERIMENTS

A small lump of sulphur is placed in a bulb-tube through
which dry hydrogen is conducted. An elbow attached to
the end of the bulb-tube dips into lead acetate solution. No
change is observed in the lead acetate solution until the sul-
phur is heated, when, almost immediately, the presence of
hydrogen sulphide is shown in the issuing gas by the forma-
tion of a black precipitate of lead sulphide in the solution.

Instead of using the bulb-tube, the sulphur may be placed
in a dry test-tube, fitted with a two-holed cork. Hydrogen
is conducted through a glass elbow in the cork extending
to the bottom of the test-tube, and issues through a glass
elbow in the other hole of the cork. A paper moistened
with lead acetate solution held in the issuing gas remains
unchanged until the sulphur is warmed, when it is imme-
diately blackened by the hydrogen sulphide formed.

Ho + S = H,S.
Bulb-tube ; H generator ; S.

13. From the reduction of sulphur dioxide by means of
hydrogen in the presence of platinized asbestos. — Sulphur
dioxide, when mixed with hydrogen and passed over heated
platinized asbestos, is reduced to sulphur, which is depos-
ited in the tube. The excess of hydrogen reacting on the
heated sulphur produces a small amount of hydrogen sul-
phide, which may be tested in the issuing gas.

The apparatus (Fig. 69, p. 159) is adapted for this pur-
pose, hydrogen being substituted for the oxygen. The hy-
drogen and sulphur dioxide bubbling through the sulphuric
acid mix and pass out through the third neck into the
bulb-tube containing platinized asbestos. Until the plati-
num is heated no reaction takes place, but on warming
the bulb the platinized asbestos will be seen to glow, and
a deposit of sulphur will appear in the farther end of the

HYDROGEN SULPHIDE 137

tube. The issuing gas, when tested with a piece of paper
moistened with lead acetate solution, shows the presence of
hydrogen sulphide.

3-necked Wolff bottle ; H generator ; S02 generator ; platinized

asbestos.

14. From ferrous sulphide and hydrochloric or sulphuric
acid. — Ferrous sulphide, when treated with dilute sulphuric
acid, or, better, hydrochloric acid, liberates large quantities
of hydrogen sulphide. Though the gas generated by this
operation is not perfectly pure, containing, as it does, con-
siderable quantities of hydrogen, it is used, nevertheless,
for almost all analytical operations, as it is an indispensable
adjunct in analytical chemistry. Unfortunately the evil-
smelling and poisonous properties of the gas necessitate
special precautions in its preparation, collection, and use.

The gas is readily prepared by placing a few lumps of
ferrous sulphide in the gas generator (Ex. 7, p. 43). Dilute
sulphuric acid (1 volume of concentrated acid to 14 of
water), or, better, dilute hydrochloric acid (1 volume of con-
centrated acid to 1 of water), is poured through the thistle-
tube. The reaction begins almost immediately. The gas
should be dried by means of calcium chloride only, as it is
decomposed by sulphuric acid.

In case but a small quantity of the gas is desired, the
apparatus as above described is satisfactory, though it is
necessary to prevent any quantity of the gas from escaping
into the room. This can best be accomplished by inserting
after the wash-bottle a three-way stop-cock, such as is shown
in Fig. 39, p. 81. One arm of the stop-cock is connected
with the flue or with some suitable absorbing bottle, the
other directly with the apparatus into which the hydrogen
sulphide is to be conducted.

Innumerable devices for the evolution of hydrogen sul-

138 CHEMICAL LECTURE EXPERIMENTS

phide have been described in chemical journals, but as yet
no ideal portable apparatus for supplying a constant stream
of this gas has been devised. The simplest form is proba-
bly the Kipp generator, the middle bulb being filled with
lumps of ferrous sulphide as large as can conveniently pass
through the tubulature, while the acid chamber is filled with
sulphuric or hydrochloric acid diluted as described above.
The replenishment of this apparatus with acid and ferrous
sulphide is, however, a very disagreeable task, and conse-
quently a great drawback to its general use.

In most laboratories large quantities of hydrogen sulphide
are prepared for use with classes in qualitative and quanti-
tative analysis. The ideal arrangement is that in which
distilled water is supercharged with the gas and retained in
tin-lined steel cylinders. This method is the one adopted
in the chemical laboratory of Harvard College. The num-
ber of forms of apparatus for preparing the gas on the
small scale is only exceeded by the number of devices for
preparing it on a large scale for classes of students. While
each has its merits, a description is given in the Appendix
(p. 420), of the apparatus used in Wesleyan University,
which for regularity, simplicity, and economy is not excelled
by any other form known to the writer.

For lecture-table purposes the arrangement for obtaining
hydrogen sulphide is to conduct a separate pipe (preferably
a quarter-inch lead pipe) from the large generator to a glass
stop-cock securely fastened to a partition under the lecture
table. A second tube is then connected with the glass stop-
cock, which conducts the gas to a metal cock on the top of
the table, where by simply turning the cock a full supply of
the gas is instantly secured. The glass stop-cock is used to
cut off the gas when not in use, and is preferable to a metal
cock on account of its non-corrosive character. During the
lecture the metal stop-cock on the upper part of the desk

HYDROGEN SULPHIDE 139

may be used for regulating the supply of gas, though the
supply should be cut off with the glass stop-cock at the end
of the lecture. This arrangement can be applied to many
of the existing forms of hydrogen sulphide generators, and
is by far the most satisfactory method of obtaining this gas
for lecture table purposes.

FeS + 2 HC1 = FeCl2 + H2S.
FeS + H2S04 = FeS04 + H2S.
Gas generator (Ex. 7, p. 81) ; three-way cock ; FeS.

15. By the action of hydrochloric acid on antimony sul-
phide. — -Native antimonious sulphide (stibnite) yields, when
treated with hydrochloric acid, a very pure form of hydrogen
sulphide uncontaminated with free hydrogen.

A few grams of the pulverized mineral are placed in a
300 cc. Erlenmeyer flask fitted with a dropping-funnel and
elbow (Fig. 3, p. 11). Concentrated hydrochloric acid is
allowed to drop into the flask, which is gently warmed. A
steady evolution of pure hydrogen sulphide is obtained.

A measured volume of this gas will be almost completely
absorbed by sodium hydroxide, as shown in Ex. 18.

Sb2S3 + 6 HC1 = 2 SbCl3 + 3 H2S.

300 cc. Erlenmeyer flask ; dropping-funnel ; eudiometer (Fig. 11,
p. 26) ; stibnite.

PROPERTIES

16. Collection of the gas. — (a) In many experiments it is
necessary to use dry hydrogen sulphide in dry containers.
As this gas is somewhat heavier than air, it can be collected
by displacement, though provision should be made to conduct
the excess of the gas into the flue or some proper absorber.

A cylinder is fitted with a two-holed rubber stopper. A
glass tube extends to the bottom of the cylinder through one

140 CHEMICAL LECTURE EXPERIMENTS

of the holes in the cork, and through the other hole a glass
elbow is thrust. The hydrogen sulphide is conducted through
the long tube to the bottom of the jar, where it collects and
forces the air out through the elbow at the top. When the
jar is full, the cork is rapidly withdrawn and a glass plate
slipped over the mouth of the jar. The cork should be
immediately thrust into a second cylinder.

The acid nature of the gas, as well as its aqueous solution,
should be shown.

(b) Owing to its solubility in cold water, it is essential
when collecting this gas over water, to have the water as
warm as possible, and to use only a porcelain or glass dish
as a pneumatic trough. The gas is much less soluble in salt
solution than in water, and may accordingly be collected over
brine.

Porcelain or glass pneumatic trough ; II2S generator ; hot water ;
sat. sol. NaCl.

17. Solubility in water. — (a) Hydrogen sulphide is read-
ily absorbed by water.

A eudiometer tube is two-thirds filled with hydrogen sul-
phide, the thumb placed over the mouth of the tube and the
tube shaken thoroughly. The gas will dissolve in the water
remaining in the tube, producing a suction, and if the tube
is opened under water, the water will rise inside. The cur-
rent of hydrogen sulphide used to fill the tube should be
very rapid, so as to prevent the water from being saturated
with the gas while the tube is being filled.

(b) The eudiometer (Fig. 11, p. 26) may be used in this
experiment, in which case it is filled with hydrogen sulphide
over water and ice-cold water allowed to flow down the
inside of the tube into the gas. As the gas is absorbed, the
level of the water in the tube rises.

H2S generator ; eudiometer (Fig. 11, p. 26) ; ice-water.

HYDROGEN SULPHIDE 141

(c) A flask is rapidly filled with hydrogen sulphide over
water until half ofjthe water in the flask has been driven
out. The palm 01 the hand is then placed on the mouth of
the flask, which is thoroughly shaken. The gas is absorbed
by the water, producing a suction capable of supporting the
flask in a hanging position in the palm of the hand.

In case the water in the flask becomes saturated with the
gas, which is almost sure to happen if the current is not
rapid, the^pperaJlon is best performed by filling the flask
completely wi^r the gas and then pouring in one-third of its
volume of ice-cold water. On covering the flask with the
moistened palm and shaking it, a very strong suction will be
obtained.

Stout- walled flask ; H2S generator ; ice-water.

(d) A saturated solution of the gas may be obtained by
using the apparatus, Fig. 85, p. 196.

18. Solubility in sodium hydroxide. — The solubility of
hydrogen sulphide in sodium hydroxide is shown by filling
the eudiometer (Fig. 11, p. 26) with hydrogen sulphide over
a saturated solution of sodium chloride. Sodium hydroxide
is allowed to flow through the stop-cock into the gas, which
will immediately be absorbed and the liquid will rise inside
the tube.

If the hydrogen sulphide is prepared from commercial
ferrous sulphide, considerable hydrogen gas will be present
in the evolved gas and therefore be unabsorbed by the sodium
hydroxide.

If the hydrogen sulphide is prepared from the action of
hydrochloric acid on antimony sulphide, the gas will be
much more pure, and but a small quantity of gas will remain
unabsorbed, i.e., less than half a cubic centimeter out of
100 cc. of hydrogen sulphide.

142 CHEMICAL LECTURE EXPERIMENTS

19. Combustion in air. — Hydrogen sulphide, though a
non-supporter of combustion, burns witl^ blue tlanie.

A lifted candle lowerecfcinto a jar containing hydrogeil
sulphide is extinguished, ancrthe hydrogen sulphide ignited.
The gas burns at the mouth of the jar, but owing to the
deficiency of oxygen in the lower portions of the jar, the
sulphur is deposited instead of being oxidized as fast as it is
liberated, hence the walls of the jar betome covered with a
thin film of flowers of sulphur. ^L $

To demonstrate especially this latter plr%omenon, it is
advisable to have a tall jar, as this form retards the entrance
of the air.

Tall jar of H2S ; candle on wire.

20. Deposition of sulphur in the incomplete combustion of
hydrogen sulphide. — If air is burned in an atmosphere of
hydrogen sulphide, the heat from the flame will be sufficient
to cause a decomposition of the surrounding gas with an
accompanying deposition of sulphur.

The apparatus with which this ttanie of air is produced, is
that shown in Fig. 142, p. 341. A strong ciirrenl of hydro-
gen sulphide is conducted* through the elbow in the bottom
of the lamp chimney and is ignited at the orifice at the top.
A gentle current of air, best obtained from the water blast,
is passed through the long tube, which may be pushed up
through the hole in the cork into the centre of the hydrogen
sulphide flame at the top of the lamp chimney. On slowly
lowering the tube, the air will be seen to be burning in the
atmosphere of hydrogen sulphide, and a deposit of sulphur
will be obtained on the walls of the chimney.

Lamp chimney and fittings (Fig. 142, \\ 341) ; HjS generator ; air-
blast or gasometer.

21. Decomposition in a hot tube. — Dry hydrogen sulphide,
when passed through a glass tube which is strongly heated

HYDROGEN SULPHIDE

143

with a Bunsen burner, is decomposed, and sulphur is de-
posited on the cooler portions of the tube. 9

* H2S = H2 + S. t

22. Explosion of a mixture of hydrogen sulphide and
oxygen. — A round-bottorned ginger-ale bottle is filled with
three volumes of oxygen and tw^o volumes of hydrogen
sulphide. The mixture is well shaken, and then a flame
held at the mouth of the bottle.

2 H2S + 3 02 = 2 H20 + 2 S02.

23. Action on sulphur dioxide. — (a) In the presence of a
small amount of moisture, hydrogen sulphide reacts with
sulphur dioxide, with the liberation of sulphur. This re-
action is of especial interest in indicating the deposition of
sulphur in volcanoes. The operation may be carried out in
the simplest manner bj# inverting a cylinder of hydrogen
sulphide collected over water, mouth downwards, on top of a
cylinder of equal size, containing sulphur dioxide. When
the glass platesjpre slipped from between the two cylinders,
the gases unitcwith a heavy deposition of sulphur on the
walls of tl^cylinders. As the sul-
phur dioxine is nearly twice as heavy
as the hydrogen sulphide, the diffu-
sion of the two gases is somewhat
slow, and gives an excellent illustra-
tion of this phenomenon. In case
it is desired to hasten the action, the
cylinders are shaken.

The reaction may be shown on a
much more extended scale by con-
ducting the two gases from suitable
generators into a large three-necked Wolff bottle (Fig. 65).
Hydrogen sulphide is conducted through one neck of the

Fig. 65

144 CHEMICAL LECTURE EXPERIMEN

Wolff bottle, and sulphur dioxide through another. T^ie
tlyrd neck is fitted with a cork, carrying a glass elbow mni-
nected with th^flue. After a few minutes, the whofc
interior of the Wolff bottle becomes coated with a layer
of finely divided sulphur.

The bottle should be cleaned immediately after use, as
the sulphur, if allowed to dry on the walls of the bottle, is
very hard to remove. The reaction is not altogether as
simple as is given in Equation (1) below, as a certain small
quantity of pentathionic acid is formed.

(1) S02 + 2 1LS = 2 HX> + 3 S.

(2) 5 S02 + 5 II2S = H2S,0« + | JL.o + 5 S.

Wolff bottle (3-necked) ; H*S generator ; 80s generator ; cylinder

of II2S ; cylinder of S( >2.

(b) The interaction of hydrogen sulphide and sulphur

dioxide may also be carried out in wieous solution. Aque-
ous solutions of the two gases, when mixed, produce a heavy
precipitate of sulphur.

By conducting hydrogen sulphide into a^olution of sul-
phur dioxide, or by conducting sulphur diorlde into a solu-
tion of hydrogen sulphide, the precipitate of sulphur is also
obtained.

24. Combustion of iron. — A bundle of iron wires, or
better, a bit of steel wool (Ex. 10, p. 23), when held in the
flame of burning hydrogen sulphide, will take tire in the
gas and burn, forming ferrous sulphide.

H2S supply ; steel wool.

25. Ignition by fuming nitric acid. — Strong oxidizing
agents, such as fuming nitric acid, effect the rapid oxida-
tion and subsequent ignition of hydrogen sulphide.

A 300 cc. cylinder is filled with hydrogen sulphide,

HYDROGEN SULPHIDE 145

covered with a ground-glass plate, and placed mouth up-
wards on the table. A few cubic centimeters of fuming
nitric acid are gently warmed and poured into the jar of the
gas. The hydrogen sulphide is ignited, with a slight ex-
plosion, and care should be taken to avoid danger from the
spurting out of drops of acid. Dense fumes of nitrogen
oxides are evolved, and sulphur is deposited on the walls of
the cylinder.

300 cc. cylinder of H2S ; fuming HNOs.

26. Decomposition by sodium. — Hydrogen sulphide, when
passed over heated sodium, is decomposed, the sulphur
uniting with the sodium to form sodium sulphide, and the
hydrogen escaping from the tube.

A few small pieces of sodium, which should be dried and
freed from crust, are placed in a hard-glass bulb-tube
through which a current of hydrogen sulphide is being
passed. On heating the metal gently it takes fire, glowing
brightly, and the issuing hydrogen, when ignited, burns with
a yellow sodium flame. The yellow residue in the bulb con-
sists of sodium sulphide, which may be dissolved out with
water and tested.

H2S + 2Na = :NTa2S + H2.

Bulb-tube ; H2S supply ; Na.

27. Action on solutions of metallic salts. — The great
importance of the use of hydrogen sulphide in analytical
chemistry renders a study of its action on solutions of me-
tallic salts essential. The simplest method of showing its
action is by adding small portions of an aqueous solution
of hydrogen sulphide to solutions of the various metals in
small cylinders. The following selection of metals shows
the great variety of color in the sulphides and the necessity
of an alkaline solution to effect the precipitation of the sul-

146 CHEMICAL LECTURE EXPERIMENTS

phide from certain salt solutions. The cylinders should
contain respectively solutions of cupric sulphate, antimoni-
ous chloride, cadmium chloride, lead nitrate, zinc sulphate,
manganese sulphate, and cobalt nitrate. In preparing the
solution of antimonious chloride the addition of tartaric
acid will prevent the precipitation of the white oxychloride.
The solutions of zinc, manganese, and cobalt give no precipi-
tate with hydrogen sulphide, though on the addition of a
small quantity of ammonium hydroxide the sulphides are
immediately precipitated.

The operation may also be carried out by passing hydro-
gen sulphide through the various salt solutions contained
in gas washing-bottles. The hydrogen sulphide generator
used in this experiment must have a very long safety-tube
to permit an increase of pressure within the generator
sufficient to cause the gas to bubble through the successive
liquids. To hasten the operation, dilute solutions of the
salts are used. The cylinders are connected in series in
the order above indicated. In case a Kipp generator is
used to furnish the hydrogen sulphide, the necessary press-
ure is obtained by inserting a cork carrying a short glass
tube, a rubber tube, and a pinch-cock into the opening in
the top of the generator. By closing the pinch-cock when
the generator is in operation the acid is prevented from
rising into the acid reservoir, and consequently a greater
pressure is obtained. The rubber tube and pinch-cock may
be replaced by a safety-funnel containing mercury.

CuS04 + H2S = CuS + H2S04.

2 SbCl3 + 3 H2S = Sb2S3 + 6 HC1.

etc. etc.

Seven gas washing-bottles ; H2S generator, with extra long thistle
or Kipp H2S generator ; solutions of CuS04, SbCl3, CdCl2, Pb(N03)2,
ZnS04, MnS04, Co(N03)2.

HYDKOGEN PERSULPHIDE 147

HYDROGEN PERSULPHIDE

28. Preparation by the action of hydrochloric acid on
calcium polysulphide. — Calcium polysulphicle is made by
adding 40 g. of sulphur flowers to 300 cc. of water, to which
20 g. of quicklime have been added. The mixture is boiled
ten minutes, and then allowed to settle. The cooled liquid
is decanted off and poured in a thin stream into a mixture
of 100 cc. of hydrochloric acid and 50 cc. of water, in a
liter separating-funnel, which is shaken during the addition.
After a few minutes the greater portion of the hydrogen
persulphide formed will have settled to the bottom of the
funnel as a heavy, yellowish oil. The oil is drawn off into
a small flask containing fused calcium chloride, where it
is dried.

CaS5 + 2 HC1 = H2S2 + CaCl2 + 3 S. [?]

Liter separating-funnel ; small flask ; CaO ; S flowers ; fused CaCl2.

29. Solubility in carbon disulphide. — Hydrogen persul-
phide is mixed in a test-tube with two or three times its
volume of carbon disulphide. The two liquids are perfectly
miscible, and the solution remains undecomposed much
longer than the pure hydrogen persulphide.

H2S2 ', CS2.

30. Bleaching action. — Very dilute litmus solution, when
added to two drops of hydrogen persulphide in a test-tube,
is bleached. The reaction is not immediate, and follows
only after vigorous shaking. Sulphur is precipitated.

31. Decomposition in an alkaline solution. — Hydrogen
sulphide, like hydrogen peroxide, is more stable in an acid
than in an alkaline solution. The compound decomposes in
a dilute alkaline solution, setting free sulphur and forming
hydrogen sulphide.

148

CHEMICAL LECTURE EXPERIMENTS

Fifty cubic centimeters of water are added to 2 drops of
hydrogen persulphide in a 100 cc. flask. One drop of sodium
hydroxide solution is added, and the mixture vigorously
shaken. Almost immediately, even in the cold, the liquid
becomes turbid from sulphur precipitated, and on warming
the solution, hydrogen sulphide is expelled.

H2S2 = H2S + S.

32. Reduction of silver oxide. — Hydrogen persulphide,
like hydrogen peroxide, reduces silver oxide. A few centi-
grams of silver oxide are allowed to fall upon 2 drops of
hydrogen persulphide in a dry test-tube. The reaction is
vigorous.

SULPHUR MONOCHLORIDE

33. Preparation by the action of chlorine on sulphur. —

Dry chlorine acts on sulphur with the production of a yel-
low, oily liquid, sulphur monochloride.

A 400 cc. tubulated retort is one-third filled with flowers
of sulphur. Dry chlorine is conducted through a glass elbow

inserted in the tubulature,
and the neck of the retort
is thrust into a filter bottle,
whose side tube is connected
with a draft (Fig. 66). Pro-
vision should be made for
heating the sulphur and
cooling the receiver. The
sulphur is strongly heated,
and the chlorine current
maintained at a rapid rate.
The tube conducting the
chlorine should be lowered so as to almost touch the sur-
face of the melted sulphur. After a few cubic centimeters

^ — , 7

1 1

Fig. 66

SULPHUR DIOXIDE 149

of the chloride have collected in the receiver the operation

should be stopped.

2 S + Cl2 = S2C12.

400 cc. tubulated retort ; filter-flask ; S flowers ; CI generator.

34. Solubility of sulphur in sulphur monochloride. — A

few pieces of sulphur are placed in a test-tube and cov-
ered with sulphur monochloride. By shaking, or more
rapidly by gentle boiling, the sulphur is completely
dissolved.

35. Decomposition by water. — Sulphur monochloride,
when allowed to stand in contact with water, is gradually
decomposed with the liberation of sulphur and hydrogen
sulphide. One cubic centimeter of sulphur monochloride is
placed in a test-tube with 2 or 3 cc. of water and vigorously
shaken. The decomposition is rapid and the contents of
the tube become warm.

SULPHUR DIOXIDE AND SULPHUROUS ACID

PREPARATION

36. From sulphur and oxygen. — Sulphur burns in the
air or in pure oxygen to form sulphur dioxide.

A 40 cm. length of combustion-tube, provided with a
cork at each end, is clamped in a horizontal position, and a

wad of asbestos or glass wool ^

placed at one end of the tube. *^

A boat, in which a few pieces
of roll sulphur are placed, is
inserted in the other end of the tube, and a gentle stream
of oxygen is admitted, driving out all air. The cork is
withdrawn, the sulphur ignited, and the current of oxygen
continued through the tube. The sulphur burns with a blue
flame, forming sulphur dioxide, which escapes at the other

150

CHEMICAL LECTURE EXPERIMENTS

end of the combustion-tube. The plug of asbestos serves
to retain any unburned sulphur which may distil over.
The issuing gas may be collected in cylinders by displace-
ment and used in any of the experiments described beyond.

40 cm. length combustion-tube (Fig. 67) ; porcelain boat ; glass
wool or fibrous asbestos ; S ; O supply.

37. Volumetric relation of the sulphur dioxide formed to
the oxygen used. — Sulphur, when burned in an atmosphere
of oxygen, yields one volume of sulphur dioxide for each
volume of oxygen consumed, hence in burning sulphur in
a confined volume of oxygen the volume of the product
remains the same as the volume of the oxygen used.

A 700 cc. Jena glass distillation flask is filled with dry
oxygen by displacement, and the arm connected with one
limb of a U-tube half filled with mercury (Fig. 68). The

cork is provided with a glass rod
carrying a small platinum defla-
grating-spoon at the end, in which
sulphur is burned. The deflagra-
ting-spoon is easily made from
a small piece of platinum foil
which is fastened to the glass
rod by means of platinum wire.
A 4 mm. piece of roll sulphur is
placed in the platinum spoon, and
after ignition in the air, is im-
mediately thrust into the flask,
where it continues to burn with
great brilliancy. The cork must be firmly inserted in the
neck of the flask, and the union between the U-tube and the
flask must be very tight. As the sulphur burns, the gases
expand, and the mercury rises in the open arm of the U-
tube. On cooling, the gases contract, and at the end of the

Fig. 68

SULPHUR DIOXIDE 151

operation the level in the arms of the U-tube will be found
to be the same.

700 cc. Jena glass distillation flask; 1 -holed rubber stopper;
U-tube ; platinum deflagrating-spoon ; Hg ; S.

38. From sulphuric acid and copper. — Sulphuric acid,
when heated with copper, becomes reduced, liberating sul-
phur dioxide. This reaction was formerly used to prepare
the gas on the lecture table, but the method of Experiment
41 is preferable.

The gas may be prepared on the small scale by heating a
few grams of copper clippings with concentrated sulphuric
acid in a 100 cc. Erlenmeyer Jena glass flask.

Cu + 2 H2S04 = CuS04 + 2 H20 + S02.
100 cc. Erlenmeyer flask ; Cu clippings.

39. From sulphuric acid and powdered charcoal. — Char-
coal reduces sulphuric acid, with the formation of varying
amounts of sulphur dioxide, carbon monoxide and dioxide.

The impure gas may be made by heating a thin paste of
powdered charcoal and concentrated sulphuric acid in a 100
cc. Jena glass Erlenmeyer flask. The reaction requires con-
siderable heat to start, but after a short time sulphur
dioxide may be detected at the mouth of the flask.

4 H2S04 + 3 C = 4 H20 + 4 SOa + COa + 2 CO.

100 cc. Jena glass Erlenmeyer flask ; powdered charcoal.

40. From sulphuric acid and sulphur. — Sulphur reacts
with hot concentrated sulphuric acid to form sulphur
dioxide.

A thin paste of sulphur flowers and concentrated sul-
phuric acid is heated in a 100 cc. Jena glass Erlenmeyer
flask. As the temperature of the sulphuric acid rises
almost to the boiling point, the reaction begins. The

152 CHEMICAL LECTURE EXPERIMENTS

sulphur melts to a globule, and thus presents but little sur-
face for the action of the acid, hence the quantity of
sulphur dioxide formed is very small.

2 H2S04 + S = 2 H20 + 3 S02.
100 cc. Jena glass Erlenmeyer flask; S flowers.

41. By the action of sulphuric acid on sodium acid sul-
phite.— By far the most satisfactory method for the prepa-
ration of sulphur dioxide is that in which the reaction
between sulphuric acid and sodium acid sulphite is used.
This latter compound can be readily obtained in the mar-
ket at a very low price.

Sodium acid sulphite is placed in the bottom of the 300
cc. Erlenmeyer flask of the apparatus (Fig. 45, p. 92). The
dropping-funnel is filled with dilute sulphuric acid, made
by pouring one volume of concentrated sulphuric acid into
an equal volume of water and cooling the mixture. The
glass elbow is connected with a gas washing-bottle contain-
ing concentrated sulphuric acid, and the dry gas is col-
lected by displacement in two or three empty cylinders.
On allowing the dilute sulphuric acid to drop slowly upon
the sodium acid sulphite, a very regular evolution of sul-
phur dioxide is obtained.

2 NaHS03 + H2S04 = Na2S04 + 2 S02 + 2 H20.

300 cc. Erlenmeyer flask ; dropping-funnel ; NaHS03 ; dil. H2S04
(1:1).

PROPERTIES

42. Liquefaction of sulphur dioxide. — Pure dry sulphur
dioxide, when passed through a tube immersed in a freez-
ing mixture, condenses to a colorless liquid.

Sulphur dioxide generated according to the method of
the preceding experiment is first dried by passing through
a gas washing-bottle containing sulphuric acid, and then

SULPHUR DIOXIDE 153

conducted into a U-tube immersed in salt and ice. The gas
is there liquefied. Many expensive tubes in which to con-
dense the gas are on the market, though, unless large
quantities of the liquid sulphur dioxide are required, the
operation is well shown by the ordinary U-tube.

The liquefied gas is readily obtained in small tin cylin-
ders at a low price, and is best used in this form for the
experiments on the production of cold by its evaporation.
The cans are cooled in a mixture of salt and ice before
being opened, and if they are kept immersed in the freez-
ing mixture, there will be no great loss by evaporation.

U-tube ; ice and salt ; S02 generator.

43. Freezing action of liquefied sulphur dioxide. —

(a) Liquid sulphur dioxide, when allowed to evaporate
spontaneously, produces an intense cold which may be
utilized to freeze water.

Five cubic centimeters of liquid sulphur dioxide are
poured on 10 cc. of water in a small beaker. The mixture
is stirred and immediately solidifies to a crystalline mass.
Provision should be made for the escape, into the flue or
hood, of the vapors of sulphur dioxide.

(b) A few drops of water are placed on a block of wood
and a small beaker set on the wet portion. On pouring 5 cc.
of liquefied sulphur dioxide into the beaker, the liquefied
gas evaporates, producing an intense cold. The water
under the beaker freezing causes the wood to adhere to the
beaker.

Block of wood ; liquefied S02.

44. Production of the Leidenfrost phenomenon with lique-
fied sulphur dioxide. — Liquefied sulphur dioxide, when
thrown into a hot platinum dish, assumes the spheroidal
state, giving a striking illustration of the Leidenfrost

154 CHEMICAL LECTURE EXPERIMENTS

phenomenon of a liquid, which boils below zero, remaining
in the liquid form in a red-hot dish.

A platinum dish is brought to a red heat in a powerful
Bunsen lamp and 10 cc. of liquefied sulphur dioxide poured
into it. Instantly the liquid assumes the spheroidal form,
and may be poured out of the dish upon a plate.

The experiment may be made still more striking by fol-
lowing the introduction of the liquid sulphur dioxide by an
immediate addition of 10 cc. of water to the contents of the
platinum dish. If the dish is then quickly removed by
means of crucible tongs and the contents thrown on a plate,
it will be seen that sufficient sulphur dioxide has remained
unvolatilized to freeze the water, which will remain in the
plate in the form of ice.

Platinum dish ; plate ; liquefied SO2.

45. Specific gravity of gaseous sulphur dioxide. — Sul-
phur dioxide is twice as heavy as air, and when a liter
of the gas is poured into a beaker on a balance arm, as
in Ex. 9, p. 47, a marked deflection of the pointer is
obtained.

If a liter of the gas is poured upon the paper wheel de-
scribed in Ex. 36, p. 313, it may be made to rotate.

Lecture-balance ; paper wheel (Fig. 125, p. 313) ; liter cylinder of
S02.

46. Action on litmus.- — A moistened strip of blue litmus
paper is thrust into a jar of the gas, where, owing to the
acid nature of the sulphur dioxide, it is instantly turned
red.

47. Action on potassium dichromate solution. — Five cubic
centimeters of potassium dichromate solution, when poured
into the gas, are immediately turned green, owing to the
reducing action of the sulphur dioxide.

SULPHUROUS ACID 155

48. Solubility in water. — (a) If a small piece of ice or
a few drops of water are allowed to enter a tube of the gas
collected over mercury, the absorption is very rapid, the
mercury rising to take the place of the absorbed gas.

(b) A cylinder filled with sulphur dioxide is opened
mouth downwards under water. The gas is absorbed and
the water rises and completely fills the cylinder.

S02 in tube collected over mercury; ice.

49. The gas does not support the combustion of a candle.

— A lighted candle or a burning taper, when lowered into
the gas, is immediately extinguished.

50. Bleaching action. — Sulphur dioxide is a powerful
bleaching agent and is much used for this purpose in techni-
cal chemistry. Its bleaching action is best shown by de-
colorizing a red rose with the gas. The rose is lowered into
a jar of sulphur dioxide and allowed to remain there some
minutes. The color will rapidly disappear. The color may
be restored by holding the flower in chlorine or in the vapor
of fuming nitric acid. The restoration of the color depends
upon the fact that the sulphur dioxide is oxidized to sul-
phuric acid by chlorine and fuming nitric acid.

SO2 gas ; jar of CI ; fuming HNO3 ; red rose.

51. Restoration of the color to a rose bleached by sulphur
dioxide. — The colorless compound formed by the union of
sulphur dioxide with the coloring matter of the flower is
destroyed by the action of sulphuric acid, hence by immers-
ing the rose bleached in the preceding experiment in 50
per cent sulphuric acicl the color is restored. The acid
should be prepared and cooled before use.

Rose from preceding experiment ; H2SO4 (50 per cent).

156 CHEMICAL LECTURE EXPERIMENTS

52. Combustion of iron or tin. — Sulphur dioxide, while
not supporting the combustion of carbonaceous material,
will support the combustion of certain of the metals.

A small quantity of iron or tin powder is placed in a
bulb-tube through which a gentle stream of sulphur dioxide
is conducted. On heating the iron powder it glows, with
the formation of iron sulphide and oxide.

Bulb-tube ; S02 generator ; Fe powder ; powdered Sn.

53. Union of sulphur dioxide and lead dioxide. — Sulphur
dioxide and lead dioxide unite directly to form lead sul-
phate.

A small quantity of well-dried lead dioxide is placed on
a piece of asbestos paper covering the bowl of a deflagrat-
ing-spoon. On lowering the spoon into a jar of dry sulphur
dioxide the dark-colored oxide is converted to white lead
sulphate, the change being accompanied by a strong glowing.

The union may also be accomplished by conducting a
stream of sulphur dioxide through a bulb-tube containing a
quantity of the lead dioxide.

Pb02 + S02 = PbS04.

Bulb-tube ; deflagrating-spoon ; asbestos paper ; S02 supply ; jar of
S02 ; Pb02.

54. Reduction of potassium permanganate solution. — The

intense color of the solution of potassium permanganate is
immediately discharged by adding sulphur dioxide water to
it in a cylinder.

The experiment can be varied by allowing the deep-col-
ored permanganate solution to flow from a burette into a
cylinder of the sulphur dioxide solution. As the perman-
ganate drops into the sulphurous acid its color vanishes
until all the sulphurous acid has been oxidized, when one

HYDROSULPHUROUS ACID ' 157

more drop of the permanganate will permanently color the
whole solution. The permanganate solution should in each
case be acidified with sulphuric acid to prevent the precipi-
tation of oxides of manganese.

Burette ; KMn04 solution ; S02 water.

55. Electrolysis of sulphurous acid. — Nascent oxygen and
hydrogen react with sulphurous acid, forming in the first
case sulphuric acid, and in the second reducing the sulphu-
rous acid to sulphur.

A 10 per cent solution of sulphuric acid is saturated with
sulphur dioxide and the liquid placed in the electrolytic
apparatus (Fig. 46, p. 95). On passing a current from a
bichromate battery through the platinum electrodes, it will
be found that very little, if any, gas collects in the tubes.
The oxygen liberated at the positive pole is used up in oxi-
dizing the sulphurous acid to sulphuric acid, while the
hydrogen formed at the negative pole immediately effects
the reduction of the sulphurous acid to sulphur. The liquid
around the negative pole becomes milky from the liberation
of free sulphur.

Electrolytic apparatus (Fig. 46, p. 95) ; Pt electrodes ; bichromate
battery ; 10 per cent H2S04 saturated with S02.

HYDROSULPHUROUS ACID

56. Preparation. — Sulphur dioxide water or sulphurous
acid in the presence of finely divided zinc is reduced to
hydro- or hyposulphurous acid.

A 100 cc. Erlenmeyer flask is half filled with a saturated
solution of sulphur dioxide in water and a few grams of pul-
verized zinc are added. The solution, which contains free
hydrosulphurous acid, becomes somewhat yellowish, and a
portion of the zinc is dissolved. As the reaction continues,

158 CHEMICAL LECTURE EXPERIMENTS

the acid is decomposed and a small quantity of sulphur is
precipitated.

H2S03+H2 = H2S02 + H20.

S02 water ; granulated Zn.

57. Bleaching action. — Indigo solution, which is not
bleached by sulphurous acid, is readily bleached by hydro-
sulphurous acid. A small quantity of indigo solution is
placed in each of two cylinders. Sulphurous acid is added
to the first, and hydrosulphurous acid to the second. The
latter only is bleached. Litmus paper is similarly bleached.

H2S02 ; indigo solution.

58. Reducing action. — Hydrosulphurous acid possesses
strong reducing properties and precipitates the metals mer-
cury and silver from solutions of their soluble salts. The
reactions may be carried out in test-tubes by adding a small
quantity of hydrosulphurous acid to the respective salt
solutions.

The reaction with cupric sulphate proceeds in two stages.
A small quantity of the hydrosulphurous acid is added to
the dilute cupric sulphate solution, which is rapidly turned
from blue to green. As the reaction proceeds, the solution
changes to a dark brown, and a precipitate is obtained con-
sisting of metallic copper and cuprous hydride.

The addition of sulphurous acid to cupric sulphate solu-
tion produces no precipitate.

Solutions of H2S02, H2S03, HgCl2, AgN03, CuS04.

SULPHUR TRIOXIDE

PREPARATION

59. By the union of oxygen and sulphur dioxide in the
presence of platinized asbestos. — (a) When a mixture of

Fig. 69

SULPHUR TRIOXIDE 159

sulphur dioxide and oxygen is passed over heated platin-
ized asbestos, sulphur trioxide is formed.

A 500 cc. 3-necked Wolff bottle is half filled with concen-
trated sulphuric acid. A current of sulphur dioxide is con-
ducted through a glass tube inserted in one of the necks of
the Wolff bottle and dipping beneath the surface of the
sulphuric acid. A glass tube, conducting oxygen, is thrust
through another neck of
the bottle and likewise
dips beneath the surface
of the acid. A short glass
elbow is inserted in the
cork in the third neck
and is connected with a
bulb-tube or combustion-
tube containing a 3 or 4 cm. length of platinized asbestos
(Fig. 69). The gases are passed with approximately the
same degree of rapidity into the bottle and proceed un-
changed through the platinized asbestos and bulb-tube into
the air. On heating the platinized asbestos, however, dense
white clouds of sulphur trioxide are formed.

2 S02 + 02 = 2 S03.

500 cc. 3-necked Wolff bottle (Fig. 69) ; bulb-tube ; S02 generator ;
O supply ; Pt asbestos.

(b) Instead of passing a mixture of gaseous oxygen and
sulphur dioxide over platinized asbestos, the simpler process
of passing oxygen first through strong sulphur dioxide water,
and then through concentrated sulphuric acid, and finally
over platinized asbestos, may be used.

A current of oxygen is passed through a saturated solu-
tion of sulphur dioxide in water in a 200 cc. Erlenmeyer
flask, which is gently warmed. The oxygen there mixes
with the sulphur dioxide, and the two gases are conducted

160 CHEMICAL LECTURE EXPERIMENTS

through a gas washing-bottle containing concentrated sul-
phuric acid. The mixed gases are then conducted through
a bulb-tube or combustion-tube containing platinized asbes-
tos. On heating the platinized asbestos dense clouds of sul-
phur trioxide issue from the tube.

200 cc. Erlenmeyer flask ; bulb with platinized asbestos ; H2S04gas
washing-bottle ; 0 supply ; saturated solution of S02.

60. From fuming sulphuric acid. — ISTordhausen or fuming
sulphuric acid, consisting, as it does, essentially of a solution
of sulphur trioxide in sulphuric acid, readily liberates the
trioxide on heating. The fuming acid is placed in a 500 cc.
retort, whose neck is thrust into a 250 cc. flask immersed in a
freezing-mixture of salt and ice. On gently heating the acid
the sulphuric trioxide is given off and condenses in the
receiver. Owing to the intensely corroding properties of
the acid the retort must be very carefully heated to avoid
danger of breakage. The danger is minimized if a sand-
bath is used.

H2SA = H2S04 + S03.

500 cc. retort ; 250 cc. flask ; sand-bath ; Nordhausen sulphuric acid.

61. From sulphuric acid and phosphorus pentoxide. —

Phosphorus pentoxide abstracts water from sulphuric acid,
setting free sulphuric anhydride.

A few drops of strong sulphuric acid are placed in a test-
tube, and sufficient phosphorus pentoxide is added to make a
thin paste. On gently heating the mixture a vigorous reac-
tion takes place, clouds of sulphur trioxide being given off.

3 h2S04 + PA = 2 H3P04 + 3 S03 .

62. By heating potassium disulphate. — Potassium disul-
phate, when heated in a test-tube, forms potassium sulphate
and sulphur trioxide.

SULPIJUR TRIOXIDE 161

A bell-jar whose sides have been moistened with water is
held over the test-tube containing potassium disulphate and
the fumes allowed to condense in the bell-jar. On washing
out the contents of the jar into a cylinder and adding barium
chloride solution, a white precipitate of barium sulphate will

be formed.

K2S207 = K2S04 + S03.

Bell-jar ; K0S0O7 ; BaCl2 solution.

PROPERTIES

63. Action on water. — (a) A bottle containing sulphur
trioxide fumes on removing the stopper. The fumes of
ISTordhausen or fuming sulphuric acid are due to the pres-
ence of large quantities of the trioxide.

The anhydride is very deliquescent, and, when solid, is
best removed with a glass rod. Enough will cling to the
rod to illustrate its properties.

The fundamental precaution, not to pour water into sul-
phuric acid, may be here repeated. The danger is infinitely
greater if water is poured into a vessel containing sulphur
trioxide. The results of such an operation are seen in the
following experiments. The acid nature of a solution of
sulphur trioxide in water may be shown by immersing a
piece of blue litmus paper in it.

S03 + H20 = H2S04.

(b) The intensity of the reaction between sulphuric anhy-
dride and water is so great that the addition of water to the
anhydride becomes a very dangerous operation. On the
small scale, the experiment may be made without danger, as
follows : —

A small quantity of sulphur trioxide is placed in a plati-
num crucible, imbedded in a layer of sand, at the bottom of

162

CHEMICAL LECTURE EXPERIMENTS

a glass cylinder (Fig. 70). A glass funnel is inserted in
the mouth of the cylinder, and its stem, which should be as
long as possible, directed so as to allow water
to drop into the crucible. On pouring a few
drops of water into the funnel, they will fall
upon the trioxide in the crucible, the union
taking place with almost explosive violence.

"sA^Mgjgli

Apparatus (Fig. 70) ; glass cylinder
sand ; funnel ; S03.

Pt crucible

Fig. 70

^ water and a few crystals, or 5 cc. of liquid

sulphur trioxide are dropped into it. As each

particle comes in contact with the water, there

is a hissing and explosion. The column of air in the

cylinder intensifies the sound.

Cylinder one -third filled with water ; S03.

(d) A small dry test-tube is drawn out at the middle, so
as to leave a hook of glass at the bottom of the upper part,
to which a weight may be fastened (Fig. 71).
One cubic centimeter of liquid sulphur trioxide,
or its equivalent amount in crystals, is placed
in the test-tube to which the weight has been
fastened. It is then allowed to drop into a tall
cylinder containing about a liter of water. The
cylinder should not be more than three-fourths
full. As the tube sinks beneath the surface of
the water, the sulphur trioxide unites with the
water with explosive violence.

Gauntlets ; drawn-out test-tube with weight ; liter cyl-
inder ; SO3.

Fig. 71

64. Action of sulphur. — Sulphur dissolves in sulphur tri-
oxide to form a blue liquid, the so-called sulphur sesquioxide.

SULPHUR TRIOXIDE 163

On standing, the liquid decomposes, loses its blue color, and
forms sulphur dioxide.

A small quantity of sulphur trioxide is placed in a dry
test-tube, and a very small pinch of sulphur flowers added
to it. The solution becomes blue, but by gently warming,
the color disappears, and a paper moistened in potassium
dichromate solution indicates the presence of sulphur
dioxide. SOs + g = SA> p-j

Sulphur trioxide ; S flowers.

65. Action with phosphorus. — Phosphorus reduces sul-
phur trioxide, with the liberation of sulphur dioxide.

Two cubic centimeters of liquid sulphur trioxide are placed
in a dry test-tube, and a 5 mm. piece of well-dried phos-
phorus is added. The phosphorus catches fire of itself and
burns on the surface of the liquid, obtaining its oxygen
from the sulphur trioxide. Large quantities of sulphur
dioxide are evolved. The residue in the test-tube at the
end of the reaction may be carefully immersed in a large
cylinder of water, and it will be seen that the phosphorus
has all been oxidized, as there will be little, if any, insoluble
matter in the residue. Owing to the fumes evolved, it is
better to conduct the experiment under the hood.

5 S03 + 2 P = P205 + 5 S02.
S03 ; P.

66. Action with barium oxide. — Barium oxide combines
with sulphur trioxide to form barium sulphate.

A small quantity of sulphur trioxide is placed in a dry
test-tube, and powdered barium oxide carefully sifted into
the tube. The union of the two compounds is accompanied
by an evolution of heat and light.

BaO + S03 = BaS04.
Screens ; gauntlets ; barium oxide ; sulphur trioxide.

164

CHEMICAL LECTURE EXPERIMENTS

SULPHURIC ACID

FORMATION AND PREPARATION

67. By the oxidation of sulphur with nitric acid. — Sul-
phur, when heated with fuming nitric acid, is oxidized to
sulphuric acid.

Two grams of sulphur flowers are heated to boiling in a
100 cc. Erlenmeyer flask with 10 cc. of fuming nitric acid.
On diluting the mixture with water and pouring it upon
a filter, the filtrate will be found to contain considerable
free sulphuric acid, which will give a white precipitate with
barium chloride.

S flowers ; fuming HN03.

68. By the action of nitric acid on sulphur dioxide. — Sul-
phur dioxide, when conducted into concentrated nitric acid,
becomes oxidized, forming sulphuric acid and setting free

nitrogen peroxide. In
case dilute nitric acid
is used, nitric oxide
rather than nitrogen
peroxide is liberated.

A current of sulphur
dioxide is conducted
into a 300 cc. flask con-
taining 75 cc. of con-
centrated nitric acid.
The cork of the flask
is provided with two
holes, through one of
which the sulphur di-
oxide is conducted, while the other allows for the escape
of the nitrogen peroxide formed. An elbow in the second
hole conducts the nitrogen peroxide to the bottom of an

Fig. 72

SULPHURIC ACID 165

empty glass cylinder fitted with a two-holed cork (Fig. 72).
All connections should be made with the glass tubes as
nearly touching each other as possible, since the nitrogen
peroxide fumes attack rubber. On conducting sulphur
dioxide into the nitric acid, the liquid warms up of itself
and deep reddish-brown fumes of nitrogen peroxide escape
and fill the glass cylinder. After a few moments the liquid
in the flask may be diluted with water and tested for the
presence of sulphuric acid by means of barium chloride.

If the concentrated nitric acid in the apparatus is replaced
by an acid of the specific gravity of 1.15 and the experi-
ment repeated, it will be found that the gas escaping into
the glass cylinder, while somewhat colored, consists chiefly
of nitric oxide, as can be seen by opening the mouth of the
cylinder and allowing the gas to come in contact with the
air. The formation of red fumes indicates the presence of
nitric oxide. It will be found necessary to warm the dilute
nitric acid somewhat in order to start the reaction. At the
end of the experiment, the liquid may be tested as before
for sulphuric acid.

S02 + 2 HN03 = H2S04 + 2 N02.

3 S02 + 2 HNO3 + 2 H20 = 3 H2S04 + 2 NO.

Flask with 2 -holed cork ; glass cylinder ; S02 generator ; HN03
(sp. gr. 1.15); con. HN03.

69. Chamber crystals by the action of concentrated nitric
acid on sulphur dioxide. — Nitric acid oxidizes sulphur diox-
ide, forming sulphuric acid.

A piece of asbestos paper fastened to a wire is dipped
into concentrated nitric acid and lowered into a cylinder of
sulphur dioxide. A marked reaction, filling the jar with
red fumes, is observed. The walls of the cylinder soon
become coated with chamber crystals.

Jar of S02 ; con. HN03.

166

CHEMICAL LECTURE EXPERIMENTS

70. By the oxidation of sulphur dioxide by means of nitric
oxide in the presence of air and water vapor. — In the manu-
facture of sulphuric acid on a large scale the oxidation of
sulphur dioxide is effected by means of nitric oxide in the
presence of air. On the lecture-table the substitution of a
gaseous for a liquid oxidizing agent may be successfully
carried out by conducting the gaseous compounds, i.e. sul-
phur dioxide, nitric oxide, air, and water vapor, into a large
flask, where the reaction takes place.

A 4 or 5 1. flask is provided with a four-holed cork,
through three holes of which glass tubes are thrust about

halfway to the bottom of the flask. In
the fourth hole a short glass elbow is
inserted, which connects with a flue
(Fig. 73). The flask must be per-
fectly dry and is first filled with nitric
oxide from a generator, consisting of a
300 cc. Erlenmeyer flask, fitted with a
thistle-tube and a glass elbow. A layer
of copper turnings is placed in the
bottom of the generator and sufficient
water added to cover them. Concen-
trated nitric acid is poured through
the thistle-tube, and soon the reaction
begins. The colorless nitric oxide com-
bines with the oxygen of the air in the
large flask, filling it with deep ruddy
fumes of nitrogen peroxide. At this
point the evolution of nitric oxide is
stopped by pouring water into the nitric oxide generator.
If it is desirable to start the action again, it is only neces-
sary to add a little more concentrated nitric acid.

The second tube in the cork of the large flask is con-
nected with a sulphur dioxide generator, such as is de-

Fig. 73

SULPHURIC ACID 167

scribed in Ex. 41. The sulphur dioxide is first conducted
through a gas washing-bottle containing a small amount of
water to note the rapidity of its evolution. A vigorous
stream of sulphur dioxide is then allowed to flow into the
flask for two or three minutes. The third tube in the cork
of the flask is connected with a 100 cc. Erlenmeyer flask
containing 25 cc. of water and so provided with a cork and
glass elbows that a stream of air may be blown through the
water into the large flask. During the previous operations
the water is brought almost to a boil. After the current of
sulphur dioxide is stopped air is blown through the hot
water, thereby carrying a small amount of moisture into the
chamber. If care is taken not to admit too great a quantity
of moisture, the sulphur dioxide and nitrogen peroxide will
interact with the small amount of water, and the sides of
the vessel will become covered with crystals, the so-called
" chamber crystals."

The decomposition of the chamber crystals and the
regeneration of the nitrogen peroxide are effected by pass-
ing into the flask considerable quantities of water vapor.
The contents of the small flask are vigorously boiled, and
the steam escapes into the large flask. The tube through
which air is conducted, dipping under the surface of the
water in the small flask, is sealed, and the steam is thus
prevented from escaping into the air of the room. After
the steam has entered the large flask for a few moments,
the crystals are rapidly decomposed with effervescence,
nitric oxide being liberated. By blowing air into the
flask, its contents once more become red from the formation
of nitrogen peroxide. If sulphur dioxide is now conducted
into the flask, the red fumes will disappear, but the excess
of moisture in the flask will probably prevent the reappear-
ance of the chamber crystals. *

In case the flask becomes too warm from the reaction, the

168 CHEMICAL LECTURE EXPERIMENTS

formation of chamber crystals may be somewhat accelerated
by cooling the outside of the flask with a cloth wet with
cold water. When the crystals are once started, they
spread with considerable rapidity all over the surface of
the flask.

If the formation of sulphuric acid only is desired, and the
introduction of chamber crystals avoided, it is only neces-
sary to conduct simultaneously into the large flask nitric
oxide, sulphur dioxide, water vapor, and air. On adding
water and pouring out the contents of the flask, they will
be found to give a strong test for sulphuric acid with barium
chloride.

S02 + H20 + N02 = H2S04 + NO.

2NO + 02 = 2JST02.

yO ' NO.

4 S02 + 4 N02 + 02 + 2 H,0 = 4 S02<

X)H.

4 or 5 1. flask ; 4-holed cork and tubes ; S02 generator ; NO gen-
erator ; steam generator,

71. From sulphur dioxide, fuming nitric acid, air, and
water vapor. — The technical manufacture of sulphuric acid
is considered of sufficient importance to demand a special
and elaborate treatment in most text-books on chemistry.
It is desirable, therefore, to present on the lecture-table a
demonstration of the technical process for the manufacture
of this acid, which shall not be too elaborate and yet shall
be sufficiently detailed to show the essential steps. While
the fundamental reactions are admirably illustrated in the
apparatus described in the preceding experiment, a number
of technical features of economic importance warrant illus-
trative consideration on the lecture-table, and accordingly
the apparatus shown in Fig. 74 has been devised for this
purpose.

SULPHUKIC ACID

169

The chamber consists of a 2 or 3 1. three-necked Wolff
bottle, through the middle neck of which
is inserted a two-holed rubber stopper car-
rying a dropping-funnel and a glass elbow.
The other two necks are provided with one-
holed rubber stoppers carrying glass tubes
of the special form indicated in the figure.
Two Liebig condenser jackets filled with

Y/)0

Fig. 74

broken bits of pumice-stone serve as the Gay-Lussac and
Glover towers, respectively. The condenser jackets should

170 CHEMICAL LECTURE EXPERIMENTS

have the water-tubes on opposite sides if possible, as other-
wise it will be necessary to bend glass tubes to make the
proper connections. One of the condensers is clamped
in an upright position, its lower end dipping into a small
beaker one-third filled with concentrated sulphuric acid. A
piece of combustion-tube 25 cm. long is fastened to the
lower water-tube of the condenser by means of a rubber
stopper, and a small plug of glass wool is thrust into the
combustion-tube. A porcelain boat, filled with bits of roll
sulphur of such a size as can conveniently pass into the
combustion-tube, is inserted part way in the tube. In case
the combustion-tube does not remain in a level position, it
may be necessary to support it with a ring from the large
retort stand.

The upper water-tube of the condenser is connected by
a long glass elbow to one of the necks of the Wolff bottle.
The second condenser jacket is clamped in a vertical position
on the other side of the Wolff bottle, in such a manner that
its lower end will be 3 or 4 cm. higher than the upper end of
the other condenser. The two condensers are connected
by a long, small-bored glass tube, thrust through the corks
inserted in the end of the condensers. The glass tube
should extend several millimeters below the cork in the top
of the lower condenser, and should be just flush with the
end of the cork thrust into the lower end of the upper con-
denser. As this cork is subject to the action of concentrated
sulphuric acid, it is best to coat it with paraffin and thrust
it, while still warm, into the condenser. Care should be
taken in coating the cork that the paraffin does not seal the
glass tube by running into it and solidifying. The lower
water-tube of the upper condenser is connected with a long
glass elbow to the third neck of the Wolff bottle. The upper
water-tube is connected with a suction-pump, a gas washing-
bottle containing water being inserted at some point between

SULPHURIC ACID 171

the condenser tube and the pump. A one-holed rubber
stopper, carrying a dropping-funnel filled with concentrated
sulphuric acid, is inserted in the upper end of the upper con-
denser. Concentrated sulphuric acid is allowed to flow down
over the pumice-stone in the upper condenser, which it thor-
oughly drenches. The acid collects in the bottom of the
condenser and flows through the small tube into the lower
condenser, trickling down over the pumice-stone, and finally
is collected in the beaker.

The following arrangement is provided for sending water
vapor through the glass elbow in the middle neck of the
Wolff bottle. A 100 cc. Erlenmeyer flask, one-fourth filled
with water, is fitted with a two-holed rubber stopper. A
glass elbow, 7 mm. in diameter, is thrust through one hole
in the cork, and a small glass elbow, 2 mm. in diameter, is
thrust through the second hole. The large elbow carries a
piece of rubber tubing and a pinch-cock. The small elbow
is connected with the elbow leading into the middle neck of
the Wolff bottle. The flask is supported on a stand and
gently warmed with a Bunsen burner, the water being kept
at or near boiling. The pinch-cock should be moved up on
the glass elbow, thus allowing free escape for the water
vapor through the large glass elbow and the rubber tube.
Steam condenses in one end of the small glass elbow, and
the drop clinging to the end of the tube prevents the escape
of the steam into the Wolff bottle. When it is desired to
introduce steam into the acid chamber, the flame is raised
and the water in the flask brought to a vigorous boil. By
closing the rubber tube on the large elbow with the pinch-
cock, the steam forces its way through the small elbow into
the acid chamber. On releasing the pinch-cock, the steam
issues from the large elbow into the air of the room, as before.
A few bits of pumice-stone or glass beads promote the regu-
larity of ebullition.

172 CHEMICAL LECTURE EXPERIMENTS

The preparation of sulphuric acid by means of this appa-
ratus is extremely simple. Ten to fifteen drops of fuming
nitric acid are allowed to fall into the Wolff bottle, which
should be perfectly dry. If the stem of the dropping-funnel
has been previously filled with acid, the regulation of the
dropping will be much simplified. The boat containing sul-
phur is then drawn halfway out of the tube, and the sulphur
strongly ignited by heating with a lamp. When burning
well, the suction is started and air drawn through the com-
bustion-tube over the burning sulphur into the apparatus.
After the current of air is started, it is necessary to maintain
it at a rate just sufficient to draw the flame of the burning
sulphur into the combustion-tube. In this manner a mixture
of air and sulphur dioxide is carried into the chamber.
After a few moments the walls of the flask will become
covered with a deposit of chamber crystals. Water vapor is
then admitted, and consequently the chamber crystals are
decomposed with the liberation of nitrous fumes.

The formation of chamber crystals, being dependent on a
certain proportion of water, nitric oxide, and sulphuric acid,
is a matter of considerable difficulty, and cannot always be
relied on. When the operation is carried out as described,
however, the chamber crystals are, as a rule, readily obtained.

The interaction of the various products in the acid cham-
ber is accompanied by a formation of fumes, showing that
chemical reaction has taken place. On disconnecting the
tubes and removing the Wolff bottle, it will be found that
the contents diluted with water will give a strong test for
sulphuric acid. When sulphur is burned in this manner a
portion of it sublimes, but it is retained by the glass wool
in the combustion-tube. The current of air entering the
combustion-tube passes through the Glover tower into the
chamber. Any nitrogen oxides carried away by the current
of air are absorbed by the sulphuric acid in the Gay-Lussar

SULPHURIC ACID 173

tower. The acid containing the nitrogen fumes flows down
through the long glass tube into the upper end of the Glover
tower, where, in trickling down over the pumice-stone, it
comes in contact with the sulphur dioxide, which reacts
with it, setting free the nitrogen oxides.

While the actual absorption of the nitrogen oxides in the
Gay-Lussac tower, and their subsequent regeneration in the
Glover tower, cannot be observed, the process is interesting
as being a duplicate of that used in the commercial manu-
facture of this acid. The supply of sulphuric acid in the
dropping-funnel in the top of the Gay-Lussac tower should
occasionally be replenished, as the acid should continuously
drop upon the pumice-stone.

Obviously, nitric oxide, instead of fuming nitric acid, may
be conducted through the middle neck, in case the gaseous
oxidizing agent is desired.

Apparatus (Fig. 74) ; 3-necked Wolff bottle ; two Liebig con-
denser jackets filled with pumice-stone ; dropping-funnel ; porcelain
boat ; combustion-tube ; glass wool ; steam generator ; suction-pump ;
S; fuming HN03.

PROPERTIES

72. Intense acidity. — The intense acid nature of sul-
phuric acid is shown by adding 1 drop of the concentrated
acid to 2 1. of water in a large beaker. It will be found that
the water is acid enough to redden a strip of blue litmus.

2 1. beaker ; blue litmus paper.

73. Evolution of heat by mixing sulphuric acid with
water. — (a) When sulphuric acid and water are mixed,
there is considerable rise in temperature, sufficient to boil
ether.

Two hundred cubic centimeters of water are placed in a
500 cc. flask, and 5 cc. of ether are added. On holding a

174

CHEMICAL LECTURE EXPERIMENTS

Fig. 75

match at the mouth of the flask no flame will appear. On

the addition of 100 cc. of concentrated sulphuric acid the

temperature of the mixture is so increased that the ether

boils vigorously, and the issuing vapor may

be ignited at the mouth of the flask.

After the flame has gone out, an ether
thermometer, made by blowing an 8 or
10 mm. bulb on the end of a long piece of
3 mm. glass tubing, is half filled with ether,
and the bulb thrust into the hot mixture
of acid and water (Fig. 75). The ether
boils vigorously, and on applying a flame
burning ether vapor issues from the mouth
of the tube

500 cc. flask ; long tube with bulb ; ether.

(b) The evolution of heat, on mixing these two liquids,
is sufficient to give a temperature to the mixture of consid-
erably over 100°. Sixty cubic centimeters of water and
120 cc. of concentrated sulphuric acid are simultaneously
poured (to insure thorough mixing) into a 300 cc. beaker
standing on wire gauze or asbestos paper. A thermometer
inserted in the mixture will indicate a temperature of 115°
to 120°.

A small quantity of alcohol in a thin-walled test-tube is
immersed in the hot liquid. The alcohol boils, and the vapor
may be ignited at the mouth of the tube.

Two cubic centimeters of water in a thin-walled test-tube
may be quickly brought to a boil by immersing the tube in
the hot solution.

300 cc. beaker ; gauze ; thin- walled test-tubes ; 120 cc. con. HoS04;
alcohol.

74. Dehydrating action (drying of gases). — Sulphuric
acid, owing to its intense hygroscopic properties, is of the

y*4frA

U+

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MSB

fflB&BSB%BBm

*>■'■■■.'

ISP

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SULPHURIC ACID

175

Fig. 76

greatest importance in drying many gases. The interior
surface of a bell-jar is moistened by holding it over a
Bimsen or, better, a hydrogen flame. A small evaporating
dish filled with lump pumice-
stone, which has been drenched
with sulphuric acid, is placed
on a plate under the moistened
bell-jar (Fig. 76). In a few min- J-jggg_
utes the walls of the jar will be-
come clear and unclouded as the
water vapor is rapidly absorbed by the sulphuric acid. The
rapidity of the absorption is still more emphasized by pre-
paring a second bell-jar as before and placing it over pumice-
stone drenched with water. In the second case the bell-jar
remains clouded with the condensed water vapor.

H flame ; 2 bell-jars ; 2 evaporating dishes ; 2 plates ; pumice-stone.

75. Carbonization of sugar by sulphuric acid. — Sixty
grams of lump sugar are added to 45 cc. of warm water in
a 500 cc. beaker. The sugar will soon dissolve in the water,
forming a thick syrup. The beaker is placed on a white
plate and 60 cc. of concentrated sulphuric acid rapidly
poured into it. The reaction is almost instantaneous, the
solution blackening, and large quantities of steam being
driven off. The residue is a porous, carbonaceous mass.
The mixture will froth up and run over the edge of the
beaker upon the plate.

500 cc. beaker ; lump sugar.

76. Action on paper. — Dilute sulphuric acid has no ap-
preciable effect on paper, but if paper moistened with dilute
acid is gently warmed, the water is vaporized, leaving the
non-volatile sulphuric acid.

A dilute sulphuric acid is made by adding 10 cc. of con-

176 CHEMICAL LECTURE EXPERIMENTS

centrated sulphuric acid to 250 cc. of water. A letter is
made on paper with this dilute acid, and the paper then
allowed to dry in the air. When perfectly dry no change
is noticeable. If the paper is held high over a Bunsen flame
and simply warmed, the acid, concentrated by evaporation,
will carbonize all portions of the paper with which it is in
contact, and the character will appear in a charred outline.

SELENIUM

1. Sublimation. — Selenium, when heated, sublimes with-
out melting.

A small piece of selenium is heated in a dry test-tube.
The element sublimes, and the upper part of the sublimate
will consist of fine needles of selenium dioxide formed by
the combustion of the vapor in the air of the tube.

2. Combustion in air. — Selenium, when heated in the air,
burns with a blue flame, forming selenium dioxide.

A small piece of selenium is heated on a crucible cover
and ignited. It burns with a characteristic blue flame, but
it is necessary to keep the crucible cover heated during the
combustion.

Crucible cover ; Se.

3. Solubility in strong sulphuric acid. — (a) Powdered
selenium is covered in a test-tube with fuming sulphuric
acid and strongly heated. The selenium dissolves with the
liberation of sulphur dioxide. The sulphuric acid con-
taining selenious acid becomes green. The green solution
is carefully poured into a 300 cc. cylinder half filled with
cold water. Selenium separates out of the solution in the
form of a fine, dark red powder.

Se ; fuming H2SO4 ; K2Cr207 solution.
n 177

178

CHEMICAL LECTURE EXPERIMENTS

(b) Selenium, when heated with fuming sulphuric acid,
dissolves with a green color. If the solution is then diluted
with concentrated sulphuric acid and heated to boiling for a
few moments, it will finally be decolorized as the selenium
is oxidized by the sulphur trioxide. On pouring the de-
colorized solution into water no precipitate of selenium will
occur. 2 S03 + Se = 2 S02 + Se02.

Fuming H2S04 ; Se.

SELENIUM DIOXIDE

4. Preparation. — Selenium burns in a current of oxygen to
form selenium dioxide. A few lumps of selenium are placed
in a bulb-tube, which is fitted to the mouth of a dry filter-
flask, the side tube of which is
connected with a flue (Fig. 77).
A current of oxygen is passed
through the bulb- tube and the
selenium heated to ignition.
The product condenses on the
arm of the tube and in the re-
ceiver as a white powder.

Se + 02 = Se02.

Fig. 77

Apparatus (Fig. 77) ; bulb-tube
filter flask ; O supply ; Se.

5. Green color of the vapor. — A small quantity of selenium
dioxide is heated in a test-tube. The greenish vapor is best
seen by holding the tube in front of a white background.

SELENIOUS ACID

6. Oxidation of selenium with nitric acid. — When pow-
dered selenium is heated in a test-tube with concentrated
nitric acid, it rapidly dissolves, with the liberation of nitrous

SELENIC ACID 179

fumes, forming selenious acid. After neutralization with
ammonia the solution gives any of the reactions for seleni-
ous acid.

7. By dissolving selenium dioxide in water. — Selenium
dioxide dissolves readily in water, forming selenious acid.
The aqueous solution may be used in the following experi-
ments.

8. Action with hydrogen sulphide. — Hydrogen sulphide
solution, when added to a solution of selenious acid, pro-
duces a bright yellow precipitate of selenium sulphide.

9. Reduction by sulphurous acid. — Sulphurous acid re-
duces selenious acid to selenium. Sulphur dioxide, or a
solution of sulphur dioxide in water, is added to a dilute
solution of selenious acid. In the cold, or more rapidly by
warming, a brick-red precipitate of finely divided selenium
is obtained.

H2Se03 + 2 S02 + H20 = 2 H2S04 + Se.

H2S03 ; H2Se03.

SELENIC ACID

10. Preparation. — Chlorine water oxidizes selenium diox-
ide to selenic acid.

Selenium dioxide is covered with chlorine water and
gently warmed ; sufficient chlorine water should be added
to complete the oxidation, and, on boiling off the excess of
chlorine, selenic acid is obtained.

Se02 + Cl2 + 2 H20 = H2Se04 + 2 HC1.
Se02 ; chlorine water.

NITROGEN

PREPARATION

1. By the decomposition of ammonium chloride and
sodium nitrite. — The decomposition of ammonium nitrite
results in the formation of nitrogen and water according to
equation (1) below. The instability of ammonium nitrite
precludes its use in the pure state for this reaction, hence it
is prepared and instantly decomposed by using ammonium
chloride and sodium nitrite, wdiose interaction produces
sodium chloride and ammonium nitrite, equation (2).

A mixture of 10 g. of ammonium chloride and 15 g.
of sodium nitrite is placed in a 200 cc. Erlenmeyer flask
fitted with a thistle-tube and a delivery-tube. Thirty cubic
centimeters of water are then added and the flask gently
heated. The nitrogen is liberated considerably below the
boiling point of water, and it is advisable not to overheat
the mixture, as frothing is likely to occur. In case the
frothing is too strong, the introduction of a few cubic cen-
timeters of water through the thistle-tube will immediately
check it. Nitrogen may be collected at the pneumatic
trough in cylinders.

(1) NH4N02 = N2 + 2 H20.

(2) NaN02 + NH4C1 = NaCl + NH4N02.

200 cc. Erlenmeyer flask ; thistle-tube and delivery-tube ; NH4C1 ;
NaN02.

180

NITROGEN 181

2. By the ignition of a mixture of ammonium chloride and
potassium dichromate. — The decomposition of ammonium
dichromate yielding nitrogen, water, and chromic oxide is
described in Ex. 6, p. 361. As ammonium dichromate is
rather deliquescent and not common in the laboratory, the
same results may be obtained by using a mixture of ammo-
nium chloride and potassium dichromate.

Eight grams of powdered ammonium chloride and 25 g.
of powdered potassium dichromate are intimately mixed
and placed in a 100 cc. Jena glass Erlenmeyer flask. The
flask is fitted with a very wide delivery -tube, preferably
1 cm. internal diameter, which leads to a pneumatic
trough (Fig. 128, p. 319). On heating the mixture nitrogen
is evolved and some of the ammonium chloride is sublimed,
hence the necessity of a wide delivery-tube. The Jena
glass flask will stand a very high heat without danger.

2 NH4C1 + K2Cr207 = 2 KC1 + O20a + 4H20+ N2.

100 cc. Jena glass Erlenmeyer flask ; wide delivery-tube ; K2Cr207;
NH4C1.

3. From potassium nitrate and iron powder. — Iron pow-
der combines with the oxygen of potassium nitrate, liberat-
ing nitrogen.

A mixture of 10 g. of iron filings and .5 g. of pow-
dered potassium nitrate is heated in a hard-glass test-
tube fitted with a delivery-tube leading to the pneumatic
trough. When the mixture is heated, a gas is rapidly evolved
which on testing is shown to be nitrogen.

Hard-glass test-tube ; cork and delivery-tube ; KNO3 ; Fe powder.

4. By abstraction of oxygen from air by means of phos-
phorus. — The commonest source of nitrogen is air, which
consists essentially of nitrogen mixed with oxygen. To

182 CHEMICAL LECTURE EXPERIMENTS

remove the oxygen some material, such as phosphorus,
which forms a solid or non-gaseous oxide, is selected.

A flat cork, some 2.5 or 3 cm. in diameter and a centime-
ter thick, has the ring of a porcelain crucible lid pressed
into a slit in one side, and on the other side a small weight
of lead or iron is fastened to give the apparatus when floated
on water a greater stability. The float is placed on the sur-
face of the water in a pneumatic trough and a 5 mm. piece
of well-dried phosphorus laid on the crucible lid. A tubu-
lated bell-jar, with a rather wide mouth to permit of the

insertion of a candle on a wire, is
*)^^ tightly corked and placed immedi-

ately above the float (Fig. 78). The
phosphorus is ignited by touching
with a hot iron wire, and the bell-
jar immediately lowered until its

t mouth is sealed with water. The

phosphorus burns rapidty, and the
FlG 78 heat generated by the combustion

causes the gas in the bell-jar to ex-
pand and bubble out to a certain extent under the mouth of
the bell-jar. As soon as the phosphorus goes out, however,
the water will rise in the bell-jar, indicating a marked con-
traction in volume. On lowering the bell-jar until the level
of the liquids inside and outside is the same, the cork may be
removed and a burning candle on the end of a wire lowered
into the residual gas. It will be immediately extinguished.

Large cork ; crucible cover ; tubulated bell-jar ; candle on wire ; P.

5. By the removal of oxygen from the air by burning hydro-
gen. — When hydrogen is burned in air water is formed, the
greater portion of which is immediately condensed. Hydro-
gen from a Kipp generator is passed through a glass tube
(Fig. 79) so bent as to rise under a tubulated bell-jar and

NITROGEN

183

C — _^s

-~\

IB^EZ^Z

Fig. 79

have its tip at least 5 cm. above the level of the water. The
glass tube is provided with a platinum tip consisting of a
small piece of foil rolled around a glass rod and inserted
in the end of the glass tube. After
lighting the hydrogen flame, which
should not be too high, the tubu-
lated bell-jar, securely corked at
the tubulature, is lowered over the
burning jet. The oxygen is rapidly
burned to form water, which de-
posits on the sides of the jar as a
mist. As it is somewhat difficult
to observe the hydrogen flame, it is

best to moisten the tip of the platinum with a little sodium
chloride solution to impart a color to the flame. The instant
the flame is extinguished the supply of hydrogen should be
cut off and the burner removed, as otherwise the admission
of unburned hydrogen will contaminate the nitrogen. The
level of the water on the inside of the bell-jar will have
risen considerably and, as in the preceding experiment, the
bell-jar should be lowered until the inner and outer levels
are the same before removing the stopper. The tubulature
should be large enough to permit the introduction of a burn-
ing candle in testing the gas. It is of the utmost impor-
tance that the hydrogen flame should be watched and the
supply of hydrogen cut off the moment the flame is ex-
tinguished. This separation of oxygen and nitrogen is
extremely simple and not difficult of comprehension by ele-
mentary students, as oxygen, hydrogen, nitrogen, and water
are familiar substances.

Tubulated bell-jar ; jet with Pt tip ; H supply ; NaCl solution.

6. By the combustion of air and ammonia on copper. — When
large quantities of nitrogen are desired, by far the most sat-

184

CHEMICAL LECTURE EXPERIMENTS

isfactory method for obtaining it is that in which a mixture
of air and ammonia gas is passed over a hot copper coil,
which is alternately oxidized by the air and reduced by the
ammonia, forming water and nitrogen. The air is obtained
from an ordinary water-blast, and the ammonia vapor from
the strongest aqua ammonia, which is placed in a gas wash-
ing-bottle (Fig. 80). The air is allowed to bubble through
the liquid and become saturated with the ammonia gas. The
gaseous mixture is then passed into a 30 cm. length of com-
bustion tubing contain-
ing a coil of copper wire
and fitted with a deliv-
=[H§ Buna n]=^ ery-tube at the other end

leading to a pneumatic
trough containing acidu-
lated water. The copper
coil is heated by means of
a strong Bunsen burner
at the end nearest the
entrance of the gases. The copper will become oxidized
by the oxygen of the air, and the copper oxide thus formed
be immediately reduced by the ammonia gas, forming water
and nitrogen. The reduced copper is then immediately
oxidized and reduced, the process being a continuous
one. The air, deprived of its oxygen by the copper,
passes on as nitrogen into the pneumatic trough. To this
nitrogen is, of course, added the nitrogen liberated from
the ammonia. As the reaction proceeds, the copper coil
becomes intensely hot and the external heat may be with-
drawn. There should always be an excess of ammonia gas
in the air current, and consequently all of the spiral but
the front end should be in the reduced state. As soon
as it begins to oxidize for any distance it is an indication
that the supply of ammonia is becoming exhausted. By

Fig. 80

NITROGEN 185

observing the color of the spiral, the operation can be well
regulated. The excess of ammonia vapor carried along to
the pneumatic trough will be dissolved in the water, and
unless large quantities of nitrogen are to be prepared and
the water becomes saturated with the ammonia, no precau-
tion is necessary. It may, however, be necessary after a
while to have free sulphuric acid present to neutralize the
ammonia as it is dissolved. When very strong ammonia
water is used in the gas washing-bottle, it is found that a
good strong air-blast is necessary.

2 NH3 + 3 CuO = 3 H20 + 3 Cu + Na.

Air-blast ; gas washing-bottle ; combustion-tube ; strongest NH4OH ;
Cu coil.

7. Oxidation of nitrogen by burning magnesium in air. —

The heat of burning magnesium is sufficient to cause a
union of nitrogen and oxygen in small quantities.

An 8 cm. piece of magnesium ribbon is tied to a stout
iron wire and after ignition quickly lowered into a clean, dry
500 cc. cylinder having a layer of sand on the bottom. The
nitrogen and the oxygen of the air are caused to combine, and
a strong test for nitrous acid is obtained with iodo-starch
paper lowered into the cylinder. The layer of sand pre-
vents the cylinder from cracking if bits of burning magne-
sium fall to the bottom.

500 cc. cylinder ; Mg ribbon ; Kl-starch paper.

8. Formation of oxides of nitrogen by the combustion of
hydrogen in oxygen. — The union of nitrogen and oxygen
may be brought about by the intense heat of the hydrogen
flame burning in oxygen mixed with a small quantity of air.
A clean, dry Erlenmeyer flask of 1 or 2 1. capacity is filled
with oxygen by displacement and a burning jet of hydrogen
lowered into the flask. On account of the heat generated it

186 CHEMICAL LECTURE EXPERIMENTS

is necessary to have a platinum tip on the glass tube as is
recommended in Ex. 5. The mouth of the flask being
open, a certain amount of air can enter, and a portion of
its nitrogen will combine with the oxygen to form nitrous
acid. After allowing the hydrogen to burn for a few minutes
the jet is withdrawn and moistened iodo-starch paper is
held in the flask. It is immediately colored blue, indicat-
ing the presence of nitrous acid.

Jet (Fig. 41, p. 85) ; H generator; jar of 0 ; Kl-starch paper.

ATMOSPHERIC AIR

9. Determination of oxygen in air by potassium pyrogal-
late. — One hundred cubic centimeters of air are introduced
into the eudiometer (Fig. 11, p. 26), and potassium pyrogallate
solution (Ex. 21, p. 26) allowed to flow slowly down through
the gas. The absorption will have ceased when the liquid
stops rising in the tube. Before reading off the volume of
the remaining gas the reagent should be washed out of the
tube by allowing successive portions of water to flow through
the stop-cock. It will be found that the volume has dimin-
ished 20 cc, or one-fifth.

The method is capable of yielding very accurate analyses
if the eudiometer is lowered in taking each reading till the
levels of the inner and outer liquids are the same. In exact
measurements, however, fluctuations in the temperature of
the gas must be avoided.

Eudiometer, Fig. 11, p. 26 ; potassium pyrogallate solution.

10. Quantitative determination of nitrogen in air. — While
the combination of burning phosphorus and oxygen attended
by light and, heat is extremely rapid, the elements do, never-
theless, unite at ordinary temperatures.

ATMOSPHERIC AIR

187

One hundred cubic centimeters of air are introduced into
a eudiometer tube. A stick of phosphorus 3 or 4 cm. long
is carefully cleaned under water and fastened to a piece of
copper wire. The phosphorus is then thrust under the
mouth of the eudiometer tube, which
remains under water and is pushed a
considerable distance up the tube, into
the air. The copper wire is then bent
so as to rest on the bottom of the dish
and support the phosphorus in the air
(Fig. 81). The level of the water in the
tube will, of course, be depressed by as
much as the volume of the copper and
the phosphorus introduced. Hence it is
important that the eudiometer be of suffi-
cient size to allow of this expansion over
the 100 cc. After the whole apparatus

has stood over night it will be found

Fig. 81

that a diminution in volume has taken
place. By withdrawing the phosphorus and reading off the
volume of the residual gas it will be found to be approxi-
mately 80 cc, i.e., four-fifths of the original volume.

In case a graduated tube is not at hand a linear measure-
ment of the diminution may be made.

Eudiometer tube 2 cm. in diameter ; meter stick ; P ; Cu wire.

11. Quantitative absorption of oxygen from air by metallic
copper. — By measuring the quantity of air passed over a
heated copper coil and the amount of gas collected at the
pneumatic trough, the proportion of oxygen and nitrogen
present in the air may be quantitatively determined.

A stoppered cylinder is fitted with a two-holed rubber stop-
per carrying one tube leading to the bottom of the cylinder
and a glass elbow directly connected with the combustion-tube

188

CHEMICAL LECTUKE EXPERIMENTS

containing the copper coil. Connection is then made with a
faucet, so that by opening the valve, water may be allowed to
flow into the glass cylinder, expelling the air at the top
through the elbow into the combustion-tube. After making
all the connections the combustion-tube containing the cop-
per is brought to red heat, the expanded air being allowed to
escape at the pneumatic trough (Fig. 82). When a constant
temperature has been reached, noted by the absence of air
bubbles from the delivery-tube, an inverted graduated stop-
pered liter cylinder filled with water is placed over the

V —

001 —

003

006

00 1-

009

00Z

lOOG^-^Z

Pooo Ijj-^

^V^. -yZ

yrT f

—

Fig. 82

delivery-tube and water allowed to flow slowly into the
first graduate. The rate must not be too rapid, as otherwise
the absorption of oxygen would not be complete. Water is
allowed to flow into the first cylinder until it has reached
the 1000 cc. graduation. The volume of gas collected at the
pneumatic trough will be found to be about 800 cc. More
exact measurement may be made by lowering the graduate
into a deep vessel until the inner and outer levels of the
water are the same. It is thus seen that from 1000 cc. of
air, approximately 800 cc. of nitrogen remain after the

AMMONIA 189

absorption of 200 ce. of oxygen. Both cylinders should be
protected from any undue heating by asbestos screens placed
between them and the burner.

Two 1000 cc. graduated stoppered cylinders ; combustion-tube ;
Cu coil.

12. Quantitative combustion of phosphorus in a confined
volume of air. — The regularity of the combustion of red
phosphorus in air makes this form of phosphorus better
adapted for the experiment in which oxygen is burned out of
a confined volume of air.

A crucible lid containing red phosphorus is arranged
as in Ex. 4? and a tubulated bell-jar placed over the float.
A mark on the bell-jar is made about 2 cm. from the mouth
and the remaining volume divided into fifths. The red
phosphorus in the crucible lid is provided with a small piece
of touch-paper, which is ignited. The bell-jar with the cork
removed is lowered into water to the point marked 2 cm.
above the mouth. The cork is then inserted, and when the
phosphorus itself begins to burn the water in the bell-jar
rises as the oxygen is consumed. The contraction of the
gas (one-fifth of the original volume) is very accurately
noted by means of this apparatus. The pneumatic trough
should be deep enough to lower the jar at the end of the
experiment till the inner and outer levels are the same.

Tubulated bell-jar (graduated in fifths) ; crucible lid on cork ; red P ;
touch-paper.

AMMONIA

FORMATION AND PREPARATION

13. By the ignition of organic substances. — (a) A small
quantity of gelatine or glue heated in a test-tube yields
ammonia.

Gelatine or dry glue.

190 CHEMICAL LECTURE EXPERIMENTS

(b) The presence of ammonia may be established in the
products of the dry distillation of coal (Ex. 62, p. 325) by
inserting a piece of moistened red litmus paper in the filter-
flask of the apparatus (Fig. 130, p. 325).

14. By heating organic nitrogenous matter with soda-
lime. — While gelatine and similar compounds give nitrogen
directly on ignition, many organic substances containing
nitrogen — uric acid, for example — - do not yield ammonia
by simple heating.

A small quantity of uric acid heated in a test-tube gives
no test for ammonia.

When such compounds are intimately mixed with dry
soda-lime and ignited, their nitrogen is converted into am-
monia. If uric acid is heated with an equal volume of fused
dry soda-lime in a hard-glass test-tube, ammonia is evolved.

Uric acid ; dry soda lime.

15. By heating potassium nitrate, potassium hydroxide, and
iron powder. — When iron powder is heated in the presence
of potassium hydroxide, hydrogen is liberated in a manner
similar to that shown in Ex. 5, p. 42. As is seen, however,
in Ex. 3, the ignition of iron and potassium nitrate yields
nitrogen. Heating equal volumes .5 g. each of potassium
hydroxide and potassium nitrate with 20 g. of iron fillings
in a hard-glass test-tube gives a copious evolution of
ammonia.

Ee powder ; KN03 ; KOH.

16. From hydrogen and nitric oxide. — If a mixture of
hydrogen and nitric oxide is passed over heated platinized
asbestos 5 volumes of the hydrogen combine with 2 vol-
umes of the nitric oxide and ammonia is formed.

Hydrogen from a Kipp generator is passed through a glass

AMMONIA

191

tube thrust through a three-holed cork in the neck of a small
bottle containing a 2 cm. layer of sulphuric acid. A stream
of nitric oxide (Ex. 49, p. 211) passes through a second glass
tube into the bottle. Both tubes dip beneath the surface of
the sulphuric acid that their rate of bubbling may be noticed.
Hydrogen is conducted through
the whole apparatus to drive out
all air and then the nitric oxide
generator started. The current of
hydrogen should be three times
as fast as the current of nitric
oxide. The mixed gases are then
conducted through a piece of com-
bustion-tubing or a bulb-tube containing platinized asbestos
(Fig. 83). Until the asbestos is heated no ammonia is
present in the issuing gases, which redden on exposure to
the air ; but on heating the asbestos a strong test for am-
monia is immediately obtained and no red fumes are formed.

2 NO + 5 H2 = 2 NH3 + 2 H20.

H generator ; NO generator ; wash-bottle, with 3-holed cork ; bulb-
tube ; platinized asbestos.

Fig. 83

17. From ammonium hydroxide and potassium hydroxide.

Strong ammonium hydroxide is allowed to drop from a sep-
arating-funnel upon solid potassium hydroxide, preferably in
the stick form, in a 500 cc. Erlenmeyer flask (Fig. 3, p. 11).
The dropping-f unnel is placed in a two-holed rubber stopper,
and a glass elbow conducts away the gaseous ammonia liber-
ated. In the process of the reaction the contents of the
flask become very cold from the volatilization of ammonia,
and consequently the gas is quite dry. However, in all
experiments where a perfectly dry gas is required it should
be first conducted through a U-tube containing dry quick-

192 CHEMICAL LECTURE EXPERIMENTS

lime or soda-lime. This method is by far the most conven-
ient and available one for obtaining varying quantities of
ammonia on the lecture table.

Apparatus, Fig. 3, p. 11 ; 500 cc. flask ; dropping-fuunel ; stick
KOH ; con. NH4OH.

18. By heating ammonium hydroxide. — One of the most
convenient sources of gaseous ammonia is the strongest aqua
ammonia of commerce. The simple application of heat
suffices to drive off the ammonia which, when dried, is
ready for use. The aqueous ammonia is placed in a flask
fitted with a thistle-tube and a glass elbow. On gently
warming, ammonia is driven off and passes through a gas
washing-bottle containing a small quantity of strongest
ammonia water, and then through a U-tube containing quick-
lime or fused soda-lime to dry the gas, which may be col-
lected over mercury. The gas washing-bottle with the
strong ammonia water is used to show by the bubbling the
rate at which the gas is given off. Calcium chloride cannot
be used to dry ammonia, as it forms a compound with the
gas, and hence quicklime or soda-lime is recommended.
The gas may be collected over mercury or by displacement.

Flask with thistle-tube and elbow ; gas washing-bottle ; U-tube with
soda-lime ; strongest NH4OH.

19. From ammonium chloride and slaked lime. — Powdered
ammonium chloride and slaked lime in equal quantities
(about 40 g. of each) are placed in a 300 cc. Jena glass
Erlenmeyer flask fitted with a safety-tube (such as is shown
in Fig. 85, p. 196) and a glass elbow. A small quantity of
concentrated ammonium hydroxide or mercury is placed in
the bend of the safety-tube. On the application of gentle
heat ammonia is rapidly evolved. The gas may be dried by
conducting it through a U-tube containing quicklime or

AMMONIA 193

fused soda-lime. Owing to its low specific gravity, ammonia
can be readily collected by displacement of air according to
the method of collecting hydrogen. Almost invariably this
method of collecting the gas may be used.

2 NH4C1 + Ca(OH)2 = CaCl2 + 2 H20 + 2 NH3.

300 cc. Jena glass Erlenmeyer flask ; safety -tube ; soda-lime drying-
tube ; NH4C1; Ca(OH)2.

PROPERTIES

20. Specific gravity. — Ammonia is considerably lighter
than air, resembling hydrogen in this respect.

A jar of ammonia may be opened under the mouth of an
inverted beaker suspended on the end of a balance which
has been brought into equilibrium. On allowing the ammo-
nia to rise into the beaker and expel the air the equilibrium
will be disturbed.

Lecture-balance ; inverted beaker ; jar of NH3.

21. Alkaline nature and tests. — (a) Ammonia gas imparts
the color characteristic of alkalies to papers saturated with
solutions of litmus, cochineal, turmeric, or phenol-phthalein.
The papers may be held in a jar of ammonia or at the
mouth of a bottle containing strong ammonium hydroxide.

Ammonia, however, is a volatile, as distinguished from a
fixed, alkali, and if the papers colored by ammonia are
allowed to remain in the air, the original colors, or in case of
phenol-phthalein absence of color, will return.

Litmus, turmeric, cochineal, phenol-phthalein papers, or solutions of
these indicators ; strong NH4OH ; dry red litmus paper.

(b) With gaseous hydrogen chloride. — If a rod moistened
with concentrated hydrochloric acid is held at the mouth of
a test-tube from which ammonia is escaping, white fumes of
ammonium chloride will be formed,
o

194 CHEMICAL LECTURE EXPERIMENTS

/ (c) Action on mercurous nitrate. — A piece of filter-paper
V dipped in mercurous nitrate solution is instantly turned
black in the presence of ammonia.

Hg2(N03)2 solution.

22. Solubility in water. — A tall glass cylinder is filled
with ammonia by displacement, covered with a metal disk,
and opened under water by slowly sliding the disk to one
side. The water rushes up into the cylinder with almost
explosive violence. On account of this rapid solubility of
the gas in water the use of a metal, rather than a glass, cover
is recommended, as the latter might be broken by the rapid
inrush of water.

Cylinder of NH3 ; metal disk.

23. Solubility in water producing a fountain. — A 2 1.

round-bottomed flask is filled with ammonia by displace-
ment, the gas entering through a long tube pushed through
a two-holed rubber stopper leading to the bottom of the
flask, which is supported in an inverted position. When
completely filled with ammonia, the cork and the tube are rap-
idly withdrawn and another two-holed rubber stopper, with
fittings described beyond, is rapidly inserted in the neck of
the flask. Through one of the holes in the cork a long glass
tube, whose end has been drawn out to a 2 mm. opening, is
thrust until the jet is about in the centre of the flask (Fig.
84). The other end of the tube, which must extend some
25 or 30 cm. beyond the cork, is plugged with a small piece
of rubber tubing and a bit of glass rod, and dips into a crys-
tallizing dish filled with a slightly acid solution of litmus.
Through the other hole of the cork is thrust an ordinary
medicine dropper which has been filled with water to within
a few millimeters of the end of the jet. It is important to
have the rubber bulb as well as the glass portion of the dropper

AMMONIA

195

filled with water. The whole apparatus is firmly supported
on the ring of a retort stand. On removing the plug from
the end of the tube dipping under
water no action takes place, as there
is a long layer of air in the tube be-
tween the ammonia and water. On
pinching the bulb of the dropper a
few cubic centimeters of water are
suddenly introduced into the flask,
and absorption is instantaneous, the
vacuum produced being sufficient to
cause the water to ascend the long
tube and play out of the jet as a
fountain. The alkalinity of the water
is strikingly shown by the change in
color of the litmus solution.

In case the flask has been com-
pletely filled with gaseous ammonia,
water will rush in till the flask is
full. Provision must be made for the
addition of water to the crystallizing

dish as fast as it is withdrawn. The support must be strong
enough to hold up the flask when filled with 2 1. of water.

2 1. flask (dry) ; 2-holed cork and jet ; medicine dropper ; NH3
generator ; soda-lime drying-tube ; litmus solution.

Fig. 84

24. Collection over mercury and absorption by water. —

Gaseous ammonia, owing to its great solubility in water, can
be collected only over mercury. Dried gaseous ammonia
is collected in a thick-walled test-tube over mercury, care
being taken not to have the deli very -tube dip too deeply
into the mercury, thereby increasing the pressure to be over-
come. The great solubility of ammonia is seen when a few
drops of water are allowed to enter the tube through a

196

CHEMICAL LECTURE EXPERIMENTS

hooked glass tube and to rise through the mercury and
come in contact with the gaseous ammonia. The absorption
is very rapid, the mercury rising in the tube to take the
place of the absorbed gas.

A piece of ice may be used instead of water.

Mercury trough ; NH3 supply ; ice.

25. Preparation of ammonium hydroxide (ammonia
water). — Ammonium hydroxide is prepared by saturating
water with gaseous ammonia.

Ammonia gas is generated as in Ex. 19, and conducted
directly from the flask without the introduction of a drying-
tube into an empty gas washing-bottle which serves to col-
lect any solid particles mechanically carried over.1

Fig. 85

The gas is then conducted through a series of three 3-
necked Wolff bottles of 300-400 cc. capacity, each half filled
with distilled water (Fig. 85). Each Wolff bottle is fitted
with an elbow reaching to the bottom of the bottle, a verti-
cal safety -tube dipping just beneath the surface of the water,
and an elbow extending just below the cork. As soon as all
the air is driven out of the generating flask, the bubbles

1 When a large quantity of ammonia is desired, 100 g. each of
ammonium chloride and calcium hydroxide should be heated in a
500 cc. flask.

AMMONIA 197

rising through the water in the first of the series of Wolff
bottles grow smaller, and finally all the gas is absorbed. As
soon as the water in this bottle becomes nearly saturated
the gas rises through the solution unabsorbed and passes
through the elbow into the second bottle, etc.

As the ammonium hydroxide is lighter than water, it is
important that the glass elbows extend to the bottom of
each bottle, as otherwise the upper surface of the liquid
would become saturated, while the lower strata would be but
slightly alkaline.

NH3 + H20 = NH4OH.

Apparatus (Fig. 85) ; 500 cc. Jena glass Erlenmeyer flask ; three
3-necked Wolff bottles ; NH4C1 ; Ca(OH)2.

26. Absorption by charcoal. — Freshly ignited charcoal
absorbs large quantities of ammonia.

Ammonia collected over mercury as in Ex. 24, is rapidly
absorbed by a centimeter piece of heated charcoal imme-
diately introduced under the mercury so as to come in con-
tact with the gas. As the gas is absorbed, the mercury rises
rapidly to take its place.

Tube filled with NH3 over mercury ; charcoal.

27. Absorption by fused calcium chloride. — Fused cal-
cium chloride absorbs ammonia, forming a definite chemical
compound. For this reason calcium chloride, so often used
as a dryer for gases, cannot be used for drying ammonia.
Ignited soda-lime or quicklime is usually used for this
purpose.

A small piece of fused calcium chloride is slipped under
a tube filled with gaseous ammonia over mercury (Ex. 24).
Immediately the absorption begins, and the calcium chloride
melts.

Tube filled with NH3 over mercury ; fused CaCl2.

198 CHEMICAL LECTURE EXPERIMENTS

28. Absorption by silver chloride. — Silver chloride, as
well as calcium chloride, absorbs ammonia, forming a defi-
nite compound. A few fragments of precipitated silver
chloride (residues from chlorine determinations) are slipped
under a test-tube of ammonia collected over mercury. The
ammonia is rapidly absorbed, mercury rising to take its
place.

On heating the silver compound ammonia is again ex-
pelled.

Tube filled with NH3 over mercury ; AgCl.

29. Combustion in air. — (a) Ammonia, owing to its large
percentage of hydrogen, is somewhat combustible in air,
though only noticeably so under certain conditions.

The flame of a Bunsen burner is turned very low, and
gaseous ammonia is conducted through a drawn-out glass jet
bent at the end so as to deliver the gas into the centre of
the burner. The glass jet is introduced upward into one of
the air-holes. The ammonia will burn with a characteristic
yellowish flame.

A very interesting study of the structure of the flame may
be made by allowing a gentle stream of ammonia to enter
the air-holes in the bottom of a Bunsen burner. The burner
should give a good flame and be turned on full. The am-
monia will impart a yellowish cast to the whole flame
and the outlines of the several cones will be distinctly
seen.

When a Bunsen burner is held at the mouth of a tube at
which ammonia gas is escaping, the flame is colored yellow,
and on close inspection it will be observed that particularly
when the end of the tube becomes hot there is a distinct
combustion of the ammonia itself.

NH3 supply.

AMMONIA

199

Fig. 86

(b) Ammonia gas issuing from a glass jet will not con-
tinue to burn in air, as the temperature of its
own flame is not sufficiently high to dissociate
the ammonia gas. The necessary heat is easily
furnished by passing the gas through the ring
of flame at the mouth of a central draft burner.

The flame of an Erlenmeyer burner is turned
as low as possible and yet leave a small ring
of blue flame around the central draft tube
(Fig. 86). In the base of this tube a cork
carrying a glass elbow is inserted. Ammonia
gas is led through the glass elbow and burns at the top
with a yellowish flame.

Erlenmeyer burner ; NH3 supply.

30. Combustion in oxygen. — A gentle stream of ammonia,
generated by warming 20 cc. of the concentrated liquid in a
50 cc. Erlenmeyer flask, is made to enter an
open tube filled with oxygen. The glass tube
conducting the ammonia is passed through a
two-holed rubber stopper fitted into the end
of a short piece of wide glass tubing (Fig. 87).
A gentle stream of oxygen is allowed to enter
through a glass elbow and maintain an atmos-
phere of oxygen about the open tube leading
from the ammonia flask. The ammonia burns
with a distinctly luminous flame.

Apparatus (Fig. 87) ; con. NH4OH ; 0 supply.

„-jy

N H
Fig. 87

31. Combustion of oxygen in ammonia. — A 150 cc. beaker
is half filled with the strongest ammonium hydroxide and
very gently warmed. A slow current of oxygen is passed
through a long tube 3 or 4 mm. in diameter whose end
almost touches the surface of the liquid. A flame is then

200 CHEMICAL LECTURE EXPERIMENTS

brought to the mouth of the beaker, and soon the oxygen is

seen burning at the end of the tube. The tube is then
quickly immersed in the liquid and the
current of oxygen simultaneously in-
creased (Fig. 88). A green flame of
considerable size appears in the beaker,
and the oxygen is seen to be burning
beneath the surface of the liquid. In
a very few moments the ammonium hy-
droxide will have lost so much of the

dissolved ammonia as to be too dilute for the continuation

of the experiment.

Strongest NH4OH ; 0 supply.

32. Decomposition by metallic potassium. — Potassium
unites with ammonia, setting free some of the hydrogen.

A 7 mm. piece of potassium is placed in a hard-glass bulb-
tube and a gentle current of dry ammonia passed through
it. On heating the bulb the potassium melts, and if heated
strongly, the molten globule suddenly bursts, filling the bulb
with the characteristic green vapor of potassium. The hydro-
gen set free may be ignited at the open end of the bulb-tube.

Bulb-tube ; K ; NH3 supply.

33. Decomposition of ammonia by platinized asbestos. —

When dry ammonia is passed over heated platinized asbestos
in a combustion-tube, the gas is dissociated and three volumes
of hydrogen and one of nitrogen are set free. The gases so
liberated may be collected over water in the pneumatic
trough and, owing to the large percentage of hydrogen, may
be ignited.

Ammonia dried by passing through a U-tube filled with
soda-lime or quicklime is conducted through a 25 cm. length
of combustion tubing fitted with a cork and a delivery-tube

AMMONIA 201

leading to the pneumatic trough. A 5 cm. length of platin-
ized asbestos is placed in the middle of the combustion-tube
and brought to a low red heat by means of a Bunsen burner.
On conducting the dry ammonia through the tube all the gas
will be absorbed in the pneumatic trough as soon as air has
been driven out of the apparatus ; but as the platinized
asbestos begins to be heated, small quantities of gas, rapidly
increasing with the increased temperature, will be collected
at the pneumatic trough. On applying a match the gas will

bum- 2 NH3 = K2 + 3 H2.

25 cm. length combustion tubing ; U-tube containing soda-lime or
quicklime ; platinized asbestos ; NH3 supply.

34. Electrolysis of ammonium hydroxide. — Ammonia is
decomposed into the elements hydrogen and nitrogen when
subjected to electrolysis.

Strong ammonium hydroxide, to which some sodium chlo-
ride has been added to give conductivity to the solution, is
poured into the electrolytic apparatus (Fig. 46, p. 95) and
decomposed by means of a current of from four to six
cells. Platinum electrodes must be used. In a short
time gas will be collected at both arms of the
tube in the proportion of three volumes in one
arm to one volume in the other. The larger
volume of gas can be tested and shown to be
hydrogen by opening the gas-cock and applying
a match. The sodium chloride in the solution
will, however, impart a yellowish color to the jrIG# §9
flame. The smaller volume of gas can be trans-
ferred to a test-tube in the manner shown in Fig. 89, and
proved to be nitrogen by extinguishing a match.

2NH3 = N2 + 3H2.

Electrolytic apparatus (Fig. 46, p. 95); battery 6 cells; con.
NH4OII ; NaCl.

202 CHEMICAL LECTURE EXPERIMENTS

35. Quantitative decomposition of ammonia by chlorine.

— Chlorine acts on ammonium hydroxide with the forma-
tion of hydrochloric acid and the liberation of nitrogen.
Chlorine abstracts the hydrogen from ammonia, and conse-
quently for every three volumes of chlorine used one volume
of nitrogen is liberated.

The eudiometer (Fig. 11, p. 26) is filled over a salt solu-
tion with a rapid stream of pure chlorine. When the tube
is completely filled, a well-fitting rubber stopper is crowded
into the open end of the tube while still under the salt
solution, care being taken to enclose no liquid in the tube.
A few cubic centimeters of strongest ammonium hydroxide
are then allowed to flow through the funnel into the gas,
though the stop-cock must be but slightly turned. As the
ammonia comes in contact with the chlorine, the reaction is
very vigorous and, owing to the condensation in gas volume, a
partial vacuum is produced inside the tube. The ammonium
hydroxide in the bulb of the eudiometer is replaced by
water acidulated with sulphuric acid, successive portions
poured into the funnel and, by opening the stop-cock,
allowed to flow into the eudiometer till the internal and the
external pressure are the same, and no liquid will enter.
The volume of colorless, residual gas will be found to be
one-third the volume of the chlorine originally in the tube.
The tube may be previously roughly graduated in thirds by
rubber rings, allowance being made for the space occupied
by the cork. A simpler method is to measure the distance
from the base of the cork to the stop-cock in centimeters.
The residual gas will measure one-third of this distance
when the bulb is held in an upright position. By removing
the cork the gas may be tested and shown to be nitrogen by
extinguishing a splinter.

A glass tube, 1 m. long and 15 to 20 mm. in diameter,
sealed at one end and fitted with a one-holed rubber stopper

AMMONIA 203

through which the stem of a small dropping-furinel passes,
may be used in case the eudiometer is not at hand. The
tube is filled with chlorine, as above, inverted with the
thumb over the mouth of the tube, and the cork on the stem
of the dropping-funnel quickly thrust into the open end of
the tube. The stem of the dropping-funnel should have
been previously filled with strongest ammonium hydroxide.
The funnel is then filled with the hydroxide, and a few cubic
centimeters allowed to fall drop by drop into the gas. As
each drop falls, it is seen to emit a feeble flash of light, a
phenomenon not observable when the other form of eudiom-
eter is used. The remaining operations are identical with
those described above.

2 NH3 + 3 Cl2 = 6 HC1 + N2.

NH3 + HC1 = NH4C1.

Eudiometer (Fig. 11, p. 26) ; CI generator; glass tube sealed at one
end, 1 in. long, 15-20 mm. diameter ; dropping-funnel ; rubber stop-
pers ; strongest NH4OH.

36. Decomposition of gaseous ammonia by sodium hypo-
bromite and the volumetric relation of the nitrogen liber-
ated.— The volumetric relation of the nitrogen liberated
from a given volume of ammonia by the action of sodium
hypobromite is easily shown by filling the eudiometer
(Fig. 11, p. 26) with dry gaseous ammonia and introducing
a strong solution of sodium hypobromite through the stop-
cock. The eudiometer must be perfectly dry and is filled
with ammonia, either by conducting the gas through a long
glass tube thrust up into the eudiometer, which is clamped
in a vertical position, or by conducting a stream of the dry
gas through a cork inserted in the funnel bulb at the top.
In the latter case the stop-cock is open and the air is driven
out of the eudiometer at the lower opening. Where the

204 CHEMICAL LECTURE EXPERIMENTS

long glass tube is used to introduce the ammonia it must be
withdrawn slowly so as to leave the eudiometer completely
filled with the gas. A perfectly dry, well-fitting rubber stop-
per is then inserted in the bottom of the eudiometer and
a strong solution of sodium hypobromite, made by adding
10 cc. of bromine to 50 cc. of strong sodium hydroxide solu-
tion, poured into the bulb. The stop-cock is carefully
opened, and one drop of the hypobromite solution allowed
to enter and come in contact with the gas. Inasmuch as
there will probably be a slight pressure inside the tube,
caused by the insertion of the rubber stopper, a bubble or
two of the gas may escape. As soon as the liquid has
entered the large volume of gas, rapid absorption takes
place and the hypobromite solution will be drawn into the
tube. Care must be taken to allow no air to enter, and
accordingly the stop-cock must be closed before all the liquid
has entered the eudiometer. A vigorous evolution of nitro-
gen will take place, and on filling the bulb with water and
carefully opening the stop-cock, liquid will be drawn into
the tube until it is half full. The residual gas may be
tested by inverting the eudiometer, removing the stopper,
and inserting a burning splinter. From two volumes of
ammonia one volume of nitrogen is obtained.

2 NH3 + 3 NaBrO = 3 NaBr + 3 H20 + N2.

Eudiometer (Fig. 11, p. 26) ; rubber stopper ; supply of dry NII3 ;
NaBrO (10 cc. Br, 50 cc. NaOH sol.).

NITROGEN CHLORIDE

37. Preparation. — When chlorine reacts on an excess of
ammonia, it combines with the hydrogen, liberating nitrogen
(Ex. 35). If, however, an excess of chlorine is allowed
to act on ammonia or ammonium chloride, a portion of

NITROGEN IODIDE 205

the chlorine unites directly with the nitrogen, forming a
violently explosive, oily liquid, nitrogen chloride. The
preparation of this body can be safely carried out only
on a very small scale.

By electrolyzing a solution of ammonium chloride, chlorine
is liberated at the positive pole, and in the nascent condition
reacts with the excess of ammonium chloride, forming small
quantities of nitrogen chloride. The electrolysis must be
carried out in an open vessel (Fig. 36, p. 74) from which
the graduated tubes have been removed. The electrodes,
which are made by fusing pieces of platinum wire into bent
glass tubes which are afterwards filled with mercury, are
immersed in a strong solution of ammonium chloride, and
the current from 4 or 5 cells of a bichromate battery should
be passed through the solution. A millimeter layer of tur-
pentine should be poured on the surface of the ammonium
chloride solution, and it will be found that as the bubbles of
chlorine ascend they will carry with them minute quantities
of nitrogen chloride, which on coming in contact with the
turpentine will explode. As the explosion may at times
ignite the turpentine, a metal plate should be at hand with
which to cover the dish and extinguish the flame. Occa-
sionally small globules of nitrogen chloride will settle to
the bottom of the dish ; in that case it is best at the conclu-
sion of the experiment to render the solution strongly alka-
line with ammonium hydroxide and allow it to stand until
the nitrogen chloride has of itself decomposed.

Electrolytic apparatus (Fig. 36, p. 74) ; battery.

NITROGEN IODIDE

38. Preparation. — (a) When iodine is allowed to act on
strong ammonium hydroxide, a portion of the hydrogen of
the ammonia is replaced by iodine, forming a mixture of

206 CHEMICAL LECTURE EXPERIMENTS

compounds containing nitrogen, hydrogen, and iodine, called
nitrogen iodide. The direct precipitation of this compound
is most easily effected by adding to a concentrated alcoholic
solution of iodine an equal volume of the strongest ammonia
water. The nitrogen iodide is immediately precipitated in
the form of a black powder.

(b) The preparation of any quantity of nitrogen iodide
is best secured by digesting powdered iodine with strongest
ammonia for a few minutes. A few crystals of iodine are
placed in a mortar and pulverized. Sufficient strong am-
monia is added to cover the iodine completely, and the mix-
ture is stirred from time to time. After a few minutes the
mixture may be thrown on a filter-paper, washed with alco-
hol, and finally with water. The filter-paper is removed
from the funnel and the still moist precipitate spread on
several small pieces of filter-paper and laid on a porous plate
to dry. Without the application of artificial heat the
material will require about one hour to dry sufficiently to
be explosive.

Porous plates ; strongest NH4OH ; powdered I ; alcohol.

39. Explosive character of nitrogen iodide. — The great
sensitiveness of this compound to friction or heat is shown
by the following experiments.

A piece of filter-paper on which a small quanity of nitro-
gen iodide has been dried is carefully placed on a table and
then touched with a feather. Even this gentle friction is
sufficient to cause it to explode.

A piece of paper containing nitrogen iodide is held in
crucible tongs, and suddenly depressed over a Bunsen flame.
The explosion is sufficent to blow out the gas.

A moistened filter-paper on which nitrogen iodide has
been placed is stretched tightly over the mouth of a 7 cm.
funnel. After drying, the nitrogen iodide may be exploded

HYDROXYLAMINE 207

with a feather. The explosion will blow a hole through the
paper.

A dry paper containing some of the nitrogen iodide may
be exploded on a moistened filter-paper stretched over the
mouth of the funnel as above.

Nitrogen iodide may be exploded by a sudden puff of air.
Air is blown from the lungs through a long glass tube upon
dry nitrogen iodide on a piece of filter-paper. The nitrogen
iodide is exploded. Successive papers may be blown on, and
though the papers do not move, the iodide will be exploded.

A peculiar characteristic of the explosion produced by
the nitrogen iodide is its inability to impart its explosion
to a piece of dry guncotton. A small quantity of moist
nitrogen iodide is laid on a small piece of guncotton. After
the iodide has become thoroughly dry, it may be exploded by
friction, but the guncotton will be unchanged. The com-
bustible nature of the guncotton is shown by applying a
flame.

Nitrogen iodide on filter-paper ; guncotton ; feather.

HYDROXYLAMINE

40. Reduction of copper sulphate solution. — The reducing
action of hydroxylamine on an alkaline copper solution is
shown by adding sodium hydroxide in excess to 1 drop of
copper sulphate solution, diluting till nearly colorless, and
adding a few drops of the hydroxylamine chloride solution.
On heating the mixture, a yellow precipitate is obtained.
This reaction serves as a very delicate test for hydroxyl-
amine.

Hydroxylamine chloride solution ; CuS04 solution.

41. Alternate reducing and oxidizing action on iron solu-
tions. — A colorless solution of ferrous ammonium sulphate

208 CHEMICAL LECTURE EXPERIMENTS

is treated with sodium hydroxide, with the formation of the
green ferrous hydroxide. On adding a few drops of hy-
droxylamine chloride solution to the ferrous hydroxide sus-
pended in the alkaline liquid, the precipitate is immediately
turned brown, indicating the formation of ferric hydroxide.
Hydroxy lamine chloride, when acting on slightly acid
solutions of ferric salts, effects their redaction, discharging
the color of the solution. A portion of the suspended pre-
cipitate from the above experiment is treated with hydro-
chloric acid until completely dissolved, any great excess of
acid being neutralized with sodium hydroxide. The solution
must, however, have an acid reaction. On adding hydroxyl-
amine chloride solution, the ferric salt is reduced and the
solution becomes colorless.

Ferrous ammonium sulphate solution ; hydroxj^lamine chloride.

NITROUS OXIDE

PREPARATION

42. By heating ammonium nitrate — Ammonium nitrate
on heating is decomposed quantitatively into nitrous oxide
and water.

Ten grams of the powdered salt are heated in a 100 cc.
Jena glass Erlenmeyer flask fitted with a cork and a wide
delivery-tube. The salt is somewhat hygroscopic, and hence
it is advisable to dry it thoroughly by heating in an air-bath
to 120°. A considerable quantity of the salt may be thus
dried and preserved in well-stoppered bottles. On heating,
the salt first melts and then decomposes, liberating nitrous
oxide. As the liberation of the gas is likely to be somewhat
violent, a wide delivery-tube is advisable. In heating, care
should be taken to heat no more than is necessary to secure
a regular flow of the gas. If the melted salt froths, or the

NITROUS OXIDE 209

gas evolution is too great, the lamp should be removed, but
replaced before water can rise in the delivery-tube and fall
into the hot flask and break it. The explosive nature of the
salt requires some care in its use, though if the previously
dried salt is used, and the flame is turned very low, the
experiment is very successful. The heating should be
stopped before all the material is decomposed.

Owing to the solubility of nitrous oxide in cold water, the
water in the pneumatic trough should be warmed to a tem-
perature of between 30° and 40°. On the gradual application
of heat, the gas is liberated, and may be collected as described.
As no safety-tube is used in this experiment, it is advisable
to remove the delivery-tube immediately after the gas has
ceased to be evolved.

NH4N03 = 2 H20 + N20.

100 cc. Jena glass Erlenmeyer flask ; wide delivery -tube ; pneumatic
trough ; warm water ; dried NH4N03.

PROPERTIES

43. Combustion of a splinter. — If a glowing splinter is
thrust into a cylinder of nitrous oxide, it is immediately
rekindled and burns with a degree of intensity similar to
that of its combustion in pure oxygen.

Occasionally, in preparing the nitrous oxide, considerable
quantities of free nitrogen are formed which diminish to a
marked degree the activity of this gas in supporting com-
bustion. The presence of nitrogen first effects the rekindling
of a glowing splinter. If the gas relights the splinter, it is
an indication of its purity. A burning splinter will, how-
ever, always burn with increased brilliancy in the gas, even
if somewhat contaminated with nitrogen.

Cylinder of N20 ; splinter.
p

210 CHEMICAL LECTURE EXPERIMENTS

44. Combustion of hydrogen. — Hydrogen is allowed to
burn from the recurved jet (Fig. 41, p. 85) and is then
lowered into a cylinder of nitrous oxide. The flame under-
goes a marked change in color, becoming covered with a blue
envelope. The presence of nitrous acid after the combustion
is shown by thrusting a piece of iodo-starch paper into the
cylinder, where it is instantly turned blue.

Recurved jet (Fig. 41, p. 85) ; cylinder of N20 ; H supply ; KI-
starch paper.

45. Explosion of hydrogen and nitrous oxide. — A thick-
walled cylinder is half filled over warm water with nitrous
oxide, the remaining volume being filled with hydrogen.
The cylinder is covered with a glass plate and a towel
wrapped around it. On the application of a lighted taper
an explosion occurs.

N20 + H2 = H20 + N2.

Cylinder ; pneumatic trough filled with warm water; H generator;
N20 supply.

46. Combustion of sulphur. — Sulphur, burning feebly in
a deflagrating-spoon, when lowered into a cylinder of nitrous
oxide, is extinguished. If, however, it is strongly heated
and brought almost to a boil before being introduced, it will
burn brilliantly, forming sulphur dioxide.

S+2N20 = S02 + 2N2.

Jar of N20 ; sulphur in deflagrating-spoon.

47. Combustion of phosphorus. — A small piece of phos-
phorus is placed in the deflagrating-spoon, and after being
ignited is quickly thrust into a jar of nitrous oxide. The
combustion, similar to that in pure oxygen, continues with
great brilliancy.

Jar of N20 j P.

NITRIC OXIDE 211

48. Combustion of iron. — A cylinder or tall beaker, hav-
ing a piece of asbestos paper or wire gauze in the bottom, is
filled with nitrous oxide. A bundle of iron wires, tipped
with a bit of molten sulphur, is ignited and lowered into
the jar. The combustion proceeds with great brilliancy,
the particles of molten iron oxide falling to the bottom and
striking on the asbestos. It is advisable to have a centi-
meter layer of water on the bottom of the cylinder.

Cylinder with asbestos in bottom, filled with N20 ; bundle of iron
wires tipped with sulphur.

NITRIC OXIDE

PREPARATION

49. From nitric acid and copper. — The action of copper
on dilute nitric acid results in the formation of nitric oxide.

To prepare this gas, copper clippings are placed in a
500 cc. Erlenmeyer flask fitted with a thistle-tube and a
delivery tube, the thistle-tube extending to the bottom of
the flask. The copper is covered with water, and concen-
trated nitric acid added through the thistle-tube. The gas
is evolved without the aid of heat and may be collected
at the pneumatic trough. If the gas evolution is too violent,
water is added through the thistle-tube to dilute the acid.
If, on the other hand, the flow of gas is slow, concentrated
nitric acid is added. After the reaction has been running
for a few minutes the gaseous contents of the flask become
colorless, while any of the gas escaping into the air has a
deep reddish brown color. The cylinders of gas collected
at the pneumatic trough are also colorless.

Provision must be made for conducting the excess of gas
into a hood, as the fumes are very irritating.

3 Cu + 8 HN03 = 3 Cu(NOi)2 + 4 H20 + 2 NO.

600 cc. Erlenmeyer flask ; Cu clippings ; thistle-tube and glass elbow.

212 CHEMICAL LECTURE EXPERIMENTS

50. By the action of sulphuric acid on copper and potas-
sium nitrate solution. — Instead of adding nitric acid directly
to copper, the acid may be formed by adding sulphuric acid
to a strong solution of a nitrate covering a quantity of
copper clippings.

Copper clippings in the bottom of an Erlenmeyer flask
are covered with a saturated solution of potassium nitrate.
Concentrated sulphuric acid is allowed to drop from a drop-
ping-funnel upon the liquid. A steady evolution of nitric
oxide is obtained, the rate of which is determined by the
dropping of the sulphuric acid.

2 KN03 + H2S04 = K2S04 + 2 HNO3.

3 Cu + 8 HNO3 = 3 Cu(N03)2 + 4 H20 + 2 NO.

Apparatus (Fig. 3, p. 11); Erlenmeyer flask; dropping-fuimel ;
saturated solution of KN03 ; Cu clippings.

51. From sodium nitrite and acidulated ferrous chloride. —

When a strong solution of sodium nitrite is allowed to drop
into a solution of ferrous chloride to which hydrochloric
acid has been added, a regular evolution of nitric oxide is
obtained.

A handful of iron nails is placed in a 500 cc. Erlenmeyer
flask and covered with 200 cc. of concentrated hydrochloric
acid, and the flask is allowed to stand over night. Suffi-
cient ferrous chloride will have been formed during this
time to give a strong evolution of nitric oxide with sodium
nitrite. A two-holed rubber stopper fitted with a drop-
ping-funnel containing a saturated solution of sodium
nitrite and a delivery-tube is inserted in the neck of
the flask.

500 cc. Erlenmeyer flask ; dropping-funnel ; cork and delivery-tube ;
iron nails ; saturated solution of NaN02.

NITRIC OXIDE 213

PROPERTIES

52. Neutrality of pure nitric oxide to litmus. — A stream
of nitric oxide is conducted through a clean delivery -tube
under a cylinder inverted over a crystallizing dish of water.
The water should be neutral and the cylinder should not be
completely filled, the supply of nitric oxide being cut off that
it may not come in contact with the air, thereby turning the
liquid slightly acid. A piece of blue litmus paper fastened
to the end of a copper wire is then pushed up into the inte-
rior of the flask, care being taken that no air is admitted.
No change will be observed in the blue litmus until a small
quantity of air is admitted. The nitrogen peroxide formed
will then turn the litmus red.

NO generator ; cylinder and crystallizing dish ; pure neutral water ;
blue litmus paper ; copper wire.

53. Solubility in ferrous sulphate solution. — Nitric oxide
is collected in the eudiometer (Fig. 11, p. 26), and ferrous
sulphate solution allowed to flow slowly through the gas by
opening the stop-cock. The nitric oxide is rapidly absorbed,
the solution becoming a dark brown.

To prepare a considerable quantity of a solution of nitric
oxide in ferrous sulphate, the gas is conducted into a gas
washing-bottle containing a solution of ferrous sulphate or
ferrous ammonium sulphate (Mohr's salt). In case the lat-
ter is used, the color change is more noticeable ; for the salt
solution before the introduction of the gas is colorless, while
as the gas is absorbed, the color passes rapidly to a very
dark brown.

On heating the liquid, nitric oxide is again liberated.

Eudiometer (Fig. 11, p. 26); gas washing-bottle; NO generator;
FeS04 solution ; (NH4)2Fe(S04)2 solution.

214 CHEMICAL LECTURE EXPERIMENTS

54. Absorption by nitric acid. — (a) Nitric oxide is absorbed
by nitric acid, with the formation of nitrous acid and nitro-
gen peroxide. The variation in the nature of the products
formed corresponds to the variations in strength of the
nitric acid used.

Three gas washing-bottles are connected in series and
nitric oxide allowed to pass through them. The first bottle
contains nitric acid of a specific gravity of 1.25 ; the second,
nitric acid of the specific gravity of 1.35 ; and the last, acid
of the specific gravity of 1.5. The gas issuing from the
last bottle is then conducted into a flue. On allowing the
nitric oxide to pass through this system for some time, a
series of color changes is observed in the different bottles.
The first bottle contains nitrous anhydride and nitrous acid,
and will acquire a blue color, especially if cooled in a beaker
of ice-water. The second will possess a green color and the
last the deep brown color of fuming nitric acid.

Three gas washing-bottles ; NO generator ; HN03 of 1.25, 1.35, and
1.5 specific gravities ; ice.

(b) Nitric oxide is collected in the eudiometer (Fig. 11,
p. 26) over water and concentrated (not fuming) nitric acid
is allowed to flow down into the gas through the stop-cock.
The absorption is quite rapid, as is indicated by the rise of
the liquid in the tube.

Eudiometer (Fig. 11, p. 26) ; NO generator; con. HN03.

55. Absorption by acidulated potassium permanganate
solution. — Nitric oxide is oxidized to nitric acid by potas-
sium permanganate in the presence of sulphuric acid. The
absorption of the gas and the decolorization of the per-
manganate solution may be shown by collecting a quantity
of the nitric oxide in the eudiometer (Fig. 11, p. 26) and
allowing a solution of potassium permanganate, strongly

foNOf

NITRIC OXIDE 215

acidulated with sulphuric acid, to flow slowly down through
the gas.

6 KMn04 + 9 H2S04 + 10 NO = 10 HN03 + 3 K2S04

+ 6 MnS04 +- 4 H20.

Eudiometer (Fig. 11, p. 26) ; NO supply ; KMn04 + H2S04.

56. Nitric oxide and air. — A tall glass cylinder filled with
nitric oxide and covered with a glass plate is placed mouth
upwards on the table. A cylinder filled with air is placed
mouth downward on top of the glass plate covering the
cylinder of nitric oxide. On slipping out the glass plate
between the two cylinders red fumes appear where the air
and nitric oxide come in contact. As the nitrogen peroxide
formed is much heavier than either air or nitric oxide, the
experiment is especially interesting in showing the diffusi-
bility of the gases.

Cylinder of NO ; empty cylinder.

57. Union with pure oxygen. — Nitric oxide unites with
pure oxygen quantitatively, forming nitrogen peroxide. In
this union a contraction takes place, as two volumes of nitric
oxide combine with one volume of oxygen to form two
volumes of nitrogen peroxide.

A liter bottle is fitted with a two-holed rubber stopper
carrying a straight glass tube extending to within 7 cm. of
the bottom of the bottle and drawn out to a jet 2 mm. in
diameter. A glass elbow is thrust through the second hole
of the rubber stopper. Eubber tubes and pinch-cocks are
slipped on the ends of both glass tubes, and the rubber stop-
per and fittings thrust under water into the mouth of the
bottle, which has previously been three-fourths filled with
nitric oxide at the pneumatic trough (Fig. 90). Both
pinch-cocks being closed, the apparatus is supported mouth

216

CHEMICAL LECTURE EXPERIMENTS

downwards, and a glass tube dipping into a beaker of blue
litmus solution is connected with the rubber tube connected
with the jet in the bottle. Oxygen under pressure, prefer-
ably from a cylinder of the compressed gas, is forced through

the glass elbow after opening the pinch-
cock until a few bubbles have entered
the bottle. As each bubble of the oxy-
gen comes in contact with the nitric
oxide, red fumes of nitrogen peroxide
will appear. These are soon dissolved
by the water remaining in the bottle,
and the gas again becomes clear. The
process is repeated a number of times,
and finally the pinch-cock connecting
the glass jet with the blue litmus solu-
tion is opened. On account of the
vacuum inside the flask caused by the
solubility of nitrogen peroxide in water, the blue litmus
solution will rise rapidly through the jet and enter the
flask in the form of a fountain. There in the presence of
acid fumes the color will be turned from blue to red.

Apparatus (Fig. 90) ; liter bottle ; rubber stopper (2-holed) ; pinch-
cocks and tubes ; 0 supply ; blue litmus solution.

Fig. 90

58. Combustion in nitric oxide. — A glowing or burning
splinter when thrust into nitric oxide is extinguished.

A burning candle on being lowered into nitric oxide is
extinguished.

Burning sulphur on a deflagrating-spoon is extinguished
when lowered into the gas.

Phosphorus when feebly burning on a deflagrating-spoon
is likewise extinguished when lowered into nitric oxide.

If, however, a piece of phosphorus is placed on a defla-
grating-spoon and allowed to burn vigorously in the air and

NITRIC OXIDE 217

is then lowered into the nitric oxide, the heat generated by
its combustion is sufficient to dissociate the gas, and con-
sequently the combustion proceeds even more vigorously
than in air.

Jars of NO ; clefiagrating-spoons ; candle ; P ; S.

59. Combustion of charcoal. — A piece of charcoal fastened
to a stout iron wire is heated to glowing in a Bunsen flame.
On thrusting it into a cylinder of nitric oxide the flame is
extinguished.

If, however, the charcoal is placed in a bulb-tube and
strongly heated with a Bunsen flame, it will glow in a cur-
rent of nitric oxide. Provision should be made for con-
ducting the escaping gas into a flue.

NO generator ; jar of NO ; bulb-tube ; charcoal.

60. Combustion of carbon disulphide. — When the vapor
of carbon disulphide is mixed with nitric oxide and the
mixture ignited, a characteristic blue flame is produced
which has great actinic power, and has consequently been
used as artificial illumination for taking photographs.

Three or four cubic centimeters of carbon disulphide are
rapidly poured from a test-tube into a 250 cc. cylinder of
nitric oxide covered with a plate. The glass plate is
slipped to one side to permit the introduction of the
carbon disulphide, and then the cylinder is immediately
closed. The cylinder is then thoroughly shaken to mix
the vapors, the glass plate removed, and the mixture
ignited.

A blue flame results, the sulphur being deposited on the
sides of the vessel. The cylinder should be immediately
washed, as otherwise the sulphur will be hard to remove.

Jar of NO ; CS2.

218 CHEMICAL LECTUKE EXPERIMENTS

NITROUS ANHYDRIDE AND NITROUS ACID

61. Preparation of nitrous anhydride from arsenic trioxide
and nitric acid. — When arsenic trioxide is oxidized by nitric
acid of a specific gravity of from 1.3 to 1.35, gaseous nitrous
anhydride is liberated.

Twenty-five grams of arsenic trioxide are placed in a
250 cc. flask fitted with a thistle-tube and an elbow. The
arsenic is covered with nitric acid of the above-mentioned
specific gravity and the mixture gently warmed. The gas
is heavy, and may be collected by displacement in a large
flask. When collected in this manner, the deep reddish
brown color is very noticeable.

2 As203 + 4 HN08 + 4 H20 = 4 H3As04 + 2 N203.

250 cc. flask ; thistle-tube and elbow ; large flask ; HN03 specific
gravity 1.3-1.35; As203.

62. Liquefaction of nitrous anhydride. — The gaseous
nitrous anhydride obtained from the preceding experiment
is passed successively through a gas washing-bottle im-
mersed in a beaker of cold water to condense the steam
formed by the reaction, and then through a U-tube packed
in a freezing-mixture of ice and salt. The water in the first
beaker must not be below 8° C. On removing, the U-tube
from the freezing-mixture a blue liquid will be found ; but as
some nitrogen peroxide often condenses with it, the color is
not always clear. On the addition of a small quantity of ice-
water, the color immediately appears perfectly blue. The
liquid boils readily on the application of a very gentle heat.

N203 supply ; gas washing-bottle ; U-tube ; freezing-mixture of ice
and salt.

63. Phenylenediamine reaction for nitrous acid. — Phe-
nylenediamine solution, when added to a solution of sodium
nitrite, to which a few drops of sulphuric acid have been
added, gives an intense orange-yellow color.

NITROGEN PEROXIDE

219

The delicacy of this reaction is so great as to make its use
of great importance in determining minnte quantities of
nitrites in potable waters. A few drops of acidulated
sodium nitrite solution are added to 2 1. of water in a large
beaker. On the addition of a few drops of phenylenediamine
solution, a distinct yellow coloration will appear even at this
great dilution.

NaN02 ; phenylenediamine solution.

NITROGEN PEROXIDE

PREPARATION

64. By ignition of lead nitrate. — Lead nitrate on ignition
is decomposed into lead monoxide, nitrogen peroxide, and
oxygen. Nitrogen peroxide, being easily condensed, is re-
tained in a U-tube packed in salt and ice, while the oxygen
is collected at the pneumatic trough.

Fifty grams of previously dried lead nitrate are placed in
a 200 cc. Jena glass distilling flask, connected to one limb
of a U-tube packed in ice and
salt; the other limb is fitted
with a cork and a delivery-tube
leading to the pneumatic trough
(Fig. 91). The neck of the dis-
tilling flask is securely corked,
and the lead nitrate carefully
heated with a Bimsen burner.
After all the air has been driven
out of the apparatus, the oxy-
gen may be collected and tested
at the pneumatic trough. On

disconnecting the apparatus, the impure nitrogen peroxide
will be found as a red liquid condensed in the U-tube. The

Fig. 91

220 CHEMICAL LECTURE EXPERIMENTS

lead nitrate used for this experiment should be dried by
heating in a porcelain evaporating-dish till red fumes just-
appear.

200 cc. Jena glass distilling-flask ; U-tube in freezing-mixture ; dried
pulverized Pb(N03)2.

65. By the action of tin on concentrated nitric acid. — Tin

and nitric acid react vigorously, nitrogen peroxide being
evolved.

The bottom of a 300 cc Erlenmeyer flask is covered with
granulated tin, and strong nitric acid is introduced through
a thistle-tube reaching to the bottom of the flask. A glass
elbow thrust through the cork in the neck of the flask is
connected to a gas washing-bottle, which is in turn con-
nected with a U-tube immersed in a freezing-mixture of
salt and ice. As soon as the acid is added, the reaction be-
gins and great heat is developed. Most of the steam formed
is condensed in the gas washing-bottle. The nitrogen per-
oxide is condensed in the U-tube. By disconnecting the
U-tube and connecting a glass tube to the gas washing-bottle,
the gas may be collected by displacement.

5 Sn + 20 HN03 = Sn505 (OH)10 + 5 H20 + 20 N02. [?]

300 cc. Erlenmeyer flask ; thistle-tube and glass elbow ; 2-holed
cork ; gas washing-bottle ; U-tube ; freezing-mixture ; Sn.

PROPERTIES

66. Vaporization of liquid nitrogen peroxide. — A few

drops of liquid nitrogen peroxide are placed in a flask, the
bottom of which is warmed with the hand. The liquid
immediately evaporates, filling the flask with deep brownish
red fumes.

250 cc. flask ; liquid N02.

NITROGEN PEROXIDE 221

67. Dilution of fuming nitric acid. — On diluting fuming
nitric acid with water the excess of nitrogen peroxide in the
nitric acid undergoes decomposition in the presence of water,
forming nitrous anhydride, the various steps in the dilution
being characterized by color changes in the solution.

Twenty cubic centimeters of fuming nitric acid in a beaker
are gradually diluted with water. The reddish brown acid
becomes light yellow and then green. If the green solution
is cooled with ice, a blue color will be obtained.

The reverse of this operation may be carried out by grad-
ually adding to some crushed ice in a beaker fuming nitric
acid. In this case the solution becomes first blue, then
green, light yellow, and finally dark brown.

Fuming HN03 ; ice.

68. Combustion of charcoal. — Glowing charcoal when in
contact with liquid nitrogen peroxide burns brilliantly in the
oxygen liberated from this compound.

Two cubic centimeters of liquid nitrogen peroxide are
placed in a test-tube clamped in a vertical position. A
piece of charcoal fastened to one end of an iron wire and
brought to a glow in a Bunsen flame is carefully lowered till
it just touches the surface of the liquid. It continues to
burn with increased brilliancy.

Liquid N02 ; piece of charcoal.

69. Combustion of potassium in gaseous nitrogen peroxide.

— Potassium combines with the oxygen of nitrogen perox-
ide, burning with considerable brilliancy.

A 3 mm. piece of potassium is placed in a deflagrating-
spoon, slightly warmed, and lowered into a cylinder of
nitrogen peroxide having a layer of sand at the bottom.
The potassium takes fire and burns brilliantly.

Jar of NO2 ; deflagrating spoon ; K.

222

CHEMICAL LECTURE EXPERIMENTS

"TUT

70. Absorption of nitrogen peroxide by sulphuric acid.
(Formation of chamber crystals.) — The formation of nitrogen
peroxide and the subsequent absorption of this compound by
sulphuric acid is shown by conducting
nitric oxide from a suitable generator into
a large flask, the sides of which have
been moistened with concentrated sul-
phuric acid. A two-holed rubber stopper
in the neck of the flask contains a glass
tube extending halfway to the bottom
of the flask and a short glass elbow which
is connected with the draft or flue.

Nitric oxide is conducted through the
long glass tube into the flask, where it
combines with the oxygen of the air, form-
ing the deep red fumes of nitrogen per-
oxide, which are immediately absorbed by
the sulphuric acid. The whole interior of the flask be-
comes covered with a crystalline deposit of chamber crystals
(Fig. 92).

Large flask (2-6 1. ) ; NO generator.

NITRIC ACID

PREPARATION

71. From potassium nitrate and sulphuric acid. — The gen-
eral principle of using a stroug acid to drive a weaker out of
combination is made use of in the preparation of nitric acid.
Thirty grams of powdered potassium nitrate are placed in a
500 cc. glass-stoppered retort and 18 cc. of concentrated sul-
phuric acid are carefully poured through a funnel upon the
mixture, care being taken to prevent any acid from getting
into the neck of the retort. The retort is then gently agi-

NITRIC ACID

223

tated to insure a thorough mixture of the ingredients. It is
then clamped so that it may be heated on a wire gauze, its
neck being thrust deep into
a 500 cc. flask partially im-
mersed in water in a large
crystallizing-dish (Fig. 93).
On applying a very gentle
heat, nearly colorless nitric
acid distils over and con-
denses in the flask.

KN08 + H2S04

= KHS04 + HNO3.

Fig. 93

500 cc. glass-stoppered retort ; 500 cc. flask ; crystallizing-dish ;
KNO3.

PROPERTIES

72. Intense acid reaction. — Nitric acid possesses a strong
acid reaction which is readily shown by dipping a glass rod
into fuming nitric acid and then into a beaker containing
a liter of water. Even at this great dilution the acidified
water will instantly redden a strip of blue litmus paper.

73. Action on organic matter. — Nitric acid attacks organic
matter, especially that of an animal nature, staining it yel-
low. The simplest example of this property of nitric acid
is the familiar fact that the acid stains the fingers yellow.
A large white feather has approximately the same composi-
tion as the human skin, and when dipped into fuming nitric
acid in a beaker is stained a brilliant yellow, while a con-
siderable portion of the feather is actually destroyed. On
washing off the excess of acid and dipping the feather into
dilute ammonium hydroxide, the color is somewhat intensi-
fied and becomes fixed.

Acid spots on clothing, if caused by sulphuric or hydro-

224 CHEMICAL LECTURE EXPERIMENTS

chloric acid, are easily effaced by moistening with ammo-
nium hydroxide. Spots resulting from the action of
nitric acid, however, cannot be removed.

Large white feather ; fuming HN03.

74. Action on turpentine. — Strongest nitric acid oxidizes
turpentine, even in the cold, with such rapidity as to ignite
the hydrocarbon.

A small evaporating dish is placed on a layer of sand in
the bottom of a 1 or 2 1. beaker and one-third filled with
a mixture of equal volumes of fuming nitric acid and con-
centrated sulphuric acid. This mixture is easily secured by
slowly pouring 5 cc. of concentrated sulphuric acid into an
e<ffel volume of fuming nitric acid held in a test-tube, keep-
ing the test-tube cool if necessary under the water tap,
though care should be taken not to get any water in the
mixture of acids. A few drops of turpentine are drawn up
into a long (1 m.) glass tube with an elbow at one end,
the short arm (15 cm.) of which is drawn out to a point
(Fig. 50, p. 102). By raising the thumb from the open end
of the tube the turpentine is allowed to drop on the acid
mixture in the evaporating-dish. As each drop comes in
contact with the acid, it bursts into flame. Care should
be taken to prevent any drops of acid from flying out of the
beaker, and provision should be made for carrying off the
vapors rising from the combustion.

2 1. beaker ; small evaporating-dish ; long bent glass tube ; finning
HN03 ; cone. Ii2S04 ; turpentine.

75. Action on sawdust. — Sawdust is heated in a small
evaporating-dish till it is just about to char, and 3 cc. of
fuming nitric acid are poured upon the mass. The carbo-
naceous material is immediately oxidized and the mixture
undergoes a vigorous combustion.

NITRIC ACID 225

76. Action on sugar. — Nitric acid does not act upon
sugar in the cold, as may be seen by pouring 5 cc. of the
acid over 2 g of sugar in the bottom of a test-tube. On
warming the mixture, however, a violent reaction takes
place, the sugar being oxidized

77. Action on wood, carbon disulphide, and illuminating

gas — The vigorous oxidizing action of nitric acid is best
shown when the acid is freshly prepared by heating a mix-
ture of potassium nitrate and sulphuric acid. Such a mixture
is heated in a small wide-mouthed flask and a glowing
splinter thrust into the liquid. The wood is instantly
ignited and burns brightly.

If a few drops of carbon disulphide are poured from a
test-tube into the flask and a flame held instantly at the
mouth, combustion ensues in a most brilliant manner, the
carbon disulphide burning with a deep blue flame.

A slow stream of illuminating gas passing through a long
bent glass tube is ignited and thrust into the neck of the
flask. Combustion proceeds vigorously.

78. Combustion of illuminating gas in fuming nitric acid.

— Fuming nitric acid, containing, as it does, an excess of
the oxides of nitrogen, supports the combustion of il-
luminating gas even when the end of the tube conduct-
ing the burning gas is thrust beneath the surface of the
acid.

Fuming nitric acid is placed in a beaker in a strong draft.
A flame of illuminating gas about 2 cm. long is allowed to
burn at the end of a long glass elbow, and on thrusting the
burning flame under the surface of the acid the combustion
will continue.

Beaker ; long glass elbow ; fuming HN03.
Q

226

CHEMICAL LECTURE EXPERIMENTS

79. Decomposition of nitric acid by heat. — At a high
temperature nitric acid undergoes decomposition, with the
formation of nitrogen peroxide and oxygen. A very simple
and efficient method for showing this decomposition consists
in allowing the nitric acid in vapor form to pass over pumice-
stone heated in a piece of combustion tubing 40 cm. long
and 15 mm. in diameter, preferably of Jena glass (Fig.
94). A thick piece of rubber tubing is slipped over one
arm of a large glass elbow 10 mm. in
diameter which is then crowded into one
end of the combustion-tube, thereby mak-
ing a tight joint. In the other end of
the glass elbow a dropping-funnel con-

spytfi

Fig. 94

taining strong nitric acid is fitted by thrusting the stem of
the funnel through a piece of rubber tube slipped over the
end of the elbow.

A roll of previously ignited asbestos paper 6 cm. long is
inserted in the combustion-tube and so arranged that the
glass elbow is pushed a short distance into its core. The
rest of the tube is filled with broken bits of pumice-stone
and the end closed with a cork carrying a small glass elbow,
the other end of which is thrust some distance through a
two-holed rubber stopper. The rubber stopper is inserted
in the mouth of a large test-tube, kept cool by being im-
mersed in water, and a delivery-tube connects the test-tube
with the pneumatic trough. The combustion-tube is first
strongly heated over a four-tube burner and concentrated

NITRIC ACID 227

nitric acid then allowed to drop slowly (10 to 15 drops per
minute) into the glass elbow. If the tip of the dropping-
funnel is below the rubber connection, the rate of dropping
may be easily determined. The nitric acid flows down the
glass elbow and comes in contact with the asbestos coil.
This, acting as a wick, conducts the liquid toward the
warmer portion of the tube, where it is gradually vaporized.
The vapor then passes over the heated pumice-stone and
there undergoes decomposition. The water and nitrogen
peroxide condense in the test-tube and the oxygen may be
collected at the pneumatic trough. If the burners are so
arranged that the asbestos roll is heated only at one end, i.e.,
that nearest the pumice-stone, by placing a burner directly
under this end of the asbestos, a regular gradation of tem-
perature is secured along the asbestos roll, which is very
hot at the inner end and cool at the end nearer the cork.
A roll of wire gauze may be wound around the outside of
that portion of the combustion-tube which is occupied by
the pumice-stone and consequently requires the highest heat.
By use of the asbestos roll the contact of the liquid with hot
glass is avoided, and the glass tube is therefore seldom broken.
After considerable use the rubber connections in each end
of the combustion-tube are destroyed by the action of the
strong nitric acid.

By allowing the acid to drop continually at a very slow
rate the dropping-funnel acts as a safety-tube ; for should the
pressure inside the tube be materially increased, the drop-
ping of the acid would cease. The dropping-funnel should,
however, have a constricted tip of not more than 3 mm. in
diameter, and not more than 10 cc. of acid should be placed
in the dropping-funnel at a time.

4 HN03 = 2 H20 + 4 N02 + 02.

Combustion-tubing, Jena glass ; dropping-funnel ; large glass elbow ;
4-tube burner ; pumice-stone ; asbestos paper ; large test-tube ; pneu-
matic trough and cylinders.

228

CHEMICAL LECTURE EXPERIMENTS

80. Test for nitric acid. — The brown ring produced by the
action of a solution of ferrous sulphate on concentrated sul-
phuric acid containing nitric acid is strik-
Jft ingly shown by placing 150 cc. of sulphuric

=J|§i acid containing a small quantity of potassium

nitrate in a 500 cc. cylinder and allowing a
concentrated solution of ferrous sulphate to
flow from a dropping-funnel through a glass
tube which delivers the liquid on the surface
of the sulphuric acid solution (Fig. 95). In
this way the two liquids are introduced into
the cylinder without unnecessary mixing, and
a deep brown ring is formed at their surface
of contact.

Fig. 95

500 cc. cylinder ; con. H2S04 + KN03 ; FeS04 solution.

HYDRAZINE

81. Reducing action on solutions of copper and silver. —

Hydrazine sulphate is a strong reducing agent, causing
the reduction of alkaline solutions of copper and silver
salts.

A solution of cupric sulphate to which tartaric acid and
potassium hydroxide have been added is treated with a
solution of hydrazine sulphate. Even in the cold some
reduction is obtained, and on warming a little, cuprous oxide
is precipitated.

A solution of silver nitrate to which has been added suf-
ficient ammonium hydroxide to redissolve the precipitate
first formed is treated with a solution of hydrazine sulphate,
which, on warming, effects the reduction with a deposition
of finely divided silver.

Solutions of hydrazine sulphate, AgN03, CuS04 and tartaric acid.

HYDRAZOIC ACID 229

82. Action with potassium iodate. — Hydrazine sulphate
reduces potassium iodate, precipitating iodine, and in the
process of the reaction the hydrazine is decomposed, liber-
ating nitrogen.

A strong solution of potassium iodate is treated with a
solution of hydrazine sulphate. A vigorous evolution of
nitrogen is obtained, and the mixture becomes colored with
liberated iodine. If the two solutions are hot, the iodine is
vaporized and escapes from the mouth of the tube as a violet
vapor. A drop of starch solution produces the characteristic
blue color with the iodine.

15 N2H4 . H2S04 + 12 KI03 = 15 N2 + 36 H20 + 6 K2S04

+ 9 H2S04 + 6 I2.
Hydrazine sulphate ; KI03 ; starch solution.

83. Decomposition of hydrazine sulphate by heat. — Hydra-
zine sulphate decomposes on heating, with the liberation of
sulphur dioxide, hydrogen sulphide, and free sulphur. A
few crystals of the salt are heated in a test-tube and the
issuing gas tested for sulphur dioxide and hydrogen sul-
phide. Free sulphur will be deposited on the sides of
the tube.

On dissolving the residue in water and adding a few drops
of sulphuric acid sulphur will be precipitated.

HYDRAZOIC ACID

84. Preparation. — Nitric acid, of a specific gravity of 1.3,
when allowed to act on hydrazine sulphate, gives a very
good yield of hydrazoic acid.

One and one-half grams of hydrazine sulphate are placed
in a test-tube fitted with a cork carrying a glass tube doubly
bent so as to dip into a second test-tube containing silver

230

CHEMICAL LECTURE EXPERIMENTS

Fig. 96

nitrate solution (Fig. 96). Four cubic centimeters of nitric
acid of a specific gravity of 1.3 are added to the hydrazine
sulphate, the cork inserted, and the mix-
ture very slightly warmed. As the tem-
perature rises, the gas will be evolved and
bubble through the silver nitrate solution,
producing a curdy white precipitate of
silver nitride. A piece of moistened lit-
mus paper, held in the mouth of the test-
tube at the end of the operation, shows
the acid character of the gas. The silver
nitride formed should be filtered off, thor-
oughly washed with water, and allowed
to stand till ready for use in the following experiments.
Owing to its dangerously explosive nature but small quanti-
ties must be dried at a time.

Hydrazine sulphate ; HN03 (1.3 specific gravity) ; AgN03 solution.

85. Preparation of hydrazoic acid (silver nitride) from
hydrazine sulphate and silver nitrite. — Silver nitrite reacts
with a solution of hydrazine sulphate, forming silver nitride.

Twenty-five cubic centimeters of a saturated solution of
hydrazine sulphate in water are placed in a 50 cc. flask to
which silver nitrite in small quantities is gradually added.
The reaction is quite marked, the white, curdy silver nitride
remaining suspended in the liquid. The precipitate should
be filtered and dried as above. But very small quantities
should be prepared at one time.

N2H4 + AgX02 = AgN3 + 2 H20.

Hydrazine sulphate ; AgN02.

86. Explosive nature of silver nitride. — The great explosi-
bility of silver nitride necessitates that experiments on this
compound be carried out on a very small scale only. A

HYDRAZOIC ACID 231

minute quantity (2 or 3 mg.) is heated on a knife-blade
thrust into the Bunsen burner. The explosion is very great.

If a minute quantity of the precipitate is placed in the
centre of a thin copper sheet which is then suddenly thrust
into the flame, the force of the explosion is such as to make
a dent in the copper.

Silver nitride is equally sensitive to friction, and a small
piece placed between paper on an anvil and struck with a
hammer detonates with great violence.

Hammer and anvil; dry AgN3 (Care I ! !); thin sheet copper.

PHOSPHORUS

MANIPULATION

1. Precautions in handling phosphorus. — Owing to its
inflammable nature and the dangerous character of the
wounds resulting from its burns, phosphorus must be han-
dled with the greatest care. It may be handled beneath
water with perfect impunity, though too much care cannot
be exercised in avoiding danger from particles adhering to
the fingers and finger nails. In all operations where phos-
phorus is to be removed from the water it should never be
touched with the naked fingers, but with pincers or crucible
tongs. Small pieces can be cut from a piece of phosphorus
by submerging the knife and hand as well as the phosphorus
in water. A more satisfactory method of obtaining small
pieces is to use the globules as prepared in Ex. 4, or to break
off pieces of the desired length from sticks of small calibre
prepared as in Ex. 3. In drying a piece of phosphorus
between filter-paper the greater portion of the water should
be allowed to drain off by capillary attraction, and then the
paper should be folded once over the phosphorus and gently
pressed with the fingers. Under no circumstances should
the fingers come in direct contact with the phosphorus. In
cutting phosphorus it is important that the vessel used

232

PHOSPHORUS

233

should be thick, so as not to be broken by the accidental
slipping of the knife.

Phosphorus is always kept under water, and care should
be taken that the phosphorus after long standing does not
become uncovered by the evaporation of the water in the
vessel.

Wounds resulting from burns of phosphorus demand spe-
cial and immediate treatment. They are very persistent
and slow to heal, often resulting in running sores of a seri-
ous nature. The burn should immediately be washed in
water and moistened with sodium bicarbonate or a dilute
solution of bleaching-powder.

Burning phosphorus should be extinguished as directed
in Ex. 8.

2. Melting and casting phosphorus. — Commercial phos-
phorus is ordinarily obtained in the form of sticks. Since
after keeping for some time, especially on exposure to the
light, the phosphorus acquires a dark color, it is desirable to
show the translucent, waxy appearance of pure phosphorus
by melting the commercial material and
recasting it in sticks of convenient size.

Several sticks of phosphorus are placed
in a beaker and completely covered
with water. The beaker is then placed
in an evaporating-dish partially filled
with water, which
is brought nearly to \ ^3

the boiling point.
As the water in
the beaker becomes

warm, the phosphorus melts and settles to the bottom of
the beaker. The phosphorus is best cast in small thin-glass
test-tubes, which are filled with water and immersed in a

Fig. 97

Fig. 98

234

CHEMICAL LECTURE EXPERIMENTS

large beaker of warm water. If the beaker in which the
phosphorus has been melted is small enough, it also may be
immersed in the water in the large beaker and the phos-
phorus poured under water into the test-tubes (Fig. 98).
It is necessary to leave a centimeter layer of water on top
of the phosphorus in each test-tube.

The molten phosphorus may be drawn up into a pipette
and then allowed to run into the test-tubes. A 25 cc. pipette
with a rather wide deli very -tip is immersed in a tall cyl-
inder filled with warm water (Fig. 99).
The pipette is then withdrawn, allowing
the water to flow out, and while still
warm dipped into the beaker containing
the melted phosphorus. A layer of water
is first drawn into the pipette and then
the end dipped beneath the molten phos-
phorus. The pipette is nearly filled with
phosphorus and then transferred to the
beaker holding the test-tubes. As in this
transference a few drops of melted phos-
phorus are liable to fall out of the tip of
the pipette, it is best to seal the tip by
dipping it into a deflagrating-spoon filled
with water. The pipette should occasion-
ally be dipped in the water in the tall
cylinder to keep it warm enough to prevent the phosphorus
from solidifying. After a few test-tubes are filled they may
be removed from the beaker and placed in a test-tube rack,
the layer of water on top preventing oxidation. After a few
minutes the contents of the tubes will have solidified, and by
making a hole in the bottom of each tube the stick of phos-
phorus may be forced out under water. Made in this man-
ner, the sticks show the true color of the yellow phosphorus,
and should be preserved under water in the dark. If care is

" \

*d_

Fig. 99

PHOSPHORUS 235

always taken to draw a little water into the pipette before
the phosphorus and to keep the tip of the pipette always
under the phosphorus or water, the suction may be applied
with the mouth, though it should always be borne in mind
that carelessness will result in drawing melted phosphorus
into the mouth. A safer method of operating is to insert a
gas washing-bottle containing a small amount of water be-
tween the mouth and the pipette. The air should be drawn
through the glass tube whose end terminates just below the
cork. If any phosphorus should accidentally be drawn over,
it would pass through the long tube extending to the bottom
of the bottle, and there be delivered under water.

Large evaporating-dish ; tall cylinder ; gas washing-bottle ; 25 cc.
pipette ; deflagrating-spoon ; thin test-tubes ; P.

3. Preparation of stick phosphorus. — Phosphorus may
also be obtained in the stick form by drawing the molten
liquid up into a glass tube of the diameter of the sticks
desired.

A glass tube, from 8 to 10 mm. internal diameter and 20
cm. long, is provided with a one-holed cork or rubber connec-
tion which is attached to a gas washing-bottle as described
in the preceding experiment. The tube is dipped beneath
the surface of the molten phosphorus under water in a beaker,
and by means of gentle suction a column of the liquid some
10 cm. long is drawn into the tube. The lower end of the
tube is then sealed with a small deflagrating-spoon filled
with water and the tube immersed in a beaker of cold water.
In a few moments the phosphorus will have solidified and, by
removing the rubber tube, the stick may be forced out under
water with a glass rod. By selecting tubes of different sizes
it is easy to obtain rods of phosphorus of any size desired.
A rubber tube should connect the gas washing-bottle with
the mouth, and a pinch-cock may be advantageously employed

236

CHEMICAL LECTURE EXPERIMENTS

to close the tube after the phosphorus has been drawn up.
In using a deflagrating-spoon to seal the end of the tube it is
essential that a layer of water should remain in the spoon
when it is withdrawn into the air, as otherwise the phos-
phorus may easily become ignited.

Glass tubes of different sizes ; gas washing-bottle ; deflagrating-
spoon ; P.

4. Preparation of globules of phosphorus. — In the greater
number of experiments in which phosphorus is used the
amount required is exceedingly small, and consequently it is
necessary either to cut off small pieces of phosphorus from
a large stick or to subdivide the molten phos-
phorus in such a manner that it may solidify in
small globules. This latter operation is easily
performed by allowing molten phosphorus to
flow out of a jet down through a column of ice-
cold water.

A 25 cc. pipette is filled with phosphorus, as
described in Ex. 4, and its tip thrust just be-
neath the surface of water in a tall cylinder.
The cylinder is nearly filled with ice-water and
then a 2 cm. layer of warm water carefully
poured on top. The layer of warm water pre-
vents the solidifying of phosphorus in the tip of
the pipette. The phosphorus is then allowed
to trickle slowly out of the pipette and fall
through the long column of ice-cold water.
During its passage the globules solidify and collect in
small beads at the bottom of the cylinder. By varying
the size of the tip of the pipette and regulating the How
of the phosphorus, larger or smaller globules can be ob-
tained. The glass cylinder should be at least 40 cm. high
(Fig. 100).

Fig. 100

PHOSPHORUS 237

Minute globules, which are often advantageous for oper-
ating with phosphorus, may be obtained by melting a few
grams of phosphorus under 25 cc. of water in a 100 cc. flask.
When the phosphorus is melted, the flask is tightly corked
and the contents well shaken. The phosphorus solidifies in
very fine globules, which should be kept under water in a
tightly corked bottle.

25 cc. pipette ; cylinder 40 cm. high ; P.

5. Purification of phosphorus. — Ordinary phosphorus may
be purified and deprived of its dark-colored coating by melt-
ing it under a dilute solution of potassium dichromate and
sulphuric acid.

The acid mixture and phosphorus should be placed in a
beaker, which is in turn partly immersed in hot water in an
evaporating-dish or water-bath. The phosphorus soon melts
and, at the end of 15 minutes, the impurities will have been
so far dissolved as to leave the phosphorus a clear, almost
colorless liquid in the bottom of the beaker. The oxidizing
mixture may be washed from the beaker by decantation and
the purified phosphorus cast into sticks as described in Ex. 2.

Water-bath ; beaker ; yellow P ; K2Cr207.

PROPERTIES

6. Spontaneous inflammability. — Phosphorus at the ordi-
nary temperatures is energetically oxidized by the oxygen of
the air and is often spontaneously ignited. A clean piece of
phosphorus, if allowed to stand exposed to the air in a warm
room, will oxidize and ultimately ignite. To slioiv the spon-
taneous inflammability of phosphorus it is necessary to have
the phosphorus finely divided. The fine globules of phos-
phorus prepared in Ex. 4, if dried on filter-paper and ex-
posed to the air, will oxidize more rapidly than a large
piece, and the subdivision obtained by the evaporation of a

238 CHEMICAL LECTURE EXPERIMENTS

solution of phosphorus in carbon disulphide leaves a residue
of phosphorus so finely subdivided as to ignite immediately.

Phosphorus is very easily soluble in carbon disulphide, and
a solution may be prepared by dissolving a 7 mm. piece of
dry phosphorus in 5 cc. of carbon disulphide in a test-tube.
A piece of filter-paper dipped in the solution and exposed
to the air will soon take fire ; for as the carbon disulphide
evaporates, the dissolved phosphorus is deposited all over
the fibre of the paper, and in this finely divided condition
is rapidly oxidized in the air. Owing to the non-volatile
nature of the phosphorus pentoxide formed, the paper itself
is not burned, but only partially charred.

As the paper is not ignited under these circumstances, a
letter or design may be drawn on the paper with a camel's-
hair brush dipped in the solution of phosphorus. On evap-
oration of the carbon disulphide the phosphorus is ignited
and chars the design on the paper.

The luminosity of the oxidizing phosphorus is well shown
in a darkened room by drawing a design with the liquid on
a board. As the carbon disulphide evaporates and the phos-
phorus is oxidized, the design appears in lines of fire.

CamePs-hair brush; CS2 solution of P.

7. Spontaneous combustion effected by powdered charcoal.

— A piece of well-dried phosphorus, when placed on a filter-
paper and covered with powdered charcoal, is ignited. The
action requires some little time, but owing to the gases con-
densed in the charcoal as well as its non-conductivity for
heat, the temperature within the mass ultimately reaches
the ignition point of phosphorus.

8. Extinguishing a flame of burning phosphorus. — Burn-
ing phosphorus is difficult to extinguish by the addition of
water.

PHOSPHORUS 239

A piece of clean, dry phosphorus is placed in a small tin
saucer (the cover to a baking-powder can) or iron sand-bath,
and ignited. When the phosphorus is burning well, a few
centimeters of water are added from a test-tube, and it will
be seen that the phosphorus, melted by the heat, will par-
tially float and continue to burn and sputter in the dish.
A similar piece of phosphorus placed on an iron plate and
ignited is, however, readily extinguished by covering it with
sand. In experimenting with phosphorus it is advisable
to have a beaker full of sand within easy reach. After the
phosphorus is extinguished some care is necessary to remove
the sand and extinguished phosphorus without accident, and
hence it is often advisable to allow small pieces of phos-
phorus to "burn out," exercising care that no damage is
done.

Tin saucer ; iron plate ; sand ; gauntlets ; P.

9. Combustion on cotton. — Phosphorus pentoxide, the
product of the combustion of phosphorus in air, is volatilized
with difficulty, and hence forms a protective coating to com-
bustible material, when phosphorus is burned in contact
with it. This was seen in Ex. 6, where the coating of
phosphorus pentoxide prevented the combustion of filter-
paper.

The experiment may be carried out on a larger scale by
placing an 8 mm. piece of dry phosphorus in a little depres-
sion made in a large wad of cotton batting. On igniting
the phosphorus it burns quietly, and the cotton fibres in the
immediate vicinity of the burning phosphorus become some-
what charred. It will be found, however, on examining
the piece of cotton, after the complete combustion of the
phosphorus, that the flame has not been communicated to
the fibre.

Wad of cotton batting ; 8 mm. piece of dry P.

240

CHEMICAL LECTURE EXPERIMENTS

10. Combustion under water. — When a stream of oxygen
is conducted through melted phosphorus, the phosphorus
burns, combining with the oxygen even under water.

A few grams of phosphorus are melted under water in a
large test-tube, which in turn is half immersed in a beaker
of water warmed to 80°. A gentle stream of oxygen is con-
ducted through a piece of clay pipe-
stem, which is inserted in the test-tube
(Fig. 101). As the oxygen comes in
contact with the melted phosphorus, it
burns brilliantly, forming phosphorus
pentoxide, which unites with the water
above the phosphorus to form phos-
phoric acid. A portion of the phos-
phorus becomes converted by the heat
of the combustion into the red modifi-
cation, which remains suspended in the
liquid. It will be found that when the
initial temperature of the phosphorus
and water is as low as 60°, combustion
will take place, though, owing to the
heat of the combustion of the phosphorus, the water is
soon warmed above this temperature. The water above
the phosphorus will be found to have an intensely acid
reaction at the end of the combustion.

•w

--W--

Fig. 101

3H20 + P205 = 2H3P04.

Apparatus (Fig. 101) ; clay pipe-stem ; O supply; P.

11. Vaporization in a current of steam. — (a) Phosphorus
in the presence of steam is rapidly volatilized, and the re-
action of this vapor on a paper moistened with silver nitrate

PHOSPHORUS 241

solution furnishes a delicate test for the presence of free
phosphorus.

A phosphorus match head is covered with 20 cc. of boiling
water in a 500 cc. flask. After a few moments the water is
poured out, leaving the match head in the flask. Apiece
of filter-paper moistened with silver nitrate solution is fas-
tened to a wire in a cork and lowered into the flask. In
the course of a few minutes the paper becomes brownish
in color and finally black from the formation of silver
phosphide.

A paper moistened with lead acetate solution, suspended
in the flask at the same time, proves that the blackening
cannot be due to the formation of hydrogen sulphide, as the
lead acetate paper remains unchanged.

500 cc. flask ; solutions of AgN08, Pb(C2H302)2.

(b) The phosphorescence of a current of steam containing
phosphorus vapor is readily obtained by heating the head of
a phosphorus match with 20 cc. of water in a 100 cc. flask
provided with a cork carrying a short piece of glass tubing
(6 mm. internal diameter). On bringing the water to a boil
steam will escape from the glass tube, and in a darkened
room the jet will be found to be feebly luminous from the
oxidation of the phosphorus vapor.

12. Phosphorus colors the hydrogen flame green. — One of

the most delicate tests for the presence of free phosphorus
is based on the fact that phosphorus tints the colorless
hydrogen flame green.

A hydrogen generator is constructed by inserting a straight
glass tube 7 mm. in diameter through a two-holed rubber
stopper in a small Erlenmeyer flask (Fig 102). The second
hole carries a glass tube so bent as to form a jet, and a
platinum tip such as that described in Ex. o, p. 183, should

242

CHEMICAL LECTURE EXPERIMENTS

be inserted in the glass tube. A few pieces of zinc are
placed in the bottom of the flask and covered with water.
The wide glass tube should extend to within
5 mm. of the bottom of the flask, and serves
to introduce sufficient sulphuric acid to start
the generation of hydrogen. After the addi-
tion of acid the flask should be shaken, and,
as soon as all air is driven out, the hydro-
gen is lighted at the platinum tip. A phos-
phorus match head is softened in hot water
for a few moments, and then dropped through
the wide glass tube into the generator. The
hydrogen flame, which was colorless, is soon
colored green from the phosphorus of the
match head.

Fig. 102

150 cc. Erlenmeyer flask ; glass tube (7 mm. diameter) ; platinum

jet.

13. Action of fuming nitric acid. — At times fuming nitric
acid oxidizes phosphorus to phosphoric acid with almost ex-
plosive violence. The commercial method
of preparing phosphoric acid depends on
this reaction, and its regulation is there-
fore a matter of considerable importance.

A crucible one-third filled with fuming
nitric acid is imbedded in a layer of sand
at the bottom of a tall glass beaker or
cylinder (Fig. 103), which is placed in the
hood. A 7 mm. piece of dried phosphorus
impaled on the "end of a long iron wire,
bent in such a manner as to be easily
thrust into the cylinder, is brought in
contact with the fuming nitric acid in the crucible. After
a few moments the phosphorus bursts into flame. When

Fig. 103

PHOSPHORUS 243

the combustion is completed, the crucible may be carefully
removed with the gloved hand, and the contents diluted
with water. The liquid contains phosphoric acid.

Crucible ; cylinder with sand ; iron wire ; gauntlets ; fuming HN08 ;
yellow phosphorus.

14. Action on potassium chlorate. — Phosphorus and po-
tassium chlorate form a violently explosive mixture, which
must be handled on a very small scale only.

A very intimate mixture of phosphorus and potassium
chlorate is obtained by allowing 1 or 2 drops of a strong
solution of phosphorus in carbon disulphide to fall from a
dry test-tube upon a very small heap of finely powdered
potassium chlorate placed on a brick or a piece of asbestos
paper. The carbon disulphide soon evaporates, leaving a
fine deposit of phosphorus all through the finely powdered
potassium chlorate. As soon as the phosphorus ignites, the
combustion proceeds through the whole mass with a very
sharp explosion.

Powdered KC103 ; CS2 solution of P.

15. Effect of pure oxygen on the glowing of phosphorus. —

A stick of phosphorus, suspended by a thread, glows in a
darkened room, but if lowered into a jar of oxygen, the glow-
ing ceases.

The experiment may be varied by placing the phosphorus
in a cylinder containing air, where it glows as usual. On
conducting oxygen into the cylinder the glowing ceases.

Cylinder of 0 ; stick of P.

16. Glowing in oxygen under diminished pressure. —

While phosphorus will not glow in pure oxygen at atmos-
pheric pressure, if the oxygen is partially removed from the
vessel, the phosphorus will glow in the rarefied gas.

244 CHEMICAL LECTURE EXPERIMENTS

A stick of phosphorus is lowered into a tall, narrow cylin-
der of oxygen fitted with a one-holed rubber stopper carrying
a glass elbow. The elbow is connected with a filter-pump.
The phosphorus will not glow in the cylinder of oxygen, but
as soon as the filter-pump is started the glowing begins.
On allowing oxygen to enter again the glow ceases. Ad van ^
tageous use may here be made of a three-way stop-cock, one
arm of which is inserted in the rubber stopper, the other arm
connected with an oxygen supply, and the stem connected
with the filter-pump. The three-way cock may be so turned
as to connect with the filter-pump to produce the desired
diminished pressure. By turning the cock again oxygen
may be readmitted.

Tall, narrow cylinder ; filter-pump ; three-way cock ; O supply ;
stick of P.

17. Action of vapors on the glowing of phosphorus. — (a)

A stick of phosphorus placed in a glass cylinder and ex-
posed to the air glows in a darkened room. On allowing
2 or 3 drops of ether to fall into the cylinder the glowing
immediately ceases. On withdrawing the phosphorus into
the air the glowing reappears. Turpentine or carbon di-
sulphide instead of ether may be used with similar effect.
Stick phosphorus ; ether ; CSg ; turpentine.

(b) The fact that phosphorus will not glow in oxygen
containing traces of certain other vapors is well shown by
lowering into a jar of oxygen a piece of filter-paper on which
a few drops of a solution of phosphorus in carbon disulphide
have been placed. A cardboard cover should be laid over
the mouth of the jar. A similar piece of paper when held
in the air is ignited in a few moments, while that in the
atmosphere of oxygen is not. On withdrawing the paper
into the air it almost instantly catches fire.

Jar of 0 ; cardboard cover ; CS2 solution of P.

AMORPHOUS PHOSPHORUS 245

18. Reduction of metallic salt solutions. — Phosphorus is a
strong reducing agent, and precipitates many metals from
their solutions.

(a) Oupric sulphate. A stick of clean phosphorus is
immersed in a solution of cupric sulphate which is strong
enough to appear decidedly blue. After a few minutes the
phosphorus will become covered with a coating which con-
sists of copper mixed with some copper phosphide. If the
phosphorus is allowed to remain in the solution till the next
exercise, all of the copper will be removed from the solution,
and the clear colorless solution will give no test for copper
when ammonium hydroxide is added to it.

Concentrated CuS04 solution ; stick of P.

(b) Silver nitrate. A piece of clean phosphorus, when im-
mersed in a solution of silver nitrate, becomes covered with
a metallic, crystalline coating of a mixture of silver and
silver phosphide.

AgN03 solution ; stick of P.

(c) Gold chloride. A piece of clean phosphorus im-
mersed in a rather strong solution of gold chloride is imme-
diately coated with a deposit of gold, which, owing to its
fine subdivision, appears black.

AuCl3 solution ; stick of P.

AMORPHOUS PHOSPHORUS
(RED PHOSPHORUS)

FORMATION AND PREPARATION

19. By the combustion of ordinary phosphorus. — Ordinary
yellow phosphorus, when burned in the air, is partially con-
verted into the allotropic form known as red phosphorus.
In Ex. 4, p. 182, where phosphorus is burned in a con-

246 CHEMICAL LECTURE EXPERIMENTS

fined volume of air, considerable quantities of red phosphorus
will be found remaining in the crucible lid.

20. By the action of light on yellow phosphorus. — Pure

yellow phosphorus always turns dark on exposure to the
light, hence it is recommended to keep the purified phos-
phorus in a dark place.

The change in color undergone by exposure to the light is
very markedly shown by exposing to the sunlight for a few
hours a tightly corked test-tube containing a stick of pure
phosphorus, which is covered with water. In the course of
a day of bright sunlight the phosphorus will have materially
reddened, as may be seen by comparing the exposed piece
with a fresh piece of pure phosphorus. The color change is
still more noticeable if the lower half of the test-tube is
wrapped with black paper which cuts off the light from the
lower half of the stick of phosphorus. If such a piece is
exposed to the sunlight, the upper half will turn a dark red,
while the lower part remains unchanged.

Black paper ; freshly prepared stick P.

21. By the action of iodine. — A 5 mm. piece of well-
dried yellow phosphorus is heated to boiling in a test-tube.
Very little, if any, change in color will be obtained. On
adding a minute crystal of iodine and reheating, the whole
mass becomes converted to red phosphorus.

Yellow P ; I.

PROPERTIES

22. Conversion to yellow phosphorus by heat. — Ked

phosphorus, when heated at a high temperature, becomes
converted to yellow phosphorus.

An 8 cm. length of small glass tubing is sealed at one end
and a quantity of red phosphorus introduced into the tube.

AMORPHOUS PHOSPHORUS

247

On heating the phosphorus a gas escapes, which is spontane-
ously inflammable, the impure hydrogen phosphide resulting
from the decomposition of a small amount of phosphorous
acid in the red phosphorus. As the heat is increased, yellow
phosphorus is formed and condenses in oily drops in the
upper part of the tube.

Red phosphorus contains an appreciable quantity of phos-
phorous acid, and if water is allowed to pass through it on a
filter-paper the filtrate will be decidedly acid to litmus.

8 cm. length small glass tubing ; red P ; litmus.

23. Difference in the ignition point of the two modifica-
tions of phosphorus. — The ignition point of red phosphorus

is very much higher than that of yellow phosphorus. This
difference may be shown by placing a small quantity of yel-
low phosphorus on the end of an iron bar about 15 cm. long.
A small heap of red phosphorus is placed on the other end.
The bar is then suspended on the ring of a retort stand and
heated in the middle with a Bun sen burner. After a few
moments the yellow phosphorus will ignite, but it will re-
quire considerable time and a much higher
heat to cause the ignition of the red phos-
phorus.

The experiment may be varied some-
what by placing the yellow phosphorus at
a greater distance from the flame than the
red. For this purpose a strip of brass,
some 20 cm. long and 2.5 cm. wide, is
clamped at one end in a horizontal posi-
tion (Fig. 104). A small heap of red phos-
phorus is placed at a point about 4 cm.
from the free end and a small piece of yel-
low phosphorus is placed at a distance of 10 cm. from the
red. The end of the brass is then heated with a Bunsen

Fig. 104

248 CHEMICAL LECTURE EXPERIMENTS

burner. In a few moments sufficient heat will have been
conducted along the strip of brass to ignite the yellow phos-
phorus, while the red phosphorus, which is nearer the flame,
remains unchanged. On increasing the heat somewhat the
red phosphorus will finally be ignited.

Iron bar (15 cm. long) ; brass strip 20 cm. by 2.5 cm. ; red P ; yel-
low P,

24. Combustion in air. — That the product obtained by
burning red phosphorus in the air is the same as that ob-
tained by burning yellow phosphorus, is an indication of the
chemical identity of these two forms of the element.

A small quantity of red phosphorus is placed in a crucible
on a plate and covered with a bell-jar. On igniting the
phosphorus the combustion proceeds as with yellow phos-
phorus, and the bell-jar is filled with dense white fumes of
phosphorus pentoxide. The oxide falls as a white powder
on the plate and possesses all the properties of the product
obtained by burning yellow phosphorus under the same con-
ditions.

P4 + 5 02 = 2 P205.

Crucible ; plate ; bell-jar ; red P.

25. Combustion with potassium chlorate. — (a) A mixture
of red phosphorus and potassium chlorate explodes with
heat or concussion.

A piece of white paper 20 mm. square is folded in the
form used by druggists to dispense powders. A pinch of
finely powdered potassium chlorate and about one-third the
volume of red phosphorus are placed in the paper, which is
very carefully folded in the original creases, care being
taken to exert no pressure. The paper is then placed on
an anvil and struck with a hammer in a gloved hand. The
report is quite sharp.

HYDROGEN PHOSPHIDE 249

The union between red phosphorus and potassium chlo-
rate may be brought about by placing a small pinch of each
in an unglazed mortar. By rubbing the ingredients with a
pestle in the gloved hand the mixture may be exploded.

Folded paper ; mortar and pestle ; hammer and anvil ; gauntlets ;
red P ; powdered KC103.

(b) The igniting surface of a safety match-box contains
red phosphorus.

A stick of potassium chlorate is prepared by carefully
melting the dry, powdered salt in a small test-tube. After
the contents of the tube have become liquid it is allowed to
cool, and the glass is broken off, leaving a stick of solid po-
tassium chlorate. Such a stick when rubbed on the igniting
surface of a safety match-box produces a flash of fire. If
the operation is conducted over a Bunsen burner through
which gas is issuing, the spark produced by the friction will
ignite the gas.

Stick of KCIO3 ; safety match-box.

HYDROGEN PHOSPHIDE

ORMATION AND PREPARATION

26. By the action of hydrogen on red phosphorus. —

Hydrogen combines with red phosphorus directly to form
hydrogen phosphide.

Dry hydrogen is conducted over red phosphorus in a 20
cm. length of combustion tubing fitted with a cork at each
end, one carrying a glass tube conducting the hydrogen, the
other a delivery -tube. Hydrogen is first passed through the
system until all air is expelled and then the red phosphorus
gently heated. Soon sufficient hydrogen phosphide is formed
to render the gas collected in cylinders capable of ignition

250 CHEMICAL LECTURE EXPERIMENTS

by fuming nitric acid. If the end of the deli very -tube is
allowed to dip in concentrated nitric acid, the gas becomes
ignited as it comes in contact with the air.

P4 + 6 H2 = 4 PH3.

20 cm. length of combustion tubing ; H generator ; red P ; fuming
HN03.

27. From phosphorus and alcoholic potash. — Phosphorus
acts on potassium hydroxide, forming potassium hypophos-
phite and hydrogen phosphide. Certain by-products are
formed in the reaction which impart to the hydrogen phos-
phide evolved the property of spontaneous combustibility on
exposure to the air. This by-product (P2H4) is absorbed by
alcohol, and accordingly, if a quantity of strong alcohol is
added to the potassium hydroxide used in the reaction, the
issuing gas will not inflame on exposure to the air.

A few pieces of phosphorus are placed in a 100 cc. Erlen-
meyer flask fitted with a one-holed rubber stopper with a
delivery-tube. The phosphorus is covered with 30 cc. of
strong alcohol to which 15 cc. of concentrated potassium
hydroxide solution have been added. The flask is gently
warmed, and as soon as all air has been driven out the cork
is inserted. The gas collected at the pneumatic trough is
pure hydrogen phosphide. Several small jars should be
collected for use in experiments on the properties of the
pure gas.

P4 + 3 KOH + 3 H20 = 3 KH2P02 + PH8.

100 cc. Erlenmeyer flask ; small cylinders ; con. KOH solution ;
alcohol ; P.

28. Impure hydrogen phosphide from phosphorus and
sodium or potassium hydroxide. — Impure hydrogen phos-
phide is especially interesting owing to its spontaneous in-
flammability. When prepared as described in the preceding

HYDROGEN PHOSPHIDE

251

experiment, but without the addition of alcohol, a gas is ob-
tained consisting chiefly of hydrogen phosphide, carrying with
it small quantities of a liquid hydrogen phosphide (P2H4)
which is spontaneously inflammable on exposure to the air.
Consequently it is essential, in preparing the impure gas, to
replace all air in the apparatus with hydrogen, coal gas, or
other oxygen-free vapor.

Two or three 5 mm. pieces of phosphorus in a 300 cc. Jena
glass flask are covered with 100 cc. of concentrated sodium or
potassium hydroxide solution. Hydrogen or coal gas is
passed through a tube in a two-holed rubber stopper in
the neck of the flask, driving
the air out of the apparatus
through the delivery-tube (Fig.
105). When all air has been
expelled, the supply of hydro-
gen is cut off and the flask is
gradually heated. When the
temperature of the contents of
the flask is near the boiling
point of sodium hydroxide,
the reaction begins, and a gas
is soon regularly evolved and

passes over into the pneumatic trough. The first bubbles
of gas rising through the water in the trough consist chiefly
of hydrogen and present no special appearance. As the
hydrogen is expelled and the hydrogen phosphide begins to
come over, each bubble, on coming in contact with the air, is
seen to take fire, burning with the formation of a white
smoke. If the reaction is so regulated that the individual
bubbles rise through the liquid, white rings rotating in a
vortex result from the combustion of the gas. The air
should be as free as possible from drafts to obtain the best
results.

Fig. 105

252 CHEMICAL LECTURE EXPERIMENTS

To insure the formation of large-bubbles the delivery-tube,
or at least the end of the delivery-tube, should be of tubing
of not less than 8 mm. internal diameter. On an ordinary
tube the end may be enlarged by connecting to it, by means
of a rubber tube, a wide tip of glass tubing. The heat must
be so regulated that the gas evolution is not rapid enough to
prevent the isolation of each ring.

At the end of the experiment hydrogen may be passed
through the apparatus to expel the hydrogen phosphide, the
current of gas being continued until the issuing bubbles
are no longer ignited. The cork is then removed and water
added, care being taken not to wash out any of the unused
phosphorus, which should be carefully washed and trans-
ferred to the bottle containing phosphorus.

Instead of using a current of hydrogen the air may be
expelled from the apparatus by adding 2 cc. of ether to the
liquid in the flask before heating. In that case at the end
of the reaction the flask is allowed to become perfectly cold,
care being taken to have the end of the delivery -tube a con-
siderable distance under water. As the flask cools, water is
sucked back through the delivery-tube, nearly filling the
flask.

Apparatus (Fig. 105) ; wide delivery -tube ; H generator ; con.
NaOH; P; ether.

29. Impure hydrogen phosphide from calcium phosphide
and water. — Water acts on calcium phosphide, with the
liberation of hydrogen phosphide, which, as it is not pure,
takes fire on exposure to the air.

A few lumps of calcium phosphide are thrown into a small
cylinder containing a few cubic centimeters of water. The
reaction is very rapid and large quantities of gas are liber-
ated. As the gas comes in contact with the air at the mouth
of the cylinder, it ignites and continues to burn.

HYDROGEN PHOSPHIDE

253

The impure hydrogen phosphide thus formed may be
collected if the calcium phosphide is allowed to fall into
water in a small three-necked Wolff bottle. One neck of
the bottle is provided with a w7ide, straight glass tube
which dips beneath the surface of the water in the bottle.
The second neck is provided with a cork
and a glass elbow connected with an
illuminating gas-jet, and the third neck
carries a delivery-tube leading to a pneu-
matic trough (Fig. 106). The Wolff bot-
tle should be about half full of water.
Illuminating gas is first passed through
the system until all air is removed. The
current of illuminating gas is then cut
off, and lumps of calcium phosphide -pm. 106

small enough to pass through the wide
tube are then allowed to fall into the bottle. Soon suffi-
cient hydrogen phosphide will have collected in the bottle
to escape at the pneumatic trough, where, as each bubble
comes in contact with the air, it becomes ignited.1

Ca3P2 + 3 H20 = 3 CaO + 2 PH3.

Apparatus (Fig. 106) ; small 3-necked Wolff bottle ; wide delivery-
tube ; Ca3P2.

30. Action of calcium phosphide on water. — The rapidity
of the action of calcium phosphide on water renders it diffi-
cult to obtain well-formed rings in the combustion of the
hydrogen phosphide formed from the reaction. By enclosing
the lump of calcium phosphide in a piece of sheet lead, ac-
cording to the method described in Ex. 1, p. 39, where
sodium is covered with sheet lead, the action of the water is
confined to one point on the surface of the phosphide, and

1 See note concerning delivery-tube in the preceding experiment.

254 CHEMICAL LECTURE EXPERIMENTS

hence the gas evolution is much more regular. A lump of
calcium phosphide wrapped in this manner is thrown into
water in a crystallizing-dish. As the bubbles of gas rise
they are ignited and, in the absence of drafts, well-formed
rings may be obtained.

Crystallizing-dish ; sheet lead ; CadP2.

31. Purification of hydrogen phosphide. — (a) By alcohol.
The impurity in hydrogen phosphide, which causes its spon-
taneous combustibility, may be removed, as has been before
stated, by conducting the impure gas through alcohol. The
gas is conducted through alcohol in a gas washing-bottle
from which all air has been expelled by a current of hydro-
gen or coal gas. The hydrogen phosphide issuing from the
wash-bottle will be found to be so far deprived of its
impurity as to be no longer spontaneously combustible.

(b) By hydrochloric acid. Concentrated hydrochloric acid
acts on the impurity in hydrogen phosphide, decomposing it
and forming a solid compound of phosphorus and hydrogen,
which is deposited as a yellowish precipitate in the hydro-
chloric acid. In the apparatus used in the above experi-
ment concentrated hydrochloric acid instead of alcohol is
placed in the gas washing-bottle. After driving out the air
impure hydrogen phosphide is conducted through the hydro-
chloric acid. The impurity is decomposed, a yellow precip-
itate appears, and the issuing gas is no longer spontaneously
inflammable.

(c) By means of cold. Impure hydrogen phosphide when
conducted through a freezing-mixture is likewise purified
to such an extent that it is no longer spontaneously inflam-
mable. The small quantity of liquid hydrogen phosphide
present in the gas is condensed by the freezing-mixture.

HYDROGEN PHOSPHIDE 255

A current of impure hydrogen phosphide is conducted
through a U-tube immersed in a freezing-mixture of salt and
ice. The issuing gas is not spontaneously inflammable.
The condensed impurity is present in such small quantities
as to be seen only after a long passage of the gas. The
tube may be removed from the freezing-mixture while the
gas is still passing through it and allowed to become warm
in the room, when it will be observed that the issuing gas is
again spontaneously inflammable.

2 gas washing-bottles ; U-tube ; supply of impure PH3 ; ice and
salt ; alcohol.

PROPERTIES OF THE PURE GAS

32. Combustion in the air. — A cylinder of pure hydrogen
phosphide is ignited by applying a flame. The gas burns
with a bright flame, forming white clouds.

33. Ignition by heat. — A glass rod whose end has been
heated in a Bun sen flame causes the ignition of a jar of hy-
drogen phosphide when thrust into it.

34. Ignition by fuming nitric acid. — A jar of hydrogen
phosphide is instantly ignited when a glass rod which has
been dipped in fuming nitric acid is thrust into it.

35. Ignition by chlorine. — Chlorine reacts with hydrogen
phosphide, causing an ignition of the gas.

A 500 cc. cylinder is filled with chlorine into which is
lowered the recurved jet from which issues pure hydrogen
phosphide. As the gas comes in contact with the chlorine,
it is ignited and burns with a greenish light.

The experiment may be varied by collecting over water
25 cc. of chlorine in a 100 cc. cylinder and allowing individ-
ual bubbles of pure hydrogen phosphide to rise inside the
cylinder and come in contact with the gas. As each bubble

256 CHEMICAL LECTURE EXPERIMENTS

of gas is not instantly ignited, the cylinder must be firmly
held to resist the explosion of the accumulated quantity of
gas in the cylinder.

Recurved jet ; 500 cc. cylinder of chlorine ; 100 cc. cylinder of CI ;
supply of PH3.

36. Action with bromine vapor. — When bromine vapor
is allowed to come in contact with hydrogen phosphide, a
violent reaction takes place, which causes the ignition of the
gas. The hydrogen phosphide used in this experiment must
be pure, and not spontaneously combustible. A rod is dipped
in bromine and then thrust into a small cylinder of pure
hydrogen phosphide. The gas is immediately ignited.

Jar of pure PH3 ; Br.

37. Ignition by silver nitrate solution. — When a strong
solution of silver nitrate is poured into a cylinder of pure
hydrogen phosphide, the gas is ignited.

One or two cubic centimeters of strong silver nitrate so-
lution are poured into a 50 cc. cylinder of pure hydrogen
phosphide. The gas catches fire with an explosion, and a
black deposit of silver phosphide covers the walls of the
cylinder.

500 cc. jar of pure PH3 ; AgN03 solution (concentrated).

PROPERTIES OF THE IMPURE GAS

38. Explosion in air. — If impure hydrogen phosphide is
allowed to come in contact with a confined volume of air,
the combustion is of an explosive nature.

A 100 cc. glass cylinder is filled with water and inverted
in a pneumatic trough. A few bubbles of air are introduced
into the cylinder, and then individual bubbles of impure
hydrogen phosphide are allowed to rise and come in contact
with the air. As each bubble comes to the surface, a slight

HYDROGEN PHOSPHIDE 257

explosion results, and accordingly care should be taken that
the bubbles of the hydrogen phosphide ascend in the cylin-
der only one at a time, and that the cylinder is firmly held
in the hand.

100 cc. cylinder; supply of impure PH$.

39. Combustion in oxygen. — (a) The combustion of hy-
drogen phosphide In pure oxygen may be effected by con-
ducting the gas in a slow stream into an apparatus consisting

Of a wide glass tube Carrying a two-holed cork in one end.
Oxygen is conducted through one hole, and the second hole
carries a doubly bent, glass tube having a few drops of
mercury sealing the bend. The apparatus is clamped in
an upright position, and a gentle stream of oxygen is con-
ducted into the tube. As each bubble of impure hydrogen
phosphide passes the mercury and ascends into the atmos-
phere of oxygen, it burns with a brilliant Hash.

Apparatus (Fig. 87, p. L99) with haul tube; 0 supply; supply of
impure I'll- ; Hg.

(6) If impure hydrogen phosphide is allowed to come in
Contact with a confined volume; of Oxygen, the union is of
an explosive nature.

A stout-walled 100 cc. cylinder is one-third filled with
oxygen at a metallic pneumatic trough. Impure hydrogen
phosphide, is conducted, one bubble at a time, under the
mouth of the cylinder, and allowed to rise and come in

Contact with the oxygen. The combustion is very sharp,

making it necessary to hold the cylinder down bard on the
bottom of the pan. The slow stream of hydrogen phosphide
required for this experiment is best secured from the appa-
ratus described in Ex. 21). The greatest Caution must be
observed to prevent an excess of the gas from rising in the
cylinder.

100 cc. cylinder; O supply ; supply of impure PH§.
B

258

CHEMICAL LECTURE EXPERIMENTS

(c) A 100 cc. cylinder is filled with oxygen, covered with
a pasteboard cover, and then one-fourth rilled with warm
water. A few centigrams of powdered calcium phosphide
are then shaken into the cylinder, and the mouth nearly
closed with the cardboard cover. The liberated hydrogen
phosphide coming in contact with the oxygen produces a
series of brilliant flashes.

100 cc. cylinder of 0 ; Ca3P2.

PHOSPHONIUM IODIDE

-»<IF— ^

40. Preparation. — The action of hydrogen phosphide on
iodine produces a small quantity of phosphonium iodide,
which serves to illustrate the preparation of this compound.
A current of pure hydrogen phosphide is conducted
through a 60 cm. length of glass tubing 2 cm. in diameter,
containing a few grams of iodine near the entrance end.
The iodine is gently warmed by playing a low Bunsen flame

on the tube at intervals
of 10 to 15 seconds. A
25 cm. length of the tube
near the open end is cooled
by allowing ice-water to
drop on a piece of filter-
paper wrapped around it
(Fig. 107). If the cur-
rent of hydrogen phos-
phide is rapid, a deposit
of transparent crystals of phosphonium iodide will appear
in the cooled portion of the tube. The reaction is explained
as taking place in two steps : the first in which hydrogen
phosphide and iodine unite to form hydriodic acid and
iodide of phosphorus ; in the second the excess of hydro-

PHOSPHORUS TRICHLORIDE 259

gen phosphide combines with the hydriodic acid to form
phosphonium iodide.

Apparatus (Fig. 107) ; 60 cm. length of combustion tubing ; supply
of pure PH3 ; I ; ice.

41. Decomposition by water. — Water decomposes phos-
phonium iodide with the formation of hydrogen phosphide
and hydriodic acid.

Two or three grams of phosphonium iodide are placed in
a small evaporating-dish on the bottom of a large beaker or
battery jar, covered with a cardboard having a small hole
in the centre. One or two cubic centimeters of water are
poured from a test-tube on the end of a long stick, through
the hole in the cardboard, upon the phosphonium iodide.
At first a hissing is heard, which is followed almost imme-
diately by an explosion.

Large beaker or battery jar ; cardboard cover ; evaporating-dish j
test-tube on stick ; PH4I.

42. Ignition by fuming nitric acid. — Fuming nitric acid
oxidizes phosphonium iodide with the liberation of iodine.

One gram of phosphonium iodide is placed on a watch-
glass, and a drop of fuming nitric acid allowed to fall on it.
The oxidation is accompanied by a slight noise, and iodine
fumes are liberated.

Watch-glass ; PH4I ; fuming HN03.

PHOSPHORUS TRICHLORIDE

43. Preparation. — By the action of dry chlorine on phos-
phorus, phosphorus trichloride is formed. The experiment
is similar to that in which sulphur monochloride is formed
(Ex. 33, p. 148).

Ten grams of yellow phosphorus are placed in a 300 cc.
tubulated retort (Fig. 66, p. 148), the neck of which is

260 CHEMICAL LECTURE EXPERIMENTS

thrust through a rubber stopper deep into a filter-flask
immersed in ice-water. A glass elbow extends through a
cork in the tubulature, and is so arranged that it can be
readily raised or lowered. Carbon dioxide is first passed
through the apparatus and then a current of dry chlorine
introduced. The phosphorus should be melted and suffi-
ciently heated to have an excess of phosphorus vapor rather
than of chlorine, as otherwise the excess of chlorine would
tend to form solid phosphorus pentachloride instead of the
liquid trichloride. The tube conducting the chlorine into
the retort is depressed until it nearly touches the Burfai
the melted phosphorus. The neck of the retort should be
tightly inserted in the neck of the filter-flask and a rubber
tube should conduct the issuing gas from the sulo tube to a
flue or some suitable absorption apparatus filled with concen-
trated sodium hydroxide solution. As the chlorine comes in
contact with the phosphorus vapor, it ignites and burns with
a feeble gi3enish flame. By raising the chlorine tube an
excess of chlorine may be introduced in the upper part of
the apparat us, when it will be seen that the neck of the retort
becomes coated with crystals of phosphorus pentachloride.
In order to avoid the excess of chlorine it is best to stop the
operation before all tin1 phosphorus is combined, finally cool-
ing the apparatus in a current of carbon dioxide.

P4 + 6 Cls = 4 PC1S.

Apparatus (Fig. G6, p. 148) ; r>00 cc. retort (tubulated); filter-flask ;
C02 generator ; CI supply; ice-water; yellow P.

44. Decomposition by water. — Phosphorus trichloride is a
colorless liquid somewhat heavier than water and not imme-
diately miscible with it.

Three cubic centimeters of the chloride are placed in a
test-tube and covered with 18 ec. of water. The phosphorus

PHOSPHORUS PENTACHLORIDE

261

trichloride remains in the bottom of the tube and does not
mix with the water. On warming the tube with the hand,
the water and the trichloride soon react, liberating bubbles of
hydrochloric acid gas, which are absorbed before they reach
the top of the liquid. By immersing the test-tube in ice-
water the reaction can be entirely stopped. Decomposition
again ensues on warming. If the decomposition is allowed
to continue, the liquid soon becomes warm, and ultimately
the phosphorus trichloride is completely converted to phos-
phorous and hydrochloric acids. The presence of phosphorous
acid may be established by adding a few drops of gold chlo-
ride solution, which will be reduced on warming.

PC13 + 3 H20 = H3PO3 + 3 HC1.

PCI3: ice-water ; AuCl3 solution.

PHOSPHORUS PENTACHLORIDE

PREPARATION

45. By the combustion of phosphorus in
chlorine. — A small piece of phosphorus is
lowered into a liter flask filled with dry
chlorine and provided with a cork carrying
a calcium chloride tube. The phosphorus
takes fire and burns in the excess of chlorine
to form phosphorus pentachloride, which will
remain as a white powder on the walls of the
flask (Fig. 108). In order to insure an excess
of chlorine a piece of phosphorus having a di-
ameter of not more than 2 mm. must be used.

P4 + 10 CI, = 4 PCI*

Deflagrating-spoon ; liter flask of dry CI ; cork
with CaCl3 tube ; 2 mm. piece of yellow P.

Fig. 108

262

CHEMICAL LECTURE EXPERIMENTS

46. By the action of chlorine on phosphorus trichloride. —
As was seen in Ex. 43 an excess of chlorine, when that ele-
ment is acting on phosphorus, produces the pentachloride
rather than the trichloride of phosphorus. Accordingly it
is only necessary in preparing the pentachloride to act on
the trichloride with an excess of chlorine.

The union of chlorine and phosphorus trichloride to form
the solid phosphorus pentachloride may be effected by pour-
ing 3 cc. of phosphorus trichloride into a liter flask filled
with dry chlorine. A cork carrying a tube filled with cal-
cium chloride (Fig. 108) is immediately inserted in the
neck of the flask, which is then allowed to stand. After a
few minutes the color will nearly all disappear from the
flask, and the phosphorus pentachloride will remain as a
solid mass on the bottom and walls.

PCI, + CI, = PCI,

Cork and CaCl2 tube ; liter flask of dry CI ; 3 cc. PCI3.

PROPERTIES

47. Sublimation. — Phosphorus penta-
chloride sublimes without melting. A
small quantity of the powder is heated

in a test-tube, which is loosely corked.
A sublimate soon appears on the upper
part of the tube.

48. Decomposition of phosphorus penta-
chloride by water. — If a small quantity
of water is allowed to drop on phosphorus
pentachloride, the decomposition is very

violent, resulting in the formation of the
oxychloride.

The apparatus shown in Fig. 109 con-

PHOSPHORUS BROMIDES 263

sists of a wide-mouthed bottle with a cardboard cover in
which an opening is made large enough to admit a test-
tube. A few grams of the pentachloride are placed in the
test-tube and 1 drop of water from a long bent glass tube
is allowed to fall upon it. To prevent particles of the
material from flying about, a large funnel having a cork in
its stem is suspended mouth downwards over the test-tube.
As more water is added, the conversion to phosphoric and
hydrochloric acids becomes complete, the liquid remaining
in the test-tube consisting of mixture of these two acids.

Phosphorus pentachloride, when allowed to drop into a
large mass of water, hisses and undergoes decomposition, re-
sulting in the formation of phosphoric and hydrochloric acids.

Apparatus (Fig. 109) ; PC15.

PHOSPHORUS BROMIDES

49. Preparation of phosphorus tribromide by the union of
phosphorus and bromine. — (a) Phosphorus and bromine
unite with explosive violence, and while no quantity of phos-
phorus tribromide can be prepared by this method, the inter-
action of the two elements may be shown by placing 1 cc.
of bromine in the test-tube of the apparatus (Fig. 109)
and introducing a 2 mm. piece of yellow phosphorus
by means of a long stick. The phosphorus is immediately
ignited, and as a rule blown out of the tube into the funnel.
Care must be taken to avoid danger from the burning phos-
phorus, and the hands should be protected with gloves.

P4 + 6 Br2 = 4 PBr3.

Apparatus (Fig. 109) ; long stick ; Br; yellow P.

(b) The explosive violence of the reaction between phos-
phorus and bromine may be considerably modified by add-
ing the bromine to phosphorus under water.

2G4 CHEMICAL LECTURE EXPERIMENTS

A 3 mm. piece of yellow phosphorus is placed in the test-
tube of the apparatus used in the preceding experiment and
covered with 10 cc. of water. Five drops of bromine are
poured from a test-tube on the end of a stick upon the phos-
phorus. The reaction is very vigorous, and a flame is seen
under the water as the two elements unite. In case the
bromine is not in excess, the presence of phosphorous acid in
the solution may be shown by testing with gold chloride
solution.

(c) Phosphorus, when lowered into bromine vapor, ignites
of itself and forms phosphorus tribromide, which, in exoi
of bromine, becomes converted to phosphorus pentabroroide.

A liter flask is filled with bromine vapor by introducing a
few drops of bromine and then wanning the flask to expel
the air. A 3 mm. piece of well-dried phosphorus is placed
in a deflagrating-spoon attached to a cork and then lowered
into the bromine vapor. After a few moments the phospho-
rus catches lire of itself and burns with a yellowish tlame.

Liter flask ; deflagrating-spoon; Br; P.

PHOSPHOROUS ACID

PREPARATION

50. By the slow oxidation of phosphorus. — The energetic

oxidation of phosphorus produces phosphorus pentoxide,
Which, in the presence of water, forms phosphoric acid. If

phosphorus is allowed to oxidize slowly in the air, as in Ex.
32, p. 33, in the preparation of ozone, the higher state of

oxidation is not reached and considerable quantities of phos-
phorous acid are formed. The water remaining in the flask
after the preparation of ozone, when tested with gold

chloride solution, shows the presence of phosphorous acid.
The ozone apparatus should be arranged and allowed to

PHOSPHOROUS ACID 265

stand, if possible, over night, when a strong test for phos-
phorous acid may be obtained.

P4 + 3 02 = 2 P203. [?]
3H20 + P203 = 2H3P03. [?]
Ozone apparatus (Fig. 14, p. 34) ; AuCl3 ; P.

51. By the action of phosphorus trichloride on water. —

Water reacts energetically with phosphorus trichloride, form-
ing phosphorous acid and hydrochloric acid. The hydro-
chloric acid liberated is to a large extent absorbed by the
water used in the operation, though, by boiling, the excess
of gas may be driven off, leaving a solution containing phos-
phorous and hydrochloric acids.

A few cubic centimeters of phosphorus trichloride are al-
lowed to fall from a dropping-funnel into 20 cc. of water in
a small distilling-flask. The dropping-funnel is inserted in
the neck of the flask in a one-holed rubber stopper, and the
side tube of the flask should be provided with a rubber tube
to conduct away the hydrochloric acid fumes that are formed.
As the phosphorus trichloride comes in contact with the
water, a vigorous reaction takes place and large quantities of
hydrochloric acid are liberated. On removing the dropping-
funnel and corking the neck of the flask, the contents may
be brought to a boil and the excess of hydrochloric acid
driven off. The liquid will now give strong tests for phos-
phorous acid. A small portion of the liquid heated in a
test-tube gives off first hydrochloric acid and then water.
Finally, if the heating is carried to a sufficient degree, the
phosphorous acid will decompose, yielding hydrogen phos-
phide, which may be ignited at the mouth of the test-tube.

PC13 + 3 H20 = H3P03 + 3 HC1.

Dropping-funnel ; 200 cc. distilling-flask ; PC13.

266 CHEMICAL LECTURE EXPERIMENTS

HYPOPHOSPHOROUS ACID

52. Preparation of the sodium or potassium salts by the
reaction between phosphorus and the alkaline hydroxides. —
See Exs. 27 and 28.

53. Reduction of sulphurous acid by sodium hypophosphite.

— Hypophosphorous acid and its salts are very strong re-
ducing agents. Sulphurous acid, itself a strong reducing
agent, is reduced by solutions of sodium hypophosphite.

Strong sulphur dioxide water is treated with a solution of
sodium hypophosphite and gently warmed in a test-tube.
The reaction requires a little time for its completion, but
soon a precipitate of sulphur is obtained.

Solution of NaHfPOi ; S02 water.

PHOSPHORUS PENTOXIDE AND PHOSPHO-
RIC ACIDS

54. Preparation of phosphorus pentoxide by combustion of
phosphorus in air. — See Ex. 26, p. 1>(.>.

55. Sublimation of phosphorus pentoxide. — Phosphorus
pentoxide, on heating, sublimes without melting.

A small quantity of the powder is placed in a clean, dry
test-tube and heated. The oxide sublimes on the upper
part of the tube, while the residue, which is combined with
a small quantity of water, melts in the form of glacial phos-
phoric acid.

56. Evolution of heat by the action of phosphorus pen-
toxide on water. — When water is added to phosphorus
pentoxide, sufficient heat is generated to ignite a piece of
guncotton.

PHOSPHORUS PENTOXIDE 267

A small heap of the pentoxide is placed on a watch-glass
and a piece of guncotton laid on it (Fig. 110). Water is
allowed to drop on the oxide from
the tip of a glass tube drawn out to
a fine jet. As the first drop of water
comes in contact with the powder,
the heat generated ignites the gun-
cotton.

Watch-glass ; P205 ; guncotton.

57. Preparation of phosphoric acids by the action of water
on phosphorus pentoxide. — Phosphorus pentoxide when
added to water combines with it, forming phosphoric acid.

Phosphorus pentoxide is allowed to fall in small quanti-
ties into 50 cc. of cold water in a beaker. As each particle
comes in contact with the water, it hisses. Not all the oxide
is dissolved, as white flocks appear in the liquid. The liquid
is divided into two equal parts, one of which is brought to
the boiling point; the other is filtered. On heating, the
white flocks all disappear, and the solution then contains or-
dinary orthophosphoric acid.

The filtrate from the filtered portion contains metaphos-
phoric acid, which gradually becomes converted to the ortho
acid. This conversion is, as might be expected, instanta-
neous upon heating.

3H20 + P205 = 2H3P04.
H20+P205 = 2HP03.

ARSENIC

1. Purification of commercial arsenic. — (a) Commercial
arsenic is generally a dull black, and in order to exhibit the
metallic lustre of this element the coating must be removed.
This is readily accomplished by heating the arsenic with a
strong solution of potassium dichromate to which some sul-
phuric acid has been added. Tin' purified material should
be washed thoroughly with water and then dried witli alco-
hol and ether.

Commercial As ; K2CrjOi solution ; alcohol ; ether.

(b) A solution of sodium hypochlorite may be used in
place of the acidulated potassium dichromate.

(c) The dull coating on commercial arsenic may also be
removed by heating the arsenic with a small quantity of
iodine in a hard-glass test-tube. The iodine first sublimes
and covers the arsenic with a yellowish coating of arsenic
iodide, which, on further heating, sublimes in the upper por-
tion of the tube as a reddish sublimate of arsenic tri-iodide.
The arsenic is by this operation purified, and remains as a
bright metallic-looking mass in the test-tube.

But a small quantity of iodine is needed for this operation,
and in a few minutes a large quantity of the impure com-
mercial arsenic may be rendered clean and bright.

Hard-glass test-tube ; As ; I.

208

AKSEXIC HYDRIDE 269

2. Sublimation. — Arsenic, though commonly obtained as
a dull black mass, sublimes on heating to form a crystal-
line metallic deposit.

A few pieces of arsenic are heated in a dry hard-glass test-
tube with the burner and the chimney shown in Fig. 2, p. 8.
A portion of the arsenic sublimes and condenses on the
upper part of the tube, that part of the sublimate nearest
the source of heat having a brilliant metallic lustre and crys-
talline structure, while farther up the tube the deposit is of
a dull gray amorphous nature.

Burner and chimney (Fig. 2, p. 8) ; hard-glass test-tube ; As.

ARSENIC HYDRIDE (ARSINE)

3. Preparation. — Nascent hydrogen reduces solutions
containing arsenic to arsenic hydride, which is given off as
a gas with the excess of hydrogen. The extremely poi-
sonous nature of this gas renders it necessary to prepare
it on a very small scale only, and to destroy it before it is
allowed to escape into the room.

A hydrogen generator may be set in operation and the
gas, after being conducted through a chloride of calcium
tube, may be ignited at a glass jet, taking all precautions to
prevent an explosion. Since the flame coloration is an
essential feature of this experiment, the tube should be
provided with a platinum tip or be replaced by a metallic
blowpipe jet, as otherwise the naturally colorless hydrogen
flame would melt the glass and become colored yellow with
sodium. On adding a few drops of a solution containing
arsenic the flame will be colored a bright blue by the pres-
ence of arsine in the issuing gas.

A much more satisfactory method of experimenting with
this gas is shown in Fig. 111. A small wide-mouthed bottle,

270

CHEMICAL LECTURE EXPERIMENTS

containing a few grams of granulated zinc covered with
water, is provided with a three-holed cork. Hydrogen is

conducted from a Kipp gener-
ator through a glass elbow in
one of the holes in the cork
and issues through a second
elbow provided with a calcium
chloride tube and a jet with
a platinum tip. A small this-
tle-tube is inserted in the third
hole of the cork, its lower end
being sealed with water. Hy-
drogen is conducted through the apparatus until all air
is removed, and then sufficient hydrochloric acid is poured
through the thistle-tube to produce a slow evolution of hydro-
gen in the bottle. On adding a few drops of a solution con-
taining arsenic, arsine will be formed and will be conducted,
along with the main hydrogen current, to the platinum jet,
where it will impart a blue color to the flame.

H generator; Kipp generator for H; apparatus (Fig. Ill); Zn ;
AsCl3 solution.

Fig. Ill

4. Decomposition by heat. — When arsine, or its mixture
with hydrogen, is conducted through a glass tube which is
strongly heated, the arsine is decomposed, liberating hydro-
gen, and arsenic is deposited on the colder portions of the
tube.

A jet is prepared by drawing a piece of 7 mm. hard-glass
tubing out to a fine point. The end of the fine jet is bent
at right angles, and the jet is then connected to the calcium
chloride tube in the apparatus (Fig. 111). On passing
hydrogen mixed with arsine through the tube and heating it
strongly with a Bunsen burner, the arsenic will be deposited
as a metallic mirror in the constricted portion of the tube.

ARSENIC SULPHIDE 271

If the current of arsine is not too rapid, all of the arsenic
may be deposited in this manner, and consequently the color
of the flame changed. For this purpose, however, it is bet-
ter to use a jet of the form shown in Fig. Ill, which is pref-
erably made out of hard-glass tubing. The hydrogen should
be ignited at the platinum jet and the characteristic color
of the arsine flame noted. On strongly heating the tube
half way between the bend and the calcium chloride tube,
the arsine will be decomposed, the arsenic deposited between
the flame and the bend, and the color of the arsine flame
will disappear, leaving the colorless flame of hydrogen.

4 AsH3 = As4 + 6 H2.

AsH3 apparatus (Fig. Ill) ; hard-glass tubing (7 mm.); Pt jet.

5. Deposition of arsenic by cooling a flame containing
arsine. — If a cold porcelain dish is held in the flame of
arsine burning at the jet in Fig. Ill, arsenic will be depos-
ited as a dark, metallic-appearing spot, which may be
removed by the addition of a few drops of sodium hypo-
chlorite solution, or by gently warming with nitric acid of a
specific gravity 1.25. (For further consideration of arsenic
spots, see under antimony, Ex. 3.)

ARSENIC SULPHIDE

6. Commercial arsenic sulphide in white fire. — Two parts
of commercial arsenic sulphide (realgar, As2S2), when
mixed with two parts of sulphur flowers and four parts of
potassium nitrate, form a mixture which, on ignition, gives
an intense white light.

Powdered realgar ; KN03 ; S flowers.

272

CHEMICAL LECTURE EXPERIMENTS

ARSENIC TRIOXIDE

7. From the combustion of arsenic in oxygen. — Arsenic,
when strongly heated in an atmosphere of oxygen, burns,

forming arsenic trioxide.

The combustion of arsenic in oxygen
' and the sublimation of the arsenic tri-
oxide are shown by heating a small
quantity of the element in a 40 cm.
glass tube 15 mm. internal diameter,
sealed at one end. The tube is fitted
with a two-holed cork carrying a long
elbow extending nearly to the bottom
of the tube and a short glass elbow con-
nected with a flue (Fig. 112). The tube
is clamped in an inclined position and
a current of oxygen conducted through
it. On heating the arsenic, it catches

^^ 1 fire and burns brilliantly. Some of the

FlG 112 arsenic is volatilized and deposited as a

crystalline sublimate in the cooler por-
tions of the tube. A considerable quantity of the arsenic
trioxide formed is deposited as a white sublimate in the

tube.

As4 + 3 02 = 2 As203.

40 cm. glass tube 15 mm. diameter ; cork and tubes ; 0 supply j As.

ANTIMONY

1. Fusibility. — Antimony is easily melted with a blow-
pipe by directing the flame npon a small piece of the metal
placed in a cavity scooped out of a piece of charcoal. The
strongly heated globule, if allowed to fall upon a piece of
white paper, breaks into numerous small globules, which
run in all directions, each globule charring the paper over
which it runs. A large pasteboard box cover may be used,
or the edges of the paper may be turned up to prevent the
particles of antimony from running all over the table.

White paper or box cover ; blowpipe ; charcoal ; Sb.

2. Combustion of powdered antimony. — Pulverized anti-
mony, when blown through a Bunsen flame, burns brilliantly,
giving a white light. The finely powdered metal is placed in
a glass elbow, such as is described in Ex. 18, p. 24, and blown
lengthwise through the flame, either by a puff of air from
the mouth or better by oxygen from a cylinder.

Glass elbow ; powdered Sb ; O supply.

ANTIMONY HYDRIDE (STIBINE)

3. Preparation. — The preparation of pure antimony
hydride is never attempted, as hydrogen containing a small
quantity of the gas gives all the characteristic tests of the
hydride itself. When hydrogen is generated in solutions

t 273

274 CHEMICAL LECTURE EXPERIMENTS

containing antimony, a portion of the antimony is converted
to stibine, which escapes with the hydrogen.

The apparatus used is similar to that described for arsine
(Ex. 3, p. 270). Hydrogen is generated in an Erlenmeyer
flask, fitted with a cork and a thistle-tube, by means of zinc
and sulphuric acid. The issuing gas is dried with calcium
chloride and burned at a jet. A few drops of antimony
chloride solution are introduced through a funnel, and in a
few moments the color of the flame will be considerably
changed and a white smoke, consisting chiefly of antimony
trioxide, will ascend. The reactions of stibine are very simi-
lar to those of arsine.

A cold porcelain dish held in the flame produces a dull
black deposit of antimony, distinguished from the arsenic
spots, which have a more metallic lustre, by being insoluble
in a solution of sodium hypochlorite.

If the gas is conducted through a heated glass tube, the
antimony will be deposited as a black mirror on the tube ;
but while arsenic is only deposited on that portion of the
tube nearer the exit, antimony will be deposited on both
sides of the heated portions of the tube.

The gas, when conducted through a glass elbow dipping
into a beaker of silver nitrate solution, produces a black
precipitate of silver antimonide.

The distinction between the reactions of the arsenic and
antimony spots with sodium hypochlorite is markedly shown
by holding a white dinner plate in the stibine flame and
moving it in such a way that the symbol of antimony (Sb)
will be written in the form of a black deposit on the plate.
The plate should then be held in an arsine flame and the
antimony entirely covered with a deposit of arsenic. On pour-
ing sodium hypochlorite solution into the plate, the arsenic
deposit is completely dissolved, and the antimony deposit
unaffected stands out as originally deposited.

ANTIMONY TRISULPHIDE 275

If arsine as well as stibine is present in the burning hy-
drogen, both elements will be deposited on a cold dish held
in the flame. If, however, the dish is held in a vertical
position and the spot deposited in an elongated form, the
arsenic, by reason of its greater volatility, will be chiefly de-
posited in the upper portions of the spot. If sodium hypo-
chlorite is allowed to act on such a deposit, the outer and
upper portions will be seen to disappear, while the lower
portions, consisting as they do, chiefly of antimony, remain

unacted upon.

r 2 SbH3 = 2 Sb + 3 H2.

4 AsH3 = As4 + 6 H2.

Erlenmeyer flask ; thistle- and delivery-tubes ; evaporating-dish ;
plate ; hard-glass tube ; SbCl8 sol. ; NaCIO sol. ; AsH3 generator.

ANTIMONY CHLORIDES

4. Combustion of antimony in chlorine. — Finely divided
antimony burns brightly in chlorine, forming antimony
trichloride and pentachloride.

A small quantity of antimony powder is sifted from a
cheese-cloth bag into a 500 cc. cylinder filled with chlorine
and placed in a strong draft. As each particle of antimony
falls into the chlorine, it burns with a bright light, forming
antimony trichloride, which, in the presence of an excess of
chlorine, is converted to the pentachloride.

2 Sb + 3 Cl2 = 2 SbCl3.

2Sb + 5Cl2 = 2SbCl5.

Jar of CI ; finely powdered Sb.

ANTIMONY TRISULPHIDE

5. Combustion in a current of oxygen. — Antimony trisul-
phide, owing to the oxidizable nature of both of its elements,

276 CHEMICAL LECTURE EXPERIMENTS

burns brilliantly in oxygen, forming antimony trioxide and
sulphur dioxide.

Dry antimony trisulphide is heated in a bulb-tube in a
current of oxygen. The sulphide soon takes fire and burns
brilliantly. The issuing gas may be tested for the presence
of sulphur dioxide by a paper dipped in potassium dichro-
mate solution. The antimony trioxide formed is given off
as a white smoke, which escapes from the tube, though a
portion of the oxide is deposited as a white sublimate.

2 Sb2S3 + 902 = 2 SbA + G S02.

Bulb-tube ; 0 supply ; K2Cr207 solution ; Sb2S3.

6. Combustion in fused potassium nitrate. — Antimony
sulphide is readily oxidized by being dropped into fused
potassium nitrate. A small quantity of the potassium
nitrate is fused in a hard-glass test-tube which is clamped
in a vertical position, and antimony sulphide in the form
of a fine powder is shaken into the tube. As the sulphide
comes in contact with the potassium nitrate, it burns with
a brilliant light. Potassium chlorate may be substituted
for potassium nitrate.

Hard-glass test-tube, clamped ; KN03 ; KCIO3 ; Sb2S3.

7. Use in Bengal fires. — Native antimony sulphide,
when powdered and mixed with sulphur flowers and potas-
: /mm nitrate, gives on ignition an intense white light.

One gram of finely powdered stibnite is mixed on a paper
with 2 g. of flowers of sulphur and 7 g. of finely pow-
dered potassium nitrate, avoiding all unnecessary press-
ure or friction. The mixed powder is placed on an asbestos
paper or brick in a strong draft and ignited with a piece of
touch-paper.

Powdered stibnite ; S flowers ; powdered KN03 ; touch-paper.

ANTIMONY TRISULPHIDE 277

8. Preparation of antimony cinnabar. — An oxysulphide
of antimony of complex composition, possessing a beautiful
color and called antimony cinnabar, is obtained by slowly
heating a solution of antimony chloride with a solution of
sodium thiosulphate. Antimony chloride solution, to which
the least possible quantity of hydrochloric acid has been
added, is mixed in a flask with a solution of sodium thiosul-
phate and slowly heated with constant stirring to 90° on a
water-bath. After a few minutes the red precipitate appears.

Water-bath ; thermometer j SbCl3 sol. ; Na2S203.

BOKON

1. Preparation of boron by the reduction of boric anhy-
dride by magnesium. — Magnesium powder reduces boric
anhydride at a high temperature, forming magnesium oxide
and amorphous boron.

Equal volumes of finely powdered magnesium and finely
pulverized boric anhydride are mixed in a hard-glass test-
tube and strongly heated in a blast-lamp. The ignition tube
should not be more than one-fourth filled with the mixture,
and should be continually rotated while being heated.
Soon a temperature will be reached at which the reaction
begins, and immediately the contents of the tube glow. The
tube is allowed to cool, is then broken, and the contents
digested with pure dilute hydrochloric acid without warm-
ing. The excess of magnesium and the magnesium oxide
are dissolved, leaving a black powder of amorphous boron,
which is filtered off and allowed to dry on the paper.
Preserve paper for use in the next experiment.

B203 + 3 Mg = 3 MgO + 2 B.

Ignition-tube ; B203 powdered ; Mg powder.

2. Combustion of boron in the air. — Amorphous boron,
when strewn into a Bunsen flame, burns brilliantly. A
small quantity of the amorphous powder is sifted through
a Bunsen flame or blown through a glass elbow (Ex. 18, p. 24)
into the flame.

278

BOKON

279

(p=*%jr=^

The filter-paper, on which the amorphous powder obtained
in the preceding experiment was collected and dried, retains
a considerable quantity of the powder and, when ignited,
the particles of boron burn with scintillations.

Glass elbow ; filter-paper from preceding experiment ; amorphous B.

3. Preparation of boron trifluoride. — Hydrofluoric acid
gas reacts with boron anhydride, forming boron trifluoride.

Hydrofluoric acid gas is generated in the presence of boric
anhydride by heating a mixture of 24 g. of powdered
calcium fluoride, 10 g.
of powdered boric anhy-
dride, and 20 g. of con-
centrated sulphuric acid
in a 100 cc. Jena glass
Erlenmeyer flask. A one-
holed cork, carrying a
glass elbow, is inserted
in the neck of the flask
and two dry cylinders

are arranged as in Fig. 113. Provision is made for con-
ducting the escaping gas into a flue. The flask is then
gently heated, and the boron trifluoride evolved soon expels
the air from the flask and the two cylinders, and fumes
strongly in the air as it escapes into the flue. The corks
are then withdrawn from the cylinders, which are quickly
covered with glass plates.

H3BO3 + 3 HF =BF3 + 3 H20.

Apparatus (Fig. 113) ; 100 cc. Jena glass Erlenmeyer flask; two
200 cc. cylinders ; CaF2 powdered ; B203 powdered.

4. Properties of boron trifluoride. — A cylinder of the
gas, when opened to the air, gives off dense white fumes,
which are acid to litmus paper.

Fig. 113

280 CHEMICAL LECTURE EXPERIMENTS

A cylinder of the gas is opened with its month under
water. The gas is absorbed, water rising in the cylinder
with almost explosive violence.

5. Preparation of boric acid from borax. — Hydrochloric
acid decomposes sodium diborate (borax), setting free boric
acid, which, owing to its insolubility in cold water, may be
easily crystallized therefrom.

Sixty grams of borax are dissolved in 240 cc. of boiling
water, and concentrated hydrochloric acid is added to the
alkaline solution until the reaction is decidedly acid to
litmus. The beaker is then immersed in a large vessel of
cold water, and the boric acid on cooling, separates out in
large crystals.

Na2B407 + 2 HC1 + 5 H20 = 2 NaCl + 4 H3BOs.

Large vessel of cold water ; Na2B407 ; litmus paper (blue).

6. Dehydration of boric acid by heat. — Boric acid, when
strongly heated in a crucible, loses water and fuses to a
colorless anhydride which resembles melted glass.

A platinum crucible is half filled with crystallized boric
acid and gently heated with a Bun sen flame. Large quan-
tities of water vapor are evolved, and on increasing the heat
the contents of the crucible are fused to a colorless liquid.
If a glass rod dipped in the melted mass is withdrawn, a
portion of the liquid will adhere to it and be drawn up
as a fine thread, which, on cooling, solidifies. When cold,
the contents of the crucible become hard as glass and are
best removed by dissolving in water.

2 H3BO3 = B A + 3 H20.

Pt crucible ; H3BO3.

7. Action of boric anhydride on water. — Twenty-five
grams of powdered boric anhydride, when mixed with 30

BORON

281

cc. of water, combine with the water to form boric acid, with
the liberation of great heat. An ether thermometer, such as
was shown in Fig. 75, p. 174, when thrust into the liquid,
becomes so heated that ether vapor is driven out of the top
of the tube and may there be ignited. Considerable water
vapor escapes into the air as a result of the heat from the
reaction. ^ + 3 ^ = 2 -^^

Ether thermometer (Fig. 75, p. 174) ; finely powdered B203.

8. Decomposition of sodium chloride by boric acid. —

Though hydrochloric acid decomposes solutions of borates
with the liberation of boric acid, boric acid will, when fused
with sodium chloride, drive off the hydrochloric acid, form-
ing sodium borate. This reaction is due to the non-volatile
nature of the boric acid.

Equal volumes of fused, pulverized so-
dium chloride and powdered boric acid
are strongly heated in a crucible. Water
is first driven off from the boric acid, and
finally hydrochloric acid fumes are evolved.
The presence of hydrochloric acid is easily
established by blue litmus paper or a rod
moistened in strong ammonium hydroxide.

Porcelain crucible ; fused and powdered NaCl ;
H3BO3 powdered.

9. Coloration of an alcohol flame by boric
acid. — Alcohol, to which a small quantity
of a solution of boric acid has been added,
is poured over some asbestos in an evapo-
rating-dish. On igniting the liquid it burns
with a green flame.

A much larger flame may be obtained
by boiling the mixture of alcohol and boric Fig. 114

282 CHEMICAL LECTURE EXPERIMENTS

acid and igniting the vapor. Three grams of finely powdered
borax are mixed with 3 cc. of concentrated sulphuric acid
and 20 cc. of ethyl alcohol in a 50 cc. flask, fitted with a
one-holed cork carrying a short piece of glass tubing (Fig.
114). A piece of combustion tubing, 10 cm. long and 15 to
20 mm. in diameter, is vertically clamped over the small
glass tube through which the vapor of alcohol is issuing.
The alcohol vapor mixes with air drawn in at the lower
end of the combustion tube and burns, when ignited, in a
large flame at the top of the tube. The intense green color
produced by the presence of boric acid is strikingly shown.

50 cc. flask ; cork and short tube ; 10 cm. length of combustion
tubing ; Na2B407 ; alcohol.

SILICON

1. Preparation by the reduction of silicon dioxide by mag-
nesium powder. — Silicon dioxide, when mixed with finely
powdered magnesium and strongly heated in an ignition-
tube, is reduced by the magnesium to silicon. In case the
magnesium is in excess, the silicon and magnesium unite to
form magnesium silicide.

The reduction is well shown by heating 1 g. of clean, dry,
fine, white sand with 1.5 g. of fine magnesium powder. The
mixture is placed in a hard-glass test-tube, which is gradually
heated by constant rotation in the flame. As the tempera-
ture increases, a point will finally be reached at which the
reaction starts, and it then proceeds throughout the whole
mass, which glows vividly. The black residue in the tube
consists chiefly of magnesium silicide.

The preparation of a considerable quantity of crude sili-
con, which is used in Ex. 7, is easily accomplished by heat-
ing a mixture of 100 g. of dry, fine sand with 50 g. of
magnesium power in a Hessian crucible over a blast-lamp.
It is of the greatest importance that the materials should be
perfectly dry. An asbestos cover and an iron plate should
be laid on top of the crucible. The mixture is carefully
heated, and the reduction, when once started, proceeds of
itself. This product, owing to the deficiency of magnesium
in the mixture, contains but a small quantity of magnesium

283

284 CHEMICAL LECTURE EXPERIMENTS

silicide. After cooling, the product should be treated with
dilute hydrochloric acid to destroy any traces of magnesium
silicide formed, washed carefully with water, and dried ready
for use. gi()2 + 2 Mg = 2 MgO + Si.

Ignition-tube ; Hessian crucible ; asbestos ; iron cover ; blast-lamp ;
fine sand ; fine Mg powder.

2. Preparation of magnesium silicide. — Silicon dioxide,
reduced with an excess of magnesium, forms magnesium
silicide.

Twenty grams of magnesium powder are mixed with 12 g.
of fine, dry sand and heated over a Bunsen burner in an
iron saucer. The mixture should be covered with a piece of
asbestos paper to prevent the entrance of air. On strongly
heating with the burner the reduction is completed and a
product rich in magnesium silicide is obtained. The material
should be powdered and placed in a dry, tightly stoppered
bottle. 4 Mg + gi0j _ 2 MgQ + giMfo

Iron saucer ; asbestos paper ; bottle ; magnesium powder ; fine,
dry SiOa.

SILICON HYDRIDE

3. Preparation of silicon hydride from magnesium silicide
and hydrochloric acid. — (a) Magnesium silicide reacts with
hydrochloric acid, with the liberation of silicon hydride, a
spontaneously inflammable gas.

A small quantity of pulverized magnesium silicide is sifted
into 10 cc. of concentrated hydrochloric acid in a 50 cc. cyl-
inder. The gas liberated catches fire on exposure to the air.

The cylinder may be filled with oxygen, thus having an
atmosphere of oxygen rather than air above the hydrochloric
acid. The reaction on adding magnesium silicide is very
sharp.

SILICON HYDRIDE

285

(b) A considerable quantity of silicon hydride may be
prepared and burned at a jet by means of the apparatus,
Fig. 115. A 300 cc. bottle fitted with a two-holed rubber
stopper is completely filled with water and a few grams of
magnesium silicide, prepared as in the preceding experiment,
are placed on the bottom. A straight glass
tube extends through the cork nearly to
the bottom of the bottle, and is fitted by
means of a cork to the tubulature of an
inverted 500 cc. bell-jar. A glass elbow,
inserted in the second hole of the cork,
is connected by means of a rubber tube
and pinch-cock with a glass jet 2 mm.
internal diameter. Twenty cubic centi-
meters of concentrated hydrochloric acid
are poured into the bell-jar, and, flowing
down through the straight glass tube, come
in contact with the magnesium silicide. The silicon hydride
formed collects in the top of the bottle and forces the liquid
up into the bell-jar. By carefully opening the pinch-cock
a stream of silicon hydride, mixed with some hydrogen,
escapes. On coming in contact with the air the gas sponta-
neously ignites, burning with a bright flame.

An iron plate held in the upper part of the flame becomes
covered with a white deposit of silicon dioxide, one of the
products of combustion.

A white porcelain dish held in the lower part of the flame
is covered with a brown deposit of amorphous silicon.

Fig. 115

SiMg2 + 4 HC1 = 2 MgCl2 + SiH,.

SiH4 + 2 02 = Si02 + 2H20.

Apparatus (Fig. 115); 300 cc. bottle; bell-jar ; tubes and pinch-
cock ; iron and porcelain dishes ; SiMg2.

286 CHEMICAL LECTURE EXPERIMENTS

(c) Silicon hydride mixed with varying amounts of hydro-
gen (which for most experiments does no harm) may easily be
obtained by using as a generator a small three-necked Wolff
bottle, in which the magnesium silicide is placed and cov-
ered with water. Hydrogen from the Kipp generator
enters through a glass elbow, which is thrust into one neck
of the bottle and extends beneath the surface of the water.
A dropping-funnel in the middle neck contains concentrated
hydrochloric acid, while the third neck is provided with a
cork and a delivery -tube. Hydrogen is first passed through
the apparatus to drive out all air, and then concentrated
hydrochloric acid is allowed to fall upon the magnesium
silicide. The silicon hydride generated, mixed with con-
siderable quantities of hydrogen, passes out through the
delivery-tube and ignites upon coming in contact with the
air. By carefully regulating the flow of hydrogen from the
Kipp generator quite pure silicon hydride may be obtained.

500 cc. three-necked Wolff bottle ; dropping-funnel ; cork and deliv-
ery-tube ; H generator.

4. Decomposition by heat. — Hydrogen containing silicon
hydride or the pure gas, silicon hydride, is passed through
a glass tube, which is strongly heated. A deposition of
brown, amorphous silicon is obtained.

5. Combustion in the air. — A cylinder of silicon hydride
is collected over water, covered with a glass plate, and placed
mouth upwards on the table. On removing the plate, the
gas ignites of itself and burns. Owing to the deficiency of
air, a deposit of brown amorphous silicon is left on the
inside of the cylinder.

6. Explosion with air or oxygen. — Air or oxygen, when
allowed to enter a confined volume of silicon hydride, pro-
duces an explosion.

SILICON TETRACHLORIDE

287

Twenty cubic centimeters of silicon hydride are collected in
a 100 cc. cylinder, and one or two bubbles of air are allowed
to rise inside the cylinder. A sharp explosion is obtained.

If oxygen is admitted to a confined volume of the hydride,
the greatest care must be exercised that not more than one
bubble is introduced at a time.

The conditions of this experiment may be reversed and a
bubble of silicon hydride allowed to enter a confined volume
of air or oxygen. The introduction of silicon hydride is
best made from the apparatus of Fig. 115, p. 285, which
admits of a careful regulation of the flow of the gas.

Pneumatic trough ; cylinders ; 0 supply ; SiH4 supply.

SILICON TETRACHLORIDE

7. Preparation by the action of chlorine on crude silicon. —
A quantity of dry, crude silicon, prepared as in Ex. 1, is placed

Fig. 116

in a 50 cm. length of combustion tubing, through which dry
chlorine is conducted (Fig. 116). As the quantity of silicon

288 CHEMICAL LECTURE EXPERIMENTS

tetrachloride formed varies greatly with the temperature,
it is necessary to heat the tube in an air-bath consisting of
a tin or sheet-iron trough covered with a piece of asbestos
paper. A thermometer is placed in the air-bath, which
should be heated by means of a four-tube burner to 345° C.
The issuing gas is conducted through a U-tube immersed in
ice-water, and the silicon tetrachloride condenses to a light
yellow liquid.

Si + 2 Cl2 = SiCl4.

50 cm. length combustion tubing ; air-bath ; four-tube burner ; ther-
mometer ; U-tube immersed in ice- water; CI generator (Fig. 39,
p. 81) ; crude silicon from Ex. 1.

8. Decomposition by moisture. — (a) Silicon tetrachloride
fumes strongly in the air, from which it abstracts moisture.
The reaction is accompanied by a liberation of hydrochloric
acid and a white powder consisting of silicic acid remains. A
few cubic centimeters of the liquid are poured into a glass
crystallizing dish and are allowed to stand exposed to the
air. A piece of moist blue litmus paper is immediately red-
dened when exposed to the fumes. When the reaction is
complete, a white powder is left in the bottom of the dish.

Glass crystallizing dish ; litmus paper (blue) ; SiCl4.

(b) Silicon tetrachloride unites directly with water, form-
ing hydrochloric acid and gelatinous silicic acid.

A few drops of the tetrachloride are allowed to fall into
2 cc. of water in a test-tube. Gelatinous silicic acid is
formed and hydrochloric acid escapes.

SiCl4 + 4 H20 = H4Si04 + 4 HC1.

SILICON TETRAFLUORIDE 289

SILICON TETRAFLUORIDE AND HYDRO-
FLUOSILICIC ACID

9. Preparation of silicon tetrafluoride. — When hydro-
fluoric acid gas is generated in the presence of silicon
dioxide, silicon tetrafluoride is formed.

Thirty grams of finely pulverized calcium fluoride are
mixed with an equal weight of fine sand and heated with
sufficient concentrated sulphuric acid to make a thin paste.
The mixture is placed in a 250 cc. flask fitted with a two-
holed rubber stopper. "A double safety-funnel, such as is
shown in Fig. 85, p. 196, containing mercury, is placed in
one hole of the stopper, and the issuing gas is conducted
through a glass elbow in the second hole to the bottom of a
dry 400 cc. cylinder arranged as in Fig. 113, p. 279. Two
cylinders are placed in series and filled with the dry gas by
gently heating the flask.

Si02 + 4 HF = SiF4 + 2 H20.

250 cc. flask ; two-holed rubber stopper ; safety-funnel ; two 400 cc.
dry cylinders ; fine Si02 ; finely pulverized CaF2 ; Hg.

10. Silicon tetrafluoride is a non-supporter of combustion. —

A burning candle thrust into a jar of silicon tetrafluoride is
immediately extinguished. The gas itself does not burn.

Candle on wire ; jar of SiF4.

1 1 . Decomposition of silicon tetrafluoride by water vapor. —

Silicon tetrafluoride is decomposed by the action of water,
forming hydrofluosilicic and silicic acids. A jar of silicon
tetrafluoride, when opened in moist air, fumes strongly.

A glass rod moistened with water, when lowered into a
jar of the gas, will become covered with a deposit of white
silicic acid.

290 CHEMICAL LECTURE EXPERIMENTS

If silicon tetrafluoride is slowly conducted into the lower
end of a vertically clamped piece of combustion tubing 60 cm.
long, the decomposition of the gas by water-vapor may be
more strikingly shown. Moisture should be introduced into
the combustion tube just before use by blowing through it
with the mouth. As the gas slowly rises in the tube, the
walls become covered with a white deposit of silicic acid.

60 cm. length of combustion tube ; jars of SiF4 ; SiF4 supply.

12. Preparation of hydrofluosilicic acid by the action of
silicon tetrafluoride on water. — Silicon tetrafluoride is con-
ducted into water, and, to prevent the stoppage of the tube
by the silicic acid formed, the end should dip under a
2 cm. layer of mercury. The mercury may also be placed
in a small crucible in the bottom of the cylinder. As each
bubble of gas rises through the water it becomes coated with
a film of silicic acid, which collects as a froth on the surface
of the water.

3 SiF4 + 4 H20 = H4Si04 + 2 H2SiF6.
200 cc. cylinder ; small porcelain crucible ; SiF4 supply ; Hg.

CARBON

1. Preparation of charcoal by heating organic material
out of contact with the air. — Organic material, when heated
out of contact with the air, loses a great part of its water
and becomes converted to charcoal.

(a) A few small pieces of wood are placed in the bottom
of a small Hessian crucible, covered with a layer of fine
sand, and strongly heated till no more fumes are given off.
The combustible nature of the gases evolved may be shown
by igniting them. The crucible is allowed to become cool,
the sand is shaken out, and the small pieces of charcoal
removed. The great shrinkage in the wood may be shown
by having a number of pieces of wood of the same size, of
which only a part are heated.

(b) Sugar may be charred in a porcelain crucible and the
carbonaceous residue exhibited.

Hessian crucible ; porcelain crucible ; sand ; small pieces of wood ;

2. The electrical conductivity of carbon. — The electrical
conductivity of the various forms of carbon may be shown
by closing an electric circuit with a piece of charcoal, a bit

291

292

CHEMICAL LECTURE EXPERIMENTS

of electric-light carbon, a pencil sharpened at both ends, and
a piece of graphite. A fine piece of iron wire or a piece of
platinum wire, such as is used in suspending Welsbach
mantles, connects the two upright wires shown in Fig. 22,
p. 53. Four or five cells of a bichromate battery are con-
nected with the terminals of these wires, leaving a gap in
the circuit which can be closed by the carbon conductors.
On closing the circuit, the platinum wire will be heated to
redness or even melted, while the iron wire, if used, will be
ignited and burn in the air. The circuit between a dry bat-
tery and an electric bell may be used in place of the platinum
wire and large battery.

Wires on block (Fig. 22, p. 53) ; bichromate battery ; fine Fe or Pt
wire ; pieces of charcoal ; electric-light carbon rod ; lead-pencil ;
graphite.

3. The absorption of hydrogen sulphide by charcoal. —

(a) Air from a water-blast or gasometer is conducted
through a gas washing-bottle one-third filled with a strong
aqueous solution of hydrogen sulphide. A T-tube connects
the gas washing-bottle with an 80 cm. length of combustion

*feffigapgfc^ c| l}=^>

Fig. 117

tubing filled with coarsely pulverized charcoal. The stem
of the T-tube is connected by means of a short piece of rub-
ber tubing and a pinch-cock with a glass tube dipping into
a dilute solution of lead acetate in a beaker (Fig. 117). The
other end of the combustion tube is provided with a cork and
a glass elbow dipping into a beaker containing lead acetate

CARBON 293

solution. By opening the pinch-cock and closing the end of
the combustion tube, the air containing hydrogen sulphide is
caused to bubble through the lead acetate solution, produc-
ing a black precipitate. On closing the pinch-cock, the air
and hydrogen sulphide proceed through the combustion-tube
filled with charcoal, and then bubble through the lead acetate
solution in the beaker at the end of the combustion-tube.
Here it will be observed that no discoloration will take place,
as all the hydrogen sulphide has been absorbed by the char-
coal. The rate at which the air is conducted through the sys-
tem should not be too fast to admit of counting the bubbles.

Gas washing-bottle ; 80 cm. length of combustion tubing ; current
of air ; H2S solution ; coarsely pulverized charcoal.

(6) Bone-black absorbs gases from their solution in water
as well as from air, and if a weak solution of hydrogen* sul-
phide is shaken with an excess of bone-black and then filtered,
it will be found that the filtrate will no longer smell of the
gas nor give any of its reactions.

H2S solution ; bone-black.

4. Absorptive power of carbon for coloring matter. —

The use of finely divided carbon, especially in the form of
bone-black, in decolorizing liquids is shown by boiling 50 cc.
of litmus solution with 10 g. of bone-black. On filtering off
the bone-black, the filtrate will be found to be colorless.

If double the quantity of bone-black is used and the flask
is vigorously shaken, the application of heat is unnecessary.

The bone-black may be placed in a vertically clamped
wide glass tube having a layer of asbestos next the one-holed
cork in the lower end. If litmus solution is allowed to per-
colate slowly through the long layer of bone-black, the color
is discharged.

40 cm. length tubing (15 mm. diameter) ; asbestos ; bone-black ;
litmus solution.

294 CHEMICAL LECTURE EXPERIMENTS

5. Absorption of salts from their solutions by bone-black. —

Finely divided carbon removes salts, as well as coloring mat-
ters, from solutions, as can be seen by boiling 100 cc. of a
solution of lead nitrate containing .5 g. of salt to the liter
with 10 g. of animal charcoal. On filtering off the liquid,
the addition of a solution of hydrogen sulphide to the clear
filtrate will produce no precipitate, while the original solu-
tion will yield, on the addition of hydrogen sulphide, a
black precipitate of lead sulphide.

A solution of acid sulphate of quinine possessing a de-
cidedly bitter taste may be similarly treated with animal
charcoal, and afterward the filtrate will no longer taste of
quinine.

.5 g. Pb(N03)2 in 1 1. of water; bone-black; acid sulphate of qui-
nine.

6. Combustion of graphite in oxygen. — In spite of the
great fire-resisting properties of graphite, it will, when
heated to a sufficiently high temperature, burn in an
atmosphere of oxygen to form carbon dioxide.

A small piece of pipe-stem or fire-brick is fastened to a
piece of stout wire, which is in turn fastened to a cork. A
hollow should be made in the brick, by means of a file and
a small piece of graphite laid in it. By directing a jet of
oxygen through a glass tube, held in a small gas or candle
flame, sufficient heat will be developed to ignite the graphite.
When glowing strongly in the air, the graphite is lowered
into a wide-necked flask filled with oxygen by displace-
ment, where it will continue to glow and burn to carbon

dioxide.

C + 02 = C02.

200 cc. flask (wide-necked) ; fire-brick or pipe-stem ; stout wire ;
O supply ; graphite.

CARBON 295

7. Combustion of a diamond in oxygen. — Diamond, like
other forms of carbon, when heated strongly, burns in
oxygen to form carbon dioxide.

A piece of pipe-stem, 1 cm. long, is hollowed a little
in one end with a file and the hole plugged with a piece
of asbestos paper. A copper wire is bent like a hook
and the pipe-stem fitted on the end. The wire is fastened
to a cork fitting a 250 cc. wide-mouthed flask filled with
oxygen, and is cut at such a length that when the cork rests
in the neck of the flask the bend in the wire nearly touches
the bottom. The diamond l is placed in the hollow in the
upper end of the pipe-stem and heated to incandescence with
a small gas flame, through which a gentle current of oxygen
is directed (Fig. 118). The table should be
covered with a large piece of glazed paper,
such as is used in transferring precipitates,
to catch the diamond in case it should be
shaken off the wire. When the diamond is
strongly glowing, the gas flame may be ex-
tinguished and the stream of oxygen allowed
to play upon it. The combustion is very
vivid. The oxygen stream should then be
cut off and the diamond allowed to cool in Fig. 118
the air. It will be seen that the glowing
almost immediately stops. On again heating the diamond
and lowering it into the flask of oxygen, it will glow for
some little time, and the presence of carbon dioxide in the
flask may be established by adding 20 cc. of a solution of
barium hydroxide and shaking the flask. A precipitate of
barium carbonate will be formed.

1 Small crystals of diamond, with the longer axis approximately
2 mm. long, maybe obtained of George L. English & Co., 3 and 5 West
18th St., New York City, at a cost of 25 cents per crystal. Crystals
of this size and cost have been used by the writer and are large enough
to give good results in this experiment.

296 CHEMICAL LECTURE EXPERIMENTS

To prevent the possible introduction of carbon dioxide
into the flask from the flame used in heating the diamond,
it is best to cut off the gas supply and allow the diamond to
glow in the jet of. pure oxygen a moment before lowering it
into the flask. The flask should be filled with oxygen by
displacement, in order to avoid wetting the interior.

250 cc. wide-mouthed flask ; wire and pipe-stem ; O jet ; small crys-
tal or fragment of diamond ; Ba(OH)2 sol.

8. Oxidation of carbon at low temperatures. — The oxida-
tion of carbon at the temperature of the room is interestingly
shown by electrolyzing dilute sulphuric acid in an electro-
lytic apparatus, using carbon electrodes (Ex. 24, p. 95). It
will be found that, while there is a very vigorous evolution
of hydrogen from the negative pole, there will be very little,
if any, gas ascend from the positive pole. If the two elec-
trodes are carefully filed and rubbed with emery paper
before the experiment, the positive electrode will be found
to be considerably corroded, while the negative electrode
will appear unacted upon. The disintegration of the posi-
tive electrode is further made apparent by the presence of
small particles of carbon in the liquid and on the rubber
stopper holding the electrode.

Electrolytic apparatus (Fig. 46, p. 95), with carbon electrodes ;
10 per cent H2SO4 ; battery.

CARBON MONOXIDE

PREPARATION

9. From carbon dioxide and carbon. — Carbon dioxide,
when passed over heated carbon, becomes reduced to car-
bon monoxide.

Coarsely pulverized charcoal is placed in a 30 cm. length
of combustion-tubing, and a gentle current of dry carbon

CARBON MONOXIDE

297

dioxide is conducted through the tube, which is strongly
heated with a four-tube burner (Fig. 119). The issuing gas
is conducted through a U-tube containing soda-lime, and
issues through a vertical piece of glass tubing, which serves

•Cn

^@»8f^

rpD^=5i

K_J

U>*

Fig. 119

as a jet. The gas issuing from the jet, when ignited, burns
with a blue flame. The gas may be collected in cylinders
at the pneumatic trough. A large flame is obtained by fill-
ing a liter cylinder with the gas and, after igniting it,

pouring

water rapidly into the cylinder.
C02 + C = 2 CO.

30 cm. length combustion-tubing ; 4-tube burner ; liter cylinder
soda-lime ; U-tube ; C02 generator ; charcoal.

10. From carbon dioxide and zinc. — Zinc dust at a low
red heat effects the reduction of carbon dioxide to carbon
monoxide.

A Jena glass combustion-tube is filled, for about 30 cm.
of its length, with a layer of zinc dust, over which a current
of carbon dioxide is passed. A cork, carrying a glass elbow
which serves as a jet, is inserted in the other end of the tube.
On gradually heating the tube with a four-tube burner,
the reduction begins, and soon sufficient carbon monoxide

298 CHEMICAL LECTURE EXPERIMENTS

will issue from the jet to be lighted and continue to burn.
At the end of the operation it will be seen that a portion of
the zinc dust has been converted to white zinc oxide.

C02 + Zn = ZnO + CO.

Jena glass combustion-tube ; C02 generator ; 4-tube burner ; Zn
dust.

11. By the action of sulphuric acid on oxalic acid. — Sul-
phuric acid reacts with oxalic acid to form equal volumes of
carbon monoxide and carbon dioxide.

Thirty grams of crystallized oxalic acid are placed in a
liter flask and mixed with 100 cc. of concentrated sulphuric
acid. The flask is provided with a two-holed cork carry-
ing a long thistle-tube and a delivery -tube connected with
a gas washing-bottle. The contents of the flask are gen-
tly heated, and the evolution of the gas is controlled by
the application of heat. The liberated gas is conducted
through a strong solution of potassium hydroxide in a gas
washing-bottle, to deprive it of the greater portion of carbon
dioxide. A U-tube filled with soda-lime, connected to the
exit tube of the gas washing-bottle, removes the last traces
of carbon dioxide, and the pure carbon monoxide may be
ignited at a glass jet. The apparatus is identical with that
shown in Fig. 120, save that the thermometer there shown
is not used. H^A = ^ + CQ + jj^

Liter flask ; thistle-tube ; delivery-tube ; gas washing-bottle ;
U-tube ; soda-lime ; H2C204 ; KOH.

12. By the action of sulphuric acid on potassium fer-
rocyanide. — The complex reaction between sulphuric acid
and potassium ferrocyanide furnishes a ready means of
obtaining pure carbon monoxide, and for preparing this gas
in large quantities on the lecture-table this method is by far
the best.

CARBON MONOXIDE

299

Forty-five grams of pulverized potassium ferrocyanide are
mixed with 300 cc. of concentrated sulphuric acid in a 2 1.
flask. The flask is closed with a three-holed rubber stop-
per, carrying a thistle-tube extending below the liquid in
the flask, a glass elbow, and a thermometer, the bulb of
which is immersed in the liquid. Care should be taken
to have that portion of the thermometer reading between
150° and 175° uncovered by the cork. The issuing gas is
conducted through a gas washing-bottle containing potas-

Jb=a==^

K>=

Fig. 120

sium hydroxide, followed by a U-tube containing soda-lime
(Fig. 120). The flask is gradually heated and the tempera-
ture maintained at 170°, where a very regular evolution of
the gas will be obtained. The pure gas issuing from the
soda-lime tube may be ignited or collected in jars at the
pneumatic trough, for use in any of the experiments
described beyond. On removing the flame and allowing
the contents of the flask to cool, the evolution of gas ceases.
By heating the mixture again to 170°, even after long stand-

300 CHEMICAL LECTURE EXPERIMENTS

ing, a steady evolution of carbon monoxide is obtained. If
the temperature is not allowed to rise above 175°, no diffi-
culty in the preparation of the gas by this method will be
experienced.

2 1. flask; thistle-tube; elbow; thermometer; soda-lime; U-tube ;
pulverized K4FeCy6-

13. Preparation of water gas by the action of steam on
hot charcoal. — By passing steam over glowing charcoal,
the water vapor becomes partially reduced by the carbon,
and a mixture of hydrogen and carbon monoxide, i.e., water
gas, issues from the tube.

A combustion-tube is prepared in a manner similar to
that described for the decomposition of nitric acid (Ex. 79,
p. 226). The tube is filled with fine lumps of charcoal,
which are strongly heated by means of a four-tube burner.
Steam, generated in the apparatus described in Ex. 2,
p. 41, is conducted through a glass tube, surrounded with
a roll of asbestos paper inserted in one end of the combustion-
tube, which prevents the deposition of water and subsequent
fracture of the tube. If the issuing gas is collected at the
pneumatic trough, it will be found to be combustible.

H20 + C = CO + H2.

Combustion-tube surrounded with wire gauze (Ex. 79, p. 226) ;
asbestos paper; steam generator (Ex. 2, p. 41); 4-tube burner;
charcoal.

PROPERTIES

14. Influence of moisture upon the combustion of carbon
monoxide in the air. — Carbon monoxide, dried bypassing
through a U-tube containing pumice-stone drenched with
sulphuric acid, will burn in the air; but if the jet is low-
ered into a cylinder containing dry air, the flame will be
extinguished.

Twenty-five cubic centimeters of concentrated sulphuric

CARBON MONOXIDE 301

acid are poured into a 500 cc. glass-stoppered wide-mouthed
specimen bottle, and the air is thoroughly dried by care-
fully shaking the well-stoppered bottle. A current of carbon
monoxide, dried in the manner described, is allowed to
burn from a recurved jet. On removing the stopper of
the specimen bottle and lowering the jet into the jar, the
flame will be extinguished. The gas should be passed
through solid absorbents for carbon dioxide and water to
prevent the flickering of the flame caused by the bubbling
of the gas through a liquid. A U-tube filled with soda-lime
and a similar tube containing pumice-stone and sulphuric
acid will effectively purify and dry the gas.

500 cc. glass-stoppered wide-mouthed specimen bottle ; recurved
jet (Fig. 41, p. 85); CO supply.

15. Explosion of a mixture of carbon monoxide and oxy-
gen.— A mixture of 2 volumes of carbon monoxide and
1 volume of oxygen explodes with considerable violence.

A 100 cc. cylinder is two-thirds filled with carbon monox-
ide and the remaining third with oxygen. The mouth of
the cylinder should be covered with a piece of cardboard
having an 8 mm. hole in the centre. The cylinder should
be removed from the pneumatic trough, placed mouth
upward on the table, and the flame applied at the hole in
the cardboard. The explosion is quite sharp, blowing the
cardboard into the air.

The explosive gaseous mixture may also be made in a
round-bottomed ginger-ale bottle, as in Ex. 30, p. 67, and
there exploded.

100 cc. cylinder ; cardboard with hole in centre ; ginger-ale bottle ;
CO supply ; O supply.

16. Absorption by cuprous chloride. — (a) A hydrochloric
acid solution of cuprous chloride absorbs carbon monoxide
readily.

302 CHEMICAL LECTURE EXPERIMENTS

A quantity of the gas is collected in the eudiometer
(Fig. 11, p. 26), and an acid solution of cuprous chloride
is allowed to flow down through it. If no impurities are
present, the gas will be completely absorbed.

(b) The absorption of this gas in cuprous chloride solution
may also be shown by conducting the gas through a series
of three wash-bottles, the middle one of which contains the
cuprous chloride solution, the others containing water. The
wash-bottles are not more than a third filled with liquid.
If a current of carbon monoxide is passed through the
system, the difference in the rate of bubbling in the first
and last bottles will be very apparent. On heating the
solution, carbon monoxide is again liberated.

Eudiometer (Fig. 11, p. 26); 3 gas washing-bottles; CO supply;
Cu2Cl2 in HC1.

17. Action on an ammoniacal solution of silver nitrate. —
Carbon monoxide reduces an alkaline solution of silver.

A gentle current of the gas, when conducted through a
solution of silver nitrate, to which a slight excess of
ammonium hydroxide has been added, produces a black
precipitate of metallic silver.

CO supply ; AgNOs solution.

18. Action on palladious chloride. — Carbon monoxide
reduces solutions of palladious chloride to black metallic
palladium.

A paper moistened with palladious chloride solution fur-
nishes a delicate test for carbon monoxide, for, when held
in this gas, it is immediately blackened.

CO supply ; PdCl2 solution.

19. Reduction of palladious chloride by a cuprous chloride
solution of carbon monoxide. — The delicacy of the reaction

CARBON DIOXIDE 303

between carbon monoxide and palladious chloride is shown
by adding 3 drops of a cuprous* chloride solution of carbon
monoxide to 400 cc. of water in a beaker. One drop of pal-
ladious chloride solution is added with thorough stirring.
In a few moments the contents of the beaker become a deep
black from the precipitated palladium.

CO dissolved in Cu2Cl2 solution ; PdCl2 solution.

20. Reduction of a solution of iodic acid. — A current of
carbon monoxide, conducted into a warm solution of iodic
acid, reduces the acid, forming carbon dioxide and liberating
iodine.

A solution of iodic acid is gently heated in a beaker, and
a current of carbon monoxide is allowed to bubble through
the liquid. A filter-paper moistened with starch solution
and held above the liquid is turned blue by the iodine
liberated and vaporized.

CO supply ; HI03 solution ; starch solution.

CAEBON DIOXIDE

PREPARATION

21. Combustion of charcoal in a confined volume of oxygen.
Volumetric relation of the carbon dioxide to the oxygen con-
sumed. — Carbon burns in oxygen to form 1 volume of car-
bon dioxide for every volume of oxygen used. If charcoal
is burned in a confined volume of oxygen, the volume of the
product will be the same as that of the oxygen consumed ;
hence there will be no difference in pressure in the interior
of the vessel at the end of the combustion.

The apparatus used for this experiment is that shown in
Fig. 68, p. 150, A 6 mm. piece of charcoal, preferably that
used in blowpipe work, is placed on a platinum spoon,

304

CHEMICAL LECTURE EXPERIMENTS

ignited in the air, and thrust into the flask previously filled
with oxygen. The heat of the burning carbon expands the
gases and causes the mercury to rise in the open arm of the
U-tube. After the operation is completed and the flask has
regained its normal temperature, the level of the mercury in
the arms of the U-tube will be found to be the same.

Apparatus (Fig. 68, p. 150); 700 cc. Jena glass distilling flask;
U-tube ; II g ; charcoal.

22. Preparation from magnesite by heat. — A thick-walled
test-tube is partially filled with 5 or 10 g. of magnesite such

as is used for analysis. A cork
with a delivery-tube dipping into
a glass cylinder containing lime-
water is inserted in the mouth of
the test-tube, which is then clamped
in an inclined position (Fig. 121).
On heating the magnesite, consider-
able quantities of carbon dioxide
are given off and produce a marked
cloudiness in the lime-water.

FlG* 121 MgC03 - MgO + C02.

Hard-glass test-tube ; magnesite ; lime-water.

23. From calcium carbonate and hydrochloric acid. — By

far the most satisfactory method for obtaining carbon
dioxide is to act upon calcium carbonate in the form of
marble, with a mixture of equal parts of concentrated
hydrochloric acid and water.

As a constant supply of carbon dioxide is very advan-
tageous for many experiments, it is advisable to prepare
a Kipp generator (Fig. 17, p. 46), filling the receptacle with
small fragments of marble and using hydrochloric acid
diluted as above.

CARBON DIOXIDE 305

The general use to which cylinders of the liquefied gas
(Ex. 29, p. 307) have been applied renders it easy to procure
them. They may be advantageously used for obtaining a
constant stream of the gas.

Owing to its great specific gravity , carbon dioxide is
almost invariably collected by displacement. Its solu-
bility in water renders it advisable to collect the gas
over mercury,, in case the displacement method cannot
be used.

CaC03 + 2 HC1 = CaCl2 + H20 + C02.

Kipp generator for C02 ; marble fragments.

24. From baking-powder. — A few grams of baking-powder
are heated in a dry test-tube and the issuing gas tested with
a lighted splinter. The presence of organic vapors inter-
feres with this experiment somewhat, and the powder should
be but gently heated.

Hydrochloric acid added to some baking-powder in a
cylinder gives rise to an evolution of carbon dioxide.

25. Carbon dioxide a product of fermentation. — The

importance of fermentation, with the liberation of carbon
dioxide during the process, makes it desirable to show this
operation on the lecture table.

A mixture of 50 cc. of molasses and 400 cc. of water with
about one-half of a fresh, compressed yeast-cake is placed
in a 500 cc. flask fitted with a cork and an elbow. A gas
washing-bottle containing lime-water is connected with the
elbow, and the whole apparatus allowed to stand in a warm
place till the next exercise. The carbon dioxide liberated
will force its way through the lime-water, rendering it turbid.
An empty gas washing-bottle may be inserted between the
elbow and the bottle containing lime-water, and the gas
x

306 CHEMICAL LECTURE EXPERIMENTS

in this cylinder may be tested with a lighted candle at the
close of the experiment.

500 cc. flask ; 2 gas washing-bottles ; molasses ; yeast-cake ; lime-
water.

26. Carbon dioxide in beverages. — (a) The presence of
carbon dioxide in wine or beer may be shown by heating a

portion of the liquor in a flask fitted with a

y^Q cork and a bent glass tube dipping into lime-

jQp^y water. On the application of gentle heat, the

Jtt( gas is liberated, and a cloudiness is produced

in the lime-water.

(b) A glass siphon of " soda-water " (Fig.
122) is inverted, and, by pressing the valve,
a large quantity of carbon dioxide is with-
drawn.
Fig i4>2 ^ little of the liquid from a siphon is poured

into the flask used above, and the carbon di-
oxide, given off on standing or more quickly by gentle heat-
ing, is conducted into lime-water as before.

Wine or beer; siphon of " soda-water" ; lime-water.

27. Presence of carbon dioxide in air. — If a small quan-
tity of lime-water or barium hydroxide solution is allowed
to stand for several hours in a crystallizing dish in the open
air, the liquid will be covered with a white film of calcium
or barium carbonate.

The formation of the carbonate may be more rapidly
obtained by drawing a current of air with a filter-pump
through a gas washing-bottle containing either of the above
solutions. In a few minutes a marked turbidity will
appear in the liquid.

Filter-pump ; gas washing-bottle ; crystallizing dishes ; lime-water ;
Ba(OH)2 solution.

CARBON DIOXIDE 307

28. Carbon dioxide in expired air. — That expired air
contains carbonic acid in considerable quantities is simply
shown by blowing through a glass tube into 50 cc. of lime-
water in a small beaker. A white precipitate of calcium
carbonate is immediately formed. Continued blowing
through the tube results in redissolving the calcium car-
bonate by the excess of carbonic acid, forming calcium acid
carbonate. Heating the solution in a test-tube drives off
the carbonic acid and causes the precipitate to reappear.

In case barium hydroxide is used, the precipitate will not
easily be redissolved.

100 cc. beaker ; lime-water ; Ba(OH)2 solution.

PROPERTIES

29. Preparation of solid carbon dioxide. — When liquid
carbon dioxide is allowed to expand suddenly, the tempera-
ture is lowered to such an extent that a portion of the liquid
solidifies.

Liquefied carbon dioxide is an article of commerce readily
obtained at a very low price, being much used in preparing
aerated beverages. It is ordinarily transported in steel cyl-
inders about 1.5 m. high and 20 cm. in diameter. When
standing in an upright position with the valve end upper-
most, the valve may be opened and carbon dioxide gas with-
drawn. If, however, the cylinder is inverted and the valve
opened, the liquefied gas is forced out at the bottom in a fine
stream, which immediately expands to the gaseous form,
producing a great lowering of the temperature. Numerous
forms of apparatus have been devised into which the stream
of gas is allowed to expand with a solidification of a portion
of the gas. A black flannel bag, some 20 to 30 cm. square, is
an excellent^ substitute for apparatus of this kind, and when
securely fastened to the valve-nozzle permits the collection

308

CHEMICAL LECTURE EXPERIMENTS

of considerable quantities of solid carbon dioxide. The bag
is preferably made with a drawstring which may be used to

fasten it securely to the valve-piece
(Fig. 123).

As it is not infrequent in charging
these cylinders with the liquefied gas
that varying quantities of water are
inadvertently introduced, it is im-
portant to open the valve carefully
and draw off any water before fasten-
ing the bag to the valve-piece. This
operation should be carried out before
the lecture. As soon as all the water-
is forced out, the gas will begin to
escape and the nozzle will become
covered with frost. The bag is then

3 attached, and, by opening the valve,

a brisk stream of the liquefied gas
allowed to enter it. The finer particles of the solidified gas
will be forced through the cloth and will fall as a white fog
to the floor.

On removing the bag a considerable quantity of the solid
carbon dioxide will be found as a snow-like mass which is
shaken into a cardboard box. If the bag is turned inside
out, it will be found to be lined with the white solid. The
operation may be repeated, and the solid obtained in any
quantity.

In spite of the very low temperature of the solid it re-
mains quite a long time in the air without disappearing, and
this property is especially well shown if the solid is pressed
into a cake or rod, which may then be placed on a piece of
felt on a plate and passed around the lecture room. A mould
is made by boring a 1.5 cm. hole in a block of wood. A
paper tube is fitted to the hole, and the end bent in upon

CARBON DIOXIDE 309

itself to make a bottom for the tube. It is then filled with
the solid carbon dioxide, which is pressed down hard with a
pencil or rod of wood. When the paper tube is filled, it is
withdrawn, the paper unrolled, and the rod of solid carbon
dioxide placed on a piece of felt or cotton-wool.

The greatest care should be exercised in handling the solid
not to press it hard with the fingers ; for though the rod may
be laid on the hand with no sense of discomfort, the effect
of pressure is to break the film of gas between the solid
and the warm hand and thus cause a severe burn. So long
as no pressure is applied the solid may be handled with
impunity. In general, a paper scoop or a horn spatula will
be found most serviceable in handling the solid.

Steel cylinder of liquefied C02 ; valve-wrench ; flannel bag ; card-
board box ; block of wood with 1.5 cm. hole ; paper tube ; paper scoop ;
horn spatula ; rod of wood or lead-pencil ; felt ; plate.

30. Experiments with solid carbon dioxide. — A few pieces
are placed in a clean, dry cylinder and allowed to- stand for
a few moments. Sufficient gas will be evolved from the
solid to fill the cylinder, and a lighted taper will be extin-
guished when thrust into the jar.

A piece of the solid is placed in the ginger-ale bottle of
Ex. 30, p. 67, which i^ then corked with a rubber stopper.
In a short time the evolution of gas within the bottle will
have generated enough pressure to blow the stopper out of
the neck.

A one-holed rubber stopper carrying a delivery-tube is in-
serted in the mouth of the bottle and the evolved gas caused
to bubble through lime-water, where a turbidity will appear.

A portion of the gas escaping from the delivery -tube is also
collected in a cylinder over waiter at the pneumatic trough.

Dry cylinder ; ginger-ale bottle (Ex. 30, p. 07) ; rubber stopper ;
delivery-tube ; lime-water.

310 CHEMICAL LECTURE EXPERIMENTS

31. Freezing water with solid carbon dioxide. — A small
beaker is placed upon a few drops of water on a block of
wood, and fragments of solid carbon dioxide are placed in
it. In a very few moments the water will be frozen, and the
beaker will be cemented to the wood.

Block of wood ; small beaker ; solid C02.

32. Freezing mercury with solid carbon dioxide. — Inas-
much as the temperature of solid carbon dioxide is — 79°,
mercury, when cooled with it, may be frozen to a hard solid.

(a) A few cubic centimeters of dry mercury are placed in an
evaporating-dish, which is in turn placed on a wad of cotton-
wool, and a centimeter layer of solid carbon dioxide is placed
upon it. A wad of cotton-wool or a piece of cardboard should
be placed over it and the dish allowed to stand for several
minutes. On inverting the dish the mercury will be found
to be a solid, which may, at times, adhere to the dish. By
gentle tapping it may be dislodged, or a piece of paper may
previously be placed in the dish between the mercury and
the porcelain. The evaporating-dish should be inverted and
the frozen mercury manipulated over a larger dish to catch
any drops of the mercury as it melts. An iron wire may
advantageously be frozen into the mercury to facilitate in
lifting the solid.

(b) A much more striking method of showing the solidi-
fication of mercury consists of freezing the metal in the
form of a ring, which is subsequently suspended and lowered
into a jar of cold water. For this purpose a mould consist-
ing of a block of wood in which a circular groove has been
cut approximately 1 cm. deep and 1 cm. wide, the internal
diameter of which is about 7 cm., is necessary (Fig. 124).
The circular space is filled with a 7 mm. layer of mercury,
and, after placing the mould on a large porcelain dish, the
mercury is covered with a centimeter layer of solid carbon

CARBOX DIOXIDE

311

V~\7tA ~tezf~l

dioxide. It is advisable to fill in the spaces around the
block of wood with cotton-wool and to cover the dish with
a piece of cardboard. Af-
ter several minutes the
mercury will be frozen
solid, and by inverting
the mould the ring will
fall out. The mercury is
then quickly raised with
the horn spatula, placed
upon a glass hook, and
lowered into a large ves-
sel of water which is near
the freezing point. In-
stantly the mercury ring becomes covered with an ice ring,
then melts, and the mercury falls to the bottom of the vessel.
The ice ring remains on the glass hook for several moments
before melting.

While the addition of anhydrous ether lowers the temper-
ature of the solid carbon dioxide somewhat, the mercury can
be frozen without the addition of ether, provided sufficient
time is allowed to complete the solidification.

Cotton-wool ; evaporating-dish ; large porcelain dish ; wooden mould;
horn spatula ; glass hook ; large vessel of ice-cold water ; dry Hg ;
Fe wire ; solid C02.

Fig. 124

33. Specific gravity. — Carbon dioxide is much heavier
than air, and is the subject of many experiments illustrating
this property.

A liter beaker is supported on the arm of the lecture-
balance and the system brought into equilibrium. If a cur-
rent of carbon dioxide is allowed to flow from a tube held
above the beaker, it will collect in the bottom, expelling the
air and causing a marked increase in weight.

312 CHEMICAL LECTURE EXPERIMENTS

Instead of conducting the carbon dioxide into the beaker
in a stream, a large cylinder may be rilled with the gas,
which may then be poured rapidly into the suspended
beaker. A marked inclination of the pointer on the
balance is immediately observed.

Lecture-balance ; 2 1. beakers ; C02 generator.

34. Quantitative estimation of the specific gravity of
carbon dioxide. — It is possible to determine with consider-
able accuracy the specific gravity of carbon dioxide in a
manner analogous to that described for determining the
specific gravity of hydrogen (Ex. 10, p. 48).

A narrow-necked, graduated liter flask is suspended on
one arm of the lecture-balance with the mouth uppermost.
The system is then brought into equilibrium. A current of
dry carbon dioxide is conducted through a long glass tube
inserted in the neck of the flask and extending to the
bottom. In a few minutes the air will have been entirely
driven out, and by slowly withdrawing the tube the flask is
completely filled with carbon dioxide. As the air originally
in the flask has been replaced by a heavier gas, it will be
necessary to add more weights to the other pan of the bal-
ance to restore the equilibrium. With a normal barometric
pressure and a temperature of 15°, 0.G3 g. will have to
be added. A liter of air under these conditions of tempera-
ture and pressure weighs 1.225 g., hence a liter of carbon
dioxide weighs 1.225 plus 0.63, which equals 1.855 g. Com-
pared to the weight of a similar volume of air it is readily
calculated that the specific gravity of carbon dioxide is
1.51.

If the barometric and thermometric conditions vary
widely from those given above, it will be necessary, if the
greatest accuracy is desired, to apply the usual corrections

CARBON DIOXIDE

313

to determine the weight of a liter of air under the observed
conditions.

Lecture-balance ; liter graduated flask ; weights ; H2S04 gas wash-
ing-bottle ; C02 generator.

35. Soap-bubbles float on carbon dioxide. — If a soap-
bubble is allowed to fall into a large jar which is half full
of carbon dioxide, it will settle in the jar to the level of the
carbon dioxide and then float on top of this gas.

A tall, wide-mouthed jar, such as is used for large speci-
mens in museums, is half filled with carbon dioxide. A
small soap-bubble, blown on the end of a thistle-tube, is
allowed to fall into the jar, where it will float on the sur-
face of the carbon dioxide.

Thistle-tube ; large jar (8 or 10 1.) half filled with C02 ; soap sol.

36. Carbon dioxide rotates a paper wheel. — The great
specific gravity of carbon dioxide may also be shown by
pouring a liter of the gas upon a cardboard wheel having
paper cups on its periphery. As the
carbon dioxide collects in the cups
the wheel is caused to rotate on its
axis.

A piece of stout cardboard is cut
into a circle 20 cm. in diameter, ten or
twelve small paper cups are pasted
on the rim, and a long needle is thrust
through the centre of the wheel (Fig.
125). Two stout copper wires fast-
ened to a block of wood may be so
bent as to form the bearings on which the needle is set. In
balancing the wheel it will probably be necessary to add a
bit of wax at different points before securing perfect equi-

Fig. 125

314 CHEMICAL LECTURE EXPERIMENTS

librium. When once arranged, the wheel will rotate quite
rapidly if a liter of carbon dioxide is poured into the cups.

Cardboard wheel ; liter cylinder of C02.

37. Carbon dioxide may be siphoned. — By reason of its
great specific gravity, carbon dioxide may be siphoned from
one vessel to another.

A 2 1. cylinder is filled with carbon dioxide and its pres-
ence established by lowering a lighted candle into it. An
empty cylinder of the same size is likewise tested with the
candle and the absence of carbon dioxide shown. A glass
tube, with an internal diameter of not less than 7 mm., bent
in the form of a siphon, is inserted in the jar of carbon
dioxide, which should be placed on a box or other support
above the table. The siphon is started by gentle suction
with the mouth on the longer arm, and, when the gas has
filled the tube, the lower end is thrust into the empty cylin-
der. However, as the uppe* cylinder is fixed, it is better
to arrange to have the lower cylinder brought up from
beneath. The presence of the gas in the longer arm of the
siphon will be known by the taste. After a few minutes
the gas will all have left the upper cylinder, and a candle
will continue to burn when lowered into it, while if a
lighted candle is inserted in the lower cylinder, it will be
extinguished.

Two 2 1. cylinders ; siphon ; C02 supply ; candle on wire.

38. Carbon dioxide extinguishes the flame of a candle. —
That carbon dioxide is heavier than air and is a non-sup-
porter of combustion is interestingly shown by pouring 2 1.
of the gas down into a wooden or metal trough in which
five small candles are burning. As the carbon dioxide flows
down the trough, the candles are extinguished in rapid
succession.

CAKBON DIOXIDE

315

Fig. 126

The trough may be made by bending a piece of tin 1 m.
long or by tacking two pieces of wood together at right
angles. The trough should be in-
clined at an angle of 45°, and the
candles so attached as to burn in
an upright position. To prevent
an upward current of air, it is
best to cut off the lower part of the
trough by means of a block of
wood or a piece of cardboard (Fig.
126). The candles should be of
the smallest size and are placed approximately 15 cm.
apart.

Trough (Fig. 126); small candles ; 2 1. beaker of C02.

39. Carbon dioxide in expired air extinguishes a candle
flame. — Air from the lungs is collected in a cylinder over
water. By taking the last portion of one exhalation, that is,
that which has had the longer sojourn in the lungs, a gas
quite rich in carbonic acid is obtained, and, indeed, the
per cent of this gas will be so great as to cause the flame of
a candle, when it is lowered into the cylinder, to be extin-
guished. By using a flexible rubber tube, which can be
pushed clear up the inner wall of the cylinder, the gas may
be drawn back into the lungs to become still richer in car-
bonic acid. In this case the rubber tube should have its
end out of water inside the cylinder when the air is with-
drawn, to prevent water from being sucked back into the
mouth. After removing the cylinder from the pneumatic
trough by covering it with a glass plate, the lighted candle
is immediately introduced.

300 cc. cylinder ; pneumatic trough ; candle on wire ; long clean
rubber tube ; glass plate.

316

CHEMICAL LECTURE EXPERIMENTS

40. Preparation of a supersaturated solution of carbon
dioxide (soda water). — The technical preparation of a satu-
rated aqueous solution of carbon dioxide may be admirably
illustrated on the lecture table by means of a patent device 1
in which small steel capsules containing the liquefied gas
are used.

The apparatus consists of a wire or wicker-covered, stout-
walled bottle and a special screw-top. As explicit direc-
tions are given with each apparatus, it need
only be stated here that the bottle is seven-
eighths filled with cold distilled water, the top
screwed on carefully, the steel capsule inserted
in the upper portion of the metallic top, and the
gas liberated by screwing down a small screw-
cap (Fig. 127). The gas is forcibly driven in
a fine jet into the water which, after unscrewing
the top, will be found to be supercharged with
carbon dioxide. On pouring some of the water
into a beaker the excess of gas will ascend in
fine bubbles.

The capsules are especially interesting, and the
difference in weight when filled and when empty
is very marked. The gas may be withdrawn from the
capsule and collected over water by attaching a rubber tube
to the end of the jet and very carefully screwing down the
small cap, a slow liberation of the gas resulting. The gas
issuing from the other end of the rubber tube may be col-
lected in a liter cylinder over water.

The intense cold produced by the evaporation of the
liquid may be shown by discharging a capsule in the air,

1 The apparatus is distributed by the Compressed Gas Capsule
Company of New York, and may be obtained in nearly every city in
the United States. The small steel capsules are sold under the trade
name "Sparklets."

Fia. 127

CARBON DISULPHIDE 317

pointing the nozzle clown. As the liquid escapes, it forms
for a moment a thin fog and the end of the jet becomes
extremely cold.

Sparklet apparatus (Fig. 127) ; liter cylinder ; rubber tube ; pneu-
matic trough.

CARBON DISULPHIDE

PROPERTIES

41. Solvent action on fats. — Carbon disulphide dissolves
fats readily. A small lump of tallow in a test-tube is cov-
ered with carbon disulphide, in which it readily dissolves.

A piece of paper, a portion of which has been greased, is
dipped into carbon disulphide and allowed to remain three
minutes. On withdrawing the paper and allowing the car-
bon disulphide to evaporate, the grease spot will have dis-
appeared.

Tallow ; greased paper ; CS2.

42. Production of cold by the rapid evaporation of carbon
disulphide. — Fifteen cubic centimeters of carbon disulphide
are placed in a small flask and covered with 5 cc. of water.
A strong blast of air is passed through the mixture, care
being taken to provide for the removal of the vapors of car-
bon disulphide to a flue or hood. In a few moments the
water in the flask will be frozen.

If a current of air is passed through carbon disulphide in
which a thermometer is placed, the temperature will rapidly
fall to 15° below zero. -

Small wide-mouthed flask ; air-blast ; thermometer ; CS2.

43. Comparative inflammability of ether and carbon disul-
phide. — A glass rod which has been heated at one end is
dipped into ether, which is not ignited by it, and then into
an evaporating-dish containing carbon disulphide. Sum-

818 CHEMICAL LECTURE EXPERIMENTS

cient heat will have been retained to ignite the carbon disul-
phide. The ether and the carbon disulphide are both placed
in evaporating-dishes which stand about 30 cm. apart.

Two evaporating-dishes ; CS2 ; ether.

44. Combustion in oxygen. — One cubic centimeter of
carbon disulphide is placed in a deflagrating-spoon and after
ignition lowered into a liter cylinder of oxygen. The com-
bustion proceeds with great brilliancy. If the spoon is
shaken somewhat so as to swash the liquid upon the hot
sides of the spoon, it will evaporate more rapidly, and con-
sequently a larger flame will be obtained.

Deflagrating-spoon ; liter cylinder of 0 ; CS2.

45. Explosion of a mixture of carbon disulphide vapor
and oxygen. — A mixture of carbon disulphide vapor and
oxygen explodes vigorously, though by selecting a stout-
walled cylinder the experiment may be safely performed.

A strong 200 cc. cylinder is filled with oxygen into which
2 cc. of carbon disulphide are poured. The cylinder is cov-
ered with a cardboard having a hole in the centre, and is
then vigorously shaken. On applying a match to the open-
ing a sharp explosion is obtained. If a heavy-walled
cylinder is not at hand, it is advisable to wrap the apparatus
with a towel to prevent damage from the explosion.

Stout-walled cylinder ; O supply ; CS2.

46. Combustion of potassium. — Potassium burns in the
vapor of carbon disulphide, forming polysulphides of
potassium.

Carbon disulphide in a 100 cc. flask is heated in a beaker
of hot water, and the vapor conducted through a glass elbow
into a bulb-tube containing a piece of potassium. Eubber
must be avoided in making any of the connections. As soon

METHANE (MARSH GAS)

319

as the tube is filled with the vapor of the disulphide, the
potassium is heated. The metal burns vigorously.

100 cc. flask ; bulb-tube ; beaker of hot water ; CS2 ; K.

47. Combustion of iron. — Fine iron wire, when thrust
into the flame of burning carbon disulphide, burns strongly,
forming ferrous sulphide.

The vapor of carbon disulphide issuing from the glass
elbow in the flask of the preceding experiment is ignited
and the size of the flame regulated by the temperature of
the water in the beaker. Iron wires which have been
twisted together are inserted in the flame. The molten
globules of iron sulphide formed may be tested with hydro-
chloric acid, and the evolution of hydrogen sulphide shown.

100 cc. flask ; beaker of hot water ; cork and elbow ; CS2 ; bundle
of fine iron wires.

METHANE (xMARSH GAS)

48. Preparation from sodium acetate. — Sodium acetate,
when heated in the presence of soda-lime, decomposes, lib-
erating methane or marsh gas.

Fifteen grams of fused so-
dium acetate are pulverized
and mixed with an equal
weight of fused soda-lime.
The mixture is placed in a
100 cc. Jena glass Erlenmeyer
flask fitted with a one-holed
cork and a wide delivery -tube
(Fig. 128). The flask is grad-
ually heated and, after all air

has been driven out, the gas is collected in several cylinders
for use in the following experiments. The importance of

■?

"jfpEz

k\\

— o —

■ -W

oO '

—

Fig. 128

320 CHEMICAL LECTURE EXPERIMENTS

having water-free materials cannot be too strongly empha-
sized, as condensed water is likely to break the flask.

100 cc. Jena glass Erlenmeyer flask ; pneumatic trough ; several
cylinders ; fused sodium acetate ; fused soda-lime.

49. Marsh gas a non-supporter of combustion. — A burn-
ing candle thrust into an inverted cylinder of marsh gas is
immediately extinguished.

Candle on wire ; liter cylinder of CH4.

50. Explosion with oxygen. — Two volumes of oxygen
and 1 volume of marsh gas are introduced into a thick-
walled 100 cc. cylinder having a cardboard cover with a
5 mm. hole in the centre. On igniting the mixture, a strong
explosion will be obtained. A thick-walled cylinder or a
round-bottomed ginger-ale bottle should be used for this
experiment, and as a special safeguard the vessel should be
wrapped with a towel.

100 cc. stout- walled cylinder rilled | with CH4 and § with O.

ETHYLENE

51. Preparation from alcohol and sulphuric acid. — Sul-
phuric acid extracts water from ethyl alcohol, liberating
ethylene.

One hundred and twenty cubic centimeters of concentrated
sulphuric acid are cautiously poured, with constant stirring,
into 80 cc. of ethyl alcohol. After cooling, the mixture is
poured into a liter flask one-fourth filled with coarse sand.
The flask is fitted with a cork, a safety-tube, and a wide
delivery-tube (Fig. 129). On gently heating the mixture a
rapid evolution of ethylene is obtained, which may be col-
lected in a large tubulated bell-jar for Ex. 53, and in several

ETHYLENE

321

small cylinders for other experiments. As the mixture is
liable to char and froth badly, the heat should be very care-
fully applied. The gas ob-
tained in this reaction is not
perfectly pure, and should
be washed by conducting it
through a solution of sodium
hydroxide, if the pure gas is
desired. Owing to its solu-

cold water, it is

to have the water

pneumatic trough

bility in
advisable
in the
warm.

C2H60=C2H4 + H20

■*

■EZr£Z

-=fr^=^

— -

Fig. 129

Liter flask ; gas washing-bottle ; tubulated bell-jar ; pneumatic
trough with warm water ; cylinders ; sand ; ethyl alcohol.

52. Preparation from ethylene dibromide. — One cubic
centimeter of alcohol and 2 cc. of ethylene dibromide are
warmed with a few pieces of granulated zinc in a test-tube.
The zinc combines with the bromine, setting free ethylene,
which may be ignited at the mouth of the tube.

C2H4Br2 + Zn = ZnBr2 + C2H4.

Alcohol ; ethylene dibromide ; granulated Zn.

53. Decomposition by heat. — Ethylene is decomposed at
a high temperature with the liberation of carbon.

The gas from a gas-holder, or from the bell-jar, Ex. 51, is
conducted through a bulb-tube. After all air has been driven
out of the apparatus, the bulb-tube is strongly heated in a
blast-lamp. By rotating the bulb, a thin mirror-like deposit
of carbon may be obtained all over the interior of the bulb.

Bulb-tube ; blast-lamp; C2H4 supply.

322 CHEMICAL LECTURE EXPERIMENTS

54. Absorption by cold water. — The absorption of ethy-
lene in cold water may be shown by a series of experiments
similar to those nsed to illustrate the solubility of hydrogen
sulphide in water (Ex. 17, p. 140).

55. Union with bromine. — Ethylene and bromine unite
directly, forming ethylene dibromide.

A 2 1. flask is filled with ethylene, and 2 cc. of bromine
are added. The bromine fumes are all absorbed, and, after
a thorough shaking, a colorless oil, ethylene dibromide,
remains on the bottom of the flask. If an excess of bromine
is used, the oil will be colored, and it will be necessary to
wash it with a little sodium hydroxide solution to remove
the free bromine. The oil, which possesses an ethereal odor,
may be poured into a cylinder containing water. The oil
is heavier than water.

C2H4 + Br2 = C2H4Br2.

2 1. flask filled with C2H4 ; cylinder ; Br.

56. Absorption by bromine. — The absorption of ethylene
by bromine is markedly shown by collecting 100 cc. of the
gas in the eudiometer (Fig. 11, p. 26), and allowing one cubic
centimeter of bromine to trickle very slowly down the inside
of the tube. The bromine in the bulb should be covered
with water to prevent the escape of bromine fumes. As
the bromine comes in contact with the gas, its color is imme-
diately discharged, the volume of the gas rapidly diminishes,
and the oily dibromide formed drops to the bottom of the
vessel.

Eudiometer (Fig. 11, p. 26) ; C2H4 supply ; Br.

57. Action of chlorine on ethylene. — Chlorine and ethy-
lene unite to form ethylene dichloride, an oily liquid.

Two hundred cubic centimeters of ethylene are introduced

ACETYLENE 323

at the pneumatic trough into a 500 cc. cylinder filled with
water, and chlorine is then admitted, a few bubbles at a time.
It will unite with the ethylene, forming oily drops of the
dichloride, which float as a film on the surface of the water,
and finally settle to the bottom of the trough. The volume
of the gas is diminished.

C2H4 + Cl2 = C2H4CI2.
500 cc. cylinder ; C2H4 ; CI supply.

ACETYLENE

58. Preparation from ethylene dibromide and alcoholic
potash. — Potassium hydroxide, in alcoholic solution, ab-
stracts hydrobromic acid from ethylene dibromide, with the
formation of acetylene.

Alcoholic potash is made by adding a stick of caustic
potash to 10 or 15 cc. of alcohol, and pouring off the solution
when saturated.

If 3 or 4 cc. of alcoholic potash in a test-tube are heated
just to boiling, and a few drops of ethylene dibromide added,
a gas is given off, which, on ignition, is readily recognized
as acetylene.

C2H4Br2 + 2 KOH = 2 KBr + 2 H20 + C2H2.

Alcohol ; potassium hydroxide (stick) ; ethylene dibromide.

59. Preparation from calcium carbide. — (a) A few pieces
of calcium carbide in a dry test-tube are treated with a few
drops of water. The evolution of gas is very rapid, and on
ignition, the characteristic luminous, sooty flame of acetylene
is readily recognized.

CaC2 + H20 = CaO + C2H2.

CaO + H20 = Ca(OH)2.
Calcium carbide in small pieces.

324 CHEMICAL LECTURE EXPERIMENTS

(b) A more striking decomposition of calcium carbide by
water is obtained when a 5 cm. piece is placed on a plate,
and a fine jet of water from a wash-bottle or tap is directed
on it. The escaping gas can be ignited, and the flame
increases as more water is added.

Calcium carbide is now obtainable in the market in tin
cans for use with bicycle lamps. It should be preserved in
tightly sealed bottles, as it absorbs moisture from the air,
and thereby is decomposed.

Wash-bottle ; plate ; CaC2.

60. Formation by the incomplete combustion of illumi-
nating gas. — In the incomplete combustion of illuminating
gas (Ex. 6, p. 345) small cpiantities of acetylene are formed.
This phenomenon is also observed when a Bunsen burner
" strikes back."

A Bunsen burner, burning at the base, is placed under
the inverted thistle-tube in the apparatus (Fig. 31, p. 62).
A sufficient quantity of ammoniacal cuprous chloride solu-
tion is placed in the U-tube to cover the bend. A gentle
suction is maintained through the apparatus and in a few
moments a precipitate of red cuprous acetylide is formed.

Apparatus (Fig. 31, p. 62) ; ammoniacal cuprous chloride solution.

ILLUMINATING GAS (COAL GAS)

61. Preparation. — Coal or wood, when subjected to dry
distillation, yields considerable quantities of a gaseous mix-
ture consisting chiefly of hydrogen and methane, together
with some of the higher hydrocarbons.

A few grains of pulverized anthracite coal are strongly
heated in a hard-glass test-tube. The gas evolved may be
ignited at the mouth of the tube, where it burns with a
feebly luminous flame.

ILLUMINATING GAS (COAL GAS)

325

Bituminous coal, when heated in a test-tube, yields large
quantities of a gas which burns at the mouth of the tube
with a luminous, smoky flame.

Bits of wood heated in a test-tube yield a gas which burns
with a luminous flame.

Hard-glass test-tubes ; anthracite and bituminous coal ; chips of
wood.

62. Preparation by the distillation of bituminous coal. —

A 500 cc. Jena glass retort is one-third filled with pulverized

bituminous coal, and the neck

is thrust into a filter-bottle

whose side tube is provided

with a glass jet (Fig. 130).

The retort is cautiously

heated, and the gas evolved

is allowed to drive out all

air before it is ignited at the

jet. The gas burns with a

luminous flame. A certain

amount of tarry matter is

distilled over and condenses

with some water in the filter-flask, which should be kept

cold by immersion in water.

Apparatus (Fig. 130); 500 cc. retort; sand-bath; filter-bottle;
glass jet ; pulverized bituminous coal.

63. Soap-bubbles filled with illuminating gas rise in
the air. — Soap-bubbles may be blown with illuminating
gas, as described in Ex. 13, p. 52. As they ascend, the
bubbles may be ignited by touching them with a burning
taper on the end of a long stick.

Fig. 130

Thistle-tube ; candle on long stick ; soap solution.

326

CHEMICAL LECTURE EXPERIMENTS

64. Explosion of a mixture of illuminating gas and air.

(a) The explosion of a mixture of air and illuminating
gas is best shown by means of the fol-
lowing apparatus. The middle neck
of a liter three-necked Wolff bottle
(Fig. 131) is provided with a cork and
a 20 cm. length of combustion tubing,
1 cm. internal diameter. Coal gas is
conducted through a glass tube in one
of the necks, and the third is closed
with a solid cork. All the necks

" should preferably be as wide as pos-
sible. Illuminating gas is conducted
through the glass tube, extending to
the bottom of the bottle until all air
is expelled, and the gas is then ignited
as it issues from the large glass tube
in the middle neck. On cutting off
the gas and simultaneously removing
the cork in the third neck, the flame
increases in size, though diminishing in intensity, and as
soon as enough air has been drawn through the open neck
to produce an explosive mixture in the bottle, the flame
strikes back through the tube, producing a loud, though
harmless, explosion.

Apparatus (Fig. 131); 1 liter 3-necked Wolff bottle; combustion
tubing.

(b) The tubulated bell-jar, with cork and glass tube used
in Ex. 29, p. 67, may also be used to produce an explosion
of illuminating gas and air.

Fig. 131

65. Combustion on platinized asbestos. — Platinized as-
bestos (Ex. 24, p. 61) is heated to incandescence in a Bunsen

ILLUMINATING GAS (COAL GAS) 327

burner. On turning out the gas the asbestos ceases to be
luminous. If the gas is now turned on, the asbestos will
immediately glow, but the gas is re-ignited with difficulty.
If the air-holes at the base of the burner are closed so that
no air can enter, the asbestos will again cease to glow,
as there is no air in the middle of the gas-jet to cause
combustion. On opening the air-holes, the asbestos again
becomes luminous, owing to the presence of the mixture of
gas and air.

Pt asbestos (Ex. 24, p. 61).

THE NATURE OF FLAME

STRUCTURE OF FLAME

1. The Bunsen burner. — A burner having an air-regu-
lating device for closing the air-holes at the base of the
burner-tube should be used in the following experiments.

The air-holes should be
closed, and then the
burner lighted. The
large, luminous, flicker-
ing flame should be
compared with the
flame obtained by un-
screwing the burner-
tube and lighting the
gas as it issues from
the fine jet (Fig. 132).
The ratio of the cross-
sections of the tubes
through which the gas
is issuing in both cases
should be noted.
After replacing the burner-tube, the air-holes still being
closed, the burner should again be lighted and the air-holes
gradually opened. The variations in the nature of the flame
from the flickering, luminous flame to the steady, non-lumi-
nous flame should be noticed.

328

Fig. 132

STRUCTURE OF FLAME

329

That a certain ratio must exist between the proportion of
gas and air mixing in the burner-tube in order to have the
flame burn quietly at the top of the burner is observed by
gradually turning off the supply of gas, the air-holes being
wide open, until the proportion of gas and air in the tube is
such as to cause the flame to strike back and burn at the
base of the burner. To accentuate the change in position
of the flame, the gas should again be turned on full and the
character of the flame appearing above the burner-tube
noted. By means of a pair of pliers the hot burner-tube
may be unscrewed, as before, while the flame is still burning.

2. Striking back of a Bunsen flame. — The

striking back of a Bunsen flame may also be
shown by means of the apparatus (Fig. 133).
(See Ex. 6, p. 345.)

By turning on a good supply of gas it is easy
to get a perfect Bunsen flame burning at the
top of the chimney. Several trials will prob-
ably be necessary before the best quantity of gas
will be found. When the proportions of gas
and air entering the base of the chimney are
correct, a great blue Bunsen flame will be ob-
tained at the top. By turning down the gas
slowly the flame will strike back with a sharp,
though harmless report, and burn at the base
of the burner.

It is important that the metal part of the
burnej should not be allowed to become too hot
by burning the gas at the base of the chimney,
for the hot metal increases the difficulty of
securing a well-formed Bunsen flame. If the
metal becomes too hot, it is better to wait a few minutes
before attempting to relight the burner. As most A r gaud

Fig. 133

330

CHEMICAL LECTURE EXPERIMENTS

burners have a small gas-regulating device at the base, the
proportions may well be established before the lecture, and
in order to get a good flame it will only be necessary to open
the gas-cock on the desk and light the gas.

Argand burner and chimney (Fig. 133).

3. The inner portion of a flame is cool. — (a) A striking
demonstration of the fact that the inner portion of a flame
is cool is made by employing a burner consisting of an ordi-
nary glass funnel 5 cm. across the top, which has a piece of
fine copper or brass gauze over the mouth
(Fig. 134). The stem of the funnel is
connected by means of a rubber tube to
the gas-cock. A small heap of gunpowder,
about 15 mm. in diameter, is placed in the
centre of the wire gauze, care being taken
that no small particles of the powder are
scattered on the gauze away from the
middle of the heap. After protecting the
apparatus from strong draughts, the gas
is turned on and a match brought down
from above until the gas is ignited. It
burns with a large flame, and the gun-
powder remains on the wire gauze uncon-
sumed. Ordinary matches may be thrust
suddenly through the flame, and their heads laid on the
heap of gunpowder, without being ignited. On slowly
turning down the gas, the flame will diminish in size and
soon play over the surface of the gunpowder and cause its
ignition.

In repeating the experiment, care should be taken to allow
the gauze covering to become perfectly cold, and in no case
must the powder be added from the bottle or other container,
but rather from a small piece of paper. In introducing the

Fig. 134

STRUCTURE OF FLAME 331

phosphorus matches, care should be taken not to disturb
the heap of gunpowder and scatter the grains. While the
explosion of such a small quantity of gunpowder is not dan-
gerous, the eyes and face should be protected from any pos-
sible accident.

5 cm. funnel ; fine wire gauze ; gunpowder ; shields or eye-glasses.

(b) A pin or needle is thrust through a match just below
the head. On allowing the match, supported on the needle,
to hang down the tube of a Bun sen burner, the gas may be
lighted and the match remain unlighted in the centre of the
non-luminous flame. The match, to avoid touching the edge
of the cone, and thereby becoming ignited, should be so
placed that it is as near as possible to the centre of the
inner cone. A Bunsen burner giving a perfect flame is
necessary for this experiment.

4. Pictures of flames with asbestos paper. — An interest-
ing study of the temperature zones of an ordinary Bunsen
flame may be made by depressing for a few moments a piece
of paper on the flame. The hotter portions of the flame will
soon char the paper, while the paper in the cooler zones will
not become darkened, the intensity of the charring showing
the intensity of the heat. It will thus be seen that the cen-
tre of the flame is comparatively cool, as a small circle 7
mm. in diameter will be unburnt.

The most satisfactory paper for this experiment is ordi-
nary thin asbestos paper. In the manufacture of this paper
certain quantities of grease or oil are incorporated with the
asbestos. On thrusting the paper into the flame the heat
chars the oil, producing a blackening of the paper, and one
can readily determine, by noticing the intensity of the color,
the relative temperatures of different parts of the flame.
Asbestos paper possesses another advantage, i.e., it is not com-

332

CHEMICAL LECTURE EXPERIMENTS

vy////,

bustible. If a 15 cm. square piece of thin asbestos paper is
held vertically in the flame, a remarkably good picture of

the cross-section of the flame
may be obtained. Some slight
degree of skill is necessary to
avoid heating the paper too
hot, and thereby charring too
much of it, though the eye
readily perceives when the
paper should be withdrawn
from the name. Pictures of
the flame in almost any posi-
tion may be made by using
this paper (Fig. 135).

/■ §>ro v

Fig. 135

5. Pictures of a flame on metallic copper. — The beauti-
ful colors formed in the oxidation of copper may be advan-
tageously used to form a picture of a Bunsen flame.

A 20 cm. square of thinnest sheet copper is carefully
cleaned and polished. The sheet is then held in the Bun-
sen flame, as described in the preceding experiment. Im-
mediately the copper will take on in colors the outline of
the flame, but on account of the metal's great conductivity
of heat, the sheet must be heated for only a few moments.

In case the experiment is to be repeated, the picture can
be instantly effaced by washing with a few drops of potas-
sium dichromate solution to which some sulphuric acid has
been added.

Pictures of the flame in numerous positions can be readily
obtained by this method.

Thin sheet copper ; KoCr207 solution.

6. Ignition of the gas arising from a recently extinguished
candle. — That the candle flame is due chiefly to the burn-

STRUCTURE OF FLAME

333

ing of the gas formed by the action of heat on the solid
portion is shown by blowing out the candle and holding
the match 1 or 2 cm. above the wick, when it will be seen
that the gas or smoke rising from the wick will catch fire
and run back, communicating its flame to
the wick. To show the ignition of the
gas more strikingly, the candle is placed
inside of an ordinary Argand lamp chim-
ney (Fig. 136). The chimney must be
raised from the table to allow a good
current of air to enter, and sufficient air
must be furnished to allow the candle
to burn steadily. On blowing out the
candle the gas will rise, and a match
held at the top of the chimney will set
fire to the gas and ultimately to the can-
dle as described above. It is not unusual
to have the flame descend some 6 or 8 cm.
to the wick. Instead of a match a flame from a blowpipe
jet or a glass tip may be directed across the top of the
chimney, and the distance from the top of the chimney to
the top of the wick measured as the distance that the flame
has travelled.

Argand lamp chimney ; candle.

Fig. 136

\LR

Fig. 137

7. Collection of combustible gases
from the interior of a candle flame.

— A 300 cc. glass cylinder is fitted
with a two-holed rubber stopper car-
rying a short glass elbow and a long
glass tube reaching to the bottom of
the cylinder and bent over on the
outside so as to descend to the wick
of a wax candle (Fig. 137;. The

334 CHEMICAL LECTURE EXPERIMENTS

candle is so held that the tip of the wick just touches the
end of the long glass tube. On lighting the candle and
applying a gentle suction to the glass elbow, the unburned
gases generated by the heat of the candle are drawn over
into the cylinder. After a few moments, sufficient gas will
have been collected to burn when the cork is removed and a
flame applied. If the cylinder is not completely filled with
the gas, enough air may remain to cause a slight explosion.

300 cc. cylinder ; suction-pump ; candle.

8. Cooling a Bunsen flame with wire gauze. — When a
Bunsen flame is allowed to play upon a piece of wire gauze,
the heat is conducted from the flame along the wire so

rapidly as to prevent the gas that rises through
the meshes from being ignited.

A piece of wire gauze is suddenly depressed
on the top of the inner cone of a Bunsen flame.
The flame will remain entirely on the lower side
of the gauze, though in a few moments, as the
wire becomes heated, an ignition of the gas
above the gauze results.

The experiment may be varied by turning on
the gas without lighting it, holding a piece of
wire gauze horizontally about 4 cm. above the

I^p of the burner, and applying a flame from

above. The gas will burn on top of the gauze,
and it will be impossible to generate sufficient heat to ignite
the gas below (Fig. 138).

This cooling effect of wire gauze finds practical use in the
Davy safety-lamp.

9. The Davy safety-lamp. — The use of the Davy safety-
lamp in the presence of explosive gaseous mixtures is well
illustrated by lowering it into a mixture of ether vapor and
air.

STRUCTURE OF FLAME 335

A 2 1. beaker is used to hold the explosive mixture ob-
tained by pouring 5 cc. of ether vapor into the beaker and
then covering its mouth with a cardboard cover. A Davy
lamp is lighted (care being taken that the flame is not too
high) and carefully lowered into the beaker. As it comes
in contact with the gaseous mixture, a flame may be seen
playing for a few seconds inside the wire gauze surrounding
the lamp. As the lamp is lowered, the flame is extin-
guished, owing to the deficiency in oxygen, and the gaseous
mixture is not ignited.

2 1. beaker ; cardboard cover ; Davy safety-lamp ; ether.

10. Increased illumination of a Bunsen flame by the intro-
duction of particles of carbon. — (a) The incandescence of
small particles of carbon which are caused to pass through
a Bunsen flame renders it luminous.

The simplest method of introducing the particles of
carbon is to rub together two pieces of charcoal near the
air-holes at the base of the burner. The fine charcoal dust
will be drawn up into the tube and cause the flame to
become luminous.

Two pieces of charcoal.

(b) By introducing very finely divided carbon into a
colorless Bunsen flame a luminous flame is obtained. An
extremely finely divided form of carbon is obtained as lamp-
black from the flame of burning turpentine, and if a current
of air ladened with the soot from a flame of this nature is
conducted into a Bunsen flame, the flame is rendered lumi-
nous.

Turpentine is burned in a small lamp made by thrusting
a short piece of glass tubing into a cork, having a slit cut
in one side, fitting the mouth of a small bottle. A piece of
round cotton wick is drawn through the glass tube, and the

336

CHEMICAL LECTURE EXPERIMENTS

bottle is one-half filled with turpentine. On lighting the

free end of the wick, a small smoky flame will be obtained.
A 12 cm. length of combustion-tubing is
so clamped that it serves as a chimney
to deflect the products of combustion into
the lower part of a Bunsen flame. The
column of soot rising through the com-
bustion-tube enters the Bunsen flame and
there becomes heated to incandescence.

The products of the incomplete com-
bustion of a candle may be conducted
into the base of a Bunsen burner by
means of a glass elbow thrust into one
of the air-holes (Fig. 139). On lighting
the Bunsen burner, sufficient draft will
be obtained to conduct the products of
combustion of a burning candle, the tip
of whose wick is thrust into the lower

end of the glass elbow, up into the Bunsen flame. The

flame is rendered luminous.

Turpentine lamp ; 12 cm. length of combustion- tubing ; glass elbow ;
candle.

Fig. 139

11. Carburetting a flame of hydrogen. — The introduction
of solid particles of carbon into a non-luminous flame may
be effected by introducing vapors of carbon compounds
which are decomposed readily by heat, liberating finely
divided carbon.

A current of hydrogen is conducted through a test-tube
containing some cotton-batting and fitted with a three-holed
cork (Fig 140). In one hole is a glass elbow, extending to
the bottom of the test-tube, through which the hydrogen
enters. The hydrogen issues through a bent glass tube
serving as a jet in another hole. A small dropping-funnel

STRUCTURE OF FLAME

337

Fig. 140

containing benzine is fitted in the third hole. After all air
is driven out of the apparatus, the hydrogen is ignited at
the jet, where it burns with a non-luminous
flame. A platinum tip should be used. On
opening the stop-cock of the dropping-funnel
and allowing a few drops of benzine to fall
upon the cotton, the flame immediately be-
comes luminous. The benzine vapor carried
along with the hydrogen is decomposed by
the hot hydrogen flame, setting free carbon,
a part of which becomes heated to incan-
descence. The actual liberation of carbon
is proved by the soot deposited on a cold
porcelain dish depressed upon the luminous
flame. A dish depressed upon the hydrogen
flame produces no deposit.

A similar apparatus may be used to illustrate the car-
buretting of ordinary coal gas, in which case, however, it
is better to replace the platinum tip by a regular gas-burner.
Coal gas issuing from a jet saturated with benzine vapor
burns with a much more luminous flame than the uncar-
buretted gas, as may be readily seen by holding an ordinary
gas-flame beside it.

Large test-tube ; three-holed cork ; dropping-funnel ; cotton-batting ;
Pt jet ; H supply ; benzine.

12. Luminosity of a Bunsen flame increased by finely
divided nickel. — In Ex. 9, p. 418, carbon monoxide, satu-
rated with the vapor of nickel tetracarbonyl, is conducted
into the air-holes of a Bunsen burner. The vapor mixes
with the illuminating gas, and the heat of the flame is
sufficient to decompose the tetracarbonyl, setting free finely
divided nickel which is burned in the flame, imparting to it
an intense luminosity.

Waste gases from Ex. 9, p. 416.

338

CHEMICAL LECTURE EXPERIMENTS

Fig. 141

13. Increase in brilliancy of a non-luminous flame by heat-
ing.— A piece of platinum foil, at least 15 cm. long, is
rolled in the form of a tube, bound with some pieces of

platinum wire, and slipped over the
end of a Bunsen burner, forming an
extension to its main tube. The
burner is clamped in an inclined
position, and on opening the air-
holes at the base, the flame is so
regulated as to appear just non-
luminous at the top (Fig. 141). On
heating the platinum tube with a
strong burner, the issuing gas at
the end of the platinum tube will
be seen to have acquired a decided luminosity. It is advis-
able to heat the platinum thoroughly before using it for
this experiment, in order to burn off all dust, which would
otherwise color the flame.

Platinum foil 15 cm. long.

14. Luminosity of a flame decreased by dilution with an
indifferent gas. — Illuminating gas, when diluted with carbon
dioxide, loses its illuminating power.

Carbon dioxide from a Kipp generator is introduced into
one of the air-holes in the base of a Bunsen burner by means
of a small cork and a glass tube (Fig. 139). The other air-
hole is closed with a cork. Illuminating gas is conducted
through the burner and ignited at the top, where it burns
with a flickering, luminous flame. Carbon dioxide is then
slowly admitted, with the result that the flame diminishes
in luminosity until finally it becomes blue.

The same effect may be obtained by using the chromium
oxychloride-hydrogen, in place of the illuminating-gas,
flame.

RECIPROCAL COMBUSTION 339

By heating the diluted gas with the platinum extension-
tube of Ex. 13, the luminosity may again be restored.

Bunsen burner with cork and tubes in air-hole ; C02 generator ; Pt
tube (Ex. 13).

15. Effect of the dilution of air on a luminous flame. —

The diminution in luminosity in a flame, resulting from the
dilution of the combustible gas by an indifferent gas, may
also be obtained by diluting the atmosphere with a non-
combustible gas such as carbon dioxide. An artificial
atmosphere, containing one-third carbon dioxide, is pre-
pared by filling two-thirds of a large bottle with air and
the remaining volume with carbon dioxide. Illuminating
gas is conducted through the recurved jet (Fig. 41, p. 85)
and ignited. A luminous flame, 3 or 4 cm. high, is ob-
tained, and the jet is lowered into the artificial atmos-
phere of air and carbon dioxide. The luminosity of the
flame disappears, though by withdrawing the jet it can be
seen that the gas has not been extinguished.

Hydrogen, burning from the recurved jet having a plati-
num tip on which a small amount of sodium chloride solu-
tion has been placed, burns in the air with a brilliant yellow
flame. When lowered into the diluted atmosphere, the
luminosity disappears.

A candle lowered into such an atmosphere is immediately
extinguished.

Large bottle containing one-third C02, two-thirds air ; jet (Fig. 41 ,
p. 85) ; NaCl solution ; H generator ; candle on wire.

RECIPROCAL COMBUSTION

1. Combustion of oxygen in hydrogen. — (a) A jet of
oxygen will burn as well in an atmosphere of hydrogen
as a jet of the latter gas will burn in the presence of air or

340 CHEMICAL LECTURE EXPERIMENTS

oxygen. That the terms " combustible " and " supporter of
combustion " are only relative is well shown by an experi-
ment in which oxygen, ordinarily considered non-combusti-
ble, burns in an atmosphere of hydrogen which extinguishes
the flame of a candle.

A liter cylinder filled with hydrogen is held mouth down-
wards and the gas ignited at its mouth. A slow stream of
oxygen is passed through a glass tube which is carefully
thrust up into the jar of hydrogen (Fig. 42, p. 85). As
the tip of the glass tube passes the burning gas the oxygen
is ignited. If a small platinum tip is provided, the flame
will be seen to be colorless. If the oxygen tube is with-
drawn, the flame will be extinguished as soon as it leaves
the atmosphere of hydrogen. The tube is again introduced,
and the gas will continue to burn until the hydrogen is con-
sumed. To prevent the possibility of the formation of an
explosive gaseous mixture, care must be taken that the oxy-
gen flame is not extinguished by accidental pressure on the
rubber tube conducting the oxygen. Should the flame be
extinguished, the glass tube must be immediately withdrawn
and the jar refilled with hydrogen, after expelling all the
remaining gas.

Liter cylinder of hydrogen ; current of oxygen.

(b) The liter cylinder of hydrogen may be advantageously
replaced by an apparatus for furnishing a constant supply
of hydrogen. The simplest form of apparatus consists
of a small lamp chimney vertically clamped with a one-
holed cork fitted into the upper end. A slow stream of
hydrogen is passed through a glass tube in this cork, and the
gas lighted at the lower end of the chimney. The glass tube
conducting the oxygen is now thrust into the lamp chimney
from below, with all the precautions described above.

Kipp II generator ; lamp chimney ; current of oxygen.

RECIPROCAL COMBUSTION 341

2. Continuous combustion of oxygen in hydrogen. — Ox^

gen may be made to burn continuously in an atmosphere

of hydrogen by means of the apparatus, Fig.

142.

Hydrogen is conducted through the elbow
in the cork at the bottom of the lamp chim-
ney, and is ignited at the opening in the cover
at the top. A long glass elbow, which may be
easily raised and lowered, is thrust through
the second hole in the cork until the end is
just on a level with the cover. After hydro-
gen has displaced all air in the apparatus,
and has been lighted as it issues from the
top, a gentle current of oxygen is passed
through the long glass elbow, and is seen to fl

burn in the interior of the hydrogen flame. F 142
The tube may be then slowly lowered, and it
will be seen that the oxygen burns in the atmosphere of
hydrogen. As the heat of this flame is very intense and
is liable to melt the glass, it is advisable to provide for
the glass tube a platinum tip, such as is described in Ex. 5,
p. 183.

The greatest precaution must be exercised to prevent the
formation of a gaseous explosive mixture in the interior of
the lamp chimney ; and in case the inner flame is extin-
guished by accidental pressing or kinking of the rubber tube,
the oxygen supply must be immediately cut off, as otherwise
a dangerous explosion might easily occur.

Apparatus (Fig. 142) ; lamp chimney ; cork and tubes ; H and 0
supply.

3. Combustion of air in illuminating gas. — A simple
apparatus for showing this phenomenon consists of an
Argand lamp chimney (Fig. 143) fitted with a large cork, car-

-J

342 CHEMICAL LECTURE EXPERIMENTS

Tying a small elbow and a 10 cm. length of combustion-tubing.
The combustion-tubing should be provided with a platinum
tip, made by rolling a piece of platinum foil in
such a manner that it will snugly fit the interior
of the tube. The chimney is then clamped in
an upright position with the open end upper-
most, and a cover of thick asbestos card, or
better, a brass cap, is fitted on the top of the
chimney. A 2 cm. opening should be made in
the centre of the cap.

On closing the opening in the cap and ad-
mitting illuminating gas through the elbow,
the air in the lamp chimney is soon driven out,
and the gas may be ignited as it issues from
the lower end of the combustion-tube. On opening the
orifice in the cap, the gas rises and the flame recedes through
the combustion-tube, and appears at the platinum jet inside
the chimney. The escaping gas may be lighted at the top
of the chimney and there simultaneously appears a flame of
gas burning in air and a flame of air burning in gas. It
may be necessary to choke the piece of combustion-tubing
by means of a small cork with a slit cut in one side, to pre-
vent too large a volume of air from entering the chimney
through the tube. By properly regulating the supply of
coal gas and the admission of air, a flame 2 or 3 cm. high
is easily obtained.

While the two flames do not appear markedly different, it
will be found on thrusting a piece of paper or a visiting
card on the end of a wire through the opening at the top of
the chimney into the inner flame, that only that portion of
the card will be burned which is actually in the flame itself.
By carefully inserting the card, a picture of the flame may
be obtained by charring the card.

Apparatus (Fig. 143) ; lamp chimney ; corks and tubes ; asbestos or

T"»Y»

aco r»ov»

RECIPROCAL COMBUSTION

343

Fig. 144

4. Combustion of air in hydrogen. — By using an apparatus
similar to that shown in Fig. 143, in which, however, the
large glass tube in the cork has a U rather than a straight
form, the combustion of air in hydrogen may be well
studied. The apparatus is shown in
Fig. 144, and consists of a lamp chim-
ney provided with a two-holed cork at
the bottom, carrying a small glass elbow
and a large U-tube 1 cm. in diameter.
Each end of the U-tube should be pro-
vided with a platinum tip (Ex. 3). A
cork should be inserted in the top of
the chimney and hydrogen admitted.
After all the air is expelled, the hydro-
gen escaping from the outer limb of the
U-tube is ignited. On removing the cork
from the top of the chimney, the flame recedes through the
U-tube, and soon appears burning at the other end inside the
chimney as a flame of air burning in an atmosphere of hydro-
gen. On again inserting the cork in the top of the chimney,
the hydrogen will escape through the U-tube, and the flame
recede and appear as a jet of burning hydrogen at the outer
end of the U-tube. The operation may be repeated as often
as is desired. The best results are obtained when the flame
at the open end of the U-tube is not more than 1 or 2 cm.
high.

The operation is even more satisfactory when illuminating
gas is used in place of hydrogen, since it has the advantage
of giving a luminous flame.

Apparatus (Fig. 144); lamp chimney; large U-tube ; corks ; H supply.

5. Reciprocal combustion of illuminating gas and air. —

An interesting modification of the experiment illustrating
the relative combustibility of gas and air is made by means

344

CHEMICAL LECTURE EXPERIMENTS

of the apparatus (Fig. 145). An ordinary lamp chimney is
fitted with a two-holed cork carrying a glass elbow and a
glass tube, 7 mm. internal diameter. The
cork is clamped in a vertical position and
illuminating gas is conducted through the
small glass elbow and ignited. The chim-
ney is then placed over the cork. The flame
will continue to burn, a liberal supply of
air entering the lamp chimney through the
large glass tube. On turning on more gas,
however, the flame will soon ascend and
burn at the asbestos cover on the upper
part of the chimney, while a current of air
drawn through the large glass tube will
burn at the end of the tube inside the
chimney. A small glass tube is drawn out
to a long, fine jet, through which illumi-
nating gas is conducted and allowed to burn.
The small flame of burning illuminating
gas may then be thrust through the large tube into the
centre of the flame of air burning in the chimney. The
illuminating gas will still continue to burn, and there is
simultaneously obtained a flame of illuminating gas burn-
ing at the top of the chimney in the air, a flame of air
burning in illuminating gas inside the chimney, and a flame
of illuminating gas burning inside the flame of air. That
this last flame will burn only in air is seen by thrusting the
glass tube through the air flame into the atmosphere of
illuminating gas. On withdrawing the tube the gas is
again ignited and continues to burn in the air. It is
important that the long, fine tube be of small diameter, as
a large tube will so obstruct the passage of air as to make
it impossible to secure a good flame. If the illuminating
gas admitted through the glass elbow is now slowly turned

Fig. 145

RECIPROCAL COMBUSTION

345

off, the flame at the top of the chimney will diminish in
size and finally recede into the chimney and burn at the
end of the glass elbow as at first.

Apparatus (Fig. 145) ; lamp chimney ; asbestos disk with 2 cm.
hole ; cork and tubes ; long glass jet.

6. Combustion of air in illuminating gas. — By means
of the apparatus (Fig. 146) the combustion of air in illumi-
nating gas may be very easily shown.

An Argand gas-burner is provided with a
large chimney, such as is shown in the figure.
This form of chimney is not designed for use
on an Argand gas-burner, but the constriction
just above the flame makes it especially desir-
able in connection with this experiment. A
piece of sheet copper or galvanized iron, with
a 7 mm. hole in the centre, is laid over the top
of the chimney after the gas is lighted and
burning with a flame approximately 2 cm. high.
When the disk is placed over the chimney, the
gas smokes inside the chimney, the flame re-
cedes, and may be seen to be burning at the
central air-draft instead of at the ring where
the gas issues through the burner.

By regulating the supply of gas, a flame some
1 or 2 cm. high may be obtained. The gas issu-
ing from the hole in the disk may be lighted,
and it will burn with a feebly luminous flame.

It is thus possible to have a flame of air burning in illu-
minating gas at the base of the burner and a flame of gas
burning in air at the top. This is one of the simplest meth-
ods of showing the phenomenon of reciprocal combustion.

Argand burner and chimney (Fig. 146); copper or galvanized iron
disk with 7 mm. hole in centre.

Fig. U6

346 CHEMICAL LECTURE EXPERIMENTS

7. Combustion of oxidizing agents in an atmosphere of
hydrogen. — A number of substances furnishing a supply of
oxygen may be made to burn in an atmosphere of hydrogen.
The hydrogen is held in a liter bell-jar clamped mouth
downwards, or use may be made of a lamp chimney through
which a stream of hydrogen is sent from the top, issuing at
the bottom. Potassium chlorate is placed in a small porce-
lain crucible suspended in the loop of a stout iron wire
long enough to extend up into the jar or lamp chimney.
The potassium chlorate is then melted and strongly heated.
When oxygen begins to be liberated it is suddenly thrust
through the burning hydrogen at the mouth of the bell-jar
or lamp chimney. The salt will burn with intense bril-
liancy with the characteristic color of potassium salts. By
the use of strontium or barium chlorates the flame will be
colored respectively red and green. An intense yellow
flame may be obtained by using a mixture of four parts
potassium chlorate and one part sodium nitrate.

Nitric and iodic acids, both rich in oxygen, burn in an
atmosphere of hydrogen when heated. A small quantity of
fuming nitric acid is placed in a crucible and
heated to boiling. Without waiting long enough
to allow much of the oxides of nitrogen to es-
cape, the crucible is thrust into the atmosphere
of hydrogen, where it will burn. A small quan-
tity of iodic acid placed in a crucible and heated
very hot will burn on being introduced into the
hydrogen atmosphere, large quantities of iodine
being liberated and deposited on the walls of
the jar.

As the intense heat of the hydrogen burning
at the mouth of the jar or lamp chimney is likely to break
the glass on long-continued heating, it is advisable to pass
the hydrogen through the bottom of an ordinary Argand

RECIPROCAL COMBUSTION 347

lamp chimney clamped in a vertical position, fitted with a
one-holed cork and a glass elbow at the bottom, and covered
at the top with a disk of thick asbestos with a 2 cm. open-
ing in the centre (Fig. 147). In this form of apparatus
the hydrogen burns at the opening of the asbestos, caus-
ing no undue heating of the glass. The materials to be
introduced into the hydrogen atmosphere must, however,
be held in a crucible suspended from a long iron wire
capable of being lowered through this opening.

Lamp chimney ; H generator ; deflagrating-spoon ; apparatus (Fig.
147); asbestos disk ; KC103 ; Ba(C103)2 ; Sr(C103)2 ; NaN08 ; fuming
HN03; I2O5.

METALS

The division of the elements into the two groups, non-
metals and metals, though more or less arbitrary, is here
made in the customary manner.

The size of this book will not permit of an exhaustive
list of experiments on the metals, and hence those here
selected are to be looked upon only as suggestive additions
to the usual precipitations.

348

SODIUM

1. Metallic lustre. — Metallic sodium, as ordinarily ob-
tained in the market, is covered with a crust, and the metal
must be cut in order to show the metallic lustre.

A piece of the metal is laid on dry filter-paper to remove
the excess of naphtha and then cut with a knife. The
freshly cut surface shows the bright metallic lustre of this
element, but almost immediately, i.e., in a very few seconds,
becomes covered with a tarnish.

A piece of sodium from which the thick outer crust has
been removed may be freed from all tarnish by immersing
it for a few moments in absolute alcohol. The sodium re-
acts with the alcohol somewhat, and the outer surface is
entirely freed from oxides. The piece of sodium must then
be thrust under naphtha, where its lustre will be preserved
for some time.

Absolute alcohol ; naphtha ; Na.

2. Melting the metal. — Sodium may be readily melted if
several small pieces are heated under kerosene in a large,
dry test-tube. The metal melts at 94° C. to a silver-colored
liquid, which preserves its lustre for some time if well
covered with kerosene.

If the test-tube is allowed to become cold, the metal solid-
ifies, taking the form of the interior of the tube.

Large, dry test-tube ; kerosene ; Na.

349

350

CHEMICAL LECTUKE EXPERIMENTS

_^r

3. Action of sodium on water. — The action of sodium on
water with the liberation of hydrogen and the formation of
sodium hydroxide is best shown by means of the apparatus

(Fig. 148). A glass tube, 20 cm. long
and 9 to 10 mm. internal diameter, is
a clamped in a vertical position with its

lower end dipping 3 cm. below the sur-
face of water in a 300 cc. cylinder. The
water should about three-fourths fill the
cylinder and should contain a few drops
of phenol-phthalein solution. A piece
of sodium is pressed into a spherical
mass not more than 4 mm. in diameter.
In preparing this pellet of sodium it is
important that the hands should not be
— ^ wet or too moist from perspiration. On
Fig. 148 dropping the sodium into the vertically

clamped tube the decomposition of the
water is immediately effected, and in a few moments hydro-
gen may be ignited at the upper end of the tube. The
sodium hydroxide obtained in the reaction, being heavier
than water, settles to the bottom of the cylinder in currents
and, by reason of its alkalinity, imparts a strong color to
the phenol-phthalein solution.

If care is taken to prepare a spherule of sodium, it will
remain in the centre of the cup formed on the surface of
the water by the capillarity of the tube and regularly evolve
hydrogen. At times, however, especially if the sodium
is not spherical in form or if the interior of the glass
tube is wet above the level of water in the cylinder, the
sodium will stick to the glass, and a slight explosion will
occur.

Apparatus (Fig. 148) ; 20 cm. length glass tube 10 mm. diam. ;
phenol-phthalein solution ; Na.

SODIUM 351

4. Color change of sodium peroxide by heat. — One gram
of sodium peroxide is heated in a test-tube. The powder
undergoes a marked change in color from white to yellow.
This change in color, however, indicates no chemical change,
as the introduction of a glowing splinter fails to detect any
evolution of oxygen, and, on cooling, the yellow disappears.

Sodium peroxide ; splinter.

5. Oxidizing action of sodium peroxide. — (a) With phos-
phorus.— A very small quantity of sodium peroxide is care-
fully mixed on paper with an equal volume of red phosphorus.
The mixture is then wrapped in a powder paper (Ex. 25, p.
248), placed on an anvil, and struck with a hammer. A
sharp report is heard. (Gauntlets.)

Hammer and anvil ; powder paper (Ex. 25, p. 248) ; gauntlets ;
Na202 ; red P.

(b) With carbon. — A small quantity of powdered char-
coal is mixed with an equal volume of powdered sodium
peroxide and gently heated. The oxidation is very vigorous.

The sodium peroxide should first be placed in the test-
tube and then the charcoal added and the mixture well
shaken. At times the reaction will take place even in the
cold.

The mixture of charcoal and sodium peroxide may be
caused to explode by adding one drop of water. The exper-
iment should be performed behind a glass screen.

A few drops of nitrobenzene are allowed to fall upon 1 or
2 g. of powdered sodium peroxide in a dry test-tube. On
gently heating the tube an explosion is obtained.

Glass screens ; Na202 ; nitrobenzene ; powdered charcoal.

6. Supersaturation of sodium sulphate solution. — The

phenomenon attending the disturbance of a supersaturated
solution is well shown by the solution of sodium sulphate.

352 CHEMICAL LECTURE EXPERIMENTS

Two hundred grams of crystallized sodium sulphate are
heated in a 500 cc. flask until the salt has completely melted.
A plug of cotton should then be placed in the mouth, and
the flask allowed to stand until cold. If the operation is
performed with care, the salt will remain in the liquid con-
dition. On removing the cotton plug, and dropping a small
crystal of sodium sulphate into the melted liquid, the con-
tents of the flask immediately solidify.

If the bulb of the ether thermometer (Ex. 73, p. 174) is
inserted in the liquid, the rise in temperature resulting from
the solidification of the salt will cause the ether to boil and
escape from the mouth of the tube.

The solidification of the supersaturated solution may also
be accomplished by rapidly pouring it into a crystallizing
dish.

By agitating it with a glass rod, the liquid may be caused
to solidify while in the flask.

500 cc. flask ; cotton-batting ; ether thermometer (Ex. 73, p. 174) ;
crystallized Na2S04.

7. Freezing mixture of sodium sulphate and hydrochloric
acid. — Crystallized sodium sulphate, when mixed with
hydrochloric acid, produces a lowering in temperature
amounting to nearly 30° C.

Eighty grams of the crystallized salt are finely pulverized
and mixed in a flask wTith 40 cc. of concentrated hydro-
chloric acid. If the flask is placed upon a few drops of
water on a block, the water will be frozen and the flask
cemented to the wood. The acid must be previously cooled
to 10° C. .

Flask ; block of wood ; Na2S04 + 10H2O ; con. HC1.

8. Formation of metallic silicates in a solution of sodium
silicate. — The metallic silicates may be formed in a solution

SODIUM

353

of sodium silicate by dropping crystals of the various salts
into the liquid. As the silicate forms it spreads out in a
treelike structure.

A liter beaker is filled with a solu-
tion of sodium silicate having a specific
gravity of 1.10. Crystals of cobalt ni-
trate, nickel sulphate, uranium nitrate,
manganese sulphate, ferrous sulphate,
and copper sulphate are allowed to fall
in the beaker and rest on different parts
of the bottom (Fig. 149). The forma-
tion of the silicates requires some time,
though frequently marked indications of
their formation may be observed at the end of half an hour.
The beaker should be placed in a quiet place, and not dis-
turbed until the next exercise.

Large beaker; water-glass solution (sp. gr. 1.10); crystals of
Co(N03)2, NiS04, Ur02(N08)2, MnS04, FeS04, CuS04.

Fig. 149

POTASSIUM

1. Vaporization. — Potassium, when strongly heated in a
glass test-tube, yields a green vapor.

A small piece of potassium, carefully cleaned and dried,
is placed in a dry test-tube and strongly heated. The metal
is vaporized and rapidly attacks the glass, liberating the
silicon. The interior of the tube becomes blackened.

The color of the potassium vapor may be better seen if a
piece of clean, dry potassium is heated in a bulb-tube through
which a current of dry hydrogen is passed. After making
sure that the bulb is filled with hydrogen and that all air is
expelled, the potassium is strongly heated in a blast-lamp,
the supply of hydrogen being cut down to a minimum.
If the heat is supplied quickly, the globule of molten potas-
sium bursts, filling the whole bulb with a green vapor.

The current of hydrogen may be increased, and the issuing
gas will burn with the violet flame of potassium.

H generator ; dry test-tube ; dry bulb-tube ; blast-lamp ; K.

2. Union of potassium and bromine. — Potassium and
bromine unite with explosive violence to form potassium
bromide.

A 3 mm. piece of potassium is carefully dried between
filter-paper and dropped into a test-tube containing a few
drops of bromine. As the reaction is so violent, special
precautions are necessary when performing this experiment.

354

POTASSIUM 355

The test-tube must be placed inside a wide-mouthed bottle
(Fig. 109, p. 262) to collect the bromine in case of accident.
The closed end of the test-tube is thrust through a hole in a
cork or piece of cardboard. A large inverted funnel, with a
cork in the stem, is suspended by a ring-stand 15 cm. directly
above the tube, to prevent pieces of potassium or drops of
bromine from coming out of the tube. Finally, the hands
should always be protected with gauntlets.

2 K + Br2 = 2 KBr.

Apparatus (Fig. 109, p. 262) ; wide-mouthed bottle ; cardboard ;
funnel ; gauntlets ; K ; Br.

3. Union of potassium and iodine. — When heated, potas-
sium and iodine unite directly with explosive violence.

A 3 mm. piece of potassium is gently warmed in a clean,
dry test-tube, with a crystal of iodine. The elements unite
with an explosion.

Dry test-tube ; K ; I.

4. Use of potassium nitrate in touch-paper. — Unsized
paper drenched in concentrated potassium nitrate solution
and then dried finds much use as touch-paper for igniting
combustible mixtures. A quantity of the paper should be
prepared for general lecture-table use.

A solution of potassium nitrate, saturated at the tempera-
ture of the room, is placed in a small beaker. Strips of
filter-paper are then thoroughly moistened with the solution,
hung up, and allowed to dry (not by a flame). If the solu-
tion is saturated at the boiling temperature, an excess of
nitre will be crystallized on the surface of the paper in such
a way as to be continually rubbing off.

On igniting one end of a strip of the dried paper the
combustion will slowly proceed till the paper is completely

356 CHEMICAL LECTURE EXPERIMENTS

consumed. The fire cannot be extinguished by blowing
on it.

By means of a fine camel' s-hair brush a letter or word is
written on a sheet of unsized paper with a concentrated
solution of potassium nitrate.. After the paper has become
thoroughly dry and suitably suspended, a match touched to
one corner of the word will cause a lively combustion, which
will follow the line of the word and ultimately burn it out.
A brush marking lines not over 3 mm. in width should be
used, as otherwise there is danger of the whole paper
taking fire.

Unsized paper ; fine camel' s-hair brush ; saturated solution of
KN03.

5. Preparation of gunpowder. — Thirty grams of finely
powdered potassium nitrate, 5 g. of powdered charcoal, and
5 g. of sulphur flowers are intimately mixed on paper.
Three-fourths of this mixture is placed on a plate or a piece
of asbestos paper and ignited in the hood. When the mix-
ture is ignited, it burns brightly, leaving a residue which
contains potassium sulphide. On moistening the residue
with hydrochloric acid, hydrogen sulphide is liberated.

The value of pressing and granulating gunpowder is
markedly shown by the following experiment : The remain-
der of the above mixture is placed on one square of asbes-
tos and an equal quantity of gunpowder is placed on a
second square. Two strips of touch-paper are cut of equal
length and inserted in the two heaps of powder. After
placing the asbestos squares in the hood the touch-paper
is ignited. The commercial gunpowder burns with an
instantaneous flash, while the mixture burns much more
slowly.

Asbestos paper ; touch-paper ; gunpowder ; KX03 ; powdered
charcoal ; S flowers.

POTASSIUM 357

6. Combustion of phosphorus in potassium chlorate. — A

depression is made in the top of a small heap of finely pul-
verized potassium chlorate on asbestos paper. A 3 mm.
piece of well-dried phosphorus is laid in the depression and,
after placing the asbestos plate in a strong draft, the phos-
phorus is ignited by means of a candle or taper on the end
of a long stick. The phosphorus burns fiercely in the
oxygen liberated from the potassium chlorate.

Asbestos paper ; candle on long stick ; KC103 ; P.

7. Use of potassium chlorate in colored fires (Bengal fires).

— In all mixtures containing potassium chlorate it is of the
utmost importance that each substance should be reduced to
a fine powder before mixing, and that the mixing should
be done on paper with the fingers (never in a mortar ! ! !),
causing as little friction as possible. With reasonable care
no difficulty will be experienced.

The ignition of colored fires is most satisfactorily effected
by igniting a piece of touch-paper inserted in the top of the
conical pile of powder. Ignition from a match is exceed-
ingly uncertain and at times dangerous.

A characteristic fire may be prepared by mixing 2 g.
of copper sulphate, 2.5 g. of sulphur flowers, and 15 g. of
potassium chlorate. This mixture, when ignited, burns
with a purple flame.

Asbestos paper ; touch-paper ; CuSOi ; KC103 ; S flowers.

AMMONIUM COMPOUNDS

1. Preparation of ammonium amalgam. — This interest-
ing amalgam is prepared by the action of sodium amalgam
of a soft, waxy consistency on a warm saturated solution of
ammonium chloride. The sodium amalgam, when kneaded
with the fingers in the ammonium chloride solution, which
it rapidly attacks, swells up and forms a butterlike mass,
which is porous and rapidly decomposes.

Sodium amalgam ; saturated NH4C1 solution.

2. Preparation of ammonium amalgam by the electrolysis
of a solution of ammonium sulphate. — By the electrolysis

of ammonium sulphate free ammonium is
liberated at the negative pole, and if an
electrode of mercury is used, the ammonium
amalgamates with it, forming ammonium
amalgam.

A saturated solution of ammonium sulphate
is placed in a 150 cc. cylinder having a 2 cm.
layer of mercury on the bottom (Fig. 150). A
well-insulated copper wire is thrust into the
solution and the bare end pressed under the
mercury. The positive electrode should con-
sist of a small piece of platinum. On pass-
ing a current from 4 cells of a " bichromate "

battery through the solution the decomposition is effected.

The mercury at the bottom of the cylinder swells up with

Fig. 150

AMMONIUM COMPOUNDS

359

the formation of ammonium amalgam, and care should be
taken to stop the current before the mercury has reached
the platinum electrode. A piece of ordinary annunciator
wire which is well covered with paraffin will serve as a
conductor to the mercury electrode.

Battery ; 150 cc. cylinder; annunciator wire ; Pt electrode ; Hg ;
(NH4)2S04 saturated solution.

3. Union of ammonia and hydrochloric acid to form ammo-
nium chloride. — (a) A liter cylinder is filled with hydro-
chloric acid gas either by downward displacement or by
shaking 5 cc. of concentrated hydrochloric acid about in it
for a few minutes, and is then covered with a glass plate.
A brush such as is used for cleaning lamp chimneys is
drenched with strongest ammonium hydroxide, and plunged
suddenly into the jar of hydrochloric acid. A piece of card-
board large enough to cover the jar may be slipped over the
brush handle and the brush suspended in the middle of the
jar, the glass plate being quickly removed at the moment
of inserting the brush. The cardboard prevents any escape
of ammonium chloride fumes. As the
strongest ammonium hydroxide is disagree-
able to use in an open room, it is advisable
to crowd the brush down into a cylinder just
large enough to hold it before pouring on
the ammonium hydroxide. A small quan-
tity of ammonium hydroxide will thereby
suffice to drench the brush thoroughly.

Brush ; cardboard ; con. HC1, or HC1 generator ;
con. NH4OH.

(b) Two tubulated bell-jars, each fitted FlG

with a one-holed rubber stopper carrying
a short piece of glass tubing, are connected by a piece of
rubber tubing slipped over the glass tubes (Fig. 151). The

360 CHEMICAL LECTURE EXPERIMENTS

bell-jars are clamped in a vertical position and the rubber
tube closed with a pinch-cock. The lower bell-jar is filled
with ammonia by displacement and the upper with hydro-
chloric acid gas by displacement. On opening the pinch-
cock the ammonia, by reason of its smaller specific gravity,
ascends through the rubber tube and forms white clouds in
the upper bell-jar.

Two tubulated bell-jars ; corks ; tubes and pinch-cock ; NH3 sup-
ply ; HC1 gas supply.

4. Union of ammonia and hydrogen sulphide. — Crystal-
lized anhydrous ammonium sulphide results from the inter-
action of dry ammonia gas and dry hydrogen sulphide.

A clean, dry, 3 1. flask is filled with ammonia gas

by displacement. When completely filled a current of

hydrogen sulphide, dried by passing over calcium chloride,

is conducted into the flask. On cooling the flask somewhat,.

a deposit of fine crystals of ammonium sulphide will appear

on the interior.

2 NH3 + H2S = (NH4)2S.

3 1. flask ; NH3 supply ; H2S supply.

5. Dissociation of ammonium sulphate solution. — Two
grams of ammonium sulphate are dissolved in 300 cc. of
water in a 500 cc. retort. Blue litmus solution is intro-
duced, one drop of ammonium hydroxide being added, if
necessary, to give a decidedly alkaline color. The retort is
placed on a ring-stand and clamped, with the neck dipping
into a 500 cc. flask containing 100 cc. of litmus solution
colored red by the addition of one drop of dilute sulphuric
acid. On gently heating to the boiling point (care being
taken to prevent too violent ebullition, as otherwise some
of the fluid made alkaline is liable to be mechanically car-
ried over), ammonia gas distils over, and soon the upper

AMMONIUM COMPOUNDS 861

portion of the liquid in the receiver will be seen to have
acquired a blue color, while the liquid in the retort gradu-
ally turns a decided red. The complete change in color is
noticed after boiling for thirty minutes.

500 cc. retort ; 500 cc. flask ; litmus solution ; 2 g. (NH4)2$04.

6. Decomposition of ammonium dichromate by heat. —

Ammonium dichromate, when heated, undergoes a complete
decomposition, resulting in the formation of nitrogen, water,
and chromium sesquioxide.

One or two grams of powdered ammonium dichromate are
heated in a hard-glass test-tube till the decomposition, which
is characterized by an increase in volume of the mass and
an appearance of fire, begins. The heat of the decomposi-
tion, when once started, is sufficient for completion, and the
mass expands, filling the tube with a tealike substance,
chromic oxide. Nitrogen gas is given off, and a lighted
match thrust in the tube is extinguished. At the end of
the reaction the water-vapor formed escapes as steam at the
mouth of the tube. The residue of chromic oxide formed
may be poured upon a white plate, where its peculiar form
is more easily observed.

(XH4),Cr2Or = Cr203 + 4 H20 + N*
Hard-glass test-tube ; white plate ; (XH^Ci^Oy.

7. Decomposition of solid ammonium nitrate by zinc dust.

— If ammonium nitrate in the solid form is mixed with zinc
dust, the reduction is so vigorous as to produce a great in-
crease in temperature, which, under certain conditions,
causes the ignition of the zinc.

A mixture of 8 g. of ammonium nitrate and 1 g. of am-
monium chloride is spread out in a thin layer on an iron
plate. A layer of equal thickness of zinc dust is sprinkled
on top of this layer. On allowing one drop of water to come

362 CHEMICAL LECTURE EXPERIMENTS

in contact with this mixture, the reaction takes place, and
the heat developed is so great as to cause an ignition of the
zinc dust. The ammonium nitrate should be previously
dried, for, owing to its hygroscopic nature, it will retain
enough moisture to cause a premature ignition of the zinc
without the addition of water. In fact, the experiment may
be performed by using a moist ammonium nitrate, and the
addition of water dispensed with. Care should be taken,
however, to prevent any danger from the premature igni-
tion of the zinc dust, as it will probably be ignited before
the mixture of the ammonium salts can be entirely covered
with it.

Iron plate ; NH4N03 ; NH4C1 ; Zn dust.

8. Preparation of ammonium carbonate (carbamate ? )
from ammonia and carbon dioxide. — Dry carbon dioxide,
when allowed to come in contact with dry ammonia, forms
ammonium carbamate, a constituent of commercial ammo-
nium carbonate.

A dry 3 1. flask (Fig. 92, p. 222) is filled with ammonia
by displacement, and a slow stream of dry carbon dioxide con-
ducted into it. After a short time the walls of the flask become
covered with a crystalline deposit of ammonium carbamate.

3 1. flask ; NH3 supply ; C02 generator.

9. Preparation of ammonium carbonate by the inter-
action of ammonia and carbon dioxide in an alcoholic solu-
tion.— When carbon dioxide is conducted into an alcoholic
solution of ammonia, a white crystalline deposit of ammo-
nium carbonate (ammonium carbamate ? ) is formed.

Fifty cubic centimeters of alcohol are saturated with am-
monia gas and a rapid stream of carbon dioxide conducted
through the solution in a beaker.

Alcohol ; C02 generator ; NH3 supply.

CALCIUM

1. Action of calcium oxide with water. — Calcium oxide
unites with water, with, the liberation of great heat, to form
calcium hydroxide.

A piece of freshly burned quicklime is immersed in water
for two or three seconds and then placed on a plate. In a
few moments the lime becomes very much heated, swells up,
and falls to a powder.

Four or five lumps of quicklime may be placed in a large
evaporating-dish and moistened with hot water. The lime
swells up, filling the evaporating-dish, and giving rise to
intense heat. A match may be ignited by placing the head
in one of the crevices formed as the lime crumbles.

If an especially good piece of lime is available, the heat
is often sufficient to ignite gunpowder. The lime should
be placed on a plate and drenched with boiling water. As
soon as the reaction begins, .5 g. or less of gunpowder should
be sifted from a piece of paper or card upon the lime. Care
should be taken to close the powder-container and remove it
from any possible danger of accidental explosion before pour-
ing the water upon the quicklime.

Crockery plates ; hot water ; fresh quicklime ; gunpowder.

2. Calcium oxide as a drying agent. — The affinity of cal-
cium oxide for moisture makes this compound an effective
drying agent for many gases.

363

364

CHEMICAL LECTURE EXPERIMENTS

The absorption of moisture from a gas by calcium oxide
may be shown by moistening the interior of a bell-jar by
holding it over a hydrogen flame and then placing it on a
porcelain plate in the centre of which are a few lumps of
good quicklime. A second bell-jar may advantageously be
moistened and placed over a plate containing no lime. In
a short time all the moisture on the walls of the bell-jar
covering the lime will disappear, while the other jar will
remain unchanged (Fig. 76, p. 175).

Two 1. bell-jars ; 2 plates ; H flame ; fresh quicklime.

3. Preparation of calcium phosphide. — Phosphorus,
when in contact with heated quicklime, forms calcium phos-
phide.

Five grams of well-dried yellow phosphorus are inserted
in a 50 cm. length of combustion tubing, 1.5 cm. internal

€U>Q t£^'&^f%S&3g&& Q

K-J

C-W

Fig. 152

diameter, closed at one end. A plug of asbestos is then
introduced and a 20 cm. length of the tube filled with lumps
of good quicklime (Fig. 152). The tube is so placed over a
four-tube burner that the lime may be strongly heated before
heating the phosphorus. When the lime has become hot, the
phosphorus is brought to a boil and the vapor passed over

CALCIUM 365

the heated lime. The phosphorus end of the tube should be
heated with a Bunsen burner held in the hand, and a plate
of sand should be placed beneath the boiling phosphorus.
As the phosphorus vapor comes in contact with the hot lime,
the lime glows and turns black, forming calcium phosphide.
The decomposition of the product by wrater is shown in
Exs. 29, 30, p. 252.

50 cm. length combustion-tubing; plate of sand; 4-tube burner;
fresh quicklime ; P.

4. Hydration of anhydrous calcium sulphate. — When
anhydrous calcium sulphate (plaster of Paris) is mixed with
water, the water combines with the salt, forming a hard mass
which may be used to take impressions.

A coin may be placed in the bottom of a small pill-box
and the box filled with a thick, freshly prepared paste of
plaster of Paris and water. On allowing the mixture to
stand for half an hour it will harden. The bottom of the
box can be cut away and the coin removed, leaving an im-
pression in the plaster.

The absorption of water by plaster of Paris may be shown
by simply mixing the plaster and water to a thick paste.
In a few moments the mixture will have set sufficiently to
remain in the beaker when it is inverted.

Pill-box ; plaster of Paris.

5. Decomposition of calcium carbonate in an atmosphere
of air or hydrogen. — While calcium carbonate is not decom-
posed in an atmosphere of carbon dioxide (see Ex. 22, p. 304),
it is readily decomposed when heated in an atmosphere of
hydrogen or air. (Burning limestone.)

A few lumps of calcite are placed in the bulb-tube through
which a current of hydrogen freed from carbon dioxide is
being passed. The issuing gas is conducted through a glass

366 CHEMICAL LECTURE EXPERIMENTS

elbow dipping into a beaker of lime-water. Until the calcite
is heated the lime-water remains clear. As soon as the bulb
is strongly heated, carbon dioxide is evolved and is carried
by the hydrogen current into the lime-water, where it pro-
duces a precipitate.

On cooling and leaching out the contents of the bulb with
water, they will be found to be strongly alkaline on account
of the formation and the subsequent hydration of the cal-
cium oxide.

The experiment may be repeated with the same results by
using air freed from carbon dioxide in place of hydrogen.

CaC08=CaO + C02.

Bulb-tube ; H generator ; lime-water ; calcite.

STRONTIUM AND BARIUM

1. Deflagration of strontium nitrate on charcoal. — A

crystal of strontium nitrate, when thrown on glowing char-
coal, deflagrates vigorously, giving rise to a red flame.

If charcoal powder is heated to glowing in an iron saucer
and powdered strontium nitrate is thrown into the dish, the
combustion is brilliant.

Iron dish ; charcoal ; Sr(N03)2.

2. Use of strontium nitrate in red fire. — Strontium
nitrate is the essential coloring ingredient in red fire.

A mixture of 1 g. of potassium chlorate, 11 g. of stron-
tium nitrate, 4 g. of sulphur flowers, and .5 g. of lamp-black,
all of which have been previously finely powdered and care-
fully mixed on paper, burns with an intense red flame.
The mixture, which should be placed in the hood, is ignited
with a short piece of touch-paper.

Asbestos paper ; Sr(N03)2 ; KC103 ; S flowers ; lamp-black ; touch-
paper.

3. Preparation of barium peroxide. — When barium oxide
is heated in the presence of oxygen, it absorbs oxygen, form-
ing barium peroxide.

A 20 cm. length of combustion-tubing provided with a
one-holed rubber stopper at each end is three-fourths filled
with barium oxide and so supported that it can be heated
with a four-tube burner (Fig. 153). A current of oxygen,

367

368

CHEMICAL LECTURE EXPERIMENTS

which is allowed to bubble through sulphuric acid in a gas
washing-bottle, is passed through the tube, the issuing gas
bubbling through a second gas washing-bottle at the other

mmp^^^^^iry^B

Fig. 153

end. On heating the barium oxide oxygen will be absorbed
and the rate of bubbling in the second bottle will be much
less than that in the first.

The barium oxide should not be heated too much, as other-
wise the oxygen will again be expelled.

2 BaO + 02 = 2 Ba02.

Two gas washing-bottles ; 20 cm. length combustion-tubing ; 4-tube
burner ; O supply ; BaO.

4. Decomposition of barium peroxide by heat. — A por-
tion of the barium peroxide from the preceding experiment
may be heated in a test-tube and the liberated oxygen tested
with a glowing splinter.

Hydrated barium peroxide on heating yields large quanti-
ties of water, which are likely to condense and break the
tube. If, however, it is carefully heated until no more
steam escapes, the temperature may be raised and the
oxygen liberated. The residue on treatment with water
yields an alkaline solution of barium hydroxide.

5. Action of hydrogen on barium peroxide. — When barium
peroxide is heated in an atmosphere of hydrogen, the reac-

STRONTIUM AND BARIUM 369

tion is very vigorous, the barium peroxide becoming heated
to incandescence.

A small quantity of barium peroxide is placed in a bulb-
tube through which a current of hydrogen is being passed.
On heating the barium peroxide slight explosions of oxy-
hydrogen gas take place in the bulb, the barium peroxide
appearing brilliantly incandescent.

Bulb-tube ; H generator ; Ba02.

6. Barium sulphate from barium oxide and sulphur tri-
oxide. — Sulphur trioxide unites directly with barium oxide
to form barium sulphate. The evolution of heat in the
operation is great and consequently the sulphur trioxide
(or fuming sulphuric acid) should be placed in a test-tube
clamped over a dish of sand. On carefully sifting a small
quantity of barium oxide into 2 g. of the sulphur trioxide,
the reaction takes place accompanied by light

BaO + S03 = BaS04.

Plate of sand ; S03 or fuming H2S04 ; BaO.

7. Insolubility of barium sulphate in water. — The great
insolubility of barium sulphate in water may be interest-
ingly shown by adding sulphuric acid to successive quan-
tities of increasingly diluted solutions of barium chloride.
Fifty cubic centimeters of a saturated solution of barium
chloride are placed in a 100 cc. cylinder. Five cubic centi-
meters of this solution are placed in a second 100 cc. cylinder
and sufficient water added to dilute the solution to 50 cc.
Five cubic centimeters of this dilute solution are placed in
a third cylinder and diluted to 50 cc, the operation being
carried out to the fifth dilution. On adding equal quan-
tities of dilute sulphuric acid to each of the cylinders
various degrees of turbidity will be obtained, the fifth cylin-

370 CHEMICAL LECTURE EXPERIMENTS

der containing, however, a distinct precipitate of barium
sulphate.

This experiment may be reversed by using concentrated
sulphuric acid and diluting, adding a solution of barium
chloride as the reagent.

BaCl2 + H2S04 = BaS04 + 2 HC1.

Five 100 cc. cylinders ; BaCl2 solution.

8. Deflagration of barium nitrate and chlorate on char-
coal. — A piece of charcoal having a small hollow scooped
out on one side is heated to glowing in the Bunsen flame. On
throwing a few crystals of barium nitrate on the charcoal
the salt deflagrates vigorously.

If barium chlorate instead of barium nitrate is used, a
most violent combustion takes place.

Charcoal ; Ba(N03)2 ; Ba(C103)2.

9. Use of barium nitrate in green fire. — Barium nitrate
is the essential coloring ingredient in green fire.

A mixture of 3 g. of finely powdered potassium chlorate,
8 g. of finely powdered barium nitrate, and 3 g. of sulphur
flowers, when intimately mixed and ignited on asbestos
paper, burns with an intense green flame.

Asbestos paper ; touch-paper ; KC103 ; Ba(N03)2 ; S flowers.

10. Deflagration of barium chlorate. — Barium chlorate,
when heated on a platinum wire in a Bunsen burner, defla-
grates, imparting an intense green color to the Bunsen flame.

The deflagration may be carried out on a much larger scale
by directing the Bunsen burner on a small heap of barium
chlorate on asbestos paper.

When thrown on hot charcoal, the salt deflagrates vigor-
ously.

Asbestos paper ; Pt wire ; Ba(C108)2.

MAGNESIUM

1. Combustion in water vapor. — The decomposition of
water by magnesium, even when in a finely divided state, is
at best very slow, and the hydrogen is liberated in such a
manner as to prevent its collection.

At a high temperature, however, the reaction between
magnesium and water vapor is intense, large quantities of
hydrogen being liberated.

Three hundred cubic centimeters
of distilled water are vigorously
boiled in a Jena glass Erlenmeyer
liter flask with a wide neck, and a
lighted taper is introduced into the
neck of the flask to demonstrate that
water vapor is a non-supporter of the
combustion of wood and to indicate
that all the air is driven out of the
flask. A small quantity of magne-
sium powder is ignited with a match
on a deflagrating-spoon designed to
be turned over and thus spill its con-
tents (Fig. 154). A crude, though
thoroughly practical and satisfactory

spoon may be made by fastening to a stout iron wire about
30 cm. long a round piece of cork, 1 cm. thick and 2.5 cm.
in diameter, on which rests a small porcelain crucible cover,

371

Fig. 154

372 CHEMICAL LECTURE EXPERIMENTS

whose ring is pressed into a small slit in the cork thus
making it secure. The iron wire is thrust into the edge of
the cork and bent upright close to it to permit of lowering
the spoon into the flask. A piece of string 30 cm. long is
fastened to a tack or pin in the rim of the cork 90° from
the point where the iron wire is inserted. By pulling this
string, if the cork is not fastened too tightly to the iron
wire, the spoon may be turned through an angle of 90° and
its contents spilled out.

After ignition in the air the magnesium powder is lowered
one-third of the way into the flask and the string pulled,
thereby allowing the powder to fall through the steam. A
blinding flash equalled only by the burning of the powder
in air follows.

If the string catches fire in the air, it is instantly extin-
aished on lowering the spoon into the flask.
/ Inasmuch as the combustion is very rapid it is necessary
to cover the hand holding the spoon with a gauntlet.

all

Mg + H20 = MgO + H2.

Apparatus (Fig. 154) ; 1 1. Jena glass Erlenmeyer flask ; defla-
grating-spoon of special construction ; gauntlets ; Mg powder.

2. Combustion of magnesium in carbon dioxide. — A 300 cc.

cylinder containing a layer of sand and a carbon dioxide
delivery -tube extending to the bottom is filled with carbon
dioxide and the dry gas allowed to flow continuously into it.
Twenty-five hundredths of a gram of finely powdered mag-
nesium (the finer the powder, the better) is placed on a 2 em.
disk of previously ignited asbestos paper, which can be
easily cut out of sheet asbestos by means of a large-sized
cork borer. The asbestos disk and the magnesium powder
are laid on a loop in a stout iron wire thereby forming a
deflagrating-spoon. On igniting the powder and quickly

MAGNESIUM 373

lowering it into the jar till the spoon touches the sand a
marked increase in the intensity of the combustion takes
place. A piece of asbestos cardboard with a slit in it wide
enough to hold the glass tube is quickly slipped over the top
of the jar. In this way air currents formed by the combus-
tion of the magnesium will be prevented, and thus no con-
siderable amount of air admitted. The glass tube through
which the carbon dioxide is passing is now held directly
over the burning magnesium, and a lighted match inserted
in the slit of the asbestos. If there is a sufficient supply of
carbon dioxide, the match should be extinguished.

After the glow has died out the spoon is withdrawn and
the rather compact mass of magnesium oxide and carbon is
transferred by means of a spatula from the asbestos disk to
a white plate. While the exterior of the mass appears white
from the coating of magnesium oxide, on cutting the lump
in two the interior will be seen to be perfectly black, the
carbon completely covering the color of the magnesium
oxide.

300 cc. cylinder ; asbestos deflagrating-spoon ; white plate ; dry
C02 supply.

3. Magnesium and nitric acid. — Metallic magnesium
reacts with nitric acid, forming magnesium nitrate with
the liberation of heat and light.

Five cubic centimeters of fuming nitric acid are gently
warmed in a wide-mouthed flask. On removing the lamp
and dropping .25 g. of fine magnesium powder on the hot
acid, the metal takes fire, burning with almost explosive
violence. (Use gauntlets and glass shields.)

The great quantity of oxides of nitrogen evolved make it
necessary as a rule to perform this experiment in a hood or
draft. In case the first lot of powder does not catch fire, a
like quantity must immediately be poured into the neck of

374 CHEMICAL LECTURE EXPERIMENTS

the flask, gently tapping the paper in order not to drop the
whole at once.

Gauntlets ; shields ; Mg powder ; wide-mouthed 100 cc. flask ; fum-
ing HN03.

4. Reduction of metallic oxides and salts. — Magnesium is
a very powerful reducing agent and will abstract the oxygen
from many metallic oxides with explosive violence.

(a) Magnesium and silver oxide. — Equal volumes of mag-
nesium powder and dry silver oxide are mixed on a paper
and a centimeter layer poured into a small, dry test-tube.
The tube is clamped to a retort-stand in such a position that
a Bunsen flame may be set under it and the bottom of the
tube come in the hottest part of the flame. The retort-stand
is now placed between glass shields, and the lamp, resting
on a plate filled with sand or on a piece of asbestos paper,
is placed under the tube. (Gauntlets.) After a moment's
heating, the reduction of the silver oxide takes place with an
explosion. Should the tube be intact, the black metallic
silver will be seen as a fine coating on the sides.

(b) Magnesium and lithium carbonate. — Lithium carbon-
ate is energetically reduced by magnesium powder when the
two are heated in equal volumes as described above.

At the moment that the reaction takes place, the fine red
color of the burning lithium vapor is apparent.

Ag20 + Mg = MgO + 2 Ag.

Li2C03 + Mg = MgO + CO, + 2 Li.

Glass shields ; gauntlets ; Ag20 ; Li2C03 ; Mg powder.

5. Combustion of magnesium with potassium chlorate. — A

mixture of equal parts by volume of finely pulverized dry
potassium chlorate and magnesium powder, when ignited
on an asbestos plate, gives an instantaneous flash of blind-

MAGNESIUM 375

ing intensity. A long taper or a touch-paper fuse should
be used in igniting the mixture. Care should be taken to
protect the face, owing to the great volume of smoke given
off. The above mixture is commonly used in many of the
so-called flashlight cartridges.

Asbestos paper ; touch-paper ; gauntlets ; colored glasses ; powdered
KCIO3 ; Mg powder.

6. Formation of magnesium nitride. — At a high tempera-
ture magnesium combines with free nitrogen to form the
nitride. The conditions for the formation of the maximum
quantity of this compound are best secured when 1 g. of
magnesium powder is heated in a porcelain crucible with a
Bunsen burner. The crucible should not be more than half
full of the powdered metal. The powder soon begins to
burn on the surface, the product being chiefly magnesium
oxide. The burning mass is gently stirred with an iron
wire, and the combustion will slowly proceed for a few
minutes. Under these conditions the oxygen is quickly
removed from the air, and at the temperature of the com-
bustion nitrogen is readily absorbed. The resulting product
is a yellowish powder consisting of white magnesium oxide,
with a varying proportion of magnesium nitride. This
operation shows the method of separating atmospheric nitro-
gen from argon. The cooled product should be securely
sealed in a bottle.

3Mg + N2 = Mg3N2.
Porcelain crucible ; Mg powder ; iron wire.

7. Decomposition of magnesium nitride by water. — Mag-
nesium nitride is decomposed by water, forming magnesium
oxide and ammonia.

A few drops of water are allowed to fall on some of

376 CHEMICAL LECTURE EXPERIMENTS

the nitride in a test-tube. A brisk evolution of a gas is
obtained, which, when tested, is seen to be ammonia.

MgaN2 + 3 H20 = 3 MgO + 2 NH3.

8. Action of hydrogen on magnesium nitride. — A current
of dry hydrogen is passed through a bulb-tube containing
a small quantity of magnesium nitride. On heating, am-
monia will be formed and may be tested at the open end of
the bulb-tube.

Bulb-tube ; H generator ; Mg3N2.

ZINC AND CADMIUM

1. Granulated zinc. — When melted zinc is poured in a
thin stream from a height of 2 or 3 m. into a pail of cold
water, the drops of melted metal
spread out on striking the water,
producing a form of zinc called
granulated zinc. The zinc should
have been previously melted in a
large Hessian crucible, which is
then brought into the lecture room.

Instead of melting a large quan-
tity of zinc before the lecture, the
apparatus shown in Fig. 155 may
be used to melt and granulate the
zinc. A Hessian crucible, provided
with a 3 or 4 mm. hole in the bot-
tom, is strongly heated with a blast-
lamp. Small lumps of zinc are
added from time to time, and a pail
of water is placed beneath the cru- FlG 155

cible. As the zinc melts, it flows

out of the opening in the bottom of the crucible and drops
into the water below.

Hessian crucible ; ditto with 3 mm. hole in the bottom ; blast-lamp ;
tongs ; pail of water ; Zn.

377

•

378 CHEMICAL LECTURE EXPERIMENTS

2. Deposition of zinc on iron (galvanized iron). — Iron
that is freed from all oxide, when heated and dipped into
melted zinc, becomes covered with a firmly adhering coating
of the metal.

A Hessian crucible is filled with zinc, which is then
melted. A large " cut " iron nail is strongly heated in the
blast, and then, after cooling, carefully cleaned with hydro-
chloric acid and sand. After washing off all acid and dirt,
the nail is again heated, dipped into a little olive or cotton-
seed oil, and then plunged into the molten zinc. On remov-
ing and cooling the nail, it will be found that that portion
dipped into the zinc will have become " galvanized."

Hessian crucible ; tongs ; cut nail ; Zn ; olive or cotton-seed oil.

3. Combustion of zinc dust and potassium chlorate. —

Ten grams of zinc dust are mixed with 5 g. of finely
powdered potassium chlorate on asbestos paper The mix-
ture, when ignited, burns with a white flame, leaving a yel-
low residue of zinc oxide, which, when cold, becomes white.

Asbestos paper ; Zn dust ; KC103.

4. Zinc sulphide from zinc dust and sulphur flowers. —

A mixture of zinc dust and sulphur flowers burns with
great brilliancy, forming zinc sulphide.

Ten grams of zinc dust and 5 g. of sulphur flowers
(molecular amounts) are carefully mixed on paper to pre-
vent friction and then lighted on a piece of previously
ignited asbestos paper under the hood. A brilliant green-
ish flame is observed. The zinc sulphide is intensely
yellow while hot, but bleaches out to a considerable extent
on cooling.

Zn + S = ZnS.

Asbestos paper ; Zn dust ; S flowers.

ZINC AND CADMIUM 379

5. Distillation of cadmium. — Cadmium boils at 770°,
and, when heated in a bulb-tube through which a current of
hydrogen is being passed, the metal vaporizes and condenses
as a metallic sublimate in the cooler portions of the tube.

A 4 or 5 mm. piece of metallic cadmium is placed in one
arm of a bulb-tube equidistant between the bulb and the
end of the arm. A current of hydrogen is then passed
through the bulb, and, after all air has been expelled, the
cadmium is heated until it boils. The interior of the bulb
becomes covered with a metallic deposit.

Bulb-tube ; H generator ; Cd.

6. Combustion of cadmium in air. — Cadmium, at a red
heat, is easily oxidized in the air.

One gram of cadmium is heated in a small porcelain cru-
cible by means of a good strong Bunsen flame. The metal
melts and soon begins to boil. The vapor ignites and gives
rise to dense clouds of the brown oxide. On removing the
lamp suddenly, the vapor can be seen burning in the cru-
cible, though after a few seconds the flame goes out. The
inside of the crucible will be covered with brown cadmium
oxide.

A small piece of cadmium is placed in a hollow scooped
out of a piece of charcoal. By directing the mouth of the
blowpipe, or, better still, the blast-lamp, or oxy hydrogen jet
upon it, the metal burns with more or less vividness accord-
ing to the source of heat. A brown smoke of cadmium
oxide rises from the burning globule.

2 Cd + 02 = 2 CdO.
Porcelain crucible ; blowpipe and charcoal ; Cd.

7. Preparation of cadmium sulphide. — When hydrogen
sulphide is conducted into a cold, neutral solution of cad-
mium chloride, a yellow precipitate of cadmium sulphide is

380 CHEMICAL LECTURE EXPERIMENTS

obtained. If, however, the cadmium solution is acidified
and kept hot, the sulphide precipitated is of an orange-red
color.

A current of pure hydrogen sulphide is conducted into a
series of two gas washing-bottles, the first of which contains
a cold, neutral solution of cadmium chloride, the second con-
taining a hot solution of cadmium chloride acidified with
hydrochloric acid. The second gas washing-bottle is placed
in a beaker containing hot water. On passing hydrogen
sulphide through the system, cadmium sulphide is precipi-
tated in both bottles and is of a yellow color in the first
and of an orange-red in the second. The solution in the
first bottle should not contain an excessive amount of cad-
mium chloride, as otherwise considerable time will be
required to saturate it with hydrogen sulphide.

Two gas washing-bottles ; large beaker of hot water ; H2S generator ;
CdCI2 solution.

MERCURY

1. Purification and filtration. — Mercury may be freed
from much foreign material by filtering through fine linen
or cambric, or through a dry, folded filter-paper having a
pinhole in the bottom.

The chemical purification of mercury is effected by shak-
ing the metal with very dilute nitric acid or dilute ferric
chloride solution in a large separating-funnel. The purified
metal should be well washed with water, the excess of water
being removed by placing filter-papers on the surface of the
metal.

Large separating-funnel ; linen cloth ; Hg.

2. Iron amalgam. — Under ordinary conditions iron does
not amalgamate. If, however, a piece of clean sheet-iron is
rubbed with liquid sodium amalgam and a filter-paper wet
with saturated ammonium chloride solution, the resulting
ammonium amalgam produces an amalgamation of the iron.

Sheet iron ; Na amalgam ; saturated NH4C1 solution.

3. Preparation of mercurous iodide from mercury and
iodine. — Mercury and iodine, when intimately rubbed in
molecular proportions, form an amorphous green powder
consisting of mercurous iodide.

Sixteen grams of mercury are placed in a mortar with
10 g. of iodine. A few drops of alcohol are then added,

381

382 CHEMICAL LECTURE EXPERIMENTS

and the mixture intimately rubbed with a pestle. In a few
moments a green amorphous powder will be formed. At
times certain portions of the powder will appear red, but
when all the globules of mercury have disappeared, the whole
mass will be green. The compound should be preserved in
the mortar for use in the following experiment.

2Hg + I2 = Hg2I2.
Mortar ; Hg ; I.

4. Preparation of mercuric iodide from mercurous iodide
and iodine. — When mercurous iodide is rubbed in a mortar
with an excess of iodine, it is converted to mercuric iodide.

Ten grams of iodine are added to the mercurous iodide in
the mortar from the preceding experiment, and the mixture
thoroughly rubbed with the pestle. In a short time the green
mercurous iodide will be completely converted to the red
mercuric iodide, all the iodine being taken up in the reaction.

Hg2I2 + I2 = 2HgI2.

Mortar and contents of preceding experiment ; I.

5. Formation of mercuric iodide from potassium iodide
and mercuric chloride. — A striking example of a dry reac-
tion is afforded by rubbing together equal weights of finely
powdered mercuric chloride and finely powdered potassium
iodide in a porcelain mortar. The two powders, when first
placed in the mortar, are perfectly white, but on intimately
mixing them with the pestle the mixture becomes red from
the formation of mercuric iodide.

Mortar and pestle ; finely powdered HgCl2 ; finely powdered KI.

6. Preparation of artificial cinnabar. — A solution of mer-
curic chloride is treated with ammonium hydroxide as long
as any precipitate is formed. A strong solution of sodium

MERCURY 383

thiosulphate is then added to the liquid until the precipi-
tate is completely dissolved. If the liquid thus prepared is
heated for some time in a beaker of water at a temperature
of 70°, a red precipitate of cinnabar is formed.

If a portion of the liquid is suddenly brought to a boil, the
cinnabar is immediately precipitated, but it has a brownish
red color.

Beaker of hot water ; HgCl2 solution ; Na2S203 solution.

COPPER

1. Deposition on iron. — Iron replaces copper in solutions
of cupric sulphate, forming ferrous sulphate and copper.

A cleaned knife-blade immersed for a few moments in rc
solution of cupric sulphate becomes covered with a thir
coating of metallic copper.

The complete removal of copper from solutions may b<
shown by placing three or four nails in a solution of cupri<
sulphate and allowing the vessel and its contents to stanc
twenty-four hours. All the copper will have been precipi
tated on the iron, the solution will have lost its blue color
and on the addition of ammonium hydroxide a greenisl
precipitate instead of a deep blue color will be obtained.

A piece of zinc when immersed in cupric sulphate solu
tion likewise replaces the copper, and this metal may b(
used in place of iron in the above experiment.

CuS04 + Fe = FeS04 + Cu.

Knife ; iron nails ; Zn rod ; CuS04 sol.

2. Electrical deposition of copper (copper plating). —

When a current of electricity is passed through a cupric
sulphate solution, copper is deposited on one electrode while
oxygen is liberated at the other (Ex. 7, p. 13).

Two platinum electrodes are connected with a bichromate
battery and then immersed in a solution of cupric sulphate

384

copper 385

Immediately the positive electrode becomes covered with a
red coating of copper. The negative electrode remains
unchanged. By reversing the current the copper is depos-
ited on the clean electrode while the other gradually loses
its coating, ultimately becoming perfectly bright and free
from copper.

Cards with the plus and minus signs should be placed
beside the electrodes.

Bichromate battery ; 2 Pt electrodes ; + and — signs; CuS04 solu-
tion.

3. Color of copper. — The color noticed on ordinary cop-
per is partially due to the presence of small quantities of a
superficial coating of the oxides of copper. The true color
of copper is shown by the reduction of hot cupric oxide by
alcohol vapor.

One cubic centimeter of ethyl or methyl alcohol is poured
into a good-sized test-tube loosely fitted with a rubber
stopper. A copper spiral (Ex. 38, p. 37) is then heated till
it is thoroughly oxidized, and while still hot carefully intro-
duced into the- test-tube containing alcohol. Immediately
the cupric oxide coating on the spiral is reduced, and the
color of metallic copper is seen. The rubber stopper is
held loosely in the test-tube until the expansion of the
gases in the tube ceases. At that moment the cork is
firmly introduced to prevent any air from entering the tube.

After cooling, the cork is withdrawn, and the spiral may
be taken out and examined. This is essentially the method
of preparing the reduced copper spiral used in elementary
organic analysis.

Copper spiral (Ex. 38, p. 37) ; alcohol.

4. Action of light on cuprous chloride. — Sunlight acts on
cuprous chloride, changing its color from white to dark violet.

386 CHEMICAL LECTURE EXPERIMENTS

A quantity of the freshly precipitated chloride may be
exposed to sunlight on a porcelain plate.

On immersing a strip of polished sheet copper in a con-
centrated solution of cupric chloride, the copper will become
covered with a coating of insoluble cuprous chloride. The
copper should then be washed with running water, and a
figure cut out of heavy paper placed over it. On exposure
to sunlight it will be found that the uncovered portion of
the sheet will become dark colored, while the covered por-
tion will remain light.

Cu sheet ; heavy paper ; CuClo solution ; freshly precipitated Cu2Cl2.

5. Flame coloration by cuprous chloride. — The colora-
tion of a flame by cuprous chloride may be produced by

holding a piece of copper gauze in the flame

and conducting a current of chlorine into

the opening at the base of a Bun sen burner

(Fig. 156). A coloration due to the cuprous

chloride is imparted to the flame.

The gauze should first be strongly heated

and all shellac and foreign material burned

^^ffa off. Chlorine admitted at the base of the

~ ~ burner, one bubble at a time, produces in-
Fig. 156 ' \ r

termittent flashes of color in the flame

which become continuous with a steady introduction of

chlorine.

Cu gauze ; small CI generator.

6. Solubility of cupric chloride in alcohol. — Cupric
chloride dissolves readily in alcohol, yielding a colored
solution which may advantageously be used to show the
flame coloration produced by this salt.

A piece of previously ignited asbestos paper is saturated

copper 387

with an alcoholic solution of cupric chloride. On igniting
the alcohol, a green flame is obtained.

Asbestos paper previously ignited ; alcohol ; CuCl2.

7. Use of cupric chloride in colored fire. — A mixture of
2 g. of powdered charcoal, 2 g. of cupric chloride, and 4 g.
of potassium chlorate, ignited on asbestos paper, yields a
blue flame.

Asbestos paper ; KC103 ; CuCl2 ; powdered charcoal.

SILVER

1. By electrolysis. — (a) When an electric current is
passed through a solution of potassium cyanide containing
silver, the silver is deposited at one pole.

Sufficient potassium cyanide solution is added to a solu-
tion of silver nitrate to redissolve the precipitate first
formed. The electrode connected with the zinc of a bichro-
mate battery should consist of a well-cleaned and polished
strip of copper. The other electrode may be a piece of
platinum. On passing a feeble current through the solu-
tion, a fine deposit of silver is formed on the copper.

Bichromate battery ; Cu sheet ; Pt foil ; AgNC>3 solution ; KCN
solution.

(b) By the electrolysis of a neutral solution of silver
nitrate silver may be deposited in a crystalline form.

A concentrated solution of the salt is placed in a beaker,
and two platinum electrodes, which are connected with two
bichromate cells, are immersed in the liquid. On the nega-
tive pole silver will be deposited in a crystalline mass.

Bichromate battery ; 2 Pt electrodes ; AgN03 solution.

2. Precipitation by mercury. — A few grams of mercury
are placed in a small, fine-meshed linen bag and immersed

388

SILVER

389

beneath the surface of silver nitrate solution in a large
beaker (Fig. 157). In the course of a day or two a fine net-
work of crystallized silver will be found
clinging to the bag, forming the so-called
silver tree.

Large beaker ; fine-meshed linen bag ; AgX03 ;

Hg-

3. Formation of silver iodide in dilute
solutions. — In a solution containing a
mixture of a chloride, a bromide, and
an iodide, to which a solution of silver
nitrate has been added, the iodide is fig. 157

always first precipitated, then the others.
To illustrate this, a saturated solution of sodium chloride
is used, to which 5 drops of a solution containing 2 g.
of potassium iodide in 50 cc. of water are added. This
gives a very small amount of the iodide in the pres-
ence of a large amount of the chloride. The addition of
3 to 5 drops of silver nitrate solution, containing 2.5 g.
in 50 cc. of water, produces a decidedly yellowish precipi-
tate consisting of silver iodide. On adding the same
amount of silver nitrate to a saturated solution of sodium
chloride free from iodide, the color of the precipitate is a
pure white. In the presence of a very large excess of a
chloride, the small amount of iodide is therefore first pre-
cipitated. The slight difference in color prevents the
demonstration of the analogous case of the bromide, for,
while the color of silver iodide is markedly different from
the color of the chloride, the same is not true of the differ-
ences in color between the bromide and the other two com-
pounds.

Saturated NaCl solution ; 2 g. of KI ; 2.5 g. of AgN03.

390 CHEMICAL LECTURE EXPERIMENTS

4. Color change of silver iodide on heating. — Silver
iodide, when heated, changes its color, becoming intensely
yellow.

A figure or character is marked with a dilute solution of
silver nitrate on a card, which is then dried out of contact
with the light. The card is then flowed with a solution of
potassium iodide, which converts the silver nitrate to silver
iodide. After all excess of potassium iodide has been
washed off, the card is carefully dried. On heating it
above a Bunsen flame, the character, which was originally
very indistinct, appears in bright yellow lines. On cooling,
the color disappears.

Card prepared with Agl.

ALUMINIUM

1. Combustion in air. — Aluminium wire or aluminium
sheet does not burn in the air. A piece of wire held in the
flame melts with superficial oxidation, but does not burn.
Aluminium sheet acts in a similar manner. Aluminium fil-
ings, unless very fine, do not readily burn by being strewn
through a flame. Aluminium powder strewn through a
flame burns with great brilliancy.

Aluminium sheet, wire, filings, leaf, powder.

2. Combustion in oxygen. — Aluminium leaf, when
strongly heated in a current of oxygen, burns brilliantly to
form aluminium oxide.

A bulb-tube is filled with aluminium leaf, and a small bit
of string or a shred of filter-paper is introduced to serve as
a kindler. On passing a current of oxygen through the
bulb and strongly heating the leaf, the string catches fire
and imparts the flame to the aluminium leaf, which burns in
the atmosphere of oxygen with a brilliant flash.

4 Al + 3 02 = 2 A1203.
Bulb-tube ; string ; O supply ; Al leaf.

3. Action of sodium amalgam. — Mercury does not unite
readily with aluminium to form an amalgam, though if liquid
sodium amalgam is used the aluminium amalgam is readily
formed. Aluminium, when amalgamated, is easily oxidized,

391

392 CHEMICAL LECTURE EXPERIMENTS

and in the presence of moist air aluminium oxide is rapidly
formed.

A character or letter is drawn on a piece of sheet alumin-
ium, well cleaned and free from oil, by using a clean copper
wire dipped in liquid sodium amalgam. Almost immediately
a mossy growth of aluminium oxide appears, rising perpen-
dicularly from the aluminium sheet in sharply cut lines to
a height of several millimeters.

Al sheet ; Cu wire ; Na amalgam (liquid).

4. Reduction of metallic oxides by aluminium powder. —

Ferric oxide, when mixed with half its weight of aluminium
powder and strongly heated in a crucible, is reduced by the
aluminium with an explosion. The powders should be inti-
mately mixed and placed in a small crucible, and a disk of
asbestos paper should be pressed down upon them. As con-
siderable heat is required to start the reaction, it may be
necessary to use the blast-lamp.

Lead monoxide, when mixed with aluminium powder and
heated, is likewise reduced, producing an explosion. Four
grams of litharge are mixed with .25 g. of aluminium powder.

Cupric oxide in the form of a powder, when mixed with
one-third its weight of aluminium powder, also explodes on
ignition.

Small crucibles ; asbestos paper ; powdered Al, Fe203, PbO, and
CuO.

5. Explosion of aluminium powder and sodium perox-
ide.— When aluminium powder and anhydrous sodium
peroxide are mixed and moistened with a drop of water, the
mixture explodes.

Sodium peroxide is placed in a clean, dry test-tube and
an equal volume of aluminium powder added. The two
powders are well mixed by shaking, and the test-tube is

ALUMINIUM 393

clamped behind a glass screen. One drop of water is allowed
to flow from a long glass tube into the test-tube. The result-
ing explosion shatters the tube.

Glass screen ; long glass tube ; Na202 ; Al powder.

6. Union of aluminium and bromine. — Aluminium and
bromine while not uniting in the cold react very energeti-
cally at a higher temperature. Aluminium filings are placed
in the bottom of a test-tube clamped in a vertical position.
After heating until the glass is just red, 10 drops of bromine
are carefully poured from a dry test-tube into the heated
tube. The elements unite with a vivid combustion, yielding
anhydrous aluminium bromide.

On cooling, 2 or 3 drops of water may be allowed to fall
into the tube, where they react with the anhydrous bromide
with a hissing sound.

2 Al + 3 Br2 = 2 AlBr3.
Al filings ; Br.

7. Union of aluminium powder and iodine. — One-fourth
of a gram of aluminium powder is heated in a thick-walled
test-tube to faint redness. One-half a gram of finely pow-
dered iodine is shaken into the tube out of a folded paper.
The aluminium unites with the iodine with brilliant combus-
tion. If the Bunsen flame is held at the mouth of the tube
for a moment, the vaporized aluminium iodide will catch fire
and burn. On cooling, a mass of aluminium iodide mixed
with some uncombined aluminium will be seen in the bottom
of the tube.

If 1 or 2 drops of water are allowed to fall on the
cooled aluminium iodide in the test-tube, a vigorous action
takes place, accompanied by great heat.

2 Al + 3 I2 = 2 All*
Al powder ; I.

394 CHEMICAL LECTURE EXPERIMENTS

8. Absorptive power of aluminium hydroxide for coloring
matter. — Aluminium hydroxide absorbs certain coloring
matters, and this property is much used in the process of
dyeing.

An infusion of logwood is prepared by boiling for two
minutes a few pieces of the wood with water. One hundred
cubic centimeters of the colored liquid are placed in a large
mortar, and one-third of its volume of a thick paste of
moistened, well-washed, freshly precipitated aluminium
hydroxide is added. The mixture is rubbed with a pestle
for several minutes, and then washed upon a large filter.
Unless a too concentrated solution of logwood has been used,
the filtrate will appear perfectly colorless.

If aluminium hydroxide is precipitated from an alum
solution which is somewhat colored with logwood extract,
the hydroxide will combine with the coloring matter and
settle as a colored precipitate, leaving the supernatant
liquid clear. The alum solution should be distinctly
colored, and then aluminium hydroxide added in slight
excess.

Cotton fibres, when boiled with logwood extract, absorb
but a very small amount of the coloring matter. If, on the
other hand, the fibres are impregnated with aluminium salts,
sufficient color is deposited on the fibre to make the process
applicable for dyeing.

A strip of well-washed white cotton cloth is soaked in a
solution of aluminium acetate, prepared by dissolving alu-
minium hydroxide in an insufficient quantity of acetic acid.
The strip of cloth, together with a fresh strip, is immersed
in logwood extract and boiled, with constant stirring for a
few minutes. The cloth impregnated with the aluminium
salt will acquire a deep color.

Mortar and pestle ; cotton cloth ; logwood chips ; Al(OH)3 paste ;
KA1(S04)3 solution.

ALUMINIUM 395

9. Preparation of potassium aluminium sulphate (potas-
sium alum). — One molecule of aluminium sulphate com-
bines with 1 molecule of potassium sulphate, forming a
double sulphate which crystallizes with 24 molecules of
water. Owing to its relative insolubility in water, it is
readily prepared by mixing equal volumes of saturated
solutions of potassium sulphate and aluminium sulphate.
On shaking the test-tube, a crystalline precipitate is obtained.

A saturated solution of potassium chloride may be used,
in the place of the potassium sulphate solution, with the
same result.

10. Utilization of alum in clarifying water. — When a
solution of alum is added to a natural water which is slightly
alkaline, aluminium hydroxide is precipitated in a very finely
divided condition, and, as the flocculent precipitate settles,
it entangles with it any solid organic matter or sediment
which may be present* in the water.

A few cubic centimeters of alum solution are added to
some turbid water in a 2 1. beaker, and the solution is allowed
to stand over night. A second beaker should be filled with
the water and no alum solution added to it. The next day
it will be found that the beaker containing the alum solu-
tion in the water will be perfectly clear, all the impurities
having settled to the bottom with the aluminium hydroxide.
The contrast between this and the other beaker will be very
marked.

Two 2 1. beakers ; turbid water ; alum solution.

TIN

1. Deposition by electrolytic action. — A small porous
cup half filled with very dilute sulphuric acid is placed in a
beaker containing concentrated stannous
chloride solution. A rod of zinc, to which
a copper wire is attached, is placed in the
porous cup and the end of the copper wire
immersed 1 cm. beneath the surface of the
stannous chloride solution. The appara-
tus thus arranged is placed in a quiet spot
and covered with a bell-jar. In the course
of 24 hours, a net-work of tin crystals will
be formed in the liquid surrounding the
porous cup (Fig. 158).

Fig. 158

500 cc. beaker ; porous cup ; Zn rod with Cu wire ; SnCl2 solution.

2. Deposition on zinc. — A solution of stannous chloride
is decomposed by the action of metallic zinc, tin being
deposited in the form of fine crystals.

A zinc rod is immersed in a rather concentrated solu-
tion of stannous chloride. A mossy deposit, consisting of
minute crystals of tin, forms about the zinc.

That the mossy vegetation obtained by immersing a strip
of zinc in tin chloride solution consists of minute crystals
of the metal, is shown by firmly pressing a quantity of the

396

tin 397

spongy mass between the fingers until all water is removed.
The crystals knit together so closely that the mass appears
as a solid lump, which may be polished by rubbing with a
piece of chamois skin.

By using a more dilute solution of the chloride and allow-
ing the reaction to take more time, larger crystals of tin
may be obtained, and a treelike deposit will be formed.

SnCl2 + Zn = Sn + ZnCl2
SnCl2 ; Zn rod.

3. Crystalline structure. — On bending a rod of tin or a

piece of tin pipe, the crystals rub on each other producing
a peculiar crackling sound called the " tin cry."

When molten tin is allowed to cool, it assumes a crystal-
line structure.

A piece of common tinned iron is heated over a Bunsen
burner until the tin begins to be discolored. It is then
thrust quickly into cold water and the surface rubbed with
a piece of filter-paper moistened with dilute aqua regia.
After removing the excess of acid by rubbing with a lit-
tle dilute sodium hydroxide solution, the surface of the
metal will be found covered with well-marked crystalline
figures.

Block tin rod or pipe ; sheet tinned iron.

4. Preparation of stannic chloride. — Chlorine when
brought in contact with heated tin unites with it, forming
stannic chloride.

A few pieces of granulated tin are placed in the larger
distilling flask shown in Fig. 159. A current of dry chlorine
is conducted through the glass elbow in the neck of the
flask and caused to play upon the surface of the tin. The
side tube is connected with a small distilling flask immersed

398

CHEMICAL LECTURE EXPERIMENTS

in ice-water. The excess of chlorine, together with any un-

condensed vapors
of stannic chlo-
ride, is conducted
to a flue.

The tin is care-
fully heated till it
melts, when it will
be seen that the
reaction with the
chlorine has begun
as the flask fills
with dense white
fumes. The chlo-
ride condenses for
the most part in

Fig. 159

the small flask to a light-colored, fuming liquid.

Sn + 2 Cl2 = SnCl4.
Apparatus (Fig. 159) ; CI generator ; Sn ; ice.

5. Action of stannic chloride in the air. — Stannic chlo-
ride fumes strongly in the air and rapidly absorbs moisture,
forming a crystalline hydrate.

One cubic centimeter of stannic chloride is poured into
a dry 400 cc. crystallizing-dish, and a piece of filter-paper
placed over it. The chloride soon absorbs moisture from
the air, and forms a solid crystalline mass on the bottom
and sides of the dish.

Much larger crystals are obtained by pouring 1 cc. of the
chloride into a 500 cc. flask, which is allowed to stand over
night. The stannic chloride will slowly evaporate and, ris-
ing through the narrow neck, come in contact with the
moisture of the air and form a network of crystals across

tin 399

the mouth of the flask. The flask is filled with the fumes
of stannic chloride, and by blowing moist air through a
glass tube into the flask dense white clouds are formed.

400 cc. crystallizing-dish ; 500 cc. flask ; SnCU.

6. Stannous iodide from stannous chloride and potassium
iodide. — When concentrated solutions of stannous chloride
and potassium iodide are mixed, a yellow crystalline pre-
cipitate of stannous iodide appears suddenly in the solution.

SnCl2 + 2 KI = Snl2 + 2 KC1.
Concentrated solutions of SnCl2 and KI.

7. Preparation of stannic sulphide (mosaic gold). — A

mixture of equal parts of powdered tin and sulphur flowers
is mixed with one-eighth of its volume of powdered ammo-
nium chloride. The mixture is then placed in a porcelain
crucible, covered with a 2 mm. layer of powdered ammonium
chloride, and the covered crucible heated with a Bunsen
burner. As a result of the reaction, the ammonium chloride
vaporizes as a white smoke, and stannic sulphide sublimes
as a brilliant yellow crystalline deposit on the crucible lid.

Porcelain crucible ; Sn ; S flowers ; NH4C1.

LEAD

1. Preparation of pyrophoric lead. — Finely divided lead
ignites spontaneously when exposed to the air. By the
ignition of lead tartrate, a mixture of finely divided lead
and carbon is obtained.

Five grams of lead tartrate are gently heated in an igni-
tion tube until the evolution of gas ceases. It is important
that the heat should not be carried to too high a degree, as
the small particles of lead are liable, under those circum-
stances, to fuse together partially, and thus spoil the experi-
ment. As soon as the gases cease coming off, the tube is
corked with a well-fitting rubber stopper to insure an
air-tight closure. After the tube has become perfectly cold,
the cork may be removed and the finely divided lead poured
out upon a plate, best from a height of half a meter. On
exposure to the air, the lead catches fire spontaneously.

Preparation of lead tartrate. — Lead acetate solution is
added to a solution of tartaric acid till there is no more
precipitate formed. The precipitate, which is quite insoluble
in water, may be filtered off, washed with water, and dried
in an air-bath. It loses its crystal water at 130°, and in this
form is best suited for the above experiment, since the water
is likely to condense and break the tube.

Hard-glass test-tube with well-fitting rubber stopper ; white plate ;
lead tartrate.

400

LEAD

401

2. Deposition on zinc (lead tree). — The deposition of
lead from a solution of lead nitrate upon a zinc rod is
obtained by covering a rod of zinc, such as is
used in batteries, with one layer of asbestos
paper. The rod is then suspended in a mod-
erately strong (10 per cent) solution of lead
nitrate, and allowed to stand till the next exer-
cise. Crystals of lead will appear on the out-
side of the rod (Fig. 160).

A similar rod, not covered with paper, when
dipped into a solution of lead nitrate, is im-
mediately covered with a black, mossy deposit
of finely divided lead.

Pb(N03)2 + Zn = Zn(N03)2 + Pb.

Asbestos paper ; Pb(N03)2 solution (10 percent) ; Zn rods.

3. Crystalline structure of lead. — If a piece of sheet-lead
is brushed over with strong nitric acid, a crystalline structure
will be' developed. The excess of acid should be removed
by washing with water.

As the lead oxidizes rapidly, the figures soon disappear.

Sheet-lead ; concentrated HN03.

Fig. 160

4. Action of water on lead. — A large strip of clean, bright
lead is suspended in a beaker of distilled water for several
hours. A white precipitate is formed, part of which settles
to the bottom, while quite a large quantity coats the lead,
giving it a corroded appearance.

Hydrogen sulphide added to the water produces a black
precipitate of lead sulphide.

By dissolving slight quantities of certain salts in water in
different beakers, and allowing the lead to remain in them,
a very striking comparison may be made of the respective
2d

402 CHEMICAL LECTURE EXPERIMENTS

merits of potable waters containing those salts when used
with lead pipes.

The above described experiment is repeated, using a beaker
containing a liter of water, in which .30 g. of dry potas-
sium carbonate and .04 g. of potassium nitrate have been
dissolved. After standing 24 hours, the solution is tested
with hydrogen sulphide. While in the beaker of pure dis-
tilled water an intense black is formed, the water containing
the salts gives no reaction with hydrogen sulphide, since the
salts entirely prevent any solvent action of the water.

2 large beakers ; 2 large pieces of sheet Pb ; distilled water ; K2C03 ;
KN03.

5. Oxidizing action of lead peroxide. — (a) On sulphur. —
When dry, freshly prepared lead peroxide is rubbed in a
mortar with a small bit of sulphur, the mixture takes fire.

Gauntlets ; mortar and pestle ; Pb02 ; S flowers.

(b) On hydrogen sulphide. — A stream of hydrogen sul-
phide is allowed to impinge on a gram or two of dry, freshly
prepared lead peroxide. On coming in contact with the
oxide, the gas is oxidized, and bursts into a flame. The
surface of the lead peroxide soon turns a lighter color, owing
to the formation of lead sulphate. By stirring the powder,
and thereby exposing fresh surfaces to the action of the gas,
nearly the whole mass may ultimately be converted to lead
sulphate.

The powder may be allowed to fall by the end of a tube
through which hydrogen sulphide is issuing. The gas will
be ignited.

H2S generator; Pb02.

LEAD 403

with 2 or 3 drops of nitrobenzene in a test-tube clamped
behind glass screens. On heating the tube an explosion
occurs.

Glass screens ; Pb02 ; nitrobenzene.

6. Explosion of lead nitrate and sulphur. — Lead nitrate,
when rubbed with sulphur, oxidizes it with explosive vio-
lence.

Equal quantities of finely pulverized lead nitrate and
sulphur flowers should be placed in an un glazed mortar,
and rubbed with the pestle in the gloved hand. Very small
quantities of the mixture should be used.

Mortar and pestle ; gauntlets ; Pb(N03)2 ; S flowers.

BISMUTH

1. Fusion and crystallization. — Bismuth melts at a com
paratively low temperature and, on cooling, crystallizes ii
rhombohedrons which appear almost cubical. The crystal
lization is much facilitated by heating the metal for som
time with a small quantity of potassium nitrate. Th
fusion is made in a porcelain crucible or a Jena glas
beaker. As soon as the mass has cooled sufficiently t<
form a crust on the surface, a hole is made in the crust an<
the molten metal poured out. On breaking open the shell
the cavity will be found to be lined with crystals.

The play of colors observed in heating and cooling coppe
(Ex. 5, p. 332) is also observed in heating bismuth.

Porcelain crucible or Jena glass beaker ; Bi ; KN03.

2. Fusible alloys. — Tin and bismuth form ingredient
of all of the fusible alloys, the most interesting of which i
the so-called Wood's metal, having a melting point of abou
70° C, and consequently melting in hot water.

This alloy is made by melting together 15 g. of cadmium
20 g. of tin, 40 g. of lead, and 80 g. of bismuth.

Other alloys formed by varying these proportions an
Kose's metal, melting at 93°.5, and Newton's metal, meltiin
at 94°.5.

Wood's metal ; Rose's metal ; Newton's metal ; Pb ; Bi ; Cd ; Sn.

404

CHROMIUM

1. Preparation of anhydrous chromium chloride. — A

mixture of equal volumes of powdered anhydrous chro-
mium oxide and charcoal powder is placed in a bulb-tube
through which a current of chlorine is being passed. On
heating the mixture strongly with a large flame, a violet
crystalline deposit of chromium chloride is obtained in the
colder portions of the tube.

The anhydrous salt is insoluble in water.

Cr203 + 3 C + 3 Cl2 = 2 CrCl3 + 3 CO.

Bulb-tube ; CI generator ; Cr203 ; charcoal powder.

2. Preparation of chromium trioxide (chromic acid). —

Sixty cubic centimeters of concentrated sulphuric acid are
slowly poured into 40 cc. of a cold saturated solution of
potassium dichromate. The mixture is then cooled, and
the resulting crystalline precipitate, consisting of chromium
trioxide, filtered on a funnel containing glass wool or fibrous
asbestos.

K2Cr207 + H2S04 = K2S04 + 2 Cr03 + H20.
Funnel ; glass wool ; cold saturated solution of K2Cr207.

3. Oxidizing action of chromium trioxide. — (a) On alco-
hol. — If absolute alcohol is allowed to drop upon a few

405

406 CHEMICAL LECTURE EXPERIMENTS

crystals of dry chromium trioxide, the alcohol is oxidized
and ignited.

Cr03 crystals ; absolute alcohol.

(b) On wood. — Chromic acid, or potassium dichromate
in the presence of sulphuric acid, oxidizes wood to carbon
dioxide even in the cold. A splinter of wood, when thrust
into a warm solution of potassium dichromate and sulphuric
acid, is instantly colored brown, and small quantities of a
gas are evolved.

Sawdust, when mixed with a solution of potassium dichro-
mate and sulphuric acid, is rapidly oxidized to carbon diox-
ide with the liberation of great heat. The mixture is made
in a 500 cc. flask, fitted with a one-holed cork, and a delivery-
tube dipping into lime-water. In a few moments, even with-
out the application of external heat, a reaction begins, large
quantities of carbon dioxide are evolved, and the mixture
becomes very hot. The battery solution described on p. 3
may be used in these experiments with success.

Splinter ; sawdust ; K2Cr207 or battery solution ; lime-water.

4. Dyeing with chrome yellow. — By precipitating chrome
yellow on the fibres of cloth, the color is sufficiently re-
tained to dye the fabric.

A strip of well-washed cotton cloth is dipped in a solution
of lead acetate and then immersed in a solution of potassium
dichromate. The cloth becomes covered with a bright yel-
low, finely divided precipitate of lead chromate.

Cotton cloth ; solutions of K2Cr207 and Pb(C2H302)2.

5. Oxidizing action of lead chromate. — Lead chromate
readily gives up its oxygen when heated with organic mat-
ter, and is much used as an oxidizing agent in elementary
organic analysis.

CHROMIUM 407

A small quantity of pulverized sugar is mixed with three
or four times its volume of lead chromate, and the mixture
is heated in a test-tube. The carbon dioxide mav be con-
ducted through a glass tube into lime-water, where it will
produce a white precipitate.

Test-tube with cork and delivery -tube ; sugar ; PbCr04 fused and
powdered ; lime-water.

6. Preparation of chromium oxy chloride (chromyl chlo-
ride). — When a mixture of sodium chloride and potassium
chromate is heated with concentrated sulphuric acid, a dark
red liquid, chromium oxychloride, distils over.

Ten grams of fused, powdered sodium chloride should be
heated to fusion in a crucible with 17 g. of potassium chro-
mate. The cooled mass is then pulverized and placed in a
500 cc. glass-stoppered retort, the neck of which is thrust
into a filter flask used as a receiver (Fig. 93, p. 223). Thirty
grams of fuming sulphuric acid or 25 g. of concentrated
sulphuric acid, mixed with 5 g. of sulphur trioxide, are
poured through a long-stemmed funnel or thistle-tube
upon the mixture of the salts. When the retort is gently
warmed, dense red fumes, which distil over and condense
in the receiver to a dark -colored liquid, appear.

The oxidizing action of chromium oxychloride may be
shown by dropping a 1 or 2 mm. piece of well-dried
phosphorus into 2 or 3 drops of the liquid placed in
the test-tube shown in Fig. 109, p. 262. As the phos-
phorus comes in contact with the liquid, an explosion is
obtained.

A current of hydrogen sulphide, directed upon a small
quantity of the liquid in an evaporating dish, is immedi-
ately oxidized and ignited.

Ammonia gas likewise, when directed upon the liquid,
reacts with evolution of dense fumes.

408 CHEMICAL LECTURE EXPERIMENTS

A filter paper moistened with alcohol is touched with a
drop of liquid. The alcohol is ignited.

K,Cr04 + 2 NaCl + 2 H2S04 = Na2S04 + K2S04 + CrO,Cl2 +

2 H_< >.

500 cc. glass-stoppered retort ; filter flask ; apparatus (Fig. 100, p.
262) ; HoS generator ; NII3 generator ; fused, powdered NaCl ; KjCr< )4 ;
alcohol ; P.

IRON

1. Reduction of ferric oxide by hydrogen. — Ferric oxide
is reduced to metallic iron when heated in a current of
hydrogen. If the temperature at which the reduction is
carried out is not too high, the reduced iron is pyrophoric.

A thin layer of ferric oxide is placed in a 20 cm. length
of combustion-tubing fitted at each end with a one-holed
rubber stopper and a glass tube. A current of well-washed
hydrogen is passed slowly through the tube, and the iron
oxide is heated to as low a temperature as will suffice to
effect the reduction. When no more water escapes from
the open end of the tube, the reduction is complete and the
reduced iron is allowed to cool in a current of hydrogen.
On shaking a small quantity of the cold powder upon a
plate, it will rapidly oxidize and glow in the air.

Some of the cooled powder may be allowed to fall upon
a small heap of gunpowder. The precautions described in
Ex. 3, p. 330, should be carefully observed here.

Precipitated, well-washed, and dried ferric hydroxide is
best used for reduction when pyrophoric iron is desired.
The combustion-tube may be drawn out at both ends and
sealed off after the reduction is complete. The tube thus
prepared can be kept indefinitely and the pyrophoric
character of the iron remain unchanged.

Fe203 + 3 H2 = 2 Fe + 3 H20.

20 cm. length combustion-tubing ; 1-holed stoppers ; H generator
with gas washing-bottles ; gunpowder ; Fe203 ; Fe(OH)3.

409

410

CHEMICAL LECTURE EXPERIMENTS

ration,
drawn.

2. "Passive" iron. — When iron is immersed in fuming
nitric acid, it becomes resistant to the action of acids and
other reagents, being in the so-called passive state. The
passivity is explained as the result of a thin, resistant coat-
ing on the iron of either iron oxide or oxides of nitrogen.

A piece of sheet iron is freed from all oil and carefully
cleaned. The iron is then suspended on a fine platinum wire

and is completely immersed in
fuming nitric acid. As the iron
enters the acid, a vigorous evo-
lution of oxides of nitrogen is
obtained. The reaction is, how-
ever, of only a few seconds' du-
The iron is then carefully with-
immersed in water, and then in
ordinary concentrated nitric acid. The
iron is no longer acted upon by the acid.
Iron in the passive state loses its prop-
erty of depositing copper from solutions
of copper salts, and, when immersed in a
saturated solution of copper nitrate, the
iron will retain its original grayish color.
The iron should be carefully withdrawn
from the solution of copper nitrate, and then sharply struck
on one edge with a lead-pencil or glass rod. The passivity
is destroyed by the blow, and the iron is immediately
covered with a red film of copper precipitated from the
saturated solution of copper nitrate adhering to the iron.
If a large sheet of iron is used and the blow is care-
fully struck, the deposition of copper will proceed from the
point of contact and rapidly extend all over the surface of
the iron (Fig. 161).

The experiment may be repeated, removing the film of
copper by immersing the iron in dilute nitric acid. The

Fig. 1(31

IRON 411

iron may be again rendered passive by immersion in fuming
nitric acid.

The sheet iron may be readily prepared by removing the
coating of tin on a piece of common tinned iron. The tin
plate should be immersed in hydrochloric acid until all the
tin has been dissolved.

Sheet iron cleaned and freed from grease ; Pt wire ; Cu(N03)2 ;
fuming HN03.

3. Carbon in iron. — The carbon in iron may be separated
by dissolving a piece of cast-iron in hydrochloric acid. The
insoluble carbon will separate as a black powder. The pres-
ence of combined carbon as iron carbide gives rise to the
formation of hydrocarbons, which are noticeable by the odor
they impart to hydrogen obtained by the action of hydro-
chloric acid on iron.

Cast-iron ; HC1.

4. Combustion of gunpowder and powdered iron. — The

comparative combustibility of gunpowder and iron powder
may be shown by allowing a mixture of equal weights (one-
tenth of a gram of each)- to fall from an iron spoon through
the flame of burning alcohol. Fifteen cubic centimeters of
alcohol are poured into a porcelain evaporating-dish and
ignited. As the mixture of gunpowder and iron powder
falls through the flame, the iron powder burns with brilliant
scintillations, but the gunpowder is not ignited. As the
alcohol is burnt out of the dish, the gunpowder remaining
in the bottom is finally ignited.

Evaporating-dish ; gunpowder ; Fe powder ; alcohol.

5. Combustion of iron powder and potassium chlorate. —

A mixture of 2 parts of iron powder and 1 part of pow-
dered potassium chlorate burns when ignited. The mixture
should be placed on an asbestos paper in the hood.
Asbestos paper ; Fe powder ; KC103 ; touch-paper.

412 CHEMICAL LECTURE EXPERIMENTS

6. Reduction of ferric oxide by aluminium. — When alu-
minium powder is mixed with anhydrous, finely powdered
oxides of the metals and the mixture ignited, the aluminium
extracts the oxygen from the oxide, forming aluminium oxide
and setting free the metal.1

This reaction is especially satisfactory when using a mix-
ture of aluminium powder and ferric oxide. The two pow-
ders are mixed in equal volumes and ignited with a 2 cm.
strip of magnesium ribbon. The mixture burns brightly,
leaving a white residue of aluminium oxide. The iron in the
finely divided condition immediately burns and reoxidizes.

If a quantity of the mixture of the two powders is placed
in a crucible and ignited from the top, the reoxidation of
the iron is not so immediate.

Fe208 + 2 Al =Al2Os + 2Fe.

Fe203 powder ; Al powder ; Mg ribbon.

7. Action of light on potassium ferricyanide. — The reduc-
tion of potassium ferricyanide by light is used in photogra-
phy to produce " blue-prints. "

A solution of the salt is mixed with a solution of u citrate
of iron and ammonia" and unsized paper is coated with the
liquid. When dry the paper is sensitive to light, and if a
piece is exposed to bright sunlight in a photographic print-
ing frame and subsequently washed in very dilute hydro-
chloric acid, a coating of Prussian blue will be left on it.
By using a design cut out of paper or a photographic nega-
tive, the design or picture may be reproduced.

Photographic printing frame ; unsized paper ; design or photograph

negative ; citrate of iron and ammonia ; K3Fe(CX)o.

1 This reaction is the basis of a series of special experiments
recently devised by Goldschmidt. The apparatus and materials are to
be had of any dealer in chemical supplies.

COBALT AND NICKEL

1. Deposition of cobalt by magnesium. — A piece of
bright, clean magnesium ribbon, when immersed in a solu-
tion of cobalt sulphate, becomes covered with a blue-black
deposit of metallic cobalt The salt solution should not con-
tain too much free acid.

CoS04 + Mg = MgS04 + Co.
C0SO4 solution ; Mg ribbon.

2. Dehydration of cobalt chloride on filter-paper. — Filter-
paper saturated with cobalt chloride and exposed to the
action of dry air undergoes a change in color, so much so
that the tint is an approximate indication of the moisture
content of the air.

Two pieces of filter-paper, which have been previously
soaked in concentrated cobalt chloride solution and allowed
to dry in the air, are suspended
by means of a piece of thread
and a bit of wax to the interior
of each of 2 bell-jars (Fig. 162).
The jars are placed on plates, the
one over a crystallizing dish con-
taining water, the other over a FIG
crystallizing dish containing an-
hydrous calcium chloride. The calcium chloride abstracts
the moisture from the air, and the paper soon acquires a

413

414 CHEMICAL LECTURE EXPERIMENTS

deep blue color, while the paper over the vessel of water is
unaffected and remains red. On interchanging the 2 bell-
jars the colors are changed on both papers.

2 bell-jars ; 2 plates ; 2 crystallizing dishes ; CaCl2 (anhydrous) ;
CoCl2.

3. Sympathetic ink. — A word is written on a piece of
white paper with dilute cobalt chloride solution. When
dry the word is not visible. On heating high above a Bun-
sen flame the word appears in blue lines, which gradually
fade on cooling.

4. Preparation of potassium cobalt nitrite (Fischer's salt)
— A characteristic reaction of cobalt, whereby it may be
readily distinguished from nickel, is its formation of a yel-
low crystalline precipitate (potassium cobaltic nitrite) with
a solution of potassium nitrite.

Cobalt nitrate solution is acidified with acetic acid and
then a solution of potassium nitrite added. On standing
over night a yellow crystalline precipitate of the double
nitrite will be formed.

Co(N03)2; KN02.

5. Reduction of nickel oxide by hydrogen. — The reduc-
tion of nickel oxide and the pyrophoric nature of the finely
reduced metal is well shown by heating the oxide in a short
length of combustion-tubing in a current of pure hydrogen.
When the reduction is complete, a one-holed cork bearing a
short piece of glass tubing should be inserted in the open
end of the combustion-tube and the nickel allowed to cool
in a current of hydrogen.

The color change from green nickel oxide to black nickel
is so marked that the green rather than the black oxide
should invariably be used.

COBALT AND NICKEL 415

A small portion of the still hot metal remaining in the
tube after the reduction is complete will burn when allowed
to fall through the air.

Finely divided nickel, resulting from the reduction of
the oxide, is readily oxidized in the air, and while, when
cold, it does not burn with the brilliancy of pyrophoric lead
(Ex. 1, p. 400), sufficient heat will be generated on exposing
the metal to the air to ignite a small heap of gunpowder.

A few grams of gunpowder are placed on a square of
asbestos paper, and the cold reduced nickel poured out of
the tube upon it.

If a small quantity of the reduced metal is poured upon
the heads of 2 or 3 matches, they will also become ignited.

NiO + H2 = H20 + NL

H generator ; combustion-tube ; 4-tube burner ; NiO ; gunpowder.

6. Deposition of nickel by electrolysis (nickel plating).

— A polished strip of sheet copper is connected to the zinc
pole of a bichromate battery and immersed in a solution of
ammonium nickel sulphate. The negative pole may be a
piece of nickel or platinum. On closing the electric circuit,
a gray deposit of nickel will be formed on the copper
electrode.

Bichromate battery ; sheet Cu ; Pt ; Ni ; ammonium nickel sul-
phate.

7. Oxidation of nickel in the air. — A sheet of polished
nickel, when heated in the air, becomes covered with a thin
iridescent coating of the oxide.

8. Solubility of nickel sulphide in sodium sulphide. —

Hydrogen sulphide added to an alkaline solution containing
nickel produces a deep black solution without the formation
of a precipitate.

416 CHEMICAL LECTURE EXPERIMENTS

Nickel chloride solution is treated with a small quantity
of tartaric acid, and then sufficient sodium hydroxide solu-
tion is added to make the liquid feel soapy. On conducting
a current of hydrogen sulphide through the solution, a jet-
black solution is formed, which, even on boiling, does not
yield a precipitate. On pouring the liquid upon a filter, the
black solution runs through the paper, and on washing the
filter with hot water the absence of any precipitate may be
seen.

This reaction furnishes an excellent means of distinguish-
ing nickel from cobalt in solutions, tor with cobalt the sul-
phide is precipitated, the supernatant liquid remaining
colorless.

H2S generator ; solutions of tartaric arid and NK'b.

9. Preparation of nickel tetracarbonyl by the action of
carbon monoxide on reduced nickel. — Carbon monoxide.
when conducted over finely reduced nickel, unites with the
metal at the ordinary temperatures, Forming nickel tetra-
carbonyl. The vapor passes along with tin1 excess of
carbon monoxide, and may be condensed to a colorli
liquid if conducted through a tube immersed in a freezing-
mixture.

The nickel for this experiment should lie very finely
divided, and is best obtained by reducing nickel oxide
mixed with fibrous asbestos and loosely packed in a 40 cm.
length of combustion-tubing. The finely powdered nickel
oxide should be thoroughly mixed with the asbestos, to
which a large quantity of the powder will cling. Hydro-
gen, purified by being passed through a solution of potas-
sium permanganate, is conducted through the tube, which

is then heated to low redness. As the reduction is effected,
the green nickel oxide becomes converted to black nickel.
When no more water vapor escapes from the tube, tin1 re-

COBALT AND NICKEL

duction may be considered complete, and the nickel is
allowed to cool in a current of hydrogen.

Carbon monoxide from the generator (Ex. 12, p. 298) is
conducted through a calcium chloride drying-tube and then
directly through the tube containing the reduced nickel.
The issuing gas is passed through a long glass elbow ex-
tending nearly to the bottom of a test-tube fitted with a
two-holed cork. The gas issuing through a shorter elbow
in the second hole of the cork should be conducted into the

•HS ^^w^f&ip^m^m^ diN^vi^3-

Fig. 163

flue. The test-tube should be immersed in a freezing-mix-
ture of salt and ice (Fig. 163).

As the carbon monoxide comes in contact with the nickel,
the temperature of the tube is materially increased, indi-
cating the chemical action. The gas escaping from the glass
elbow in the test-tube consists of carbon monoxide contain-
ing a quantity of uncondensed vapor of nickel tetracar-
bonyl, which, owing to its poisonous character, should not
be inhaled. The preparation of any considerable quantity
of the tetracarbonyl requires too long a time for demonstra-
tion on the lecture table, though, if the operation is begun
before the hour, 2 or 3 cc. may be obtained. If the test-tube
2e

418 CHEMICAL LECTURE EXPERIMENTS

is somewhat constricted in the middle, the condensed liquid
may be sealed off in the glass tube.

If the escaping gas is conducted into the base of a Bunsen
burner, the flame becomes brilliantly luminous from the in-
candescence of fine particles of nickel. The structure of the
Bunsen flame is markedly shown by the varying intensity
of brilliancy in its different parts.

The escaping gas may be ignited at the end of a glass jet,
where it will burn brightly, giving a green smoke consisting
of nickel oxide. If a white porcelain dish is held in the up-
per portion of the flame, a green deposit of nickel oxide will
be obtained, while, if the dish is depressed on the flame,
black metallic nickel will be deposited.

The nickel tetracarbonyl vapor is easily decomposed by
heat into nickel and carbon monoxide, and consequently, if
the glass tube through which the gas is bein^r conducted is
strongly heated, a black metallic deposit of nickel will be
obtained, and the luminosity of the flame will be diminished
until ultimately the blue flame of carbon monoxide alone is
obtained. By gently heating the tube, a mirror possessing
a brilliant metallic lustre will be formed. The brilliancy
of the mirror is a function of the temperature, and if the
tube is heated to about 200° C, the best results are secured.
By attaching a Y-tube to the tube conducting the waste
gases the gas may be suddenly switched into a glass tube
which has been heated to 185° in an air-bath. Instantly
the interior of the tube becomes coated with a nickel mirror.

Ni + 4CO==Ni(CO)4.

4-tube burner ; 40 cm. length combustion-tubing; test-tube, cork,
and elbows ; porcelain dish ; air-bath and thermometer ; fibrous asbes-
tos; CO generator (Fig. 120, p. 209); II generator ; gas washing-bottle

containing KMnU4 solution ; NiO ; ice and salt freezing-mixture.

APPENDIX

BIBLIOGRAPHY

Arendt, R., Technik der Experimentalchemie. 3te Auf.

Hamburg, 1900. (Voss.)
Heumann, K., Anleitung zum Experimentiren. 2te Auf.

Braunschweig, 1893. (Vieweg.)
Newth, G. S., Chemical Lecture Experiments. 2d Edition.

London, 1900. (Longmans, Green & Co.)

The following works, though not primarily designed for
lecture use, are especially rich in experimental sugges-
tions : —

Faideau, F., La Chimie Amusante. Paris.

Mixter, W. G., An Elementary Text-book of Chemistry.

New York, 1889. (John Wiley & Sons.)
Remsen, L, Inorganic Chemistry (Advanced Course). New

York, 1889. (Henry Holt & Co.)
von Richter, V., A Text-book of Inorganic Chemistry

(translated by E. F. Smith). Philadelphia. (P. Blak-

iston & Co.)
Roscoe and Schorlemmer, A Treatise on Chemistry. Lon-
don. (Macmillan & Co.)
Torrey, J., Elementary Studies in Chemistry. New York,

1899. (Henry Holt & Co.)
Williams, R. P., Elements of Chemistry. Boston. (Ginn

&Co.)

419

420

CHEMICAL LECTURE EXPERIMENTS

Description of the hydrogen sulphide generator in use in
the laboratory of Wesleyan University: —

"It consists principally of three glass bottles, A, B, and
C, each provided with an orifice near the bottom. .1 is the
generator proper, whose mouth is wide so as to admit large
lumps of iron sulphide, and whose height is about three
times its diameter. It has a capacity of about 1G liters.

To Flue

To H,S
Hood

To Flue

<=F=CZI=

^^^

:§il

Fig. 1(14

Through the rubber stopper which closes its mouth pafi
the gas main, controlled by the main cock, l\ and terminat-
ing at a suitable hood in as many distributing cocks as may
be desired. Students have aCC688 to the distributing W>
only. Through the same stopper enters the acid-Mip|»ly
tube, drawn down at the end K toa jet capable of delivering

APPENDIX 421

a stream of acid not thicker than the shank of an ordinary
pin. This jet projects as little as possible below the stopper.
Through the tubulure at the bottom, with its inner end just
flush with the stopper, passes a rather thick-walled tube
controlled below by a pinch-cock, as shown. By means of
this tube the spent acid is delivered either into a sink or
waste-pipe capable of thorough- flushing, or into a small bot-
tle, D, connected with a flue, which • may be detached just
below the pinch-cock and emptied as required. The gener-'
ator bottle is charged with large pieces of iron sulphide
until completely full, and should not be allowed to become less
than' half full before recharging.- The spent acid must never
be- allowed to accumulate in such quantities as to reach the
-top of the sulphide.

" B is the acid reservoir, wide in proportion to its height,
with a capacity of about 8 liters. The stopper at its mouth
admits a funnel whose neck is aon tinned by a glass tube
^passing to the bottom of the bottle. This reservoir is con-
nected with a flue as shown. The acid used is commercial
hydrochloric, diluted with an equal volume of water. A
proper charge of acid is the amount necessary to fill B half
full when acid is running from, (3r stands at, the jet E. The
height at which the reservoir itself is- fixed depends, of
course, largely on the pressure to be overcome by the gas'.
A difference of level of 6 inches between the bottom of B
and the top of A has been found ample for ordinary analyti-
cal work.

" C is the gas reservoir, designed chiefly to retain what-
ever gas is made after the distributing cocks, or F, are closed.
Like B, it is wide and low. It has a capacity of about 4
liters. Its mouth should be on exactly the same level as
that of A, and the vertical portions of the tube connecting
C and A are made as short as possible.

" The tubing used in the apparatus is of glass. The rubber

422 CHEMICAL LECTURE EXPERIMENTS

stoppers are protected with a thin coating of paraffin, crowded
into place while the latter is still warm and soft, and firmly
wired. The rubber connections are coated within with par-
affin (by pouring hot paraffin through them when perfectly
dry), and securely wired."

(W. P. Bradley, in Am. Chem. Journal, XXI., 370.)

INDEX

Absorption of coloring matter by
aluminium hydroxide, 394 ; by
bone-black, 293.

Acetylene: from calcium carbide,
323 ; from ethylene dibromide, 323 ;
from incomplete combustion of
illuminating gas, 324.

Actinic action of light, 87, 90, 91,
217, 385, 412.

Air : analysis of, 186 ; carbon dioxide
in, 306, 307 ; combustion in hydro-
gen, 343 ; combustion in illuminat-
ing gas, 341, 343, 345 ; explosion
with hydrogen, 66; quantitative
combustion of iron in, 27; quan-
titative combustion of magnesium
in, 27 ; quantitative combustion of
phosphorus in, 29.

Alloys: fusible, 404.

Alum : use in clarifying water, 395.

Aluminium: action with sodium
hydroxide, 43 ; amalgam, 391 ;
combustion in air, 391 ; combustion
in oxygen, 24, 391 ; explosion with
oxygen, 25 ; explosion with sodium
peroxide, 392; reduces metallic
oxides, 392, 412; union with
bromine, 393 ; union with iodine,
393.

Aluminium hydroxide: absorptive
power for coloring matter, 394.

Amalgam : aluminium, 391 ; ammo-
nium, 358 ; iron, 381 ; sodium, 358 ;
zinc, 3.

Ammonia: absorption by charcoal,
197 ; absorption by fused calcium
chloride, 197; absorption by silver
chloride, 198 ; action with carbon
dioxide, 362; action with hydro-
chloric acid, 193, 359; action with
hydrogen sulphide, 360; action
with mercurous nitrate, 194; col-
lection, 195; combustion in air,
198; combustion in oxygen, 199;
combustion of oxygen in, 199;
decomposition, 200-203; drying of,
192, 196 ; from ammonium chloride
and slaked lime, 192; from ammo-
nium hydroxide, 192 ; from ammo-
nium hydroxide and potassium
hydroxide, 191 ; from hydrogen
and nitric oxide, 190 ; from organic
substances, 189, 190; from potas-
sium nitrate, potassium hydroxide,
and iron, 190; solubility in water,
194-196; specific gravity, 193; tests
for, 193; volumetric relation of
nitrogen in, 203; water, ammo-
nium hydroxide, 196.

Ammonium amalgam, 358.

Ammonium carbamate, 362.

Ammonium carbonate : preparation,
362.

Ammonium chloride : electrolysis
of, 205 ; from ammonia and hydro-
chloric acid, 359.

Ammonium dichromate : decomposi-
tion, 181, 361.

423

424

INDEX

Ammonium hydroxide: electrolysis
Of, 201 : preparation, 196.

Ammonium nickel sulphate: elec-
trolysis of, 415.

Ammonium nitrate: decomposition
by heat, 208; decomposition bj
zinc dust, 361.

Ammonium nitrite: formation, 180.

Ammonium Bulphate: dissociation
(.i solution, 380; electrolysis of,

A i union in in sulphide : formation, 380.

Anti-bleach, 152.

Antimoniuretted hydrogen: see
stibine, 273.

Antimony : combustion in air,
combustion in chlorine, 275; depo-
sition from burning stibine, 27 i .
fusibility, 273; spots, 274; union
wiiii bromine, 107«

Am imonj cinnabar, 277.

Antimony hydride : stibine, 21

Antimonj pentacblorlde, 275

Antimonj sulphide 148; action with

hydrochloric acid, I mbus-

tiou in oxj gen, 275 . combustion

in potassium nitrate, 276 ; in Ben-

i fires, 276,

Antimony trichloride, 278.

Arsenic : combustion in oxj gen, 272 ;
deposition from burning arsine,
270, 271, 274, 275; purification,
. solubility in sodium hypo-
chlorite, 274 : spots, 271, 27 I,
Bublimation, 269; onion with bro-

mine, 107.

arsenic hydride : arsine. 280,27 1, 275
Irsenic iodide, -'

Arsenic sulphide : in w bite fin

Arsenic trioxlde: action With nitric

acid, 218] from arsenk and oxy-

M. 272.

Arseniuretted hydrogen: see arsioe,

280.
Asbestos : deflagrating-*] o,

paper, i. 381 ; platinised, 61, 158,

190.

Aspirator, d.

Balloons. 19, SO.

Barium chlorate, deflagration, 370.

Barium nitrate: deflagration on

charcoal. 370; in green tire.
Barium oxide : absorption ol oxygen

h\ . ."><'>7 : action with sulphur tri-

oxide, i

Barium peroxide: action with hy-
drogen, 368 : action with sulphuric

acid, 7.". : decomposition by beat,

• '/.•He from, 31 ; preparation,

Barium sulphate: from barium ox-
ide and sulphur trioxide,

Solubility in ua

Batteries : electric
Batterj solution,

preparation, 276,
tfa cryi tion, 104; fu-

104; in alto] b, 104.
Bleaching: by chlorine, B6; by hy-
drogen peroxide, 7^ ; b] h\ d i
lulpbide, i 17 , b] bydrosulphn-
i. 158 : by perchloric
I0S bj so lium h\ pochlorite, 101 ;
by sulphur d
Blue Hi'.

Bone-black, 2

ol alcohol
nam decomposition "i so-

dium chloride, hydration,

preparation, 2fi
i anhydride ; action on «

280 . !• h\ maj

Boron : combustion la i"<t-

aration, 278.
i;«. ron trifluoride,

Brass : action of chlorine on.

Bromine: action with hydrogen sul-
phide, l1 n |rith hydi
phosphide, 258 ; action with naph-
thaline. 1 10 . from potassium bro-
mide, 108; solidification,
union i nti aluminiun union
w ith antimony, i"7 j union
arsenic, 107 • anion \n ith ethj

union with phosph

INDEX

425

union with potassium , 354 ; vapori-
zation, 107; water, 107.

Bunscn burner, 321).

Burner : for oxyhydrogen flame, 64.

Cadmium: combustion in air, 370;
distillation, 379; oxide, 379; sul-
phide, 146, 379.

Calcium carbide, 323.

Calcium carbonate: action with hy-
drochloric acid, 304; decomposi-
tion by heat, 365.

Calcium chloride : absorption of
ammonia by fused, 197 ; use as
drying agent, 46, 120, 147.

Calcium fluoride: action with sul-
phuric acid, 127, 279.

Calcium hydroxide : action with
ammonium chloride, 192 ; action
with zinc dust, 43.

Calcium hypochlorite, 100.

Calcium light, 65.

Calcium oxide: action with water,
363 ; formation, 366 ; incandes-
cence of, 65 ; use as drying agent,
863.

Calcium phosphide: action with
water, 252, 253, 258; preparation,
364.

Calcium polysulphide, 147.

Calcium sulphate: hydration, 365.

Candle: Christmas, 4; combustion
in oxygen, 18; increase in weight
on burning, 28.

Carbon : absorbs coloring matter,
293 ; electrical conductivity, 291 ;
in iron, 411; oxidation at low
temperatures, 296; oxidation by
sodium peroxide, 351.

Carbon dioxide : action with ammo-
nia, 862; extinguishes candle
flame, 314, 315; freezing mercury
with solid, 310; from baking-pow-
der, 305 ; from calcium carbonate
and hydrochloric acid, 304; from
charcoal and oxygen, 303; from
fermentation, 305 ; from magnesite,
304; from oxalic acid, 298; in air,

306, 307; in beverages, 306; in ex-
pired air, 307; liquefied, 307;
preparation of solid, 307, 308 ; prep-
aration of supersaturated solu-
tion, 316; reduction by carbon,
296; reduction by magnesium,
272 ; reduction by zinc, 297 ; rotates
paper wheel, 313; siphoning, 314;
specific gravity, 311, 312,313; volu-
metric relation to oxygen con-
sumed, 303.

Carbon disulphide : action with nitric
acid, 225; cold produced by evap-
oration of, 317; combustion in
nitric oxide, 217; combustion in
oxygen, 318; combustion of iron
m, 319; combustion of potassium
in, 318; dissolves fats, 317; explo-
sion with oxygen, 318; inflamma-
bility, 317.

Carbon monoxide: absorption by
cuprous chloride, 301 ; action on
palladious chloride, 302; action
on reduced nickel, 416; explosion
with oxygen, 301 ; from carbon
dioxide and carbon, 296; from
carbon dioxide and zinc, 297 ; from
oxalic acid, 298; from sulphuric
acid and potassium ferrocyanide,
298; reduces iodic acid, 303; re-
duces silver salt solutions, 302.

Chamber crystals: decomposition,
167; formation, 165, 167, 172,
222.

Charcoal: absorbs ammonia, 197;
absorbs hydrogen sulphide, 292;
action with sulphuric acid, 151 ;
combustion in liquid nitrogen per-
oxide, 221 ; combustion in nitric
oxide, 217; combustion in oxygen,
18, 19; combustion in perchloric
acid, 105; effects combustion of
phosphorus, 238; explosion with
oxygen, 25; preparation, 291; use
in gunpowder, 356!

Chemical harmonica, 60.

Chloric acid, 104.

Chloride of lime, 100.

426

INDEX

Chlorine : absorption in water, 84 ;
action on brass, 88; action on
ethylene, 322; action on hydro-
bromic acid, 111; action on hydro-
gen phosphide, 355; action on
iodo-starch paper, 83; action on
mercuric iodide, 98, 99; action
on phosphorus, 259, 261 ; action on
silicon, 287; action on sulphur,
148; action on turpentine, 86;
bleaching action, 86; by Deacon's
process, 82; combustion of anti-
mony in, 275; combustion of
candle in, 86; combustion of hy-
drogen in, 85; crystalline hydrate
of, 84; explosion with hydrogen,
85; from hydrochloric acid and
manganese dioxide, 80; from hy-
drochloric acid and potassium
dichromate, 82; generator, 80;
manipulation, 81 ; union with tin,
397.

Chlorine monoxide: action with
phosphorus, 99; action with sul-
phur flowers, 99; explosion, 99;
from mercuric oxide and chlorine,
98.

Chlorine peroxide: action with
alcohol, 103; action with phospho-
rus, 103 ; action with sugar, 102 ;
from hydrochloric acid and potas-
sium chlorate, 102 ; from potassium
chlorate and sulphuric acid, 101.

Chlorine water : decomposition by
light, 87; preparation, 84.

Chlorophyl of green leaves : oxygen
from, 13.

Chrome yellow : dyeing with, 406.

Chromic acid, 405.

Chromium chloride: preparation of
anhydrous, 405.

Chromium oxychloride : oxidizing
action, 407 ; preparation, 407.

Chromium trichloride: oxidizing
action, 405; preparation, 405.

Chromyl chloride, 407.

Cinnabar: antimony, 277; artificial,
382.

Coal : distillation, 325 ; gas, 324 ; tar,
325.

Cobalt: chloride, 413; deposition by
magnesium, 413; sulphide, 146.

Collodion: balloon, 49; for protect-
ing corks, 81.

Colored fires: blue, 387; green, 370;
purple, 357; red, 367; white, 271.

Combustion: reciprocal, 339; spon-
taneous, 238, 251, 284, 400; under
water, 103, 240.

Copper: action on nitric acid, 211;
action on sulphuric acid, 151 ;
action of salts with hydrochloric
acid and air, 82 ; color of, 385 ;
deposition of metallic, 14; deposi-
tion on iron, 384; electrical depo-
sition, 384; melting, 65; precipi-
tation by phosphorus, 245 ; prepa-
ration of reduced spiral, 385;
union with sulphur, 134.

Copper phosphide, 245.

Copper sulphate : electrolysis of, 13,
384.

Cupric chloride: solubility in alco-
hol, 386; use in colored fire, 387.

Cupric oxide: reduction by alcohol,
385 ; reduction by hydrogen, 62, 63.

Cuprous chloride: absorbs carbon
monoxide, 301 ; action of light on,
385 ; flame coloration by, 386.

Cuprous hydride, 158.

Davy Safety Lamp, 334.

Deacon's process for preparing chlo-
rine, 82.

Deflagrating-spoon : asbestos, 372;
reversible, 371.

Diamond: combustion in oxygen,
295.

Diffusion of gases: of chlorine and
hydriodic acid, 123; of hydrogen,
55, 56, 57; of hydrogen sulphide
and sulphur dioxide, 143; of nitric
oxide and air, 215; separation of
hydrogen and oxygen by, 58.

Dissociation of ammonium sulphate,
360.

INDEX

427

Druramond light, 64.

Drying of gases: by calcium chlo-
ride, 46; by quicklime, 192; by
soda-lime, 192; by sulphuric acid,
46, 174.

Dutch metal, 88.

Electrolysis : of ammonium chlo-
ride,205; of ammonium hydroxide,
201 ; of ammonium nickel sulphate,
415; of ammonium sulphate, 358;
of copper sulphate, 13, 384; of hy-
drochloric acid, 94, 96; of hydro-
gen peroxide, 77; of silver cya-
nide, 388 ; of silver nitrate, 388 ; of
stannous chloride, 396; of sulphu-
rous acid, 157 ; of water, 71, 72.

Electrolytic apparatus, 74; Hoff-
mann's, 72, 95.

Erlenmeyer flask, 2.

Etching glass, 128.

Ether thermometer, 174.

Ethylene : absorption by cold water,
322; decomposition by heat, 321:
dibromide, 322; dichloride, 322;
from alcohol and sulphuric acid,
320; from ethylene dibromide,
321 ; union with bromine, 322 ;
union with chlorine, 322.

Euchlorine, 26.

Explosion: of hydrogen generator,
68, 69.

Eyeglasses, colored, 5.

Fermentation: carbon dioxide
from, 305.

Ferric oxide: action on potassium
chlorate, 9; reduction by alu-
minium, 412; reduction by hydro-
gen, 409.

Ferrous sulphate: formation, 384,
solubility of nitric oxide in, 213.

Ferrous sulphide : action with acids,
137; formation, 133, 134, 144, 319.

Fire-damp indicator, 56.

Fischer's salt, 414.

Flame: Bunsen, 329, 334, 335, 337;
carburetting hydrogen, 336; in-

crease in brilliancy of non-lumi-
nous, 338; luminosity of, 335, 336,
337 ; pictures of, 331, 332 ; struc-
ture, 198, 330.

Flashlight cartridges, 375.

Fountain produced by absorption : of
ammonia in water, 194; of hydro-
chloric acid gas in water, 94; of
nitrogen peroxide in water, 216.

Freezing-mixture of sodium sulphate
and hydrochloric acid, 352.

Fuming: nitric acid, 221; sulphuric
acid, 160.

Galvanized iron, 378.

Gases: absorption by bone-black,
293 ; collection by displacement, 17,
305 ; collection from interior of can-
dle flame, 333; cylinders of com-
pressed, 4; drying, 46, 174, 192;
ignition of, from extinguished
candle, 332.

Gasometers, 14, 15.

Gauntlets, 5.

Generator, Kipp, 3.

Glass: etching, 128; Jena, 2.

Glover tower, 169, 170, 173.

Gold: precipitation by phosphorus,
245 ; reduction of chloride by phos-
phorous acid, 261, 264.

Graphite : combustion in oxygen, 294.

Guncotton, 207.

Gunpowder: combustion with iron
powder, 411 ; preparation, 356.

Hoffmann electrolytic apparatus,
72, 95.

Hydrazine sulphate: action with
nitric acid, 229 ; action with potas-
sium iodate, 229 ; action with silver
nitrite, 230; decomposition by
heat, 229; reducing action, 228.

Hydrazoic acid, 229.

Hydriodic acid: decomposition by
chlorine, 122; decomposition by
heat, 121 ; from hydrogen and
iodine, 117; from iodine and rosin,
119; from phosphorus iodide and

428

INDEX

water, 118; oxidation by nitric
acid, 122; purification, 119; solu-
bility in water, 120, 121.

Hydrobromic acid : action with am-
monia, 111 ; decomposition by
chlorine, 111 ; from bromine and
hydrogen, 108; from bromine and
hydrogen sulphide, 108; from bro-
mine and naphthaline, 110; from
potassium bromide, 109; hygro-
scopic nature, 111; purification,
109, 110; solubility in water, 111.

Hydrochloric acid : analysis of gases
obtained by electrolysis of, 98;
electrolysis of, 94, 96; from com-
mercial acid, 92; from hydrogen and
chlorine, 89; from sulphuric acid
and ammonium chloride, 92 ; from
sulphuric and hydrochloric acids,
93 ; from sulphuric acid and sodium
chloride, 91 ; generation of heat by
absorption in water, 93; prepara-
tion of aqueous, 94 ; solubility in
water, 93; union with ammonia,
359.

Hydrofluoric acid : action on boric
anhydride, 279; action on glass,
128, 129; action on silicon dioxide,
289; preparation, 127.

Hydrofluosilicic acid, 289.

Hydrogen: action on barium perox-
ide, 368; action on magnesium
nitride, 376 ; burning removes oxy-
gen from air, 182; carburetting
flame of, 336; collection, 45; com-
bustion in air, 59; combustion in
chlorine, 85; combustion in ni-
trous oxide, 210 ; combustion of air
in, 343; combustion of oxidizing
agents in, 346; conductivity for
heat, 53, determination of specific
gravity, 48; diffusibility, 55; dif-
fusion and fire-damp indicator, 56;
diffusion from oxygen, 58; diffu-
sion out of porous cup, 55 ; diffu-
sion producing a fountain, 56;
diffusion through rubber, 57 ; dry-
ing, 46; explosion with air. (56 ;

explosion with chlorine, 85 ; explo-
sion with nitrous oxide, 210; ex-
plosion with oxygen, 69; flame,
59; from aluminium and sodium
hydroxide, 43 ; from calcium hy-
droxide and iron powder, 43; from
calcium hydroxide and zinc dust,
43; from sodium and water, 39,
350; from sodium hydroxide and
iron, 42 ; from water vapor and
iron, 41 ; from water vapor and
magnesium, 42; from water vapor
and zinc, 42 ; from zinc and hydro-
chloric acid, 43; from zinc and
sulphuric acid, 43; ignition by
platinized asbestos, 61; non-con-
ductivity for sound, 54; purifica-
tion, 46; siphoning, 60; specific
gravity, 47, 48; soap-bubbles, 52;
testing, 45; use in balloons, 49-51.

Hydrogen generator: care in testing,
67 ; danger of premature lighting,
68; explosion of , 67-69.

Hydrogen peroxide : action on lead
sulphide, 76; action on potassium
dichromate, 76; bleaching action,
77 ; electrolysis of, 77 ; from ba-
rium peroxide and sulphuric acid,
75; from cooling hydrogen flame,
74 ; from sodium peroxide and
water, 75; oxidizing action, 77.

Hydrogen persulphide : action with
silver oxide, 14S ; bleaching action,
147; decomposition, 147; prepara-
tion, 147; solubility in carbon
disulphide, 147.

Hydrogen phosphide: action with
bromine vapor, 256; action with
iodine, 258; combustion in air,
255: combustion in oxygen, 257;
from calcium phosphide and water,
252, 253; from hydrogen and red
phosphorus, 249; from phosphorus
and potassium or sodium hydrox-
ide, 250 : ignition by chlorine, 255 ;
ignition by heat, 255; ignition by
nitric acid, 255; ignition by silver
nitrate solution, 256; purification,

INDEX

429

250, 254; spontaneous inflamma-
bility, 250.

Hydrogen sulphide: absorption by
charcoal, 292; action with bro-
mine, 108; action with solutions
of metallic salts, 145 ; action with
sulphur dioxide, 143; collection,
139 ; combustion in air, 142 ; com-
bustion of iron in, 144; decompo-
sition by heat, 142; decomposition
by sodium, 145; description of
large generator, 420 ; drying, 137 ;
explosion with oxygen, 143; from
antimony sulphide, 139 ; from fer-
rous sulphide, 137 ; from hydrogen
and sulphur, 135; ignition by ni-
tric acid, 144; incomplete combus-
tion, 142; manipulation, 138; oxi-
dation by lead peroxide," 402 ; solu-
bility in sodium hydroxide, 141 ;
solubility in water, 140; test for,
136; union with ammonia, 360.

Hydrosulphurous acid : bleaching
action, 158; preparation, 157.

Hydroxylamine : alternate reducing
and oxidizing action, 207; reduc-
ing action, 207.

Hypochlorous acid : action on silver
oxide, 101 ; from calcium hypo-
chlorite, 99; from chlorine and
mercuric oxide, 99.

Hypophosphorous acid; preparation
of sodium or potassium salts, 250,

Illuminating gas : combustion in
nitric acid, 225; combustion of
air in, 3+1; combustion on platin-
ized asbestos, 32(5; explosion with
air, 326; from distillation of coal
or wood, 324, 325; reciprocal com-
bustion of air and, 343; soap-bub-
bles, 325.

Ink: sympathetic, 414

Iodic acid : combustion in hydrogen,
346; decomposition by heat, 124;
reduction by carbon monoxide,
303 ; reduction by sulphurous acid ,

125; from iodine and nitric acid,
124.

Iodic anhydride: formation, 124;
oxidizing action, 124.

Iodine: action with ammonia, 206;
action with hydrogen phosphide,
258 ; action with mercurous iodide,
382; action with nitric acid, 124;
action with rosin, 119; action with
starch, 114; distillation, 113; from
potassium iodide, 112; melting,
113; monochloride, 123; solubility,
114; starch test for, 114; trichlo-
ride, 123; volatilization, 114;
union with aluminium, 393; union
with hydrogen, 117 ; union with
mercury, 116, 381 ; union with
phosphorus. 117, 355; union with
potassium, 116; union with zinc
dust, 116.

Iodo-starch paper: action of ozone
on, 35; preparation, 35; test for
chlorine, 83

Iodo-starch solution: effect of
heat on, 115; test for chlorine,
83.

Iron ; absorption of oxygen by rust-
ing, 30; action of sodium hydrox-
ide with powdered, 42; amalgam,
381 ; carbon in, 411 ; combustion in
carbon disulphide, 319; combus-
tion in hydrogen sulphide, 144;
combustion in nitrous oxide, 211 ;
combustion in oxygen, 24; com-
bustion in sulphur dioxide, 156;
combustion of gunpowder and
powdered, 411 ; combustion of
potassium chlorate and powdered,
411 ; combustion (quantitative) in
air, 27; deposition of copper on,
384: deposition of zinc on, 378;
explosion of oxygen with pow-
dered, 25; galvanized, 378; oxide,
15(5; preparation of passive, 410;
preparation of pyrophoric, 409;
union with sulphur, 133.

Jena : glass, 2.

430

INDEX

Kipp: generator, 3; description of, 46.

Lead: action of water on, 401 ; crys-
talline structure, 401 ; deposition
on zinc, 401 ; preparation of pyro-
phoric,400 ; spontaneous inflamma-
bility of pyrophoric, 400 ; tree, 401.

Lead chromate : oxidizing action of,
406.

Lead dioxide : union with sulphur
dioxide, 156.

Lead monoxide, 219.

Lead nitrate : decomposition on
ignition, 219; explosion with sul-
phur, 403.

Lead peroxide, 402.

Lead sulphide, 36, 146.

Lead tartrate, 400.

Leidenfrost phenomenon: produc-
tion of, 153.

Light: action on chlorine water, 87;
action on cuprous chloride, 385 ; ac-
tion on green leaves, 13; action on
potassium ferricyanide, 412; ex-
plosion of chlorine and hydrogen
by, 90.

Lime: chloride of, 100; light, 64;
slaked, 363; use in drying ammo-
nia, 192.

Lithium carbonate : reduction by
magnesium, 374.

Magnesite : decomposition by heat,
304.

Magnesium: action with nitric acid,
373; combustion in air (quantita-
tive), 27; combustion in carbon
dioxide, 372; combustion in oxy-
gen, 24; combustion in sulphur
vapor, 135; combustion in water
vapor, 371 ; combustion with po-
tassium chlorate, 374; explosion
of chlorine and hydrogen by, 90;
reduces boric anhydride, 278; re-
duces metallic oxides and salts,
374; reduces silicon dioxide, 283;
union with nitrogen, 375.

Magnesium nitride: action with

hydrogen, 376; decomposition,
375; formation, 375.

Magnesium silicide : action with
hydrochloric acid, 284; formation,
283, 284.

Magnesium sulphide, 135.

Manganese : action of dioxide on hy-
drochloric acid, 80; action of diox-
ide on potassium chlorate, 9, 10;
silicate, 253; sulphide, 146.

Marsh gas, 319.

Mercuric chloride : action with po-
tassium iodide, 382.

Mercuric iodide, 116; preparation,
3S2.

Mercuric oxide : action with chlo-
rine, 98, 99; oxygen from, 8;
ozone from, 31.

Mercurous iodide, 381, ,382.

Mercurous nitrate and ammonia, 194.

Mercury: action of ozone on, 36;
filtration, 381 : freezing with solid
carbon dioxide, 310; from mer-
curic oxide, 8; precipitation of
silver by, 388 ; purification, 381;
union with iodine, 116, 381.

Metaphosphoric acid, 267.

Methane: explosion with oxygen,
320 ; non-supporter of combustion,
320; preparation, 319.

Mohr's salt, 213.

Moisture: in bleaching, 87; influ-
ence on combustion, 300.

Mosaic gold, 399.

Naphthaline: action with bro-
mine, 110.

Newton's metal, 404.

Nickel: deposition by electrolysis,
415; ignition of gunpowder by
pyrophoric, 415: oxidation in air,
415; pyrophoric, 414: reduction of
oxide, 414: silicate, 353; solubil-
ity of sulphide in sodium sulphide,
415: tetracarbonyl, 416. 418.

Nitric acid : action with carbon
disulphide, 225; action with cop-
per, 211; action with hydrogen

INDEX

431

sulphide, 144; action with illumi-
nating gas, 225; action with io-
dine, 124; action with organic
matter, 223, 224, 225; action with
tin, 220; action with turpentine,
224; combustion in hydrogen, 346;
combustion of illuminating gas in,
225; decomposition by heat, 226;
dilution of fuming, 221 ; from po-
tassium nitrate and sulphuric acid,
222 ; test for, 228.

Nitric oxide : absorption by nitric
acid, 214; absorption by potas-
sium permanganate solution, 214;
action of air on, 215; combustion
in, 216; combustion of carbon
disulphide in, 217 ; combustion of
charcoal in, 217; from copper and
nitric acid, 211 ; from copper,
potassium nitrate, and sulphuric
acid, 212; from sodium nitrite
and ferrous chloride, 212; neu-
trality, 213; reduction by hydro-
gen, 190; solubility in ferrous
sulphate solution, 213; union with
oxygen, 215.

Nitro-benzene : oxidation by lead
peroxide, 402; oxidation by sodium
peroxide, 351.

Nitrogen : from air, ammonia, and
copper, 183; from air and burn-
ing hydrogen, 182; %om air and
phosphorus, 181 ; from ammonium
chloride and potassium dichro-
mate, 181 ; from ammonium chlo-
ride and sodium nitrite, 180; from
ammonium dichromate, 361 ; from
potassium nitrate and iron, 181;
oxidation by burning hydrogen,
185; oxidation by burning mag-
nesium, 185; quantitative determi-
nation of, in air, 186 ; volumetric
relation in ammonia, 203.

Nitrogen chloride, 204.

Nitrogen iodide: explosiveness of,
206 ; prepar \ M on , 205 .

Nitrogen peroxide: absorption by
sulphuric acid, 222; combustion

of charcoal in, 221 ; combustion of
potassium in, 221; decomposition,
221; formation of, 164, 166, 167,
215 ; from decomposition of nitric
acid, 226; from lead nitrate, 219;
from tin and nitric acid, 220;
vaporization of liquid, 220.

Nitrous acid : formation of, 185, 186 ;
phenylenediamine reaction for,
218.

Nitrous anhydride : formation of,
214, 221 ; from arsenic trioxide and
nitric acid, 218; liquefaction, 218.

Nitrous oxide : combustion of hydro-
gen in, 210 ; combustion of iron in,
211 ; combustion of phosphorus in,
210; combustion of splinter in, 209;
combustion of sulphur in, 210; ex-
plosion with hydrogen, 210; from
ammonium nitrate, 208; solubility
in water, 209.

Nordhausen sulphuric acid, 160.

Orthophosphoric acid, 267.

Oxygen : absorption by burning phos-
phorus, 21; absorption by potas-
sium pyrogallate, 26 ; absorption by
rusting iron, 30; absorption from
air by copper (quantitative), 187;
abstraction from air by phosphorus,
181; combustion in ammonia, 199;
combustion in hydriodic acid gas,
122; combustion in hydrogen, 339-
341; combustion of candle in, 18;
combustion of charcoal in, 18, 19;
combustion of iron and magnesium
powder in, 24 ; combustion of phos-
phorus in, 20, 22; combustion of
steel wool in, 23: combustion of
sulphur in, 20, 149; combustion
of wood in, 17 ; combustion of zinc
in, 24; compressed, 34-16; deter-
mination of , in air, 186; explosion
with carbon monoxide, 301 ; ex-
plosion with powdered aluminium,
charcoal, iron, zinc, 25; explosion
with hydrogen, 69; from chloro-
phyl of green leaves, 13; from

432

INDEX

electrolysis of copper sulphate,
13; from mercuric oxide, 8; from
potassium chlorate, 9 ; from potas-
sium chlorate and mauganese di-
oxide, 10; from silver oxide, 9;
from sodium peroxide, 11 ; removal
from air by burning hydrogen, 182 ;
separation by diffusion, 58; union
with nitric oxide, 215; union with
sulphur dioxide, 158.

Oxyhydrogen gas : burner, 64 ; ex-
plosion, 70; flame, 70; heat of
flame, 64, 65] preparation, 71,
369.

Ozone: action on alcohol, 32, 33;
action on ether, 33 ; action on lead
sulphide, 36; action on mercury,
36 ; action on phosphorus, 32 ; action
on potassium iodide, 34, 35 ; action
on rubber, 34 ; action on silver, 33 ;
action on sulphur, 32; decomposi-
tion by copper oxide, 3(5; decom-
position by heat, 37 ; decomposition
by rubber, 38; from barium per-
oxide, 31 ; from mercuric oxide, 31 ;
from potassium chlorate, 31 : from
potassium permanganate, 32 ; from
slow combustion of ether, 34 ;
from slow oxidation of phosphorus,
33; paper, preparation, 35.

Palladium: precipitation by car-
bon monoxide, 302.

Paper wheel, 313.

Pentathionic acid, 144.

Perchloric acid: action on organic
matter, 105; bleaching action, 105;
combustion of charcoal in, 105 ;
formation, 104.

Perchromic acid, 76.

Permanganic anhydride, 32.

Phoxphonium iodide, 258, 259

Phosphoretted hydrogen : see hydro-
gen phosphide, 249.

Phosphoric acid: formation, 240,
242, 263.

Phosphorous acid: formation, 261,
264, 265.

Phosphorus : abstraction of oxygen
from air by, 181 ; action with bro-
mine, 263; action with chlorine,
259, 261 ; action with chlorine mo-
noxide, 99; action with nitric acid,
242; action with potassium chlo-
rate, 243; action with potassium
or sodium hydroxide, 250; action
with quicklime, 364; action with
sulphur trioxide, 163; burns from,
233; colors hydrogen flame, 241;
combustion affected by charcoal,
238; combustion in air (quantita-
tive), 29, 189; combustion in chlo-
rine peroxide, 103 ; combustion in
nitric oxide, 216; combustion in
nitrous oxide, 210; combustion in
oxygen, 20; combustion in oxygen
(quantitative) , 22 ; combustion in
potassium chlorate, 357 ; combus-
tion on cotton, 239; combustion
under water, 103, 240: difference
in ignition points of modifications,
247; effect of diminished pressure
on glowing, 243; effect of oxygen
on glowing, 243; effect of vapors
on glowing, 244: inflammability,
237 ; oxidation by sodium peroxide,
351; precautions in handling, 232;
preparation of globules, 236; prep-
aration of stick, 235; purification,
237; red, see amorphous: reduc-
tion of metallic salt solutions by,
245: slow oxidation, 33; solubility
in carbon disulphide, 238; test for
free, 241 ; union with iodine, 117;
vaporization in steam, 240.

Phosphorus, amorphous: action with
hydrogen. 249: combustion in air,
248; combustion with potassium
chlorate, 248; conversion to yellow
by heat. 246: formation. 240: from
combustion of yellow phosphorus,
245; from action of iodine on yel-
low phosphorus, 246 ; from action
of light on yellow phosphorus. 246.

Phosphorus iodide : action with
water, 118.

INDEX

433

Phosphorus pentachloride, 261.

Phosphorus pentoxide: action with
sulphuric acid, 160; action with
water, 266, 267 ; from combustion
of phosphorus in air or oxy-
gen, 21, 22, 248, 266; sublimation,
266.

Phosphorus tribromide, 263.

Phosphorus trichloride : decomposi-
tion by water, 260, 265; prepara-
tion, 259.

Plaster of Paris, 365.

Plating: copper, 384; nickel, 415;
silver, 388.

Platinized asbestos, 61 ; action with
hydrogen and sulphur dioxide,
136; action with oxygen and sul-
phur dioxide, 159; decomposes
ammonia, 200.

Platinum: deflagrating-spoon, 150;
melting, 65.

Porous cell, 55.

Potable waters: action on lead
pipes, 402.

Potassium : combustion in carbon
disulphide, 318; combustion in
nitrogen peroxide, 221 ; decompo-
sition of ammonia by, 200; union
with bromine, 354; union with io-
dine, 116, 355; vaporization, 354.

Potassium alum, 395.

Potassium chlorate : action with hy-
drochloric acid, 102; action with
phosphorus, 243 ; action with sul-
phuric acid, 102; combustion in
hydrogen, 316 ; combustion of
phosphorus in, 357 ; combustion
with magnesium, 374; combustion
with powdered iron, 411; combus-
tion with zinc dust, 378; in Bengal
fires, 357; oxygen from, 9, 10;
ozone from, 31.

Potassium cobaltic nitrite, 414.

Potassium dichromate : action with
ammonium chloride, 181; action
with hydrochloric acid, 82; action
with hydrogen peroxide, 76 ; action
with sulphur dioxide, 154.

Potassium disulphate : decomposi-
tion, 160.

Potassium ferricyanide: action of
light on, 412.

Potassium ferrocyanide : carbon
monoxide from, 299.

Potassium hypophosphite, 250.

Potassium iodate : action with chlo-
rine, 98; action with mercuric
chloride, 382 ; action with stannous
chloride, 399 ; reduction by hydra-
zine sulphate, 229.

Potassium nitrate: in gunpowder,
356; in touch-paper, 355;. reduc-
tion by iron, 181.

Potassium perchlorate: action with
sulphuric acid, 104.

Potassium permanganate : absorp-
tion of nitric oxide by, 214 ; ozone
from, 32 ; reduction by sulphur di-
oxide, 156.

Potassium pyrogallate : absorbs oxy-
gen, 26, 186; preparation of solu-
tion, 26.

Pressure regulator, 15.

Pyrophoric: iron, 409; lead, 400;
nickel, 415.

Realgar, 271.

Recurved jet, 85.
Rose's metal, 404.
Rosin: action with iodine, 119.
Rubber: action with ozone, 38; dif-
fusion of hydrogen through, 57.

Safety Lamp, 334.

Safety matches, 249.

Screens : glass, 5, 102.

Selenic acid: preparation, 179.

Selenious acid : action with hydro-
gen sulphide, 179; reduction by
sulphurous acid, 179.

Selenium: combustion in air, 177;
solubility in sulphuric acid, 177;
sublimation, 177.

Selenium dioxide: preparation, 178.

Selenium sulphide: formation, 179.

Silicates: formation of metallic,

434

INDEX

in solution of sodium silicate,
352.

Silicon: preparation, 283; union
with chlorine, 287.

Silicon dioxide : action with hydro-
fluoric acid gas, 289.

Silicon hydride : combustion in air,
286; decomposition by heat, 286;
explosion with air or oxygen, 286 ;
spontaneous combustibility of,
285 ; preparation, 284.

Silicon tetrachloride, 287, 288.

Silicon tetrafluoride, 289, 290.

Silver: absorption of oxygen by,
65; action with ozone, 33; boiling,
65; by electrolysis, 388; from
silver oxide, 9; precipitation by
carbon monoxide, 302; precipita-
tion by mercury, 388; precipita-
tion by phosphorus, 245.

Silver antimonide, 274.

Silver chloride : absorption of am-
monia, 198.

Silver cyanide : electrolysis of, 388.

Silver iodide : color change on heat-
ing, 389; formation, 390.

Silver nitrate: electrolysis of, 388;
precipitation of silver from, 388;
reduction by carbon monoxide,
302.

Silver nitride : explosiveness of, 230 ;
preparation, 230.

Silver nitrite, 230.

Silver oxide: action with hydrogen
persulphide, 148; action with hy-
pochlorous acid, 101; preparation,
9; preparation of oxygen from,
9; reduction by magnesium, 374.

Silver phosphide: formation, 241,
245, 256.

Slaked lime, 363.

Soap-bubbles: float on carbon diox-
ide, 313; hydrogen, 52; illumi-
nating gas, 325; oxyhydrogen, 70;
solution for, 52.

Soda-lime: absorption of carbon
dioxide by, 299; use in drying am-
monia, 192.

Soda water: carbon dioxide in, 306;
preparation, 316.

Sodium: action on hydrogen sul-
phide, 145; action on water, 40,
350; manipulation of, 39; melting,
349; metallic lustre, 349.

Sodium acetate: decomposition, 319.

Sodium acid sulphite : action with
sulphuric acid, 152.

Sodium amalgam: action on alu-
minium, 391.

Sodium chloride : decomposition by
boric acid, 281.

Sodium hypochlorite: action on ar-
senic, 275; bleaching action, 101.

Sodium hypophosphite, 266.

Sodium peroxide: action on water,
75 ; color change by heat, 351 ; ex-
plosion with aluminium, 392; oxi-
dizing action with carbon, 351;
oxidizing action with phosphorus,
351 ; oxygen from, 11 ; preserva-
tion of, 12.

Sodium silicate: formation of me-
tallic silicates in, 352.

Sodium sulphate: freezing mixture
with hydrochloric acid, 352; su-
persaturated solution, 351.

Sodium sulphide: formation, 145;
solubility of nickel sulphide in,
415.

Sparklets, 316.

Splinters: cigar-box wood, 4.

Spontaneous combustion : of hydro-
gen phosphide, 251 ; of phosphorus,
238; of pyrophoric iron, 409: of
pyrophoric lead, 400 ; of pyrophoric
nickel. 415 ; of silicon hydride, 284.

Stannic chloride, 397, 398.

Stannic sulphide, 399.

Stannous chloride : action with po-
tassium iodide, 399; electrolysis
of, 396.

Stannous iodide, 399.

Starch: action with iodine, 114.

Steam generator, 41, 171.

Steel wool: combustion in oxygen,
23; rusting in air, 30.

INDEX

435

Stibine, 273.

Stibnite, 139.

Strontium nitrate: deflagration on
charcoal, 367; in red fire, 367.

Suction pump, 6.

Sugar: carbonization by sulphuric
acid, 175; charring, 291 ; oxidation
by nitric acid, 225.

Sulphur: action with sulphuric acid,
151 ; combustion in air or oxygen,
149; combustion in nitrous oxide,
210; combustion in oxygen, 20;
deposition of, 143, 144 ; distillation
of, 130 ; explosion with lead nitrate,
403 ; increase in weight on burning,
30; octahedral, 133; oxidation by
nitric acid, 164; plastic, 131; pris-
matic, 132; roll, 130; solubility
in carbon disulphide, 133; solu-
bility in sulphur monochloride,
149; union with chlorine, 148;
union with copper, 131 ; union with
hydrogen, 135; union with iron,
133; union with magnesium, 135;
union with zinc, 135.

Sulphur dioxide : action with hydro-
gen, 136; action with hydrogen
sulphide, 143; action with nitric
acid, 164-169; action with potas-
sium dichromate, 154 ; action with
potassium permanganate, 156;
bleaching action, 155; combustion
of iron in, 156; combustion of tin
in, 156; freezing action of, 153;
from charcoal and sulphuric acid,
151 ; from copper and sulphuric
acid, 151; from sulphur and oxy-
gen, 149; from sulphur trioxide
and phosphorus, 163; from sul-
phuric acid and sodium acid sul-
phite, 152 ; from sulphuric acid and
sulphur, 151; liquefaction of, 152;
solubility in water, 155; specific
gravity, 154 ; union with lead di-
oxide, 156 ; union with oxygen, 158 ;
volumetric relation to oxygen con-
sumed, 150.

Sulphur flowers: action with chlo-

rine monoxide, 99; combustion
with zinc dust, 378; deposition,
142; in gunpowder, 356; prepara-
tion, 130; union with tin, 399.

Sulphur monochloride : decomposi-
tion by water, 149; from chlorine
and sulphur, 148; solubility of
sulphur in, 149.

Sulphur sesquioxide, 163.

Sulphur trioxide : action with barium
oxide, 163, 369; action with phos-
phorus, 163; action with sulphur,
162 ; action with water, 161 ; from
fuming sulphuric acid, 160; from
oxygen and sulphur dioxide, 158;
from potassium disulphate, 160;
from sulphuric acid and phos-
phorus pentoxide, 160.

Sulphuretted hydrogen : see hydro-
gen sulphide, 135.

Sulphuric acid : absorbs nitrogen
peroxide, 222 ; action on paper,
175; carbonization of sugar by,
175 ; dehydrating action, 174 ; from
sulphur and nitric acid, 164 ; from
sulphur dioxide and nitric acid,
164-173 ; heat of union with water,
173; reduction by carbon, 151; re-
duction by charcoal, 151; reduc-
tion by copper, 151 ; reduction by
sulphur, 151 ; technical manufac-
ture, 168.

Sulphuric anhydride, 160.

Sulphurous acid : 155 ; action with
zinc, 157 : electrolysis of, 157 ; re-
duction by sodium hypophosphite,
266.

Sympathetic ink, 414.

Tea Lead: use of, 40, 253.

Thermometer : ether, 174.

Time of reaction, 125.

Tin: action on nitric acid, 220; com-
bustion in sulphur dioxide, 156;
crystalline structure, 397 ; deposi-
tion by electrolytic action, 396;
deposition on zinc, 396; in fusible
alloys, 404 ; union with chlorine,

436

INDEX

397 ; union with sulphur flowers,

399.
Touch-paper: preparation, 355.
Turpentine: action with chlorine,

86; action with nitric acid, 224.

Volumetric Decomposition : of
ammonia by chlorine, 202 ; of am-
monia by electrolysis, 201 ; of am-
monia by sodium hypobromite,
203; of hydrochloric acid by elec-
trolysis, 95-97 ; of water by elec-
trolysis, 71, 72.

Water: action with sodium, 40,
350; electrolysis of, 71, 72; from
combustion of hydrogen, 61, 62,
18;>; from cupric oxide and hydro-
gen, 63.

Water blast, 6.

Water gas: preparation, 300.

Water vapor : reduction by iron, 41 ;
reduction by magnesium, 371; re-
duction by zinc, 42.

Wood: combustion in oxygen, 17;
oxidation by chromic acid, 406.

Wood's metal, 404.

Zinc: combustion in air, 26: com-
bustion in oxygen, 24 ; combustion
with potassium chlorate, ;>7*.
combustion with sulphur, 135;
combustion with sulphur flowers,
378; deposition of lead on, 401:
deposition on iron, 378; explosion
with oxygen, 25; granulated, 377 ;
ignition by ammonium nitrate,
'.MA : union with iodine, 116; use

in galvanising,

Zinc oxide : formation, 26.

Zinc sulphide: formation, loo, 146,
378.

Date Due

QD43 .B46

3 5002 00249 8488

Benedict, Francis Gano
Chemical lecture experiments.

CHEMISTRY LfBRARY

43
B46

52606

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