A_Text-Book_Of_Inorganic_Chemistry_Vol-VI_Part_II

A TEXT-BOOK OF

INORGANIC CHEMISTRY.

VOLUME VI. PART II.

In ELEVEN VOLUMES. Medium 8vo. Cloth. Prices are net. Postage extra.

A TEXT-BOOK OF

J.

VOLUME I.
VOLUME II.
VOLUME III.

VOLUME IV.
VOLUME V.

VOLUME VI. <

VOLUME VII.

VOLUME VTII.

VOLUME IX.

VOLUME X.

VOLUME XI

EDITED BY

NEWTON FRIEND, D.Sc., PH.D., F.T.C.,

Carnegie Gold .Medallist.

[ An Introduction to Modern Inorganic Chemistry. By J. XKWTOX
) Fnn-xi), D.So. (B ham), Ph.D. (VVurx) ; K. V. V. LITTLI:, B.Sc.
< (Loud.), A.B.C.S., Chief Chemist to Thorium, Ltd. , W. E. S.
TURNED, .D.Sc. (Lond.). The Inert Gases. By H. V. A. BRISCOE,
D.Sc. (Loud.), A.R.C.S.

f The Alkali Metals and their Congeners. By A. JAMIESOX WALKER,
\ Ph.D. (Heid.), B.A. (Q.U.B.), F.I.C. Pp. i-xxvi +379. 20s.
/PART 1. The Alkaline Earth Metals. By MAY SYBIL BURR (nee
I LESLIE), D.Sc. (Leeds). Pp. i-xxvi + ;U6. 20s.
\ PART II. Beryllium and its Congeners. By JOSHUA C. GREGORY,
B.Se. (Lond.), F.I.C., and MAY SYBIL" BURR, D.Sc. (Leeds).
V Pp. i-xxvi + 320. 18s.

f Aluminium and its Congeners, including the Rare Earth Metals.
j By H. F. V. LITTLTD, B.Sc. (Lond.), A.K.C.S., Chief Chemist to
{ Thorium, Ltd. Second Edition. Pp. xxvin + 485. 18s.
/ Carbon and its Allies. By R. M. CAVEN, D.Sc. (Lond.), F.I.C.
1 Second Edition. Pp. i-xxi + 468. JSs.

PART I. Nitrogen. By E. B. K, PRIDEAUX, M.A., D.Sc., F.I.C.,
and H. LAMBOURNE, M. A., M.Sc., F.I.C. Pp. i-xxviii 242 1 Ss.
PART II. Phosphorus. By E. B. R. PRIUEAUX, M.A., D.Sc.,

F.I.C. Pp. i-xxviii+23S.
PART III. Vanadium, Niobium, and Tantalum. By SYDNEY

MAKKS, M.Sc., A.i.C. Pp. i-xxvi +222. IS*.
PART IV. Arsenic, Antimony, and Bismuth. By \V. E. THORXKY-

CROI-T, B.Sc., and B. D. SirAW, .B.Sc., Ph.D. J n Preparation.
PART I. Oxygen. By J". XEWTON "FRIEND, D.Sc., and DOUGLAS

F. TWJSS, D.Sc., F.I.C. Pp. i-xxvi + 370. 18s.
PAP.T 11. Sulphur, Selenium, and Tellurium. By RELXJK H.
VALLANCE, M.Sc., F.I.C., DOUGLAS F. Twis?, D.Sc., F.I.C., and
Miss A. R. RCSSELL, B.Sc., A.I.C. Pp. i-xxviii + 420. 2f)S.
PART 11J. Chromium and its Congeners. ByREECE H. VALLAXCK,
M.Sc., A. I.C., and ARTHUR A. ELD RIDGE, B.Sc., F.I.C.
Pp. i-xxvi + 380. 18s.

The Halogens and their Allies. By GKOFFEEY MARTIX, D.Sc.,
Ph.D., and EBXICST A. DAXCASTER, B.Sc. (Lond.). Second
Edition.

PART I. Cobalt, Nickel, and the Elements of the Platinum
Group. By J. NEWTON FRIEND, D.Sc. (B ham). Second Edition.
Pp. i-xxvi +367. 18s.
PART II. Iron and its Compounds. By J. XEWTOX FRIEND,

D.Sc. Pp. ]-xxvi + 20fx 18s.

j The Metal- Ammines, with a General Introduction to the Theory
of Complex Inorganic Substances. By Miss M. ]\I. J. SUTHEJR-
V LAND, D.Sc.. F.I.C. Pp. i-xxvi + 2GO. " ISs.
Organometailic Compounds.

PART I. Derivatives of tlie Elements of Groups I to IV.
By ARCHIBALD E. OODDARD, "M.Sc., A I C., and
DOROTHY GODDATID, M.Sc Pp. i-xxviii -: 418. ^os.
PART II. Derivatives of Arsenic. By ARCHIBALD E. COD DARD,

M.Sc., A.I.C. Pp. i-xxviii ~- GOo. 42s.

PART III. Derivatives oi the Elements of Groups V to VIII
(excluding Arsenic). By ARCHIBALD E. GODDARD,
M.Sc.. A. I.C. In Prcjxiruiit.,,!,.

LONDON: CHAIILES GllLFFIX

CO.. LTD., 4-2 DUURY LAXE. W.

xt-book of Inorganic Chemistry, Vol. VI., Part //.]

[Frontispiece.

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A TEXT -BOOK OF

INORGANIC CHEMISTRY.

EDITED BY

J. XEWTON FFJEND, D.Sc., PH.D., F.I.C.,

CARNEGIE GOLD MEDALLIST.

VOLUME VI, PART II.

PHOSPHORUS.

BY

EDMUND B. E. PRIDEAUX,

M.A., B.8c.(N.Z.), D.Sc.(Loncl), F.I.C.

limit b ^frontispiece anD JIUistrattons.

L N D X :

CHARLES GRIFFIN & COMPANY, LIMITED.

42 DRURY LAXE, W.C. 2.

1934.

[All rights reserved.]

Printed in Great Britain by
NEILL & Co, LTD.. EDINBURGH

GENERAL INTRODUCTION TO THE SERIES.

DURING the past few years the civilised world has begun to realise the
advantages accruing to scientific research, with the result that an ever-
increasing amount of time and thought is being devoted to various
branches of science.

No study has progressed more rapidly than chemistry. This
science may be divided roughly into several branches : namely, Organic,
Physical, Inorganic, and Analytical Chemistry. It is impossible to
write any single text-book which shall contain within its two covers a
thorough treatment of any one of these branches, owing to the vast
amount of information that has been accumulated. The need is rather
for a series of text-books dealing more or less comprehensively with
each branch of chemistry. This has already been attempted by
enterprising firms, so far as physical and analytical chemistry are
concerned ; and the present series is designed to meet the needs of
inorganic chemists. One great advantage of this procedure lies in
the fact that our knowledge of the different sections of science does not
progress at the same rate. Consequently, as soon as any particular
part advances out of proportion to others, the volume dealing with
that section may be easily revised or rewritten as occasion requires.

Some method of classifying the elements for treatment in this way
is clearly essential, and we have adopted the Periodic Classification
with slight alterations, devoting a whole volume to the consideration
of the elements in each vertical column, as will be evident from a glance
at the scheme in the Frontispiece.

In the first volume, in addition to a detailed account of the elements
of Group 0, the general principles of Inorganic Chemistry are discussed.
Particular pains have been taken in the selection of material for this
volume, and an attempt has been made to present to the reader a
clear account of the principles upon which our knowledge of modern
Inorganic Chemistry is based.

At the outset it may be well to explain that it was not intended
to write a complete text-book of Physical Chemistry. Numerous
excellent works have already been devoted to this subject, and a
volume on such lines would scarcely serve as a suitable introduction
to this scries. Whilst Physical Chemistry deals with the general
principles applied to all branches of theoretical chemistry, our aim
has been to emphasise their application to Inorganic Chemistry, with
which branch of the subject this series of text-books is exclusively
concerned. To this end practically all the illustrations to the laws
and principles discussed in Volume I. deal with inorganic substances. _

Again, there are many subjects, such as the methods employed in
the accurate determination of atomic weights, which are not generally
vpo-flrflecl as forming; part of Phvsical Chemistry. Yet these are

viii PHOSPHORUS.

subjects of supreme importance to the student of Inorganic Chemistry
and are accordingly included in the Introduction.

Hydrogen and the ammonium salts are dealt with in Volume II.,
along with the elements of Group I. The position of the rare earth
metals in the Periodic Classification has for many years been a source
of difficulty. They have all been included in Volume IV., along with
the elements of Group III., as this was found to be the most suitable
place for them.

Many alloys and compounds have an equal claim to be considered
in two or more volumes of this series, but this would entail unnecessary
duplication. For example, alloys of copper and tin might be dealt
with in Volumes II. and V. respectively. Similarly, certain double
salts such, for example, as ferrous ammonium sulphate might very
logically be included in Volume II. under ammonium, and in Volume IX.
under iron. As a general rule this difficulty has been overcome by
treating complex substances, containing two or more metals or bases,
in that volume dealing with the metal or base which belongs to the
highest group of the Periodic Table. For example, the alloys of copper
and tin are detailed in Volume V. along with tin, since copper occurs
earlier, namely, in Volume II. Similarly, ferrous ammonium sulphate
is discussed in Volume IX. under iron, and not under ammonium in
Volume II. The ferro-cyanides are likewise dealt with in Volume IX.

But even with this arrangement it has not always been found easy
to adopt a perfectly logical line of treatment. For example, in the
chromates and permanganates the chromium and manganese function
as part of the acid radicals and are analogous to sulphur and chlorine
in sulphates and perchlorates ; so that they should be treated in the
volume dealing with the metal acting as base, namely, in the case
of potassium permanganate, under potassium in Volume II. But the
alkali permanganates possess such close analogies with one another
that separate treatment of these salts hardly seenis desirable. They
are therefore considered in Volume VIII.

Numerous other little irregularities of a like nature occur, but it is
hoped that, by means of carefully compiled indexes and frequent cross-
referencing to the texts of the separate volumes, the student will
experience no difficulty in finding the information he requires.

Particular care has been taken with the sections dealing with the
atomic weights of the elements in question. The figures given arc not
necessarily those to be found in the original memoirs, but have been
recalculated, except where otherwise stated, using the following
fundamental values :

Hydrogen = 1-00762. Oxygen = 16-000.

Sodium = 22-996. Sulphur = 32-065.

Potassium = 39-100. Fluorine = 19-015.

Silver = 107-880. Chlorine = 35-457.

Carbon = 12-003. Bromine = 79-916.

Nitrogen = 14-008. Iodine = 126-920.

By adopting this method it is easy to compare directly the results of
earlier investigators with those of more recent date, and moreover it
renders the data for the different elements strictly comparable through
out the whole series.

Our aim has not been to make the volumes absolutely exhaustive,

GENERAL INTRODUCTION TO THE SERIES. ix

as this would render them unnecessarily bulky and expensive ; rather
has it been to contribute concise and suggestive accounts of the various
topics, and to append numerous references to the leading works and
memoirs dealing with the same. Every effort has been made to render
these references accurate and reliable, and it is hoped that they will
prove a useful feature of the series. The more important abbreviations,
which are substantially the same as those adopted by the Chemical
Society, are detailed in the subjoined lists, pp. xvii xix.

The addition of the Table of Dates of Issue of Journals (pp. xxi-xxviii)
will, it is hoped, enhance the value of this series. It is believed that
the list is perfectly correct, as all the figures have been checked against
the volumes on the shelves of the library of the Chemical Society by
Mr. F. W. Clifford and his staff. To these gentlemen the Editor" and
the Authors desire to express their deep indebtedness.

In order that the scries shall attain the maximum utility, it is
necessary to arrange for a certain amount of uniformity throughout,
and this involves the suppression of the personality of the individual
author to a corresponding extent for the sake of the common welfare.
It is at once my duty and my pleasure to express my sincere appre
ciation of the kind and ready manner in which the authors have
accommodated themselves to this task, which, without their hearty
co-operation, could never have been successful. Finally, I wish to
acknowledge the unfailing courtesy of the publishers, Messrs. Charles
Griffin Co., who have done everything in their power to render the
work straightforward and easy.

J. NEWTON FRIEND.

January 1934.

PREFACE.

A GENERAL survey of Group V. of the Periodic Classification has
already been given in Part I. of this Volume, Chapter I. The position
of phosphorus, and its importance in the progress of pure chemistry
and technology, call, however, for a further brief introduction.

Like nitrogen, phosphorus is a key element in agriculture, with the
following important differences however. Nitrogen compounds are
"wasting assets 7 which require to be vigorously supplemented by the
application of manures which may be natural or artificial. A supply
of phosphates in a finely divided state represents more permanent
capital, which is not much drawn upon except by the actual require
ments of plant life. The industry of phosphatic fertilisers is mainly
concerned with supplying phosphates in a more soluble form and also
in admixture with other essential materials, such as lime, potash
and ammonia. Recognition of the importance of phosphatic manures
dates from about the middle of the XlXth century, when they were
applied in the form of bones, bone-dust, bone-ash, guano and super
phosphates as a result of a sequence of operations which has developed
into the present great phosphate industry.

The luminosity of phosphorus, due to its smouldering combustion,
attracted much attention on the discovery of the element towards
the end of the XVIIth century. Although Boyle was able to describe
some of the properties of the element and to prepare the pent oxide,
knowledge of this active clement did not make much progress until
about the end of the XVII It h century, when Schccle discovered a.
more abundant source in bone-ash, and also an efficient method of
preparation. From the beginning of the XlXth century, however,
much research was undertaken into the numerous compounds of
phosphorus, many of which are volatile without decomposition, and
hence played a leading part in establishing atomic and molecular
weights.

Phosphoric acid was the original of the three water molecule
type"; replacement of these molecules by basic oxides in typical
phosphates, investigated by Clark, led Graham to the theory of basicity.
In aqueous solutions phosphoric acid has played a no less important
part as an example of successive dissociation of hydrogen ions. The
theory of isomorphism, enunciated by Mifcschcrlich and others, was
founded on the phosphates and arsenates.

An important technical development which took place from about
the middle of the XlXth century was the manufacture of friction
matches, which was largely due to the discovery of red phosphorus
at this period.

The systematic chemistry of phosphorus was known in considerable
detail by the third quarter of last century; its thermochemistry had
been largclv worked out bv Thomsen. Bcrthelot and Giran, while

xii PHOSPHORUS.

numerous physical constants had been obtained by Gladstone, Sir
Edward Thorpe and others. These data, and their references, lend a
somewhat antique air to parts of this book, but are nevertheless the
accepted data of to-day.

Most types of combination are shown by this most reactive element;
the number and variety of its compounds with other non-metallic
elements are especially noteworthy. The halide series is more complete
than that of any other non-metal, including the congeners nitrogen
and arsenic. In number and variety of hydrogen compounds, however,
phosphorus is surpassed by nitrogen. Alkyl compounds are well
developed with all three elements; there is. however, a greater variety
of organic nitrogen compounds, while the extensive discovery of organo-
arsenic compounds due to their importance in medicine has necessitated
a special treatise in this Series, i.e. Volume XL, Part II.

Phosphorus is almost exclusively tervalent in its organo-compounds
and lower halides, etc.. and quinquevalent in the compounds PX 5 ,
phosphonium compounds and the phosphoric acids; according to
modern theory, however, this quinquevalency is really quadricovalency.
Compounds showing other valencies are not common, and sometimes
are of doubtful individuality.

In the Fifth Group the higher stage of oxidation appears to attain
a maximum stability in the case of phosphorus, as is seen by comparing
the pentoxide or phosphoric acids with the corresponding compounds
of nitrogen and arsenic. Phosphoric oxide and acid are formed with
the greatest decrease of total energy, and do not, like nitric and arsenic
acids, behave as oxidising agents under ordinary conditions. Connected
with this is the fact that the lower oxides ancl acids of phosphorus act
as reducing agents in solution to a greater extent than nitrous and
arsenious acids.

Phosphoric acids form many auto- and hetero-complexes, in which
respect they are similar to the acids of vanadium and its congeners,
as well as those of silicon. Three degrees of hydration, known as ortho-,
pyro- and met a-, are also found, with certain differences, with other
members of Group V.

In addition to the original memoirs in recognised scientific journals
the writer has found it convenient to consult Mellor s Comprehensive
Treatise and the detailed contributions by Brauner arid Schenck in the
third part of the third volume of Abegg s Handbuch der anorganischen
Chernie. For special sections free use has been made of S mils Theory
of Allotropy and other monographs, the appropriate original papers,
and the Annual Reports of the Chemical Society. The principal sources
of technical information are: Parrish and Ogilvie s Artificial Fertilisers
(Benn) 5 FritscLvs The Manufacture of Chemical Manures (Scott, Green
wood and Company), the various Reports on Applied Chemistry, and
articles in the technical journals.

In conclusion, it is again a pleasant duty to express my thanks to
the General Editor of this Series, Dr. J. Xewton Friend, for his unfailing
care, and to Mr. W. E. Thorncy croft for further useful criticisms of the
proofs.

E. B. R. PRIDEAUX,
UNIVERSITY COLLEGE, XOTTIXGHAM,
January 1934.

CONTENTS.

PAGE

THE PERIODIC TABLE (Frontispiece) . . . iv

GEXERAL INTRODUCTION TO THE SERIES . . . vii

PREFACE . . . . . . xi

LIST OF ABBREVIATIONS ..... xvii

TABLE OF DATES OF ISSUE OF JOURNALS . . . xxi

CHAPTER I. Phosphorus, General . . . .3

Occurrence History -Commercial Preparation of White and Red Phosphorus
Uses Physiological Action.

CHAPTER II. Phosphorus, The Element . . .14

SOLID PHOSPHORUS: General Melting and Freezing of White Phosphorus
Specific Heats Latent Heat of Fusion Density Compressibility
Crystalline Form Refractivity Electrical Conductivity Dielectric and
Magnetic Properties lonisation Potential Solubility.

LIQUID PHOSPHORUS: Density and Specific Volume Vapour Pressure Latent
Heat of Vaporisation Surface Tension.

PHOSPHORIC VAPOUR: Density and Dissociation Refractivity Spectra of
Phosphorus and its Compounds Absorption of Radiation Fluorescence
Mass Spectrum.

CHEMICAL REACTIONS OF PHOSPHORUS: General Action on Solutions of Metal
lic Salts Red Phosphorus Scarlet Phosphorus Colloidal Phosphorus.

DETECTION AND ESTIMATION OF PHOSPHORUS.

CHAPTER III. Allotropic Forms of Phosphorus and Condi
tions of Transformation . . . . .31

RED PHOSPHORUS : Preparation Physical Properties.

VIOLET PHOSPHORUS: History and Preparation Physical Properties.

THEORY OF THE ALLOTROPIC FORMS: Phase Diagram "Molecular Species."

BLACK PHOSPHORUS: General Physical Properties.

SCARLET PHOSPHORUS, AND THE TRANSITIONS TO VIOLET PHOSPHORUS: Pre
paration.

ATOMIC WEIGHT OF PHOSPHORUS: Historical Standard Methods and Results
General Conclusions.

CHAPTER IV. Phosphorus in Combination . . .51

PHYSICAL PROPERTIES: Atomic Volume of Element Molar Volumes of Com
pounds Structure of Compounds Volume of Phosphorus in Liquid Com
pounds under Conditions of Maximum Contraction Parachors of Phos
phorus Compounds Atomic and Molar Refractions Stereochemistry
Dipolc Moment of Phosphine Representation of Phosphorus Compounds
by Electronic Theories of Valency.

VOL. VI. : II. xiii b

xiv PHOSPHORUS.

PAGE

CHAPTER V. The Phosphides . . . . .60

Methods of Preparation Alkali Phosphides Alkaline Earth Phosphides
Copper. Silver and Gold Phosphides Zinc Group Phosphides Boron and
Aluminium PhosphidesTitanium Group Phosphides Tin and Lead Phos
phides Arsenic, Antimony and .Bismuth Phosphides Chromium, Molyb
denum and Tungsten Phosphides Manganese Phosphides Iron, Cobalt,
and Xickcl Phosphides Platinum Phosphides.

CHAPTER VI. Phosphorus and Hydrogen . . .68

PHOSPHIXE: Comparison with XH. n and PLS Historical Occurrence Pre
parationGeneral Properties Physical Properties Liquid Phosphine
Chemical Properties.

PHOSPHO^IUM COMPOUNDS: Chloride Bromide Iodide.

LIQUID HYDROGEN PHOSPHIDE: Composition, Properties and Preparation.

SOLID HYDROGEN PHOSPHIDE: Preparation, Properties, Chemical Reactions.

Higher Hydrogen Ph osphidcs H y droxyphosphidcs Alkylphosphines, Alkyl-
phosphine Oxides and Sulphides.

CHAPTER VII. Phosphorus and the Halogens . . 86

FLUORIDES: Trirluoridc - Pentafluoride Irifiiiorodichloride Trinuorodi-

bromide Pluophosphoric Acid.
CHLORIDES: Bichloride Trichloride Pcntachloride Chlorobromidcs

Chloroiodides.

BROMIDES: Tribromide Pentabromide.
IODIDES: Diiodide Tniodide.

CHAPTER VIII. Oxy- and Thio-Halides . . . 105

OXY-HALIDES: Oxytriftuoridc Fluo phosphoric Acids Oxy trichloride Pyro-
phosphoryl Chloride Metaphosphoryl Chloride Phosphoryl Monochloride
Phosphoryl Dichlorobrornide Phosphoryl CMorodi bromide Oxv-
tribromide Metaphosphoryl Bromide Oxy iodides.

THIO-HALIDES:- Thiotrinuoridc Thiotrichloride Thiotribromide Mixed
Thiotrihalid.es -Thioiodides.

CHAPTER IX. The Slow Oxidation of Phosphorus . . 116

The Glow of Phosphorus Effect of Pressure upon Oxidation of Phosphorus
Velocity of the Reaction Effect of Temperature Production of Oxono
Inhibition of the Glow Nature of the Chenn hnninesccnce lonisation bv
the Glow -The Emission Spectrum.

CHAPTER X. The Oxides of Phosphorus . . . 125

Suboxides Trioxidc Dioxide or Tet roxide Pentoxide.

CHAPTER XL The Oxyacids of Phosphorus Unsaturated . K35

Hypophosphorous Acid Phosphorous Acid Hypophosphites and Phosphites,
Structure and Tauiomensrn Mcta- and Pyre-phosphorous Aoids--I)etec-
tion and Estimation of Phosphites and Hypophosphites Hypophosphoric
Acid- Detection and Estimation of Hypophosphates.

CHAPTER XII. Phosphoric Acids .... 155

HISTORICAL AND GENERAL.

ORTHOpiioSPiroRTC ACID : PreparationPhysical ^Properties of Solid Hydrates
of P 2 0- Solubilities, Melting-points " and Eutectics of the System
H-iPOj-HoO Densities of Aqueous Solutions Vapour Prossuros- Con
ductivities of Concentrated and .Dilute Solutions Viscosities Refractive
Index Basicity and Neutralisation of the Phosphoric Acids Constitution

CONTEXTS. xv

PAGE

Chemical Properties Physiological Action Uses Dehydration and Pro
duction of Pyro- and Meta-acids.

Pyrophosphoric Aci d Pol yphosphonc Acids Metaphosphoric Acid Complex
Metaphosphoric Acids and their Salts Properties and Reactions of Ortho-,
Meta- and Pyro-phosphates Common and .Distinctive Reactions -Estima
tion of the Phosphoric Acids Phosphorus in Alloys Pcrphosphoric Acids.

CHAPTER XIII. Phosphorus and Sulphur or Selenium . 186

PHOSPHORUS AND SULPHUR: HistoricalPhysical Mixtures The System
Phosphorus-Sulphur and Compounds Tetraphosphorus Trisulphide Di-
phosphorus Trisulphide Tetraphosphorus Heptasulphide Phosphorus
Pentasulphide Uses of the Sulphides of Phosphorus Oxysulphides Thio-
phosphites, Thiohypophosphates and Thiophosphates.

PHOSPHORUS AND SELENIUM: Selenides Selenophosphates Sulphoselenid.es.

CHAPTER XIV. Phosphorus and Nitrogen . . . 197

Amido-derivativcs of Phosphorous and Orthophosphoric Acids Amido- and
Imido-dcrivatives of Metaphosphoric Acid Amides and Traides of Con
densed Phosphoric Acids Xitrilophosphoric Acids Amido-, Imido- and
Xitrilo-thiophosphoric Acids Phosphorus Halonitrides or Amidohalides
Phosphorus Nitride.

CHAPTER XV. Phosphatic Fertilisers .... 208

OCCURRENCE AXD CIRCULATION O.F PHOSPHORUS: Mineral Phosphates Assimi
lation by Plants Sources of Phosphates The Composition of Phosphorites
The Distribution of Phosphatic Hocks Oceanic Deposits and Guanos
The World s Production of Phosphate Rock.

BASIC SLAG : Production High-grade Slag :: Open-hearth" Slag .Fertiliser
Action.

SUMMARY OF PrrosriiATic FERTILISERS.

THE SYSTEM LIME AND PHOSPHORIC ACID: Solubility of Calcium Phosphates
Conditions of Formation of .Basic and Acid Calcium Phosphates Composi
tion of Solutions Saturated with Calcium Hydrogen Pliosphat.cs Equilibria
between Solid Phases and Solutions at Various Temperatures Changes
during Neutralisation The Acid .Phosphates Manufacture of Superphos
phate Retrogression Treatment of Special Ores Phosphoric Acid
Commercial Preparation and Extraction from Rock The History and
Technology of Superphosphate .Manufacture Mixed and Concentrated
Phosphoric Fertilisers Potassium Phosphates -.Ammonium Phosphates.

NAME INDEX . . . . . . .229

SUBJECT INDEX ...... 236

LIST OF CHIEF ABBREVIATIONS EMPLOYED
IN THE REFERENCES.

ABBREVIATED TITLE.
AJ handl. Fys. Kcm.
Amer. Chem. J. .
Amer. J. SCL.
Anal. Fis. Qiiim.
Analyst .
Annalen .
Ann. Chim.
Ann. Glum. anal.

Ann. Cfiim. Phys.

Ann. Mines

Ann. Pliarm.

Ann. Phys. Chem.

Ann. Physik

Ann. Physik, Beibl. .

Ann. SOL. Univ. Jassy

Arbeiten Kaiserl. Gesiindheits-

amte .

Arch. exp. Pathol. Pharmak.
Arck. Pharni.
Arch. Sci. phys. nat.
Atli Ace. Torino .
Atli R. Accad. Lincei .
B.A. Reports

Bar

tier. A lead. Ber. .
Ber. Deut. pharm. Gas.
Bar. Deut. physilcal. Ges.
Bot, Zeit. .
Bid. Soo. Stiifite Clnj. .
Bull. Acad. roy. Bdg.

Bull. Acad. Sci. Cracow

Bull, de Bdg.

Bull. Sci. PharmacoL .

Bull. Soc. chim. .

Bull. Soc. /mtL$. Min. .

Bull. Soc. min. de France

Bull. U.S. Gcol. Swvaij

Centr. Miti.

Glitm. Ind.

Chem. S~eivs

Chem. WeMlad .

C he-in. Zeit.

Chem. Zentr.

Cotript. rend.

CrelVs Annalen .

JOURNAL.

Afliandlingat i Fysik, Kemi och Mineralogi.
American Chemical Journal.
American Journal of Science.

Anales de la Sociedad Espanola Fisica y Quimica.
Tlie Analyst.

Justus Lie big s Annalen der Cliemie.
Annalcs de Cliirnie (1719-1815, and 1914+).
Annales dc Chimie analytique appliquee a T Industrie, a

T Agriculture, a la Pharmacie, et a la Biologic.
Annalcs de Chimie et de Physique (Paris) (1816-1913).
Annalcs des Mines.
Annalen der Pharmacie (1832-1839).
Annalen der Physik und Chernie (1819-1 899).
Annalen der Physik (1799-1818, and 1900 + ).
Annalen der Physik, Beiblattcs.
Annalcs scientiiiques de 1 Universite de Jassy.

Arbeiten aus dem Kaiscrlichcn Gcsundheitsamte.

Archiv fur experimentellc Pathologic und Pharmakologic.

Archiv der Pharmazie.

Archives des Sciences physique ct naturclles, Geneve.

Atti della Keale Accademia dolle Scienzc di Torino.

AtLi dclla Kcale Accademia Lincei.

British Association Kcports.

Bcrichte der Deutschcn chcmischcn Gesellschaft.

See Sitzuncjsber. K. Akad. Wiss. Berlin.

Berichte der Deutschen pharmazeutischen Gesellschaft.

Berichte der Deutschen physikalischen Gesellschaft.

Botanischc Zeitung.

Bulctinul Socictatei de Stiinte din Cluj.

Academic roy ale dc Belgique Bulletin de la Classe des

Sciences.
Bulletin international de TAcademic des Sciences do

Cracovie.

Bulletin de la Societe clurnique Belgique.
Bulletin des Sciences Pharmacologiques.
Bulletin de la Si)ciete clurnique de Franco.
Bulletin de la Societe i raiicaise de IMineralogie.
Bulletin dc la Societe mineraLogiquo de France.
Bulletins of the United States Geological Survey.
Ccntralblatt fur Mineralogie.
Die Chemisclic Industrie.
Chemical Xews.
Chcmisch AVeckblad.
Chemiker Zeitung (Cotlicn).
Chemisches Zcntralblatt.
Comptcs rendus hebdomadaires des Seances do 1 Academic

des Sciences (Paris).
Chcmische Annalen fur die Freunde der Xaturlehrc, von

L. CreUe.

Diiigler s porytechriischcs Journal,
xvii

PHOSPHORUS.

ABBREVIATED TITLE.
Drude s Annalen
Electroch. Met. Ind.
Eng. and Min. J.
Gazzetta .
Gehlen s Allg. J. Chem.
Gaol. Mag.
Gilbert s Annahn
Giorn. di Scienze Naturali ed
Econ. ....
Helv. Chim. Ada
Int. Zeitsch. Metallographie .
Jahrb. kb. geol. Reichsansl. .

Jalirb. Miner.

Jahresber. ....

J enaisclie Zeitsch.

J. Arne.r. Chem. Soc. .

J. Chein. Soc.

J . Chim. phys. .

J. Gasbeleuc/itung

J. Geology ....

J. Ind. Eng. Chem.

J. lust. Metals .

J. Miner. Soc.

J. Pliarm. Ckir/i.

J. Physical Chem.

J. Physique

J. pralct. Chem. .

/. RIMS. Phys. Chem. Soc.

J. Soc. Chem. Ind.

L/aiidw. Jahrb.

Mem. ColL Sci. Kyoto.

Mem. Paris A cad.

Mon. scient.

Munch. Med. WochenscJir. .

Nature ....

Nnovo dm.

Oestc.rr. (Jhc.ni. Zc.it.

Oj vers. K. Vet.- A Lad. Fork. .

Proc. J*o>/. J rixlt,

Proc. Jioy. J hil. Soc. Glasgow

Proc. Roy. Soc. .

Proc. Roy. Soc. Edin. .

JOURNAL.

Annalen der Physik (1900-1906).
Electrochemical and Metallurgical Industry.
Engineering and Mining Journal.
Gazzetta chimica italiana.
Allgemeines Journal der Cheniie.
Geological Magazine.
Annalen der Physik (1799-1824).

Giornale di Scienze Naturali ed Economiche.

Helvetica China. Acta.

Internationale Zeitschrift fur Metallographie.

Jahrbuch der kaiseiiich-koniglichen geologischen Rcichsan-

stalt.

Jahrbuch f iir Mineralogie.

Jahresbericht iiber die Fortschritte der Chemie.
Jenaische Zeitschrift fur Xaturwissenschaft.
Journal of the American Chemical Society.
Journal of the Chemical Society.
Journal de Chimie physique.
Journal fur Gasbeleuchtung.
Journal of Geology.

Journal of Industrial and Engineering Chemistry.
Journal of the Institute of Metals.
Mineralogical Magazine and Journal of the Mincralogical

Society.

Journal de Pharmacie et de Chimie.
Journal of Physical Chemistry.
Journal de Physique.
Journal fur praktischc Chemie.
Journal of the Physical and Chemical Society of Russia

(Petrograd).

Journal of the Society of Chemical Industry.
Landwirtschai tliohe Jahrbuch or.
Memoirs of the College of Science, Kyoto Imperial

University.
Memoirs presentes par divers savants a 1 Academic de

Sciences de rinstitut de Prance.
Monatshefte fur Chemie und verwaridte Thcile anderer

VVissnnschafton.
MoniU ur scienlifique.
JMiinchener Medi/inisclie Wochenschrii t.
Nature.

II nuovo CJinicnto.
Ocstcnv.ichischo (/lu inikc r-Zciturig.
()fvci si^t at K(mgliga Vetcnskaps-Akademiciis Fcjrluind-

Jingar.
Arcliiv iur die gesammto Physiologic dcs Mcnsclion und

der Thirn:.

Phanna/.cuti.sc.lie Post.
IMiarnia /cutisclu: Zcnt/ralhalle.
Phih/sopliical Maga/ino (Tlit* London, Edinburgh, and

Dublin).
Philosophical Transactions of UK; Royal Society of

London.

Physical Pu-vic\v.
Physikahsclut Z(-if sohrift.
PogL fiidorirs Annalen cli-r Physik und Choniio (182-1

"1S77).

.Proceedings of the Chemical Society.
Koninklijke Akadenn e van \\ etensehappen t(^ Amsterdam

Proceedings (English Version).
Proceedings oi the- Uoyal Irish Academy.
Proceedings of the Royal Philosophical Soeicty of Glasgow.
Proceedings of the Royal Society of London.
Proceedings oi the Ruya.1 Society of Edinburgh.

LIST OF CHIEF ABBREVIATIONS.

ABBREVIATED TITLE.
fee. Trav. chim.

loy. Inst. Reports
ichweigge-r s J.
;d. Proc. Ron. Dubl. &oc.
iitzunysbzr. K. A had. Wis$.

Berlin.
Htzungsb&r. K. Akad. Wiss.

Wien ....
^echn. JaJiresber.

Brails. Amer. Electrochem. Soc.
"rans. C/<cm. Soc.
"rans. Inst. Min. Eng.
V<m et Mem. du Bureau

intern, des Poids et lies.
7 erh. Ges. deut. X alurforsch.

Aerzte.
Vied. Annahn .

V issenschaftl. AbJiandl. pJiys.-

tech. Reichsayisl. .
eitsch. anal. Chem.
eitech. annew. Chem. .
eitsch. anorg. Chem. .

tsch. Chem.
eitach. Chem. Ind. Kolluide .

JOURNAL.
Recueil des Travaux chimiqucs des Pay-Has et de la

Bclgique.

Reports of the Royal Institution.
Journal i iir Chcmie and Physik.
Scientific Proceedings of the Royal Dublin Society.
Sitzungsberichtc der Koniu lich-Preussi^chcn Akadeinie de

\\isscnsciiatten zu l^erlin.
Sitzungsberichte der Koiiiglich-Bayerischcn Akademie

der Wissenschaiten zu \\ ien.
Jahresbericlit iiber die Lcistungen der Chemischen

Teclmologic.

Transactions of the American Electrochemical Society.
Transactions of the Chemical Society.
Transactions of the Institution of Mining Engineers.
Travaux ct Memoires du Bureau International des Poids

et Mesures.
Verhandlung der Gesellschaft deutscher Xaturforscher und

Aerzte.
A\ r iedernann"s Annalen der Physik und Cliemie (1877-

1899).
Wisscnschaftliche Abhandlungen der physikalisch-tech-

nischen Reichsanstalt.
Zeitschrift fur analytischc Chemie.
Zeitschi it t fur angewandte Chemie.
Xcitschnft lur anorganischo Chcmie.
Kritische Zcitscliritt fur Chcmie.

Zeitschrift fur Chernic und Industrie des Kohoidc (con-
tinned as Kolloid-Zeitsclnift).
Zeitscln-ii t fur Elektrocheinie.
Zeitschi ift fur Krystallnprraplrio und M ineralogie.
Zeitschril t fur I ntersuchun^ der Xahrungs- und Genuss-

mittel.
Zeitschnft fur ])hysikalische Chemie., Stuchiometric und

\Vr\vand1sclia ft <lchre.

iloppe-Soyler s Zeitschrift lur physiolo.Lrischc Chemie.
Zeitschrift fur v/is^cnschaftliche IMiotograpliio, Photo-

physik, und Photnchemie.

TABLE OF DATES OF ISSUE OF JOURNALS.

FOR the sake of easy reference, a list is appended of the more
important journals in chronological order, giving the dates of issue of
their corresponding series and volumes. In certain cases the volumes
have appeared with considerable irregularity ; in others it has occa
sionally happened that volumes begun in one calendar year have
extended into the next year, even when this has not been the general
habit of the series. To complicate matters still further, the title-pages
in some of these latter volumes bear the later date a most illogical
procedure. In such cases the volume number appears in the accom
panying columns opposite both years. In a short summary of this kind
it is impossible to give full details in each case, but the foregoing
remarks will serve to explain several apparent anomalies.

Year Amer - ! 5 Aim -
J. Sci. a -g Min.

" c J^

Gilbert s
Annalcn.

gg Mag.

1-3

Phil. $*
Trans.

1800 ... (1)32-35

4 6

5 8

90

1 ; ... ; 36-39

7-9

... 8-11

91 !..

2 : ... 40-43

10-12

... 11-14

92 . ...

3 ; ... 44-47

.!. I

13-15

... ! 14-17

93 ...

4 i .. 48-51

16-18

... 1 17-20

94 1 ..

1805 . . 52-55 :

19-21

... ; 20-23

95

6 ... 56-60 :

2 9.. 9 4

23- 9 6

96

i 7 i ... 61-64

9-j 27

97

8 ... 65-68

28-30

.. > 29-32

98 .".

9

69-72 ...

3133

(1) 1* j 33, 34

99

1810

73-76

34-36

2 35, 36

100

11

77-80 :

37-39

3 37, 38

101

12

81-84 ;

40-42

4 . 39, 40

102

13

85-88 ...

43-45

5 41,42

103

14

89-92

46-48

6 43, 44

104

1815

93-96

49-51

(2) 1 ,; 45, 46

105

16

(2) 1-3 ... j

52-54

2 ; 47, 48

106

17

... ; 4-6 1, 2

55-57

3 ! 49, 50

107

18

7-9 3 :

58-60

4 i 51, 52

108

19

(1)1 ; 10-12 4

61-63

5 i 53, 54

109 ; ...

1820

2 13-15 5 ... : 1-3

64-66

6 55, 56

110 i ...

21

3 16-18 6 ... ; 4-6 67-69

7 57, 58

Ill ...

! 22

4, 5 ; 19-21 7 1, 2 7-9 70-72

8 ! 59, 60

, 112 ; ..

23

6 22-24 8 3-6 ^ 10-12 73-75

9 61, 62

113 , ...

24

7, 8 : 25-27 9 7-10 13-15 76

10 j 63, 64

114 1, 2

: 1825

9 28-30 , 10, 11 ; 11-14 16-18 ^

11 65, 66

115 : 3-5

i 26

10, 11 31-33 12, 13 .15-19 19-22 3 f

12 67, 68

116 6-8

27

12 34-36 (2)1,2 20-23 23-26

~ $ 5

13 (2)1. 2

117 9-11

: 28 ,1-^,14 37-39 3, 4 24-26 27-30 5^

14 3, 4

118 12-14

29 15, 16 40-42 5, 6 : 27-30 31-34 p rf< ^

15 5, 6

119 15-17

* First series known as Bulletin de J J har f niacie.

XYl

PHOSPHORUS.

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TABLE OF DATES OF ISSUE OF JOURNALS. xxiii

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TABLE OF DATES OF ISSUE OF JOURNALS. xxvii

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lO -- Ci r < CO CO Ci Ol XO OO

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lO CO t~- OC Ci O r-H Ol CO -- xo CO t--. OO Ci O r-H (N CO -Q 1
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A TEXT-BOOK OF

INORGANIC CHEMISTRY.

VOLUME VI. FART II.

A TEXT-BOOK OF

INORGANIC CHEMISTRY

VOL. VI. PART II.

PHOSPHORUS.

CHAPTER I.
PHOSPHORUS, GENERAL.

Symbol, P. Atomic number, 15. Atomic weight, 31-02 (O=16).

Occurrence. Phosphorus does not appear to occur in the free state
in nature. If it wore produced by the reduction of phosphatic minerals
at high temperatures it would be liberated as vapour, which would
condense to liquid or solid white phosphorus, and would again be
oxidised rapidly under most conditions. Sulphur, which resembles
phosphorus in so many respects, docs, however, occur as element in
considerable quantities, because it is produced in many reactions
which take place at comparatively low temperatures (such as that
between II 2 S and S0. 2 ), and, when once produced, is far less easily
oxidised than phosphorus. Phosphorus (0-142) is actually more
abundant than sulphur (0-09. 3), the numbers in brackets referring to
the percentage of the earth s 10-mile crust, with atmosphere and
hydrosphere, 1 constituted by the element. Phosphorus is thus twelfth
in the order of abundance, coming below chlorine but above carbon.
In the 10-mile crust composed of the lithospherc only, phosphorus is
present to the extent of 0-157 per cent., being now in the tenth place,
since hydrogen and chlorine in the rocks occupy a position below
phosphorus, although they are still above carbon. The average pro
portion in igneous rocks is 0-13 per cent., whilst the element is also
common in sedimentary rocks, chiefly as phosphate of lime, and to a
less extent as phosphates of iron and alumina. These secondary
deposits arc by far the most important sources of phosphates. They
are derived probably from the widely but sparsely diffused ingredients
of igneous rocks and from the well-crystallised but more stable minerals
such as apatite (calcium lino- or chloro-phosphate), which gradual! v
disintegrate, 2 pass into the soil, and are concentrated in plant tissues

1 Clark and Washington, /W. Sal. Acad. Xc.i. U.U.A., J!)2, 8, 1.08. SJoo also Jlarkms,
J. Ani.tr. Cho.ni. tioc., 1 ( JJ7, 39, 856; Tamrnann, Zc.-tf.pcJi,. unary. Chun., \ 9:23, 131, 9(1

2 Linclgren, Kcon. Gcol., 1923, 18, 419; also Blackwelder, Amer. J. 8ci., 1916, [4],
42, 285.

4 PHOSPHORUS.

and in the bones of animals, which eventually yield deposits of phosphate
of lime. The compositions of the principal phosphatic rocks are detailed
in Chapter XV.

Phosphorus is present to the extent of about 0-1 per cent, in ordinary
soils. From this source plants draw the supplies which are essential
to their growth the phosphorus is found mainly in the seeds, and is
more concentrated in the germ of these. It is estimated that 100 Ibs.
of corn contain nearly J Ib. of phosphorus. Phosphorus is also present
in the bodies of animals, and although a minor constituent of the soft
parts, is absolutely necessary to life. It is present as soluble phosphate
in the blood, milk and other fluids, as a constituent of organic com
pounds in the brain, spinal cord, and other parts, and as calcium phos
phate in the bones. The proportions vary considerably in different
parts of the body. Ox brain has been found to contain nearly 2 per
cent., human liver i per cent. In animal fats phosphorus occurs com
bined in the tc lipoid " form for example, as lecithin. Bones contain
over 40 per cent, of calcium and magnesium phosphates. The human
skeleton, weighing about 14 Ibs., contains about 5 Ibs. of calcium
phosphate, or 1 Ib. of phosphorus. Since the bones form about 10 per
cent, of the total weight of the body, and the rest of the body, exclusive
of the bones, contains of the order of 0-1 per cent, of phosphorus, it
will be seen that there is slightly over 1 Ib., or about 500 grams, of
this element in the body. Analysis of certain parts of the body shows
that about 90 per cent, of the phosphorus is present in the bones,
8 per cent, in the muscles, and a total of 2 per cent, in the brain, liver,
lungs, and blood. 1

While plants use phosphorus very sparingly, animals require a
greater proportion for their metabolism.

The continual secretion of phosphorus necessitates a constant
supply. About 1 gram a day for the adult is required to maintain
the body equilibrium.* An adequate supply is also one of the
factors which control growth. The milk of the cow contains about
0-2 per cent, of PoOg, that of the rabbit nearly ] per cent. In. other
cases also there is a relation between the percentage of phosphorus in
the milk and the reciprocal of the number of days required to double
the weight at birth.

History. As just explained, phosphorus is concentrated in plant
and animal products. These arc not only more widely distributed than
the rich phosphatic minerals, but they also form a more interesting and
attractive object of experiment, and, what is perhaps more important,
they contain their own reducing agents. It is not surprising, therefore,
that the clement was first discovered in its organic, sources by the doctors
and pharmacists who formed the majority of the experimentalists
in the latro-chcnucal and succeeding periods of chemical history.
By distillation of the residue from the evaporation of urine (which
contains phosphates and organic matter) the alchemist Brand in 1609
obtained a substance which glowed without any noticeable evolution
of heat. 2 Brand s process was described by Kirchmaier in 1070 and
discovered independently by Kunkcl in 1678, who designated the

PHOSPHORUS, GENERAL. 5

product " noctiluca " and " phosphorus mirabilis " respectively, by
which names it was distinguished from Bolognese phosphorus ( lapis
bononicnsis ") and Baldwin s phosphorus ( i: phosphorus hermeticus "),
which are phosphorescent sulphides of the alkaline earths.

Brand s secret was bought by Krafft, who exhibited " das kalte
Feuer _ at various Courts, and in 1677 at that of King Charles II.,
where it was seen by Boyle, who, being informed that it was prepared
from an animal source, worked out the method of preparation and
described this in a sealed paper which was deposited with the Royal
Society in 1080 and published in 1693. l The urine was evaporated
down to a syrup, which was mixed with three times its weight of clean
sand and distilled at the highest available temperature from a retort,
the neck of which almost touched the surface of some water. White
fumes given off at first were followed by a vapour which condensed and
fell to the bottom of the water. At the beginning of the eighteenth
century the c: noctiluca " was made and sold by Boyle s assistant
Hanckewit/ , and consequently it became known as *" Boyle s phos
phorus or English phosphorus."

Phosphorus was detected also in mustard seed by Albums in 1688. 2
The existence of large supplies in minerals had been established by
Gahn towards the end of the eighteenth century, who also recognised
it in bone-ash (1769) and in the mineral pyromorphite (1779).

Phosphorus was prepared in various European countries during the
eighteenth century, but it remained an expensive chemical curiosity until
Gahn, about 1770, discovered in bone-ash a more suitable source of
phosphorus, and Schcele developed a method of preparing the element
which was described in several communications. 3 According to this
method the acid liberated from bone-ash by means of nitric acid and
freed from lime by precipitation with sulphuric acid, was distilled with
charcoal, phosphorus being collected under water. This method has
the advantage of yielding the phosphorus at a comparatively low tem
perature 1 , but the mctaphosphoric acid liberated by the nitric acid is
partly volatilised and so partly escapes reduction. The present method
of preparation proceeds by the following stages :

Ca 3 (P0 4 ) 2 4-3l-IoS0 4 =3CaS0 4 + 2H 3 P0 4 . . (1)

The calcium sulphate is filtered off and the phosphoric acid concen
trated to a syrup and strongly heated in order to convert it into
meta phosphoric acid

H 3 P0 4 =HP0 3 -fII 2 . . . (2)

This acid is mixed into a paste with charcoal or ground coke and
distilled, (inishing at a yellow heat

6 PHOSPHORUS.

COMMERCIAL PREPARATION OF PHOSPHORUS.

Preparation of White Phosphorus.

(a) By Reduction of Phosphoric Acid. The world s supplies
of phosphorus were for nearly a century obtained by a method sub
stantially identical with that of Scheele. Scheele s raw material bone-
ash, containing as it does from 34 to nearly 40 per cent, of P 2 O 5 and
decomposed easily by sulphuric acid, is still the best which can be used.
Precipitated phosphate of lime obtained as a by-product in the manu
facture of glue from bones also contains nearly 40 per cent, of P 2 0o and
is otherwise suitable. If phosphatic minerals are used for the pre
paration they must contain less than 10 to 12 per cent, of calcium
carbonate, with only small quantities of the oxides of iron, aluminium,
magnesium and the alkali metals, since these dissolve in the acid and
reappear in the retorts with undesirable effects. The aqueous phos
phoric acid liberated by the sulphuric acid is concentrated by
evaporation in lead-lined wooden tanks heated by lead pipes through
which passes superheated steam. Evaporation is continued with
stirring until the density of the liquor is raised to 1-325 or to 1-50,
according to the nature of the next process. After the removal of
any gypsum, CaSO 4 .2H 2 O, or anhydrite, CaSO 4 , the concentrated
acid is mixed with saw-dust or charcoal, the former of which is suitably
mixed with an acid of lower density, or the latter with syrupy acid.
The mixture is evaporated in a cast-iron pot to expel any sulphuric
acid which may remain. The charred mass is then introduced into
fireclay bottles, a number of which, say 24, are placed back to back
in a galley furnace similar to that used in the distillation of ziiic by the
Belgian process. The necks of these bottles are luted to malleable
iron pipes, which dip beneath water in closed troughs. Gases which are
evolved during the distillation are trapped and led away to be burnt.
Finally the retorts are raised to a white heat. The phosphorus vapour
is completely distilled over in about 16 hours. The liquid which
collects under water in the sloping troughs is ladled occasionally into
boxes made of malleable iron for transport to the refinery. Here the
crude product, which may be buff to brick-red or nearly black, is
agitated under water with sulphuric acid and diehromatc of potash
or soda. The liquid is afterwards siphoned and filtered through a
canvas bag, then being rcmelted and run into tin moulds, where it
solidifies in the form of sticks or wedges. The yield is slightly less
than 70 per cent., or about two-thirds of the weight of combined
phosphorus present in the charge, the loss being due in part to the
fact that metaphosphoric acid is volatile above a red heat, and there
fore escapes the reduction which is symbolised by equation (3), p. 5.
Consequently the original procedure of Scheele was modified by the
addition of only so much sulphuric acid as would form monocaleium
phosphate, CaIi 4 (PO 4 ) 2 , which, on ignition, yields the metaphosphatc.
When this metaphosphate is strongly heated it loses two- thirds of its
phosphoric anhydride, which as it is liberated is reduced by the carbon
as follows :

3 ) 2 = Ca 3 (P0 4 ),+2P 2 5
2P 2 S + IOC =P 4 + 10CO

PHOSPHORUS, GENERAL. 7

yield in this process is diminished by the production of phosphide,
ddition to carbide, thus

Ca 3 (PO 4 )o + 14C = 3CaC -i- 2P + SCO

Ca 3 (PO 4 ) 2 -f 8C = Ca. 3 P 2 + SCO *

> stated that phosphorus can be made in the ordinary blast furnace
300 C., but it rapidly oxidises to the pentoxicle, the production of
>n of which requires about 4 tons of coke. 2

(b) Electric Furnace Processes. The intermediate preparation
phosphoric acid and acid phosphates can be avoided by taking
ant age of the fact that the less volatile silica can expel the more
itile phosphoric anhydride, which can be reduced by carbon. 3
h temperatures are required for these reactions, and these are best
lined by electrical heating, although gas-fired furnaces lined with
Dorundum have also been employed.

The more acid phosphates oi ? lime melt below 1500 C. CaO.P 2 O 5
370 to 980 and 2CaO.P O 3 at 1230 4 while tribasic and more
ic calcium phosphates melt above 1550 C., 3CaO.P 2 5 at 1670.
s last compound combines with silica at about 1150 C. to form
ipounds such as 3CaO.3SiO 2 .P 2 O 5 (m.pt. 1760 C.), which are rather
*e easily reduced by carbon than the original phosphate, on account
:he increase in vapour pressure of the P 2 O 5 , which also combines
i excess of silica to form completely reducible compounds such
SiO 2 .P 2 O 5 and SSiC^.I^Os- The whole process may be summarised
the equation :

2Ca 3 (P0 4 ) 2 +6Si0 2 -f IOC =GCaSiO 3 -!- 10CO +P 4

The mixture of bone-ash or ground phosphate rock, sand and coal
t or wood charcoal is introduced continuously into a furnace heated
the electric current, passing between carbon electrodes (sec p. 8).
\ reaction begins at about 1100 C., but a much higher temperature
cquired to melt the charge and slag of calcium silicate which is
\vn off continuously, while the phosphorus distils at about 1.300 C.

> yield is said to be about 02 per cent, of the theoretical.

The first proposals for the employment oC electrical heating in the
duct ion. of phosphorus were made by Rcadman, Parker and Robin-
. 5 The simultaneous production of an alkali silicate by heating
ill phosphate, silica and carbon in a regenerative furnace was
ented by Folie-Desjardins. 6 In the Rcadman -Parker-Robins on
cess, as worked later, the phosphate, carbon and fluxes, previously
ted to a high temperature, are introduced into the upper part of an
:tric furnace made of iron lined with refractory bricks and fitted
h. condensing pipes in its upper part. The gases pass through a
es of copper condensers, the first of which contains hot water, the
ers cold water (or see p. 9). It has been found advisable to replace

Liilbert and Frank, Carman Patent (1805), 02838.
Roys to i: and Turpentine, hid. J ^/ /g. Cham., 1982, 24, 223.
Rcadman, J. Sue. Chc.tn. Ind., 1800, 9, 16.3, -173; 1801, 10, 4-15.
Dieckman and Houdremont, Zf-d.sch. anorq. Cfiein.. 1921, 120. 120.

8 PHOSPHORUS.

the electric arc originally employed by an electrically heated resister, 1
shown in fig. 1. The current is carried by the graphite rod 11, which
is packed into the walls of the furnace with blocks of carbon. The rod
radiates heat on to a charge C which consists of 100 parts of calcium
phosphate and 50 parts of sand and carbon. This charge is introduced
through. D, is melted on the hearth, and the slag Hows away through E.
The phosphorus vapour and the gases are drawn off through the pipe P.
The product is said to be more free from impurities than that made
7 the reduction of the free acid. The phosphorus vapour, in an

bv

n;. 1. Electric Resistance Furnace for the Manufacture of Phosphorus.
(Kltclrir /i<-<litc!ion Cum^iny.)

atmosphere of carbon monoxide, is condensed in a slanling tube, which
is connected by a set of vortical tubes with another slanting tube which
conducts the gases to a condensing tower containing flat plates wetted
with a solution of a copper salt or other reagent which will remove the
last suspended globules of phosphorus. The issuing gas containing
carbon monoxide is burnt, and supplies heat for the distillation of the
crude condensed phosphorus. The second dist.illa.tc is condensed in a
box under water ami may be pun" lied as described later.

An experimental study of the reaction in a graphite tube resist

fo

llowing conclusions. 2 The mixture was still solid at

1500. The phosphorus volatilised ranged from CK) to 00-8 per cent.
of thai present. Volatilisation of phosphorus from mixtures of tri-
calcium phosphate and carbon begins at 1150 C., and under favourable

1 Electric Reduction Co., En- jli^fi Patent (.1898), f>79(>. See
angcw. 6V/.e ///.., 190;"), 18, 1, J2, 401; Neumann, -ibid., 190f), 18, 289.

2 Jacob and KeynokLs, lad. Eny. Chew., 1928. 20, 1204.

also Hempel, Zattsch.

PHOSPHORUS, GENERAL.

9

conditions the reaction is complete in one hour at 1325 C., or in 10
minutes at 1500 C. Less than 0-2 per cent, of the phosphorus is con
verted into phosphide at such temperatures. The reaction, in the
presence of excess of carbon, is unimoleciila.r between 1250 and 1400 C.

Fin. "2. Distillation of Pliosphorus.

Condensation and Redixtilldtion,. The condensation of the phos
phorus vapour, mixed as it is with dust and furnace louses, presents
special difficulties. The sketch (fig. 2) shows, diaoTammatically only,
how these have been overcome in the patent of Billnndot ct (lie. 1

The phosphorus vapour, escaping from the furnace, passes up a
vertical tube which can be cleared of obstructions from time to time by
a movable weight. It then passes down an inclined tube 13, which
is connected with another tube E by a set of vertical tubes T. Both

1 German Palt,d (1929), 106408.

10 PHOSPHORUS.

the lower and the upper end of D can be closed by valves. The
phosphorus vapour condenses in droplets at about 50 C. Its flow
can be further regulated by the introduction of gases from a compressor
through the holes in the vertical tubes. The semi-fluid mixture is thus
pushed through the valve h into a mixing chamber, and then into one
of two distillation retorts H. These are built into the wall and heated
by carbon monoxide from the escaping gases. The distillate drops
into a double lead-lined and water-cooled box, which is inclined at an
angle to the horizontal and furnished with an outflow cock. This
condenser is not shown in the elevation (fig. 2).

The gases escape through f and a valve into one of three plate-
condensing towers G, and through a fan A which delivers them where
required, or through a flue F. The plate towers are supplied with a
solution of a copper or other metallic salt, which absorbs the last traces
of phosphorus vapour.

Purification is effected mainly by the methods already described.
Crude phosphorus may be melted under dilute solutions of chromic
acid, nitric acid or chlorine. Arsenic may be removed by distilling in
a current of steam and carbon dioxide, and condensing under water.
Phosphorus can be granulated if desired by melting under water and
shaking until cold.

Preparation of Red Phosphorus.

For many of the purposes to which phosphorus is applied the red
form is equally suitable, and when this is the case this form is greatly
to be preferred on account of its non-poisonous and non-inflammable
character (see p. 28). The conditions of transformation are now
accurately known (see Chap. III.).

On the large scale white phosphorus is heated in an iron pot em
bedded in a sand-bath which is contained in an external iron vessel
with double walls, the space between which is filled with an alloy of tin
and lead. The pot containing the phosphorus is lined with porcelain
and is provided with a tight cover bearing a bent tube of iron or
copper which can be closed by a tap. The end of this tube, which
acts as a safety valve against too high a pressure, dips under water or
mercury. The external metal pot is heated to 220-250, and not
above 260 C., for about ten days. Transformation proceeds more
quickly if the operation is conducted in an autoclave at higher tempera
tures. The product, a purplish-red mass, is ground and boiled with
caustic soda to remove any unchanged white phosphorus, then washed
and dried at a steam heat.

USES OF Pjro.spnoiirs.

Pyrotechnic Uses. The quantity of phosphorus consumed in the
match industry exceeds by far that required for all other purposes.
The total consumption exceeds 1000 tons per annum, the greater part
of which is worked up for matches, hundreds of millions of which are
made per annum in factories in all parts of the world. The phosphorus
is now applied in the red or scarlet form or as one of the sulphides (q.v.).
The materials used in friction matches have varied greatly at different
periods.

PHOSPHORUS, GENERAL.

and were manufactured from 1812. They contained no phos
but consisted of sticks of wood tipped with melted sulphur ai
coated with a mixture of sugar and chlorate of potash. The
ignited by dipping in a bottle containing asbestos moistened w:
centrated sulphuric acid. Similar applications of phosphon
been described. Phosphoric tapers were made of wax coatc
phosphorus, arid were enclosed in sealed glass tubes. The*
warmed and then opened, when the phosphorus burst into flam

Friction matches, invented in England in 1827, were tipped
mixture of antimony tri sulphide, potassium chlorate and gu
ignited by rubbing on sand-paper. The recognition of the s
properties of phosphorus as an ingredient of these miniature ex
dates from about 1833, when wooden matches, the heads o:
contained phosphorus, appeared simultaneously in several co
Attempts to prepare matches from yellow phosphorus had bee
from about 1816 by Derosne and others, but it was only later dis
that the heads must be coated first with another combustible i
such as sulphur to transmit the flame of the phosphorus-*
mixture. The first matches were both explosive and dai
Chlorate was later replaced by lead peroxide, then by red k
manganese dioxide in 1.837. l The first safety matches, prep;
Eottger in 1848, * were tipped with gum, sulphur and chloi
chromates, and a similar process was patented by May in 1865.
about 1855 great quantities of safety matches were made in !
These were struck by rubbing on a surface containing red pho
worked up with gum and antimony sulphide. The red phosp
often replaced by scarlet phosphorus 2 or the sulphide,
gradients arc worked up with glue and powdered glass or em
mechanically painted on the sides of the boxes. The match st
well soaked in paraffin wax or sulphur, and the ends then di
a warm mixture of chlorate, dichromate, red lead and ai
sulphide.

Recipes for matches have been the subject of numerous
The following is a?i example of the complexity of the mixtures :

Potassium chlorate 450 parts, potassium dichromate IK
glass powder 75 parts, sulphur 60 parts, iron oxide 25 parts, r(
phonis 7- 8 parts, tragacanth 30 parts, gum arabic 110 parts.

The heads of lueifcr matches, which will ignite on any rough
contain phosphorus in addition to the ingredients of the heads c
matches. Accounts of the history and manufacture of mate!
bo obtained from the following sources :

"An Account of the Invention of Friction Matches," John
Stockton-on-Tces. 1009 ; "The True History of the Inventio
Lucifer Match." John Walker, Heavisides, Stockton-on-Tees
sec also Clayton, Chem. New, 1911, 104, 223; "The Match In
Dixon, London. 1925 : " Guide to Bryant and May s M
Simpkin and Marshall, London; see also Gore, Chem. News,
10, 31, etc.

Allied to the match industry is the use of phosphorus ah
stitucnt of fireworks, thus :

1 Bottler, Annaler,, 1843, 47, 337.

2 Muir and Bell, United States Patent (1903), 724411.

J2 PHOSPHORUS.

White Fire. Potassium nitrate 100 parts, amorphous phosphorus
10 parts.

Blue Fire, Potassium nitrate 500 parts, barium carbonate 300
parts, aluminium powder 200 parts, amorphous phosphorus 5 pares.

Red Fire. Strontium nitrate 500 parts, strontium carbonate 300
parts, aluminium powder 200 parts, amorphous phosphorus 5 parts.

Firework and match materials are all potentially explosive, and
should be mixed with care and in small quantities only.

Alloys. Phosphorus as a constituent of bronzes is chiefly valued
for its deoxidising effect, which confers a great toughness on the metal.
The principal alloys are those containing copper, tin, zinc, nickel, lead
and antimony. The phosphorus is usually added in the form of
phosphor-tin. Phosphor-coppers may be made by heating copper
phosphate or copper turnings and phosphorus in crucibles at 600-800. L 2
Phosphor-bronze may contain Cu 89, Sn 13 and ? 0-3 per ccnt. :I The
phosphorus should not exceed 0-6 per cent.

Miscellaneous Uses. Calcium phosphide is used in marine signal
lights, which are so constructed that they evolve spontaneously in
flammable phosphine when thrown into water.

Phosphides have been used to give a conducting surface to plaster
moulds for electroplating. The mould is dipped in a solution of
copper sulphate, then, after drying, in a solution containing caustic
potash and phosphorus from which phosphine is being evolved.
Copper phosphide is precipitated on or below the surface of the plaster. 4
In silver plating a slightly different procedure is employed. The
plaster mould is first covered with wax. then dipped in a. solution
of phosphorus in four times its weight of carbon disuiphidc. It is
then exposed to the air until fuming begins, whereupon it is dipped
in a solution of silver nitrate containing about 100 grains of silver to
the litre.

In the manufacture of tungsten lamps the tungstic oxide may be
reduced by heating with yellow or red phosphorus in an atmosphere of
hydrogen. The tungsten powder containing phosphide which results
is suitable for drawing into the filaments.

Physiological Action. Phosphorus in oil or emulsified in fat and
chalk has been used in medicine, but appears to have no particular
value. However, a preparation made by exposing finely divided iron
to the vapours of smouldering phosphorus is useful as an application
to wounds caused by corrosive concentrated carbolic acid.

The small doses of phosphorus which have occasionally been pre
scribed have the effect of thickening the spongy tissue of bone by the
deposition of true bone. Another effect is to stimulate metabolism,
leading to increased secretion of nitrogen as ammonium salts of lactic
and ketonie acids, which result from the incomplete oxidation oi fats
and glycogcn. Some of the unoxidised fat is deposited m the liver
and muscles and leads to degeneration, of these.

When taken internally in quantities from 1 J- grains upwards, white
phosphorus is an acute poison, producing at first symptoms of nausea
and pain, which subside for a while, and are then succeeded by jaundice

1 WockhoL-.sc, J. Aiiic.r. Cktm. >S or., 18i)7, 19, 303.

- Bovn and .Bauer, Ze.dxch,. anorg. Chem., 1907, 52, 129.

3 PhiJip, JUrass World, 1010, 6, 77.

4 Osann. J. vraU. Cham.. 1854. 66. 2X4.

PHOSPHORUS, GENERAL. 13

and finally coma. 1 2 This action is due to the fact that phosphorus
prevents the complete oxidation, of giycogen and fat. In cases of
violent internal poisoning the stomach-pump is used, followed by
copper sulphate in amounts sufficient to cause vomiting, then oil of
turpentine. Black coffee is also recommended, and also the application
of mustard plasters.

The poisonous action of the vapour of phosphorus, or that of its
lower oxide, is probably due to attack on exposed bone, e.g. in decayed
teeth. It produces necrosis, which spreads inwards and gives rise to
the disease known as t: phossy jaw," which has been found among
workers in factories where phosphorus was made or used. Apart from
the effect on bones, the vapour does not appear to be poisonous in
small amounts.

Hypophosphites and phosphates, e.g. calcium hypophosphite and
glycerophosphate, are used in considerable quantities as " patent
medicines " and in medicine generally as accessory foods. Acid
phosphates are used extensively in baking powders and various manu
factured foods. The phosphorus requirements of the animal body are
stated on p. 4, and also the supply of the element in certain vege
table products, while the probable role of phosphates in some biological
processes is indicated on p. 169. From their intimate connection with
life it will be gathered that by far the most important use of phos
phorus compounds is in the manufacture of fertilisers (see Chap. XV.).

CHAPTER II.
PHOSPHORUS, THE ELEMENT.

SOLID PHOSPHORUS.

PHOSPHORUS exhibits allotropy, and formerly was thought to exist in
two forms, yellow and red. In addition, several other varieties,
scarlet, violet, metallic and black phosphorus, were discovered later,
some of which are perhaps not to be regarded as true allotropes.
Their properties will be considered partly in the present chapter, and
partly in Chapter III.

General. White or yellow phosphorus * is a colourless or pale yellow,
translucent, lustrous solid of waxy appearance, soft at ordinary tem
peratures and brittle when cold (e.g. at C.). It melts at about
44 C., giving a transparent liquid which can be supercooled many
degrees below the melting-point without solidifying. The liquid
catches lire in the air at about 60 C. and boils at about 280 C. in an
indifferent atmosphere, giving a vapour which contains complex
molecules (P 4 ). On long heating at temperatures slightly below its
boiling-point it is transformed into red phosphorus. White phos
phorus is almost insoluble in water, but is volatile with steam, to which
it imparts a luminosity ; this serves as a delicate test for the element.
It is soluble in carbon disulphicle and in most organic solvents.

It is one of the most easily oxidised of the non-metals, having a low
ignition-point and burning in the air with great evolution of heat and the
production of the pentoxitle and some red phosphorus. It also com
bines vigorously with the halogens, and gives a more complete series
of halides than any other non-metallic element.

The Melting and Freezing of White Phosphorus. Pure white
phosphorus when slowly heated melts very sharply at 44-0 C. Under
these conditions it behaves as a ;: unary :: substance, i.e. one whose
molecules are all the same, physically as well as chemically. But, in
the account of the transformations which is given later, the theory is
put forward that the liquid contains at least two kinds of molecules,
which may be called Pa and Pp. There will be a definite concentration
of each in equilibrium at any one temperature, and if the temperature
is lowered slowly, these relative concentrations will alter down to the
melting-point, 44-0 C., at which the solid is in equilibrium with a
particular mixture of Pa and P/j. The solid is not necessarily in
equilibrium at this melting-point with those proportions of P and
P/5 which are found at a higher temperature. The expected altera
tion in the freezing-point was realised experimentally by cooling phos-

* Note. The terms as generally used are almost synonymous. We have preferred
"white" in this volume, as the most carefully purified element is very pale in colour.

PHOSPHORUS, THE ELEMENT.

15

phorus very rapidly from 100 C. to temperatures just below or just
above 44-0 in a capillary tube, then inoculating with solid phosphorus.
Temperatures were read on a resistance thermometer which had a
negligible heat capacity and lag, and hence took up the temperature of
its surroundings practically instantaneously. After a slight fall, the
temperature rose to 44-1, 44-25 and even above 45-0, an extreme range
of 1-8 being observed. The pseudo-binary character of the pure
white form was thus revealed.

The degree of supercooling to which liquid phosphorus can be sub
jected without solidification also depends on its previous history. If
the cooling be slow, pure liquid phosphorus may be kept for days at
18 C. If the liquid be heated to 100 C. and suddenly cooled to ordinary
temperatures it crystallises spontaneously in a few seconds without
inoculation. lf 2> 3

As the fusion of phosphorus is accompanied by an increase of volume
(see p. 16), the melting-point is raised by increase of pressure. The
experimental results are expressed by the formula

* m = 43-93 ~ Q Q275p -0-0 6 50p 2

in which the pressure p is expressed in kilograms per square centimetre. 4
Specific Heats. -The mean specific heat of solid white phosphorus
has been determined by several investigators with moderately con
cordant results :

Temperature Interval (C.).

Specific Heat.

Investigator.

(i)

- 78 to

+ 10

i -170-0 -174

llegnault. 5

(2)

~ r 55

-1-30

! 0-185

5?

(3)

+ 13 ,,

+ 36 C

0-202

Kopp. 6

(4)

- 21

+ 7 C

0-1788

Person. 7

(5)

-188 ..

+ 20

0-1.69

Richards and

Jackson. 8

The atomic heats arc therefore 5-33, 5-74 and 6-26 over the three ranges
of temperature (1), (2), (3). There is a slight deviation from Dulong
and Petit s law 9 at the lower temperatures, in the same sense as that
met with in the case of the elements carbon, boron and silicon. But
although phosphorus has a relatively low atomic weight, it also has a
low melting-point, and the atomic heat as usual assumes the normal
value at temperatures near the melting-point.

Latent Heat of Fusion. The, latent heat of solidification at the
melting-point, +44-2 C., is 5-031 calorics per gram or 0-1.6 Calorics

1 Sinks, Ze-Uvch. phyxtkal. Chtm., I OIK 76, 421.
- Smits, ibid., lOli; 77, 367.

;! Smits and Leemv, Proc. K. Aka<L Wf-tenM ,b. A m-xlc-rdfim, .11) J. I, 13,822. See also
Cohen and Olic, Zc.iixch. pltijxika.L Cham , It) 10, 71, 1.

- 1 Tammann, " I\ry*tf{l/.iMn /n. -tu/d fcchin-f-lztn," Leipzig, 1003.

5 Regnault, Ann. Clu>,i. PJnj*., 1840, [3"j, 26, 2SG; .1853, [3], 38, 120.

G Kopp, AntinUii XnppL, 186;"), 3, 200.

7 Person, Ann. Chhn. Phy*., 1847, [3J, 21, 205.

8 Richards and Jackson, Zcitxch. phy^lhil. Cham., 1010, 70, 445.

9 See Vol. I., this Series, or Text-booh of Physical Chemistry, Vol. 1., J. Xewton Friend

16 PHOSPHORUS.

per gram-atom l a very low value, which may be compared with
that & of sulphur, namely, 0-80 Calories per gram-atom. The latent
heat, as usual, diminishes with fall of temperature. The following
values were obtained on allowing the supercooled liquid to crystallise :

27-35 : 29-73 ; 40-05
4-744 4-744 4-070 calories per gram. 2

The latent heat increases at the higher melting-points which are obtained
at higher pressures ; thus at t =50-03 C. and p = 22 kg./sq. cm. I was
4-94, while at 69-98 C. and 959 kg. it was 5-28. 3 At still higher pres
sures the increase in I continues, as is shown by the following results,
which refer to white phosphorus :

p . . ! 1 2000

t . \ 44-2 99-3

; / . I 2-09 2-41

4000

6000

6000

148-2

191-9

-2-4

2-63

2-78

18-61

Pressure and temperature are expressed in the units given above, and
latent heats in kilogram-metres per gram. The last value refers to
black phosphorus. 4

If the latent heat of fusion is taken as 5-0 calories absorbed per
gram of phosphorus at the melting-point (T ia = 317-5 C. (abs.)), the
high value of 40-4 is obtained as the cryoscopic constant for 1 mol of
a solute in 1000 grams of phosphorus. The experimental value obtained
by dissolving naphthalene in phosphorus was 33-2. 5

Density. The density of solid white phosphorus is nearly twice as
great as that of water. The following table is compiled from the results
of different investigators :

THE DENSITIES OF SOLID WHITE PHOSPHORUS AND
OF LIQUID PHOSPHORUS AT THE MELTING-POINT.

18 20 40 44 ! 44

D ; 1-8368 G 1-828 8 , 1-8232 6 : 1-8008 6 1-805 9 1-745 (liquid) 9

; 1-82 7 : . . . . .. . . 1-748 (liquid) 8

Hence the coefficient of expansion of solid phosphorus at ordinary
temperatures is 0-0037 c.c. per degree Centigrade. The solid expands

1 Person, loc. at.

- Patterson, J.prald. Chtm., 1881, [2], 24, 120, 293.
" Tarn m arm, " Kryst. und Schmc.lz." Leipzig, 1903.

* jVo/e. The factor for conversion into calories is O426S.
1 Eridgman, Phys. ./?e?;/ci/:, 1914, [2], 3, 153.

5 Schenek and Buck, tier., 1904, 37, 915.

G Pisati and do .Franchis, Her., 1875, 8, 70.

7 Jolibois, T7ie.se, Paris, 1920.

s Boeseken, Rec. Trav. chim., 1907, 26, 289.

9 Hess, PhysikaL Zcitsch., 1905, 6, 1862.

PHOSPHORUS, THE ELEMENT. 17

by about 3 per cent, on fusion ; the ratio of the density of the solid to
that of the liquid at this temperature is 1-035 1 or 1-0345 2 to 1.

Compressibility. The coefficient of compressibility is defined as
the fractional change of volume produced by a change of pressure
amounting to 1 mcgabar (10 6 dynes per square centimetre). The
range of pressure investigated was 100 to 500 megabars, and the com
pressibilities at room temperatures were 20-3 for white phosphorus
and 9-2 for the red or violet variety. 3 Thus, as usual, a high compressi
bility was found for an element of high atomic volume, and the more
condensed form had the lower compressibility.

Crystalline Form. It was shown by the earlier investigators
that phosphorus crystallised from the liquid state in octahedra and
dodecahedra, from carbon disulphidc in octahedra, and that, when
prepared by sublimation, the crystals had about 200 distinct faces. 4
Well-shaped crystals of white phosphorus may be obtained by solidi
fication of the liquid, by slow sublimation, or by evaporation of solutions
in organic solvents. They belong to the regular system, and have a
columnar shape if obtained from one set of solvents, e.g. carbon disul-
phide, benzene, alcohol, ether, petroleum, while they have shapes
derived from the cube and dodecahedron if obtained from turpentine,
oil of almonds, etc. 5 By slow sublimation various forms of the regular
system are obtained which may have every possible number of faces
(except 48) up to 200. 6 According to Briclgman 7 white phosphorus
crystallises both in the regular and in the hexagonal system, the transi
tion temperature being raised by increase of pressure. Thus under
12,000 atmospheres the conversion occurs at -r64 -4 c C., under atmo
spheric pressure at -76-9, and under the pressure of its own vapour
at -80, which therefore appears to be the transition point between
this j8- for in and the ordinary or a-fonn of white phosphorus. The
/3-form, stable under high pressures, is produced with a volume con
traction of about 2 per cent. The density is 2-090. 8

Refract! vity. -As is to be expected from the brilliant gem-like
appearance of the crystals and drops of liquid white phosphorus, the
refractive index is high. At the ordinary temperature the refractive
index for the D line (A -589-0 to 589-6 m/x) was found to be 2-144 9
or 2-14. 10 The differences between the refractive indices of the solid
and the liquid arc shown in the table overleaf.

Electrical Conductivity. -Phosphorus is an electrical insulator.
The conductivity of the solid clement was found to be of the order of
10 -11 mhos per centimetre cube and that of the liquid 1()~ (5 mhos per
centimetre cube. 11 Black phosphorus, which must be considered the

1 Hess, Pkyxikal. Zfiil.sch., 190

3 liicharcls, Zf-if^ch. EU-.ktrochc:

4 See Dammar, " Handb-uc.h (It

5 Rctgors, Zicitxch. a/iory. C/ir.i
20, .1022; Christomanos, Zcit^.ch.

6, 1862. - Leduc, CowpL rc-nd., 1891, 113, 259.

., .1907, 13, 519; ,/. Amc.r. Chnn. ,SV;., 1915, 37, 1643.

<iiior(;(rriixch( iL Clicniir., * vol. ii., pi. i.

, 1894, 5, 218. See also Bokorny, Chew.. Zeit., 1896,

lot f/. Chc.ni., 1905, 45, 132.

.Rctgors, loc. cit.

7 Bridgman, J. A-mr-r. Cherti. froc., 1914, 36, 1344.

8 Bridgman, J. Avu-r. CliMii. Soc.., 191.4, 36, 1.344; ibid., 1916, 38, 609.

18 PHOSPHORUS.

REFRACTIVE INDICES OF SOLID AND LIQUID
PHOSPHORUS. 1

State.

Temp.

C.

Line and 7.

in m//.

D Ha

589-0-589-6. 656-3.

H/3
486-15.

Hy
434-07.

Solid

25-0 2-141

37-5 . . i 2-08873 \

2-15388

2-1946

Liquid

55

37-5

44-0

i 2-05370 :
2-05010

2-11675
2-11311

2-15634
2-15274

most metallic form of the element, is a relatively good conductor, the
specific resistance being slightly less than 1 ohm per centimetre cube
but diminishing with rise of temperature. 2

The dielectric constant of solid white phosphorus was found to
be 4-1 at 20 C., and that of liquid phosphorus 3-85 at 45. 3 The
electrochemical potential is said to lie between those of arsenic
and tellurium. 4 Phosphorus is diamagnetic. 5 The magnetic sus
ceptibility of the solid white element is about 0*9 x 10~ 6 mass units,
that of the red variety rather less. 6

lonisation Potential, V, v . This may be defined as the smallest
difference of potential through which an electron must fall in an
electric field in order that its kinetic energy, mi; 2 2, =eV\ (c is the
electronic charge), may be sufficient to raise an atom after collision
from state (1) with energy E 1 to another possible quantum state (2)
with energy E z . In changing back from quantum state (2) to (1) the
atom will emit radiation of a frequency F A given by :

eV\ = hv (h = Planck s constant; v=wave number in waves per cm.)
The wavelength A A of this radiation is calculated from :

A A =c/v (c is the velocity of light)

In the case of phosphorus, V\ -=5-80 0-1 and A v =2130 A. 7
The ionisation potential has also been determined by the method
of electronic collisions. Free electrons, from a heated platinum wire.
are introduced into the vapour of an element under low pressure. By
the application of increasing potentials increasing kinetic energies are
imparted to the electrons. After a certain threshold value has been
passed, the electrons strike the atoms in inelastic collisions, and mono
chromatic radiation is emitted by the atoms. When this method was

1 Damien, loc.cit.

2 Briclgman, Proo. Arncr. AcacL, 1921, 56, 126; Li nek and Juii, Zc.it, <ch. anorrj. Chem.,
1925, 147, 288.

3 Schlundt, J. Physical Chew., 1904, 8, 122.

Schenck, Ber., 1903, 36, 995. - Faraday, Phil Trans., 1846, 136, 4.1.

6 Quincke, Wicd. Annaltn, 1885, 24, 347; P. Curie, Compt. rend., 1892. 115, 1292;
Pascal, Ann. Chiin. Phys., 1910, [8], 19, 5; Honda, Ann. Pli.ysil, 1910, [4], 32, 1027;
Meyer, ibid., 1900, [4], i, 664.

7 Foote and Moliler, Phys. Review, 1920, [2], 15, ooo.

PHOSPHORUS, THE ELEMENT.

19

applied to phosphorus vapour the value of the potential E was found
to be 10-3 volts. 1

Solubility .White phosphorus is almost insoluble in water. It
dissolves easily in liquid ammonia, sulphur dioxide and cyanogen, also
in such compounds as phosphorus trichloride which mix with typical
organic solvents. It is moderately soluble in fatty oils, also in hydro
carbons, alcohols, ethers, halogenated hydrocarbons such as chloroform
and especially methylene iodide. One of the best solvents for phos
phorus, as for sulphur, is carbon disulphide, which seems to dissolve
it in all proportions at ordinary temperatures ; a solution has even

SOLUBILITY OF WHITE PHOSPHORUS IN AQUEOUS
SOLVENTS AND OILS.

Solvent.

Water. 2

i Acetic
Acid, 2 Paraffin. 2
96 per cent.

Oleic Almond
Acid. 2 Oil. 2

Grams Phosphorus in 100
grains Solution

0-0003

j
0-105 1-45

1-06 1-25

Alcohol 3
Solvent, (absolute).

Glycorol !
( den sit- v i
l-2f)6). ri !

Grams Phosphorus in 100
grams Solvent . . 0-208

0-25 ;

SOLUBILITY IN BENZENE. 5

10 15 , 18 20 23

Solubility in

grams ;

per 100

Solvcnt

ranis
. 1-513 : 1-99 2-31

2-4

2-7

Density of

So hi- j

Lion

. . ; . . 0-899 0-S9S5

89

2-7 3-1 3-2 3-4 3-7

0894 0-892 0-S90 8875 0-88(51

e c. 30

35 -10 ! 45

50

55

60

65 i 70 75

81.

1

i j

Solubilitvm grams

!

i

per 100 grains
Solvent ." . 4-60

5-17 5-75 6-1L

G-80

7-32

7-1)0

8-40 8-90 ; 9-40

1003

1 Compion and Mohler, Jonicnc.ru /ig^ und Aiirw/irnyritipowtuwjcn,* uberset.zt von
R. Suhrmann, Berlin, 1925. See also Mohler and .Foote, " lotiiwdwn and Resonance
Potentials of some J\~ on-Metallic Elements, * Washington, 1920.

2 Stich, Phartn,. Zeit., 1903, 48, 343; see Cficm"Zcntr., 1903, 1291.

3 Schacht, Pharm. J., 1880, [3], n, 464.

4 Ossendowsky, J. Pharm. Chim., 1907, [6], 26, 162.

5 Chnslomanos, Zeitsch. anorg. Chem., 1905, 45, 136.

20

PHOSPHORUS.

SOLUBILITY IN ETHER. 1

1 i ! : i i j ;
tC. \ : o : 8 10 i 15 IS i 20 i 23 25

Grains Phosphorus
in 100 grams
Solution

0434

0-G2

i ; !

0-79 0-85 0-90 ! 1-01 ! 1-04 1-12 1-39

Density of Solution

0-729 : 0-723 0-719 j 0-718 : 0-722 0-728

tC.

Grams Phosphorus in 100 ,

grams Solution . . . \ 1-60

1-75

1-80

2-00

SOLUBILITY IN CARBON BISULPHIDE. 2

-10 -7-5 -5-0 -3-o -3-2

i | ; __ ; ;

i ! . !

Grams Phosphorus i , \ ;

in 100 irrams j ; ! i :

Solution /" . , 31-40 : 35-8^ 41-9o 00-14 i 71-7:2 7o-0 i 81-27 | 86-3 ; 89-8

been prepared containing 20 parts of phosphorus in 1 part of carbon
disulphide. These solutions are dangerous ; the volatile and enclo-
thermic disulphide forms an explosive mixture with air at ordinary
temperatures, and the finely divided phosphorus which is left on
evaporation ignites spontaneously. This is illustrated in the well-
known lecture experiment in which the solution is allowed to evaporate
on filter-paper.

LIQUID PHOSPHORUS.

Values of the densities and specific volumes up to the boiling-
point have been determined and are as follows : -

DENSITIES AND SPECIFIC VOLUMES OF LIQUID
PHOSPHORUS. 3

t C. . . i 30

Density . . 1-7684

Specific Volume 0-5654

40 56-5 100 200 280 200 i

1-74924 1-7444; 1-6949 1-0027, 1-52SG7! 1-4850;
0-5719 0-5733 0-5899 0-6238 0-6544 0-6733,

1 Christoraanos, Zerisch. (rnorcj. Chaw., 1005, 45, 136.

2 Cohen a-nd Inouye, Zeitsch. physikal. Ch-em., 1910, 72, 41S: Cohen and Inonye,
Chem. Weelcblad, 1.910, 7, 277. Of. Giran, J. Physique, 1903, [4], 2, 807.

3 Pisati and de Fi-anchis, Bcr., 1880, 13, 2147.

PHOSPHORUS, THE ELEMENT. 21

Hence the expansion of the liquid is expressed by the formula
v t = o 50 [l + 0-0 3 5167(* - 50) + 0-0 6 370(* - 50) 2 ]

In another investigation, on 0-7669 gram of phosphorus con
tained in an evacuated glass dilatometer, the increase of volume
between 50 and 235 C. was found to be expressed by : l

v t =0-5733[1 n-0-0 3 505(/ -50) 4-0-0 6 118(* -50) 2 ]

The agreement between the two expressions is good at the lower
temperatures, and the differences at higher temperatures are about
the same value as the coefficient of expansion of glass. Thus at 200 C.
the second equation gives the specific volume as 0-6180 c.c. per gram.
Without the correction for expansion of glass the apparent specific
volume becomes 0-621 c.c.

The specific volume at the boiling-point, determined by the method
of Ramsay, 2 was 0-6744 c.c. The corresponding atomic volume 2 is
20-90-4. This constant thus lies between 20 and 21,* with a tendency
to diminish on keeping the phosphorus at this boiling temperature,
owing to the formation of the denser P/5 molecules, which are shown
by the cherry-red colour of the liquid.

Vapour Pressures. The vapour pressures of liquid phosphorus
are tabulated overpage in three sections, namely

(a) Commencing below the triple point, which is practically the same

as the melting-point, and up to about 150 C. 3> 4

(b) From about 150 C. to nearly 360 C. Over this range three

sets of measurements are available. 5 G> 7

(c) From about 500 C. to the melting-point of violet phosphorus

the pressures of the metastable or supercooled liquid are
known, 6 and the pressure curve of liquid violet phosphorus
has been followed up to over 600 C. 6

These results have been expressed by various interpolation formuke.
That originally proposed by Srnits and Bokhorst was

logp (mm.)= - 3 98 ^ 96 ,3.59 i g T + 19-2189

This was found to give pressures lower than those experimentally de
termined between 44 and 150 C. by Macllae and Voorhis, who have
altered the constants to fit this range also, as follows :

logp (mm.)= - :L ^ r -- 1-2566 log T + 11-5694

These formula; express the pressures of the liquid from 44 C. to 634 C.

I Pridoaux, Trans. Chun. Xoc., .11)06, 91, 1713.

- Ramsay and Masson, Trans. Chc/n. /S oc., 1881, 39, 50.

* The probability of maximum positive error is low.

3 Centnerszwer,"#e/Asc7i. phyaikal. Ckt-m., 1913, 85, 99.

II Duncan, MacKae and van Voorhis, J. Amcr. Cht-m. $oc., 1921, 43, 547.

5 Jolibois, Com.pt. rend., 1909, 149, 287; 1910, 151, 382.

6 Preuner and Brockrnoller, Zeitscfi. physihd. Ckem., .1912-3, 81, 129.

7 Smits and Bokliorsl, Zcitsch. physical. 6 Aev/i., 1914, 88, 608 ; 1916, 91, 249.

PHOSPHORUS.

THE VAPOUR PRESSURES OF LIQUID PHOSPHORUS.
(a) Liquid White Phosphorus.

t C. . ; 20 30 ,

p (mm.) 0-025 3 0-072 4

40

44-1 69-92
0-173 2 0-823

100-11 ! 119-85 150-0
3-66 j s-60 1 27-20 2

(b) Liquid White Phosphorus.

(From about 150 to above the boiling-point (Jolibois).)
Jolibois. 3

i

t C. .

145 173

184

192

200 205 " 219

235 239 244

p (atm.)

0-017

0-064

0-093

0-124

0-157 0-178 0-253

0-366 0-418

0-464

t C. .

247

250

254

257

259 262 268

273 275

279

p (atm.)

0-499

0-543

0-591

0-633

0-675 0-705 0-797

0-850 0-925

0-990

t C.

281 283

285

295

299 : 307 1 312

p (atm.)

1-034 1-071

1-122

1-329

1-437 1-650 ; 1-817

!

Preuncr and Brockmoller. 4

rc. . 130

140

150

1.60

165 170 180 190

200

p (atm.) 0-0145

0-01.97

0-0263

0-0355

0-0421 0-0486 0-0684 0-100

0-145

t c C. .

209

219

226

230

250 270 290

p (atm.)

0-245 0-271

0-332

0-382

0-561 ! 0-776 i 1-030 . .

: i i

Smits and Bokhorst. 5

e c.

p (atm.) .

169-0
0-04

181-3
0-07

185-3
0-09

206-9
0-18

; 210-0
; 0-20

! 229-8
; 0-32

237-9
0-42

* C. . 252-0
p (atm.) . : 0-54

261-4 265-5
0-69 , 0-74

280-5
1-00

! 298-6
i 1-38

331-8
2-47

332-9
2-61

t C.

p (atm.) .

342-0

2-95

355*7

3-SS

i . .

j

i
i

i

1 Centnerszwer, loc. at. * BK5S3 3 *, MacRae and van Voorhis, loc cit

3 Jolibojs, Compt. rend., 1909, 149, 287 ; 1910, 151, 382.

4 Preuner and -Brockmoller, Zeitsch. physilcaL Chem., 1912-3, 81, 129.

5 Smits and Bokhorst, Zeilsch. physical. Chem., J914, 88, 608 ; 1916, 91, 249.

PHOSPHORUS, THE ELEMENT. 23

(c) Liquid Violet Phosphorus^v

l t c.

504

550

581 589-5

593

608

634

695*

1 p (atm.) .

23-2

1 33-0

41-1

43-1

44-2

49-0

58-6

82-2 *

;

i

The latent heat of vaporisation of liquid yellow phosphorus at its
boiling-point has been given as 4 Cals. 2 or 3-89 Cals. 3 This subject is
further developed on p. 36, under " Violet Phosphorus."

Surface Tension. The values of the surface tension a and density
D at two temperatures were determined with the object of calculating
the molar surface energy o-(J//D)i, and its change with temperature. 4

Then, by comparison with the normal temperature coefficient, the
molar weight in the liquid state can be deduced. 5

t C.

D.

a.

.*/*,.

A(Molar surface energy); A^.

78-3
132-1

1-714
1-664

43-09
35-56

748-2
629-6

2-205 4

The molar weight M used in this calculation corresponded to a molecule
P 4 , and since the temperature coefficient calculated on this assumption
is normal, the molar weight in the liquid state is thus found to be the
same as in the gaseous state. The molar weight in the dissolved state
at the boiling-point of carbon disulphide, 6 and at the freezing-point of
benzene, also corresponds very closely to P 4 . 7

PITOSPIIOK.US VAPOUII.

The Densities of Phosphorus Vapour. That phosphorus, in
common with other non-metals, forms complex molecules in the
gaseous state was established early in the nineteenth century by deter
minations of vapour density. At a temperature of 500 C. the relative
density (air 1) is 4-35 ; 8 at higher temperatures it falls, being 3-632
at 1484 C. and 3-226 at 1677 C. 9 The molecule 1\ requires a density
of 4-294. The molecular complexity thus revealed is confirmed by the
low value of the ratio of the specific heats, namely. 3-175 at 300 C. 10

1 Smits and Bokhorst, Zr.ilxch. pkysikal. Chew.., 1916, 91, 248
* Note. Critical temperature and pressure.

2 de Forcrand, Compf. rc.nd., .190J, 132, S7S.

3 Giran, Compt. rend., 1903, 136, 550, 677; Giran, ;: llccherckes sur h phosphcre et, les
acides phosphonques, Paris, 1903.

1 Aston and Ramsay, Trans. Chem. Soc., 1894, 65, 173.

5 See "A Text-booh of Physical Chemistry" Vol. 1., J. Xewton Friend (Griffin), 1933.

Beckmann, Ztilsch, phy&ikal. Ch&m., 1890, 5, 76.

7 Hertz, Ztitsch. pJnjs-iM. Chem., 1890, 6, 358.

8 Deville and Troost, Com.pt. rend., 1S63, 56, 891.

y Meyer and Biltz, Her., 1889, 22, 725; see also Mensching and Meyer, Annalen, 1887,
240, 317".

10 de Lucchi, Nuovo dm., 1882, [3], n, 11. See also A Text-book of Physical Chemistry ,"
Vol. I., J. Xowton Friend (Griffin).

Many determinations at the higher temperatures have been made by
measuring the pressures of a known weight of gaseous phosphorus
enclosed in a fixed volume. 1 The phosphorus was vaporised by means
of an electric furnace in a completely closed vessel, the pressures being
read on a quartz spiral manometer, which obviated the necessity of
having any manometric fluid. From measurements of pressure, tem
perature and volume, the apparent molecular weight, or mean relative
weight of the kinds of molecules which are present, can be calculated by
the usual applications of the gas laws. 1 Different amounts of phos
phorus confined in the same volume exert different pressures, and a
comparison of these with the relative densities indicates the effect of
pressure upon dissociation for the particular temperature. From, about
500 C. to 600 C. densities show the presence of P 4 molecules only.
Between 600 C. (at which the density is 61-5 to 61-9 independently
of the pressure) and 1200 C. dissociation takes place progressively,
possibly in the stages

P 4 2P 2 ^4P

An attempt was made to calculate equilibrium constants for the separate
dissociations, the heats of which could thus be determined :

P 4 -> 2P -31-5 Cals.
P 2 ->2P~-45-5 Cals.

By means of the simpler assumption that each kind of dissociation is
complete before the next begins, the degrees of dissociation a at each
temperature and pressure can be calculated directly from the densities,
as in the following table. 2

DENSITY AND DEGREE OF DISSOCIATION OF

PHOSPHORUS VAPOUR.

t C.

P (771111.).

D.

a.

/ C. / > (nun.).

D.

a.

800

542

GO-9

0-01

1200 : 950

40-0

0-34

i

218

co-r

()()]

G99

44-8

0-38

,.

88

59-0

0-04

412

41-7

0-48

900

008

59-7

0-04

175

38-3

: 0-01

5>

99

55-0

0-12

1300 7(50

0-00 (calc

1000

G94

55-9

0-10

380

0-09

no

50-0

0-23

190

0-81 .,

1100

810

51-3

0-20

100

0-89

"

145

43-6

0-41

The mean heat of dissociation, calculated from the variations in
the dissociation constant between 1100 and 1200 C., is 49-2 Cals. per
mol (P 4 ). From this the constant, K, was calculated at 1300 C., and
the percentage dissociations at this temperature. At low pressures and

1 Premier and Brockmoller, Zeitsch. physical. CJitm., 1912, 81, 161.

2 Stock, Gibson and Stamm, Ber. 9 1912, 45, 3527.

PHOSPHORUS, THE ELEMENT. 25

above this temperature, the dissociation into P 2 being now complete,
it is probable that single atoms, P, will begin to appear. On the
assumption that P 4 , P 2 and P arc all present at an early stage, it is
calculated that at 1200 C. and low pressures there is already a con
siderable percentage of P. 1 2

The dissociation constants 7v 4 (P 4 ^2P 2 ) and K z (P 2 ^=2P) are
calculated to be :

L 4

K 9

. 800

1000

I 1200

. ; 350

40-0

! 2-11

. ! 7-4

9-0

! 3G-0

! :

The atomicity of phosphorus vapour under the critical conditions
may be calculated from the van dcr Waals coefficient b, which represents
the actual volume occupied by the molecules and is given by the
equation 3

Sp, 273 8X82-2 273

The value of b for phosphorus in combination is obtained additively
from the critical data of phosphine. For the compound b is 0-00233,
and for three hydrogen atoms 3b is 0-001086, whence b for combined
phosphorus (1 atom) is 0-0012 44. The ratio of this to b for the free
element gives the atomicity, 4-33, of the latter.

Refractivity. The refractivity at three, wavelengths was deter
mined by means of the Jamin refractometer, a weighed quantity of
phosphorus being gradually vaporised in an evacuated tube of fused
silica with transparent plane parallel ends. 4

A .

. i 6800 A
. 1200

; 5S93 A
1212

5100 A
1230

The equation giving n - 1 as a function of A is
n-1 =0-0011621 +

From this the value of n-l at A = 5893 is about 0-0012.

Spectra of Phosphorus and Its Compounds. When the ele
ment or some of its compounds are introduced into a llame, or when
hydrogen containing a little phosphorus vapour is burned, a green
colom^is observed which has been resolved into bands in the orange,
yellow and green. 5 The passing of an electric discharge through a tube
containing phosphorus vapour at low pressures also showed a green
colour which was resolved into similar bands. 6 Other observations

1 Stock, Gibson and Stanim, tttr., 11)12, 45, 3527.

- Prouner and Brockm oiler, Loc. cd. y Smits and Bokhorst, loc. at., p. 270.

i Cutlibertson and Metcalfc, Proc. Hoy. Sue., 1908, 80 (A), 411.
5 Dusart, Covvpi. rend., 1856, 43, 112(5.

c PI ticker and Hittorf, Plul. Trans., 1865, 155, 1; Hartley, PhiL Trans., 1894, 185 (A),
161.

26 PHOSPHORUS.

are summarised in the appropriate works of reference * and compre
hensive papers. 2 . .

It has now been established that the emission spectrum of the
element lies in the ultraviolet. Prominent lines in the are and spark
spectra are found at A = 2555-7, 2554-0, 2536-4, 2534-75 A. These are
also seen in the spectra from the vapour in a Geissler tube, and in
addition other lines at 2497-3 and 2484-1. 3 A photographic record of
the condensed spark spectrum showed lines at 2555-0, 2553-3, 2535-6,
2534 A. 4

When phosphoric acid or its salts are introduced into a carbon arc
they give a mixed line and band spectrum. There is a band at 3286
to 3246 A and others are found at 2635, 2625, 2611, 2597, 2588 and
2571 A. Sharp lines are seen at 2555-0 to 2553-37 A, which represent
the double line of the element at 2535-74 to 2534-12 A. There are
several faint streaks at 2477 to 2385 A. 5 The arc spectrum obtained
by introducing phosphorus pentoxide into a copper arc contains at
least 35 lines of wavelengths ranging from 2550 to 1672 A. Many
of these are connected together as systems of constant frequency
difference, and some of these series are due to doubly and trebly ionised
phosphorus. 6 The low-voltage arc spectrum also shows lines and
bands. 7

The spectrum oC the electrodeless discharge shows, in the spectral
region transmitted by fmorite (CaF 2 ), 12 lines between 1859-4 and
1671-5 A. 7 These also depend upon the degrees of ionisation of the
phosphorus atom. 8

From the foregoing data it is evident that these spectra are similar
to those which proceed from the slow combustion of phosphorus (p. 124).

Absorption of Radiation. Neither phosphorus vapour nor the
compounds of phosphorus with colourless elements show selective
absorption in the visible region. The vapour shows general absorption
in the ultraviolet from a wavelength of about 2500 A at 150 C., 2820 A
at 190 and 2960 A at 220. Phosphine transmits rays down to about
2230 A, and phosphorus trichloride down to about 2590 A. 9 The
infra-red absorption by PH 3 is described under that compound.

Fluorescence. When the vapour of phosphorus at 600 to 700 C.
and 1 mm. pressure (therefore containing a considerable proportion of
diatomic molecules) is confined in a sealed quartz tube and exposed to
the spark lines 2195 and 2144 A of cadmium, 2100 and 2062 A of zinc
or 1990 and 1935 A of aluminium, it gives a fluorescent emission con
sisting of a resonance series in the region 3500 to 1900 A. 10

1 Kayser, l Handbuch der Speldroscopie^ 6, 239, Leipzig, 1912; Hicks, A Treatise
on. the Analysis of Spectra., Cambridge, 1922.

2 de Gramont, Bull. See. chim., 1898, [3], 19, 54.

3 Kayser, Hayjitlinie/i der Luaen-Spckfm der lemente," J. Springer, Berlin, 1926.
1 dc Gramont, Compt. rend., 1920, 172, 1106.

5 "Atlas Typischer Syzktren" Edcr and Valcnla, 1928, Verleger d. Akad. d. Wiss.
Wien.

b Saltmarsli, Phil May., .1924, 47, 874; Sur, Nature, 1925, 116, 542.

7 Duliendack and Hutlistemer, Phys. Rtvt.eic, 1925, [2], 25, 110, 501.

8 ilillikan and Bowen, Phys. iteview, 1925, [2], 25, 591, etc.: Deiardins, Compt. rend.,
1927, 185, 1453.

9 Purvis. Proc. Camb. Phil Soc., J923, 21, 566; Dobbie and Fox, Proc. Roy. Soc.,
1920, 98 (A), 147.

10 Jakovlev and Tcrenin, Nature, 1929, 337. See also Geuther, Ztitsch. iciss. Photocliem.,
1907, 7, 1.

PHOSPHORUS, THE ELEMENT. 27

Mass Spectrum. The analysis of phosphorus by positive rays
shows that it is a pure element, consisting of atoms which all have the
same mass. 1

CHEMICAL REACTIONS OF PHOSPHORUS.

Phosphorus unites directly with many of the more electronegative
elements, forming oxides, halides, sulphides and selenides. The
conditions of formation are described under the respective sections in
this volume. The energies of combination with oxygen and the halo
gens are great. The oxidation probably always proceeds in stages, as
described under ct Oxides." The combustion proceeds not only in air
and in oxygen, but also in many compounds containing oxygen, such
as oxides of nitrogen and sulphur. Halogenation also proceeds in
stages in those cases where both a higher and a lower halide are formed
(see "Halides "). Phosphorus combines with nitrogen only under
special conditions, and under the influence of the electric discharge
nitrogen is absorbed by phosphorus. 2 A mixture of phosphorus
vapour with nitrogen under the influence of the electric discharge, forms
a solid nitride. 3

Phosphorus also unites directly with many metals giving phosphides
(see p. 60), which are described under the respective metals in the
volumes of this Series.

Phosphorus does not, like nitrogen, combine directly with hydrogen.*
In this respect it resembles the succeeding members of the Group.

Phosphorus is readily oxidised by strong oxidising agents such as
nitric acid to phosphorous and phosphoric acids, eventually the latter.
Hydrogen peroxide of concentration greater than 6 per cent, reacts
violently when warmed with red phosphorus, less violently with white
phosphorus, giving phosphine, phosphorous and phosphoric acids. 4

The reaction of phosphorus with the alkalies is described under
" Phosphine." It is really a case of hydrolysis. This can also be
effected by boiling water in the presence of certain metallic salts, which
probably act by the intermediate formation of phosphides. Super
heated steam at 238 to 260 C. and under a pressure of 57 to 360 atmo
spheres gives phosphine and orthophosphoric acid, thus : 5

4P 2 -r 12H 2 O = 5PH 3 -f 3H 3 P0 4

The simplest reaction will be represented by the equation
2P+3H 2 O=PH 3 -rH 3 PO 3

The phosphorous acid then decomposes, as it is known to do, giving
more phosphine.

The Action of Phosphorus on Solutions of Metallic Salts.

When white phosphorus is placed in solutions of the salts of the more
" noble " metals the metals are deposited and oxy-acids of phosphorus
are found in the solution. The ratios of metal deposited to phosphorus

1 Asion, " Isotopes, Churchill, 1923.

2 Newman, Proc. Phys. Soc., 1921, 33, 73.

3 Kohlsch utter and Frumkm, Ze-dsck. L"lektrocher/i., 1914, 20, 110.

* Note. Under special conditions a certain degree of combination was detected (see
p. 68).

- 1 Weyl, Zeitsch. phys. Chem. Unterricht, 1906, 39, 1307.
5 Ipatiell and Nikolaieff, Ber., 1926, 59, B, 595.

28 PHOSPHORUS.

oxidised arc not constant except under certain carefully regulated
conditions. It is stated that in the case of copper sulphate the ratio
\vas oCu : 2l 3 when only that phosphorus was included which was
present as phosphoric acid. 1 The ratio 2Cu : P (total phosphorus)
has also been" found when air was excluded. 2 The reaction proceeds
in stages. 3 When the copper has been completely precipitated from
decinormal copper sulphate about 13 per cent, is present as phosphide,
but this phosphorus is oxidised later to oxy-acids. During the later
part of the reaction the ratio is 2Cu : P, or 4 equivalents of copper
are deposited to 1 atom of phosphorus oxidised. 4 The metals which
are deposited from neutral or slightly acid solution are those which
react with phosphine, i.e. Cu, Hg, Ag, Pel, Pt, Au ; those above copper
in the electrochemical series are not deposited. In ammoniacal
solution deposits are also obtained from salts of Pb, Ni, Tl, Sn, Co,
Cd, Zn. 5 - 6

The reaction with silver nitrate has been thoroughly investigated
at different stages/ 1 - 6 The deposit is dark at first, of a bright crystalline
appearance later, and finally grey and spongy. The ratio Ag : P may
be more than 5 : 1 at the beginning and 3-6 : 1 or less at the end of the
reaction. During the middle part the ratio is 4:1. Both the phos
phorous and phosphoric acids were determined, and it w r as suggested
that these were produced in equiinolecular amounts after the first
deposition of phosphide had ceased.

The metal may be deposited on a piece of platinum, gold or carbon
at some distance from the stick of phosphorus with which this is in
contact. The silver phosphide which was first produced had the
formula Ag 3 P and phosphorous acid was formed simultaneously. The
following equations were suggested as representing the various stages :

2P + 3H = PII 3 + H 3 P0 3
PH 3 -f 3AgN0 3 = Ag 3 P +3HN0 3
Ag 3 P H- 5AgN0 3 -~ 4H 2 O = 8Ag + 5HN0 3 + H 3 PO 4

These equations perhaps give a general representation of the reactions
which occur between, phosphorus and solutions containing salts of the
" noble " metals.

Further references to the action of phosphorus on metallic salts
are: Senderens, Compt. rend*, 1887, 104, 175; Bottger, Repert. Pharm.,
1875, 24, 725; Philipp, Ber., 1883, 16, 749; Rosenstein, J. Amer.
Chem. Soc., 1.020, 42, 883 ; Poleck and Thunimel, Ber., 1883, 16,2442.

Red Phosphorus. The chief chemical properties of red or
amorphous phosphorus were determined by the discoverer and other
early investigators. As compared with white phosphorus, both red
and scarlet phosphorus are relatively inert, except in respect to certain
reactions which depend largely on the extent of surface exposed to
aqueous reagents.

Red phosphorus does not glow in the air, but shows a faint lumin
escence in ozone. When heated in the air or moist oxygen it does not

1 Bird and Diggs, J. Amer. Chem. Sac., 1914, 36, 1382.

2 Straub, Ztitsch-. an.org. Chew., 1903, 35, 4CO.

3 Taucherfc, Zeitech. an.org. Chtm., 1913, 79, 350.
* Walker, Trans. Chem. Soc., 1026, 128, 1370.

5 Ktiliscli, Annalen, 1885, 231, 327.

G Moser and Brukl, Zeitsch. anonj. Chain., 1922, 121, 73; Brukl, ibid., 1922, 125, 252.

PHOSPHORUS, THE ELEMENT. 29

ignite below about 260 C., at which temperature the vapour pressure
has become appreciable (p. 33 ). 1 2 In warm moist air it is gradually
oxidised to phosphorous and phosphoric acids. 2 - 3

It is even more readily oxidised by concentrated nitric acid than
is white phosphorus, the product in both cases being a phosphoric
acid (V/.c.). It is not affected by concentrated sulphuric acid in the
cold, but on heating SO 2 is evolved and oxidation of the phosphorus
takes place. It is not affected by aqueous alkalies but dissolves in
alcoholic potash, 4 giving a deep red solution from which acids repre-
eipitate the red element containing a suboxidc.

It combines with halogens, although not so violently as white
phosphorus ; with chlorine, either gaseous or in aqueous solution ;
with bromine in the cold ; and with iodine on warming.

Red phosphorus is less soluble than white in all solvents. In water
and alcohol it is almost insoluble. It is somewhat soluble in ether
and in hot acetic acid, from which it is reprecipitated by water. It is
slightly soluble in phosphorus trichloride. These solubilities refer to
the ordinary preparation, which, as shown on p. 82, usually contains
residual quantities of the white form. Red phosphorus is able to
reduce salts, especially those of the " noble : metals, in aqueous
solution on boiling. Salts of mercury are reduced to the metal ; those
of gold and silver give insoluble phosphides ; while ferric and stannic
salts are reduced to ferrous and stannous respectively. 5

Scarlet Phosphorus, sometimes called ic Schenck s phosphorus," 6
can be prepared by boiling a 10 per cent, solution oC phosphorus in
phosphorus tribromide. It appears to be an intermediate form
between the white and the red. The conditions of its formation and
its physical properties, so far as these arc known, arc more fully
described under ci Scarlet Phosphorus," p. 42.

The chemical properties partly resemble those of white, parti} those
of red, phosphorus. It does not glow in the air, but docs so in ozone.
It is rapidly attacked by alkalies, giving hypophosphite and phosphinc
which is not spontaneously inflammable. It is coloured intensely
black by ammonia. It dissolves in aqueous alcoholic potash giving
red solutions from which acids precipitate a mixture of phosphorus
and solid hydride. It dissolves in phosphorus tribromide to the extent
of about 6-5 gram in 100 grams of the solvent at about 200 C.
It is said to be non-poisonous ; its physiological properties probably
resemble those of red phosphorus (r/.t?.).

Colloidal Phosphorus. An aqueous collosol has been prepared
by boiling commercial red phosphorus with water to which has been
added stabilising substances such as gelatin, dextrin or sucrose, etc.
Contrary to the usual order, the last-named substances seem to have
the strongest effect in protecting the phosphorus against coagulation
by salts. 7 When an alcoholic solution of white phosphorus is poured
into water a colloidal solution is obtained. 8 A colloidal solution in

1 I-Iittorf, Ann ilen, 1865, 126, .193; Chem. Jv>;-;.?, .18(50, 13, 133; Schrottor, J.pralt.
Clitni., IS/53, [1], 58, .158.

2 Baker and Dixon, Proc. Roy. $w. t 1S80, 45, 1.

3 Personne, Compt. rend., 1857, 45, ] 13.

4 Michaelis and Arendt, Annuk.n, ] 902. 325, 301. 5 Rosonstem, lor., cit.
c Schenck, Bcr., 1902, 35, 351; ibid., 1903, 36, 97!), 4202.

7 Mullcr, Bcr., 190-1, 37, \\.

s von Weimarn, J. Russ. Phys. Chem. Soc., 1910, 42, 453.

30 PHOSPHORUS.

isobutyl alcohol was made by passing arcs between red phosphorus
suspended in this medium. 1

DETECTION AND ESTIMATION OF PHOSPHORUS.

White phosphorus is easily detected by its well-marked property of
glowing in the dark as well as by its peculiar smell and reducing pro
perties (q.v. pp. 27. 28). Smaller quantities may be detected by the
well-known Mitscherlich test. The material is boiled with water in a
flask furnished with a long glass reflux condenser cooled by air. A
luminous band is seen (in the dark) at the point where the steam is
condensed. The phosphorus may be distilled with steam arid collected
under water in small globules. The distillate will reduce ammoniacal
silver nitrate and mercuric salts. The presence of phosphorus in the
steam may also be demonstrated by allowing the latter to impinge
upon a piece of paper wetted with silver nitrate, which is at once
blackened. Other vapours and gases (such as AsII 3 ) which have the
same effect are not likely to be produced under the conditions. Traces
of white phosphorus in matches may be found by extraction with
benzene. Strips of filter paper soaked in this extract, suspended in
a glass tube and exposed to a current of air at 40-50 C. become
luminescent if 0-01 milligram or more of phosphorus is present. 2

Small quantities of red phosphorus are best detected after oxidation
by the tests given under tc Phosphoric Acid," pp. 170, 180.

Phosphorus combined in organic compounds, or as phosphide in
metals, is also estimated after oxidation by precipitation as ammonium
phosphomolybdate or magnesium ammonium phosphate, with the sub
sequent treatment which is described on pp. 181-183. The methods by
which the phosphorus is brought into solution vary with the nature
of the material which is being analysed. Organic compounds are
oxidised in a sealed tube with fuming nitric acid or in a flask by a
mixture of concentrated sulphuric and nitric acids.

Alloys of copper and tin such as the phosphor bronzes are dissolved
in nitric acid of density 1-5, and the metastannic acid, which, contains
all the phosphoric oxide, after ignition and weighing is fused with KCN.
The aqueous solution of the melt is freed from tin globules by filtration
and from traces of soluble copper and tin by BUS, then containing all
the phosphorus as potassium phosphate, which is determined as
described below.

Iron and steel are dissolved in ] : 1 nitric acid, the solution evapo
rated to dryness and the residue taken up with concentrated hydro
chloric acid until all the silica is rendered insoluble. The solution
containing the phosphoric and hydrochloric acids is evaporated to
dryness once more to get rid of the latter acid, and the residue then
taken up with nitric acid and ammonium nitrate solution and pre
cipitated with ammonium molybclate.

Small quantities of phosphorus may be estimated quickly by the
molybdate method, the amount of phosphomolybdate being estimated
colorimetrically by comparison in Xesslcr glasses or test-tubes with
a standard prepared under conditions which arc made identical as far
as possible. An account of this estimation is oiven under ct Phosphoric
Acid," p. 182.

* Svedboror, Ber., 1906, 39, 17] 4.

" Schroder, Arbaten Kaiswl. Gesundhcitsamte, 1913, 44, 1.

CHAPTER III.

ALLOTROPIC FORMS OF PHOSPHORUS AND
CONDITIONS OF TRANSFORMATION.

General. Although the allotropic forms of phosphorus are not so
numerous as those of sulphur, they are better defined ; the differences
between them are more striking. Apart from plastic sulphur, which
is really a supercooled liquid, the forms of sulphur are obviously varieties
of the same element ; the differences are found chiefly in the crystalline
form, the other physical properties not differing much. The contrast
in the appearance and obvious properties of ordinary white phosphorus
and the other varieties is so great that a casual observer would hardly
suppose that they were the same element. If the allotropic forms of
phosphorus are classified by means of their striking properties, then
at least five will be recognised, namely White, Scarlet, Red, Violet
and Black, which show great differences in other physical properties
besides colour, and also in chemical properties. These forms will now
be discussed from the view-points of their histories, preparation and
physical properties, the conditions of their transformation and the
evidence as to their molecular complexity. The chemical reactions and
some physical properties of all the forms arc given in Chapter II.

RED PHOSPHORUS.

Preparation. -The production of this form can hardly escape
observation, since it is present in the residue from the combustion of
white phosphorus in the air.

When liquid phosphorus is heated in a closed vessel or in a non-
oxidising atmosphere, such as one of carbon dioxide, the liquid gradually
turns red and is then converted into a red solid. The change is rapid
at 210 C. and very rapid just below the boiling-point, 280-5 C., of the
white form. Red phosphorus was first prepared in this way by
Schrotter 1 in 1845, and its chief properties were then investigated.

The red form is chiefly amorphous, and of vitreous appearance and
fracture. On prolonged heating it gradually turns violet and exhibits
double refraction. 2

The transformation is greatly accelerated, and takes place at lower
temperatures, in the presence of small quantities of iodine, 3 and also
of selenium. In. the presence of A1C1 3 the transformation occurs in
evacuated tubes below 100 C. 4

32 PHOSPHORUS.

When white phosphorus is treated with liquid ammonia it is con
verted into red phosphorus with simultaneous formation of amide and
nitride. 1 White phosphorus, when dissolved in. turpentine, phosphorus
tribromicle and certain other solvents, is converted into red phosphorus
by heating for several hours at 290 C. 2 Red phosphorus may be de
posited when phosphorus vapoiir is suddenly cooled (see p. 10). and it
was early shown that on account of its small vapour pressure this form
might be condensed in the hotter part of a tube (at 300 C.) from
vapour derived from white phosphorus in the cooler part of the tube. 3
All varieties of phosphorus when strongly heated in sealed tubes may
be converted into yellow liquids which deposit reel crystals at about
550 C,

A survey of the forms of phosphorus is given by Linck, Zeitsch.
anorg. Chem.. 1908, 56, 393.

The red phosphorus prepared by moderate heating may be ground
up with a solution of sodium hydroxide as in the technical preparation
(see p. 10) and may also be extracted with carbon disulphiclc until
the extract is free from white phosphorus. The resulting preparation
is considered to be the purest red phosphorus. 4

Physical Properties. -Density. There is considerable variation
in the values given by different investigators. A preparation which
would answer most closely to the description of " pure " red phos
phorus and prepared as described above has a density which varies
only within the comparatively narrow limits of 2-18 and 2-23. and the
value remains practically constant after long heating at 357 C. The
density of ordinary red phosphorus may be taken then as 2-20 0-02.
Cohen and Olie, 4 to whom these results are due, regard red phosphorus
as a solid solution of the white in the violet form. On long heating at
450 C. the density increased to a maximum, which was held to correspond
with the maximum proportion of the violet form, at a value of about
2-30. Heating to higher temperatures, between 500 and 600 C., so
that the phosphorus became liquid, in some cases increased the density
to 2-3 1, but in others the density diminished, e.g. to 2-24. The increase
in the density on heating above 360 C. was considered by Jolibois 5
to be due to the production of the form which he called " pyromorphic "
phosphorus, which was stable below 450 C., but he also considered
that red phosphorus was a distinct allotropic form, with an interval
of stability from 450 to 6IO C C.

Vapour Pressure. The vapour pressures of red phosphorus are
much lower than, those of liquid phosphorus or of solid white phos
phorus at all temperatures within the experimental range. 6 The latter
arc therefore unstable forms, or are monotropic with respect to red
phosphorus (and equally of course to the A r iolet form).

Thus at 279 C. the vapour pressure of liquid phosphorus is 753
mm., while at 289 C. that of red phosphorus is 23 mm. 5 The pres
sures of red phosphorus are not in equilibrium, but fall slowly as the
solid changes into the more stable " pyromorphic " (violet) form.

1 Stock and Johannsen, Hnr., 1908, 41, 1593.
- Colsoii, Conipi. rend., 1907, 145, 1167; ibid., 190S, 146, 71.
3 Troost and Hantetouilic, Ann.. Ckim. /%*., 1874, [5J, 2, 145.
1 Cohen and Obe, Zeiltcli. pliysihtl. Cheni..", 1910, 71, 1.

5 Jolibois, Co-iti j)!,. rc.nd., 1910, 151, 383.

6 .Hit tori , Aunctk ii, 1865, 126, 193.

ALLOTROPIC FORMS OF PHOSPHORUS.

33

The pressure of the latter, however, appears to increase more rapidly
with rise of temperature than that of red phosphorus, as is seen from the
following table, on account of which 400 C. was given as the transition
temperature 1 by Jolibois.

Red

Phosphorus. 1

"Pyromorphic"

Phosphorus. 1

fC.

p (mm.).

t C.

p (mm.).

289
398
400

23
755

1 798

345

422
430

20 :
710
1045

These measurements agree fairly well with those of Hittorf 2 and of
v. Schrotter. 3

Melting-point. According to Chapman 4 the melting-point of red
phosphorus is 610 C. ; according to Stock and Goniolka 5 620 to
625 C. It is not far removed from that of violet phosphorus. The
variability in the melting-point, vapour pressure and density is ex
plained if red phosphorus is a mixture of various forms and is not
itself a modification of phosphorus. [A c modification " is a state of
aggregation which can. exist in inner equilibrium, and which therefore
is able to behave in a unary manner. ] (See p. 39.)

The Specific Heal of red phosphorus is less than that of white
phosphorus, being 0-1698 to 0-1705 between 15 C. and 98 C. 7

The specific heats determined over other ranges of temperature

t c C. .
Specific heat

0-51 C.
0-1829

0-134 C.
0-2121

Hardness. This is
3-5 on Moh s scale.

0-199 C.
0-2 102

greater than that of white phosphorus, being

Vi o LF/r Pii osri i o K cs.

History and Preparation.- The incipient crystallisation of red
phosphorus, which has been noted already, can be carried to com
pletion by a procedure due to Ilitfcorf, 9 who dissolved red phosphorus in
molten lead, and oil cooling obtained yellowish-red translucent plates
which had a density of 2-34 and belonged to the hexagonal system of
crystals. Later investigators have obtained curved rectangular leaflets

1 Jolibois, /or;. c,t. ~ HittorT, /or. c.lt.

n v. Sohrotter, Annftff.ii, J 8">O, 81, 270.

1 Chapman, Tran,s. C/i.rm.. Hoc.., IS:)!), 75, 7:51.

5 Stock and Goniolka., Uc.r., 11)09, 42, 4510.

f> Smits, "Theory of Allotropy, translated by Thomas (Longmans, \.\} 2 2), p. 240.

7 Renault, Ann. Ckim. Phys., 1853, [3], 38 , 129.

8 Wigand, Ann. Physilc, J907, [4J, 22, 61. 9 Hittorf, he. clt.

34 PHOSPHORUS.

which were transparent, had a steely bine lustre and belonged to the
inonoclimc system. The form prepared in. this manner is known as
" Hittorfs ""or violet phosphorus, with reference to its appearance
en masse (see below). The preparation was repeated by Stock and
Gomolka. 1 Red phosphorus was heated with lead in a sealed tube at
800 C. for 48 hours. After purification from lead and glass (the
former was not completely removed, however), the phosphorus appeared
as brown transparent plates, the density of which, corrected for the
lead present, was 2-31 to 2-33. This form has also been crystallised
from molten bismuth, in which, however, phosphorus is less soluble.

The violet form can also be obtained from some preparations of red
phosphorus by the following treatment. The finest particles are
washed away in a stream of water until only dark steel-blue particles
are left ; these are boiled with 30 per cent, sodium hydroxide solution,
washed again, boiled with 5 per cent, nitric acid, washed with hot and
cold water, then with absolute alcohol and ether, and allowed to stand
until dry in a vacuum desiccator with concentrated sulphuric acid. 2
The density of this preparation is about 2-2 (2-18 to 2-23).

The preparation of violet phosphorus may conveniently be carried
out as follows : The air is displaced, by means of carbon dioxide, from
a hard glass tube, which is then one quarter filled with ordinary phos
phorus, the remainder of the tube containing pieces of lead, preferably
those which have served for a previous preparation. The carbon
dioxide is then removed, the tube sealed on the pump, and placed inside
an iron tube, the space between the walls being filled with magnesia.
The whole is heated in a tube furnace for 8 to 10 hours at a moderate
red heat. After opening., with the usual precautions, the crystalline
phosphorus is removed from the surface and the crystals from the
interior are collected after dissolving the lead in 1 : 1 nitric acid.

Crystals of violet phosphorus apparently identical with Hittorf s
phosphorus have been obtained by maintaining the element at its
melting-point in a scaled tube after start! no- the crystallisation by a
slight supercooling. The tube was opened under carbon disulphidc
and the crystals separated from the white phosphorus in which they
were embedded. They appeared as six-sided leaflets with a charac
teristic angle of 7678 and short rounded obtuse angles at the ends,
the normal or supplementary angle to which was 27-28. Violet
phosphorus from molten lead yielded two kinds of crystals, one of
which was identical with that prepared as above. Both were plcochroic,
and were described as dark orange in a direction parallel to the long
side and lighter in a direction at right-angles to this. Their density
was 2-35. 3

Violet phosphorus, when rubbed to a very fine powder, assumes a
red colour. It still exists, however, in the most stable form, i.e. the
violet, because it still exerts the characteristic lower vapour pressure
of this modification (p. 35).

Physical Properties. Density. The evidence on which this
depends has been reviewed (p. 32). On the whole it seems improbable
that the density is much, if at all, higher than 2-30.

Melting-point. Tins determination has of course been carried out

ALLOTROPIC FORMS OF PHOSPHORUS. 35

in sealed tubes. The values of different experimenters do not agree
very well; they are : 630 C., Chapman; 1 600-610 C., Stock and
Gomolka ; 2 597 C. (when heated slowly) Stock and Stamm. 3 Fusion
and solidification proceed as if the phosphorus were not a pure sub
stance, but a mixture (see p. 39). The melting-points observed
were also triple points when, as usual, the phosphorus was sealed
in an evacuated tube. The melting-points are lower if the tempera
ture of the bath is raised very slowly. In a bath at constant tem
perature the melting-point was found to be 589-5 C. by Smits and
Bokhorst, 4 who used a graphical method (see p. 38) in interpreting
their results.

Vapou? Pressure. The determination of the values given below
was beset with considerable difficulty," especially that of securing inner
equilibrium in the solid phase. The curve lies below that of liquid
phosphorus, which is unstable with respect to the violet (and red)
forms up to the melting-point, 589-5, of violet phosphorus. The
pressure at tins triple point is 43-1 atm., while that calculated from the
thcrrnodynamical equations (v. infra) is 42*9 atm.

VAPOUR PRESSURES OF SOLID VIOLET PHOSPHORUS. 4

f C.

308-5

346

379-5

408-5

433-5

450-5

p (atm.) .

0-07

0-13

0-35

i 0-79

1-49

2-30

i

r c.

463-5

472-5

486-5

505

515

522-5

p (atm.) .

3-18

3-88

5-46

8-67

10-43

11-61

j

/, c.

50 i

578

581

587-5

588

589

589-5

-/; (atm.) .

24-2

34-35

36-49

41-77

42-10

42-6

; 43-1

;
i

It has already been shown (p. 33) that red phosphorus probably
is not a unary substance, and that the difference between the vapour
pressures of red and violet phosphorus below about 400 C. are probably
due to the non-equilibrium conditions in the red form. Even in the case
of the more uniform violet modification, however, time is required for
the establishment of equilibria with vapour, and the values of the
pressures even up to 500 C. are affected by an uncertainty on this
account. Condensation of vapour proceeds in general more slowly
than vaporisation, and especially is this the case where there is a great
difference between the molecular complexities of the vapour and of the

solid. . .

II rats of Vaporisation, Sublimation and Fusions These latent
heats have* been, obtained from the respective pressure-temperature

1 Chap man, loc. ciL

2 Stook and Gomolka, Inc. cit.

Stock rmd Stamm, 7>.r., 1913, 46, 3497.

1 Smits and Bokhorsfc, Zc.Usch. ph.yxt.kfd. Cliem., 1916, 91, 248.

* Not a. A glass manometer of difficultly fusible glass was used. Jackson, J. Chem.

&>c., 1911, 99, iOGG.

5 Smits, ; Theory of Allotropy^ pp. 225 el seq.

36 PHOSPHORUS.

relations of the liquid and solid violet phosphorus (p. 38). The
Clausius equation

in which it is assumed that the vapour (P 4 ) obeys the gas laws, is
integrated and thrown into the form

(I)

If Q, the latent heat, does not vary with the temperature, a straight
line will be obtained by plotting Tlnp against T. This is so in the case
of liquid violet phosphorus. The graph of liquid white phosphorus is
slightly curved, and is a prolongation of that for liquid violet phosphorus.
The integration constant c is obtained from the equation

_ T

f 2 A 1

where a is the angle between the graph and the axis of abscissa?. By
introducing the c values into equation (1), the values of Q are obtained

T T T
for the mean temperatures 2 ^ I .

For liquid violet phosphorus c = 0-6, Q = 9,900 calories (from 551 to
591 C.), mean temp. 571 C.

For liquid white phosphorus c = ll-l, Q -12,100 calorics (from 160
to 360 C.), mean temp. 260 C.

Thus the numerical value of Q diminishes by 2.200 calories between
260 and 571 C., and the temperature coefficient a in the equation

is found to be

dQ.

a =-7- = - v -1
dt

This value of a is now introduced into the integrated form of the
Clausius equation, and another equation is obtained which includes the
variation of Q with T and which should apply to the whole vapour-
pressure curve of liquid phosphorus on the assumption that it is con
tinuous. i.e. that the liquid formed at lower pressures is really the
same as that formed at higher pressures. The equations in question
are

Q is found to be 16,400 calories.

Putting equation (4) into the form

Tlnp -i- Z-GTlnt. = - ~i- + cT

ALLOTROPIC FORMS OF PHOSPHORUS. 37

and plotting the left-hand side against T, a straight line should be
obtained, and this is very nearly the ease.

The latent heat of vaporisation of liquid phosphorus at its boiling-
point is calculated from equation (3) and is found to be

QLV = 12,500 calories at Ti, = 553 C. Abs.
Hence we have

!f= 22 - 6

which is nearly the normal value.

The heat of sublimation of violet phosphorus can be calculated from
the pressure-temperature relations in a similar manner. In the first
place, c is calculated by equation (2) (p. 36) between T x =343-5 -- 273
and T 2 = 589*5 -273 and is found to be 18-9. Since the TlnpjT graph
is found to be rectilinear over this range of temperature it follows that
Qsv does not vary much, and it was possible to write the linear
equation

18-9T- 13,050

If the value of QjR is taken as 13,000 calories in round numbers the
heat of sublimation of violet phosphorus works out at 25,800 calories.
This is an abnormally high value as can be seen by comparing the
ratio Qsv/Ts with the normal ratio of about 30. T s is the sublimation
temperature, i.e. that temperature at which the vapour pressure of
the solid is equal to 1 atmosphere. In the present case T s was found
by putting p = I in equation (1) and was 688 abs. or 415 C., the
sublimation temperature of violet phosphorus.
Hence

Qsv 25,800

T s 688

--37-5

the abnormal ratio referred to above. The excess of heat required in
this sublimation is explained as being due to the change from a poly
merised form having a lower energy content into the simpler P 4
molecule. This energy change has been found in a different way as
the difference between the heats of combustion of polymerised and
ordinary phosphorus (see p. 132), i.e. 4x4.1-00 = 17,600 calorics per
mol P 4 . The difference 25,800-17,600-8,200 calorics is the physical
latent heat of change of state solid > vapour.

Finally the molar heat of fusion Q<L is obtained in the usual way
as the difference between the latent heat of sublimation Q^v and that
of evaporation Q_LV at the triple point, 862-5 abs.

QriL =25,800 - 10,200 =15,600 calorics l

Critical Constants. These have been calculated from van dcr
\Vaals ! and other equations of state. Tims ,.^720-0 C., /;,. = 93-3
atin. 2 or Z,. = 075 C., _p,. =80 aim. 3 Another estimate is ^. = 095 C. ; ll
this value has been used to calculate the critical pressure by an

1 Smits, loo. cit.., p. 33.

2 Marckwald and Helmholtz, loc. cit.

3 van Laar, Proc. K. A/cad. Wctcnsch. Amsterdam, 1917, [2], 20, 138.

1 Whl HT t dflflri.v. flcn Fran.. F/r^/Y/ Kwnxt 101S

38

PHOSPHORUS.

extrapolation of the vapour-pressure curve from i=634- c C. The value
of p c so found is 88-2 at.ni. 1 or 82-2 atm. 2

THEORY OF THI-: ALLOTROPIC Foiois.

The phase diagram (.fig. 3) constructed with the aid of the table on
p. 35 and the data on pp. 22, 23 represents the closest approach to
equilibrium conditions which has been attained. 2 Pressures at lower
temperatures are magnified in order to show all changes on one
diagram. Lines are lettered, as usual, with the phases which can
coexist; W 2 = white phosphorus formed at high pressures, W, =

-80 44-1 _ 583-5 695 J

FJC. 3. Pressure-temperature .Diagram of .Phosphorus. 1

ordinary white phosphorus, L= liquid phosphorus, G = vapour or
gaseous phosphorus, V= violet phosphorus.

Curves which refer to unstable forms are represented by dotted
lines, as also are the transformations of the condensed forms. The
slopes of these curves can be calculated when the specific volumes of
the two forms arc known; thus the W^-pL line should slope slightly
to the right, since the specific volume of liquid phosphorus is o-reater
than that of solid white phosphorus near ~-14-l C. The melting-point
is therefore raised by an increase of pressure.

The solid white form really is only in a state of false equilibrium,
being unstable with respect to the polymerised forms at all realisable
temperatures. There are also the other forms red, scarlet and black
phosphorus the behaviour of which under definite conditions of
pressure and temperature cannot be stated with any certainty.
Further, the melting-point even of the well-crystallised white phos
phorus can be made r to vary under certain conditions (sec p. 15).
In fact, all the condensed phases, liquid and solid, behave as mixtures
rather than as single pure substances.

1 Sinits, loc. clt. - Smits and Bokhorst, loc. c-i.t.

* Note. The break at 44-1 should not appear in the V-j-G curve since this will fall
asymptotically to zero pressure.

ALLOTKOPIC FORMS OF PHOSPHORUS. 39

The existence of two or more molecular speeies is definitely postu
lated by Smits as follows : 1

(1) "Every phase, and therefore also every crystalline phase, of

an allotropic substance is a state which, in certain circum
stances, can behave as a poly-component phase."

(2) Ci The cause of this behaviour must be assumed to be the

complexity, i.e. the existence of different molecular species,
which are in inner equilibrium when the behaviour of the
system is unary, or in other words when it behaves as a one-
component system."

In the case of phosphorus there are probably several " molecular
species, " but the phenomena at temperatures which are not too high
can be explained rationally by assuming only two Pa, which is white,
with a low melting-point and high vapour pressure, and P8, which is
violet, with a high melting-point and low vapour pressure, and which
probably is highly polymerised.

The density of the vapour is the same whether it is derived from
white or red phosphorus, and at lower temperatures and not too low
pressures corresponds to molecules P 4 .

In the liquid the pseudo-components are supposed to be in a state
of dynamic equilibrium which shifts with the temperature, but does
not readjust itself instantaneously on sudden changes.

The solids, at any rate the polymerised forms, are regarded as solid
solutions of Pa and P/3 in varying proportions. Temperature-concen
tration diagrams similar to those representing a two-component system
have been constructed for these pseudo-components.

When the liquid is heated to between 400 and 500 I . it is highly
supercooled with respect to violet phosphorus, which crystallises with
explosive violence. When, however, the vapour is cooled rapidly so
that the liquid passes rapidly through this range down to 30 C., the
liquid white phosphorus, which is richer in Pa, and thus approximates
more closely to the composition of the vapour, is deposited lirst, and
subsequently solid white phosphorus, which also resembles the liquid
and the vapour much more closely than docs the polymerised form.
This appearance o(: a metastablc rather than a stable form was pointed
out long ago by Fraukcnhcim, 2 and stated formally as a generalisation,
called by Ostwalcl 3 the Law of Successive Transformations, thus :
" When a given chemical system is left in an unstable state it tends to
change, not into the most stable form, but into the form the stability
of which most nearly resembles its own, i.e. into that transient or
permanently stable modification whose formation from the original
state is accompanied bv the smallest loss of free energy."

The condensation of phosphorus vapour, however, docs not neces
sarily yield white phosphorus ; much depends upon the temperature
to which the vapour has been heated and the rate of cooling.

It was noted by Ilittorf d that the vapour evolved by red phosphorus
at 41-0 C. was deposited in the yellow form. But Arctowski 5 found
that when red phosphorus was heated in a vacuum at 100 C. it sublimed
and condensed in the same form. This phenomenon was investigated

40 PHOSPHORUS.

in detail by Stock, Schroder and Stamm. 1 The phosphorus was in
troduced in varying amounts into a sealed quartz tube, heated to
various temperatures and suddenly cooled by immersion in water.
Cooling from the temperatures stated in the first column of the following
table gave the products described in the second column :

Temperatures, C., from

which. Sudden Cooling

was efieeted.

Appearance of Product.

400 [ Colourless drops.

450 ; Pale yellow drops.

550 Distinctly yellow drops.

600 Drops with a few purple flakes.

700 ! Some brownish-red solid.

000 Opaque brownish-red solid.

1000 ! Denser and more opaque.

1200 ! Phosphorus vapour at 5 mm. gave entirely
! red phosphorus.

An examination of the behaviour of red and violet phosphorus (and
indeed all solid forms) in the light of this theory leads to the conclusion
that they are mixtures, with the difference that while violet phosphorus
is capable of behaving in a unary manner, red phosphorus is not.
Violet phosphorus is a mixture, because when it is heated to 360 C.
in a vacuum, and the vapour is thus rapidly removed, the vapour
pressure falls. 2 The inner equilibrium has not in these circumstances
time to adjust itself to the loss of the volatile Pa molecules, the residue
becomes poorer in this kind and therefore has a lower vapour pressure.
The production of red phosphorus below 400 C. may be explained
partly by an increa.se in the proportion of Pa molecules in the solid
solution of the pseudo-components, but principally by a delay in the
establishment of the equilibrium, which leads to the production of
solid solutions still richer in Pa. which are not in equilibrium but which
constitute the ordinary red phosphorus. This therefore is not an
allotropic modification, if such a modification is defined as a substance
which can exist in inner equilibrium and which is able to behave in
a unary manner.

BLACK PHOSPHORUS.

General. This form must not be confused with the black substance
which appears on the outside of sticks of white phosphorus which have
been exposed to light, and which is neither a definite form nor a pure
substance. The preparation of a dark substance by the sudden cooling
of phosphoiTis could not be repeated, and this result probably was also
due to impurities.

Black phosphorus was discovered by Bridgrnan, 3 who prepared it
by subjecting white phosphorus at 200 C. to pressures of 12,000 to
13,000 kilograms per square centimetre.

1 Stock and Stcinim, lltr., 1913, 46, 3497. Sec also ibid., 1910, 43, 4510.

2 JLcmoine, Ann. Chlm. P/i-ys., 1871, [4], 24, 129; Sinits and Bokhorst, toe. ciL, p. 288.

ALLOTEOPIC FORMS OF PHOSPHORUS. 41

Physical Properties. The density, 2-69, is much higher than
that of violet phosphorus. The vapour pressures were found to be
lower than those of the violet element at the same temperatures :

Black Phosphorus,
p (mm.).

357-1
445-2

In spite of this relation between the vapour pressures the violet form
could not be converted into the black at ordinary temperatures. Later
investigations showed that the black form probably is only in a state
of false equilibrium or suspended transformation at ordinary tempera
tures and pressures. 1

The black phosphorus was with difficulty freed from the kerosene,
through which pressure had been applied, by heating in evacuated
tubes to 550 C. The vapour pressures of the product (which might
also of course have been altered by this treatment) were now almost, if
not quite, equal to, and above 560 C. greater than, those of the violet
form. The conversion of the black into the violet was effected by
heating in the presence of about 1 per cent, of iodine at 480 C. or
without the iodine at about 575 C.

It has already been mentioned that black phosphorus has a greater
electrical conductivity than other forms, and is therefore to be con
sidered as the most t; metallic variety. 2 The conductivity, however,
like that of graphite, increases with rise of temperature, and this form
is therefore only pseudo-metallic.

X-ray Data. The structure of black phosphorus has been cal
culated from the X-ray reflection spectrum, using the powder method
of Dcbye and Schcrrcr. It is a rhombohedral space-lattice having a
characteristic angle of 00 47 , and a side of 5-96 A. The unit cell
contains 8 atoms, and therefore the volume of the unit molecular
aggregate is 3

where 2-609 is the density, A, of black phosphorus and 1-65 x 10~ 21 is

the mean value of the constant d \! ~- T in which d is the distance

v M.

between the diffracting planes.

Black phosphorus and combined phosphorus give characteristic
absorption spectra for X-rays, the limits of wavelength being different
in the respective eases. Red phosphorus shows two limits, which are
those characteristic of black and of combined phosphorus. 4 The

1 Smits, licyor and "Bock, Proc. K. Ahid. VVct.c/i.xch. Anidtrdam, 10or>, 18, U ( J2.

2 Brid^maiC J. Amcr. Chcm. Soc., 19M-, 36, li -i-l.

3 Linck arid Jun.u, Zufxch. aiiory. Chf-.m., ]i)2r>, 147, 288.

42 PHOSPHORUS.

absorption coefficient for X-rays is 5-68, as compared with 569 in the
case of lead. 1

In its chemical properties black phosphorus is on the whole similar
to red phosphorus. It ignites in air at about 400 C., and is insoluble
in carbon clisulphide.

SCARLET PHOSPHORUS, AXD THE TRANSITIONS TO
VIOLET PHOSPHORUS.

It has already been shown that the transition through the various
grades of red phosphorus to violet phosphorus proceeds continuously
as higher temperatures and longer times of heating are progressively
applied. Liquid phosphorus, when in the early stage of transforma
tion, shows a fine scarlet colour and probably then contains the form
known as scarlet phosphorus or Schenck s phosphorus, from its
discoverer.

Preparation. Scarlet phosphorus is prepared by exposing to light
a solution of phosphorus in carbon clisulphide or carbon tetrachloride,
or by boiling a 10 per cent, solution of phosphorus in phosphorus tri-
bromide. 2 In the latter case the product contains considerable quan
tities of the solvent, in which it is slightly soluble. The solvent may,
however, be removed by reducing the trihromide with mercury at a
temperature over 100 C. The remaining tribroinide and also the
mercuric bromide may then be extracted with ether. 3 The lighter
coloured preparations are more reactive than the darker, on account
no doubt of their finer state of division.

It may also be rioted that liquid phosphorus prepared by melting
in sealed tubes under high pressures may deposit scarlet crystals.

Scarlet phosphorus has a density of 2-0, i.e. slightly less than that of
red phosphorus. It is isotropic, and in this respect resembles red
phosphorus which has been prepared at comparatively low tempera
tures. Red phosphorus which has been prepared at higher tempera
tures shows distinct evidence of crystalline structure.

Scarlet phosphorus is thus a transitional form and can be converted
into the red variety by heating for some time at 300 C. in an atmosphere
of carbon dioxide.

The chemical properties of the various Cor ins of phosphorus have
already been described (Chap. II., pp. 2720).

THE ATOMIC WEIGHT OF PHOSPHORUS.

Historical. In his tables published in 1818 Berzclius 4 gave
31-36 as the atomic weight of phosphorus. Other values obtained
before and after this time did not agree even so well as this with the
value accepted to-day. The reactions principally employed in this
early period were the displacement of gold and silver from their chloride
and sulphate respectively by elementary phosphorus. These reactions.

1 Auren, Phil. May., 1917, [G], 33, 4-71. Further references include: Turner, Phyx.
fitview, 1925, [2], 26, 1-13; Bosc, Ibid., 192(5, [2 i, 27, 52 J . McLennan and Clark, Pioc. Roy.
Soc., 1922, 102, A, 405; Allison, J. Washington Acrid., 11)2(5, 16, 7.

2 Schenck, Ber., 1902, 35, 351; ibid., 1903, 36, 979 and 4202; idem, Zdlxch. Elcklro-
chem., 1905, n, 117.

3 Wolf, Ber., 1915, 48, 1272.

4 Berzclius, Schweigger s J., 1818, 23, 119; " Lehrbuch," otli ed., vol. iii., 1845, 1188.

ALLOTROPIC FORMS OF PHOSPHORUS. 43

he assumption that one atom of phosphorus precipitates -n of an
a of gold and 5 atoms of silver, led to the weighted mean just
;ed. The reactions are, however, in reality rather complex (see
S). It happened that the right condition, i.e. an excess of silver
hate, was chcseii to give the ratio P : 5Ag. If, however, the metal
mpletely deposited the ratio is P : 4Ag nearly.

>chrotter 1 determined the ratio of the element to its pentoxide
burning a weighed quantity of amorphous phosphorus in dry
>*en and weighing the oxide. The method is fraught with many
unities. Uncoiisumed phosphorus was carried forward, and the
bustion had to be completed in the successive bulbs in. which the
iuct was collect cd and weighed. It is also probable that backward
isioii or other contact with water vapour introduced an error. The
.mum atomic weight deduced from these experiments was 30-04,
naximum 31-06 and the mean 31-03. But on account of the known
mpletcness of the combustion the value 31-00 was assigned.
?his experimental result happened to agree with that of Dumas, 2
by means of the ratio PC1 3 to AgCl found P =3I-0 4 , a result which,
ig the probable accuracy as 1 in 300, is not affected by recalculating
i Dumas ratios with our fundamental atomic weights.
)eterminations of the molecular weight of phosphme by the method
miting densities led to atomic weights of 30-98 3 and 30-91. 4 The
pressibility of phosphine was not known, however, with sufficient
racy to allow a reliable calculation of the limiting density,
n an attempt to settle the question by a comparison of all the
methods known at the time, v. dcr Plaats 5 decomposed silver
ite with phosphorus, burned red phosphorus to the pentoxide and
determined the ratio of silver to its orthophosphate. The results,
d on Ag- 107-90, are

latio determined . P : 5Ag Ag,PO 4 : 3Ag 2P : P 2 O 5

Atomic weight . . 30-93 30-99 30-98

he concordance is not sufficiently good to justify a recalculation
n r fundamental value A<>* = 107-88.

Standard Methods and Results.

n the more recent determinations which have led to the accepted
c of the atomic weight the method of decomposition of the halides
been followed with the aid of all the present knowledge as to the
cr conditions for the conversion of halogen hydrides into silver
les. An interesting method has also been worked out by which
r phosphate is converted into the bromide. The results obtained
his method, which will be described lirst, give additional weight to
e obtained from the phosphorus halides.

SchroUor, An;n. Clilni.. Phys., 1853, [3], 38, 13.1; idem, ./. praJcl. CJtti/t., 1851, 53,

.Dumas, Ami. Cld ni. Pkys., 1859, [3], 55, l 2\).
BerUielot, 13., Co-nipt, rend., 1898, 126, 141.5.
Ter-Gazanan, </. Chim. ph-ya., J9U9, 7, 337.
v. dor rkiats, Co-nnpl. rtnd., 1885> 100 52.

44 PHOSPHORUS.

Atomic Weight from the Ratio Silver Eromide to Silver Phosphate.

Sliver orthophospluite, prepared by several methods, one of which
is indicated below, was converted into silver bromide, the equations
involved being :

3AgXO ;5 -XnJIPO^Ag.PO, + 2XaXO 3 -f 11X0 3 . (1)*

The silver nitrate was prepared by dissolving- preeipitated silver in
nitric- acid, which had been twice redistilled and eondensed in a platinum
condenser. The silver was precipitated from the commercial nitrate
by means of ammonium formate. Alter washing, it was fused with
suti ar charcoal, scrubbed, cleaned with ammonia and nitric acid, dis
solved in the redistilled nitric acicl, the solution evaporated to satura
tion, precipitated with more nitric acid, eentrifuged and the nitrate
re-crystallised. The hydrobromic acid was prepared by passing hydrogen
through the purest bromine (see p. 45) and then combining the mixed
gases over heated platinised asbestos. The condensed acid was twice
boiled with more bromine and once with bromine liberated by means
of potassium permanganate, then distilled through a quartz condenser.
The Xa.JIP0 4 was treated with hydrogen sulphide, boiled, filtered
free of a green precipitate (due to iron), then reerystallised fifteen
times. It contained about 0-Oi milligram of arsenic in 10 grams, an
amount entirely insufficient to affect the results. By nephclometry no
chloride or other substances were found which could be precipitated
by silver nitrate in nitric acid solution. XaXH 4 IIPO 4 was prepared
and purified in a similar manner.

The solutions which were allowed to interact were about 0-03 N
in order to avoid inclusions in the precipitates. The latter were well
washed, and allowed to stand in water for at least 24 hours. Silver
orthophosphate was stable in the presence of the moderate amounts of
acid produced by some of the reactions which were tried. If silver
nitrate is poured into excess of disodium hydrogen phosphate the
precipitate settles rapidly, but precipitation is incomplete. If di
sodium ammonium phosphate is poured into silver nitrate the precipi
tate settles rapidly and the solution remains nearly neutral, according
to the equation

Xa 2 XH 4 P0 4 -f 3AgX0 3 = Ag 3 PO 4 + 2XaX0 3 + XH 4 XO 3

By a combination of methods, for an account of which the original
paper should be consulted, pure Ag 3 P0 4 was obtained and dried by
heating in a platinum boat in a current of dry air free from carbon
dioxide. After weighing, it was dissolved in nitric acid and the solution
was poured into an excess of hydrobromic acid, wit.li the precautions
usually employed in the quantitative precipitation of silver bromide.

The ratio 3AgBr : Ag 3 P0 4 varied between 1-34558 and 1-34570 as
extremes, the mean value being 1-34562. It was considered that the
mean value was, if anything, slightly low owing to a possible occlusion

ALLOTROPIC FORMS OF PHOSPHORUS. 45

of AgolIPO 4 . It was noted that the samples of silver phosphate
prepared under more acid conditions gave a ratio of 1-34558, while
those under less aeid conditions gave a ratio of 1-34564. If Ag is
taken as 107-88 and the percentage of Ag in AgBr as 57-4453, the two
mean values of the bromide-phosphate ratio give 31-043 and 31-037
respectively as the atomic weight of phosphorus.

In view of the fact that the methods to be described each have
their own sources of error it seems that the phosphate results should
be taken into account in assigning the atomic weight.

Katios PBr 3 : SAgBr and PBr. : SAg.

The preceding method is open to the criticism that silver ortho-
phosphate contains only 7-4 per cent, of phosphorus. Phosphorus
tribromide is somewhat better in this respect, containing 11-5 per cent,
of phosphorus; but on the other hand the preparation and quantitative
decomposition of this compound in a manner suitable for atomic weight
determinations present great difficulties, the nature of which is apparent
from the following narrative. 1

Ouiline of Process. Pure dry bromine was allowed to act on pure
dry phosphorus in a vacuum ; the PBr 3 was distilled into receivers
which were sealed and weighed, then decomposed by breaking under
an ammoniacal solution of hydrogen peroxide. The solution was
acidified with nitric acid and the bromine precipitated and weighed
as silver bromide.

The Reagents. The water, nitric acid and ammonia were purified
by redistillation and the usual methods, and the silver by the methods
in common use for its preparation as a. standard element in atomic
weight determinations. The hydrogen peroxide was a c.p. sample
free from sulphuric and halogen acids. The nitrogen used in the
preparation of the PBr 3 was prepared by passing air and ammonia over
heated copper gauze (see this Vol., Part I., p. 25). The phosphorus was
twice distilled with steam in an all-glass apparatus. The bromine was
distilled from concentrated potassium bromide (which removes all but
a trace of chlorine), then converted into potassium bromide by action
on a solution of potassium oxalate. To remove iodine the solution of
potassium bromide was boiled with some of the partly purified bromine,
and finally with small portions of potassium permanganate. It was
then evaporated to diyness and fused. From this iiised potassium
bromide bromine was prepared by dissolving in water, adding sulphuric
acid and enough potassium permanganate to liberate three-quarters
of the halogen. This was distilled a second time from the bromide, which
was nearly pure. The separated bromine was dried by resublimed phos
phorus pentoxidc, from which it was distilled immediately before use.

Preparation of Phosphorus Tribromide. An excess of bromine was
necessary on account of the solubility of phosphorus in PBr 3 . Distilla
tion of this from red phosphorus yields a product winch contains too
little bromine. The phosphorus (14 grams) was freed from water bv
pressing between hardened filter-papers and placed in a distillation
flask containing dry nitrogen. The flask was then placed in boiling
water and the contents subjected to a current of dry nitrogen, with
shaking, to eliminate all steam from the liquid phosphorus. The
1 Baxter, Moore and Eoylston, J. A-mer. Chem. SGC., 1912, 34, 259.

4(5 PHOSPHORUS.

ilask was then evacuated and elosed. It was cooled with ice-water, and
the calculated amount of pure dry bromine admitted gradually from a
tap funnel. After addition of nearly the theoretical amount of bromine
the PBr- in the upper part of the flask was decomposed with hot water
and more bromine admitted until the tribromide assumed a reddish
colour due to excess of bromine, when such excess amounted to a few
centigrams. Dry nitrogen was then admitted so as to produce a
slight excess pressure, and the tribromide then fractionally distilled in
a vacuum, the fractions being collected in a number of receivers placed
in series. In this distillation a residue of a few grams was left in each
of the first two receivers, this containing any dissolved phosphorus
which was present. The bulk of the distillate in the third receiver now
contained a slight excess of bromine. This was removed by bubbling
through the warm liquid vapour derived from the second receiver.
This process was continued for some time after the distillate became
colourless. The residue in the third receiver, about 100 grams, was
redistilled into several small bulbs, which were then sealed at their
capillary junctions. The first and last samples collected showed
equally a slight yellow tint when warm. This is probably characteristic
of the pure tribromide.

A bulb and contents, after weighing, was broken by shaking
under a solution of ammoniacal hydrogen peroxide in a stout flask
closed bv a glass stopper. The decomposition of the PBr 3 was com
plete in 5 minutes, but the flask was allowed to stand for 24 hours
with occasional shaking in order to effect complete absorption of the
fumes of XH 4 Br. The cooled solution was filtered through a small
paper, which was burned at as low a temperature as possible. All the
broken glass was thus collected and weighed. The filtrate was acidified
with nitric acid, introduced by a thistle funnel at the bottom of the
solution, in order to avoid any loss of bromine set free locally and
temporarily. The bromine, present as hydrobromic acid, was then
determined in two ways

(a) By finding the amount of silver which combined with it

completely.

(b) By weighing the silver bromide precipitated.

Both determinations were carried out with the same solution.

(a) A quantity of silver which was equivalent to the bromine
present within a few tenths of a milligram was dissolved in nitric
acid with the usual precautions, the solution treated with an excess
of nitric acid and added to the solution prepared from the PBr 3 with
constant agitation. After standing, portions of the clear solution were
tested in a nephelometer for excess of bromide or of silver. The
bromide was always found to be in slight excess. The solution was
then adjusted with X/100 AgX0 3 , shaken, allowed to stand, and the
adjustment repeated until the amounts of silver and of bromine were
again equivalent. After standing for a week, a nephelometer test
showed that there was again an excess of bromide, apparently clue to
the diffusion of occluded bromide out of the precipitate. "The de
ficiency of silver was again made up, the final end-point being reached
in about a fortnight.

(/;) The precipitated AgBr was washed by decantation with water
and collected on a Gooch-Munroe-Neubauer crucible, which was then
heated gradually to 200 C. and kept at that temperature for 18 hours

ALLOTROPIC FORMS OF PHOSPHORUS. 47

or more. After cooling, the bromide was weighed by substitution
for a similar counterpoise. The precipitate was then transferred to a
porcelain crucible and fused. The loss in weight on fusion seldom
amounted to more than 0-001 per cent, of the weight of the precipitate.
The clear yellow colour of the fused bromide was an additional guarantee
of purity," since a very small percentage of impurity is sufficient to
produce a perceptible darkening. The amounts of AgBr which were
dissolved in the filtrate and wash water were also determined.

The concordance of the two methods (a) and (b) could be checked
bv means of the ratio Ag : AgBr, which as a mean of seventeen results
was 0-574462. This is almost identical with the value 0-574453 which
had already been considered to be the most probable. 1 Three series of
determinations were carried out, each including five to eight separate
experiments, and there were thirty-six in all. The means of each of
the sets carried out according to methods (a) and (b) are given in the
following tables. The atomic weight of phosphorus is calculated from
these results using Ag = 107-880 and Br = 79-916.

WEIGHTS OF PHOSPHORUS TRIBROMIDE CORRESPOND
ING TO THREE PARTS BY WEIGHT OF SILVER AND
OF SILVER BROMIDE, AND VALUES OF THE ATOMIC

WEIGHT OF PHOSPHORUS.

Method (ft). Method (6).

Ratio P.Br 3 : 3Air. Atomic Weight. : Ratio PJ3r 3 : 3 AgBr. Atomic Weight,

0-836660 31-031 0-480629 31-033

0-836640 31-022 0-480628 31-032

0-836644 31-025 : 0-480611 j 31-022

0-836648 31-026 0-480623 31-029

A given percentage error in the experimental work is multiplied nine
times in the calculation of the atomic weight, i.e. an experimental
error of 0-01 per cent, affects the calculated atomic weight of phos
phorus by 0-027 unit. The highest individual value was 31-0 -10, the
lowest 31-013. which corresponds almost exactly to 0-01 per cent,
accuracy in the experimental work. Of the thirty-six results, however,
twenty-seven fell between 31-035 and 31-021, a fluctuation only half
as great. The variations in the mean results arc about 0-002 per cent.,
which corresponds to about 0-006 unit in the atomic weight. The
means of the means agree to 0-003 unit. Giving a slightly greater
weight to method (ft) the investigators deduce from these results an
atomic weight oP 31-027.

4s PHOSPHORUS.

Ratios PC/ 3 : SJgCl and PCI, : 3Ag.

Since- the percentage of phosphorus is considerably higher in the
chloride, than in the bromide it was considered that the atomic weight
niio-ht be deduced with even greater accuracy from the former com
The methods used were similar, although not identical ;

the most important points of difference will be noted.

Chlorine, prepared from manganese dioxide and pure IIC1 was
liquefied and the dry gas evolved from the liquid was admitted to the
drv phosphorus in a vacuum. In this case phosphorus pentachloride
was formed in considerable quantity and was removed only by several
distillations. It could not be inferred with such confidence that the
trichloride was free from pentachloride as that the tribromide was free
from bromine. The trichloride was decomposed and oxidised in the
manner already described. In the subsequent estimation of the silver
chloride less difficulty was experienced in freeing this from occluded
chloride, but more difficulty in determining accurately the amount of
silver chloride remaining in solution. It was found possible, however,
to diminish the solubility by adding an excess of silver nitrate solution
and partly washing the precipitated, chloride with this solution.

The silver chloride was dried at 190 C. and weighed as usual in
series III. In series I and II the exact amount of silver nitrate re
quired for complete reaction was found by adjustment, using the
ncpheloineter as already described. The means of the experiments in
each series are given in the following table :

WEIGHTS OF PHOSPHORUS TRICHLORIDE CORRE
SPONDING TO THREE PARTS BY WEIGHT OF SILVER
AND OF SILVER CHLORIDE.

Method (6).

i i

Ratio PCi 3 : 3Ar. ! Atomic Weight. Ratio PC], : 3AgCl. j Atomic Weight.

0-424509
0-424506

31-017

31-010

i ;

0-319509

31-022

The average atomic weight is given as 31-0] S. The investigators
remark : iw If the trichloride actually contained a trace of penta
chloride it would account for the fact that the average result of this
research, is very slightly lower than that of the tribromide work."

General Conclusions. The three main determinations of the
atomic weight of phosphorus with their results are

From - - Ag,P0 4 ; PBr 3 j 1>C1 3

Atomic weight . . 31 -01- ;

1 Baxter and Moore, J. Amcr. Chem. Soc., 1912, 34, 1644.

ALLOTROPIC FORMS OF PHOSPHORUS. 49

In the fixing of standard atomic weights the results obtained from
PBr 3 have been preferred for reasons that will be evident from the
data already adduced. Although these results appear to be the least
affected by systematic errors, nevertheless they involve such errors,
and it seems hardly justifiable as yet to trust the results as far as
units in the fifth significant figure. It may. however, be asserted with
the greatest confidence that the atomic weight is known to be

31-03^0-01

Thus there is no doubt that all chemical determinations concur in
assigning to phosphorus an atomic weight slightly greater than 31-00.
Nevertheless phosphorus, when analysed by the method of mass
spectra, has hitherto proved to be a pure element ; no isotopes are
present to account for the departure from the rule of whole numbers.
There are two possible explanations

(1) " The whole number rule is not, and never was supposed to be,
mathematically exact, for this would imply an identical packing effect
in the case of ail atoms, an exceedingly improbable supposition." x

(2) It is possible that an isotope accompanying P= 31-00 in small
amount has not yet been detected, as in the case of sulphur (S =32-06),
the spectrograph of which shows two faint lines at 33 and 34, originally
ascribed to hydrides, but afterwards shown to be due to isotopes of
higher atomic weight. 2 Opinions founded on later work, however,
have been less favourable to this hypothesis, and slight deviations from
the whole number rule (on the oxygen scale) are now recognised in the
case of t: pure " : elements, as appears from the quotation below. 3

The purely chemical evidence as to the atomic weight of phosphorus
is supplemented by that derived from mass spectra. 3

i: Ever since the discovery of the whole number rule it lias been
assumed that in the structure of atoms only two entities are ultimately
concerned, the proton and the electron. If the additive law of mass
was as true when an atomic nucleus is built of protons plus electrons
as when a neutral atom is built of nucleus plus electrons, or a molecule
of atoms plus atoms, the divergences from the whole number rule
would be too small to be significant, and. since a neutral hydrogen atom
is one proton plus one electron, the masses of ail atoms would be whole
numbers on the scale 11 = 1. The measurements made with the first
mass-spectrograph were sudiciently accurate to show that this was not
true. The theoretical reason adduced for this failure of the additive
law is that, inside the nucleus, the protons and electrons arc packed
so closely together that their electromagnetic fields interfere and a
certain fraction of the combined, mass is destroyed, whereas outside the
nucleus the distances between the charges are too great for this to
happen. The most convenient and informative expression for the
divergences of an atom from the whole number rule is the actual
divergence divided by its mass number. This is the mean gain or
loss per proton when the nuclear packing is changed from that of
oxygen to that of the atom in question. It will be called the packing
fraction of the atom and expressed in parts per 10,000. Put in

1 Ast.on, " Isoiopts" chap, viii., par. 9(5 fl., Arnold, 1923; Phd. Jfug., 1020, [6], 40,
G2S; 1925., [6], 49, 1191.

2 Aston, Sat arc,, 1920, 117, 89;>. 3 Aston, Proc. Roy. Soc., 1927, A, 115, 487.
vnr ATI TT /.

50 PHOSPHORUS.

another way, if we suppose the whole numbers and the masses of the
atoms to be plotted on a uniform logarithmic scale such that every
decimetre equals a change of 1 per cent., then the packing fractions
are the distances expressed in millimetres between the masses and the
whole numbers.

Phosphorus. The element was introduced m the Jtorm 01 phosphine,

which gives the lines P, PH, PH 2 , PH 3 . If plenty of carbon monoxide
is present its line will be practically unaffected by the presence of small
quantities of Si 28 , inevitably present and of mass so far unknown.
So that the series CO : P : PH 3 can be employed to give values for
phosphorus. . . . From the known values of H, C and O and the sum
of the two intervals the packing fraction 5 of P can be calculated.
The mean of six consistent values corresponds to a packing fraction
-5-6 and therefore a mass 30-9825. No mass-spectrum has given the
slightest reason for supposing that phosphorus is complex, so that it
seems probable that the chemical atomic weight of 31-02 is too high."

The method of limiting densities when applied to phosphine also
gives a lower result for the atomic weight of phosphorus. Phosphine
was prepared from phosphonium iodide by means of potassium
hydroxide, and was fractionated. The densities were investigated at
pressures of 1 clown to 0-25 atmosphere. Assuming a linear relation
between pv and pressure, (pv\l(pv)i is calculated to be 1-0091. If the
normal litre of oxygen weighs 1-4290 gram and the coefficient of devia
tion from Boyle s law per atmosphere is -0-00096, then PH 3 = 34-000
and P- 30-977. x

CHAPTER IV.
PHOSPHORUS IN COMBINATION.

PHYSICAL PROPERTIES.

THE volume which is occupied by the atom of phosphorus when it is
combined with one or two other elements to form liquid compounds
has been deduced from the molar volumes of such compounds on the
assumption that the other elements possess constant and characteristic
atomic volumes in these compounds. Thus, from the molar volumes of
PCI 3 and PBr 3 at their boiling-points Kopp l assigned to phosphorus
the atomic volume 25-2. The exact determinations by Thorpe 2 of the
densities and coefficients of expansion of PC1 3 . PBr 3 , POC1 3 , PSC1 3 ,
POBrCU and PClo(OC 2 H 5 ) gave values for the atomic, volume of
phosphorus which ranged between 24-0 and 26-1, the mean being about
25-3. The value derived from the density of liquid PH 3 (q.v.), using
Kopp s value for hydrogen, is 29-1. These variations do not depend
on experimental errors, nor, in the comparison of such compounds as
PCL and PBr 3 . can they be ascribed to differences in constitution.
It has been suggested that the differences between the molar volumes
of the liquid compounds at their boiling-points (or other temperatures
at which the vapour pressures are equal) and the sums of the atomic
volumes of the liquid elements at the same vapour pressures are also
some function of the affinities which come into play during the com
binations. 3 The volumes measured at the respective boiling-points
are : Cl, 22-76; Br, 26-8 ; 2 P, 20-5; therefore P- 3d =88-8 and
P-f-3Br = 100-9. According to Thorpe also PC1 3 =03-34 2 and PBr 3
= 108-8. 2 The combination with chlorine under conditions of equal
vapour pressure is accompanied by an expansion of 4-5 units, and that
with bromine by 7-9 units, in excess of the values which would obtain
if Kopp s additive law held good. The comparison has been extended
to the oxyhalides 2 and the pentahalides 4 with the result that the
changes of volume on combination were found to be different in each
case.

In attempting to determine the structure of such compounds as
POClo the molar volume of the compound at its boiling-point may be
diminished by that of PC1 3 , 2 leaving 7-8, which is Kopp s value for
oxygen linked to two elements, and leads to a formula C1 9 =P -O-C1.
If, however, the molar volume of POCL is diminished by the atomic
volumes of P and 3C1, the remainder, 12-2, is the atomic volume of

1909,95,445; 1910,97,2032.

~o PHOSPHORUS.

<j~

doubly-linked oxygen, which leads to a formula^ C1 3 ^=P=O. 1 The
present views on valency, as developed, e.g., in this Volume, Part I.,
put the whole matter in rather a different, light.

It is improbable that phosphorus is trivalent in POC1 3 , and further,
in such compounds it is exercising its maximum valency. Since the
atomic volume calculated on the assumption of a double bond between
the phosphorus and the oxygen agrees most closely with the atomic
volume of elementary phosphorus, it is probable that in the liquid
element as well as in POC1 3 phosphorus is exercising this maximum
valency, which includes ci mixed bonds/ 5 thus

P=P

PEE?

See also the discussion on the structure of P 4 O 6 (p. 128).

The Volume of Phosphorus in Liquid Compounds under
Conditions of Maximum Contraction. The volumes which liquid
compounds would occupy if they remained in this state at temperatures
not far removed from the absolute zero represent the closest packing
possible at ordinary external pressure and under the influence of the
internal or intrinsic pressure alone of non-oriented molecules, i.e.
those which are not arranged in a space-lattice. These volumes can be
obtained by shorter or longer extrapolations from the actual observed
liquid volumes.

The formula of Cailletet and Mathias 2 gives the mean isobaric
densities of a liquid and its saturated vapour as a rectilinear function
of the temperature. Thus

in which the meaning of the symbols is obvious, and Z) /2 is half the
limiting density at the absolute zero obtained by the extrapolation.

The specific volumes i\ } (=1//) ) are found in the case of many
liquids to have a mean value equal to 0-20 of v ( . (the critical volume), 3
while according to van der Waals equation 4 they should be equal to
0-33 of iv (t\.=3/>). In cither case the volumes V Q at maximum con
traction are corresponding volumes and should therefore be additivcly
related to those of the constituent elements. It has been shown 5 that
the most closely additive relations arc obtained if the limiting volumes
are calculated by the equation

From the differences in molar volumes ^iV (or A/7/) ) of homo
logous series, etc.. the atomic volumes A F of each element are cal-

1 Ramsay and Masson, Tram. Cham.. Soc., 1881, 39, 52.

2 Cailletet and ^lathias, Compt. rend. 1886, 102, 1202; ibid., 1887, 104, 1563.

3 Bert-helot, D., Arch. Neerlfirt.d n.w, 1900, [2], 5, 440.

4 See this Scries, Vol. I., and ".4 Text-book of Physical Chvnistry" Vol. I., J. Xewton
Friend (Griffin), 1932.

5 Sugden, Trans. Chem, Soc., 1927, 1780.

PHOSPHORUS IN COMBINATION.

53

dilated in the usual way. The value assigned to phosphorus is 12-7.
The atomic volumes are added together to give S A V > and the sums are
compared with the molar volumes found, ^ F .

MOLAR VOLUMES OF PHOSPHORUS COMPOUNDS
AT ABSOLUTE ZERO.

Compound.

!

Formula.

iiFo.

Si ,C,

Observer.

!
i Phosphorus trichloride

PCI,

69-0

70-6

Thorpe. 1

tribromide

PBr,

78-6

79-0

Sugden, Reed and Wilkins. 2

,, oxy chloride

POC1 3

73-4

75-6

Triethyl phosphate

PO(OEt).,

140-5

139-S

,, ,, J5

Triphenyl phosphate .

PO(OPh) 3

230-2

! 226-8

5> > 1

,, phosphinc .

PPh 3

20G-4

| 206-8

\ Waldeii and Swinne. 3

Further information on the structure of phosphorus compounds is
given by the parachor, which is a function of surface tension and
molar volume, the molar volumes in effect being compared under
conditions of equal surface tension. 4 For a given liquid the expression

is independent of the temperature. 5 The molar parachor

is found to be additivcly composed of terms due to each of the atoms
(which may be called, the atomic parachors) plus terms due to double
or triple linkages, and to various types of cyclic structures. The mean
parachor of phosphorus as calculated from some binary compounds,
such as PClo, etc., is 37-3 (36-1 to 38-9). In another system it is 40-5. 6

PC1 3 .

PJBro.

Px ....

199-0 7

201-1 8

SP,v (without phosphorus)

162-9

242-9 2

204-0

607

570-0

The parachors of phosphorus and the other atoms were summed
and compared also with the molar values of POCK, etc. (p. 54). A
different series of atomic parachors has also been proposed. 6

1 Thorpe, Trans. Chem. Sue., 1880, 37, 141, 386.

2 Sugden, Reed and Wilkins, Trans. Chem. Soc., 1925, 127, 1525.

3 Waldcn and Swinne, Zeitsck. physikal. Chem., 1912, 79, 700.

4 Macleod, Trans. Far. Sue., 1923, 19, 38; Sugden, Trans. Chem. Soc., 1924, 125, 1177.
3 DL = density of liquid, J)\ = isobaric density of vapour, cr= surface tension.

6 Mumford and Phillips, Trans. Chem. Soc., 1928, 155; 1929, 2112.

7 Morgan and Daghlien, J. Amer. Chem. Soc., 1913, 33, 657.
a Ramsay and Shields, Trans. Chem. Soc., 1893, 63, 1089.

PHOSPHORUS.

! POC1 3 .

PO(OC,H,) ; ,.

I PO(OC 6 H 5 ) 3 .

1

217-6 l

i 399-1 2

i 680-5 2

220-6

! 403-0

i 687-7

-3-0

i -3-9

1 -1-2

i

The differences liave the sign and magnitude which is associated with
a * mixed " bond, and this confirms the structure assigned on p. 52.
The ethyl ester of phenylmethylphosphinic acid had a parachor of 420-5 ;
that calculated on the assumption of an ordinary double bond was
442-1, while on the assumption of a "mixed" or semipolar bond it
was 417-3. The structure was therefore given as

(CH 3 )(C 6 H 5 )(C 2 H 5 0)=P >0 3

The atomic refraction shows considerable variability with con
stitutive influences, whether it is determined by Gladstone s formula

or by Lorentz and Lorenz s formula

An, = (^

(Xote. A = atomic weight, r ( -+ =refractivity according to Gladstone s
formula, rL=refractivity according to Lorentz and Lorenz s formula.)
The atomic refraction Ar (; of the element is 18-68 (solid), 18-89 (liquid). 4
or 18-69 (mean of solid and liquid), 5 while the value A? L was 9-10 (mean
of solid and liquid). 5

The following values have been calculated from the molar refrac-
tivities of the principal liquid (or gaseous) compounds : 6

PH 3 (liquid). ;PH 3 (gaseous). P(C 2 H 5 ),. PC1 3 . : PC1 5 . PBr,. ! P 4 O . POOL, j

Ar T

13-75
9-10

13-75
8-63

17-24
9-47

14-89

8-32

16-65

S-81

20-01.
9-72

9-71
5-33

8-92
4-92

Atomic refractivities of phosphorus in its compounds arc calculated
as the difference between the molar refractivities and the sums of the
refractivities of the other atoms. They vary according to the structure
assigned, namely, whether oxygen is to be considered as singly- or
doubly-linked. Molar refractivities appear to be affected by con-

1 Ramsay and Shields, Trans. Cham. Soc., 1893, 63, 1089.

2 Sugden, Reed and Wilkins, Trans. Cham. Soc., 1U25, 127, 1525.

3 Gibson and Johnson, Trans. Chern. Soc., 1928, 92.
* Gladstone, Chew. Xew*\ 1887, 55, 300.

5 Damien, "Rich, sur le pouvoir refringent des liquides," Paris, 1881.

6 Zecchmi, Ztitsch. physikal. Clicrn., 1893, 12, 505; Gazzetta, 1893, 23, i., 97. Sco also
Kanonikoii, J.prakt. Chtm., 1885, [2], 31, 359; Haagen, Annaltii, 1867, 131, 117.

PHOSPHORUS IX COMBINATION. 55

stitutive influences to about the same extent as molar volumes at the
boiling-points, TM, since the ratios of V^ to M/* L for all the compounds
considered range between 4-77 and 5-01, mean 4-9. 1

When the refractivities of gaseous compounds are calculated to
standard conditions, the values of n - 1 or (n ~1)10 G are often found to
be nearly additively composed of those of their components, that is
(n - 1)10 6 is nearly equal to S(>ZA - 1)10 6 . The following table enables
this comparison to be made between observed and calculated refrac-
tivities. 2 The property is only approximately additive, the deviations
from this relation being great in some cases. 3 4

REFRACTIVITIES OF PHOSPHORUS COMPOUNDS
AND THOSE OF THEIR ELEMENTS.

Refractive Index

Cal

Differ

(n).

culated

Com
pound.

i
i

for Gas
from
Lorentz

Re
fract ivity

Refractivities of
Components,
P=599.

Sum. i

ence
per cent.
Columns
(5) and

Gas. Liquid.

and
Lorenz s

(7).

j

Formula.

i

i

PH 3

1-00073G j

7S6

599-r(3x69i)

807-5^

-2-7

PCJ 3

1 -001 730

1730

599 -r (3x384)

1751 =

-1-2

PBr 3

! 1-6S66

1-002450

2450

599 -f- {3 x 562-5)

2286-5

-7-1

P.S

2-06(51

1-003025

3025

(4x599) -551

2947 j

-2-6

PA

: 1-5405

1-001725

1725

(2 x599)-r(3 x!35)

1603 1

-7-7

POC1 3

1-4602

1-001715

1715

599 -135 -(3 x3S4)

1886

-9-1

PSC1 3

1-57547

1-002231

2281

599 -(3x384) -551

2302

i

-0-9

Stereochemistry. Compounds of the type POX 3 may, as already
pointed out, have one or other of two constitutions (see p. 52) or
may exist in tautomeric equilibrium, but if the halogens X are replaced
by hydrocarbon or other organic radicals R, the compound will be
fixed in one or other of the two isomeric forms. This isomerism has
been well established in the case of the compounds having the empirical
formula OP(C 6 H 5 ) 3 . 5 One of these, phenoxydiphenylphosphine, is an
oily liquid, prepared by the condensation of phenol with diphenyl-
chlorophosphine :

C 6 H 3 OH + (C 6 H 5 ),PC1 = (C e H 6 ) 2 P.OC 6 H s -rHCl

The other, triphenyiphosphine oxide, is a solid melting at 153-5 C.,
and is prepared by the action of water on triphenylbromophosphine
bromide :

H 2 + (C,,H 5 ) s PBr a = (C 6 H S ) 3 PO + 2HBr

1 Arbuzov and Ivanov, J. KHSS. Phys. Che//i. Soc., 1915. 47, 2015; A, 1925, ii., 165.

2 Cuthbcrtson, C. and M., Phil. Tians., 1905, 204, A, 323.

3 Cuthbertson and Metcalfe, Phil. Trans., 190S, 207, A, 135; Proc. Hoi/. Soc., 1908,

- G PHOSPHORUS.

That the three ordinary valencies of phosphorus in compounds of
the type FOX, or POR 3 do not act in one plane, but are distributed
in space symmetrically with respect to one another, was demonstrated
bv Ca.vcnj 1 who replaced chlorine atoms in the trichloride one at a
time but in different succession by various groups such as RXTI or

i{0 9 forming, for example, the anilino-, jj-toluidino- and then the

y>toluidino-anilino chloride.

Xo signs of isomerism were detected in the mono-, di- or tri-sub-
stitution products. It was therefore stated that ;i the centres of gravity
of the three chlorine atoms lie at the angles of an equilateral triangle,
and if an imaginary line is drawn through the centre of this triangle
and at right angles to its plane, the centres of gravity both of the
phosphorus atom and of the oxygen atom are situated on this line/

On account of the theories of valency alluded to before (p. 52), 2
compounds of the types [PR 4 JX and [OPR 3 ] are of the same stereo-
chemical type, and contain an atom of phosphorus co-ordinated to
four atoms or groups which are symmetrically disposed in space. When
the groups denoted by 11 are different, the resulting compounds
PR 1 R 2 R 3 R 4 X and POR 1 R 2 R 3 should be capable of existing in optically
active forms.

The first preparation of the type PR 3 R 2 R 3 R 4 X could not be
resolved, 3 nor could an aiiilmo-p-toluidinophosphoric acid l be resolved
into optically active isomers by fractional crystallisation, with active
bases. The first compound which was proved to contain an asym
metric phosphorus atom was phenyl-p-tolylphosphoric acid, the
JZ-hydrindamine of which

/OC,H 5
0=PA)C 7 H 7
\XHC 9 H 9

was found to be a mixture of two compounds having different melting-
points. The d- and Miydrindamines when separately prepared each
yielded on fractional crystallisation a less soluble fraction of lower
Iccvo-rotatory power and a more soluble fraction of higher lievo-rotatory
power, thus showing a resolution of the acid. 4

The compound methylethylphenylphosphine oxide .

/CII 3
O=Pf-CoII,

also contains an asymmetric phosphorus atom. 5 It was prepared by
combining ethyldiphenylphosphine with methyl iodide, setting the
base free with silver oxide and boiling with water :

(C 6 H 3 ) 2 (C 2 H 5 )(CH 3 )POH = C 6 H 6 + (C G H 5 )(C 2 H 5 )(CH 3 )PO

This compound, which could be distilled without decomposition, was
combined with the calculated amount of d-broiiiocamphorsulpnomc

1 Cavcn, Trans. Che/ti. Soc., 1902, 81, 1362.

2 See also Tart 1. of this Volume.

3 Michaelis, Annakn, 1901, 315, 3S.

4 Kipping and Lurf, Trans. C hcm. >S oc., 1909, 95, 1993.

5 Meisenhcimer and Lichtonstadt, Bcr., 1911, 44, 356. See also Eadcliffe and Brindlev,
J. tioc. Chun. Ind., 1923, 42, 64.

PHOSPHORUS IX COMBIXATIOX. 57

acicl and the product crystallised from ethyl acetate. The recrystal-
lised product had a molecular rotation, M\ ly of ~3 2I 3 while that of
bromocamphoric acid and its salts with inactive substances was -f 48.
On passing ammonia into a solution of the camphorsulphonate in
ben/ene, the ammonium salt was quantitatively precipitated, and the
solution on evaporation gave colourless crystals of the niethylethyl-
phenylphospliine oxide, which had a molecular rotation, J/p. of +39
in water and -f57 in benzene.

Further evidence as to structure in space is derived from an examina
tion of the electric moments due to the dipoles of some compounds.

The Dipole Moment of Phosphine. Molecules which are not
polar in the sense of being strong acids, bases or salts, may yet show
an inner polarity when investigated by certain physical methods.
The use of the dielectric constant and the rcfractivity in calculating
the polarisation of molecules is described in certain monographs and
text-books, e.g. tc The Dipole Moment and Chemical Structure" Dcbye-
Deans (Blackie), 1931 ; c; Recent Advances in Physical Chemistry"
Glasstone (Churchill), 1931.

The total molar polarisation, i.e. that due to 1 gramme-molecule of
the compound, is given by the Mosotti-Clausius equation :

_

+2 D ~ L " 3 3 skT

in which 6 is the dielectric constant, J/ and D have their usual sig
nificance, A r is the Avogadro number, and 7 is the molecular polaris-
ability due to induced dipoles. We are not concerned at present with
the first term on the right, which is the distortion polarisation, P\ h
i.e. that which is due to the dipoles which are set up in molecules by
the applied field of force. The second term is the polarisation due to
the permanent dipoles existing in the molecules before the field is
applied. A permanent dipole is present whenever combination with
partial separation of electric charges has taken place in such a way that
the centre of gravity of ail the positive charges does not correspond
with that of the negative charges. If the distance between the charges
e is d. then de = p, is the dipole moment of each molecule. Boltzmamrs
constant k = RjN, in which R is the universal gas constant and N is
the Avogadro number, i.e. the number of molecules in a gramme-
molecule. Since all these constants have known values and the
temperature is known, the dipole moment JJL can be calculated, and on
certain assumptions it gives the configuration of the molecule. The
following values have been found in the case of the hydrogen com
pounds of this groin) :

XH 3 . PH 3 . AsH 3 .

1-55 0-55 0-15

The existence of these permanent dipole moments indicates that the
hydrogen atoms arc not in the same plane as the tervalent element,
but that this occupies the apex of a tetrahedron, of which the three
hydrogen atoms form the corners. The diminution of the moment with
rise of atomic weight, is attributed to a decrease in the height of the
tetrahedra, and also to the distortion of the octets of electrons on the
N, P and As atoms by the positive charges on the H atoms.

58 PHOSPHORUS.

The Representation of Phosphorus Compounds by Electronic
Theories of Valency. The compounds in which phosphorus is
trivalcnt arc saturated in the sense that all the covalcnt bonds on the
element are made up, with the completion of the outer octet of electrons,
the phosphorus atom thus assuming the argon type with three com
pleted shells of 2, 8, 8 electrons of which only the outermost are shown
by the formulae 1

H Cl

H . p . H ci ; p ; ci

If we admit the hypothesis 2 that the three quantum orbits of the
second series may contain a maximum of 6, C instead of 4, 4 electrons,
it follows that PC1 5 also, and other quinquevalcnt compounds, may be
written with ordinary valencies or duplet bonds only, giving shells
of 10 0. If, however, 8 is the maximum possible (failing the com
pletion of 12), then PC1 5 must be constituted either as NH 4 C1. or it
must contribute two electrons to a pair of chlorine atoms, thus de
veloping a " mixed bond." In the first case

r Cl ^

ci P . ci j . ci ;

L Cl

would be potentially ionisable, a property which has been to some
extent confirmed experimentally (see p. 96 ). 3 One of the chlorines in
PC1 4 ~ is held by a " mixed bond." In the second case

Cl
Cl ; P ;) Q or C1 3 EEPTC1 2

Cl

also contains a c mixed bond," uniting two chlorine atoms which are
not connected with one another, and being united in a different manner
from the other three should be more easily split off and replaced as a
whole by 0, e.g. to give POC1 3 . The latter compounds, as well as
H 3 P0 4 and all others in which phosphorus is said to be quinquevalent,
can be represented by formulae of similar type. 4 They, as well as all
compounds in which non-metals from Group IV onwards show valencies
higher than the typical hydrogen valency towards other non-metals,
must be represented as having one or more mixed bonds, and as
being co-ordination compounds, according to one definition, of such
compounds. 5

The oxy-acids of phosphorus can be represented by constitutional

1 See this Volume, "Part I., Chapter IT.

2 Sidgwick, Trans. Ch&m. 8oc., 1923, 725.

3 Hofroyd, /. Soc. G kem. 2nd., 1923, 42, 3-i8.

4 Prideaux, J. Soc. Chcm. 2nd., 1923, 42, 672; Lowrv, Phil Mag., 1923, [6], 45,
1105.

5 Prideaux, J. Soc. Chem. lad., 1925, 44, 25.

PHOSPHORUS IX COMBINATION. 59

formula in which there are 3 ordinary valencies and a " mixed
bond (phosphoric) or 3 ordinary valencies with a tautomeric change
to 3 ordinary valencies and a " mixed bond ; (phosphorous and

hypophosphorous). Thus if POC1 3 is represented as C1 3 =P- Q or

C1 3 =P >0, then phosphoric acid is represented as (HO) 3 =P >0.

The phosphorus probably is the central atom, possessing the co
ordination number 4, in all compounds which were considered formerly
to contain quinquevalent phosphorus. The complete series between
the quadrivalent hydride and oxide will appear as

PH 4 I OPH 3 H 3 P0 2 H 3 PO 3 H 3 P0 4

" H "- r H i r H i- r H ";= ~ o -p

H P >H I- H P >OJ H P H- p P O 1 Ho ;O P 0| H 3 +"

L H J L H -^ L O J L O j L O ^

The corresponding formulae, e.g. for the phosphite ion. as written by
Lowry, are

|Hv ., /6:
LoXoT

The phosphites, and possibly the hypophosphites, are also capable of
existing as tervalent forms which can be fixed as the esters, such as
P(OEt) 3 , and according to the evidence of X-rays these forms pre
dominate in the solid or liquid compounds, whereas in solution they
change into the unsymmetrical tautomeric forms. The evidence is
discussed under that section which is devoted to the acids in question.

CHAPTER V.

THE PHOSPHIDES.

BINARY compounds of the metals and the less electronegative non-
metals with phosphorus are made by methods which recall those
employed in the preparation of nitrides. The most important of these
methods may be classified as follows :

(1) Direct union of the element with phosphorus under various

conditions. The metal may be heated with red phosphorus in
an indifferent gas, or the vapour of phosphorus may be passed
over the heated metal. By this means phosphides of the
alkali metals, of the alkaline earth metals, of many ferrous
and non-ferrous base metals, as well as of the Ci noble " metals
such as gold and platinum, may be prepared.

(2) Reduction of phosphates with carbon at a high temperature.

This method is chiefly applicable to the phosphates of the
alkaline earth metals.

(3) The action of phosphine or phosphorus in liquid ammonia upon

a solution of an alkali metal in liquid ammonia.

(4) The action of phosphine on aqueous solutions of metallic salts

or passage over the dry salts.

(5) Heating the metals in the vapour of phosphorus trifluoride or

trichloride.

Although the metallic phosphides are described under the respective
metals in the appropriate Volumes of this Series, a selection will also
be brought under review here, since they illustrate the reactivity of
phosphorus and of phosphine towards elements of the different groups.

Alkali Phosphides .Soon after the discovery of the alkali metals
the direct combinations of these with phosphorus vapour were recorded. 1 2
The combination can also be effected under petroleum, the unchanged
phosphorus being removed by carbon disulphiele. 3

When alkali metals arc brought into contact with red phosphorus
in liquid ammonia, ammonio-phosphicles such as XaP 3 .3XH 3 and
KP 5 .3XH 3 are formed, and can be deprived of their ammonia at
180 C., leaving the phosphides as brown solids. In liquid ammonia
sodium and potassium are also capable of displacing one hydrogen
from phosphine, giving crystalline monophosphides (phosphamides),
XaPHo and KPH 2 , which decompose on heating giving eventually
K 3 P andXaJP. 4 - 5 *

1 Davy, Phil. Trans., 1808, 98, 333.

2 Gay-Lussac and Thenard, llc-ch pliys. Chlm., 181], i, 208.

3 Vigier, Bull. Soc. clam., 1861, [1], 3, 7.

* Hugot, Compt. rend., 1895, 121, 20G; 1898, 126, 1719.
5 Joannis, Compt. rend., 1894, 119, 557.

THE PHOSPHIDES. 61

Rubidium and caesium phosphides have been made by similar
methods and by distilling phosphorus in a vacuum with the alkali
metal. The formulic are given as Rb 2 P 5 and Os.JP 5 : K 2 P 5 is also
known. 1

Alkaline Earth Phosphides. An impure calcium phosphide,
made by exposing lime at a red heat to the vapour of phosphorus, was
used in the preparation of phosphine. 2 Calcium phosphide probably
is also formed during the manufacture of phosphorus by the electric
furnace method (c/.v.). It has been prepared by heating calcium
phosphate and lam]) black in the electric are furnace, and appeared
as a crystalline reddish-black substance. 8 Calcium phosphide
prepared in this manner is only acted upon slowly by water at
the ordinary temperature, but readily by aqueous solutions of strong
acids. Concentrated nitric and sulphuric acids, and oxygen and
chlorine, do not attack it at ordinary temperatures, but on heating
it is oxidised, e.g. by chlorine above 100 C. and by oxygen above
300 C.

Strontium and barium phosphides have been prepared by similar
methods. 4

Magnesium phosphide was first obtained from the metal and organic
substances containing phosphorus, 5 but is best prepared by heating
the metal in phosphorus vapour or with red phosphorus in an atmosphere
of hvdrogen. 6 7

Phosphides of the alkali and alkaline earth metals are decomposed
by water or dilute acids, giving the hydroxides or salts of the metals
respectively, together with phosphine and other ;t hydro-phosphors."
They are only slightly affected by oxidising agents such as con
centrated nitric acid. They burn when heated slightly below a
red heat in oxygen. They arc also attacked by the halogens when
heated.

Copper, Silver and Gold Phosphides. The copper phosphides
are crystalline compounds of metallic appearance and properties which
are usually prepared by direct union of the elements. 8 Phosphorus
begins to combine with copper at about -1-00 C.. and at 700 C. the
copper was found to take up 20 per cent., 9 some of which was expelled
at higher temperatures. Slightly above the melting-point of the
phosphide 14- per cent, was retained, which corresponds to tri-cuprous
phosphide, Cu 3 P. 9 The velocity of the combination increases between
600 and 700 C. 10 At ordinary pressures 15 per cent, of phosphorus is
the limit of the amount which will remain dissolved in the fused
mixture, and some of this is present as red phosphorus. 11

1 Bosstiet and Hackspili, Co nipt. rcwL, 1913, 157, 721: 1912, 154, 209.

2 Dumas, Thcnard, loc. c//., under "Phosphine": Rose, Annalui, 1S2S, 12, ;>3.

3 Renault, Compt. ienrL, 1.899, 128, 883; Moissan, ibid., 128, 787.

4 Jabom, Cow pi. roid., 1899, 129, 765.

5 Bunsen, Airnak-n, 1868, 138, 292: SJchonn, Z^.t^cJi. annl. Chew., 1S69. 8, f>3.

6 Blunt, Trans. Chc.m. Soc., 186"), 18, 106; Parkinson, -ibid., 1867, 20, 309.

7 Gautier, Cot/ipL rend., 1899. 128, 1107.

s Pellet ier, Ami. Chim. Pnijs., 1789, [1], i, 93; Grander, Contribution a I ehf.dc,
de* plioApliinc* mct iUiquex," Pans, 1898: Lupke, Zcitch. phyv. Ohem. UnfcrricJn, 1890, 3,

62 PHOSPHORUS.

Cu P is a crystalline steel-grey or silvery-white substance which is
harder 3 than wrought iron. The melting-point is about 1018 C. and
is" lowered by additions of copper, as that of pure copper is by small
additions of phosphorus ; the Cu-Cu 3 P freezing-point curves meet at
a eutcctic which corresponds to 8-2 per cent, of phosphorus with a
freezing-point of 707 C. 1

The toughness and resistance to corrosion ot the phosphor-bronzes
are due to the presence of solid solutions of the phosphides in copper.

Cu P was also prepared by the action of phosphine on ammoniacal
cuprous oxide and on the metal at about 200 C. 2 and on cuprous
chloride. 3 Cu 5 P 2 was made by the action of PF 3 or PC1 3 on copper
at a red heat/ also by the action of phosphine on cupric hydroxide or
carbonate,- and red phosphorus on cupric nitrate. 5 When heated to a
red heat it gave Cu 3 P and Cu. Cu 3 P 2 is said to be formed by the
action of phosphine on cupric chloride. When yellow phosphorus was
boiled with cupric sulphate and the precipitate washed and treated
with acid dichromate the residue had this composition. 6 The higher
phosphides, of which CuP and CuP 2 have been reported, are powders
of uncertain composition, easily oxidised by nitric acid or by heating
in oxygen. 4 7)8)9

Other phosphides which have been prepared by direct combination,
or by reaction in solution, are Cu 5 P,, 4 CuJP, 4 Cu 3 lV 10 CuP, 4 10 -^ 12
CuP>

Silver phosphides, AgP, Ag 2 P 3 and AgP 2 , were said to be produced by
heating the elements together, or by passing phosphorus vapour over
heatecfsilver. 4 13) n Molten silver absorbs phosphorus freely, but rejects
most if not nearly all on solidification. 14 15 Silver phosphides have also
been prepared by other reactions, and it is noteworthy that the action
of phosphine on silver nitrate gives a compound, Ag 3 P.3AgX0 3 , 1G> 17
analogous to that which is first formed in the well-known test for
arsine. 16

Gold, like silver, when in the molten state dissolves phosphorus
and rejects it on solidification. 18 A phosphide AuP has been prepared
by passing a mixture of dry phosphine and ether vapour into an ether
solution of gold chloride. 10 The phosphorus is only loosely combined
and is given off when the compound is warmed. Such phosphides

1 Heyn and Bauer, lor., cit.: Hiorns, J. Soc. Chan. 2/id.. lOU o, 25, b 22.

2 Rubenovitch, Compt. rend., 1898, 127, 271.

3 Kulisch, Annahn, 1S85, 231, 242.

4 Granger, CornpL rend., 1807, 124, 896.

3 Senderens, Compt. rend., 1887, 104, 177.

6 Bottger, Met. 7?e?;., 1878, 2, 456.

7 Abc-C Trans. Cliem. Soc., 1865, 18, 249.
3 Katz, Arch. Pharm., 1904, 242, 129.

9 Christomanos, Zeitsch. anorg. Chem.., 1904, 41, 309.

Rose, Annalen, .1832, 24, 321.

1 Bmmerling, Ber., 1879, 12, 152.

- Huntingdon and Dcsch, Trans. Far. Soc., 190S, 4. 51 ; Tucker, J. Soc. CJic.rn. LuL,
1906, 25, 622.

3 Schrotter, Sitzu-ngsber. K. Alcad. Wiss. )r?c/?, 1849, 3, 301.
Pplletier, Ann. Chim. Pkys., 1792, [I], 13, 109.

5 Percy, "Silver and Gold," London, 1880, i, 137.

6 Poleck and Thummel, Ber., 1883, 16, 243o!

Vitali, VOrosi, 1892, 15, 397: ibid., 1893, 16, 10.

8 Hautefeuille and Perrev, Compt. rand., 1884, 98, 1378.

9 Cavazzi, Gazzetta, 1S84 / , 15, 40.

THE PHOSPHIDES. 63

behave like free phosphorus ; they burn in the air, are oxidised by
nitric aeid, etc., and hydrolysed by water and alkalies.

Zinc Group. Zinc phosphides have been made chiefly by reactions
(1) and (2) (p. 60). Molten zinc unites readily with phosphorus. 1
A compound Zn 3 P 2 was prepared by the action of phosphorus vapour
on zinc dust : 2 the zinc oxide present was reduced and also gave
phosphide. 3 The phosphide was a grey, well- crystallised substance
which did not mix with molten zinc. It was sublimable in hydrogen
over 1000 C. and when heated in the air oxidised to zinc phosphate. 4
It was not attacked by water, but acids gave phosphine and zinc salts. 5
The hydrophosphide. obtained by the action of phosphine on zinc
ethide in ether cooled with ice and salt, is much less stable. It is a
white powder which is at once decomposed by cold water giving
phosphine and zinc hydroxide. 6

Cadmium phosphides have been obtained by direct union, 7 as well
as by the action of phosphine on ammoniacal cadmium sulphate. 8

Mercury forms several phosphides, i.e. Hg 3 P ? Hg 3 P , HgJP 4 , which
have been described as resulting from the action of phosphine in
aqueous solution on mercurous or mercuric salts. 9 10 These products
were easily oxidised by air. halogens and aqua rcgia.

Boron is hardly affected by phosphorus even at high temperatures, 11
but there are indications of a reaction when BPO 4 is heated with
sodium. 12 A phosphoiodide BPI 2 or BPI is made by heating BI 3
with phosphorus, or by bringing the same substances together in CS
solution. When the phosphoiodide was heated to 500 C. in hydrogen,
BP was left as a maroon-coloured powder, which was not affected by
water or mineral acids up to 400 C., but was hydrolysed by boiling
alkalies or by superheated steam, giving borates or boric acid respec
tively and phosphine. 11 It was violently oxidised by nitric acid and
burned in oxygen. When heated at 200 C. in a current of ammonia
the phosphorus was displaced by nitrogen and the very stable boron
nitride, BN, was formed.

Aluminium Phosphide was made by a reaction between red
phosphorus and aluminium powder. 13 14 It formed yellow crystals.
These materials when heated in an electric furnace yielded A1 3 P and
A1P, which were crystalline substances of a metallic appearance. 15 1G
ALP 7 was obtained when phosphorus and aluminium were heated to
a white heat in a current of hydrogen.

Titanium Group. The phosphides of the elements of Group IV A

1 Pellctier, he. cit.; Lewis, Chnn. J\>:-s 1902, 87, 211.

2 Schrotter, Sitzitnyaber. K. A/cad. Wi*s. Wicn, 1849, 3, 301.

3 Renault, Compt. rend., 1873, 76, 2S3.

4 Jolibois, Compt. rend., 1908, 147, SOL

5 Lupke, loc. cit.

Sabatier, Corn-fit, rend., 1896, 123, 256.

7 Emmerlina, Bc.r., 1879, 12, 152.

s Kuhsch, Aunal&n, 1885. 231, 347; Brukl, ZtitscJi. anorg. Cham., 1922, 125, 252.

9 Brukl, Zfi,tsch. anorg. Chun., 1922, 125. 252.

Chnstomanos, Ze.it<ch. ano/g. Chc-tn., 1905, 45, 140.

1 Moissan, Ann. CJd/n. Plujd., 1895, [7], 6, 296; Besson, Compt. rend., 1S90, no,

80,

516; ibid., 1891, 113, 78.

(54 PHOSPHORUS.

have in most cases been prepared, although their compositions have
not been established with certainty. A method which seems to succeed
in cases where others fail is the double decomposition of phosphine with
the chlorides (YVohlcr s reaction), i.e. with those of silicon, titanium
and zirconium. This method was not, successful, however, with

Th(V

The phosphides of titanium and zirconium to which were assigned

the formula* TiP and %rP 2 are described as yellow or grey crystalline
substances, which conduct electricity. They burned when heated in
air, but were not affected by aqueous acids or aqueous oxidising agents.
Thorium phosphide lias been made by reducing ThCl 4 with phosphorus
vapour.

Tin Phosphides. Several well-defined phosphides of tin have
been made by the dry methods. The early work 2 was of a qualitative
nature. Phosphides of tin may be made by heating metaphos-
phoric acid or a phosphate and silica with carbon and tin or stannic
oxide. 3

When phosphorus and tin are melted together in a sealed tube, two
liquid layers are formed, and the maximum amount of phosphorus taken
up by the tin is 8 per cent., 4 while by heating tin and phosphorus in a
sealed tube at 620 C. for 10 hours grey crystals were obtained which
contained 40 per cent, of phosphorus and which after purification by
hydrochloric acid, alkali and nitric acid had the composition SnP 3 . 5
The density was 4-1 at C. Alloys of tin with about 13 per cent, of
phosphorus contained Sn 4 P 3 , 5>6 which had a density of 5-18 and was
attacked by aqueous acids.

Commercial phosphor-tin may contain up to 10 per cent, of
phosphorus as phosphides, the crystals of which are revealed by etch
ing with dilute nitric acid. Phosphor-tin is much used for making
phosphor-bronzes. 7

The action of phosphine on tin salts also gives phosphide. 8
Lead Phosphides. Phosphorus is only slightly soluble in molten
lead (about, 1-5 per cent.). 9 Most of that which is dissolved is thrown
out as violet phosphorus (q.v.) when the lead solidifies, but some
crystals of a phosphide are also formed. 10 Precipitates are obtained
by passing phosphine over lead acetate u or into alkaline or ammoniacal
alcoholic lead aeetate solutions, consisting of unstable phosphides, 12 - 13
such as Pb n P 2 , which is decomposed by acids with evolution of
phosphine.

Arsenic Phosphides, brown substances of indefinite character,
were obtained early in the nineteenth century by various methods

1 Gewecke, Arr/taJcji, 1903, 361, 79.

2 IVlIetier, Sohrotter, Emmerlin<r, loc. cit., and others.

- Xatanson and Vortmann, Bull. 8oc. chn/i., 1877, 10, 1459; Mellmarm, German
Patf.nt, 1887, 4.~)1 7. r > ; Seyboth, ibid., 1899, 106966.

4 Vivian, J. 1>L Metal*. 1920, 23, 325.
: Jolibois, Compt. rend., 1909, 148, 636.
c Stead, J. ,SY;r. Chnn. Ltd., 1897, 16, 206.
7 Xmw k y, Chnn. Z?//., 1885, 9, 641.

* v. Grottlms, Ann. CJihn. Phy*.. 1807, [1], 64, 19.

9 Pellet ier, loc. cit. See also llaiitefemlle and Perroy, Coinpt. raid., 1SS4, 98, 137S.

10 Sioc k and rjt>molka, Jh.r., 1909, 42, 4-.1JO.

11 Ivose, Annulrn, 1S32, 24, 326.

] - J.and^rcb-, , Xcinrutjnfrs J., 1S30, 60, 184.
13 2 : ;icmdloi, Compi. rc/id., 1874, 78, 1130.

THE PHOSPHIDES. 65

such as (1) by heating the elements together, 1 (2) allowing phosphorus
to stand in solutions of arscnious acid, 2 (3) by the action of phosphine
on arsenic halides. 3 The properties of these substances resemble in
general those which would be possessed by mixtures they burn in air
giving the mixed oxides, decompose on heating with vaporisation of
phosphorus, are oxidised by nitric acid, etc.

Antimony in the liquid state dissolves phosphorus giving a brittle
mass of metallic appearance. A red amorphous powder has also been
made by the action of phosphorus on antimony tribromide dissolved
in carbon disulphide. 4

Bismuth also gives a brittle substance when melted with phos
phorus. When phosphine is passed into a solution of bismuth tri
chloride or trinitrate a black powder containing phosphorus is
precipitated. 5

Chromium Phosphides have been prepared from the elements
or by the action of phosphorus vapour on potassium dichromate, or
from carbon and chromium phosphate. 6 These compounds have the
appearance of grey powders, which are hardly attacked by dilute acids
but are decomposed by alkalies.

Molybdenum and Tungsten Phosphides have been prepared by
heating the trioxides of these elements with phosphoric acid to about
1400 C. in a carbon crucible. 7 They appeared as steel-grey crystals
having densities of 5 to 6, far below the densities of the metals.
Molybdenum phosphide could be oxidised by heating in the air or with
chlorine. The tungsten compound was less reactive and could be
burnt only in oxygen or with potassium chlorate. It was not attacked
by acids. Wohlcr assigned the formula? MoP and W,P 2 to these
substances.

A phosphide \VP has been prepared by heating the diphosphide with
copper phosphide in a graphite crucible. This had a similar appearance
to Wohlers phosphide, V\ 4 P 2 , but a density of 8-5. s It was more
easily oxidised, being attacked by chlorine and hot nitric oxide, and
by nitro-hydrofiuoric acid. A higher phosphide, YVP 2 , was also pre
pared by the action of phosphine on WC1 6 at a red heat. This compound
burned in the air, and was in most respects more reactive than WP. 8
Nitrogen was found to displace the phosphorus at a high temperature,
giving the very stable nitride.

The phosphides of manganese and of the metals of the iron group
are numerous and important.

Manganese Phosphides. Compounds containing manganese and
phosphorus were prepared at the end of the eighteenth and beginning
of the nineteenth century using the methods described by Pelletier,
Percy, Rose, Schrotter and \Vohler (loc. cit.}. The freezing-point-
composition diagram of the two elements 9 shows a eutectic at 964 C.
(first additions of phosphorus), a maximum freezing-point at 1390 C.

1 Landgrebe, Schwt. ujycr s J., 1830, 60, 184.

2 BloncTlot, Compt. revd., 1874, 78, 1130.

3 Boston, Cotnpt. tend., 1890, no, 12150; Janowsky, cr., 1875, 8, 1636.

4 Ramsay and Mclvor, Jhr. t 1873, 6, 1362.

5 Cavazzi and Tivoli, Gnzzcttu, 1S!)J, 21, 306; Cavazzi, Gazzetta, 1SS4, 14, 219.
c Rose, Granger, Ann. Chin/. Phyi.^ 1898, [7], 14. 38.

7 \Vohler, Annnhn, 1851, 79, 244; ibid., 1859, 109, 374.

8 Defacqz, Compt. rend., 1900, 130, 915; ibid., 1901, 132, 32.

9 Scheiutsclrusclmy and Efrcmoii, Zdtsck. anorg. Chem., 1908, 57, 247.

66 PHOSPHORUS.

corresponding to Mi^Po, 1 another eutectic at 1095 C., and another
maximum at 1990 C. "corresponding to MnP. 2 3 Alloys containing
between 10 and 20 per cent, of phosphorus are magnetic. The mono-
phosphide 3inP was a black powder which was fairly easily oxidised
by heatinsr in the air. 3

Iron Phosphides. Cast-iron which has been made from phos-
phatic ores contains phosphides which seriously affect the properties
of the metal. Various compounds rich in phosphorus have been pre
pared by heating iron in phosphorus vapour, or iron with phosphoric
acid, bone-ash, sand and carbon (Pclletier, Wohler, loc. cit., Berzelius ;
also Hatchett 4 ). The freezing-point diagram of the system iron-
phosphorus shows several maxima and minima. The melting-point of
iron was lowered from 1510 C. to about 1400 C. by the addition of
1-7 per cent, of phosphorus, but this was not an end-point of crystal
lisation. 5 6 The first eutectic was found at 1003 C. with 10-2 per cent.
of phosphorus, the solid phases being Fe and Fe 3 P. The maximum
freezing-point corresponding to Fe 3 P was about 1100 C. 6 10 There
was a "halt-point of crystallisation, or another eutectic, between this
compound and Fe 2 P, which melted at 1350 C. 7 Solid solutions of
these compounds, which may be recognised microscopically, 8 increase
the hardness of pure iron from 3-5 to 5-0 or 5-5, but above about
1 per cent, of phosphorus render it brittle. Other phosphides which
have been reported are FeP, 9 Fe 3 P 4 9 and Fe 2 P 3 . 10 The lower phosphides
FeP and Fe P retain their phosphorus up to a red heat. The former
has also been prepared at a red heat by the action of phosphine,
thus :

2FeS -2PH 3 = 2FeP -h2H 2 S -rll* n - 12
FeCl 3 -f PH 3 =FeP +3HC1 13

Most of the phosphides are insoluble or only slowly soluble in single
acids, but are attacked by aqua regia and chlorine. Fe 3 P dissolves in
hydrochloric acid, thus : -

2Fe 3 P -f 12I-IC1 -f 8H 2 = 6FeCl 2 + 2H 3 PO 4

When iron containing phosphides is dissolved in acids one of the pro
ducts is phosphine, which is formed in greater proportion (i.e. more of
the phosphorus is present as phosphine) as the amount of phosphorus
diminishes, i.e. between 0-1 and 0-03 per cent. 14

Cobalt Phosphides. The phosphides of this metal arc produced by

1 Week-kind and Veil, Bcr., 1907, 40, 1259; Grander, Cornpt. rend., 1907, 144, 190.

2 Schfintschus-chny and Efrcmoif, Z Atsch. ananj. C/tcm., 1908, 57, 247.

3 Hilpert and Dieckinann, /, ., 1911, 44, 2831; ibid.* 1914, 47, 780.

4 JHatchctt, Phil. Trans., 1804, 94, 315.

5 Stead, /. ,Soc. Cht-ta. Ltd., 1914, 33, 173; ibid., 1903, 22, 340.

6 SakalaUvalla, J. Iron and Sled Institute, 1908, 77, ii, 92.

7 Konstantinoff, J. 7?w.s.y. P hy*. Chem. Soc., 1909, 41, 1220.

8 Arnold, J . Iron and, Si(-d Ijithtute, 1894, 45, i, 107.

9 Free.se, Zeit. Clitrn., 1808, [2], 4, 110; "Dennis and Cushman, J. Amcr. Chem. Soc.,
1894, 1 6, 477; Annalcn. 1867, 132, 225.

u Le Cliatelier and Wologdmc, Corn-pt. rend., 1900, 149, 709.

1 Freest*, loc.. c.i.t.: Schrottor, Sitzunf/tbcr. K. Akad. Wiss. \Vt(<ii, 1849, 3, 301.

2 Hvoslef, Aiiiirticii, 1S5G, 100, 99.

3 Dennis and Cushman, loc.. c,il.

4 Stead. /. Soc. Chf-m. Ind., 1897, 16, 20G.

THE PHOSPHIDES. 67

similar methods. Co 2 P 1 2 has a maximum freezing-point of 1386 C.,
and the eutectic between this and the freezing-point of the pure metal
is at 1022 C. and corresponds to 16-6 per cent, of phosphorus. 2

The combination of phosphorus with nickel was studied by Pelletier,
Davy and Maronneau (loc. cit.}, also by Lampadius 3 and Berthier. 4
The methods included heating reduced nickel in the vapour of PC1 3 ,
heating copper phosphide and nickel in an electric arc furnace, the
precipitation of a solution of the sulphate by nascent PH 3 derived
from phosphorus and alkali. 5 The thermal diagram of the nickel-nickel
phosphide system showed a first eutectic on the nickel side at about
886 C. and 11 per cent, phosphorus. 6 The first compound Xi. 3 P
freezes at about 965 C C., the second, Xi 5 P 2 , at about 1185 C. 6 The
compound Xi 2 P crystallised from the melt in grey needles at about
1112 C. ; it is insoluble in single acids, but is attacked by chlorine or
fused alkali. This compound was also made by heating copper phos
phide and nickel in an electric arc furnace 7 and by several of the
methods mentioned above. 8 Xi 3 P 2 and XiJP 3 have also been reported.

Some of the metals of the platinum group, including platinum
itself, form phosphides. These alloys were investigated in a qualitative
manner by Pelletier, 9 Granger 10 and others. The compound Pt 5 P 3 ,
formed by heating finely divided platinum with phosphorus at a white
heat, 11 was a white substance of metallic appearance, which lost phos
phorus when heated, giving Pt 2 P, and platinum when treated with
aqua regia. leaving PtP. These compounds were insoluble in single
acids and either slightly soluble or insoluble in aqua, regia. 11 The black
precipitate produced by the action of PH 3 on PtCl 4 may be a hydro-
phosphide Pt(H 2 P 2 ). 12 "

1 Maronneau, Cutnpt. tnid.^ 1900, 130, 656.

2 Schepeletf and Schemtschuselmy, J. 7? >/_<.?. Phy*. Chew. Soc., 1909, 41, 862.

3 Lampadius, Schictigrjcfs J., 1814, 10, 114.

4 Berthier, Ann. Chun. Phys., 1824, [2]. 25, 94.

5 Schenck, Trans. Ch(-m. Sac., 1873, 26, 826; 1874, 27, 214.
G Konstantinoff, Zeitsch. nnorg. Chew., 1908, 60, 410.

7 Maronneau, Compt. rend., 1900, 130. 657.

s Schenck, loc. cit. See also Struve, J. prakt. die.rn.., 1860, [1], 79, 321; Kulisch,
Attncilen, 1SS5, 231, 357.
9 Loc. cit.

10 Loc. cit.

11 Clarke and Joslin, Chcm. Xeics, 1SS3, 48, 2S5.

12 Kulisch, Annahn, 1SS5, 231, 355; Cavazzi, Gazzctta, 1883, 13, 324.

CHAPTER VI.

PHOSPHORUS AND HYDROGEN.

Phosphine.

Comparison with Ammonia and Hydrogen Sulphide. The
electronegative character of an element is shown by

(a) Electrolytic dissociation of hydrogen ion in its hydrogen

compounds.

(b) Displacement of hydrogen from hydrogen compounds by alkali

and other metals.

(c) Stability of hydrides towards heat.

With respect to condition (a), phosphorus has none of the negative
character possessed by its neighbour sulphur in the sixth group. With
respect to (b), the phosphides and the nitrides may well be compared,
and the modes of formation and stability of these compounds show
that phosphorus is less electronegative than its congener nitrogen.
With respect to (c), the dissociation of phosphinc is more rapid and
more complete than that of ammonia. There is apparently no re
versible equilibrium between phosphorus and hydrogen as there is
between nitrogen and hydrogen. Both hydrogen sulphide and
ammonia are formed to a limited extent by direct combination at
moderate temperatures and pressures, whereas phosphinc is not formed
in this way. | Note. The production of phosphinc has been observed
when white phosphorus is heated in a sealed tube with hydrogen. 1
(See also p. 27.)]

Historical. While investigating the action of alkalies on phos
phorus Gengembre 2 in 1783 prepared a spontaneously inflammable
gas. This reaction was expected to produce a " " liver of phosphorus "
or alkali polyphosphide similar to " liver of sulphur " or alkali poly-
sulphide, which is prepared from sulphur under analogous conditions.
Several other chemists about this time, prepared phosphine by similar
methods, or by heating phosphorous acid. 3 The composition of the
gas, as an analogue of ammonia, was demonstrated by Davy, 4 and the
difference in composition between the gaseous hydride and the liquid
hydride (q.v.) to which the spontaneous inflammability is due was
established by Dumas. 5 It was demonstrated by Graham 6 that the
spontaneous inflammability could be removed by means of carbon

1 Ipaheff and Xikolaieff, J>a:. 1!>2G, 59, B, 5<)5.

2 Gengembre, Mini. Ac/id., 178-5, 10, 051. Soo also Kirwan, Pft.il. Tra-ti-?., 17S6, 76,
118; Raymond. Phil. Mag., 1800, 8, 154; Crt-ll s Annalvn, \ 783, i, 450.

3 Pcllotier, Ann. Chn,/. Phys.. 1792, [! ], 13, 10].

4 Davy, Phil. Trans., 1812, 102, 405.

5 Dumas, Ann. Chini. Phys., 1826, [2], 31, 113.

6 Graham, Phil. Mag., 1834, [3], 5, 401; Trans. Roy. Soc. Edin., 1835, 13, 88.

PHOSPHORUS AXD HYDROGEX. 69

dioxide, hydrogen chloride, nitric oxide, arsenious oxide, concentrated
sulphuric, phosphoric and arsenic acids.

Occurrence. The pale glow which hovers over marshes, and which,
under the name of i; will o" the wisps/" ^ Jack o* lanterns/ etc., has
been the subject of many legends, has been attributed to traces of
phosphine with other gases produced by the decomposition of organic
matter. This is rendered probable by the observation that phosphine
is produced by the putrefaction of proteins. 1

Preparation. (a) The original method is still in general use.
The alkali employed may be hydroxide of sodium, potassium, calcium 2
or barium. The reaction is usually represented by the equation

4P 4- 3KOH -f :3II 2 - PH 3 - 3KH 2 PO 2

This reaction really amounts to a hydrolysis of phosphorus, which can
be effected also by water at high temperatures. The equations reduced
to their simplest forms and dissected are :

3P-f3HoO=30PH-f3H

P-f3~H=PH 3
3OPH-r3HoO=3E,POo

The phosphine so obtained usually inflames spontaneously on
coming into contact with the air : each bubble as it escapes forms a
beautiful vortex ring of smoke. It was early shown that the spon
taneous inflammability is due to the presence of small quantities of a
hydride, liquid at, ordinary temperatures, 3 - 4 which has the empirical
composition (PEL,),/ and the molecular composition P 2 H 4 . The
phosphorus must therefore react also according to the equation

6P -f iKOH T- 4H 2 O = 4KH 2 ?O 2 -f- P 2 H 4

The presence of hydrogen in proportions up to 50 5 or 60 3 per cent,
has been accounted for by the oxidation-hydrolysis of the hypo-
phosphite : - 6

KHJPOo ~ 211 2 = KH 2 P0 4 -r 2H 2

Details of Preparation. A tubulated retort is filled with alkali and
the phosphorus is added in small pieces. The tubulure is then closed
by a delivery tube, which is connected with a Kipp s apparatus or
other source of hydrogen (the air may also be displaced by adding a
little ether). The neck of the retort is connected with a tube which
dips under water. The air is displaced by hydrogen and the retort
then gently warmed so as to melt the phosphorus and give a steady
evolution of gas. When sufficient has been collected the residual gas
is expelled by a current of hydrogen and the phosphorus allowed to
solidify before the retort is opened.

If phosphine which is not spontaneously inflammable is required,
the gas is washed by passing it through a Woulfe bottle containing
concentrated hydrochloric acid or alcoholic potash.

The gas prepared in this manner contains hydrogen (up to 90 per

1 Gauticr and Etard, CompL rend., 1832, 94, 1357.

2 Raymond, toe. cit. 3 Dumas, loc. ciL

7Q PHOSPHORUS.

cent ) but can be prepared pure by allowing water, dilute alkali or
ume ous ether to drop on to phosphonium iodide. 1 The product may
be mixed with carbon dioxide, dried by phosphorus pentoxide and
condensed in liquid air. The condensate is distilled, rejecting the
first and last fractions, the middle being pure dry phosphine. 2

(b) Heating hypophosphorous or phosphorous acid or their salts
(tf.r.) 3 gives phosphine :

2H 3 P0 2 =PH 3 -fH 3 P0 4

(c) The action of water or dilute aeids on alkali or alkaline earth
phosphides 4 affords a method of preparation. The reactions shown
by the following equations will be succeeded by others which produce
hypophosphites, etc. :

Na 3 P -f 3HoO = PHo -f SNaOH 5
3 P 2 = - 6

Na 3 H 3 P 2 + 3H;0 =3NaOH -f 2PH 3

Similarly calcium phosphide is readily attacked by water or dilute
acids giving phosphine. 3 " - 8 A fairly pure sample of the gas may be made
from ^calcium phosphide which has been produced in the electric
furnace. 9 The reaction is more complex than that represented by the
equation

Ca 3 P 2 -f 6H 2 O =3Ca(OH) 2 + 2PH 3

Magnesium phosphide, 10 aluminium phosphide ll and phosphides of
several* other metals also yield phosphine when treated with acids.

(d) A pure phosphine" may be made by the action of alkalies or
even water upon phosphonium iodide 12 or bromide. 13 Crystalline phos
phonium iodide, prepared as described on p. 78, is mixed with broken
glass in a flask fitted with a tap-funnel and delivery tube. A solution
of one part of caustic potash in two parts of water is added slowly
through the tap-funnel. The gas is not spontaneously inflammable if
the last portions are rejected.

PH 4 I+KOH=KI+PH 3 +H 2

The gas should be washed with concentrated hydrochloric acid (to
remove any P 2 H 4 ), alkali (to remove HC1 and HI), and then dried with
phosphorus pentoxide.

(e) Among many reactions by which phosphine can be prepared
may be mentioned that which takes place between hydrochloric acid
and diamidophosphorous acid, (XH 2 ) 2 .POH. 14

1 Messinuer and Engels, Ber., 18SS, 21, 326.

- Gazarian, J. Chim. phy.s., 1909, 7, 337; Com.pl. rend., 1909, 148, 1397.

3 Dulong, Dumas, Hofmann, loc. cit.; Rose, Annalen, 1839, 46, 633.

4 Thenard, loc. cit.

5 Winter, J. Amer. Chem. Soc., 1904, 26, 1484.
G Hugot, Compt. rend., 1898, 126, 1719.

7 Pearson, Phil. Trans., 1792, 82, 289.

8 Matignon, Compt. rend., 1900, 130, 1390.

9 Moissan, Compt. rend., 1899, 128, 787.

lu Lupke, Ztitsch. phys. Chem. Unterricht, 1890, 3, 280.

11 Matignon, loc. cit. I Ponzes-Diacon, Compt. rend., 1900, 130, 1314.

12 Hofmann, Ber., 1871, 4, 200.

13 Serulks, Ann. Chim. Phys., 1831, [2], 48, 91. Sec also Mcssinger and Enscls, Ber.,
1888.21,326.

14 Thorpe and Tutton, Trans. Chem. Soc., 1891, 59, 1019.

PHOSPHORUS AXD HYDROGEN. 71

General Properties. Phosphine is a colourless gas which may
he condensed at low temperatures to a colourless liquid and frozen to
a white solid (see p. 7;3). The boiling-point of the liquid is consider
ably below that of ammonia. The gas has a strong odour recalling
that of decayed fish, and resembling rather the odour of the lower
alkylamines than that of ammonia. It does not support ordinary
combustion, and is poisonous l> 2 dilutions as large as 1 in 10,000 of
air 3 cause death in a few hours. The effects, such as embrittling of
the teeth and bones, are somewhat similar to those of phosphorus. 4
The solubility in water (about 26 volumes in 100 at 17 C.) is far lower
than that of ammonia. The gas also is only sparingly soluble in
alcohol and ether. It is easily decomposed by heat, depositing phos
phorus in the red form and giving 3 2 of its volume of hydrogen in
accordance with the equation

The molecular weight was indicated by rough determinations of the
density by the early workers ; these results were, however, in all cases
too low on account of admixture with hydrogen (r. supra}.

Physical Properties. Density. The density corresponds to simple
molecules, PH 3 , but deviations from the laws of a perfect gas are
observed. The weight of a normal litre is 1-5*203 to 1-5295 gram, 5 a
value which shows that under these conditions it agrees closely with
Avogadro s theory. At pressures of 10 atmospheres or more, however,
and at temperatures from 24-6 to 54-4 C. the compressibility is much
greater than is allowed by Boyle s law. The following values refer
to 24-6 C. : 6

1

p (atm.) . j 1-0

10 15

20

25

30

pv . . ! 1-0

0-97 0-98

0-cSO

0-75 0-70

i

Viscosity. The relative value, based on that of air (viz. 2-191 x 10~ 4
C.G.S. units at 15 C.), was found to be 1-129 x 10- 1 at 15 C. and
1-450 x!0~ 4 C.G.S. units at 100 C. 7 The relative collision area,
77-r 2 x 10 15 (in which r is the radius of the molecules in cm.), calculated
from Chapman s formula, is 0-911, while for XH 3 and AsH 3 the values
are 0-640 and 0-985 respectively.

Absorption in the Infra-red. The methods of determining this
property are briefly described as follows. 8 The radiation from a
Xernst filament was passed through a rock-salt lens, then through
either of two similar tubes, one of which was evacuated and the other
filled with the gas at a known pressure. A rocking arrangement
allowed either tube to be thrown quickly into the path of the rays.
The beam was focussed on the collimator slit of an infra-red spectro-

1 Blyth, "Poisons. Their Effects and Detection" (Gritnn), London.

2 Clark and Henderson, Chem. JVeu.v?, 1879, 39, 102.

3 Jokote, Arch. Hygiene, 1904, 49, 275.

- 1 Brenner, Zf-it. Med. St. Petersburg, 1865, 6, 4.

5 Gazarian, J. Chim. phys., 1909, 7, 837; Compt. rend., 1909, 148, 1397.

6 Briner, J. Chim. phya., 1906, 4, 476.

7 Rankine and C. J. Smith, Phil. J/a</., 1921, [6], 42, 601.

8 Robertson and Fox, Proc. Roy. Soc., 192$, A, 120, 128.

7 2 PHOSPHORUS.

meter furnished with a prism of rock salt, quartz or fluorite. On
emerging from the second slit of the spectrometer the radiation was
received by a bismuth-silver thermopile, the current from which was
registered by a Paschen galvanometer.

"Phosphine, arsine and stibine sliowed a number of deep bands, also
fine structure and smaller bands. The intensity of the bands decreased
as a rule in passing towards the visible end of the infra-red spectrum.
Bands numbered I to VI formed a nearly harmonic sequence, in which
the wavelengths of corresponding bands increased with increase in the
atomic weight of the Fifth Group element. In the following table
the wavelengths A in microns (//, = 0-001 mm.) and the wave-numbers
(per cm.) are given for corresponding bands. The percentage absorp
tion a refers to the gas in the tube under a pressure of one atmosphere.
The ratios of the wave-numbers of the corresponding bands for each
pair of gases are nearly constant.

ABSORPTION SPECTRA IN THE INFRA-RED.

Gas.

Wavelengths of Bands.

i XH 3 i 0-132, 2-998, 1-967,
I I 1-513. 1-212

6-132 1630-8

P!I 3 i 8-889. 4-297, 2-929,
! 2-193, 1-783

i

8-889 : 1125-0

! so !

AsH 3 | 9-946, 4-713, 3-235,

2-403. 1-951

!

9-946 i 1005-4

79 !

Ratio of v PH 3 /NH 3

0-689

Mean 0-685

1

Ratio of v AsHg/PHg

0-893

Mean 0-907 \

Solubility. Phosphine dissolves in 5 to 10 times its volume of
water at ordinary temperatures. The solubility, expressed as cc Bunseirs
absorption coefficient," * is 0-26 volume at N.T.P. in 1 volume of water
at 17 C. 1

When the liquefied gas was brought into contact with water and
solidified by releasing the pressure, the resulting crystalline solid was
found to be a hydrate, perhaps PH 3 .H O. 2

Phosphine is only slightly soluble in alcohol or ether. It is readily
absorbed by wood charcoal, to the extent of about 500 volumes by
1 volume of the charcoal. Coconut charcoal absorbs 69 volumes of
the gas at C. 3

* JYo/e. See Volume I. of this Series, and this Vol ume, Part 1., "Solubility of Xitro^en."
Also A Text-book of Physical ChfnnttnjS Vol. I., J. Xewton Friend (Griffin), 1932."

1 Stock, Bottgcr and Lenger, Her., 1909, 42, 2855.

- Cailletet and Bordet, Co mpL rend., 1882, 95, 58.
3 Hunter, Phil. May., 1865, [4], 29, 116.

PHOSPHORUS AXD HYDROGEX.

73

The gas may be condensed under pressure at. a temperature which
is attainable by the use of solid carbon dioxide. 1 It can be liquefied
at the ordinary temperature under a pressure of 30 atmospheres. 2

The principal thermal constants are as follows :

Boiling-point, -85 C C. ? 3 - 87-4 CV 1
Melting-point, -132-5 C. 3

Critical temperature, 54 C., 2 52-S c C., 5 51-3 C. 6 - 7
Critical pressure, 70-5, 2 Gl, 5 G4--5 atm. 6 - 7
Critical volume. 4-6 c.c. grain. 2

Liquid Phosphine. The vapour pressures and isobaric densities
of liquid \DL) and vapour (Dv) for liquid phosphine are as follows:

r C. .

\
. -49-4 j

44-4

; 39-4

i 29-4

i 24-6

i 18-4 : S-4 j

2-4 2 :

p (atm.

} 62-4 ,

56-1

1 50-8

! 41-3

1 37-1

i32-6 ,27-2 i

23-4 2 :

DL

0-417 :

0-469

0-502

0-536

! 0-545

: 0-559i 0-595 :

0-618 2 |

j

From the first set of results the density of the liquid at its boiling-point
is 0-744, and increases with falling temperature according to the
equation s

Z) T =0-744[1 -rO-OOOS(T- !( - T)]

The vapour pressure has also been expressed by the formula 4
log p = - S45-57/T -f 1-75 log T - 0-0 2 6193lT -f 4-61480

The surface tension of liquid phosphine indicates a certain degree of
association, since the coefficient of decrease of molar surface energy
with increase of temperature is about 1-7 instead of 2-0 :

. i -105-9

-101-2

- 97-6

- 93-1

. ! 22-783

22-095

21-533

20-798 8

. ! 287-2

279-G

273-4

265-4

The refr activity of the liquid is 1-323 for white light at 11-0 C. and
1-317 for the D line at 17-5" C. 9

1 Faraday, Phil. Trans., 1S45, 135, 155.

2 Skinner, Ptoc. Roy. Soc., 18S7, 42. 283.

3 Olszcwsky, Mondtsh., 1880, 7, 372; Anz. Ahtd. Krah., 190S, 375, 483: Phil. Mag.,
1895, [5], 39, 188.

1 Henninir and Stoc-k. Zeit. Phtis.. 1921. A. 226.

74 PHOSPHORUS.

The dielectric constant is 2-55 at -60 C. and 2-71 at -25 C. 1

Chemical Properties. Decomposition. Phosphine is an unstable
gas which can be decomposed by heat alone, and is easily oxidised by
oxyircn and by oxidising agents such as the halogens.

The velocity of decomposition at constant volume and at tempera
tures between 300 and 500 C. was studied by van t Hoff arid his co-
workers. 2 Concentrations of the undeeomposed phosphine at any time
can be calculated from the pressure, which, of course, rises during the
reaction. The way in which the velocity constant can be calculated
from the pressure is as follows.

The equation is arrived at in the following way : A fraction x of
1 original mol of PH 3 at a pressure p is decomposed after a time t
giving 3tf/2 mols of hydrogen and (1 +x/2) mols of the mixed gas, which
will therefore have a pressure p = (l -f #/2)_p .

If the equation of a unimolecular reaction is referred to the concen
tration c of PH 3 at the beginning and c after time t, then

01

Now

Therefore K = - log

t cl -

Also, at the end of the reaction p
The final form of the equation

is equivalent to

The reaction appears to be unimolecular in any one vessel, but the
constant K is not the same in different vessels. Hence it was supposed
that the decomposition took place on the walls of the vessel. The
constant rises with rise of temperature, and above 660 C. there is no
constant : 3

572 i 645 ! 650 656 660 i 683 ;
0-54 3-6 i 4-4 5-6 I 12 11 to 22 !

The effect of surface on the reaction has been further studied by adding
powdered fused silica, which caused a great increase in the "velocity

1 Palmer and Schlimdt, J. Physical Chem., 1911, 15, 381.

2 Kooij, Zeitsch. physikal. Chttn., 1893, 12, 156.

3 Trautz and Bhandakar, Zeitsch. anorg. Chem., 1919, 106, 95.

PHOSPHORUS AXD HYDROGEX. 75

of decomposition. 1 The heat of activation of the PH 3 molecules cal
culated from the rate of increase in the velocity constant with tempera
ture was 40,000 to 50,000 calories. 1

The effect of the electric discharge was investigated by the early
workers : red phosphorus is deposited 2> 3 and other hydrophosphors are
formed. 4 5

The effect of light has been studied, but the results are not con
sistent. Some decomposition may take place with the production of a
reddish deposit, and the spontaneously inflammable fraction may be
destroyed. 6 The amounts and intensities of the short-wave radiations
as well as other conditions were not known or controlled by the earlier
investigators. 7 8

Oxidation. Although pure phosphine does not itself in the ordinary
way inflame spontaneously with air, yet it does so when the pressure
is reduced. This observation was made almost simultaneously by
Davy 9 and de la Billardiere. 10 In the words of Davy cc I found the
phosphoretted hydrogen produced a flash of light when admitted into
the best vacuum that could be made by an excellent pump of Nairn s
construction. 57

The oxidation under reduced pressure was found to take place at a
fairly uniform speed at 50 C. and pressures of 760 down to about
400 mm. 11 If mixtures of air and PH 3 were used corresponding to about
2 volumes of PH 3 to 1 volume of oxygen, the diminution of pressure
per hour was uniformly 0-5 to 3-0 per cent, of the initial value. There
was in only one case a slight increase in the velocity immediately before
explosion occurred. Moisture retarded the reaction. Moist mixtures
of phosphine and oxygen were not explosive with air at low pressures,
but dry mixtures of phosphine and oxygen exploded when the oxygen
pressure was reduced to 0-1 atmosphere or any lower value. 12 13

Slow oxidation at low pressures proceeds according to the equation

At higher pressures both metaphosphorous and phosphorous acids are
formed, thus :

4PH 3 -f 50 2 = 2HPOo -f 2H 3 PO 3 -f 2H 2 13

If the gas was very thoroughly dried, as over phosphorus pentoxide,
soda-lime or crystallised glycerine, it took fire spontaneously in air.
The explosion which takes place after some hours of slow oxidation of

1 Hinshehvood and Topley, Trains. Chtm. Soc.., 1924. 125, 393. See also Dushman,
J. Amer. Chtm. Sac., 1921, 43^, 397; Drummond, ibid., 1927, 49. 1901.
- Dalton, Ann. Phil, 18 IS, n, 7.

3 Hofmann, Ber., 1871, 4, 200.

4 Graham, Phil. Mag., 1834, [3], 5, 401.

5 Thenard, Compt. rtnd., 1873, 76, 1508.

6 Amato, Gazze.it a, 1884, 14, 58.

7 Trantz and Bhandakar, loc. at.

8 Roy, Proc. Roy. Soc., 1926, no, A, 543.

Davy, Phil. Trans., 1812, 102, 405: Rose, Annalen, 1839, 46, 633.

10 de la Billardiere, Ann. Chim. Phys., 1817, [2], 6, 304. See also Dumas, Ann. Chim.
Pin/*., 1S2G. [2], 31, 113.

11 "Studies in Chemical Dynamics, van t Hoff-Colien, translated by Ewan (Williams
and Norgate, 1890).

12 van de Stadt, Zeitsch. physikal. Chem., 1893, 12, 322.

76 PHOSPHORUS.

phosphine with moist air has been attributed to the accumulation of
hygroscopic compounds such as H 3 P0 2 and I-I 3 P0 3J which dry the
remaining gases. 1

The explosion of phosphine with oxygen takes place at higher
pressures when the phosphine is in considerable excess. Thus 0-5 c.c.
of oxygen was mixed with 0-5 and up to G-0 c.c. of phosphine and the
expansion was determined at which the mixture would explode (at
50 C.). A total expansion of 1 volume to 5 volumes was required for
the first mixture, but only 6-5 to 9-6 volumes for the second. 2

The vigorous combustion of phosphine produces orthophosphoric
acid. A combustion with the production of 85 per cent, of this acid
crave +311 calories 3 at constant pressure. Values calculated for
the heat of formation of gaseous phosphine are -11-6 Cals., 4 5 -9-1
Cals., 6 and -5-8 Cals. 7 The free energy of formation from solid
phosphorus and hydrogen at 25 C. is -3-3 Cals. 8

Halogens attack phosphine vigorously giving halidcs of hydrogen
and usually of phosphorus as well. These reactions were early investi
gated by Thomson, Balarcl and Hofmann. 9 10 II The action of sulphur
was also investigated by Davy 12 and Dalton. 13 14> 15

Phosphine is absorbed by acid cuprous chloride giving an addition
product CuCl.PH 3 . 16 It precipitates phosphides from some metallic
salts (see under c; Phosphides ").

Phosphine reacts with the lower halicles of phosphorus giving
halogen hydracids and free phosphorus or a compound containing
more phosphorus. 17 - 18 19 With the higher halides it gives the lower
halides and halogen hydracids, thus :

3PC1 5 + PH 3 - 4PC1 3 + 3HC1 1S

In relation to halides of boron, phosphine resembles ammonia,
giving addition compounds of similar but not identical type such as
2BF 3 .PH 3 and BC1 3 .PH 3 , which are, however, more easily dissociated
than the corresponding ammines.

Phosphonium Compounds.

Phosphine. like ammonia, has a much lower affinity for water than
it has for the halogen hydracids, no doubt on account of the fact that

1 Rose, Annahn, 1832, 24, 158.

2 van t Hoff-Colien, Studies in Chemical Dynamics"

3 Lemoult, Compt. rend., 1909, 149, 554; ibid., .1907, 145, 374.

4 Ogier, Co/apt, rend., 1S7S, 87, 210.

5 Berthelot and Petit, Compt. rend., 1889, 108, 548.

6 Forcrand, Compt. rend., 1901, 133, 513.

7 Lemoult, Compt. rend., 1907, 145, 374.

8 Drummond, J. Amer. Client. Soc., 1927. 49, 1901.

9 Thomson, Ann.. Phil.. 1820, 15, 227.

Balarcl, Ann. Chhn. Phys., 1834, [2], 57, 225.

1 Hofmann, Annaleu, 1857, 103, 355; Ber., 1S70, 3, 060; 1871, 4, 200.

2 Davy, Phil Trans., 1812, 102, 405; Vauquclin, Ann. Ckim. Phys., 1824, [2], 25, 401.

3 Dalton, Phil Trans., 1818, 108, 316.

4 Jones, Trans. Chain. &oc., 1870, 29, 641.

5 Cavazzi, Gazztttu, 1886, 16, 169.

G Riban, Compt. rend., 1879, 88, 581.

7 Besson, Cornpt. rend., 1889, 109, 644; 1890, no, 516, 1258: 1890, in, 972.

8 Mahn, Zeitsch. Chem., 1869, [2], 5, 729.

D Gladstone, Phil. Mag., 1849, [3], 35, 345.

PHOSPHORUS AND HYDROGEN. 77

water gives a very low concentration of hydrogen ion and the halogen
hydracids in water high concentrations of hydrogen ion (Werner), the
hydrates in both cases being less stable than the hydrohalides. The
formation of hydroxides and hydrohalides consists partly in the addi
tion of hydrogen ion to the anhydro-base. This process takes place
to a much greater extent with ammonia than with phosphine. Indeed
phosphine does not appear to form a hydroxide at all with water, but
simply dissolves as an indifferent gas.* The case is different with the
halogen hydracids ; these do form phosphonium salts of varying
stability, the iodide being the most stable. 1

Phosphonium Chloride, PH 4 C1, is formed when the component
gases are mixed under a pressure of about 20 atmospheres. Under
atmospheric pressures it can only exist at temperatures below about
-25 C. 2 It can be melted under pressure at +28-5 C. 3 (Other
determinations gave 25 C. 4 and 26 C. 5 )

The change of volume on melting is very great, being about
-i-0-73 c.c. /gram at -f40 C. The critical volume is 3-5 c.c. - gram. 5
The criticaHemperature is given as 50 to 51 C., 6 48 C., 5 48*8 to 50-1
C., 7 49-1 C., s and the critical pressure as 80 to 90 atm., 9 96 atm., 5
74-2 to 75-0 atm. 10 and 72-7 atm. 11 The heat of formation of 1 mol of
gaseous PH 4 C1 is 4-16-4 Cals. : that of the solid is 4-43-4 Cals., and
therefore the heat of sublimation is +27-0 Cals. 12 The dissociation
pressures have also been investigated. 13

Phosphonium Bromide, PH 4 Br, was made by Scrullas in 1831
from the component gases by direct union. 11 Its dissociation pressure
reaches only 1 atmosphere slightly below -f 38 C. 13 It can also be
made by passing phosphine into the most concentrated aqueous hyciro-
bromic acid, 15 or hydrogen bromide dissolved in phosphoryl chloride, 16
or from phosphine and bromine. 14 It forms colourless cubic crystals
which sublime at about -f- 30 C. 17 The heat of formation of the solid
from the gases PII 3 and HBr is -23 Cals., while that evolved when
the initial materials are bromine (liquid), hydrogen and phosphorus
(solid) is -i-4-i-l Cals. 15

Phosphonium Iodide, PH 4 L is the most stable of these com
pounds, being formed by direct union of the gases at ordinary tempera
tures and atmospheric pressure with the production of a, crystalline

* 2\olc. A crystalline hydrate is said to be formed under high pressures see under
" Solubility of Phospiime-,"*

1 Tammann, Zeitsch. Elckfrochcm., 11*02. 8. 158. See also -Skinner, Proc. Roy. Soc.,
1SS7, 42, 283.

2 Oder, Crttnpt. rend., 1879, 89, 705.

3 Scheft er, Zeitsch. -physical. Chew., 1909, 71, 214.

4 van t Hoii, lice. Trcii. chim., 1885, 4, 305.

5 Skinner, Proc. Roy. Soc., 1SS7, 42. 283.

G van t HofT, loc. cit., and Ber., 1885, 18, 2088.

7 Tammann, " Krystal. u. Schmdzen" Leipzig, 1003.

R Briner, Compt. rend., 1906, 142, 1214, 14167

9 van t Hoit, loc. cit.

Tammann, loc. cit.

1 Briner, he. cit., and J. CJurn. phy.*., 1006, 4, 267, 476.

2 Briner, Joe. cit.

3 Johnson, J. Amcr. Cfic^n. Soc. t 1912, 34, 877.
1 Serullas, Ann. Chun. Phys., 1831, [2j, 47, 87.

15 Ogier, Compt. rend., 1879, 89, 705.

16 Besson, Compt. rend., 1896, 122, 140, 1200.

7 Bineau, Ann. Chim. PAys.,"l838, [2], 68, 430.

7s PHOSPHORUS.

compound. 1 It may also be made by a considerable number of reactions
between phosphorus, iodine and water. These substances may be
heated together in a retort:

2P -f I 2 + 4H 2 O =PH 4 I +H 3 P0 4 -f-HI 2

Or the water may be allowed to drop on to phosphorus triiodidc or on
to a mixture of phosphorus and iodine. 3 - 4 The preparation of a small
quantity is most conveniently effected as follows :

10 grams of phosphorus are placed in a retort with a wide tubulure
through which is passed a tap-funnel and a delivery tube connected
with a source of dry carbon dioxide. An equal weight of carbon di-
sulphide is added, and then 17 grams of iodine. The carbon disulphide
is then distilled off in a current of carbon dioxide by placing the retort
in a basin of warm water. The mouth of the retort is then connected
with a wide tube which fits into the mouth of a wide-mouthed bottle,
which is also connected with a draught exit to draw off the uncombined
hydrogen iodide. 8-5 grams of water are then placed in the tap-
funnel and allowed to drop slowly on to the phosphorus and iodine.
The phosphonium iodide which sublimes into the wide tube is afterwards
pushed into the bottle

51 + 9P -r 16H 2 = 5PH 4 I -f- 4H 3 P0 4

Physical Properties. The crystals appear to belong to the cubic
system and were so described by the earlier investigators. They are
really, however, tetragonal, 5 the ratio of the longer axis to the shorter
axis being 1 : 0-729. 6 X-ray photographs showed that the dimensions
of the unit cell were 6-34, 6-34, 4-62 A, 6 and that the space-lattice was
very similar to that of the form of ammonium chloride which is stable
at low temperatures. The density of the solid is 2-860. 5 The dissocia
tion pressures are tabulated on p. 80 and reach one atmosphere at about
-r62 c C. The heat of formation of the solid from gaseous 7 phosphine
and hydrogen iodide is -f 24-17 Cals., and the heat of decomposition
bv water giving gaseous phosphine and a solution of HI is 4-4-77
Cals.

Chemical Reactions. Phosphonium iodide is hydrolysed by water,
and is still more rapidly decomposed by alkalies, giving phosphine and
an iodide. The phosphine is displaced by ammonia giving ammonium
iodide. 8 and even by ethyl alcohol giving ethyl iodide, with phosphine
in both cases. 9 It is hardly affected by aqueous acids, except those
which are also oxidising agents.

As might be expected, phosphonium iodide acts as a reducing agent
in most cases, although it is not oxidised by oxygen or air at ordinary
temperatures. Chlorine water gives phosphorus and P 2 H, 10 and chlorine

1 de la Billardiere, loc. tit.

2 Serullas, loc. cd.; Rose, Pogg. Annalm, 1832, 24, 154; 1S39, 46, 636.

3 Hofmann, Trans. Chem. Sac., 1ST], 24, 380.

< v. Bayer, Ann ah ,1, 1870, 155, 266; Holt and Myers, Zc-itsch. anorg. Chem., 1913,
82, 281.

5 Wagner, Zeitsch. Krij&l. Jllin., 1911, 50, 47.

6 Dickinson, ,7. Atner. Chcm. Soc. f 1922, 44, 1489.

7 Ogier, Ann. Chrm. Phys., 1SSO, [5], 20, 5.

8 Messinger and Engels, Bar., 1888, 21, 326.

9 Serullas, loc. cit.

10 Cain, Chcm. Xcws, 1894, 70, 80.

PHOSPHORUS AXI) HYDROGEX.

DISSOCIATION PRESSURES OF PHOSPHOXIUM
HALIDES.-

Phosphor* ium Chloride.

Solid, amorphous. 1

, p (mm.

- GO
50-4

Solid, crystalline. 1

- 45

19G-0

t 2 C. .

p (mm.)

-SO
9-6

-60
62-0

-20
1260

Solid, crystalline. 1

t~ C.

p (atm.)

0-0

8-9

18-2

| 22-6

i

28-2
4S-T

Liquid.

tC.
p (atm.)

25-0

45 I

30-Ot
49 2

40-0
61-0-

45-0
67-5 :

Phosphonium Bromide.

! f C. .
I p (mm.)

Solid. 4

-80
1

Liquid. 1 -

0-0
56$

*c. .

7-5

1
19-0

31-6

38-8

p (mm.)

101

222 i

507 ;

79 -t

*C. . .1 7-6

19-8

34-3

p (mm.)

118-6

266-8 5 i

602 5

* Only a selection of the values is given.

1 Tammann, * Kryst. u. Schintlzen," Leipzig, 1903.

Triple point.

i Critical temperature.

80

PHOSPHORUS.

Plwsphonium Iodide.

Solid. 1 - 2

f C.

p (mm.) .

j 15-0 I 19-2
1 36-0 l ! 50-0

30-0 : 50-0
: 107-8 i 368 ].

62-6 ; 60-0
7GQ-0 ; 917-5 !*

t C.

p (mm.) .

! i 11-4

1 8 2 ! 24

i !
i j

; 2-4-4 45-8
74 i 286

1 |

58-4 !
536 2

;

gas gives similar products at first, while an excess gives PC1 5 even at
fow temperatures. 3 Chloric, bromic and icdic acids and their salts,
silver nitrate and nitric acid oxidise it with inflammation. 4 Carbon
disulphide at temperatures above 140 C. 5 is said to give P(CH 3 ) 3 HI.

Liquid Hydrogen Phosphide.

The analysis of this compound shows that it is hydrogen hemi-
phosphide, (PH 2 )x, and the molecular weight corresponds to tetra-
hydrogen diphosphide, P 2 H 4 .

This liquid, which is the cause of the spontaneous inflammability
of phosphine prepared by methods (#.), (&), (c) (pp. 69, 70), was isolated
by passing through a freezing mixture the gas resulting from the action
of water upon calcium phosphide. 6 7 The condensate was a mobile
liquid having a density of about 1-01 and vaporising between 30
and 40 C. The boiling-point at 735 mm. was found to be 57 to 58 C.,
and on careful distillation there is no residue. 8 The vapour density
(probably of the products of decomposition) is 74-73 to 77-0 and the
empirical formula is PH 2 ; hence, on the analogy of hydrazine the
constitutional formula has been written as H 2 =P -P =H 2 .

The compound is unstable and decomposes when heated ; when
kept it changes slowly in the dark and quickly in the light into the
gaseous and solid hydrides. Since 100 parts by weight give 38 parts
of the solid and 62 parts of the gaseous hydride this decomposition
may be represented by the equation

5PH 2 =3PH 3 -fP 2 H 8

Preparation. This is best carried out in a Woulfe bottle having
a capacity of about 3 litres and furnished with three necks, through
one of which hydrogen is admitted. Through another pieces of calcium
phosphide are introduced into water, and the third is fitted with the
exit tube which is cooled by a reflux condenser and connected, with a
spiral tube terminating in a wash-bottle, the whole of which is immersed
in a freezing-mixture. Uncondensed gas is ignited in a draught. The

3 Stock, Be,r., 1920, 53, S37. -i Serullas, loc. cit.

5 Dreclisel, J. prafd. Ckcm., 1874, [2], 10, ISO.

6 Tlienard, CompL rend., 1844, 18, 652; 1844, 19, 313.

7 Hofmann, -Be?-., 1874, 7, 531.

rend,

; Gattermann and Hausknecht, Ber., 1S90, 23, 1174. See also Croullebois, CornpL
.,1874,78,496,805.

PHOSPHORUS AXD HYDROGEX. 81

bottle is warmed to about GO" C. in a water-bath and the calcium
phosphide added as required. 100 grams of CaJP 2 give 3 to -i c.c. of
liquid phosphide. 1

Solid Hydrogen Phosphide.

A yellow solid is farmed during the decomposition of potassium
phosphide by water. 2 and this solid is formed in many other reactions
which yield the other hydrides, possiblv as a secondary product re
sulting from the decomposition of the herniphosphide by water (see
p. 80). It is also formed by the exposure of phosphine to light, 3 and
is one of the pro-duets of the action of chlorine upon phosphine.

Preparation. 4 - The mixed hydrogen phosphides generated by the
action of water on calcium phosphide, in a 3-litre flask through which is
passed a current of carbon dioxide, are passed through a condenser to re
move most of the water vapour and then through a series of wide glass
tubes packed with granular calcium chloride (which must leave no residue
when dissolved in hydrochloric acid). The tubes are protected from
the light by rolls of paper. After the whole apparatus has been filled
with carbon dioxide, the calcium phosphide is introduced into the flask
in amount sufficient to give a layer about 1 cm. deep. A steady stream
of phosphine is evolved at 60 C C., the spontaneously inflammable part
of which is immediately decomposed by the calcium chloride with de
position of the solid hydrogen diphosphide. The escaping gas is led
directly into the Hue and burnt. The solid spreads through the tubes
and appears in the final wash-bottle, which contains hydrochloric acid.
The apparatus is then again filled with C O and the last calcium chloride
tube detached and used as the first of the next repeat operation. The
contents of the calcium chloride tubes are dissolved in cold dilute
hydrochloric acid. The hydrogen phosphide, which usually floats, is
filtered off, washed with ice-cold water, then with alcohol and with ether
which has been redistilled over sodium. This dissolves a little of the
compound to give a yellowish colloidal solution. The solid is filtered
off. centrifugecl. dried for 12 hours in a vacuum desiccator over P 2 5 ,
and kept in a closed vessel of brown glass in a desiccator. 5

Properties. The diphosphide is a yellow powder, which is taste
less, odourless and insoluble in most solvents. It decomposes in the
light giving phosphine, and is easily decomposed by heating in an
atmosphere of hydrogen. It ignites in air at temperatures between
100 and 200 C. *

The empirical formula is (PH) >7 .. 6 The molar weight, deduced from
the lowering of the freezing-point of white phosphorus, corresponds to
the formula P 12 H 6 . 7 The density is 1-83 at 19 C. 4 The heat of
formation from white phosphorus and hydrogen is given as -f 35--i
Cals. s

1 Gatterraann and Hausknecht, Inc. at.

2 Rose, Annakn, 1S28, 12, o49.

3 Levcrrier, Ann. Cltin. PJnjs., 1835, [2], 60, 174: Ibid., 1837, [2], 65, 266.

4 Stock, Bottcher and Lender, />/.. 1009, 42, 2847.

5 Schenck. Jkr.. liUtf, 36, 9ij<>. 4204: Stock, Bottclier and Lender, ibid., 1909, 42,
2839.

fi Thenard, l>c. c .L. and Coin pi. .";^/., 1847. 25, S92; Schenck, tier., 1903, 36, 991,
4204: Amat. Ann. (Jhitn. I J hu.*.. 1801. f() i. 2A. 3 .">$.

82 PHOSPHORUS.

Chemical Reactions. P 12 H 6 is dissociated when heated above
70 C. in an indifferent gas into its elements at 175 C. in COo, 1 or
into phosphorus and phosphine at 215 C. The ignition temperature
in air is 120 to 150 C. 1 The only liquids which dissolve it without
decomposition are phosphorus and P 2 H 4 . It dissolves in ammonia
at - 40 C. with evolution of phosphine. After evaporation of the
ammonia a black solid is left which appears to be an ammine of a
higher hydrogen phosphide. Like the other phosphides it is easily
oxidised by halogens, chlorates and nitric acid. 2

The hydrogen of this phosphide appears to have a slight acidic
character, since the phosphide dissolves in alcoholic alkalies giving
deep red solutions which contain polyphosphides, similar to those
which are formed by the action of alcoholic alkali on finely divided
scarlet phosphorus. These compounds are easily hyclrolysed by
dilution, or by the addition of acids, with the precipitation of a yellow
or reddish mixture of solid hydrogen phosphide and scarlet phosphorus
(which possibly contains a suboxide or P 4 H.OH 3 - 4 ).

Higher Phosphides of Hydrogen.

When the diphosphide is gradually heated to 175 C. in vacuo, or
when its ammoniate is heated, a reddish powder is formed to which the
composition P 9 H 2 has been assigned : 5

This compound is fairly stable in dry air, but in moist air is converted
into phosphine and phosphoric acid. It dissolves in liquid ammonia.
A phosphide P 5 H 2 has also been reported. 6

Some hydroxyphosphides are formed also by oxidation and hydro
lysis of a mixture of phosphorus and phosphorus trichloride, 1 7 or by
the hydrolysis of tetraphosphorus diiodide, P 4 I 2 , when this is boiled
with water. 8 The solid to which the composition P 4 H.OH has been
assigned dissolves in alcoholic potash giving hydrogen and the potassium
salCP 4 H.OK.

The Alkylphosphines.

On account of the instability of the phosphines and phosphonium
salts, the hydrogen valency of phosphorus is more clearly displayed
in their alkyl substitution products which also, as is usual, possess a
more pronounced basigenic character * than the hydrogen compounds
themselves. The methods of preparation of these compounds, and
their properties, closely resemble those of the alkylamines.

The tertiary alkylphosphines were discovered by Thenard in 1845, 9
and the primary and secondary by Hofmann in 1871. 10 All may be

1 Leverrier, Ann. Chim. Phys., 1837, [2], 65, 266.

2 Thenard., Leverrier, loc. cit.

3 Schenck, he. cit.

* Stock, Bcr., 1903, 36, 1120; ibid., 1908, 41, 1603.

5 Stock, Boucher and Lender, loc. cit.

6 Hackspill, Co nipt, rend., 1013, 156, 1466.

7 Gautier, Ann. Ghrm. /%,*., 1S73, [5], 76., 49.

8 Fran eke, J. prakt. Chem., 1887, [2J, 35, 341.
* I.e. when combined with HI, CH 3 i, etc.

9 Thenard, Berzdius Jahre-sbericht, .1845, 26 ;198

10 Hofmann P.cr 1KT1 A ><.-; io n m-,. ic-o r- ic\i. i OTO * OAO

PHOSPHORUS AXD HYDRO* I EX. S3

prepared by general methods by the action of phosphoniuni iodide
on alkyl iodides or on alcohols, and by the action of zinc alkyls on
phosphorus trichloride. The primary and secondary alkylphosphines
are obtained as crystalline double salts with zinc iodide when the alkyl
iodides are heated to 15() c ( . with phosphonhirn iodicic in the presence
of zinc oxide. The primary base is iirst liberated as a gas (PH 2 CH 3 )
or as a volatile liquid (PIIoC.\JI 5 ) on the addition of water, and is
distilled off and condensed. The secondary bases PiC"II^). 2 H and
P(C 2 II 5 ).>H can be set free by the addition of potassium hydroxide to
their hydriodides. The tertiary bases are prepared (as hydriodides)
by heating phosphonium iodide with alcohols (CH OH ? CJI 5 OII) at 150
to 180 C C\, and also by the action of zinc alkyls on phosphorus trichloride.
The boiling-points of alkyh)hosphines rise with increasing molecular
weight, as is usual in homologous series :

Primary.

Boiling- Boiling- Boiling-

point, point. point,

Methylphosphinc Dimethvl Trimet hvi

P(CH 3 )H 2 -14 PiCH 3 ).,K -25 P(CK 3 } 3 - 40

Ethvl Diethy! Triethv! .

>{C\H 5 )H 2 ~ 2o P(C,H.),H S5 I\C>K-) 3 127

P/CgH-jHo 41

?(C,K 9 )H 2 62

Alkyliodides of the quaternary phosphonium bases are made by
heating (to over 150 C.) the theoretical proportions of the alcohols
with phosphonium iodide, thus :

4CH.,OH -r PH 4 I = P(CH 3 ) 4 I - 4H 2

They are well-crystallised salts, easily soluble in water, and highly
dissociated even at dilutions of 32 litres to the mol. 1 The bases,
liberated by the action of silver oxide on the iodides, are also highly
dissociated, and therefore behave as strong alkalies. Thus, in the
case of P(CH 3 ) 4 OII :

F

! A

i 16
! 214

64
! 221 |

256 litres
223

per mol

i

(Breciig. 1 )

The mobility of the ion P(CH 3 ) 4 ~ is 42-3, that of P(C 2 H 5 ) 4 - 32-T, the
mobility diminishing with increasing addition of - CH - to about 23
in the case of P(C 5 H 1] _)(C G H 5 ) 3 " : (/.s-oamyitriplienylphosphonium ion).
Alkylphosphines differ from the corresponding ammonia derivatives

84 PHOSPHORUS.

bv the great case with which they are oxidised even by atmospheric
oxygen, "either with spontaneous inflammation, as in the case of some of
the less alkylated members, or with the formation of phosphinc oxides,
as in the case of trialkylphosphines. Thus oxygen at ordinary tempera
tures combines with P"(C 2 H 5 ) 3? giving P(C 2 H 5 ) 3 O, which may bz distilled
with steam.

Triethylphosphine Oxide may be made in quantity by heating 1 part
of phosphorus with 13 parts o f ethyl iodide in a sealed tube at 175-
180 C. The product is distilled, first with ethyl alcohol to remove
excess ethyl iodide, and then with concentrated potash, which removes
the iodine" and oxidises the compound. Thus :

P(C 2 H 5 ) 4 I -r KOH = P(C 2 H 5 ) 3 -f KI + C 2 H 6 1

Triethylphosphine also combines with sulphur with evolution of
heat to give the corresponding trietliylphosphine sulphide, P(CJ-I 5 ).,S,
a very stable compound, which can also be made by oxidation or by
hydrolysis, of the curious addition compound P(C2H 5 ) :1 .CS 2 , a red
crystalline solid which is itself made by direct union of 1 3 (C 2 H 5 ), and
CS 2 . The oxidation is effected by silver oxide, according to the
equation

P(C 2 H 5 ) 3 CS 2 - 2Ag 2 O = Ag 2 S + 2Ag -i- CO 2 -f P(C 2 H 5 ) 3 S

The hydrolysis occurs at 100 C. and yields the oxide as well as the
sulphide :

4P(C 9 H 5 ) 8 CS 2 +2H 2 = 2P(CJI 5 )3S+P(C 2 H 5 ) 3 0-fP(C 2 H 5 ) 3 CH 3 OH

-:-3CS 2

The structural formulae of these compounds, whether written with
the usual bonds or with valency electrons, are clearly quite analogous
to those of the alkyl derivatives of ammonia (sec this Volume, Part I.).
Thus the presence of -even one methyl group enables the phosphorus
to accept a hydrogen ion from hydrogen iodide, giving a crystalline
product which is not dissociated under ordinary conditions :

H H

H 3 c ( ; P ; +H" + r=n 3 c ( p ;) ir + r
"H" 1i

In the alkylphosphine oxide (and sulphide) the lone pair of electrons
on the phosphorus atom completes the octet of the oxygen (or sulphur),
as in the case of amine oxides :

O

(C 2 H 5 ) 3

Oxidation of the primary and secondary alkylphosphines gives alkyl
acids, and chlorination of these with PC1 5 gives the corresponding acid
chlorides. These substances are of importance in elucidating the
structure of the phosphorous acids, etc. (q.v.), in one tautomeric" form

1 Crafts and Slilva. 7 /v//?.< Clie-m Rnr. 1N7I ->A fi-?0

PHOSPHORUS AXD HYDROGEX. 85

of which the phosphorus is not trivalcnt. but has the same valency as
exhibited in phosphoric acid or quaternary phosphonium bases. This
form is iixed in the compounds obtained as follows :

When mcthylphosphinc is passed into concentrated nitric acid it
gives a crystalline dibasic acid Cmethylphosphinic acid), P(CH 3 )O(OH)o,
and the action of PCI- on this yields P CEUOCIo. 1 ^ Oxidation of
P(CH : j) 2 H witli nitric acid gives the monobasic dimethylphosphinic
acid. Corresponding ethyl derivatives are also known. 1

1 Hofinann, loc. cit.

CHAPTER VII.
PHOSPHORUS AND THE HALOGENS.

THE FLUORIDES OF PHOSPHORUS.

Phosphorus Trifluoride, PF 3 . Some early indications were ob
tained that phosphorus reacted with fluorides of zinc and lead, 1 2 and
that the fluoride resulting was a gas. 3 This gas was prepared in 1884
by heating lead fluoride with copper phosphide in a brass tube. 4 It
is also produced by the action of fluorides of zinc, silver or lead on
phosphorus trichloride or tribromide. 5 One of the most convenient
methods of preparation is by the reaction between arsenic trifhioricle,
which is easily prepared and purified, and phosphorus trichloride,
thus :

The apparatus consists of a distillation flask fitted with a tap-funnel.
The side-tube of the flask is sealed to a condensing wash-bottle, which
can be cooled in a mixture of solid carbon dioxide and alcohol, and the
wash-bottle is joined to a condenser which is immersed in liquid air.
After the whole apparatus has been thoroughly dried, the arsenic
trifluoride is allowed to drop into the trichloride. The vapours of
these two compounds are removed in the first condenser, and the
phosphorus trifluoride is solidified in the second. 6

Phosphorus trilluoride can also be made by the action of lead fluoride
on phosphorus trichloride 7 and by the decomposition of the penta-
fluoride by means of electric sparks.

The composition has been established by the vapour density and by
analysis (e.g. with silicon, see p. 87). The fluoride is a colourless gas
which does not fume in the air, and is highly poisonous. It condenses
to a colourless liquid at - 95 C. and freezes to a white solid at - 160 C,
The heat of formation is 106-2 to 109-7 Cals. 8 per mol, therefore much
greater than that of the trichloride, and the tiiduoridc also proves to
be the more stable of the two compounds. It can be decomposed by
electric sparks with deposition of phosphorus and formation of the
pentafluoride, thus :

1 Davy, Phil. Trans., 1808, 98, 43.

2 Dumas, Ann. Ck-im. Phyx. t .1826, [2], 31, 433.
a Maclvor, Chc-.m. Xeics, IS 7,5, 32, 258.

4 Moissan, " Le Fluor et acs Composts" Steinlicil, Pans, 1900; also Cornpt. rend, .1884,
99, 655, 970.

5 Moissan, Compt. rend., 1885, 100, 272, 1348; ibid., 1886, 102, 763, 1245; ibid.,
1886, 103, 1257; ibid., 1904, 138, 789.

G Moissan, Ann. Ck-im. Pkijs., .1885, [6], 6, 433.

7 Guntz, Compt. rend., 1886, 103, 58.

8 Bertkelot, M., Ann. Chl-m. Phys.. 1885, 6j, 6, 388.

PHOSPHORUS AXD THE HALOGENS. S7

5PF 3 = 3PF 5 -f-2P l

It can be reduced by heatin with hydroen :

and also by heating with silicon or boron :

4PF 3 -r 3Si - 3SiF < -r -iP

but is not reduced by heating with sulphur, phosphorus or arsenic.
It is not affected by the metals copper, mercury, iron, cobalt and
nickel at ordinary temperatures, but the same metals give phosphides
at a red heat. 2 It is completely absorbed by sodium at the melting-
point of this metal. 1

Phosphorus trifmoride is easily oxidised. Although it does not
burn in air it can be exploded with oxygen by electric sparks, one
volume of the gas mixed with half a volume of oxygen giving one volume
of phosphorus oxyfluoride :

PF 3 -r?,0 2 =POF 3

It combines vigorously with all the halogens giving mixed pentahalides
(#.!-.). It is hydrolysed very slowly by eold water, rather more quickly
by boiling water, and quickly by aqueous alkalies, giving in the last
case alkali fluoride and phosphite. It was considered by Moissan 3
and by Berthelot 4 that the first product of hydrolysis was a fluophos-
phoric acid (q.t\). the potassium salt of which was fairly stable.

Phosphorus Pentafluoride, PF 5 . This compound was discovered
by Thorpe, who prepared it by the reaction between AsF 3 and PC1 5 : 5

5AsF 3 -r 3PC1 5 = 3PF 5 -f 5AsCl 3

The same method and precautions may be adopted as already described
for the trifluoride. The first condenser is, however, kept at about
-60 C. The pentatluoride can also be made by heating PC1 5 with
PbF 2 , 6 or by combining PF 3 with Br and warming the product : 3

5PF,B ri =3PF 5 +2PBr 5

The pentabromide being a solid is easily separated, and it only re
mains to free the gas from a small quantity of bromine by allowing
it to stand over mercury. It can be made similarly from PF 3 C1 2 . 7
It is produced, together with some PF 3 , by the action of fluorine upon
phosphorus. 8

Phosphorus pentafluoride is a heavy colourless gas with an un
pleasant smell ; it strongly attacks the skin and respiratory tract.
Unlike the triiluoride it fumes strongly in air and is rapidly absorbed
by water. It neither burns nor supports combustion. It does not
attack dry glass at room temperatures. The density is -i-o (air = l)
according to Thorpe and Moissan, and the formula is established from

1 Moissan, loc. cit., and * Le Fluor et ses Composes."

- Granger, Compt. ruid., 1896, 123, 176; 1895, 120, 923.

3 Moissan, " Lc Fluor et ses Co nipose.s.^

4 Berthelot, Ann. Chim. Pkys., 1885, [61, 6, 358.

5 Thorpe, Annalcn., 1876, 182, 201; Proc. Roy. Soc., 1S77, 25, 122.

6 Guntz, loc. cit.

7 Poulenc, Ann. Chim. Phys., 1891, [6], 24, 5-18. s Moissan, loc. cit.

88 PHOSPHORUS,

this and the analysis. It condenses to a colourless liquid at -75 C.
and freezes to a white solid at - 88 C.

This compound is by far the most stable pentahalide of phosphorus.
It is not dissociated by moderate heat or weak sparks from an induction
coil, but on strong sparking it gives PF 3 and F 2 , the latter attacking
the glass. The smalfextent of the dissociation is shown by the fact that
the pentafluoride does not react with ^soarnyl alcohol at the boiling-
point of the latter. 1 It is not attacked by oxygen, fluorine or iodine.
With dry ammonia it forms an ammine. PF 5 .5XH 3 , 2 and with X 2 O 4
an addition compound PF 5 .X 2 O 4 . 3 It is completely hydroiysed by
water (or alkalies) giving phosphoric and hydrofluoric acids (or their
salts). It is not reduced by heating with phosphorus or sulphur.

Mixed Fluohalides.

Phosphorus Trifluorodichloride, PF 3 C1 2 . This compound is
best prepared by mixing equal volumes of the trill uoride and chlorine
confined over mercury, and allowing the mixture to stand for some
days. 4 The volume diminishes to one half, and the composition and
molecular weight of the product are thus determined by Gay-Lussac s
law and by the density, viz. 5-4 (air = l) :

PF 3 +Cl 2 =PF 3 Ci 2

It is a colourless gas with an unpleasant odour, and does not burn
or support combustion. It condenses to a liquid at 8 C. When
heated to over 200 C. it decomposes according to the equation

5PF 3 C1 2 =3PF 5 + 2PC1 5

It is much more easily reduced than the pcntailuoride. Hydrogen
combines with the chlorine at 250 C. leaving PF 3 . Many metals,
e.g. aluminium, magnesium, tin, lead and iron, decompose it similarly,
forming chlorides but not decomposing the trifluoride. Sodium absorbs
it completely. Sulphur combines with the phosphorus and the chlorine,
giving PSF ;} and S 2 CI 2 . Hydrolysis with a limited amount of water
splits off the chlorine lirst, thus :

PF a Cl 2 + HoO = POF 3 + 2IIC1

Phosphorus Trifluorodibromide, PF 3 Br 2 , was first produced
by passing bromine into phosphorus triduoride cooled by a freezing
mixture. It is a pale brown fuming liquid which freezes to a yellow
solid at -20 C. and decomposes at ordinary temperatures in a similar
manner to the dichloridc :

On complete hvdrolvsis it oivcs H.>PO 15 IIF and HBr. r>

1 / / o <J <1"

The corresponding diiodide, PF 3 I 2 , is probably formed when the
trilluoride is absorbed by iodine. It is a yellowish-red solid.

1 Lucas and Ewing, J . Aintr. Ch(-in.. Soc., 1927, 49, 1270.

2 Thorpe, lac. cit.

3 Tassel, Co~in.pt. rend., 1890, no, 1264.

1 JMoissan, c; L(< Fluor ct set Cowposts "; Poulonc, A tin. Chim. Phyx., 1891, [0], 24, 548.
Moissan, * JLe Fluor et ses Composes."^

PHOSPHORUS AND THE HALOGENS. 89

Fluopliosphoric Acid. The tendency of fluorine to replace oxygen
in oxy-acids, which is exemplified in such compounds as hydrofTuo-
boric acid, is shown to some extent in the acids of phosphorus. The
existence of alkali Iluophosphates has already been alluded to (p. 87).

Salts of lluophosphovic acid are prepared by the action of alkali
fluorides on phosphorus pentachloride. The reaction between NH 4 F
and PC1 5 proceeds with some violence at 80-110 C C. The "product,
NH ;1 PF 6 , is dissolved in cold water, precipitated by nitron acetate,
and again converted into the ammonium salt by the addition of am
monia and extraction of the organic base with chloroform. The alkali
fluorides, KF and NaF, gave less violent reactions and smaller yields
of fluophosphate. These salts resemble perchlorates chemically and
halides in crystalline form. 1

THE CIILOKTDES or PHOSPHORUS.

Phosphorus Bichloride, (PCl 2 ) /t . By the action of a silent electric
discharge upon a mixture of the gaseous trichloride and hydrogen a
liquid was obtained which, after filtration to remove a yellow solid and
distillation under reduced pressure, proved to have a composition
corresponding to PC1 2 . It decomposed quickly on heating into PC1 3
and a yellow solid, boiled with decomposition at about 180 C. and could
be frozen to a solid which melted at -28 C. 2

Phosphorus Trichloride, PC1 3 . The action of chlorine on phos
phorus was investigated by Gay-Lussac and Thcnard, 3 and also by
Davy. 4 It was shown that the phosphorus burns with a pale flame
and that both a liquid and a solid compound are produced. The
preparation of the pure liquid alone (namely, the trichloride) is best
carried out in a, retort (filled with dry carbon dioxide), the bottom
being covered by a, layer of sand. The dry and clean yellow phosphorus
is introduced and niched in a current of dry carbon dioxide. The
retort is kept in warm water and a current of dry chlorine is intro
duced through the inlet tube, which should be adjustable to the dis
tance 1 above the. phosphorus which gives a brisk but not too violent
reaction. The distillate may be purified by redistilling with a little
ye. I Low phosphorus.*

Phosphorus may also be combined to form the trichloride by passing
its vapour over mcrcurous or mercuric chloride 3 or cupric chloride, 5
or by passing the vapour of sulphur moiiochloridc over phosphorus, 6
or by heating red phosphorus with sulphuryl chloride. 7 It is possible
to prepare it directly from calcium phosphate by heating this with
silica, and charcoal and passing over it the vapour of sulphur mono-
chloride; :

1-SoClo + Ca(PO 3 ) 2 -2PC1 3 + CaCl 2 +3SO 2 + 5S 8

1 Lanire and von Krue- er, Ifr.r., 1 \M 2, 65, B, 1253.

- Wesson and Founner, Co ni.pL rc./ul., 19.10, 150, 102.

:! Ga.y-Lns.sao and Thenard, " KccMrchw phy.nc.o-chi tntqucx," Paris, 1811, 2, 176.
- 1 Davy, rinL 7W/^., J 8 1 0, 100, 231; v/^/., l811, 101, 1.

* The/preeautions which arc required to secure absolutely pure halides of phosphorus
arc referred to ni the seet.ion on " Atomic Weight" (pp. 45 IS).

5 Gladstone, Phil. Mug., 1840, [3J, 35, 3-1^

< de Ckubry, Ann. Cfum. / %*., L8J8, [2], I, 213.

7 Koehliri and Heumann, tier., 1883, 16, 479.

8 Budnikoil and Shiloll, J. Sac. Chun. Ind., 1923, 42, 378T.

oo PHOSPHORUS.

Reactions of some theoretical interest which give the trichloride
are :

(a) Heating phosphorus in a sealed tube with HC1 :

2P-r3HCl=PCl 3 ~PH 3 *

(b) Reduction of the pentachloridc by hydrogen and some metals.

(c) Reduction of the oxychloride with charcoal at a red heat :

Physical Properties. Phosphorus trichloride is a colourless liquid
which boils at 76 C. and freezes at about -100 C. The vapour
density and the analysis correspond to the molecule PC1 3 . The liquid
fumes in moist air with decomposition. It is immiscible with water,
but is completely hydrolysed by it forming hydrochloric and phos
phorous acids.

Gaseous JPCZ 3 . The vapour density has been determined as 4-7464 3
and 4-75 4 (air = l). The thermal expansion is 0-00489 from 100 to
125 C. and 0-00417 from 125 to 180 C. 5 The specific heat is 0-1346
to 0-1347 between 111 and 246 C. 4 The refractive index for the
D line is given as 1-001730. 6

Liquid PC1 3 . The density has been determined by several investi
gators with the following results in grams per c.c. at C. : 1-6119
(Buff), 7 1-6162 (Pierre), 8 1-61275 (Thorpe). 9 The densities can be
calculated as the quotients of the density at C. divided by the
relative specific volume for other temperatures, i.e. as D t = D j v t , in
which v t9 the coefficient of expansion, is given by the equations of
Thorpe 9 (below) or that of Pierre. 8 The mean coefficient of expansion
between and 75 C. is 0-0013436, and the specific volumes from
C. to the boiling-point are given by the equation 9

v t = v (I+ 0-0011393* -rO-0 5 166S(m 2 +0-() 8 4012 3 )

Hence the volume at the boiling-point 75-95 C. is 1-09827 times that
at C., and the molar volume at the boiling-point is 93-34.

Another series of results has been continued to a lower temperature,
so as to include the density of the solid : 10

C C.

-95

-95

-80

-50

-30

0-0

+ 20

D .

1-9036

1-7876

1-7601

1-7046

1-6671

1-6128

1-5778

Solid

Liquid

Oppenheim, Bull. Soc, c/m/i., 1804, [2], i, 163.
Hi ban, Bull. Soc. cliini., 1883, [2], 39, 14.
Rognault, Co-mpl. rend., 1853, 36, 676.
Dumas, Ann. Chim. P hys., 1859, [3], 55, 129.
Troost and Hautofeuille, Compt. rend., 1876, 83, 333.
Mascart, CompL. rend., 1874, 78, 801.
Buff, Ann. SuppL, 1866, 4, 152.
Pierre, Ann. Chim. Phys., 1847, [3], 20, 5.
Thorpe, Trans. Chem. Soc., 1880, 37, 141, 327.
10 Koerber, Ann. Physik, 1912, 37, 1014.

PHOSPHORUS AXD THE HALOGEXS. 91

An estimate of the limiting density at -273 C. is 2-11927, and this
has been estimated to decrease with rise of temperature according to
the equation l

D t =2-11927 -0-00189994T + 0-0 6 1183T 2

The compressibility of the liquid at 10-1 C. between 1 and 500
atmospheres was found to be 0-0 4 72. 2 At 20 C. the relative volume
of the liquid was reduced from 1-0234 to 0-9862 by a pressure of
500 kilos, per sq. cm. and further to 0-7763 by 12,000 kilos. 3

The vapour pressure measurements of Regnault 4 were expressed
by the equation

log p = 4-7479108 -3-1684558a0 (between -20 and +50 C.)
in which log a = 1-9968895 ; or by 5

log p = l-2112[5-6885 - 1000(6 + 228)" 1 ]

The dielectric constant 6 at 22 C. is 4-7.

The boiling-point at normal pressure has been given as 74 to 78 C.
by different investigators. It is very close to 76 C. The carefully
determined values of Thorpe 7 are: 75-95 C. at 760 mm. and 76-25 C.
at 768 mm. More recent values are 75-5 C. at 763 mm. 8 and 75 C.
at 749 mm. 9

The latent heat of vaporisation is given as 9-0 Cals. per mol at
C. and 6-9 to 7-1 at the boiling-point. 10 - 1] - The constant Q L v/Tb -20
is therefore normal.

The critical temperature has been given as 285-5 C. 12 and as
290-5 C. 13

The melting-point is low, from -111-5 14 to -90-0 C. 9

The surface tension, as determined by Ramsay and Shields, 13 was
28-71 dynes/cm, at 16-4 C., and 24-91 dynes/cm*! at 46-2 C. Molar
surface energies corresponding to these are 562-3 and 499-8 ergs re
spectively, the decrease in molar surface energy per degree being 2-097,
which is about the normal value. More recent determinations over a
larger range arc :

D

a

-70

-20-5

+ 20-8

35-2

75-1 9

1 -7-11

1-653 1-013

1-574

1-547

1-475

37-4

31-6

29-3

27-3

25-8

21-9

The value of the paraclior has been given on p. 53.

1 Timmerinanns, Bull. Soc. chim. JJtlg., 1923, 32, 299.

2 Amagat, Ann. Chim. Phys., 1893, [6J, 29, 68.

3 Bridgman, J roc. Awer. Acad., 1913, 49, 04.

4 Rognaull, he. c-i.L, and Phil. May., 1853, [4], 5, 473.

5 Anioine, Cornpl. rand., 1888, 107, 081, 778, 830.
Walclen, Ze-Uxch. physical. Ckem., 1910, 70, 569.

7 Thorpe, loc. cit.

8 Walden, ZeM.Hck. anorg. Ckem., 1900, 25, 211.

9 Jager, Zcttuch. anorg. Cham., 1917, 101, 172.

10 Regnault, loc. cit. n Andrews, Phil. Mag., 1848, [3], 32, 321.

12 Pawlcsosky, Her., 1883, 16, 2633.

13 Kamsay and Shields, Trans. C/iem. Soc., 1893, 63, 1089.

11 Wroblowsky and Olszewsky, Wied. Annalen, 1883, 20, 243.

92 PHOSPHORUS.

The refractive index of the liquid n has been determined at several
wavelengths A (in microns = 10~ 3 mm.). 1 2

1

i A . . 0-2C3
\ n . . : 1-604

0-298
1-59983

0-394
1-54274

: 0-589
1-51215

: 0-768
1-50340

These results may be compared with the following : 3

A =0-486 0-589 0-759//,

n = 1-525 1-516 1-506

The molar depression of the freezing-point for the trichloride in
benzene 4 is 0-636 and the molar elevation of the boiling-point in the
same solvent is about 4-5.

Chemical Properties. Phosphorus trichloride mixes with organic
liquids such as benzene 4 and nitrobenzene, 5 as also with the oxy-
chloride, and with sulphur without reaction at ordinary temperatures.

In many respects the trichloride behaves as an unsaturated com
pound. Although it docs not burn in the air it seems to absorb oxygen
to some extent 6 and also ozone, giving the oxy chloride. 7

It is oxidised by sulphur trioxide, 8 9 by concentrated sulphuric acid
(to HP0 3 ), by SOC1 2 , 9 SeOCU 9 and KCl6 3 10 as follows :

PCl 3 -f-S0 3 =POCl 3 + SOo

PC1 3 -f 2I-I S0 4 = HP0 3 + H.S0 3 C1 +SOo +2HC1
3PCU 4- SOClo =POC1 3 -rPC! 5 + PSC1 3 "
3PC1 , -i- SSeOClo = 3POCL -f- SeCl 4 + Se Cl 9
3PCl 3 -hKC10 3 =3POCl 3 -i-KCl

The halogens convert it into penta-compounds. Thus fluorine gives
PF 5 n and chlorine PC1 5 . The action of bromine varies with the con
ditions ; substitution may occur, giving, e.g. PClJBr 3 , as well as PCl.J3r 2
by addition. 12 13> M Iodine may form a chloroiodide. 15 Bromine and
iodine together act vigorously according to the equation :

PCI 3 + 5Br + I = PBr 5 + IC1

3

1G

Phosphorus trichloride is chlorinated by selenium tetrachloride :

GPC1 3 + 7ScCl 4 = 3(PCl 5 ) 2 .SeCl 4 -f- 2Se 2 Cl 2 17

1 Gladstone and Dale, Phll.^ Trans., 1863, 153, 317.

- Martens, Vcrh. J)nvl.<c-h. phys. Oc^c-Ua., 1902, 4, 148.

3 Sticfelha<icn, * JJ-itpcr*. fl-iiM. trichloride," Berlin, 1905.

4 L lekerm-, Bf>r., 1891, 24, 1400.

5 Kolossowsky, J. Chun, phyj., 1927, 24, 58.

c Odlinir, i; Mfinwil of Chf"//iistry," London, 1861.

7 Kemscn, Aw.r.r. J. Xci., 1876, [3], II, 365.

h Annst.ronci, L roc. Roy. Sue., 1870, 18, 502.

Miehaelis, her., 1872 , 5, 4J I ; Ari nalcn, JS72, 164, 39.

.Dcrvin, C(>/npl. rc.mL, 1883, 97, .~>7(S.

1 Moissan, Li-, rlnor ct xf-.s ContjidM *" ; Geuther, Atuialen, 1887, 240, 208.

- Stern, Tutu*. C)>Cui. *S or., J88(), 49, 815.
:{ Pnn vault, Coi/ipl. rf-nfL, 1872, 74, 86 ( J.

1 AVichc-lhaus, 7jVr., 1868, I, 80.

5 Moot, />Yr., 1880, 13, 2029.

6 Gladstone. Tran^. C/tet/i. Soc., 1851, 3, 15.

PHOSPHORUS AND THE HALOGEXS. 93

by antimony pentachloridc :

2SbCl 5 -fPCl 3 =PCl 5 .SbCl 5 4-SbCl 3 l
and by sulphur in oiiochlori.de :

It chlorinates arsenic (in the presence of a. little AsCl 3 ) 3 at 200 to 300 C.,
also antimony, 3 4 phosphine 5 and arsine, 6 giving phosphorus in each
case.

The reaction with cold water normally gives a solution of phos
phorous and hydrochloric acids :

PC1 3 + SHoO = H 3 P0 3 + 3HC1 7

Intermediate stages in the reaction have been noted, such as the
production of phosphoryl monochloride, POC1, with small amounts
of water. 8 The solution produced at first has stronger reducing power
than the final solution, which was attributed to a. first production of
P(OH) 3 with subsequent change to the tautomeric OPH(OH) 2 . 9
In concentrated or hot solution subsequent decomposition of the
phosphorous acid may take place with the production of phosphoric
acid and red phosphorus, which change has been represented by the
equation

4H 3 P0 3 +PC1 3 = 3H 3 PO 4 + 3HC1 -i- 2P 10

The velocity constant of the decomposition, since this takes place at
a surface of separation of two immiscible liquids, is that of a uni-

molccular reaction, 11 i.e. log 1 =kt xaS. in which a is the quantity

"- a - x i

of liquid and S is the reacting surface.

Phosphorus trichloride is used in numerous reactions with organic
compounds containing hydroxyl to replace this radical by chlorine ;
by this means, for example, the chlorides of aliphatic alcohols, etc.
may be obtained. The other product is phosphorous acid.

Heats of hydrolysis and solution in much water are given as
G5-1-! Cals., 12 62-3 Cals., 1 * 63-3 Cals. 11 Using these and other data the
heat of formation of the liquid trichloride from solid phosphorus and
gaseous chlorine is 73-3 Cals., 15 76-G Cals., 14 75-8 Cals. 10

1 Kohler, S(tzunrj*brr. K. Akad. TFv .w. Wif.n, 1880, 13, 875.

- Miehaeiis, Jlrr ., 1872, 5, A]}; An.nalcn, 1872, 164, 39.

IvnifTt ami Xeuinann, 7>V ; r., 1901, 34, 5(>5.

1 .Baudnmonl, Ann. Chim. />//.?/*., 18(54, [41 2 * ~>-

5 Malm, ZeifNC.h. Chcm., 1S09, [2], 5, 720.

(; Janowsky, Sitzin^/sbc.r. K. Ahid. Wis*. W-trn., 1S73, 6, 210.

7 .Davy, Phil. Trans., 1810, 100, 231; ibid., LSI1, 101, I.

8 Bc-sson, CompL rend., 1890, in, 972; 189G, 122, 8L4; 1897, 125, 771, 1032; 1901,
132, 1 oof).

;) Mitchell, Tranx. Chcm. Soc., 1925, 127, 336.

10 Knini, J. Chcm. Roc.., 1871, 24, ii, GOO; Ann. Chim. 1 harrn., 1871, 158,332. Soo
also Gouther, Bcr., 1872, 5, 925.

11 Carrara and Zoppehiri. (tdzzr.ltn, 1890, 26, i, 493.
v - Tliom.-cn, />V /\, 1S73, 6, 710; 1883, 16, 37.

Kavn; and Sillx-rniaiin, ,/. riuirm. CJiiw.., 1S53, [3], 24, 231, 31 I, 412.

94 PHOSPHORUS.

By the action of ammonia on phosphorus trichloride in carbon
tetrachloride ammoniates such as PC1 3 .6NH 3 and PC1 3 .8NII 3 have been
obtained. 1 On heating, these ammines are decomposed with the
formation of a phosphamide and ammonium chloride.

Phosphorus trichloride reacts with liquid hydrogen, sulphide to
produce phosphorus trisulphide at ordinary temperatures. 2

Phosphorus Pentachloride, PC1 5 , is produced by the action of
excess of chlorine upon the trichloride until the mass is completely
solid, and was thus prepared by Davy. 3 Its composition was estab
lished by Dulong s analysis, but the vapour density was found to be
lower than the value which corresponds to simple molecules by
Avogadro s law. The observed densities were 5-08 at 182 C. and 3-65
over 300 C., 4 the latter density being about half the theoretical,
namely, 7-22 (air = l). This was one of the earliest known examples
of abnormal vapour densities, and the abnormality- was rightly attri
buted to a partial or nearly complete dissociation of the compound
into PC1 3 and C1 2 . This dissociation is shown by an increasingly
greenish-yellow colour in the vapour, originally colourless. 5 In
accordance with the law of concentration action the dissociation was
diminished by vaporising the compound in an atmosphere of PC1 3 in
such a way as to increase the partial pressure of this vapour. 6 The
measured density of the PC1 5 was thus brought nearer to the normal
value (see also p. 95).

The pentachloride is best prepared in a stock bottle provided with
entry and exit tubes for the chlorine and a tap-funnel for the trichloride
and cooled externally. It is kept filled with chlorine, into which the
trichloride is introduced, drop by drop.

Another convenient method is passing chlorine into a solution of
the trichloride in carbon disulphidc. The pentachloride is then
precipitated. 7

Physical Properties. The density of the liquid under the pressure
of its own vapour was determined by means of a glass dilatomctcr,
into which was melted a suitable quantity of the compound and which
was then evacuated and scaled. The volume of the liquid was read
at various temperatures. The weight was obtained by difference, as
well as from the weight of silver chloride which was obtained from the
contents after hydrolysis. 8 Another method which was found suitable
for this hygroscopic substance employed glass floats about 5xlx] mm.
which were heated in scaled tubes containing the liquid until they
sank. They were calibrated by means of similar observations in a
suitable mixture of bromoform and benzene. 9 J3y the first method
the density of the liquid by a slight extrapolation was found to be
1-601 at its boiling-point. The specific volumes were given by the
equation

1 Perperot, CompL rend., 1925, 181, 602; Jhdl /v,c. chhii., 1925, [iv], 37, 15-10.

2 Ralston and Wilkinson, J . Amc.r. Chr.ru. /S oc., 1028, 50, 258.

3 Davy, Pliil. Trnn ., LSJO, 100, 23]; LSI I, 101, 1.

r nd., 1845, 21, (>25; ibid., iStiG, 63, 14.

(1., 18(>3, 56, 105, 322; 18(10,62, 1157, 1S07, 64, 713.
d. t 1873, 76, GO].

7 Muller, ZeitMh. Chem., 1862, [1], 5, 21)5.

8 Priclcaux, Trans. Chem. Soc., 1907, 91, 17H.

9 Sugclen, Trans. Ch&m. /S oc., 1927, p. 1184.

PHOSPHORUS AND THE HALOGEXS.

95

The specific volumes were 0-629 and 0-6433 and the corresponding
densities 1-590 and 1-554 at 160 and 181 C. respectively. By the
second method the density was given as

D t = 1-624 - 0-002QS(/ - 150)

From this the densities are 1-603 and 1-559 at 160 and 181 C.
respectively.

The sublimation temperature lias been estimated at 160 C.. 3 160
to 165 C., 2 162-8 C. 3 A thermometer suspended in the vapour of
the compound which was subliming freely and condensing on the bulb
showed 160 C. 4 An extrapolation of the vapour pressure curve (see
below) would give a somewhat higher temperature.

The melting-point (166-8 C.) 3 lay only slightly above the sublima
tion temperature. The liquid which had been formed in a closed tube
under the pressure of its own vapour began to solidify at 162 C. 4

The coefficient of expansion of the liquid is stated above.

The dissociation pressure (total) at various temperatures, based on
measurements with the isoteniscope 3

t C. .

90

100

110 !

120

1 30

14-0 .150

160

p (mm.)

.18

35

67 :

117 i

191

294 j 445

670

D (grams per

c.c.) .

0-0 3 I97

0-0 : ,332

0-0.,o69

i

0-0^929

0-0,2286

0-0 2 344S

0-0 2 4913

may be used to calculate the heat of vaporisation with dissociation 5

tC.

Q.

90
. 14-2

100
15-6

110
16-6

120
16-9

1 40
15-0

150

14-9

160
14-9

Cals. per mol

The critical temperature determined in the usual manner by obser
vation of the disappearance of the meniscus, was Found to be 372 C.
The ratio between the boiling-point and the critical temperature on
the absolute scale was found to be normal.

Dissociation. The relative density (a.tr = l) diminishes rapidly with
increase of temperature, as is shown by the tables above and below.
At lower temperatures the density corresponds with single unclis.soeiatccl
molecules PC1 5 , and at 90 C. there is even a slight degree of association.

RELATIVE DENSITIES OF PC!, VAPOUR. 7

i

/c.

182

200

230 250 274 300 ; 327 330

Rcl. Density (air-1)

5-078

4-85.1

4-302 3-9!)] 3-840 3-074 \ 3-050 3-050

Per cent, dissociation

41-7

48-5

07-4 80-0 87-5 90-2 97-3 97-3

1

1 Casselmann, Annalen., 1852, 83, 257.

2 Xaumann, Be.r., 1809, 2, 345.

3 Smith and CaJverl, J. Amcr. Chnn. Xoc,., 1914, 36, 1303.

4 Prideaux, TrariH. Chew. A or;., 1907, 91, 1 7 1 ) .

5 Smith and Lombard, J. Am.cr. Chc-t/i. S oc., 1915, 37, 2055.
G Prideaux, Tranx. Faraday $00., 1910, 6, J55.

7 Cahours, Ann. Chim. Phys., 1848, [3], 23, 329; ConipL rtnd., I860, 63, 14.

96 PHOSPHORUS.

DISSOCIATION PRESSURES OF PCI,. 1

t C. . 90 100 ; 120 140 : 160

Gram-mols. PC1 5 : :

per litre . 0-0 3 945 0-00159 0-004-10 0-01090 0-02308

Pressure in mm. 18 35 117 294 070

In this table the theoretical numbers of gram-mols. PC1 3 per litre if
there were no association or dissociation have been calculated from the
formula

273 xp

n =

T x760 x22-3

Total ])ressures of the gaseous products in equilibrium with PC1 5 can
be represented from the foregoing results by the equation

log 37= - 2 / l 22 -19-1978 log jT-i- 68-9701

The total molar heat of vaporisation is calculated, from tin s equation as
in the second table, p. 95.

By a comparison of the actual with the theoretical densities the
degrees of dissociation, x, the partial pressures, p i9 /?.>, p. l9 of PC l-,
PC1 3 and C1 2 , respectively, and their concentrations can be: determined.

The equilibrium constant K ,, p\jpPx is expressed a.s a function of
temperature by means of the equation

21798
log A ,, = ---- --^-11 -50

rt " 4-;>7I/

By applying the (lapeyron equation the heat of dissociation, Q, of
PC1 5 was found to be 21-8 Cals. per mol.-

The heat of formation of solid PC1 5 from its elements in their usual
physical states is given as ;Oi-99 Cals. 3 or K):r2 Cals., 1 wliiie the heat
of decomposition by water is 123- I- or IIS-;} Cals. :i - /1

The liquid PCl 5 has a very low conductivity, both in the pure state r >
and when dissolved in some solvents, e.g. in beir/cne or IH l.,, but t.h.e
solution in nitroben/enc was found to liave a. deiinit.e low conduct ivity. (i

Chemical Properties. ~ r ^\\c. chlorine is displaeed from phosphorus
pentachloride by fluorine with great evolution of heat and the forma
tion of PF 5 . 7 Hromine has no action, f)nt iodine is converted into
IC1, which gives a,n addition compound PCi-.H l with more of the

pcl s- 8

On account of its ready dissociation the penta.chloride is a, most

1 Smith arid LoJ/ibar d, ,/. A-nn-r. C/trttt. S<jr.., J!)lf), 37, I O");").

2 Holland, Zcllwh. / >/.7/or//r/y/., l!)!i>, 18, *2\\\-.

a Thoniscn, " r l"hf rnn)( f>( ini^ti //," i ra.nshitcd by .Miss !>i;! !\c, [^oriif HKIDS, i l .)OS.
4 P>erificJoL and Lupniii, ( <n njjt. rc/xl., IST^/yS, ! (>, thcl., 1S7S, 86, S.")(;.
r> VoifrL arid Rihz, Zal.ic.ft.. <in<>r<j. Cfu-tn., \i) 2\-, 133, 211.
K liolrovd, Trait*. Cluin. ,S or., \ ( :, 2~^ 127, IM!)! .

PHOSPHORUS AXD THE HALOGENS. 97

powerful chlorinating agent. Examples of this action on the non-
metals are as follows :

Sulphur gives PSC1 3 x and also reacts according to

Selenium is converted into the monochloride :

Liquid hydrogen sulphide gives PSC1 3 . 4

Arsenic is converted into the trichloride :

6PC1 5 + 4As = 4AsCl 3 + 6PC1 3 5

Antimony reacted in a similar manner. 3 The metals, even the noble
metals, are converted into chlorides, but at higher temperatures
phosphides may be formed.

With acid anhydrides oxychlorides of the non-metal and of phos
phorus are usually formed. Thus NO 2 gives XOC1, POC1 3 and C1 2 . 6
Sulphur dioxide even when dry reacted when heated with PC1 5 , giving
thionyl chloride :

PC1 5 + S0 2 - SOC1 2 + POC1 3 7

Sulphur trioxidc, when warmed with PC1 5 , is slowly converted into
pyrosulphuryl chloride :

Selenium dioxide was found to give first a mixture of selenyl and phos-
phoryl chlorides ; the latter compound then chlorinated the selenium
completely, the final result being the transference of the whole of the
oxygen to the phosphorus and the chlorine to the selenium:

ScO 2 +PC1 5 =SeOCL> +POC1 3
3SeOCl 2 -f 2POC1 3 =P 2 O 5 + 3SeCl 4 J

Phosj)horus ])cntoxide gives phosphoryl chloride, 10 possibly through an
intermediate addition compound. 11 In. the ease of phosphorus trioxide
a reducing action was evident, phosphorus trichloride being formed
along with the oxyehloridc. 12 The reaction with arsenic trioxide and
probably with arsenic pentoxidc was found to produce AsCL and at
the same time phosphoryl chloride in the case of the pentoxide. 13 The

I Gladstone and Holmes, Phil. May., 18-10, [3J, 35, 343; Trans. Chem. Soc., 1851,
3, 5; Baudnmont, loc. cil.

- Goldschmicll,, Chem. Zmtr., 1881, [3j, 12, 489.

3 Baudrirnont, Ann. Ghitn. Phys., 1864, [4], 2, 5.

1 Ralston and Wilkinson, ./. Arn.tr. Cham, tioc., 1028, 50, 258.

r> Baudnmont , loc. cil. , Goldschmidt, loc. cit.

6 Midler, An.u t/en, 18(52, 122, J.

7 Kroi-nors, Annal.wi, 1849, 70, 207; Persoz and BLoch, Gompt. rend., 1849, 28, 86, 289.
ri Heumann and Kochlin, He.,-., 1883, 16, 479.

> Micliaehs, Aunalen., 1872, 164, 39.
10 Bakunin, GazzcUa, 1000, 30, [n], 340; Persoz and Bloch, loo. cit.

II Scbiil, Annalc.H., 1857, 102, 111; ZeU-ic-h. anorg. Chem., .1804, 7, 91.

12 Thorpe and Tutton, Proc. Roy. 8oc., J891, 59, 1019.

13 Hurtzig and Geuther, Annalcn, 1859, in, 159; Michaclis, loc. cit.

98 PHOSPHORUS.

oxides of boron and silicon were both chlorinated to BC1 3 and SiG 4 ,
respectively, on heating with PC1 5 , preferably in sealed tubes. 1

Metallic oxides as well as metals are usually converted into chlorides
by the pentachloride, while metallic sulphides usually give the chlorides
and phosphorus sulphides.

Although PC1 5 is a saturated compound it is capable of forming
addition compounds. Among those which have been described are :
PCl 5 .AsCl 3 , PCl 5 .AsCl 5 , 2 PCl 5 .SbCl 5 , 3 2PCl 5 .3HgCL>, 4 PCl 5 .FeCl 3 ,
PCl 3 .CrCl 3 . 5

Several ammoniates have been described. A white crystalline sub
stance, PC1 5 .SXH 3 , was precipitated when ammonia, was passed into a
solution of PC1 3 in CC1 4 . 6

A most important class of reactions in which PC1 5 plays a part is
its hydrolysis by water or other compound containing the hydroxyl
group with the substitution of chlorine for hydroxyl. Complete
hydrolysis with an excess of water gives orthophosphoric and hydro
chloric acids :

PCL + 4ELO = HJPO, + 5HC1

The heat of hydrolysis is 123-4 Cals., 7 118-9 Cals. 8 Steam may produce
in the first place phosphoryl chloride, thus :

PC1 5 +H 2 0=POC1 3 + 2HC1

The formation of chlorosulphonic acid, SO 2 (OH)C1, as well as of
pyrosulphuryl chloride, S 2 O 5 C1 2 , by the action of PC1 5 on sulphuric
acid has given important information as to the constitution of this
acid.

Phosphorus pentachloride is one of the most powerful reagents by
which the hydroxyl of organic compounds can be replaced by chlorine.
Alkyl chlorides, HCl, from alcohols, and acid chlorides, 11COC1, from
acids, arc often prepared by this method. The pentachloride is thereby
converted first into the oxy chloride, POC1 3 , which may itself be used
for the substitution of OH by Cl.

The structure of PC1 5 is considered under the heading "Phosphorus
in Combination " (Chap. I\ r .).

The Ghlorobromides. -Phosphorus trichloride is only partially
misciblc with bromine : two layers are formed, which, on the addition
of iodine, combine with evolution of heat and the formation of a reddish
solid resembling PBr 5 :

PC1 3 -;-2H3r 2 + U 2 =PBr 5 -f- IC1 3 9

A mixture of PCI., and Br 2 in molecular proportions when moder
ately cooled (to 10 C. or thereabouts) deposited crystals having the
composition PCl 3 Hr 2 . These, melted at 85 C 1 . with decomposition and
separation, into two layers. 10 The compound resembles phosphorus

J GusJfivson, B<f., 1870, 3, 990; \Yeber, Annalc.n, 1859, 107, :*75; ,/. pnt/cL (J/icm.,
ISoU. [Ij, 77, (if).

2 Cronandor, far., LS7.S, 6, 1406.

3 WubiT, lor., cd. ; .Baudrimorit, loc. cit. 5 Cronandcr, Inc. c/ L
r - BOS.SOTI, Cowpf. re., id., 1800, in, 072; JS92, 114, J2(M.

7 Thomson, />Vr , .1883, 16, i7.

ri JBc i ihc lot and JjU^min, Coinpt- TC/n.d., 1S7S, 86, 8o9.

- GLulsioiic, TraiM. Chc,m. &or,., 1831, 3, 15.

lu \\ ichelhaus, Annale/i Supp L, 1S68, 6, 277; Stern, Tranx. Cktrii. Soc..^ 1886., 49,

815; Mjchaohs, far., 1872, 5, 9, 412.

PHOSPHORUS AND THE HALOGEXS. 99

pentabromide (q.v.) in appearance. When brought into contact with
water it is said to give first HOBr, HBr and PC1 3 , also POBr 3 and

POClg. 1

At lower temperatures still more bromine can be combined, giving
compounds such as PCl 2 Br 3 by displacement of chlorine and PCl 2 Br 5 . 2

Many other addition compounds have been reported by various
workers. By mixing bromine with phosphorus trichloride, heating on
the water-bath and then cooling to about -5 C. brown needle-shaped
crystals have been obtained, the analysis of which leads to the formula
PCl 3 Br 8 . 3 By allowing this compound to stand with PC1 3 in a sealed
tube for some days red crystals separated which had the composition
PCl 3 Br 4 . 4

The Chloroiodides. By allowing PC1 3 to stand with an excess of
iodine, crystals were obtained having the composition PC1 3 I. 5

Iodine monochloridc or trichloride was found to react with PC1 3
giving orange-red crystals of PC1 6 I, which, by their formation, are
probably constituted as PC1 3 .IC1 3 . The compound sublimed with
partial decomposition and deliquesced in moist air with hydrolysis of
3-

THE BROMIDES OP PHOSPITOIUTS.

the PCL. 6

Phosphorus Tribrornide, PBr 3 , was .first prepared by Balard 7
who added bromine drop by drop to phosphorus. The reaction is
violent, but may be moderated by the use oC red phosphorus, by
carrying out the reaction in. CS 2 solution, 8 and by introducing the
bromine as vapour. 9 On account of the formation of volatile phos
phorus compounds it is advantageous to have an excess of bromine,
which is easily removed by distillation, any phosphorus pentabromide
also being decomposed during this operation.

It is generally prepared by dropping bromine from a tap-funnel on
to red phosphorus in a, Mask. 10 The initial reaction occurs with Hashes
of flame, and external cooling is desirable. Afterwards the bromine
is diluted by the PBr 3 and the combination proceeds less vigorously.
If the phosphorus is in excess a little remains dissolved in thctribromidc,
which must be fractionally distilled, after the addition of a slight excess
of bromine. The reaction can also be carried out in the presence of
ben /one.

Phosphorus tribromidc is a. colourless liquid which is often slightly
turbid hi the cold but becomes clear on wanning. It fumes in the air
and is hydrolysccl in a similar manner to the trichloride.

Plujxical Properties. The density at C. is given as 2-0240, 11
2-92.*ni 12 and 2-92:3. 13 The density at the boiling-point, 172-0 C., is
2-!9:)4] 12 (see also pp. 51. TOO). The vapour density, 135-14 (11 = 1),
corresponds to simple molecules PBr :J . M

1 Wiohelhaus, lor., cd.: Geurher and iVlichadis, JUKI Zc.it., J870, [ I], 6, 242.

2 Stern, loo. cU. :} Prinvault, Com.pf. rf-tid., 1872, 74, SOS; .Michaelis, lw,. cit.
4 .Prinvault, loc.. cil. 5 Moot, her., 1880, 13, 2030.

6 Baudrimont, Ann. Cfn.m. Phy*., 1804, [4], 2, 8.

7 Ann. Chl,n. Phyx., 1820, [21/32, 31)7; 18(54, [4], 2, r>.

8 Kckulc, A-tni.ulc.n, IS(J4, 130, 16.

9 .Lichen, Annalc.n., 1808, 146, 214, IVnv, Atrn. Chini. /V/ ?/.<?., 1847, [3], 20, 5.

10 Sohcnek, Her., 1902, 35, 3r>4 ; Chnstoinanos, Zcilxch.. an onj. Ckr m., 1004, 41, 276.

11 Pierre, Ann. Chim. Pkys., 1847, [3], 20,, 5.

12 Thorpe, Trans. Cham. Soo., 1880, 37, 141, 327.

13 Jager, Ztitsch. anorg. Chtm., 191.7, 101. 173. ]>l Christomanos, loc cit.

100 PHOSPHORUS.

The coefficient of expansion has been expressed by the equation

between C. and the boiling-point. Equations of this type have
also been obtained by Pierre. 1 Relative volumes obtained from
Thorpe s equation are :

t c. . . : o i 40

i: . . I 1-000 ! 1-0348

j 100
| 1-0901

172-9

i 1-171 4

Other values for the boiling-point are 170-2 C. at 750 mm., 2 172 C.
at 752 mm., 3 176 C to 177 C. at 772 mm. 1 The compound solidifies at
-41-5 C., 5 -50 C., 6 and melts at - 10 C. 6

The following table gives relations between the surface tension and
temperature : 6

SURFACE TENSIONS, DENSITIES AND MOLAR
SURFACE ENERGIES OF PBr 3 .

Another series of results was determined with the object of calcu
lating parachors 4 (sec p. 53).

PARAGHORS OF PBr,.

24 33 59-5 72-0

2-883 2-S01 2-795 2-70!

45-8 41--1 3S-1 37-1

214-4 244-0 21-1-2 2-1-2-0

The critical temperature is calculated to be J. i-V J C. 7

The refractive index of the liquid for the J) line (//,,,) is l-(>!)45 a I:
19-5 C. s

The dielectric constant at 20 C. is 3-88. IJ

Chemical Properties.-- The energy liberated during j he combination
of phosphorus and bromine to form P-Br :j is manifestly less than in the

1 Loc. at.

2 Jiiger, loc. c.il.

3 Waiden, Zf .itwh; <n>or<j. Chn,/., I JOO, 25, 2[\.

4 Sugclon, lU-odand Wilkins, Tutu*, ( hem. ;S or:., iiJiM, 127, l.l^:,.

5 Jagcr 1 , loc. c/L; Christ omanos, lor., ell.
f) Jager, loc. c.d.

7 Guldberg, Chrislia-uln I ed. tide/;., 188^,20; Zcilxch. pkyxihtl. ( -h.c.m., 1 SDn, 5, ;i7s.

8 Cliristomarios, loc. cit.

9 Schlundt, J. Physical G hc.m., 190^, 6, 157, -30,3.

PHOSPHORUS AND THE HALOGEXS. 101

corresponding case of PC1 3 . This is confirmed by measurements of
the heat of combination

P (solid) + HBr 2 (Kq.)=I J Br 3 (H q .) +42-6 Cals. 1

The superior ailinity of chlorine for phosphorus is shown by the
fact that this halogen displaces the bromine from PBr 3 giving PC1 3 .

An excess of bromine combines with PEr 3 giving the highly dis
sociated PBr 5 (q.v.).

Oxygen has no effect in the cold, but when passed into boiling
PBr 3 a vigorous and sometimes explosive reaction may take place
with the formation of bromine, POBr 3 and. P 2 O 5 . 2

The hydrolysis is complete and gives phosphorous and hydrobromic
acids. The heat of hydrolysis was found to be 64-1 Cals./ i.e. nearly
the same as that of PC1 3 .

Hydrogen sulphide was found to react with PBr 3 in a somewhat
similar manner to water :

2PBr 3 +3H 2 S =P 2 S 3 + GllBr 3

Ammonia gave first an amminc and then an amide. 1

Phosphorus tribromide attacks cork, rubber, wood, etc.. It also
reacts with hydroxylated compounds such as alcohols, and even with
ether. It mixes freely with chloroform, benzene, etc., as well as with
AsCl 3 , SnCl 4 , etc.

Phosphorus Peiitabromide, PBr 5 . In the presence of excess of
bromine phosphorus can form not only the pentabromidc 5 but also,
according to the thermal diagram, other pcrhromides. It was dis
covered early 3 that the presence of some iodine greatly facilitates the
combination, probably by the formation of ICi 3 , thus :

It is also produced by the decomposition of the dibromotriduoride
formed when triQuoridc is passed into bromine at -10 C. :

5PF 3 Br 2 = 3PF 5 -f2PBr 5 7

Properties. Phosphorus pcntabromidc is a yellow crystalline solid
which melts to a red liquid with decomposition. It fumes in the air.
A red form lias also been described, but this is probably PBr 7 . 8

The densities and specific volumes of the liquid under the pressure
of its own vapour were determined in a sealed evacuated glass dilato-
inetc! 1 . 9 One set of results was as follows :

/ C. . ! 85 100 , 130 105

v . . ! 0-3530 0-3021 ! 0-3755 ! 0-3899

1 Berlkelou and. JLuginm, A)ih.. Clilm. I } /it/;i., 1875, \_,~>\, 6, 307.

2 Clu-hstomanos, loc". cd.-, Demob, JJuli. tioc. clinn., 1SSO, [-J, 34> 201.
;i (Gladstone, loo. at.

- 1 .Besson, Com/pi, rc/od., I89U> in, 972; 1806, 122, 81-1; J897, 124, 703.

;i Balard, loc. cit.

fi J3jltz and Jeep, Zeit-ich-. u.n.or<j. C/tcm.., l. { ,)"27, 162, 32.

7 Aloissaii, c ./le Fluor et ses Co/npoxes.

102 PHOSPHORUS.

From these results and others the coefficient of expansion is calculated as

^_ 85 =^5{H-0-0019(i-85)}
and

vt-ioo =^ioox 1 + 0-0012/.}, up to 165 C,

The vapour is formed with dissociation. The pressures of the total
vapour formed were determined by a static method. 1 From the results
it was calculated that the boiling- (sublimation) point was 106 C.

The heat of formation

P (solid) -{-2Br 2 (liq.) =PBr 5 (solid) +63-5 Cals. 2

was found to be greater than that of PBr 3? but less than that of PC1 5 .
The additional heat on combination with the last two atoms of bromine
was found to be small.

PBr 3 (liq.) -f Br 2 (liq.) =PBr 5 (solid) +20-3 Cals. 2

The hydrolysis with excess of water produces hydrobromic and
phosphoric acids. The heptabromicle, PBr 7 , which was prepared by
subliming PBr 5 with Br 2 in a sealed tube at 90 C., 3 hydrolyses with
the production of the same acids and bromine in addition. In the
presence of a small amount of water the oxybromidc POBr 3 may be
produced. Hydrogen sulphide by an analogous reaction gave the
sulphobromidc :

PBr 5 -f H 2 S - PSBr 3 + 2HBr 4

The pcntabromidc may also be used to replace hydroxyl groups in
organic compounds by halogen. Thus :

PBr 5 -f- CH 3 COOH =POBr 3 -f CH 3 COBr -f HBr

An amminc, PBr 5 .9NH 3 , was formed by passing dry ammonia into
a solution of PBr 5 in CC1 4 . 5

TILE IODIDES or PITOSPITORUS.

Phosphorus reacts energetically with iodine when heated in contact
with it, or in dry organic solvents, giving orange to red crystalline
products. Two of these, the diiodide and the triiodide, have- been pre
pared by various reactions, and their properties well ascertained.

Phosphorus Diiodide, P 2 I 4 , was lirst prepared by fusing the
constituents in equivalent proportions. 6 50 grams of iodine and
4 grams of red phosphorus arc melted in a flask and, after partial
cooling, 2-5 grams of white phosphorus arc added in small pieces. 7
Or, equal parts by weight of iodine and phosphorus arc dissolved in
carbon disulphidc and the solution is cooled to C., when the coni-

1 Pridoaux, loc. cit.

2 Ogicr, Conifjt. rend., 1881, 92, So.

3 Kas-lle and ."Beatty, loc. cit.

4 Baiidrimont, Aim. Chiin. Phyn., 18G4, [4], 2, 58.
r > "Bcsson, loc. cit.

Gay-Lussac, Ann. Chim. Phys., 1814, [1], 91, 5; \Vurtz, ibid., 1854, [3], 42, .129;
Compi. rend., 1854, 39, 335.

7 Doughty, J. A-mer. Chtm. Sue., 1905, 27, 1444.

PHOSPHORUS AND THE HALOGEXS. 103

pound crystallises. 1 It has also been prepared by the action of iodine
on phosphorous oxide :

5P 4 O 6 + 8I 2 - 4P 2 !i 4- OP 2 5 2

Properties. Phosphorus diiodide forms orange-coloured crystals
which belong to the triclinic system. 3 The analysis gave (PI 2 ) rt ,. 4
The vapour density, determined in the presence of nitrogen at a
pressure slightly below 100 mm. and at 265 C., was between 18-0 and
20-2 (air 1), which corresponds to a molecule P 2 I 4 . 5 At 15 mm. and
100 to 120 C. the compound dissociates into PI 3 and P. 6 The
melting-point was given as about 110 C. 7 The heat of formation is
given as

P + Io (solid) =PI 2 - 9-88 Cals. 8

P I 4 can be ignited in a current of oxygen and burnt to phosphoric
oxide and iodine. The hydrolysis appears somewhat complex and
yields P, PH 3 , HI and H 3 PO 3 . 9 The phosphine is a secondary product.
since by gradual addition to water in the cold neither phosphine nor
red phosphorus arc formed : -

Pol* + 5H 2 O =4111 -f-H 3 PO 3 -rH 3 POo 10

P 2 I 4 is soluble in CS 2 and slightly soluble in liquid H 2 S. At about
100 C. it reacted with II 2 S giving III and a sulpnoiodide P 4 S 3 I 2 . 1:L

Phosphorus Triiodide. When solutions of iodine and phos
phorus in CSo, in the proportions of 81 to P, are mixed, a red colour
appears and on cooling dark red needles separate. 12

Other methods can be used. The action of hydrogen iodide on
phosphorus trichloride cither alone or in CC1 4 solution, or III on POCL,
also yields the triiodi.dc. G Or, PI 3 can be separated from the products
formed when PC1 5 is heated with PII 4 I :

3PC1 5 + 3PIIJ =PI 3 ~ PC1 3 + 12HC1 + 4P 1:J

Properties. Phosphorus tri iodide forms deep red tabular crystals
belonging to the hexagonal system, 3 which melt at 55 to 01 C. The
formula has been established by analysis ll and by the vapour density,
namely, 1-1-3 to 14-6 (air = l) at 250 C. and reduced pressure. The
heat of formation is slightly greater than that of the diiodide, thus :

P-i-UIo (solid) = PI 3 (solid) +10-5 Cals. 15

1 Coremvmdcr, Ann. Chun,. /Y/,y/x., 1850, [3], 30, 342; AnnuU ii, 1851, 78, 70.

2 Thorpe and Tutton, T-faiix. Chew.. *S or., I8i)l, 59, J022.

3 Xordcrskjold, Jhhan.f/. Akwl. Forfi. Stockholm, 1S7-1, 2, 2.
1 Cot cmvindor, /or-, cit.

5 Troost, Compt. -nutd., 1882, 95, 21)3.

6 13cs.son, l<jc. at.

7 Corenwindor, loc. clL: Be.sso.ri, loc. aL; luroman, AM(:/\ (Jhc.ru. J., 11)03, 30, 110.

8 Older. ComvL rt-ttd.. 1881, 02, 83.

104 PHOSPHORUS.

The surface tension of the liquid is 56-5 dynes/em, at 75-3 C. 1 The
dielectric constant is for the solid 3-66, for the liquid 4-12. 2

Chemical Reactions. The iodine can be replaced by chlorine, using
either the gas itself or chlorides, such as those of mercuric mercury,
arsenic, antimony and tin. A sulphoiodide is formed when the triiodide
is heated with the trisulphide :

2P 2 S 3 +2PI 3 =3P 2 S 2 I 2

and the same compound may be produced by the action of hydrogen
sulphide on the liquid triiodide :

2PI 3 + 2H 2 S = 4HI +P 2 S 2 I 2 3

Hydrolysis proceeded in the usual manner giving hydrogen iodide
and phosphorous acid, but a solid product was formed at the same time. 4
The reaction with ethyl alcohol gave ethyl phosphorous acid as well as
ethyl iodide :

Like the other halides it reacted with anhydrous ammonia. If
this was in the liquid form and below - 65 C. an amide was formed :

15NH 3 +PI S =P(NH 2 ) 3 + 3XH 4 (NH :i ) 3 I

1 Jaircr, Zaitsch. anorg. Chtm., 1917 101, 173.

2 Schlundt, J. Physical Chem., 1904, 8, 122.

3 Ouvrard, Ann. Chlm. Phy*. y 1894, [7], 2, 221.
1 Besson, Zoc. cit.; Corcnwindcr, loc. oit.

5 Walker and Johnson, Trans. Cham. Soc., 1905, 87, 1592.

6 Hugot, Compt. rend., 1905, 141, 1236.

CHAPTER VIII.
OXY- AND TH10-HALIDES.

OxY-llALIDES.

OxYFLUOimms are the most stable of the oxyhalides, and the stability
decreases with increasing atomic weight of the halogen. Special
methods are used in the preparation of oxy fluorides, while the other
oxyhalides can be prepared by general reactions, such as the partial
hydrolysis of the pentahalides, or the oxidation of the trihalides.
The compounds fume in the air and readily undergo further hydrolysis
giving hydrogen halides and oxyacids of phosphorus.

Phosphorus Oxytrifiuoride, POF 3 . The production of this com
pound by the partial hydrolysis of PF- or PF n Cl 2 has already been
mentioned. It may also be made by passing electric sparks through
a mixture of PF 3 and oxygen. The first method of preparation con
sisted in heating phosphorus pcntoxidc with a fluoride, such as cryolite. 1
It is also produced by the action of hydrogen fluoride on phosphorus
pentoxicle.

It is best prepared by the action of silver, zinc or lead fluoride
on POC1 3 .- 3 The oxychloridc is allowed to drop gradually on to
anhydrous zinc fluoride in a brass tube at 40 to 50 C. The gas passes
out through a lead tube, then through a condenser at -20 C. to retain
POC1 3 , through a tube of zinc chloride to absorb the last traces of
oxychloridc, and finally is collected over mercury.

It is colourless, with a pungent odour, and L limcs slightly in the air.
The vapour density is 3-08 to 3-71 (air-]) and 52-0 (Ii = ] ), 4 the
theoretical densities for POF : , being . 3 -09 and 52-0 respectively. The
gas condenses to a colourless liquid which boils at -40 C. and freezes
to a white solid at -(58 C. When cay it docs not attack glass in the
cold, but docs so when heated, although not so strongly as phosphorus
trifluoride. On the other hand, whilst the trifluoride was absorbed
very slowly by water, the oxyfluoridc was absorbed very quickly.
Neither gas is completely hydrolyscd, appearing to form f iuooxyacids.

tfluophospkoric Acids. Fluorine is pre-eminent among the halogens
in its power of replacing oxygen of oxyacids to form iluoacids, as is
exemplified by such well-known compounds as H 2 SiF G . Examples of
fluoacids are also found among the more strongly electronegative
elements of Group VI B, i.e. sulphur and its congeners.

1 Schulze, JJtilL tioc. chivt.., 1881, [2j, 35, L7, >; Tliorpo and Humbly, Trans. Chc/m.
Soc., 188!), 55, 7f>9.

2 ^loissan, " Lt Fluor c.i .s-e.s 1 Composes," Stoinlieil, Paris, 1900.

3 Guntz, Cwn.pt. rend., 1886, 103, 58.

4 Tluirnf anfl Hni-nhlv Inr.. r.i.t.

106 PHOSPHORUS.

In the case of phosphorus such compounds as P(OH) 3 OK.KF may
perhaps be regarded as belonging to this type. 1

It has already been noted that the hydrolysis of phosphoryl fluoride
is not at first complete. It reaches a stage at which the addition of
Ci nitron " (see this series, Vol. VI., Part I.) gives a salt, C 20 H 16 X 4 HP0 2 F 9
(m.pt. 230-5-232-5 3 C.), of difiuo phosphoric acid, POF 2 (OH). The
ammonium salt of this acid has been prepared. The acid is also pro
duced when phosphorus pentoxide is fused with ammonium fluoride,
or when the pentoxide is dissolved in aqueous hydrofluoric acid. 2
The last-mentioned solution, when kept at the ordinary temperature,
undergoes hydrolysis, and with * nitron " yields the " nitron " salt
of hexafluophosphoric acid, HPF ti , the ions of which have also been
prepared by dissolving phosphorus pentafluoridc in cold water. The
ions, PF 6 ~j are stable towards boiling water. Solutions of the potassium
salt do not give precipitates with salts of the alkaline earth metals. 3

Phosphorus Oxychloride. Phosphorus oxytrichloride or phos
phoryl chloride, POC1 3 , was early formed during investigations into
the action of the pentachloride on substances containing the hydroxyl
group. 4 It was also prepared by the oxidation of the trichloride by
air, by oxygen, and by many oxidising agents, e.g. nitrogen trioxide. 5
It is also produced by the action of water in small proportion or acetic
acid on PCl 3 Br 2 5 or by the action of chlorsulphonic acid on red
phosphorus. 6

Two convenient methods of preparation arc as follows :

(i) A current of chlorine is passed through phosphorus trichloride
and water is added at the same time, drop by drop. The liquid is kept
at its boiling-point, and is distilled at the end of the operation, which is
signalised by the appearance of the pentachloride. 7

(ii) 500 grams of PC1 3 (free from phosphorus) are placed in a tubu
lated retort having a capacity of 950 e.c. or more. 160 grams of
potassium chlorate are added through the tubulure in lots of about
4 grams. The POC1 3 is then distilled :

3PC1 3 -f KCIO 3 = 3POC1 3 + KC1 B

The KC10 3 should be dry and should previously be covered with some
POC1 3 before adding to the PC1 3 . 9 Dried oxalic acid may be used as the
oxidising agent, the weight used being half that of the PC1 3 . 10

Phosphoryl chloride may be produced on a large scale by passing
a mixture of chlorine and carbon monoxide over an intimate mixture
of carbon and calcium phosphate (such as charred bone) at 330 to
340 C, : n

Ca 3 (P0 4 ) 2 H- 2CU + 2CO - Ca(P(X).> -r 2C0 -f 2CaCL,
Ca(P0 3 ) 2 + 4CU -f- 4CO - 2POC1 3 V4CO 2 + CaCU

1 Wemland and AH a, Zc-tlwU. un.orfj. Clic.m.., 1801), 21, 43.

2 Lanire, tier., 1927, 60, [B], 962.

3 Lanirc, tier., 1928, 61, [B], 799.

4 Wurtz, Ann. Chvm. Pky.*., 1847, [;}], 20, 472.

5 Geuther and Michael is, tier., 1871, 4, 766.

Hcmnann and Kochlin, tier., 1882, 15, 4-1 G.

7 Vauscheidt and Tolstapiaioff, /. JIUM. Phy*. Ckcnt. Xoc., 1920, 52, 270.

8 Bervin, Co-m.pt. rend., 1SS3, 97, 570.

9 Ullmann arid Fornaro, tier., 1901, 34, 2172.

10 Gerlmrdt, Ann. Chim. P%,v., 1S53, [3J, 37, 285; 1855, [3J, 45, ]Q2.

11 Riban, Compt. rend., 1882, 95, 1160.

OXY- AXD THIO-HALIDES. 107

By a similar reaction ferric phosphate is decomposed by carbonyl
chloride at 300 to 400 C. 1

Physical Properties. Phosphoiyl chloride is a colourless fuming
liquid which resembles the trichloride in appearance but boils at a
higher temperature, 107 C., and can easilv be frozen to a solid which
melts slightly above C.

Analysis combined with determinations of vapour density led to
the formula POC1 3 . 2 According to the results of many investigators
the density of the liquid at ordinary temperatures is slightly below 1-7.
The exact experiments of Thorpe and Tutton gave the following results
for the density at C., 1-71165 to 1-71185 (1st series) and 1-71185 to
1-71190 (2nd "series), and at the boiling-point, 107-23 C., 1-50967. 3
The specific volumes and thermal expansions between these tempera
tures are summarised by the formula 4

v t = V Q (I + 0-001064309* -h 0-0 5 112666f 2 + 0-0 S 5299Z 3 )

The liquid boils at 107-22 to 107-33 C. at 760 mm. 4 and at 104-5
to 105-5 C. at 783 mm. 5 It freezes at about - 10 C. and the melting-
point of the solid was +2 C., 6 -rl-78 c C. 7 The critical temperature
is 329 C. 8

The surface tension, as determined by the capillary tube method,
was given as 31-91 dynes/cm, at 18 C. and 28-37 at 46-1 C. 8 Hence
the change of molar surface energy with the temperature is normal.
This physical constant, together with some others, was determined in
order to obtain the parachor [P]. The sample of POC1 3 had a boiling-
point of 108-7 C. at 769 mm.

PARAGHOR OF PHOSPHORUS OXYGHLORIDE. 9

t C. .

. \ 15

49

65

D

1-690

1-626

1-596

a

32-77

28-36

26-57

[P] .

217-1

217-7

218-1

The dielectric constant of the oxychloridc is 13-9 at 22 C. 10
The heat of formation is nearly twice that of the trichloride and also
greater than that of the pentachloridc according to the equation

P (solid) +i-Oo (o-as) +HCL, (gas) =POC1 3 (liquid) +146-0 Cals., 11

145-9 Cals. 12

1 du Pont de Xemours Cie, U.S. PdU-nt, 14 62732, 192.3.

2 \Vurtz, lac., ciL; Cahours, Ann. Ghim. Phys., 1847, 20, 36!).

3 Thorpe, Trans. Chan. Soc., 1880, 37, 141, 327; Thorpe ami Tutton, Trnn*. Chcm.
Soc., 1890, 57, 572; 1891, 59, 1019.

4 Thorpe, loc. cil. See also under "Surface Tension."

5 Ullmann and .Fornaro, loc. cit.

Besson, Cow.pt. rend., 1896, 122, 814.

< Oddo, Atti R. Aa-ml. Lineal, 1901, [o], 10, i, 452.

8 J^amsay and Shields, Trans. Cht-tn. Soc., 1S93, 63, 1089.

9 Sudden , Reed and AVilkins, Trans. C/iem. Soc., 1925, 127. . 1525.

10 Sehlundt, ,7. Physical Chan., 1902, 5, 157, 503.

11 Thomsen, " Therm. Unttrsuch." Leipzig, 1862.

12 Berthclot. Ann. Chim. Pliiis., 1879, To], 16, 442; 1898, [71, m, 185.

108 PHOSPHORUS.

The heat of formation from the trichloride and oxygen is also consider
able, thus

PC1 3 (liquid) +-^O 2 (gas) = POC1 3 (liquid) +70-66 Cals. 1

The heat of hydrolysis with water is 74-7 Cals. 2 If much water is
used the products are orthophosphoric and hydrochloric acids, but
when the compound deliquesces in moist air pyrophosphoryl and
metaphosplioryl chlorides (q.v.) are formed as intermediate products. 3
It is also hydrolysed by hydroxylated organic compounds and is much
used for preparing chlorinated derivatives, e.g. C 2 H 5 C1 and CH 3 COC1
from C 2 H 5 OH and CH 3 COONa respectively. By this means also
alkyl chlorophosphates and alkyl phosphates can be prepared, e.g. :

The alcohol must be added drop by drop to the phosphoryl chloride
cooled in an ice-salt mixture. 4 Sodium ethoxide yields triethyl
phosphate :

3C 2 H 5 ONa -r-POClg = PO(OC 2 H 5 ) 3 + 3NaCl r >

The oxychloride is also hydrolysed by orthophosphoric acid, which
is dehydrated to the meta-acid. and by phosphorous acid, which is
dehydrated and oxidised to metaphosphoric acid, thus :

2H 3 PO 4 + POC1 3 = 3HPO 3 + 3HC1
2H 3 P0 3 -r3POC! 3 =3HPO 3 + 2PC1 3 -r3HCl G

When the oxychloride is treated with potassium chlorate the chlorine
of the former is displaced by oxygen, according to the equation

2POC1 3 -r KC1O 3 =P 2 O 5 -r 3C1 2 + KC1 7

A similar displacement can be effected by sulphur trioxide, thus
2POC1 3 + 6SO 3 =P 2 O 5 -f 3S 2 O 5 C1 2 8

Hydrogen sulphide gives a phosphorous oxysulphidc, and, when the
reaction is carried out at 100 C., an oxychlorosulphide to which the
formula P 2 0,SC1 4 was assigned, and which could be distilled under
reduced pressure."

Phosphorus oxychloride chlorinates the oxides of several nou-
metals. The chlorides produced may form addition compounds with
excess of the oxychloride: thus SeOCU gave SeCl 4 and P 2 O 5 ; 10 TeO.>
gave TeCl 4 .POCl 3 ; n B 2 O 3 gave 13C1 3 .POC1 3 as well as BPG. 4 . 12 Other

1 Thomson, iuc. cit.

~ Bcriliolot and Lu^inin, An-ii. Chini. Pti.ys., lS7o, [;") , 6, 80S.

Be.sson, Co-nipt, rend., 1890, 122, 814; J897, 124, 151, 703, 1099; 1901, 132, looO.

1 13ala.rcf.T, Zcitxch. anorf/. Cher/i-., 1917, 99, 187.

5 GcutLer and ik ockhoil s, J. pmkt. Chem. 9 1873, [2], i, 101.

Gouther, Atinakti, 186^, 123, 113.

7 Spring, Utr., 1874, 7, 1584.

b Michacihs, Jtn.a Ztit., 1870, [ 11, 6, 86.

OXY- AND THIO-HALIDES. 109

addition compounds are as follows : SbCl 5 .POCl 3 ; * TiCl 4 .2POCl 3 ; 2
TiCl 4 .POCl 3 ; ! A1C1 3 .POC1 3 ; 3 SnCl 4 .POCl 3 . 4

Phosphorus oxychloride is a good solvent for various acid chlorides,
bromides and iodides such as those of arsenic and antimony, for
VOC1 3 , S 2 C1 2 and halides of transitional elements such as FeCl 3 and
PtCl 4 . For this reason, and on account of its relatively high freezing-
point, POC1 3 has been much used for the determination of molecular
weights by the cryoscopic method.

Combination with dry ammonia in carbon tetrachloride gave a
solid product which was said to be the hexammoniate, POC1 3 .6NH 3 , 5
while gaseous ammonia gave a white solid from which amides and
aminochlorides were isolated. 6

Metals with widely different electro-affinities ranging from the
alkalies to silver and mercury were not found to be affected much in
the cold, but when heated they gave oxides, chlorides and phosphides
in various cases.

Addition compounds such as Ca0.2POCl 3 and Mg0.3POCl 3 were
obtained by heating the constituents together. 7

Pyrophosphoryl Chloride, Diphosphorus trioxy tetrachloride,
P 2 3 C1 4 . This compound was first prepared by the action of N 2 O 3
or N 2 4 on PC1 3 . 8 It is also produced as an. intermediate product in
the hydrolysis of POC1 3 . Thus when POC1 3 is heated with a tenth
of its weight of water in a sealed tube at 100 C. the three phosphoric
oxy chlorides (phosphoryl, pyrophosphoryl and metaphosphoryl) are
present and may be separated by distillation in vacuo.* Phosphorus
pentaehloride (2 mols.) and water (3 mols.) also gave this oxychloride
when heated to 126 C. under pressure. 10 When separated by fractional
distillation under reduced pressure from POC1 3 , which is more volatile,
and P0 2 C1 } which is less volatile, the pyro-compound appeared as a
colourless fuming liquid which had a much lower freezing-point and
a higher boiling-point than POC1 3 . At ordinary pressures it distilled
with decomposition. The analysis agreed with the empirical formula
given. 11

The density is about 1-58. 12 The freezing-point is below -50 C.,
the boiling-point 210 to 215 C. 12

The liquid distils with some decomposition, which may be expressed
by the equation

<3P n n /ipnn p n

*> L oU 3 Ui 4 ^r4i UL.lo -pi 2 U 5

The reaction must be reversible since P 2 O 3 C1 4 has been obtained by the
interaction of the compounds on the right-hand side. 13

1 YYeber, A tumlc.n, 1867, 132, 452.

2 Ruff and Ipson, Bar., 1003, 36, J783.

3 Oddo and Tcaldi, GazzMa, 1903, 33, ii, 427.

- 1 Casselniann, J. pra./d. Chc-m., 1850, [i ], 69, 11).
5 Perperot, Co-inpl. rttid. t 1925, 181, 662.

(i YYurtz, CompL rc.nd., .1847, 24, 288; SchilT, J. pmld. Cham., JS57, [1], 71, 161;
ibid., [1], 72, 331; Gladstone, Tran$. Chcm. Soc., 1851, 3, 5, 135, 353.

7 Bassett and Taylor, Trim.*. Cham. Soc., 1911, 99, 1402.

8 Gcuthcr and Mich a el is, Btr., 1871, 4, 766.

9 Bcsson, 181)7, loc.. c.iL

10 Oddo, Gazzctift,, 1890, 29, ii, 330.

11 Gcuthcr and ^Michachs, loc. cil.; Oddo, loc. cil.; Huntly, Trans. Chtm. Soc., 181)1,
59, 202.

12 Geutlier and Michaebs, loc. cit.

13 Huntly, loc. cit.

110 PHOSPHORUS.

By the action of PC1 5 the ordinary oxychloride is regenerated, thus

p n n pn *3pnn

234 "*"" 5 ^^ ^3

PBr 5 reacts in a similar manner with the production of an oxychloro-
bromide, thus

Po0 3 Cl 4 -f PBr 5 = 2POBrCl, -r POBr 3

J. O -i d ^ 3

Hydrolysis leads to the same final products as are formed in the
hydrolysis of POC1 3 . Pyrophosphoryl chloride also acts in a similar
way with organic compounds containing the hydroxyl group giving,
e.g., ethyl esters of phosphoric and chlorophosphoric acids.

Addition compounds with lime, magnesia, and several other basic
oxides were formed in organic solvents such as acetone, or ethyl acetate
and other esters, and appeared as crystalline substances, associated
usually with two molecules of the solvent, e.g. CaO.P 2 O 3 Cl 4 .2(CH 3 ) 2 CO. 1

Metaphosphoryl Chloride, PO C1, was prepared by heating
P 2 5 with POC1 3 in a sealed tube at 200 C. for 36 hours, thus

and also by the slight hydrolysis of POC1 3 in moist air. Being the
least volatile of the chlorides of phosphoric acid it is found in the
residues after the others have been fractionally distilled. It has been
made in several other ways, including the regulated action of chlorine
gas on phosphorous oxide :

4C1 2 +P 4 6 =2POC1 3 -2POX1 3

It is a syrupy liquid which decomposes into PoO 5 and POC1 3 when
heated.

Phosphoryl Monochloride, POC1, an oxy-derivative of trivalcnt
phosphorus, is reported as having been produced by the partial
hydrolysis of phosphorus trichloride, the excess of which was distilled
off under reduced pressure. The residue was a waxy mass with a
pungent odour, and dissolved in water with great energy. 4

Phosphoryl Dichlorobromide, POCl 2 Br, was made by passing
a mixture of IIBr and the vapour of POC1. } through a glass tube at
400 to 500 C., 5 and also by the action of PBr 3 oirP 2 O 3 Cl 4 (q.v.). A
good yield is obtained from the halogcnated alkyl derivatives. Phos
phoryl ethyl dichloride when treated with bromine gives ethyl bromide
and POCloBr. 6 Phosphoryl ethoxydichloride, which may be obtained
from alcohol and P 2 O 3 C] 4 , is acted upon by PBr 5 according to the
equation

PO(OC 2 H 5 )C1 2 -f PBr 5 = POCUBr -!- POBr 3 ->- C Jl 5 Br 7

The formula was established by analysis and by the determination
of vapour density. 6 The density is 2-12065 at O c C". and 1-8:38-14 at the

1 Bassctt and Taylor, loc. cit.

2 Guritavson, Ber., 1871, 4, 853.

3 Thorpe and Tutton, Trans. Chtni. Soc,., 1S!)0, 57, ~>72.

4 Bcsson, Cornpt. /end., 181)7, 125, 17.1.

5 Bcsson, CompL rend., 1896, 122, 814.

Menschutkin, Annalen, 1866, 139, 343.

7 Geuthcr and Michac-lis, loc. at.; Gcuther and licr^t, Jena Zc>./., 1S76, [] 3 ii
10-1.

OXY- AXD THIO-HALIDES. Ill

boiling-point, 137-6 C. The coefficient of expansion is expressed by
the equation l

The solid melts at 11 to 13 C. 2

The chemical properties are similar to those of POC1 3 . When
heated the compound dissociates into POC1 3 and POBr 3 .

Phosphoryl Ghiorodlbrornide, POClBr 9 , was prepared by the
action of HBr on POC1 3 . It melts at about 30 C. and boils at 150 to
160 C. The chemical properties are similar to those of POCUBr.

Phosphoryl Tribromide, POBr 3 , is produced by reactions analo
gous to those which are used in the preparation of phosphorus oxy-
chloride (a) By the gradual hydrolysis of the pentabromide. 3 (b)
By the oxidation of the tribromicle at its boiling-point with oxygen, 4
or in the cold with oxides of nitrogen. 5 (c) By the mutual action
between P 2 O 5 and PBr 5 according to the equation

(d) By the oxidation of P 4 O 6 with Br 2 , thus
P 4 6 -r 4Br 2 =2POBr 3 -fS

Properties. Phosphoryl bromide is a solid which crystallises in
colourless plates. The formula was established by analysis and vapour
density. 8 The molecular weight as determined by the cryoscopic
method is 300 in benzene. 9 The density of the solid is given as 2-822. 10
The melting-point is given as 4-5 C., 11 50 C. 12 The boiling-point is
193 C. (758 mm.) 13 or 108 C, (700 mm.). 7 As would be expected, the
heat of formation from its elements is considerably less than that of
POC1 3 , and is given by the equation

P (solid) + -i-O 2 -r HBr 2 (gas) =POBr 3 (solid) + 120 Cals. 14

or +120-75 Cals. 6

P (solid) + JOo -r-HBro (liquid) = POBr 3 (solid) -f 108 Gals. 1 " 1

or -1-109-65 Cals. 6

The heat of oxidation of PBr 3 was found to be slightly less than
that of PCI 3, and is given by the equation

PI* 1-3 -r -JO 2 = POBr 3 (solid) -- (H-88 Cals. 6
Hydrolysis follows the usual course, and the heat evolved per mol

1 Thorpe, 1880, loc. c/t.

2 Geuther and Miohaeh.s, loc. cit.; Bosson, /or.. C-it.

3 Gladstones Phi. May., 1849, 18 |, 35, 345.

! Demole, Arch. ,S r/, pky*. nat., 1880, [3], 4, 20-(.
" Ooiithor and Miohaolis, />Yr., 1871, 4, 7(50.
.Bc-ro-er, CoiapL rc.nd., 1DOS, 146, 400.

7 Thorpe and Tuti.on, Inc. ctL

8 Killer, Aniifilc.ii, 18-15, 95, 210; Gladstone, loc. c/f.; .Baudrimom.-, Conipl. rend..,
1861, 53, 6ii7; Ann. Ch-itn. Phy*., I 8b 4, [4 |, 2, 08; "Berber, loc. cit.

!) Oddo and Tealdi, Gazzd/a, 11)03, 33, li, 4o.").

10 Rittor, loc. di.

11 Hitter, toe. a!.; Thorpe and Tutton, Trans. Chc.w. Soc., 1801, 59, 1019.

12 Bcsson, Comvt. rend., 181)0, in, 972; J>eru cr, loc. c/t.

112 PHOSPHORUS.

of POBr 3 hydrolysed was 75 Cals. 1 The action of hydrogen sulphide
on the tribromide is described on p. 101.

Metaphosphoryl Bromide, PQ 2 Br, was found as a less volatile
part of the products of the action of bromine on phosphorous oxide. 2

Oxyiodides. A crystalline substance having the formula P 3 I G 8
was found amongst the residues from the preparation of ethyl iodide.
It formed red crystals which melted at 140 C. and were soluble in
water and in ether. 3

THIO-HALIDES.

Phosphorus Thiotrifiuoride or tliioplwsphoryl fluoride, PSF 3 ,
was first prepared by heating a mixture of phosphorus and sulphur
with an excess of lead fluoride in a lead tube to 250 C. and leading
over the mixture a current of dry nitrogen. The gas was purified by
standing for about a day over dry lime. It was also prepared by heating
arsenic trifluoride in a sealed tube with phosphorus thiotrichloride : 4

AsF 3 +PSCl 3 =PSF 3 -f-AsCl 3

It is a transparent and colourless gas, which has no action on glass
at ordinary temperatures. The formula has been established by
analysis and from the vapour density. The compound is decomposed
by heat, giving sulphur and fluorides of phosphorus, thus :

PSF 3 =PF 3 -f-S
5PF 3 =3PF 5 + 2

It burns in air with a blue or greyish-green low-temperature flame.
The white fumes which are produced contain P 2 O 5 . The sulphur
probably burns first, leaving PF 3 , which combines with more oxygen,
giving PF 5 and P 2 O 5 , the whole reaction being summarised by the
equation

10PSF 3 + 3 5O 2 = 6PF 5 + 2P 2 O 5 ~ 10SO 2

With moist oxygen in closed vessels the reaction may proceed ex
plosively, but it does not proceed at all when the gas and the oxygen
are intensively dried. The gas was slowly absorbed and hydrolysed
by water, more rapidly by alkalies, thus :

PSF 3 ~ 4,H.O =H S + 3IIF + H 3 PO 4

PSF 3 -f- GNaOH =Xa 3 PS0 3 + 3NaF + 3H 2 O

Phosphorus Thiotrichloride or thiophosphoryl chloride, PSC1 3 , has
been prepared by many reactions :

(a) The first method, which led to the discovery of this compound,
was by the action of II 2 S on PC1 5 , with elimination of II Cl, thus :

H 2 S + PC1 5 = PSC1 3 + 2IIC1 5
The H 2 S may be supplied in the liquid form. 6

1 Bcrger, loc. c-iL

2 Thorpe and Tut.ton, lor., cit.

3 Burion, Amtr. Che.rn. J., 1SSI, 3, 280.

- 1 Thorpe and "Rodger, Trati.*. Chew. Soc., 1888, S^, 706; 1889, qq, 300.

OXY- A]STD THIO-HALEDES. 113

(b) Some sulphides of the non-metals yield their sulphur to PC1 5 in
exchange for chlorine :

CSo - 2PC1 5 = 2PSC1 3 -f CC1 4 i
P 2 S 5 +3PC1 5 = 5PSC1 3 (in a sealed tube at 120) 2

Compare also :

Sb 2 S 3 + 3PC1 5 = 2SbCl 3 + 3PSC1 3 3

(c) Sulphur combines directly with PC1 3 in a sealed tube at
130 C. :

PC1 3 +S=PSC1 3 4

(d) Sulphur monochloride combines when heated with phosphorus,
thus :

2P+3S 2 Cl 2 =2PSCl 3 -r4S 5

(e) Sulphur monochloride reacts with phosphorus trichloride in the
presence of iodine, thus :

3PC1 3 + S 2 C1 2 =2PSC1 3 +PC1 5 6

(/) Thionyl chloride when heated with tetraphosphorus deca-
sulphidc in a closed tube at 100 to 150 C. reacts according to the
equation

P 4 S 10 + GSOClo = 4PSC1 3 + 3SO 2 + 9S 7

Properties. Thiophosphoryl chloride is a transparent colourless
liquid which fumes in the air and smells of hydrogen sulphide. The
formula has been established by analysis and vapour density deter
mination. The density of the liquid is 1-66820 at C. and* 1-45599
at the normal boiling-point, 125-12 C. s The coefficient of expansion
between these temperatures is given by 8

r- t - V Q (\ + 0-() 3 99(rm -i- 0-0 6 90302J 2 -f 0-0 8 8825J 3 )

The melting-point is -35 C. 9

Thiophos]ihoryl chloride decomposes when passed through a red-
hot tube, giving PC1 :} , S and S Clo. 10 An excess of chlorine combines
with both the other elements, according to the equation

2PSC1 3 -!-3CL 2 =2PC1 5 + S 2 C1 2 ll

The com]K)und is reduced slowly by hydrogen iodide, giving PI 3 , H 2 S,
1IC1 and sulphides of phosphorus. 12 Like other halidcs of phosphorus
it combines with dry ammonia, giving a white solid, which may contain
from 30 to 60 per cent, of XII 3 . This product is said to contain thio-

1 Rathko, Zf-.itfich. Chnn., 1870, T2], 6, 57; Hofmann, Annalcn, I860, 115, 264.

2 Thorpe, Tranx. Chaw.. Xw.. J880, 37, 327; Weber, J. prakt. Chcm., 1859, [1],
77, 6r,.

3 JUudrimont, Ann.. CJum. Fhys., 1864, [-1], 2, 8.
- 1 I-Ferny, Bc.r., 1S69, 2, 638.

5 Wohfer, Arinalc/i, 1855. 93, 274.

6 Kohn and Ostersctzer, ZcMtich. anorcj. Chcin., 1913, 82, 240.

7 Prinz. An.nnlt ii. 18S-J. 22?. 368.

114 PHOSPHORUS.

phosphoryl diaminochloride, P(NH 2 ) 2 C1S, or thiophosphoryl triamme,
P(NH 2 ) 8 S. 1

Thiophosphoryl chloride dissolves sulphur and phosphorus freely
when hot, but only sparingly when cold. 2 Since the liquid is immiscible
with water the hydrolysis proceeds only on the surface at first, as is
usual with phosphorus halides. In this case the products are phos
phoric acid, hydrogen chloride and sulphide and a little sulphur. It
reacts with ethyl alcohol, giving ethyl chloride and ethyl thiophosphate :

3C 2 H 5 OH + PSC1 3 = (C 2 H 5 )H 2 PSO 3 + 2C 2 H 5 C1 + HC1 3

Thiophosphates can also be made from the thiochloride with sodium
ethoxide and aqueous alkalies. 3

Phosphorus Thiotribromide, PSBr 3 , has been prepared in a
number of different ways :

(i) By the action of phosphorus pentabromide on hydrogen sulphide,
according to the equation

PBr 5 +H 2 S =PSBr 3 + 2HBr 4

(ii) By distillation of the tribromide with sulphur,
(iii) By combination of the pentabromide with the pentasulphide :

P 2 S 5 + 3PBr 5 - 5PSBr 3 5

The product may be freed from pentabromide by washing with warm
water and dried by dissolving in CS 2 and standing over CaCl 2 . 6

(iv) By a reaction between ammonium trithiophosphatc and
hydrogen bromide. 7

Properties.- The compound crystallised from carbon disulphide in
yellow octahcdra, having a density of 2-7 to 2-87 and a melting-point
of +36-4 to -r39 c C. It gives off a pungent vapour, and distils at
about 212 C. with some decomposition at first into PBr 3 , then PSBr 3
follows, and finally there is a residue of sulphur and phosphorus. 8
It is only slightly hydrolysecl by water even at 100 C., the products
being phosphoric acid, hydrogen bromide and some sulphide, together
with some sulphur and phosphorous acid. Alcohol vsis is said to yield
ethyl thiophosphate, (C 2 H 5 ) 3 PSO 3 . 9

Thiophosphoryl bromide dissolves sulphur and mixes with other
halides such as phosphorus trichloride, also with ether, chloroform and
carbon disulphide. 3

Several other thiobromides of phosphorus have been prepared,
which can be regarded as derivatives of pyrophosphoric acid. Diphos-
phorus inonothiohexabromide, P 2 SBr 6 , is prepared by distilling PSBr 3 ,
and appears as a yellow oil which can be solidified to crystals melting
at -5 C. The boiling-point is 205 C. When mixed with water it
gives a crystalline hydrate melting at -}-35 C. P 2 S 3 Br 4 (di phosphorus

1 Gladstone and Holmes, Trans. Chew. Soc., 1865, 18, 1; Chcvrier, loc. cit.

2 Scrullas, loc. cit.

3 Cloez, Compf.. rend., 1857, 44, 482.

4 Gladstone, Trans. Che/m. Soc., 1851, 3, 5; Baudrimont, loc. cit.

5 Michaelis, Annalen, 1872, 164, 39.

G Maclvor, Chern. News, 1874, 29, 116; Michaelis, tier., 1871, 4, 777; An/nahn,
1872, 164, 44.

7 Stock, Bar., 1006, 39, 1975, 1998. s Maclvor, Michaelis, Baudrimont, loc. cit.

Michaelis, loc. cit. 10 Mac-Ivor, loc. at.

OXY- AXD THIO-HALIDES. 115

trithiotetrabromide) is prepared by the action of bromine on P 4 S 6 dis
solved in carbon disulphidc. In appearance and properties it is very
similar to the other thiobromides. 1

Mixed Thiotrihalides, PSClBr and PSCUBr, have been prepared
by passing a mixture of PSC1 3 and HBr over pumice at 400 to 500 C.,
the products being separated by fractional distillation. Amongst these
is also the starting material PSC1 3 , which is formed in a sealed tube by
the reaction :

2PSQ 2 Br=PSClBr 2 + PSCl 3 2

Thioiodides may be obtained by several methods :

(i) By the interaction of the elements, in their correct proportions,

in carbon disulphide. 3

(ii) By the action of hydrogen sulphide on heated iodides of phos

phorus, thus

2PoI 4 +3H S=P 4 S 3 Io

These compounds arc soluble in carbon disulphide, from which they
may be obtained as orange or yellow crystals. They are only slightly
soluble in other organic solvents such as benzene, chloroform, etc.
They can be burnt in air, giving oxides of phosphorus, sulphur and
iodine. They are decomposed by warm water or moist air, giving
first phosphoric and hydriodic acids, then phosphoric acid and hydrogen
sulphide. 4

1 Michaolis, lac. cit.

2 Bcsson, 1806, loc. cit.

3 Ouvrard, CowpL rend., 1902, 135, 1301.

4 See also Woltcr, Chc/m. Zc.it., 1907, 31, 640.

CHAPTER IX.
THE SLOW OXIDATION OF PHOSPHORUS.

The Glow of Phosphorus . The similarity in appearance between
the glow observed on the surface of phosphorus when exposed to air
and that observed in the case of substances like commercial calcium and
barium sulphides after exposure to light is of course only superficial.
While the name " phosphorus ?? was soon restricted to the element,
the term " phosphorescence * in its scientific usage now refers to
photoluminescence, while the glow observed on smouldering phos
phorus, or fish or wood in certain stages of decay, is called " chemi-
luminescence." The slow combustion of phosphorus is seen as a pale
blue " cold flame " which continually spreads away from the surface
and is associated with a peculiar smell. The volatile products are
poisonous and consist of phosphorous oxide, and, in the presence of
water, phosphorous acid. It was soon discovered that the presence of
air was necessary " the fire and (lame of phosphorus have their
pabulum out of the air " : but low air pressures, such as remained
in the best air pump vacua of the older experimenters, were still suffi
cient to maintain the glow, whereas the combustion of charcoal was
completely extinguished. It follows that in the well-known lecture
experiment the oxygen can be removed almost completely from the air
by smouldering \vhitc phosphorus in the presence of water. The glow,
however, is extinguished in pure oxygen at atmospheric pressure. Ozone
is produced in the combustion and its presence may be demonstrated
by the usual tests (see this Series, Vol. VII., Part I.). Since tins
striking phenomenon early challenged the attention of chemists it has
been the subject of much investigation. Many of the qualitative
effects were early demonstrated by Boyle. 2 The increase in luminosity
when the air is rarefied was described by van Maruni :5 and Davy. 1
A bibliography of the older literature is given in papers by Cent
ner s/Aver 5 and Downey. 6

Effect of Pressure upon the Oxidation of Phosphorus. --At
each temperature there is a certain critical pressure below which the
glow appears. Also at each pressure (or partial pressure) of oxygen
there is a certain critical temperature above which the glow appears. 7

1 Slare, Phil. Trans., 1681, 14, -18, 84.

2 Boyle, " Ac.rial Rodduca," London, I 080: ;i Ir>/ Xoctihic.ft,.," London, 1(180.

a van Ma mm, Ann. Chi in. Ph.-?/.*., L700, [TJ, 21. fr>S; Phd. M>t</., 1800, 8, !!;>, . Ho.
- 1 J. Davy, Edit:. Phil. J., 1820, 15, -48. "
5 Centnersz\ver, Z<-it,*ch. phyxihtl Chf-ni., .18;>8, 26, 1.
Downey, Trans. Gh,ern. tioc., 1924. 125, ;M7. }Sco also Schonbem, loc,. cil. p.

SLOW OXIDATION. Ill

Thus the pressures had to be reduced below their critical values at the
particular temperatures, or the temperatures had to be raised to their
critical values at the particular pressures, in order to initiate the slow
combustion. Some values of temperature and pressure arc: 1

t C. . 1-4 3-0 5-0 8-9 11-5 14-2

p (mm.) . ; 355 : 387 428 519 580 650

As already stated, in ordinary moist oxygen or air the glow begins
at very low pressures, increases to a maximum with pressure and then
decreases, vanishing at an oxygen pressure of 600 to 700 mm. 2

The limits of pressure within which the glow occurs have also been
found by means of a photoelectric counter of the Geiger-Mullcr type. 3
A quartz tube was coated inside with a thin film of platinum which
acted as a photoelectric emitter. Along the axis of the tube ran an
insulated tungsten wire which was connected to the earthed positive
terminal of a 1200-1 5 00- volt battery. The tube was filled with air at
a pressure of 4-7 cm. mercury. The upper threshold of the radiation to
which the counter was sensitive was at 2800 A. As is seen on p. 124
radiations of lower wavelength are emitted by phosphorus glow.
Under the influence of these a photoelcctron is emitted which ionises
the air by collision, causing a drop of potential of the wire, which acts
on the grid of an amplifying valve and is recorded as an impulse on a
standard recorder of the telephone type. A residual effect of 1015
impulses per minute due to cosmic ray was constantly present. This
number was greatly increased when the wire was surrounded by oxygen
and phosphorus vapour at glow pressures, and began to be marked
between pressures which gave a yellow and those which gave a bluish
glow. The lower limit was found to be 0-3 mm. of mercury and the
upper 595 mm. when the oxygen was pure, or 400 mm. when the oxygen
was mixed with nitrogen. It was considered that these results were
best interpreted by the c; chain reaction " theory, as proposed by
Semcnoftv 1 The oxide is built up by a series of stages, some of which
result in the production of an active molecule, thus :

O + P 4 > P 4 O , P 4 O -r Go > P 4 -j- O -i- O, P 4 O - O > P 4 O 2 ,
p o o > p o > p

~ -

In these expressions only some of the active products (marked ) have
been included. Radiation is associated with the spontaneous de-
activation of an active product according to (2) below, if it does not
happen to activate a molecule of oxygen according to (1) :

P 4 10 + 2 *P 4 IO + + . . . (1)
P 4 10 ^P 4 10 + fo, ... (2)

h and v have their usual meaning of Planck s constant and the fre
quency of the radiation.

1 Joubcrt, Comyl. rend., 1874, 78, J853.

2 Mullcr, Bcr., 1870, 3, 84; Joubcrt, loc. ciL

3 Onp-.llo.i. 7W,/.s-. Fnrn.rln.--n Rnc... 1 i)33. 20. 48fi.

118

PHOSPHORUS.

Velocity of the Reaction. Quantitative determinations of the
velocity of oxidation have been based on the diminution in pressure
which follows on absorption of oxygen. This became appreciable, with
appearance of glow, at about 700 mm. oxygen pressure.

The rate of oxidation, calculated from the rate of decrease of pres
sure in a constant volume, at lirst increases rapidly as the pressure
falls, reaches a maximum at about 300 mm., and then, falls slowly
to 100 mm. Below 100 mm. the rate diminishes rapidly with further
decrease of pressure. 1

The velocity constant K of a unimolecular reaction, i.e.

(p and P; arc the partial pressures of the oxygen at the beginnino-
and after the lapse of t minutes) is given in the following table: 2

RATE OF ABSORPTION OF OXYGEN IN MOIST
AIR BY PHOSPHORUS.

Time in Minutes.

Total Pressure in
mm. of Mercury.

Partial Pressure ~
of Oxygon. A

AY

773-1

157-8

25

750-0

135-3

0-00207

42-0

50

729-7

114-0

0-00282

1-3-1

75

714-3

99-0

0-00271

40-1

100

01)7-4

82-1

0-00284

4-2-3

130

082 -2

()G-9

0-00286

42-1

The constant /v increases on the whole with time (although somewhat
irregularly), showing that the reaction takes place somewhat faster at
a lower pressure than would he expected assuming that it is directly
proportional to the partial pressure ol. the- oxygen. Since the reaction
takes place between the phosphorus vapour and the oxygen, the
reason 1 or the increase in the constant was sought in the increased
rate of evaporation of the clement at the lower pressures. A correction
was introduced for the vapour pressure p L of the phosphorus in the
Form - -

in which P is the total pressure. The integration of this equation
gave the corrected constants /v t in the above table. The results given
above refer to air or oxygen in its usual state, i.e. slightly moist, and
apply also when the air has been partly dried, as by bubbling through
concentrated sulphuric acid, which still leaves enough water vapour for

1 Ewan, ZciteclL. phyxikal. C/if.itt.., 180,5, 16, 315; idem, J /ul. Mag., 1894, [5], 38, 305,
512.

2 Ikeda, J. Coll. tici. 1 jnp. Uuiv. Japan, 1893, 6, -43; "tituditti -in Che/nical Dy/i-anuc. 1 : ,"
vau t Hoil-Cohen, translated by Ewan, Williams & Xorgate, 1896.

SLOW OXIDATION; 119

the continuance of slow oxidation. 1 If, however, the air or oxygen is
carefully dried, the velocities at all pressures are much lower, and are
between and 70 mm. proportional to the square roots of the oxygen
pressures. The maximum velocity of oxidation is also attained at a
lower pressure (about 100 mm. of oxygen) and the upper limit of chemi-
luminescen.ce is found at lower pressures, i.e. at about 200 mm. of
oxygen. 2 If the oxygen is quite dry, no combustion takes place, no
glow is seen and no ozone is formed the production of ozone and
hydrogen peroxide is due to the presence of moisture. 3

The results in the table may be summarised in the statement that
from low pressures up to a certain limiting pressure the velocities are
proportional to the oxygen pressure and are also a function of the rate
of supply of vapour from the surface of the phosphorus. In fact, if in

the equation on p. 118, - rrr / p ~^j * s plotted against p, the graph is

& / \ ,

rectilinear from the lowest value of oxygen pressure up to 520 mm.,
then rapidly decreases to zero at 700 mm.

Loiv Pressures. The velocity of oxidation oC phosphorus vapour at
low pressures has been further investigated by Scmenoff, 4 who found
that an inert gas increases the reaction velocity and lowers the lower
critical oxidation pressure. The subject was taken up at this point
by Melville. 5

According to Scmenoff 6 "if p L ^, p 0o and p x are the pressures of
phosphorus, oxygen and inert gas respectively, then, at the lower
explosion limit

7J-, x n f 1 + - inconstant . . (1)

-i J 4 J- (Jz\ ff) i , rl / v

\ Pi i + PoJ

provided that the explosions arc confined to a vessel of a given size.
Now (1) indicates that the inert gas effect should be independent of
the nature of the gas. Subsequent work 7 has shown that (1) does

not describe cxact.lv the effect oC gases on the lower critical oxidation

"

limit of phosphorus. From (1) it is seen that if 1/^ ., is plotted against

1 + PXJ(PP I + PoJj a straight line is obtained. The slope A of this line is,
however, dependent on the nature of #."

The critical pressure or glow pressure is affected by the presence of
inhibitors (see p. ]2T).

The explanation why such a complicated reaction as the slow
oxidation of phosphorus appears to be unimolecular is one which has
often been brought forward in similar cases. The slowest part of the
process is a diffusion, either of oxygen molecules to the reaction surface,
or of phosphorus molecules from the surface, or of the inhibiting mole
cules of phosphorus oxide from the surface. According to the theory
of diffusion the rates will follow the unimolecular law. Since the
vapour pressure of phosphorus is low at ordinary temperatures, the

1 JRussell, Trans. Chcm. /S oc., 1903, 83, 1263.

2 van I Ho if -Cob en, loc. cil.

3 Baker, Pkd. Trans., 188S, 179, A, 571; Baker and Dixon, Proc. Roy. Soc., 1889,

45, I-

1 Semenotf, Zutech. Physik, 1927, 46, 109; Zeitvch. yhytikal Chan., 1929, 2, B, 161.

5 Melville, Trans. Faraday Soc., 1932, 28, 308.

6 Loc. cti.

120 PHOSPHORUS.

concentration of oxygen molecules is many times greater than that of
phosphorus molecules, even at the lower oxygen pressures. 1

Phosphorus vapour when apparently inactive in an atmosphere of
oxygen may really be combining with the oxygen at isolated centres,
but the combination does not spread, on account of the inhibitory
effect of the enormous excess of oxygen molecules. 2 The combination
has obvious similarities to the combustion of hydrocarbons, etc.. in air
or oxygen, which, as is well known, is limited and finally inhibited by
an excess either of the combustible substance or of oxygen. An excess
of oxygen probably hinders the diffusion of phosphorus across the
solid-gas interface on which a layer of vapour is continually being-
formed and removed. If the rate of formation of oxide (especially in
a dry atmosphere) exceeds that of evaporation of the phosphorus, a
protective coating of oxide will also inhibit further action. 3

The products of oxidation have been investigated. 4 When the
oxidation was carried out in moist air or oxygen the partial pressures
of which were varied between 100 and 1200 mm. the product was a
nearly constant mixture of the tetroxide and pentoxide. The empirical
composition PO 2v io i s nearly the same as that of the corresponding
product derived from P 4 O 6 . It is considered that the phosphorus
trioxide is formed as an intermediate stage which docs not accumulate
in the system.

Effect of Temperature. The pressures corresponding to the
maxima of chemiluminescence diminish with fall of temperature ; at
O c C. the maximum oxygen pressure is 320 mm., while by extrapola
tion this pressure would become zero, and the effect vanish, at - 13-8 C.
The pressures at which the glow first appears also decrease with fall
and increase with rise of temperature. At 27 C. the glow appeared
in oxygen at atmospheric pressure. 3 At higher temperatures the
velocity, as is usual, increases greatly, until at about 60 C. (or at lower
temperature if pressure is reduced) the combustion changes its character,
and the phosphorus ignites. 5

Production of Ozone. In. the first definite description of ozone
by Schonbein in 184-0 the discoverer noted that this gas is produced by
the slow oxidation of phosphorus G (see Cu Ozone," this Series, Vol. VII.,
Part I.).

It was observed later that half an atom of oxygen is activated for
every atom of phosphorus which is oxidised. 7 This may be explained
on the supposition that the reaction takes place in stages, thus : 8

1 Chariton and Walton, Zeittch. Phyfiik, 1926, 39, 547.

2 Kayleigh, "Royal Institution Discourse, Xatwrc, 19:24, 114, 80; idem, Proc. Roy.
Soc., 1922, 104, A, 322.

3 Wciscr and Garrison, J. Physical Chun., 1921, 25, 61, 349, 473.

4 Miller, Trans. Clie.ru. Soc., 1929, p. 1829.

5 Yveiser and Garrison, loc. at.; Eyclmann, Rec. Trav. cklm., 1901, 19, 401.

G Sohonbein, /. prakt. Chem., 1868, 105, 226; 1864, 93, 25; and many references back
to 1845; Macleod, Trans. Cham. Soc., 1880, 37, 188; Kingzett, ibid., 1880", 37, 392; Leeds,
Chem. News, 1881, 43, 97; Chappuis, Bull. Soc. c/iim., 1881, [2], 35, 419.

7 Ost \vald, Zeitsch. physikal. Chem., 1900, 34, 248.

8 Downey, Trans. Chem. Soc., 1924, 125, 347.

SLOW OXTDATTOX. 121

The amount of ozone formed is proportional to the intensity of the
glow, and is 0-5 to 5-0 x 10~ 6 gram per c.c. of gas which passes over
the phosphorus. The radiation from the glow has been proved capable
of producing ozone. - 1

The effect of ozone is to raise the upper critical explosion limit for
phosphorus and oxygen and to lower the lower limit. 2 The effect is
much greater than that for an ordinary neutral gas (equation, p. 119).
The presence of 5 per cent, of ozone in phosphorus vapour and oxygen
diminishes the lower critical pressure by about 20 per cent., whereas
the normal effect for an inert gas at this concentration would be 1 to
2 per cent. 3

Inhibition of the Glow. The following substances diminish or
destroy the glow at ordinary temperatures, or allow it to appear only
at higher temperatures chlorine, iodine, nitrous and nitric oxides,
hydrogen sulphide, sulphur dioxide, turpentine, alcohol, benzene, chloro
form, aniline, ethylene, acetylene and other unsaturated hydrocarbons,
and lead tetraethyl. 4 5i 6 The glow is not diminished by nitrogen,
sulphur, acetic acid, hydrogen chloride or ammonia in small quantities.
Some of the inhibitors will combine with ozone, but it has been, stated
that their relative activity in inhibiting the glow is not the same as
that shown in destroying ozone. 7

The diminution in the rate of propagation of the glow was shown
by measuring the velocity of an air current which was just sufficient
to carry the glow to a point marked in a tube. 7 This method was also
used in examining the effect of varying the partial pressures of oxygen
in nitrogen. 8 In the presence of 0-16 per cent, of ethylene this velocity
was 140 cm. per second, and when the percentage was increased to
0-43 the velocity required fell to 1 cm. per second. The temperature
at which the glow is first seen increases with increasing concentration
of ethylene, etc-., and can be raised to well over 60 C., the normal
ignition point of the phosphorus. When air containing 8 and 26 per
cent, of ethylene was heated for long periods in contact with phos
phorus a certain amount of non-luminous oxidation did occur. It has
been shown further ;) that the partial pressure of the ethylene which
will just inhibit the glow is proportional to the partial pressure of the
phosphorus over the range 60 to 97 C.

Phosphorus trioxidc itself inhibits the glow of phosphorus, being
about three times as powerful in this respect as ethylene. The ratio
of the partial pressure of trioxidc to that of ethylene which just stops
the glow 9 is about 145.

The inhibitory effect may also be expressed as a function of the
" glow pressure " at which the glow can just be detected. An empirical
equation was used by Tausz and Gorlacner 10

1 Downey, loc. ciL; \Vcisor and Garrison, loc. cit.

2 Kowalski, Ztilxch. pliyxih d. Ckem., 1929, 4, B, 288.

3 Melville, loc. at.

4 v. Vogcl, Annakfi, 1814, 48, 375; J. pra/ct. C/icm., 1840, [1], 19, 394.

5 Dcschamps, CompL rtnd.* 186J, 52, 355.

6 Tver, Chtm. JVcw.s, 1923, 127, 321; Chappms, loc. ciL
1 Emoleus, Trans. Ch&nt. &oc. f 1926, p. 1336.

8 Bloch, L. and E., Compt. rend., 1908, 147, 842.

9 Miller, Trans. Chtm. Soc., 1929, p. 1926.

10 Tausz and Gorlacher, Ztiisch. anorg. Chern., 1930, 190, 95.

122 PHOSPHORUS.

in which p x represents the partial pressure of oxygen at which the
glow appears, x is the percentage by volume of the inhibitor or anti-
catalyst and a and K are empirical constants for each substance. This
equation holds for certain percentage admixtures in the case of each
inhibitorthus for 0-1 to 0-9 per cent, sulphur dioxide ; for 2 to 10
per cent, benzene ; for 0-01 to 0-1 per cent, isoprene ; for 0-0 4 6 to
0-0 4 7 per cent, iron carbonyl. The corresponding values of the constants
are as follows :

Sulphur Dioxide. Benzene. Isoprene. i Iron Carbonyl.

23

21 ;

0-025

13520

10805

20

0-0 4 74

0-0 4 93

0-05

a 23 ; 21 , 0-025 0-0033
K 13520 10805 20 1-7

0-59

The maximum pressure at which the glow will persist is lowered by
these substances, and their activity in this respect is proportional to
IjK. It is noteworthy that lead tetraethyl (p. 121) and iron carbonyl,
which are known as " anti-knock :; additions to petrol, are both very
active inhibitors.

The results of these experiments lend support to the theory that
oxidation probably takes place only in the gaseous phase and is
catalysed by the active oxygen produced in the reaction.

Nature of the Chemilurninescence. Many observations lead to
the conclusion that the glow is produced by the combination of gases
only. The glowing zone may be removed from the surface of the
phosphorus by a current of air, leaving a dark space in the immediate
neighbourhood of the phosphorus. 1

The glow is exhibited by ordinary phosphorus trioxide, 2 but is then
really due to small quantities of dissolved phosphorus. The oxide
when purified as described on p. 12C gave only a momentary glow at
the commencement of the oxidation (by oxygen), which afterwards
proceeded without emission of light. The glow of phosphorus, which
actually is inhibited by the trioxide, is restored continuously as this is
hydrated by small amounts of water vapour. 3 The inhibitory effect
of I 3 4O 6 is also removed by ozone.

lonisation by the Glow. Air which has been drawn over smoulder
ing phosphorus is rendered electrically conducting, so that it allows
an electroscope to discharge itself 4 whether it is positively or negatively
charged; therefore gaseous ions of both signs are produced. These
may be charged atoms, O r and O~, one of which may combine with
the phosphorus and the other form ozone. 5 The conductivity is not

1 Bloch, L. and E., Com.pt. rend., 190S, 147, 842.

2 Scharff, Zcitsch. physibal. Chtni., 1908, 62, 179.

3 Miller, Tm,,.#. Chun, tioc., 1928, p. 1817

- 1 Matteuci, Cuin.pl. rend., 1851, 32, 145; 33, 663; Chrislomanos, Ztltscli. aticrg.
Cht/n., 190.3, 45, 132.

5 See also Brodic, J hil. Trans., 1850, 1862, 1863, 152, 407; Clausius, Annahu, 1858,
103, 644; 1864, 121, 250; Schonbein, loc. clt.; v. Helmholtz and Richarz, Wied. Annaltn,
1890, 40, 161; Elster and Gcitel, Wial. Annalen, 1890, 40, 191; Physikal. Zeitsch., 1903,
16, 457; " The Conduction of Electricity through Gases," J. J. Thomson, Cambridge, ]903;
Bloch, E., " Recherches sur la conductibiUtc eleclrique de Vair produite par le, pho&phore et
sur les gaz recemment prepares, Paris, 1904; Blocii, E., Ann. Chirn. Pity*., 1905, [8J, 4, 25.

SLOW OXIDATION. 123

due to the ozone itself, since after removal of this, conductivity is
retained. 1

The fact that below 100 mm. the rate of oxidation is proportional
to the square root of the partial pressure of oxygen suggests that the
active atoms of oxygen are produced before the combination. 2 The
difficulty in this supposition is that there is no apparent source of the
high energy of activation required, which could, however, be drawn
from a coupled reaction such as that formulated on p. 120, or from
the formation and decomposition of a peroxide. 3

It has been shown by numerous investigators that the connection
between ionisation, oxidation and chemiluminescence is a close one.
If air or oxygen is mixed with the vapours of turpentine, etc., the
conductivity of the mixture after passing over the phosphorus is only
slight, corresponding to the suppression of the glow. 4

The mobilities of the positive and negative ions were found to be
equal at first, but the mobilities and sizes change with time. Maxima
and minima were found at different temperatures, including a maxi
mum mobility just below the ignition temperature, at 40 C. 5

Moisture is favourable, perhaps even essential, to the ionisation,
which leads to the opinion that the conducting ions may be those of
an acid.

The gases in flames are ionised as a rule, and it has been stated that
the vivid combustion of phosphorus also gives rise to ionisation. 6

One cause of the ionisation is indicated by the observation that the
light Crom glowing phosphorus when transmitted through a window
of lluoritc, is capable of ionising air on the other side." This proves
that the light contains ultraviolet radiations. 8 This light also pro
duces ozone. 9 Under otherwise similar conditions ozone is produced
from oxygen in greater amount by light transmitted through a window
of fluorite than by that transmitted through a window of quartz. 10
Now it is known that quartz (2 mm. thick) is weakly transparent to
light of wavelength lower than 200 m//, and opaque to that of wave
length below 160 n~}jji ; while lluorite is opaque to light of wavelength
below 125 m/ji. This, taken in conjunction with the observation u
that light of wavelength 120 to 180 m/x, is a strong ozonising agent, while
that of wavelength 230 to 290, especially 257, decomposes ozone,
explains the effect mentioned above.

The Emission Spectrum. A spcctroscopic examination of the
light emitted by glowing phosphorus reveals a number of narrow
bands in the ultraviolet at

1 Schmidt, H., Phyxih.d. Zeilxch., 1013, 14, .120.

2 Loew, Zcitisch: Chc/n., 1870, [2J, 6, 65; Fudakowsky, Bcr., 1873, 6, 108.

3 Obtwald, loc. cit.; Bach, Com-pt. rend., 181)7, 124, 9ol.

4 Schonck, Banthien and Mihr, Bcr., 1906,39, I. .106; Hichar/ and Schonck, Sitzunysbcr.
K. Alad. IV Us. Bc-rUu, 11)03, p. 1102; Schcrick, tbtd., 1904, p. 37; Schonck and Brouning,
Bcr., 1914, 47, 260 L.

5 1-Jamcs, Physlkal. Zcit^ch., 1904, 5, 93; Busse, Ann. Physik, 1927, J4J, 82, 873; 83, SO.
() Schmidt, G. C., Bar. Dml. $liy*iltcbl. Gts., 1906, 4, 640; Ann. Physik, 1903, [4j, 10,

704.

7 Downey, 1924, Loc. cit.

8 Lcnard, Ann. Physilc, 1900, [4], i, 486; Hughes, Proc. Cam. Phil. Soc., 1910, 15, 483.

9 .Downey, loc. cit.; Weiser and Garrison, loc. at.

10 Downey, loc. cit.

11 Regener, Ann. Physik, 1906, [4], 20, 1033.

124 PHOSPHORUS.

A -3270 2600 2530 2470 2390 A. 1
A -3275 2630 2530 2475 2390 A. 2

The same bands are shown when phosphorus burns under reduced
pressure with a flame which lias a temperature of 125 C. 2 and in the
glow of phosphorous oxide. 3 The broader bands which have been
reported as present in the light from glowing phosphorus 4 haA r e been
shown to be due to incipient combustion ; 2 they are the same as those
shown by phosphorus burning in air enriched with oxygen at a flame
temperature of 800 C. 2 and by phosphine burning in air at reduced
pressure with a flame temperature of 160 to 230 C., and also in oxygen
at atmospheric pressure. 3 The bands have, in reality, a complex
structure. Such spectra are associated with molecular rather than
atomic vibrations. There must therefore be some excited system
common in all these kinds of combustion. In this connection it was
noted by Emeleus and Purcell 5 that the band at about A =3270 had
already been observed in the light emitted by phosphorus pentoxide
when volatilised in an oxy hydrogen flame. 6

1 Centnerszwer and Petnkaln, Zeitsch. physikal. Cher/i., 1912, So, 235.

2 Emeleus and Downev, Trans. Chem. Soc., 1924, 125, 2491.

3 Emeleus, ibid., 1925," 127, 1364.

4 Pctrikaln, Zeitsch. Physik, 1924, 22, 119.

5 Emeleus and Purcell, Trans. Chem. Soc., 1927, p. 788.
f) Hartley, Phil. Trans., 1894, 185, 168.

CHAPTER X.
THE OXIDES OF PHOSPHORUS.

P ii os PIT OR us forms two well-defined oxides, namely, diphosphorus
trioxide and diphosphorus pentoxide, having the empirical forrnuhc
P 2 O 3 and P 2 O 5 respectively : an intermediate oxide, diphosphorus
tctroxide, P 2 6 4 . and possibly the suboxides P 4 O and P O. are known.

The Suboxides. A solid substance said to be tetraphosphorus
monoxide, or phosphorus tetritoxide, P 4 O, has been prepared by
a number of reactions, amongst which may be mentioned the slow-
oxidation of phosphorus in ether, and the reduction of phosphorus
pentoxide with ammonia, followed by treatment to remove other
oxides, namely, washing and evacuation. 1 The removal of water
from hypophosphorous acid is said also to yield this product, thus

4H 3 P0 2 =P 4 O+0+6II 2 O 2

Acetic anhydride in the presence of glacial acetic acid has been iiscd
as the dehydrating agent. 3 A solution of phosphorus in 10 per cent,
aqueous caustic soda with twice its volume of alcohol yielded on acidi
fication a greenish-yellow solid to which the, same composition was
assigned. 2 The substance, prepared by various methods has a red or
orange colour and a density of about TO. It is a mixture, the com
position of which may be inferred from the facts that it retains hydrogen
and moisture, that it gives phosphorus and phosphorus pentoxide
when heated in an indifferent gas, and that when distilled in chlorine
it yields phosphorus oxychloride as well as the pentachloridc. 4

The supposed compound P.>O 3 is also a mixture of finely divided
phosphorus with phosphorous acid. 6

Phosphorus Trioxide. The formation of an oxide by the slow
combustion of phosphorus had already been noticed in the eighteenth
century, 7 and the existence of such a compound was known to Lavoisier
and Davy, while the conditions of formation and the composition were
established by Dulong. 8

The method of preparation by the slow oxidation of white phos
phorus has already been described (Chap. IX.). When a current of

126 PHOSPHORUS.

dry air, or of oxygen, the pressure of which lies between certain limits,
is passed over solid white phosphorus, this oxide is formed at a slow
rate. At higher temperatures, at or above the melting-point of white
phosphorus, the rate of formation is sufficiently great, but the product
may contain less than 10 per cent, of phosphorous oxide, with nearly
80 per cent, of phosphoric oxide, and variable quantities of phosphorus
remain unburnt in the form of the white mixed with the red element. 1
It is possible to separate the phosphorus pentoxide, as is done in. the
standard method due to Thorpe and Tutton, 2 according to which a
rapid stream of dry air is passed over liquid phosphorus in a hard glass
tube, which is connected with a brass tube containing a glass wool
filter and maintained at about 60 C. by an external current of water.
This tube retains the phosphorus pentoxide, while the trioxide passes
on and is condensed in a U-tube which is immersed in a freezing mixture.
The phosphorous oxide is melted and filtered into another U-tube.
The further purification is described below.

Phosphorous oxide has also been prepared by the action of the
trichloride on phosphorous acid, thus

H 3 P0 3 ~PCl 3 =P 2 3 -r3HCl 3

It is also produced when phosphorus trichloride is used to replace the
hydroxyl group of anhydrous acetic acid, thus

3CH 3 COOH 4-2PCl 3 =P 2 3 +3HC1 -f 3CHXOC1 4

The trioxide sublimes as a mist of solid particles which arc difficult
to condense completely. The condcnsatc forms a snow-like mass of
minute crystals, or large feathery crystals, or a wax-like mass which is
very fusible, deliquescent and inflammable. The vapour smells of
garlic and is poisonous. The material contains small quantities, up to
about 1 per cent., of phosphorus, droplets of which may appear in the
later stages of the distillation. The complete removal is difficult, but
the amount may be greatly reduced by the following method. 5 The
trioxide is crystallised from dry carbon disulphidc in an atmosphere
of carbon dioxide at -18 C. The crystals arc filtered off on a per
forated porcelain disc, washed with petroleum ether and rccrystallised
from carbon disulphidc. These operations are carried out in an atmo
sphere of dry carbon dioxide. The purified oxide is analysed by
melting under water at 40 to 50 C. It is completely absorbed, whereas
the usual preparation, which is saturated with phosphorus at 25 C.,
shows a small residue of undissolvcd phosphorus under the same condi
tions. The solubility of phosphorus in the purified oxide at 25 C. is
1-7 grams in 100 grams. The solution on solidifying assumes the
opaque waxy appearance characteristic of the ordinary preparation.

Physical Properties. Most of the available data refer to the ordinary
preparation.

Solid Phosphorus Trioxide. The density (7/| r ) is 2-135. 6 The

1 Cowper and Lewes, Trans. Chem. Soc., 1883, 43, 224; 1SS4, 45, 10.

2 Tram. Chem. Soc., 1890, 57, 543; JS91, 59, 1019.

3 Kraut, Annal&n, 1871, 158, 332; Gamier, Curnpl. rend., 1873, 76, 49, 173.

4 Thorpe, Trans. Chem. Soc.. 18SO, 37, 186.

5 Miller, Trans. Chem. Soc., 1928, p. 1847.
G Thorpe and Tutton, loc. tit.

OXIDES.

127

melting-point is 22-5 C. 1 The crystalline system is monoclinic. 2
When large crystals are examined in polarised light they may show
pinacoid, prism and complementary pairs of pyramid faces. When the
oxide is freed from all except traces of the dissolved phosphorus as
just described, it appears as a transparent crystalline solid 3 and the
physical properties are slightly modified ; in particular, the melting-
point was 23-8 C. instead of 22-4.

Liquid Phosphorus Trioxide.Thc density of the slightly super
cooled liquid at 21 C. (D^) is 1-91-31 and that of the liquid at its
boiling-point,, 173-1 C., 1-6897. The smoothed values of the specific
volume as derived from measurements in a dilatometer from 27-10 to
140-30 C. are as follows, and give the coefficient of expansion of the
liquid up to its boiling-point :

RELATIVE SPECIFIC VOLUMES OF PHOSPHORUS

TRIOXIDE. 1

~ i

t C. . 25

30

50

75

]00

125

150

170

173-1

. 1-000

1-0046

1-0228 1

0459

1-0695 1

0941 1

1200

1-1419

1-1454

i

1

The vapour pressures of the liquid arc as follows: 4

VAPOUR PRESSURES OF PHOSPHORUS TRIOXIDE.

t C.

p (mm.) .

22-4

2-7

30-8
4-1

40-8
6-0

50-0
9-5

64-4
18-4

72-7
50-8

: 91-2 i
297-9 :

A straight line is obtained by plotting log p against 1 \T up to T =336,
and if this is produced it leads to a boiling-point under normal pressure
of T = 458 C. abs. (cf. 446 above). The corresponding graph above
336 is also a straight line which, however, leads to a boiling-point of
T=374. It is considered that the measurements at higher tempera
tures are defective, probably owing to interaction of the trioxide and
moisture, with production of phosphinc. 5

The refractive index of the liquid has been determined for several
of the standard wavelengths in the visible spectrum :

670-5
1-5350

589-2
1 -5403

434-0 m/x
1-5616

These and other results arc represented by the dispersion formula l
n = 1-5171 -817670/V 2 -31659070 7 A- 4

1 Tliorpo and Tutton, loc. clt.

2 Cabcll, Chem. Ntws, 18S4, 50, 209; Thorpe and Tutton, loc. clt.

3 Miller, loc. at.

4 Schenck, Banthien and Mihr, Ber., 1006, 39, 1506.

5 Miller, Trans. Chem. Soc., .1.029, p. 1823.

128 PHOSPHORUS.

The dielectric constant at 22 C. is 3-2.

Composition and Structure. The molecular weight and structure
have heen deduced in the usual manner from physical constants. The
vapour density, as determined by Hofmarm s method, varied between
T-67 and 7-83 (air = l) at temperatures between 132 and 184 C.,
which corresponds to a molecular weight which is represented by the
formula P^g. 1 This agrees with the molecular weight calculated from
the lowering of the freezing-point of benzene.

The molar volume at the boiling-point, 130-2, minus the atomic
volumes of six singly-linked oxygen atoms ( ) leaves 83-4, which
is very nearly equal to four times the atomic volume of elementary
phosphorus at its boiling-point, i.e. 4 x20-9. It is concluded that the
molecule P 4 in P 4 O 6 occupies the same volume as the molecule P 4 of
the liquid element. Now the atomic volume of phosphorus in its
trivalent combination, as in PC1 3 , etc., is certainly greater than that of
elementary phosphorus at the same vapour pressure (see p. 51).
Whence it follows that elementary phosphorus, as well as phosphorus
in P 4 O G . is exerting its highest valency, i.e., according to p. 52, is ter-
covalent with a mixed bond. The respective structural formula for
the element and the trioxide would therefore be

/Ov

I i and O ! I

PEEP P/ ^P

A somewhat similar formula involving the transfer of electrons has
been suggested by Henstock. 2

Decomposition. Phosphorus trioxide turns yellow and then red
on exposure to sunlight, and slightly yellow in ordinary diffused light.
After months of exposure red phosphorus is formed. 1 The change
may be represented by the equation

When the oxide was heated to about 200 C. in a scaled tube it
became turbid, then yellow and finally red. These changes proceeded
still further at higher temperatures, and at 445 C!. the whole was
converted into solid products according to the equation

2P 4 O fi =3P 2 O 4 -f-2P ^

The, oxide is unaffected by molecular hydrogen.

The liquid ignites in air or oxygen at about 50 C. and burns
with a vivid flame to the pcntoxide. Like phosphorus itself phos
phorous oxide undergoes slow combustion with the emission of a glow,
which may be due in part to the small quantities of the element already
mentioned. This combustion, however, differs from that of phos
phorus in several respects. Ozone is produced only in small quantities,
if at all, and may be due to the action of light of wavelength A = 120
to 1.80 m/z on the oxygen. 3 Hydrogen peroxide is not produced by

1 Thorpe and Tutton, Inc. cil. 2 Henstock, Chwn.. Xews, 1923, 127, 25 ( J.

3 Downey, loc. cit.

OXIDES. 129

the oxidation of phosphorous oxide. Dry oxygen combines with the
oxide with increasing speed from about 10 C., and over a certain range
the speed varies as the square root of the oxygen pressure. Glowing
oxidation in the presence of water vapour has been connected with the
intermediate formation, of phosphine. 1 Ozonised air gives a strong
glow, close to the surface of the oxide.

Products of oxidation vary according to the conditions. Dry
oxygen at ordinary temperatures, and especially under reduced pressure,
gave phosphorus pentoxide, while moist oxidation at atmospheric
pressure gave tetroxiclc. 2 Further experiments have shown that (a)
the pure trioxide, (b) the ordinary trioxide (p. 126), when oxidised
cither by air or oxygen or ozonised oxygen, gives a mixture of P O 4
and P 2 O 5 in the constant proportions which correspond to an empirical
formula PO 2 . 19 . The equation suggested for this oxidation is

8P 4 6 + 40 3 + 50 2 =5P 4 8 + 3P 4 10 3

Phosphorous oxide ignites spontaneously in chlorine, burning with
a greenish flame and forming a clear liquid which on distillation yielded
phosphoryl trichloride and a residue of metaphosphoryl chloride :

P 4 6 + 4CU = 2POC1 3 -f 2PO 2 C1 2

The oxide also inflames in bromine. Slow combination yields the
pentabromidc and pentoxide, thus

5P 4 O 6 + 20Br 2 ==SPBr 5 + 6P 2 O 5

Combination, with iodine is less vigorous, but when the oxide and.
iodine in carbon disulphidc are heated in a sealed tube, orange-red
P 2 I 4 is deposited.

The oxide does not mix with sulphur, but when heated together in
an inert atmosphere to about 1(30 C. the two combine with the pro
duction of diphosphorus dithiotrioxide, P 4 O 6 S 4 .

The liquid oxide slightly above the melting-point does not mix
with water, but combines with it slowly to give phosphorous acid :

P 4 O 6 -f-6H 2 O=.-lH 3 PO3

Hot water reacts explosively giving phosphine and red phosphorus.

Hydrogen chloride dissolves in phosphorous oxide and reacts with
it in a manner which is the reverse of that by which the oxide can be
formed, this reverse equation being

l\0 G - 6IIC1 - 2PC1.3 + 2H 3 PO :J

Such a mixture may also give phosphoric acid and phosphorus,
according to the equation

4H :) PO 3 + PC1 3 - :3II 3 PO 4 -!- 2P + 3IIC1 4

Ammonia reads violently with the oxide, reducing it to red phos
phorus. When, however, the ammonia is passed into a solution of
the oxide in ether, it gives a diamide of phosphorous acid, IIOP(XI1 2 ) 2 .

1 Kinclo, Arkiv. C/IC.HI. Mm.. GtioL, I9J7, 7, Xo. 7; .Miller, Pruc. .Hoij. Xoc,. fatm., 10-26,
46, 76, i>39.

2 Thorpe and Tutton, loc,. at. :i Miller, 192i), loc. cit.
- 1 Gcuther, J. praJct. Ghcm. 9 1873, [2], 8, 359.

130 PHOSPHORUS.

The oxide acts vigorously upon ethyl alcohol, and by the regulation
of this reaction diethyl phosphite has been obtained :

The chemical properties of the purified oxide differ in some respects
from those of the ordinary preparation. It has a pungent acid smell
which does not recall the smell of phosphorus. When exposed to
light, either in an evacuated bulb or in one filled with carbon dioxide,
it does not turn red. It does not absorb oxygen at pressures of about
100 to 80 mm. even at 25 C. and in the presence of water vapour.
When heated in a sealed tube containing dry oxygen at 300 mm. it
shows no glow below 200 ., and the oxygen is only slowly absorbed at
220 C.

Phosphorus Dioxide, [PO 2 ] K . or Tetroxide, P 2 O 4 . The formula
P 4 is sometimes assignee! to this oxide by analogy with X,,0 4 , but
by analogy with the other oxides of phosphorus the formula would
be P 4 8 . ""

The formation of this oxide by the decomposition of P 4 O G has been
described already (p. 129). By heating in a sealed evacuated tube
the products of the slow combustion of phosphorus, a crystalline
sublimate is obtained, 2 which was show]) by Thorpe and Tutton 3 to
be a distinct new oxide, probably formed according to the expiation

The oxide may also be formed directly by slow oxidation of phosphorus
in oxygen at a pressure of GOO mm. and containing water vapour
(0-1 mm.).

It sublimes at about 180 C. in colourless crystals which arc of
rhombic appearance. The density, D~~^ , is 2-537. rj The vapour
density, determined at a temperature above 1 1-00 C ., corresponded to
a molecular weight of 458-0, and therefore io the formula I ) S 1G . 5
This oxide is stable in oxygen ut the ordinary temperature, but is
oxidised to pcntoxide at 350 to -I-OO C . G

As the tctroxide has been shown to have the formula, of a i; mixed
anhydride." it should yield phosphorous and phosphoric acids on
treatment with water. Actually, the solution, after neutralisation
with sodium hydroxide, showed I lie reactions of phosphites and nieta-
phosphatcs. The; hydration may therefore be represented by an
equation

L PO, f L lLO-.-ILPO, i I1PO.,

Phosphorus Penloxicle. Vigorous combustion of phosphorus in
air produces a voluminous white powder which is very deliquescent
and hisses when dropped into water, evolving much heat and <> ivm<> a
liquid of acid reaction. These salient facts were observed bv i he carlv
workers on phosphorus, e.g. bv Robert Hovlo in 10S1. Flic compound
was analysed by many of the leading chemists at I he beginning of the
nineteenth century, and the empirical formula P..O- was established.

1 Thorpe and N ortl

- 1 lautcfciiiIK and

3 Lor., c/l.

1 Miller, lac. df., Russell, Tntttx. C/K-M. ,S ur., !.!)():>, 83, l 2( C>.

- \Vrst, Tnin* Chnn. Nor., 1<JO:>, Si. (rl:\.

OXIDES. 131

This oxide is formed by combustion, in a full supply of air or oxygen,
of white phosphorus (ignition temperature about 60 C.), of phosphorous
oxide (50 C -70 C.), of red phosphorus (about 260 C.), and of the
phosphincs and other combustible compounds. The white powder
prepared in the laboratory or technically by these methods is always
impure, containing a little phosphorous oxide, metaphosphoric acid,
etc., while a part of the phosphorus usually escapes combustion and
remains as reel phosphorus. The preparation of a pure product re
quires further treatment. Thus the pentoxide may be thrown into
a red-hot porcelain basin and stirred in a current of oxygen. 1 The
crude oxide may also be resublirned in a current of oxygen and passed
over platinised asbestos or platinum sponge. 2 The product used by
Baker in experiments on. intensive drying was also distilled, without
the aid of a catalyst, in a current of oxygen at 180 to 210 C. The
yield was about 10 per cent. A convenient apparatus for this pre
paration was described by Finch and Peto. 3 The ordinary pentoxide
was pushed continually through a glass tube down the vertical limb
of a heated iron T-piece which was traversed by a current of oxygen.
The product, which, was collected in a wide-mouthed glass bottle, was
partly crystalline and partly amorphous. 4

The purified oxide should be devoid of any alliaceous odour or
odour of phosphinc, and should not reduce a boiling solution of
mercuric chloride. When dissolved in water and the solution neutral
ised with alkali (to methyl orange) it should give a white precipitate
with silver nitrate which should not darken after boiling for five
minutes.

Properties. The pcntoxide exists in crystalline nnd vitreous forms,
the transformation temperature of which has been given as 4 !0 C. 5
Sublimation proceeds with moderate speed between 180 and 250 C. 6
and the vapour pressure: may reach 700 nun. at 360 C\" When it is
sublimed at :5GO C C. in a current of oxygen the oxide forms brilliant
crystals together with some of the amorphous material which is con
sidered to be a product of polymerisation. The crystalline form, by
X-ray examination, is that of the rhombohcdral system with 12P 5
in a unit cell ; the lengths of the axes arc a = 31-:r2, b -1-12 A. s

The melting-point was found to vary between 560 and 570 C.
according to the time of heating. 7

The vapour density indicated a molecular weight of 336 at a red
heat !) and ;3<)0 at 1400 C. LU At the higher temperature, therefore, the
molecule approximates to P 4 O 1(J (J/ 281).

The inconsistent behaviour on sublimation suggests that phosphorus
pentoxidc, like sulphur trioxide and phosphorus itself (q.i-.) 9 contains
at least two crystalline forms, a mctas table form with, a higher and a
stable form with, a lower vapour pressure. These are present as a

1 Trover*, " Kx[)Cfi.m.(:ntal S7 ndij of Ga&w, Macmillan, J901, etc.

2 Threli aH, Phil. May., 181). .$, j vj, 35, 1; Shcnstone and Beck, Trim*. Chain-. Sac.,
1893, 63, 47;").

; Fmch and Polo, Trun*. C/n-m. *SV,t., 11)22, 121, 092.

1 Sec also Finch and Frase.r, Trans. Chcm. Sue., 102(5, p. 117.

5 Thorpe and Tutt.on, Inc. al.\ Tilden and .Bamett, Twin-*. Chr-m. Soc., 1896, 69, 154.

t; Kcinpf, ,/. prakt. Chcm., 1908, |2j, 78, 22S.

Hodlake and Scheii er, Lite. T r<u : . clu-m., 11)26,45, -191.

b Saiifourchc, Hernette and Fair, Ball. Sac. c/ti/n., 1930, [4], 47, 273.

9 Tildeii and Barnctr, lor,, r//.

iu West. Tram. Chun. Soc., 1902, 81, 923.

132

PHOSPHORUS.

mixture below 300 C., at which temperature the vapour pressure of
the meta stable form becomes appreciable and then increases rapidly,
reaching- 3-5 atm. at 400 C. From this temperature upwards the
pressure of the stable form becomes appreciable and equilibrium
conditions are more easily obtained. 1 The more volatile form may be
sublimed away : consequently an abrupt fall of pressure above 400 C.
has been observed. 2 A stable vapour pressure curve has been obtained
up to and beyond the triple point. 1 Pure dry oxygen was passed over
English P 2 O 5 3 which was heated to 270 C C. The sublimate was
received directly in the tensimeter, which was contained in an electric
furnace wound with nichrome wire which gave temperatures above
400 C., which were controlled within : ;2 C. The pressures were
measured by a glass manometer with quartz thread indicator. 4 The
following typical values arc taken from the tabulated results :

VAPOUR PRESSURES OF PHOSPHORUS PENTOXIDE,

Solid.

Liquid.

i
I
i

t C.

p cm. mercury

419 522-5 557-5
2-3 32-6 32-7

59G-5 G13-5 ! 656
68-7 83-9 135-6

TOO
216

The triple point is found at 55-5 cm. of mercury and 580 C.

The affinity of formation of P 2 O 5 evidently is very great, since no
dissociation was observed at the highest temperatures mentioned
above. When heated in the oxyhyclrogen flame the oxide gives a
continuous spectrum. 5 In respect of this great stability l 3 oO 5 differs
markedly from its congeners X 2 O 5 and As 2 O 5 .

The heat of formation is also by far the highest in the Group and
is higher than the heat of oxidation per atom of any other non-metal.
The value per niol of solid I 3 2 O.- from solid white phosphorus and
gaseous oxygen is given as 369-1) Cals.," 360-4 Cals. 7 As already
mentioned (p. 37) the heats of formation from red phosphorus are
rather lower.

Phosphoric oxide lias also an exceptionally high affinity of hydra-
tion, on which account it is universally used, where its chemical pro
perties permit, as the most powerful drying agent for neutral or acid
gases and liquids and also in desiccators. The heat of hyd ration oC
crystalline P.,0- is given as 1-1 -0 Cals.,* i-0-8 Cals/ The amorphous
variety when dissolved in much water evolved 33-8 Cals. and the
vitreous variety 29-1 Cals. 10 Hence heat is evolved when the crystalline
variety is transformed into the amorphous variety.

1 Sjiuts, Zdtwh. phyxtlcal. Chan., 1930, 149, :337.

2 Smith and Rutgers, 7 /v///.x. Ch(-;n. Xoc.. .1924, 125, 2f>73.
:i liopkin ;md Williams, Alanuhictum s.

4 Jackson, Ti <ti,.<. Chc.tn. ,SVx:., 19J1, 99., 1000.
" 1-1 art ley, Chan, ^c/r.^ J8(i. i, 67, 271).

<; Thomson, " ThtrnKic.hc-tfiixchKn U nt.c-rHHc.hnwjt-.n," 1882, Leipzig.
7 Giran, Co-nipt, rwd., 1903, 136, o.lO, G77.
s Hautufeuillo and rorrcy, loc. ell.

9 Giran, loc. ciL, and Ann. Chim. Phya., 1903, [7j, 30., 203.
10 Giran, loc. cit.

OXIDES. 133

Structure. Many possible structures may be assigned to the mole
cule. Whichever of these is adopted the phosphorus must be quinquc-
valent according to the old representation, or quadrivalent with a
semipolar bond according to the " octet " tlieorv. Thus

O O or O O

\ /c\ / \ ^\ /

o=p<; >P = O o<....p< >P....>O

\ / \o/

Chemical Properties.- Phosphorus pentoxidc was reduced by
hydrogen at a red heat in the presence of nickel, 1 and by carbon at
high temperatures, but not by silicon. 2

The alkali and alkaline earth metals react with great energy when
heated with the oxide, giving oxides and phosphides. 3

When heated with haliclcs of phosphorus the two molecules give
oxyhalides, the change being represented by the equation 4

P 4 O 10 -f 6PC1 5 = 10POC1 3
or P 4 O 10 -f- 6PBr 5 = 10POBr 3

The pentoxide also gives the oxychloridc when heated with the halides
of other non-metals, although the other non-metal docs not necessarily
give oxyhalide also. Thus with boron trichloride

P 2 O 5 -r 2BC1 3 = POCU.BCl, -r BPO 4
and with carbon tctrachloridc in a sealed tube l)etwcen 200 and 300

P 2 O 5 -r 2CC1 4 = COC1 2 -;- CO o -;- 2POC1 :J
With an excess of P 2 O 5

2P 2 O 5 -f3CC! 4 =:3C0 2 -!-4POCL 5

Oxyhalides of phosphorus arc also ])roduced when the pentoxidc is
heated with (luoridcs or chlorides of the alkali and alkaline earth
metals : thus POF 3 is produced with calcium fluoride G and POC1 3
with sodium chloride. 7

When brought into contact with water under various conditions
phosphorus pentoxide forms one or more of diiTcrcntiy hydrated acids.
Metaphosj)horic acid (q.v.) probably is the first product.

The pentoxidc has a powerful dehydrating effect upon oxyacids
and is therefore used in preparing anhydrides from tlicse (see under
cc Nitrogen Pentoxidc," this Volume, Part I.), it also removes halogen
from halogen hydracids under some conditions, giving oxyhalides, e.g.

1 Xeo<u and Adlucary, Zultch. unory. C/icm., 1010, 69, L>0!).

2 KalilonboTo and Trautinann, Twit.*. A mcr. Elcc.huc lH-.nt.. >s oc., \ { .Y1\, 39, ;>77.

3 Davy, Phil. Tmn.s., 1818, 108, 316.

1 BoT ger, Contpt. rv,<l., 1U08, 146, 400.

5 Gustavson, JJcr., 1871, 4, 853; 1872, 5, 30.

Thorpe and llambly, Trans. Ckcm. Sue., J880. 55, ~r,9.

7 Kolbc and Lautemann, An.naUn, 1860, 113, 2-10.

134 PHOSPHORUS.

POF 3 from HF. 1 Hydrogen chloride is completely absorbed by
oxide and gives a liquid from which POC1 3 can be distilled. 2

Phosphorus pcntoxide cannot be oxidised further by ordi
oxidising- agents, except to compounds of the " pcracid " type.
oxygen is displaced by metathesis as just shown, but not by a
drons halogens, except iluorine, which at a dull red heat gives
and POF 3 . 3

Diy ammonia gives amido- or imido-phosphoric acids (q.v.) 9
also salts such as diammonium amidopyrophosphate. 4

1 Gore, Trans. CJirm. Soc., 1869, 22, 368.

2 .Bailey and Fowler, Trdiis. Chc-m. Soc., 1888, 53, 755.

3 Moissan, Bull. Soc. chim., 1891, [3], 5, 458.

1 Sanfourchc, Hernctte and Fair, loc. ctt. See also SehitT, Anna! en, 1857, 103, 1

CHAPTER XI.
THE OXYAGIDS OF PHOSPHORUS UNSATURATED.

THE numerous oxy acids of phosphorus may be regarded as derived
from three prototypes, namely, hypophosphorous acid, H 3 PO 9 , phos
phorous acid, H/PO n , and orthophosphoric acid, H 3 PO 4 , in all of
which phosphorus probably has the co-ordination number 4 (see p. 59).

In the hypophosphorous and phosphorous series the phosphorus
undoubtedly is in a lower state of oxidation, and may be wholly in the
trivalcnt state, which corresponds to a symmetrical structure of the
molecules. ^lore probably, however, these acids consist of a mixture
containing the more symmetrical molecules in tautomeric equilibrium
with less symmetrical molecules which contain hydrogen directly
united to phosphorus. In cither form the unsaturated acids and their
salts are powerful reducing agents and are easily oxidised to the stable
phosphate series.

Hypophosphorous Acid. The alkali salts of this acid were dis
covered among the products of the decomposition of phosphides by
water. 1 A method of preparing hypophosphites by boiling milk of
lime with phosphorus was also discovered early in the nineteenth
century. The resulting solution of calcium hypophosphite could then
be decomposed by oxalic acid. 2 Hypophosphite was also prepared by
heating the phosphorus with a solution of baryta. 3 The barium salt,
Ba(II 2 PO 2 ) 2 , is easily recrystallised, and from it the free acid may be
prepared by double decomposition of a fifth molar solution with the
calculated amount of 20 to 25 per cent, sulphuric acid. 4 The filtered
solution may be evaporated first to one- tenth of its volume and then
until the temperature rises to 105 C. It is filtered hot and then further
evaporated to a temperature of 310 C., and this evaporation by stages
is continued until the temperature rises to 130 or even 138 C. without
decomposition. The liquid should then be poured into a closed flask
and cooled to C 1 ., when it nearly all solidifies to a mass of crystals.
Crystallisation may be induced if necessary by seeding with a crystal
of the acid. 5 The commercial acid usually contains calcium salts.
These may be removed by the addition of alcohol and much ether to
the evaporated solution, when the salts arc precipitated. The alcohol
and ether arc removed by distillation and the acid is further concen
trated as above. 6

1 Dulong, Plul. j;V/., 1816, 48, 271.

2 Rose, Airualf-tt, 184;), 58, 301.

3 Dulono-, (oc. at.- Ann. Cfdiu. riajs., 1816, [2], 2, 141.

4 Thomson, JJtr., 1874, 7, 994; Aiinakn, 1871, 143, 354, 497.

5 Marie, Co-mpt. rtiuL, 100-4, 138, 1216.

6 Micliachs and von Arend, Annahn, 1901, 314, 266.

135

136

PHOSPHORUS.

Properties. The density of the crystallised aeid is given as 1-4625. 1
The melting-point, 17-4 C. 2 or 26-5 C.. 3 no doubt varies with small
variations in the proportion of water present.

The latent heat of fusion (heat absorbed) is 2-4 Cals., the latent
heat of solution of the crystals from -0-2 to -0-17 Gals., and of the
fused aeid from +2-2 to +2-14 Gals, (per mol in each case).

The heats of formation (heat evolved) from the elements

P (solid) -fO 2 (gas)

lo (gas)

are -f- 137-7 Cals. (liquid acid), +140-0 Gals, (solid aeid), +139-8 Cals.
(dissolved acid). 4

The pure acid decomposes rapidly when heated above 130 C. and
below 140 G. mainly according to the equation

3H 3 PO 2 =PH 3 -

-2H 3 P0 3

while between. 160 and 170 C. the main decomposition (consecutive
reaction) is symbolised as

4H 3 PO 3 =PH 3 +3H 3 PO 4 3

Aqueous Solutions of Hypo-phosphorous Acid. The effect of dilution
on the molar conductivity of hypophosphorous acid shows that the
acid is moderately strong, but however obeys the law of mass or con
centration action suflicicntly well to give a cc constant * ? (K below)
which, remains of the same order although it diminishes steadily with
increasing dilution.

MOLAR CONDUCTIVITIES OF HYPOPHOSPHOROUS

ACID AT 25 C. 5

2 4 : 8

1C

82

64

128

140 ! 172 : 207

245

281

312

, 335

. ; 0-1012 0-0876 0-0757

0-0670

0-0587

0-0508

0-0417

. : . . . . 0-1015

0-1014

0-1017

0-1014

0-1019

256

512

1024

1 2048 ;

GC

352

361

367

: 368-3

389

0-0336

0-0234

0-0154

: 0-0082

0-1024

0-1008

0-1014

0-1028 :

The values of a ( =^,/^c cc ) in the expression a 2 , (1 - a)f 7 = K were cal
culated from ^=389 based on the work of Arrhcnius. 6 The ionic

1 ]\licliaelis and von Arend, toe. cit. - Thom.sen, lac. clL

3 Marie, Joe. al.

Thomson, luc. cit., and Bv\, 1870, 3, ]87, 503; 1871, 4, 1^08, 586; /. prrtkl. Chcm.,
187;"), [-J, ii, J-.

5 Oslwald, ; Lfikrbuch der Allg^m. Chcm., 1903, 2, Leipzig.
Arrhcnius, Zeifsch. physical. Ckein., 1689, 4, 96.

OXYACIDS UXSATURATED.

137

conductivity L x of H^ = 347, which gives Z, M of H 2 PO 2 ~ as 42-0, in

agreement with the value 41-8 deduced from the sodium salt. 1

These values have been recalculated to the newer units 2 and an
empirical constant K (see table) lias been found which shows a better
constancy, i.e. : 2

i

K =-r VT--+ log V
(l-a)V 35

The constant A" has been recletermined by Kolthoff 3 as 0-01 at
F = 1000 and 0-062 at F = 20. In another series of results the values
of a and K were derived from A^ =392-5, which was based on the
limiting conductivity of NaH 2 POo (at 25 C.) : 4

mols/litre

0-5004
137-1

0-2502
168-5

0-1251
205-0 i

()-0625 5

242-9 !

0-03128

279-5

whence K may be calculated in the usual manner.

The conductivity increases at first with the temperature as is usual ;
the rate of increase then diminishes and the conductivity reaches a
maximum at about 50 C., the exact temperature varying with the
concentration and being 57 C. in the case of normal acid. 5 The con
ductivity then decreases. It is supposed that the effect of the normal
increase in ionic mobility with temperature is diminished and finally
reversed by the opposite effect of: decreasing dissociation. Since the
dissociation constant decreases with rise of temperature the dissociation
into ions must take place with evolution of heat, i.e. the heat of ionisa-
tion is positive. Therefore the neutralisation of the acid with alkali
must result in a production of heat greater than the heat of formation.
of water from its ions, which may be taken as 13-52 Cals. per mol.
If the heat of dissociation is Qj Cals. per gram-ion and the undissociated
portion of the free acid is I -a, then the total heat of neutralisation
Q u will be given by the equation

Q M =13-52-r(l-a)Qa Cals.

At 21-5 C. a is 0-44-9 at a certain concentration and (l-a)Q,i has

the value -i- 1-769 Cals. Therefore Q_ n is 15-289 Cals. by calculation,

while the experimental value was 15-316 Cals. 6

The transport number of the anion was found to be 41-8. 1
Kuxicity. The results of conductivity measurements indicate that

only one of the hydrogens is dissociable as ion, the dissociation taking

place according to the equation

In the process of neutralisation also only one hydrion takes part, as is
shown by the fact that the heat evolved practically reaches a limit

1 Bred IX, Zuteck. plyxik tL C/icm., 1894, 13, 101.

2 Mitchell, Trans. Cka-m. >S oc., 10:20, 117, 1)57.
;! Kolthoff, Rc.c. Trav. clu.-m.., 10:27, 46, :>n().

4 Ramstcdt, Mcddcl. VtL Akw.L X^d^^idut, 10.15, 3, Xo. 7.

138 PHOSPHORUS.

when one equivalent of alkali has been added to one mol of the acid.
Thus when 2, 1 and 0-5 mols oF the acid were added to one equivalent
of XaOH the heats observed were 15-4, 15-2 and 7-6 Cals. 1

The monohasicity is confirmed by the formulae of all the known
salts.

Oxidation in Solution. Hypophosphorous acid and its salts arc
strong reducing agents and are oxidised to phosphorous acid or finally
to phosphoric acid and their salts. The self-oxidation and -reduction
to phosphine and phosphorous acid is described on p. 136. A similar
reaction is brought about by hydrogen iodide :

3H 3 PO 2 -i- HI - 2H 3 PO 3 + PH 4 I 2

Hypophosphorous acid is also oxidised to phosphorous acid by sulphur
dioxide with deposition of sulphur, 3 and by phosphorus trichloride
with deposition of phosphorus, thus :

3H 3 PO 2 +PC1 3 = 2H 3 PO 3 +2P + 3HC1 4

It is oxidised by alkali with evolution of hydrogen :-
XalI 2 PO 2 -f-XaOH = Xa 2 HPO 3 +H 2 5

The velocity constant of this reaction has been measured at tempera
tures slightly below 100 C. It is slightly greater for KOH than for
NaOH at equivalent concentration, and increases faster than the
concentration, of the alkali. 6

Salts of the noble metals are reduced by hypophosphorous acid or
hypophosphitcs, and in many cases phosphorous acid can be isolated
among the products. The reduction of silver nitrate was noticed by
the early workers. 7 Phosphoric acid was formed with or without the
evolution of hydrogen, thus :

2XaH 2 POo + 2AgXO 3 -r 4H 2 O = 2H 3 PO 4 + 2XaXO 3 + 3H 2 -1- 2Ag
or the nascent hydrogen gave more silver :

2TI -r 2AgX0 3 = 2HXO 3 -r 2Ag 8

The formation of phosphorous acid is represented by the equation
2AgXO 3 + H t ,PO 2 + H 2 = 2Ag + H 3 PO 3 + 2HXO 3

Copper sulphate is reduced to copper with the production of an acid
solution :

4CuS0 4 + Ba(H 2 PO 2 ) 2 + 4H 2 = 2H 3 PO 4 + 4Cu + BaSO 4 + 3H 2 S0 4 9

It has also been stated that copper hydride is first produced, which

1 Thomson, loc. cit.

2 Poundorf, Jena Zeit. SuppL, 1876, [2], 3, 4f>.

3 Poundorf, loc. cit.; Rothcr, Pharm. J., 1879, [31, 10, 280.

4 Geuther, J. pralcl. Chzm., 1874, [2], 8, 366.

5 Loessncr, "Utber reakL d. uider phosphor. Sdure, c.tc." \\ oida i Thurm, .1911.

Loessner, loc. cit.; Sieverts and Loessner, ZeiU-c/i. anortj. Chc/iti., 101.2, 76, 10; Majoj ,
" Zur Ktnntnis dtr phosp h. u. unterphosph. Saure," A\ eida i Thurm, 1908.

7 Dulong, loc. cit.

8 Sieverts, Zcitsch. anorg. Chevi., 1909, 64, 29; Sieverts and Loessner, loc. cit.

9 Rose, Annalen, 1827, 9, 225; 1.828, II, 92; l828, 12, 77, 288; 1834, 32, 467; 1843,
58, 301.

OXYACIDS UXSATURATED. 139

decomposes with evolution of hydrogen. 1 It appears further that,
"with excess of the hypophosphite, hydrogen also is evolved, while with
excess of copper salt copper only is precipitated. 2 The spongy copper
appears to act as a catalytic agent in liberating hydrogen from excess
of hypophosphorous acid. Cuprous oxide probably is first formed,
and the substance first precipitated from an acid solution may contain
this with hydride and. phosphate. 3

Mercuric chloride is reduced to mercurous chloride and mercury. 4
In this case also phosphorous acid was produced, and by a reaction
which was quicker than that which led to phosphoric acid, thus :

H 3 POo -2HgCl 2 -rH 2 =H 3 PO 3 +Hg 2 Cl 2 + 2HC1 5

Fallacious salts oxidise the acid to phosphoric acid with deposition
of palladium. 6

The velocities of some oxidations have been determined. Thus in
the reaction

H 3 PO 2 -f I 2 +H 2 O =H 3 PO 3 + 2HI

the velocity was independent of the concentration of iodine if this was
more than 0-00 IN, and unimolecular with respect to H 3 PO 2 . 7 The
hypothesis has been advanced that the reducing agent is an active
form H 5 PO 2 , which is produced with a measurable velocity (catalysed
by hydrogen ions) when the equilibrium amount is diminished. 8

The Hypophosphitex. Hypophosphites of most of the metals have
been prepared by a few general reactions :

(1) By heating aqueous solutions of the alkali or alkaline earth

hydroxides with white phosphorus.

(2) By the double decomposition of barium hypophosphitc with

the sulphate of the required metal.

(3) By dissolving the hydroxide or carbonate of the metal in hypo-

phosphorous acid.

The hypophosphitcs are all soluble. Those of barium and calcium,
which arc the least soluble, dissolve in 2-5 to 3-5 and G to 7 parts of
water respectively. Those of the alkali metals and ammonium dissolve
also in alcohol. Solutions of hypophosphites of the alkali metals are
fairly stable, especially in the absence of air, and the salts generally
may be obtained in well-crystallised forms by evaporation. More
concentrated solutions often decompose, especially if alkaline, with
evolution of phosphinc. The dry salts are also fairly stable in the
cold, but when heated decompose giving phosphinc and hydrogen and
leaving the pyro- or meta-phosphate.

The electrical conductivities of the sodium salt 9 and of the barium
salt 10 give the mobility of the II 2 PO 2 ~ ion.

1 Wurtz, An.,*. Cliihi. Phyx., 1844. [3], n, 2/50; 1846, [31, 16, 190.

2 Sicvcrts, lor.. c,d.\ M.uthmann and MaAvrow, -ibid., 1896, n, 2(>8.

3 Firth and Myers, Trail*. Chcm. Soc., 1911, 99, 1329.
11 Rose, loc. cit.

5 Mitchell, Trans. Chc.t,-,. Soc., 1921, 119, 1266.
15 Sievcrts, SievcM ts and Loosener, loc. cit.

7 SteoJe, Tm,<*. Chvn. Soc., 1007, 91, 1641.

8 KolthotT, Pharm. Wcckblad, 1916, 53, 909; 1924, 61, 954; Mitchel
Soc., 1920, 117, 1322.

9 Ramstedt, Mtddd. Vet. A had. Nobdinstitut, 1915, 3, No. 7.
10 \ValJon, ZtUsch. physihd. Chem., 18S7, i, 529.

140 PHOSPHORUS.

The formula? of some typical hypophosphites are as follows :

LiII 2 P0 2 .H 2 O, monoclinic prisms ; XaII 2 PO 2 .II 2 O, monoclinic
prisms : KH.,PO , hexagonal plates ; XH 4 H.>PO.->, rhombic tables ;
Mg(lI 2 PO 2 ) 2 .()"lI 2 6, tetragonal ; Ca(lI 2 PO 2 ) 2 f monoclinic leaflets ;
Ba(H 2 PO 2 ) 2 .H 2 (X monoelinic needles or prisms ; Cu(H 2 PO 2 ) 2 , white
precipitate ; Pb(I-I P0 9 ) , rhombic prisms ; Fe(H PO )9.6H O, green
octahedra; Fe(H 2 P0 2 ) 3 .^H 2 O, white precipitate ; "Co(lI 2 POo) 2 .CH 2 0,
reel tetragonal : Xi(H 2 PO 2 ) 2 .CH 2 O, green crystals.

The hexahydrated salts of magnesium and the iron group are said
to be isomorphous. Further eletails about each salt are given under
the metal in the appropriate volume of this Series.

Ammonium and hydroxylamine hypophosphites have been prepared
by double decomposition between the sulphates and barium hypo-
phosphite. The ammonium salt, XH^-IJPOo, 1 was crystallised from
water or alcohol. When heated to about 200 C. it melted and de
composed, giving off ammonia, phosphine and hydrogen and leaving
a mixture of pyro- and m eta-phosphoric acids. Hydroxylamine hypo-
phosphite, XHoOH.HgPOo, has also been prepared by reaction between
KHoPOo and "XH 2 OH.HC1, and was extracted with hot absolute
alcohol. 2 Solutions of this salt must be evaporated in an atmosphere
of COo, etc. in order to avoid oxidation. The crystals obtained were
very deliquescent. They began to decompose at about 60 C., melted
below 100 C. and exploded at a higher temperature. 3

The detection, estimation and structure of hypophosphitcs are
discussed under " Phosphites " (q.v.}.

In contradistinction to phosphorus itself and the products of its
slow oxidation, hypophosphorous acid and the hypophosphites do not
appear to be toxic. 4 Calcium hypophosphite appears to be completely
eliminable from the system. 5 Hypophosphites of calcium, sodium and
iron, have been prescribed in medicine, but although in some cases they
appear to have done good there is no conclusive evidence of the value
of the hypophosphite radical apart from the basic radical or other
constituent of tlie mixture.

Phosphorous Acid, H 3 PO 3 . The production of an acid liquid by
the slow combustion of phosphorus in the presence of water was
observed by le Sage in 1777. G The aeid was prepared by Pelleticrby
drawing a slow current of air over phosphorus enclosed in fine tubes
which dipped into water. 7 The distinction between this acid and
phosphoric acid was recognised in the early nineteenth century, as also
was the fact that the slow combustion of phosphorus could vield a
mixture of the two acids. 8

The method of preparation just mentioned is not a good one.
Phosphorous oxide dissolves only slowly in cold water and phosphoric
acid is continuously produced from the first, while hot water gives a

1 Dulono-, loc. cd., and Ann. Phil, 1818, n, 134; Raimnclsbercr, An.nal(>n., 18G7,
132, 401 ; Trans. Chf-.w. Xor,., 1ST. ), 26, 1, 13; Michaolis and von Areml, loc. cit.

2 Hoi mann and Kohlschutter, Zei-twh. u.uory. Chew., 1898, 16, 409.

3 SabaneefT, Bcr., 1897, 30, 287; Z&dsch. anor<j. Chtm,., 1898, 17, 483; 1809, 20, 21.

4 Paqm lm and July, Compt. rtn.d., 1878, 86, loOo; J. Phttrm. Chini., J878, [4 ], 28,
314; Polk, Phrmn. J., 1874, [3], 5, 42.1

5 Panzer, Zcitsck. Scthr. Genu^-m., 1902, 5, 11.
c le Sauc, 3/fcw, Acad., 1777, p. 321.

7 .Pclletiei , Ann. Chim. Phy*., 1.792, [1], 14, 113.

8 Davy, Phil. Tram., 1812, 102, 405; 18.18, 108, 316; Dulono-, Ann. C him. Ph.ys.,
1816, [2], 2, 14-1; Phil. Mag., 1816, 48, 271; Sornmer, J. Soc. Cham. Lid., 1885, 4, 574.

OXYACIDS UXSATURATED.

141

variety of products. A better method is that recommended by Davy, 1
namely, by the hydrolysis of phosphorus trichloride. Some white
phosphorus is placed in a deep cylinder -and covered with water. The
element is melted and chlorine is passed in through a tube which dips
well into the phosphorus. 2 Large quantities may be quickly obtained
by this method, but the product contains phosphoric acid. Regulated
action of PC1 3 on water may be effected by passing a current of dry
air through the trichloride kept at 60 C. and then through two wash-
bottles containing water. 3 The action is also much less violent if an
acid such as concentrated aqueous hydrochloric acid is used in place
of the water. Oxalic acid is most suitable, since it is dehydrated with
decomposition when heated in a flask with phosphorus trichloride.
The flask is furnished with a reflux condenser. Much of the IIC1 is
evolved and a concentrated solution of phosphorous acid remains :

PCI 3 + 3II 2 C 2 O 4 = H 3 PO 3 -r 3CO + SCO 2 ->- 3HC1 4

In these preparations it is usually necessary to remove the hydro
chloric acid which is produced ; this may be done by distilling the
solution up to a temperature not exceeding 180 C. A syrupy liquid
is then obtained which, after cooling, crystallises quickly, or at any rate
within a few hours. The process may be hastened as usual by seeding.

Physical Properties. The crystalline acid was found to melt at
70-1 C., 5 74 C. 6 The density of the liquid supercooled at 21 C. was
1-651. 5 The latent heat of fusion of the acid was found to be 7-07 Cals. 5
The heat of solution of the acid per mol dissolved in 400 mols or more
of water was +233 Cals. 5 The heat of formation of the crystallised
acid has been given as +227-7 Cals. 5

Aqueous Solutions. The conductivities of phosphorous acid arc
lower than those of hypophosphorous acid at corresponding dilutions,
showing that the former acid, is less dissociated, as appears from the
following values : - 7

MOLAR CONDUCTIVITIES OF PHOSPHOROUS
ACID AT 25 C.

2

4

8

10

32

04 128

250

512

102-1

. 120

150

187

222

252

202 318

337

351

358

,

Since phosphorous acid is dibasic, the dissociation constant was
not calculated from the conductivities, but from the hydrogen-ion
concentrations set up during neutralisation, which may be expressed
by a neutralisation curve. This 8 gave A 1 =0-05 and K 2 ^2- -I x 10~ 5
or 9 K l -0-010 at c =0-001 to 7^= 0-062 at c = 0-1 and 7v 2 "=0-7 xlO" 6 .

J Loc. oil.

2 Droquet. /. Ckim. MM.., 182S, [I], 4, 220.

3 Groshemtx, Bull. tior.. c/ntn., J877, i_2], 27, 43:*.

4 Hurtzio and. Geuthor, J. prald. Ch.t-.m., ]Sf>{), [4], III, 170.

5 Thomson, lor. cit..

G Hurt/iLi", " E urine, llci-trimc. znr /laJic ri ii Kt. n.iifi/ix drr titiuikti dc* I^ioxnliors uad

142 PHOSPHORUS.

As in the case of hypophosphorous acid, the molar conductivity, while
increasing at first with temperature, reached a maximum at about
70 C. and then diminished. 1

The lowering of the freezing-point, - A, and the elevation of the
boiling-point, -rAt, of water, which is made 6 -normal with respect to
phosphorous acid, are taken as proving that polymerisation had taken
place as well as electrolytic dissociation.

LOWERING OF FREEZING-POINT OF WATER
BY H 3 P0 3 .

c . .

1-186 ;

0-539*

0-296

148

- A/. c C.

2-941

1-538

0-835

455

i . . .

1-128

1-143

1-515

1

050

RAISING OF THE BOILING-POINT OF WATER
BY H 3 P0 3 .

1 c . . 0-976 < 0-488 0-244 0-122

i +AZ, . i 0-51 I 0-28 0-1G 0-13

I i . . i 0-960 I 1-063 1-215 1-972

The factors or activity coefficients ? are calculated on the assump
tion that the original molecules dissociating are the simplest / e

ii 3 i CV

Bax-K itij.- In the neutralisation ot the acid by NaOl! in dilute
solution it was .found that

11-jPO.j -f NaOII = XalloPO., + !I,,O + 1 1-8 (als.
II, PO., -r2NaO! I -.XaoIIPO., 4-211,0-1- 2 xl 12 C als.
II : jl ) : ,-r3NaOII=XaJIPO 3 -f 2!lol) i-XaOII -;-3 x 0(> Cals.

whence only two of the hydrogens arc ionisable. 3 So far as the ionmihe
of j)hosphites arc known (v. rujrfi, p. 1 t(5), tlicy coniain a. niaximimi
of two equivalents of a ha.se combined with 1 mol of the acid. Attempts
to prepare 1 Xa.jPO.j liavc not been successful. 1 Dibasicit.y is also con
firmed by a study of the neutralisation curves.

Oxidation. In Solution.- -Phosphorous acid and the phosphites arc
not quite such strong reducing agents as hypophosphorous acid and
the hypophosphitcs. The free acid undergoes self-oxidation and
-reduction at a higher temperature than hypophosphorous acid
(see p. 138).

Atmospheric oxygen docs not oxidise the acid at ordinary fern-

OXYACIDS UXSATURATED. 143

peratures, nor is such oxidation catalysed by iodine in the dark. In
the light, however, hydrogen iodide is formed according to the equation

H 3 PO 3 -r I + EUO = IIJP0 4 + 2HI

O i> ^ i O 4:

being reoxidised rapidly by oxygen, thus

The oxidation of phosphites by iodine was found to proceed to com
pletion in neutral solution 2 (see "Estimation," p. 149). Over a
narrow range of concentrations the reaction was found to be uni-
moleeular with respect to iodine and phosphorous acid. 3 It is said
to be catalysed by hydrogen ions which are formed as the reaction
proceeds. 4 A further study of the velocity constants showed that the
mechanism was more complicated than had previously been supposed,
and that the two tautomeric forms participated in different wavs. 5
A solution of iodine in potassium iodide contains the ions I and I 3 ,
and also molecular iodine, I 2 . The latter reacts directly with the
normal form of phosphorous acid and this reaction is repressed by
hydrogen ions. Simultaneously, the phosphorous acid changes into
another form with which the L, ion reacts. This second reaction is
accelerated by hydrogen ions either directly or, more probably, because
they accelerate the tautomeric change.

General Reactions. Various products were obtained when phos
phorous acid was heated with halogens in a sealed tube. Iodine gave
phosphoric and hydriodic acids, phosphonium iodide and an iodide
of phosphorus, whilst bromine gave phosphoric acid, phosphorus tri-
bromidc and hydrobromic acid. 6 A dry ether solution of the acid was
not oxidised by bromine or dry palladium black, but oxidation pro
ceeded readily in the presence of moisture. 7

Phosphorous acid also reduced sulphurous acid, the end products
being sulphur and phosphoric acid, thus :

21I 3 PO 3 + HoSCK = 2H 3 P0 4 + S -r HoO s

Sulphuric acid, which dissolved phosphorous acid in the cold, was
reduced to sulphur dioxide on heating. 9

Salts of the noble metals, including copper and mercury, were found
to oxidise phosphorous to phosphoric acid. The metal was precipitated
from silver salts 10 and also from gold salts. 11 It is generally agreed

1 Luther and Plotnikoff, Zeiltch. phyxikal. Chew.., 1908, 61, 513.
- Rupp and Fmck, Bcr , 1002, 35," 3691.

3 1/ederlm, Zc.ittidi. pky^lhiL Chc-.in., 1902, 41, 365.

4 Sleeks Trans. Chun. Soc.., 1909, 95, 22<)3.

5 Mitchell, Trim*. Claim. /w;., 1923, 123, 2241; and luc. ciL
f> Gustav.son, J. prnkt. C/i.c.)/i., 1867, [1], 101, 123.

7 Wieland and Windier, AtUialtn, 1923, 434, 185.
;i Wohler, A-nnnlf>.tt," l$4l , 39, 252; Cavazzi, OazzcMa. 1SS6, 16, 169.
;) \Vurtz, Cu-m.pl. rend., 1844, 18, 702; 1845, 21, 149, 354: Adie, Trrn,*. Ckc-.ni. Soc.,
1S9J, 59, 230.

10 Sieverts, Ztilsch. a-norg. Chc--m., 1909, 64, 29; Vanino, Pkann. Zca.tr.-h., 1899, 49. 037.

11 Balard, Ann. Ckrm. Pkys., 1834, [2J, 57, 225; Wurtz, toe. clt ; Sieverts, Major,
" Zur Kennhii.s cler photpkoriyen -it ml unterplifjupftoriyeji Schirc,," Weidai Th., 190S.

144 PHOSPHORUS.

that copper is precipitated from copper sulphate, 1 while cuprous oxide
or hydrogen may also be liberated, according to the conditions :

3H 3 PO, + CuS0 4 -f- 3HoQ = Cu -f- 2Ho - 3H 3 PO 4 + H,S0 4
H 3 P0 3 + CuSO 4 + HoO - Cu - H 3 PO 4 + H 2 S0 4

The reduction of mercuric chloride gave mcrcurous chloride when
the mercuric chloride was in excess, and mercury when the phosphorous
acid was in excess, 2 while the total reaction can be represented by the
equations

2HgCl. 2 + H 3 P0 3 + H 2 - H 3 P0 4 -f 2HgCl + 2HC1 . (i )
or HgCl 2 +H 3 P0 3 -rH 2 0=H 3 PO 4 +Hg+2HCl . . (2)

The mechanism has not been complete!}" elucidated and may be very
complex. The reaction has been classified as of the third order in
dilute solution, and as of the first order with respect to HgCl 2 . 3 But
it has also been stated that the reaction which is chiefly responsible for
the observed velocity is the conversion of a first or normal form of
H 3 P0 3 into a second or active form, which then reacts according to
equation (2) above. In the absence of extraneous chloride ions these
arc produced by another reaction, thus-

HgCl : + H 3 P0 3 (normal) + H 2 =H 3 PO 4 + Hg + 211" + 01" *

Many other oxidising agents are capable of oxidising phosphorous
acid. The reaction with potassium persulphate is very slow, but in
the presence of hydriodic acid it is much accelerated. This is a good
example of a coupled reaction. 5

Phosphorous acid forms esters by direct union with several alcohols. 6
With ethyl alcohol it gave di ethyl phosphite. 7 Ethyl derivatives of
phosphorous and phosphoric acids have been made by the action of
bromine on sodium diethyl phosphite in ligroin. They arc separated
by fractional distillation. 8

The Phosphites. Two scries of phosphites arc known, the primary
phosphites, >II1 2 PO : >, and the secondary, MJIPO 3 , M being a univalcnt
metal. Crystalline salts have also been prepared containing an excess
of phosphorous acid. The phosphites of the alkali metals and ammonia
are soluble, those of the alkaline earths sparingly soluble, while those of
other metals are only very slightly soluble. They may be prepared by
the usual methods :-

(1) By neutralising phosphorous acid to the appropriate end point

with alkali hydroxides and evaporating to crystallisation.

(2) By neutralising a. solution of phosphorous acid, or one made

from PCI 3 , with ammonia and adding a salt of the required
metal.

(3) By dissolving the hydroxide of the base in phosphorous acid.

1 J\am.mdsl)or<j;, A-intftlc.ti-, 18(17, 131, 203, 3r>i); 132, 481; tSiovcrts, loc. c.ll.\ Major,
he. cti.

> T> 1 . . . 1 7 ... . / . \ \ ,...-< r, ? , .,. ,, , /

- Balard, loc. , , .

3 Linhart, A-n cr. J. Hc.i., 1013, |4|, 35, 3r>3.

1 Mitche]], 7V /,x. 67/r///. Xor.., ]1)1>.J, 125, 1013.

(: Sachs and Ljviusky, J. HUM. /V/.//*. 6 Ac/y/. ,Vor., 1 ( J03, 35, 2{

7 Thorpe and Xorth , Trans. Chun,. /S oc., 1800, 57, 634.

8 Arbusov, J. prakl. Cham-., 1031, [2J, 131, JU3.

OXYACIDS UXSATURATEP. 1 45

The phosphites are fairly stable in the absence of oxidising agents
and dilute solutions may even be boiled without decomposition. More
concentrated solutions may decompose, giving hydrogen: thus

Xa oHPO : > - XaOH = Na 3 PO 4 + H 2

The solid salts decompose when heated, giving phosphine or hydrogen
or both, and leaving the ortho- or pyro-phosphate of the metal ; thus

2Ba,I-IP0 3 .H =Ba 9 PoO, -f 2H,

5PblIP6 3 =PboP A +Pb 3 "(P0 4 ) 2 -f PH 3 + H 2

The formulae of typical phosphites arc as follows :

LiII 2 P0 3 ; Li 2 HPO 3 .H 2 Q, four-sided plates; XaH 2 PO 3 .2j-H 2 O,
monoclinic prisms : Xa 2 HPO 3 .5-5lL,O, rhombic bipyramiclal needles ;
KH 2 P0 3 , monoclinic prisms"; K "HP0 3 : XH 4 HoPO 3 , monoclinic
prisms; (NH ;4 ) 2 HPQ 3 .H 2 0, four-sided prisms; Ag 2 HPO 3 , white
crystalline precipitate ; 2CaHP0 3 .2ll > O J white precipitate": Ba(ILP0 3 ) ;
BaHPO 3 .-J-HoO 5 white crystals; Bao(HoPO 3 ) 3 .5l : I O ; Ms(H PO .,), ;
MgIIPO 3 .6H,O ; CuHPO 3 .2HoO, blue " crystals ; ~ ZnHPO :V 2l-ILO ;
MnIIPO 3 .H 2 6, reddish-white precipitate: >b(H 2 PO,) 2 ; PbIIPO 3 ;
?iFeO.P 2 3 , crystalline mineral; CoIIP6 3 .2H 2 O," reel crystals, blue
when dried ; (XI-I 4 ) 2 [Co :3 (HP0 3 ) 4 ].18H 2 O 5 and a corresponding nickel
compound.

Ammonium phosphite in its hydratccl form, (XH 4 ) 2 IIPO ;J .H 2 O,
or as the anhydrous salt, has been made by saturating phosphorous
acid with ammonia, 1 or by passing ammonia over the hydrogen phos
phite at 100 C. 2 It easily loses both water and ammonia when heated
or kept in a. vacuum. 3

The hydrogen phosphite XHJIJPO, is rather more stable, and has
been prepared by the neutralisation of phosphorous acid with ammonia
to methyl orange, followed by careful evaporation. 4 It melts at about
120 C. and decomposes at about 140 C., giving ammonia, phosphine
and phosphorous acid. The form and constants of the crystals have
been described. 5

Hydroxylaminc phosphite, (XH 2 OH) .H 3 PO 3 , was prepared by
double decomposition of one mol of Xa.jiPO 3 with two niols of
XH 2 Q1LHC1. The sodium chloride was crystallised out by evaporation
in vacua, and the very soluble hydroxylaminc salt crystallised from
alcohol. It melts easily, is inflammable and is a strong reducing agent.
Hydrazine phosphite, XoH^H.jPO.j, has also been prepared, from barium
phosphite and hydra /inc sulphate. 5

Structure of the Hypophosphites and Phosphites. The mono-
basicity of hypophosphorous acid points to the unsymmctrical formula.
The probable existence also of a proportion in the symmetrical form
may be indicated by the case with which the acid undergoes self-oxida
tion and -reduction on heating, thus

H0-P0= Ho H-P; = (OH) 2 >PH 3 -i-HO-PO =

1 Rose, A-tnudcn, IS^T, 9, 28, :};}, lUT); Foui-croy and V aiiquclin, Jouru.. L^objl., LTD."),
4, 055.

2 Arnal, lac,. ct L, and "",S v//- /r.s /;//,ox/.;///./^-.v d [f* iiymjikoxphUw^ 1S1M, Pans.

3 Wurtx, Ann.. Cfirnt. /V/,//x. ? lor. at. Aniat, Joe. < /.!.

5 Dufct, Bull. ,S oc. mi, i. d<- France., 1801, 14, 201).

6 SabancefT, Zcitec/i. nnora. C/icni., JS9S, 17, 488; 1899, 20, 22.

144 PHOSPHORUS.

that copper is precipitated from copper sulphate, 1 while cuprous oxide
or hydrogen may also be liberated, according to the conditions :

3H 3 PO 3 -^ CuSO 4 + 3HoO = Cu + 2I1 2 + 3H 3 PO 4 + H,S0 4
H 3 P0 3 ^CuS0 4 -rHoO =Cu +H 3 P0 4 -f-H 2 S0 4

The reduction of mercuric chloride gave mercurous chloride when
the mercuric chloride was in excess, and mercury when the phosphorous
acid was in excess, 2 while the total reaction can be represented by the
equations

2HgCl o -h H 3 PO 3 + II 2 = H 3 P0 4 + 2HgCl + 2HC1 . (1 )
or HgCl 2 +H 3 P0 3 +H 2 O=H 3 PO 4 +Hg+2HCl . . (2)

The mechanism has not been completely elucidated and may be very
complex. The reaction has been classified as of the third order in
dilute solution, and as of the first order with respect to HgCl 2 . 3 But
it has also been stated that the reaction which is chiefly responsible for
the observed velocity is the conversion of a first or normal form, of
H 3 PO 3 into a second or active form, which then reacts according to
equation (2) above. In the absence of extraneous chloride ions these
are produced by another reaction, thus-

HgCl" + H 3 PO 3 (normal) + H 2 O =H 3 PO 4 -f- Hg + 2 II -f Cl" 4

Many other oxidising agents are capable of oxidising phosphorous
acid. The reaction with potassium persulphate is very slow, but in
the presence of hyclriodic acid it is much accelerated. This is a good
example of a coupled reaction. 5

Phosphorous acid forms esters by direct union with several alcohols. 6
With ethyl alcohol it gave diethyl phosphite. 7 Ethyl derivatives of
phosphorous and phosphoric acids have been made by the action of
bromine on sodium diethyl phosphite in ligroin. They arc separated
by fractional distillation. 8

The Phosphites. Two scries of phosphites arc known, the primary
phosphites, MII 2 PO 3 , and the secondary, M 2 IIP0 3 , M being a univalent
metal. Crystalline salts have also been prepared containing an excess
of phosphorous acid. The phosphites of the alkali metals and ammonia
arc soluble, those of the alkaline earths sparingly soluble, while those of
other metals are only very slightly soluble. They may be prepared by
the usual methods :

(1) By neutralising phosphorous acid to the appropriate end point

with alkali hydroxides and evaporating to crystallisation.

(2) By neutralising a solution of phosphorous acid, or one made

from PC1 3 , with ammonia and adding a salt of the required
metal.

(3) By dissolving the hydroxide of the base in phosphorous acid.

1 Kammclsborir, Awt ilm, J8G7, 131, 203, 3f>9, 132, 481.; ftjcvorts, loc. r?/..; Major,
loc. til.

- Balard, loc. c.tl.; Wurt/., loc. c.tl.

3 Linharu Amr.r. J. tic-i., 11)13, [4], 35, 3f>3.

1 Mitchell, Tran. Che.,*. ,SV,c., 102-1, 125, 1013.

5 .Fedorlin, %i(:itt-h. ithyxikdl. Ghf-.rn., liiOi , 41, ;">70.

Sachs and Lovitsky, -/. 7. v/,s-.s-. Phyx. Ckon. Soc,., J ( J()3, 35, i>LL

7 Thorpe and Xorth^ Trans. Chem. /S wc., 1890, 57, 634.

8 Arbusov, J.praM. Chun., 1031, [2j, 131, 103.

OXYACTDS UXS ATURATED. 1 45

The phosphites are fairly stable in the absence of oxidising- agents
and dilute solutions may even be boiled without decomposition. More
concentrated solutions may decompose, giving hydrogen; thus

Xa 2 HP0 3 -r XaQH = Xa 3 P0 4 + H,

The solid salts decompose when heated, giving- phosphine or hydrogen
or both, and leaving the ortho- or pyro-phosphate of the metal ; thus

2BaIIPOo.IIoO =Ba Po0 7 -2lI

5Pbi-IP0 3 ^PboPA 4-Pb 3 "(P0 4 ) 2 +PH 3 +H 2

The formulae of typical phosphites are as follows :

LiH 2 P0 3 ; LioHP0 3 .H 2 0, four-sided plates; KaH 2 PO 3 .2pI 2 0,

moiioclinic prisms ; Na 2 HP0 3 .5-5lI 2 O, rhombic bipyramidal needles ;
KH 9 PO 3 , mono clinic, prisms : K 9 HP0 3 ; XIl.JloPO.^ monoclinic
prisms : (XH 4 ) 2 HPO 3 .H 2 O, four-sided prisms ; Ag 2 HPO 3 , white
crystalline precipitate ; 2CaHPO 3 .2H 2 O, white precipitate"; Ba(H-,P0 3 )o ;
BaHP0 3 .i-H 9 0, white crystals ; Ba,(I-L,PO 3 ) 3 .5HoO ; Msr(H 9 POo) 9 ":
MgHPO 3 .6HoO ; CuHP6 3 .2HoO, blue " crystals ; " ZnHPO 3 .2iHoO ;
MnHPO 3 .H 2 6, reddish-white precipitate; Pb(H 2 PO 3 ) 2 ; PbHPO 3 ;
nFeO.P 2 O 3 , crystalline mineral ; CoHP0 3 .2H 2 O, red crystals, blue
when dried ; (XH 4 ) 2 [Co 3 (HPO 3 ) 4 ].18H 2 J and a corresponding nickel
compound.

Ammonium phosphite in its hydrated form, (XH 4 ) 2 HP0 3 .H 2 0,
or as the anhydrous salt, has been made by saturating phosphorous
acid with ammonia, 1 or by passing ammonia over the hydrogen phos
phite at 100 C. 2 It easily loses both water and ammonia when heated
or kept in a vacuum. 3

The hydrogen phosphite XH 4 II 2 PO ;? is rather more stable, and has
been prepared by the neutralisation of phosphorous acid with ammonia
to methyl orange, followed by careful evaporation.* It melts at about
120 C. and decomposes at about 140 C., giving ammonia, phosphine
and phosphorous acid. The form and constants of the crystals have
been described. 5

Hydroxylamine phosphite, (XH 2 OH) 2 .H 3 PO 3s was prepared by
double decomposition of one mol of Xa 2 HP0 3 with two mols of
XH 2 OILI-in. The sodium chloride was crystallised out by evaporation
in vacuo, and the very soluble hydroxylaminc salt crystallised from
alcohol. It melts easily, is inflammable and is a strong reducing agent.
Ilydrazine phosphite, XoH^.TLjPOy, has also been prepared, from barium
phosphite and hydrazinc sulphate. 6

Structure of the Hypophosphites and Phosphites. The mono-
basicity of hypophosnhorous acid points to the urisymmetrical formula.
The probable existence also of a proportion in the symmetrical form
may be indicated by the ea.se with which the acid undergoes sell-oxida
tion and -reduction on heating, thus

HO - PO = ;II 2 II -Pi = (OH), > PH 3 -i-HO -PO - (OH) 2

1 Rose, AiriHilcn, 1827, 9, 2S, . i.S, 2.1 ~>; Fourcroy and Vauqnelin, Joi/r/t.. Poly!-., 1705,
4, Ci");").

2 Arrmt, lor.. ciL, a ml ; ",S ///- lr- phovpJ,./,/.^ H If* wrophoxpliitc.s" 180], Paris.
:! \Vurtz, Ann.. C/rint. 7 J ///y.v., !oc.. ciL 1 Amat, loc. cit.

5 J)ufct, Hull, A or:. mitt da France, ISO I, 14, 200.

6 SabancefT, ZciLwh. anorfj. Chem., 189S, 17, 488; J890, 20, 22.

VOL. vr. : ii. 10

146 PHOSPHORUS.

Hypophosphorous acid easily adds on benzaldehyde, and the pro
duct, di! oxybenzene] phosphorous acid, must have the unsymmetrical
formula

HO - PO - [CH(OH)C 6 H 5 ] 2 x

Alkylphosphinic acids should also be considered as compounds in
which the alkyl is directly attached to phosphorus, since they have
been obtained by the oxidation of primary alkylphosphines with fuming
nitric acid. (CH 3 ) 2 =PO -OH is hardly an acid, but rather resembles
a higher aliphatic, alcohol in its waxy appearance and melting-point
(76 C.). This compound sublimes without decomposition.

Ester acids of phosphorous acid are known, such as CH 3 .PO(OH)
(m.pt. 105 C.) and C 2 H 5 .PO(OH) 2 (m.pt. 44 C.), which are capable
of giving mono- and di- ethyl esters. 2

The tautomerism of phosphites has been proved by the preparation
of two tri ethyl phosphites. 3 The one, prepared by the action of phos
phorus trichloride on sodium cthoxide, was probably the symmetrical
ester, being formed according to the equation

PC1 3 +3XaOC 2 H 5 =P(OC 2 H 5 ) 3 + 3NaCl

Its density, Z) 1 ^, was 0-9605, it boiled at 156 C., was insoluble in water,
soluble in many organic solvents, and had a molecular weight of 154
in benzene. It reduced mercuric chloride. The other, prepared by
the action of lead phosphite on ethyl iodide, or phosphorous oxide on
ethyl alcohol, had a density, D^\ of 1-028, boiled at 108 C 1 .. and did not
reduce mercuric chloride. This was probably dicthylcthyl phosphite,
having the formula C 2 H 5 - PO = (OC 2 II 5 ) 2 . A di ethyl ester lias also been
prepared which boils at 187-188 C. and may have either formula

HO -P(OC 2 H 5 ) 2 or II -PO(OC 2 II 5 ) 2

The unsaturatccl character of these trialkyl esters wa-s shown by the
ease with which they were attacked by nitric acid, but still more clearly
by the formation, with evolution of heat, of stable crystalline addition
compounds when they were mixed with cuprous halides. Tims
CuCl.P(OC 2 H 5 ) 3 was described as consisting of colourless crystals
melting at 190 to 192 C. and soluble in organic solvents. 1 This
property they share with phosphine, alkylphosphincs and phosphorus
trihalides. The phosphoric, esters were quite indifferent to cuprous
halides. Nor were such addition compounds formed cither by phos
phorous acid itself or by the dialkyl esters, which may show that the
latter compounds have the unsyminctrical formula. Phosphorous acid
probably exists in both, forms, but first as P(OII). { , i.e. when produced
from PCl 3 and II 2 O. 5 This may he transformed into the unsym
metrical form through an addition compound I!( 1.P(()II) ;J , 1 and
probably also exists in the form of complex molecules, such as

1 Ville, Ann. CJrim. Phyx., 189.1, [(>], 23, 291.

2 Thorpe and Xorth, Tran*. Chcm. >SV., 1890, 57, ;"J4f>, (>, M. Sec also Palazzo and
Maggiacomo, Atti J{. Ac.au.L Lincc.i, .1908, [5J, 17, i, 432.

3 Kailton, Trans. Chziii. /S oc., 1855, 7, 21(5; Thorf)o and North, /or. c.it..; Micliaelis
and Becker, Bar., 1.897, 30, 1003.

4 Arbusov, /. Huns. Phyfi. Chew.. Soc., 1905, 38, 101.
3 Mitchell, Trans. Chc.m. Sue., 1925, 127, 33(3,

OXYACIDS UXSATURATED. 147

H 4 (HoP 2 O G ), the existence of which was demonstrated by the freezing-
points of concentrated solutions. 1

The X-ray K absorption spectra of phosphorous acid and the phos
phites of Xa. Al, Mn, Fe". Fe ", Ca, XL and Cd were nearly the same,
the head of the absorption band lying at A=575-l--l X-ray units. The
band of silver diethyl phosphite was at 5760-4. The values for phos
phorus in the elementary state and in different forms of combination
were as follows :

Hvpophosphites. Phosphites. Phosphates. -p T Vi 1 let _. W} ! ite

" i r J - * J - Phosphorus. Phosphorus.

5757-5 5754-1 5750-7 5771-5 5776-9 2

It was stated that the wavelengths of the absorption bands of elements
are higher than those of their compounds, and that the bands pass to
shorter wavelengths as the valency rises, provided that the successively
attached atoms or radicals are the same. The general results showed
that the structural formulae of the phosphorous diesters, triphenyl-
methylphosphorous acid and ferric monopropyl phosphite were
(RO) 2 =PG-(H), sodium diethyl phosphite (EtO) 2 PO(Xa), silver
diethyl phosphite (EtG) 2 P(OAg), monoacetylphosphorous acid (HO) 2
PO(Ac). In solution, the diesters and metal esters contained a mixture
of tautomeric forms. 3

Meta- and Pyro -phosphorous Acids. The acids HP0 2 and
H } P 5 may be regarded as partly dehydrated forms of orthophosphorous
acid. In their modes of preparation and properties they recall some
what the nicta- and pyro-phosphoric acids.

Meta phosphorous Acid was produced during the spontaneous com
bustion of dry phosphine in dry oxygen at a low pressure, probably
according to the equation

It was deposited on the walls of the vessel in feathery crystals, 4 which
were readily hydratcd by water giving H 3 P0 3 .

Pliroph.ospiioruus Acid has been made by treating PC1 3 with a little
water, or by shaking the syrupy acid with a slight excess of PC1 3 and
evaporating in a desiccator over KG II and P 2 O 5 . The crystalline acid
was very deliquescent. 5 Secondary phosphites when heated gave pyro-
phos plates with loss of water, thus

2BaIIPO 3 =Ba 2 P 2 5 -i-H 2

By the addition of the theoretical quantity of sulphuric acid the unstable
II 4 P 2 5 was obtained.

Sodium dihydropyrophosphitc was prepared by heating sodium
hydrogen phosphite in a vacuum at 160 C. :

3 =Xa 2 H 2 P 2 5 -r II 2 O 6

1 Koscnlicii-n and Italiener, Zc.ittch. ar/org. Chf-m., 1923, 129, 106.

2 Slcllintr, Znl^ Ji,. anon/. Ch.c.m.< 1023. 131, 48.

3 ttiollinir, Zf.-itxch. phi/.-iilcoL Ckc.m.., It^f), 117, 194.

4 van do Sf-.adi, Zc.it. ^.:fi. -plujxikaL Chvn., 18!)8, 12, 322.

5 Auo-er, Cunipt. mid., 1U03, 136, 814.

c Amat, "tiur Us phoK phitkx tl Us pyrophosphiies" Paris, .1801; Co-hip I. rend., 1888,
106, 1400; 1889, 109, 1050; J8 ( JO, no, 191; 1S90, in, 676; 1891, 112, 527, 614.

148 PHOSPHORUS.

The free acid was hydratcd to phosphorous acid in solution with

smary gave a 23 . e a c, e sat

Xa 2 HoP 2 5 being formed by neutralisation, with evolution of 14.3
Cals. per mol of water formed in the equation

H 4 P 2 O 5 +2X

Other salts of this acid have been prepared. As in the case of phos
phorous acid the structure may be symmetrical or unsymmctrical,
thus

/P(OH) 2 /PO(H)(OH)

0< or 0<

\P(OH) 2 \PO(H)(OH)

Detection and Estimation of Phosphites and Hypophosphites.

Solutions of hypophosphorous and phosphorous acids, as well, as
their salts, when evaporated to dryness and heated, give spontaneously
inflammable pliosphine and a residue of phosphoric acid or phosphate
respectively. The reduction of salts of copper and silver, and of
mercuric chloride, by these acids may also be used as tests. When
the alkali salts arc boiled with concentrated alkali hydrogen is evolved
and a phosphate is found in solution, thus

KHoPOo + 2KOH - K 3 PO 4 + 2lI
K 2 HP0 3 + KOH = K 3 PO 4 + H 2

Xascent hydrogen, from zinc and sulphuric acid, reduces both acids
to phosphine, which may be detected by the yellow stain which it
produces on silver nitrate :

PH 3 + 6A 5 X0 3 =PAg 3 .3AgN0 3 -i- 31IXO 3

This is similar to the stain given by arsine and, like AsAg 3 .3AgXO 3 ,
is hydrolysed and blackened by moisture :

PAg 3 .3AgX0 3 -r 3H 2 = H 3 P0 3 + 3IIXO., + CAg

Hypophosphites are all soluble in water and therefore the solutions
give no precipitates with the ions of the alkaline earths, silver, etc.
Silver salts, however, are rapidly reduced to metallic silver, and phos
phoric. acid is found in the solution :

2XaH 2 P0 2 -r2AgX0 3 -f 4-H 2 -211.^0, + 2XaXO :J + 2Ag f 3II 2

When hypophosphitcs are heated with copper sulphate solution to
55 C. a reddish-black precipitate of Cu 2 ll,, is produced, which de
composes at 100 C. into hydrogen and copper. Permanganates are
immediately reduced by hypophosphit.es. The effect of other oxidising
agents is mentioned under " Estimation."

Phosphites may be distinguished from hypophosphites by several
tests. The ions of barium and lead give white precipitates with solu
tions of phosphites. Silver nitrate gives a. white precipitate in the
cold, from which black metallic, silver is quickly deposited on
warming :

Xa oHPO-3 -i- 2AgXO, = Ag JIPO, + 2\aX(),
Ag 2 HP0 3 + H 2 6 = 2 Ai -l- II 3 P0 4

OXYACIDS UXSATURATED. 149

Copper sulphate is reduced to brown metallic copper with evolution of
hydrogen, but without intermediate formation of a hydride. Per
manganates are reduced more slowly by phosphites than by hypo-
phosphites under similar conditions.

Estimation. The course of the neutralisation curves of hypo-
phosphorous and phosphorous acids can be deduced from the values
of the dissociation constants. The curves have also been determined
with the aid of the glass electrode. 1 The curve for hypophosphorous
acid is that of a strong acid with only one inflection. That of phos
phorous acid has two inflections, at ^H = 3-4 to 4-5 and at >H=8-4
to 9-2. The first ;i end-point " can be located with dimethylamino-
azobenzene or methyl orange, and the second with phenolphthalein or
thymol blue. The first gives the sum of H 3 PO 2 , H 3 PO 3 and H 3 P0 4
if present together, while the difference between the first and second
" end-points " gives the sum of H 3 PO 3 and H 3 P0 4 . From these data
the equivalents of H 3 PO 2 can be obtained.

Hypophosphite and phosphite may also be determined by oxidation
with iodine. In alkaline bicarbonate solutions phosphites are oxidised
quickly to phosphates, while hypophosphites are hardly affected, i.e.
they do not use any measurable amount of decinormal iodine after
standing for two hours at ordinary temperatures. In acid solution
hypophosphorous acid is slowly oxidised to phosphorous acid, but no
further, according to the equation

H 3 PO 2 -f- 1 2 -!- H 2 O = H 3 P0 3 -r 2HI 2

On these reactions is based a method for determining the acids sepa
rately or in the same solution.

A phosphite solution of about JI//10 concentration is placed in a
stoppered flask with an excess of sodium bicarbonate saturated with
carbonic acid and an excess of! decinormal iodine solution and allowed
to stand for about an hour. It is then acidified with acetic acid and
the excess of iodine is back-titrated with decinormal bicarbonate-
arsenite.

1 c.c. of decinormal iodine solution ~ 0-004103 gram of H 3 PO 3

A hypo phosphite solution is acidified with dilute sulphuric acid,
treated with a known amount, in excess, of decinormal iodine solution
and allowed to stand for 10 hours at ordinary temperatures. A cream
of NaIICO 3 is then added until CO 2 evolution ceases, then fifth-normal
XaIICO 3 solution, saturated with CO 2 , whereby oxidation goes through
the next stage, to phosphate. After addition of: acetic acid the excess
of iodine is titrated with standard arsenite as before.

1 c.c. decinormal iodine solution ~ 0-00165 gram of H 3 PO 2

Phosphite, which usually is present in small amounts in hypophosphitc,
will be included and must be titrated separately in bicarbonate solution
as before. 3

Acid dichromatc and alkaline permanganate may also be used as
oxidising agents, the excess being determined iodometrically and with
ferrous sulphate solution respectively.

1 Morton, Quart. J. Pharm., 1930, 3, 438.

2 Rupp and Pinck, Btr., 1902, 35, 3691; Arch. Pharm., 1902, 240, 663.

3 \Vulf and Jung, Ztltsch. awry. Ch&m., 1931, 201, 347.

150 PHOSPHORUS.

Either of these acids may also be determined by weighing the
mercurous chloride which is produced by reaction with mercuric
chloride in slightly acid solution, according to the equations

H 3 POo + 2HoO + 4HQlo - 2Hg Clo -f 4HC1 + I1,PO 4
H 3 PO 3 -r HoO + 2HgClo = HgoCL + 2HC1 + H 3 PO 4

The mercurous chloride is washed with water and dried at 110 C.,
or with alcohol and ether and dried at 95 C. 1

Hypophosphoric Acid. This acid, together with phosphorous
and phosphoric acids, was first produced by the slow oxidation of
phosphorus in the air and in. the presence of water at a moderately
low temperature (5 to 10 C.) ; it was isolated through the formation
of a sparingly soluble sodium salt. 2

It was also produced by the slow oxidation of phosphorus with
silver nitrate in neutral or amruoniacal solution. 3

Oxidation of yellow phosphorus by copper nitrate in the presence
of nitric acid at about 60 C. also yielded hypophosphoric acid along
with phosphoric acid and copper phosphide. 4 These reactions have
been expressed by the equations

4P ~ 5Cu(XO,) 9 + 8EUO = Cu 3 Po + 2Cu + 1()HXO 3

4P -f 4Cu(XO 3 )~ + QlllO = Cu 3 P 2 + Cu + 8IIXO 3 + H 4 P 2G 5

Better yields were obtained by the electrolysis of 1 to 2 per cent.
sulphuric acid using anodes of copper or nickel phosphide. 6

The conditions Cor obtaining a good yield by the oxidation of
phosphorus have been worked out by a number of investigators. 7 In
the method of Cavalier and Cornec 8 glass rods are placed parallel to
one another in a photographic dish and sticks of phosphorus laid
across them, each pair of sticks being separated by a. glass rod, which
is also of course laid transversely to the supporting rods. Water is
added until the sticks of phosphorus are half-immersed and the whole
is covered with a glass plate resting on wa.dding at its edges. The
air is thus filtered as it enters round the edges. A temperature of 5
to 1.0 C. is the most favourable. Below 5 C. the oxidation is too
slow, while above 10 C. undue quantities of meta- and ortho-phosphoric
acids arc produced. In winter about 12 per cent, of the phosphorus
is oxidised to hypophosphorie acid. The solution may then be treated
with saturated sodium acetate, when the acid salt XaiIPO.j.. 3lL>O
separates on cooling. Or the boiling solution of the acids may be
neutralised to methyl orange with sodium carbonate and concentrated
by evaporation, when NaIL3/O :i .. 3lL>O crystallises and ma.y be re-
crystallised from boiling water. The sodium salt dissolved in hot

1 Mitchell, Tran*. Cfitm.. ,W., I92-4, 125, HUM.

2 Sal/cr, Annalcn, 1878, 194, 28: 1882, 211, 1; 1880, 232, 1 14.

3 Sunder, Anual(:u, 1880, 232, 14.

4 Kosenheim and L inskor, JJcr., 1910, 43, 200, ]; (.Ionic-, ,/. I hann. (, hrm., 1882, |;V,
6, 123.

3 Tauchert , k " U /ilt rsuc/t. uba U )i-l(-rph<ji<i)li(jr,iiiur(. , " > 11)13, Munich; idem, Zatxcji.. tuuj/ y.
Chew., J913, 79, 35U.

(5 .Rosenlicim and Pinsker, loc. c d.

7 Joh , Com.pt. rend., 1885, 101, 1058, .1150; 1886, 102, 110, 251), 7(50, 1005; R.oseri-
heim, Stadler and Jacobsohn, Jlcr., 1900, 39, 2838; JJausa, Zc.ttwh. tinonj. Chcm., 1894,
6, 128.

8 Cavalier and Cornec, lyidl. &oc. chini., 1909, [4], 5, 1058.

OXYACIDS UXSATURATED.

151

water may be treated with lead acetate and the sparingly soluble
lead hypophosphate filtered off. This is then suspended in water and
a current of hydrogen sulphide is passed, which liberates the acid.
The filtered solution is concentrated somewhat by heat in the open
and finally in a vacuum over concentrated sulphuric acid. Alterna
tively the dilute solution of the free acid may be prepared from barium
hypophosphate and dilute sulphuric acid.

General Properties. The evaporated solution prepared as above
deposited crystals of the hydrate H 2 PO 3 .H 2 O which had the form of
four-sided rectangular plates and melted at 70 C. 1 They were very
deliquescent, but when kept over sulphuric acid effloresced giving the
anhydrous acid, which melted at 55 C. A half- hydrate, H 2 P0 3 . JH 2 O,
which melted at about 80 C. was also obtained by evaporation over
sulphuric acid.

When the anhydrous acid was kept above its melting-point it
suddenly decomposed with considerable evolution of heat, thus

Phosphine was evolved at about 180 C.

The molar heat of fusion of the anhydrous acid was 3-85 Cals. 2
The hydrate dissolved with absorption of heat.

Aqueous Solutions of Hypofihosphoric Acid. The electrical con
ductivity of this acid shows that its first hydrion is largelv dissociated.

/ J G /

THE MOLAR CONDUCTIVITIES OF HYPOPHOSPHORIG

AND PHOSPHOROUS ACIDS. 3

at 25-0 ( .
at 25-0 C.

16

32

64

128

256

512

1024

184

199

222

240

275

304

370

222

252

202

318

33?

351

358

The molar conductivities of 1I 3 P0 3 at dilutions up to, and including,
512 were greater than those of IT PO 3 , and this difference would have
increased if the latter conductivities had been determined at 25 C.
The ions I.IPO 3 ~ and II 2 P0 3 ~ probably have practically the same
mobility, so that the difference is to be attributed rather to the smaller
second dissociation of HP0 3 ~ (into H r and PO 3 ~") as compared with
that of 11 2 PO 3 ~ into II" and 11PO 3 ~~. A very low second constant
would also be ascribed to H 2 P0 3 on account of the high alkalinity of
solutions containing two equivalents of alkali, (sec " Neutralisation/
p. 152).

The change in the conductivity of the salt XaIIPO 3 or Xa 2 H 2 P 2 G
with dilution shows no effect due to dissociation of a second hydrogen
until a dilution is reached between 256 and 512 litres, as is seen from
the following table :

1 Joly, loc. ciL; Koscnhcim and Pritze, Bar., 1908, 41, 2710.

2 Joly, loc. cil.

3 Rosenheim and Pmsker, loc. cit.\ Parravano and Maani, GazzttUi, 1907, 37, 268;
van Xame and Hull, Amer. J. Sci., 1918, [41. 4S, 01, 103.

PHOSPHORUS.

V

16 32

04

128

256

512

1024

p, (25 C.) .

78-8 : Sl-G 88-]

94-5

100-2

105-9

111-9 x

//, (25 C.) .

78-8 86-1 92-2

95-9

98-1

100-7

101-6 2

Basicity. The heats of neutralisation indicate a dibasic acid (per
atom of phosphorus) as will be seen from the following figures : 3

Equivalents of NaOH per : ; ; ,

mol HoPOjj . . . , 0-5 i 1 1-5 ! 2-0 3-0

Heat evolved, Cals. . . 7-57 , 15-05 : 21-36 i 27-11 27-65

During the neutralisation with alkali a sharp end-point was obtained
(to methyl orange) when one equivalent of alkali had been added,
while pheiiolphthaleiix gradually changed between 1-5 and 2-0 equiva
lents, showing that the second dissociation constant is lower than that
of the majority of organic acids (see also " Electrical Conductivity/
p. 151).

These facts can be explained equally well on the assumption that
the acid is tetrabasic, with two atoms of phosphorus, i.e. II 4 P 2 (J , and
this view is in accordance with the existence of four salts MH.jP O r
M 2 H 2 P 2 8 , M 3 HP 2 G and M 4 P 2 O 6 . 4 ~

Further evidence is collected under t; Molecular Weight " (p. 153).
The molecular weight as deduced from the (Yec/ing-poiuts of
aqueous solutions corresponded with doubled molecules, 1I ;1 P Q ( . 3
which arc highly dissociated, giving one hydrogen ion, 5 or to the
acid HoPO 3 which is very slightly dissociated even in fiftieth-normal
solution.

Ch.emicul Properties. The proof of the individuality of hypo-
phosphoric acid rests largely upon the great differences which exist
between it and a, mixture of phosphorous and phosphoric acids. These
acids were formed irreversibly when hypophosphoric acid was allowed
to stand in aqueous solution, especially when this was concentrated
and the temperature was ^0 C. (or a.bovc). A 5 per cent, solution after
, 3 years contained only phosphorous and phosphoric acids. These
acids, on the other hand, showed no tendency to condense together
when kept under ordinary conditions. The free/ing-point. curves of
mixtures of the anhydrous acids showed no intermediate maximum
and only one cutectic at -- KH)" ( . and .*>!) niols per cent, of I1. ; P(). { . (J

Decomposition of hypophosphoric acid may be represented as a.n
hydrolysis, thus

lUW; H 2 () - - II :^ >() :j f IM Oj

This reaction is catalysed by hydrogen ions and was found to he nni-,
molecular in normal hydrogen-ion concentrations. The \alues of the

jsrnhrini, Stadlrr and .Jarob.sohn, lit / , I .MMJ, 39, iis. >l).
>M nhcim and lU iilin, 7.iit^ch. niinnj. ( him., I Jlil, 120, ](). >.

)M-nlK-ini, Sladlrr and .Jarobsnlm, Iii()(J, /<. c/t.

OXYACIDS UNSATURATED. 1 53

constants were 0-000186 at 25 C, and 0-00631 at 60 C. 1 The
sodium salt, NaHP0 3 , having only a low hydrogen-ion concentration
(ca. IxlO- 1 ), could be kept for long periods without much change,
and alkaline solutions containing Xa 2 P0 3 , etc.. were still more stable.

Cold solutions of the acid did not precipitate the metals from gold,
silver or mercurous solutions. The acid was not oxidised by iodine!
hydrogen peroxide or chromic acid in the cold, but was slowly" oxidised
by potassium permanganate. Hot concentrated solutions were more
easily oxidised. When the neutral salts were heated they gave phos
phate and phosphine, or pyrophosphate, elemental phosphorus and
phosphine. Reducing agents such as hydrogen sulphide or sulphur
dioxide had no effect, and even nascent hydrogen, from zinc and acid,
gave no phosphine.

Molecular Weight. Much investigation has been carried out with a
view to ascertaining whether the molecule should be formulated as
H 2 P0 3 or H 4 P 2 Og. The evidence of electrical conductivity does not
lead to a definite conclusion. Molar weights of some esters are known.
Thus dimethyl and diethyl hypophosphates (from the silver salt and
alkyl iodide) gave elevations of boiling-point in ethyl iodide, chloro
form, etc., which corresponded to the formula (CH 3 ") 2 P0 3 , etc. 2 On
the other hand molecules such as (CH 3 ) 4 P 2 6 were indicated in benzene
solution at its freezing-point. If, as seems probable, the free acid in
concentrated solution has the formula H 4 P 2 6 , the constitution and
hydrolysis of this would be represented by

(HO) 2 OP-PO(OH) 2 -fH 2 = (

Hypophosphoric acid was not formed by any ordinary dehydration of
a mixture of phosphorous and phosphoric acids, neither was it produced
by the hyclratioii of PoO 4 , which yielded only a mixture of equal mols
of H 3 P0 3 and H 3 PO 4 . "

Hypophosphates. The salts of the alkali, alkaline earth and some
other metals were prepared and studied by Salzer, Rammelsberg,
Schuh, Joly, Palm, Bausa and others. 3 The alkali salts prepared from
excess of alkali were soluble, whilst those of the alkaline earths, silver
and other metals were only sparingly soluble.

The formuhc of some typical hypophosphates are as follows [solu
bilities in grams per 100 grams of water] :

Li 2 II 2 P 2 O 6 .2ll 2 O, crystalline, sparingly soluble; Li 4 P 2 O 6 .7H 2 O,
solubility "()-S:3 ; " Xa 2 H 2 P 2 O G .6H.,O, monoclinic, solubility 2 : () ;
Na 3 IIP 2 6 6 .9l-I 2 O, tabular monoclinic ; Xa 4 P 2 6 .10li 2 0, six-sided mono-
clinic, solubility 1-5; K 3 II 5 (P 2 O 6 ) 2 .2H 2 Of rhombic, solubility 40;
K. 2 HoP 2 O(j.2lI O, monoclinic plates : K 4 P 2 6 .8H 2 O, rhombic pyramids,
solubility 25 : (XH 4 ).JIoPo0 6 , granular or needles, stable in air, solubility
7-1; (XH 4 ) 4 P 2 O 6 .I-i 2 b, "prismatic, elllorescent, solubility 3-3 : Ag 4 P 2 O 6 ,
insoluble ; CaJl 2 P 2 O 6 .GH 2 O, monoclinic prisms ; Ca 2 P 2 O e .2H 2 O,
gelatinous, insoluble ; 13alI 2 P 2 6 , monoclinic prisms ; Ba 2 P 2 O 6 . white

1 van Xame and Unit, loc. ell.

2 Kosenheim and Pinskcr, loc. cil.; Roscnheim and Keglin, loc. cit.; Rosenhcim,
Stadlcr and Jacobsohn, loc. at.; Cornec, Lull. &oc. chi)/i., 1909, [4], 5, 1081.

3 Salzer, loc. at.; Kammelsberg, /. prakl. Chcm., 1S92, [2], 45, 153; Schuh, " Btitruye
z. Kc-unln. d. C iite.rphoH pk. &aurc," Munich, ]91l; Joly, loc. cit.; JBausa, loc. at.; Palm,
"A T cwe Vtrbind. d. U ultrphosph. Sdtire," Elbcrfeld, 1S90; Drawe, "Hiniye, ntue Salze
der Unlbrphoi>-phu rt>r.i Ui-L, Rostock, 1S88: ]3tr. t 1SS8, 21, 3401.

154 PHOSPHORUS.

precipitate; Mg 2 P 2 O $ .12H 2 O, gelatinous, slowly crystalline, solubility
0-0067; Zn 2 P 2 O 6 .2H 2 O, white precipitate ; Cu 2 P 2 O 6 .6H 2 O, insoluble";
Pb 2 P 2 O 6 , insofuble ; Xi 2 P 2 O 6 .12H 2 O, prismatic crystals.

A number of double hypophosphates of manganese, cobalt and nickel
with the alkali metals have been prepared, such as K 2 XiP 2 O 6 .6H 2 O
and 3K 2 H 2 P 2 O G .CoH 2 P 2 O 6 .15H 2 O.

Hypophosphites of hydroxylamine resemble those of ammonia.
Thus (XHoOlI) 2 .H 4 P 2 O 6 is a crystalline salt, very soluble in water and
melting with decomposition. Hydrazine dihydro- and trihydro-hypo-
phosphates, (X 2 H 5 ) 2 H 2 P 2 O 6 and (X 2 H 5 )H 3 P 2 O^, were both obtained
in the crystalline state. The latter is isomeric with ammonium dimeta-
phosphate, (NB^PC^),. 1

Detection and Estimation. The distinctive tests which distinguish
hypophosphates from phosphites have already been pointed out (p. 153).
One of the most useful is the sparing solubility of sodium hypophosphate.
Also, a sparingly soluble guanidine salt (1 per cent, at 28-5 C.) is pre
cipitated when guanidine carbonate is added to a solution of the acid. 2
The acid may be titrated with alkali and phenolphthalein ; 3 mols of
XaOH correspond to 2 mols of H 2 PO 3 , i.e. the salt Xa 3 HP 2 O ( . is formed. 3
The acid may be estimated in the presence of phosphoric and phos
phorous acids by precipitation of the silver salt at pH = 1 to 2. 4

1899, 20, 22.

oseneni an mser, oc. e.
3 Pinskor, l Z/ur anaL Bcshwm.
Berlin, 1909.

erlin, 1909.
- 1 Wolf and Jung, Ztitsch. anorg. Chtm., 1931, 201,

CHAPTER XII.
PHOSPHORIC ACIDS.

Historical and General. The production of an acid solution by
dissolving in water the products of the combustion of phosphorus was
demonstrated by Boyle. 3 - and the acid was prepared in a similar manner
by Marggraf, who described its properties. 2 It was extracted from the
calcium phosphate of bones by Scheele. 3 Lavoisier 4 obtained it from
phosphorus and nitric acid. Three forms differing in their properties
and in their mode of preparation were recognised early in the nineteenth
century.

The usual form, as prepared by Boyle and others, when partly
neutralised by soda gave a yellow precipitate with a solution of silver
nitrate. When a solution of this ordinary acid was heated in a gold
crucible until water ceased to be evolved, a thick pasty mass was left 5
which gave a white silver salt and coagulated albumin. When ordinary
sodium phosphate, Xa 2 IIPO 4 , was heated to 240 C. it was converted
into a salt which gave a white precipitate with silver nitrate. 6 It was
also shown by Graham 5 that phosphoric acid could be obtained as a
vitreous mass by long heating at 215 C., and that this; when dissolved
in. water, did not coagulate albumin or give a precipitate with barium
chloride in acid solution. When the acid was still more strongly heated
it gave a tough vitreous mass, a solution of which coagulated albumin
and gave a precipitate with barium chloride. 7 Salts of the same acid
were obtained by heating sodium bipliosphatc, namely, XaII 2 PO 4 . A
vitreous mass was left which was known as " Graham s salt," and is
now known as mctaphosphate, XaPO 3 (#..), in a polymerised condition.
The acid itself was prepared by decomposing the lead salt with BUS,
and also by heating the ortho- or pyro-acid to over 300 C., s and later
by several other methods (q.v.).- ]

Graham proved that the three acids, ortho-, H 3 PO 4 , pyro-, H 4 P 2 O 7 ,
and mcta-, HPCX, differed by the quantity of combined water. This
water determined the basicity of the acid. The hydrogen could be
replaced in stages by a metal, and e.g. in the case of orthophosphoric

1 Boyle, Phil. 7 V ,;.*., 1680, 13, 196.

2 Ahir^gL-af, ^Ckftni.^. .h.f-.h tich-nfU-.,).," .176:2, I, Berlin.

3 Sjclieele, " Chc/n. Abhandi. v. dc.r Luj l u. Feuer," Upsala, 1777.
1 Lavoisier, " Opuscules physique..* tt chyr/uques," Paris, 1774.
5 Graham, Phil. Trans., 1833, 123, 253.
(; Clark, Edin. J. Science, 1827, 7, 208.

7 Berzelius, Gil fort s Annahn, 1816, 53, 303; 1816, 54, 31; Ann. Chim. Phys., 1816,
[2], 2, 1.31, 217, 320.

H Gregory, Annaleti., .1845, 54, 94; Maddrell, Phil. Mag., 1847, [3], 30, 322.

9 See Graham, .Researches on the Arsenates, Phosphates and Modifications of

Phrxsnlinvir Ap.irl " PI; I T-r/ms 1 A AZ T^o ->r>3.

156 PHOSPHORUS.

acid different salts, the primary, secondary and tertiary phosphates,
could be produced (see also " Basicity." p. 163).

OKTIIOPTIOSPIIOKIC ACID, IT 3 FO i j.

The acid which is produced linally by the oxidation of phosphorus
in the presence of sufficient water and after heating has probably the
constitutional formula OP(OH) 3 (see p. 59). The term :t ortho,"
in accordance with Graham s description, was applied to " ordinary "
phosphoric acid. Later, on the hypothesis of the quinquevalent nature
of phosphorus, it was considered that the hypothetical acid P(OH) 5
would, strictly speaking, be the " ortho :? acid. However, the present
theories of valency do not indicate the possible existence of such an
acid, but rather that OP(OH) 3 should be the most highly hydroxylated
compound.

Preparation. The acid may be made by means of a great variety
of reactions, some of which are referred to under the Ci Oxides,"
i; Halides " and t; Phosphoric Acid (p. 224)." Only a few methods,
of technical or historical importance, will be described here.

(1) The decomposition of naturally occurring phosphates. From
this source the original supplies both of technical and refined phosphoric
acid are derived. The decomposition is effected by sulphuric acid,
supplied in the quantities required by the equation

Ca 3 (P0 4 ) 2 +3H 2 SO 4 =3CaSO. 4 -!-2lI 3 PO 4

The decomposition may he carried out in a large vat of pitch pine
saturated with tar oil, and provided with a vertical wooden shaft
bearing arms or paddles and rotating on a pivot which is protected
with cast-iron. In the vat are placed weak liquors from a previous
decomposition and steam is blown in through a. leaden pipe. Stirring
is then commenced, and a charge of 6 cwt. of finely-ground high-grade
phosphate (at least 70 per cent. ( a ; >(P0 4 ).>) is added alternately with
5 carboys of " chamber acid " of density 1-5 to 1-G (free from arsenic).
After the reaction is completed the whole charge is run on to slightly
inclined (ilter-beds made of ashes supported on clinkers and contained
in rectangular wooden tanks. The phosphoric acid which runs off
first has a density of 1-150. The deposited gypsum is kept covered
with water supplied as a spray until the density of the diluent falls to
1-010. The gypsum sludge, containing sma.ll amounts of free phos
phoric acid and phosphate of lime, is dried by waste heat and used for
mixing with superphosphate and for other purposes. The solution
of phosphoric acid is concentrated by evaporation in lead-lined wooden
tanks which are heated by lead pipes carrying superheated steam,
concentration being continued up to a density of ! -.TJ5 to !;">(). Cal
cium sulphate deposited in this part of the process is removed and
washed.

(2) The preparation of the acid by I he combustion of phosphorus
and solution of the wi (lowers of phosphorus " in water has an historical
interest only. It is obviously too expensive for large-scale work, nor
does it yield a pure product.

(3) Oxidation of red phosphorus by nitric acid was used before; the
end of the eighteenth century.- 1 An excess of nitric acid of density

1 Lavoisier, Mdf/t. Acud., 1780, , jJ.*>; .Marlivs, Ann. C/n/n. 1 hy.i., ISlO, i 1J, 73, 1)8.

PHOSPHORIC ACIDS. 157

1-20 to 1-25, namely, about 16 parts, is added to 1 part of phosphorus
in a flask carrying a reflux condenser which is fitted in by a ground-
glass joint. The phosphoric acid may be concentrated in a platinum
or gold dish and is then free from most of the impurities mentioned
later, with the possible exception of arsenic derived from the red phos
phorus. [In process (I) arsenic, if present, is generally introduced
with the sulphuric acid.] In both cases it will be converted into
arsenic or arsenious acid. It may be removed by saturation with
sulphur dioxide, which reduces arsenic to arsenious acid, followed by
boiling to remove the excess of SO 2 , precipitation of the arsenic as
sulphide by hydrogen sulphide, filtration and removal of the excess of
H S by means of a current of air.

Concentrated phosphoric acid may be further purified by crystal
lisation (see p. 158).

(4) Furnace Methods. Phosphoric acid can be prepared from the
pentoxide, which is sublimed at high temperatures from a mixture of
calcium phosphate, sand and coke. Phosphorus is first produced and
then burns to the pentoxide. Reduction proceeds according to the
equation

Ca 3 (PO 4 ) 2 -3Si0 2 - 5C =3CaSiO 3 -2P -f- 5CO

An electrically-heated furnace (p. 8) or an oil-fired furnace built of
carborundum bricks and kept at a temperature of 3500 to 1700 C. is
suitable. A regenerative system of heating is used. The mixture of
carbon, sand and phosphate is introduced at the top of a slanting
flue and meets the ascending heated gases in its descent to the hearth,
where it melts and reacts according to the equation given above. The
escaping gases are taken round and burnt in a set of channels which
surround the furnace. 1

If phosphorus is burnt in air to the pentoxide. the absorption, of
this in water is rather difficult. Oxidation by steam according to the
equation

2P-r5lI 2 O=P 2 O 5 +5lI 2

gives hydrogen as a by-product which may be converted into ammonia
and combined with the phosphoric oxide (Liljenroth process). 2

Impurities. The acid prepared by commercial methods contains
numerous impurities, some of which are difficult to remove. They
include bases such as Xa, K, Ca, Al, Fe, Mn totalling 0-5 to 3-0 per
cent., Pb up to 34 parts per million, Ag from 1 to 2-5 parts per million,
HoS0 4 from 0-1 to 1-0 per cent., IIF in about the same amount, and
HC1 from 0-01 to 0-0-1- per cent. 3

Preparation of tlic Cri/stallinc Acid. Two compounds have been
crystallised .from concentrated solutions of phosphoric acid the

1 Thomas, />V///.s-A Pof.cn/^ 24 14, 21<)(i (1S7!)); Albert., German. Pufcnl, 12r>OL (1880);
.Rose, Gc.r,ii.f.ui I utcx.t, 12372 (1880); Thomas and IVymann, British. Pntcnl, 438 (1883);
Adair and Thorn Imson, Brih*h l>(tl<nt, 747 (ISS3); Lornax, Hrilitk Patent, !)fill. (1900);
.Fan-weather, JJrif/.^/i Pattnl, 191030 (11)22). Kendall, Booue and Andrews, ,/. Amtr.
(hc:tn. ,S oc., 1917, 39, 2303; Carpenter, Chan. A jf, 11)22, 6, <S30; YVaiii;amnn and Tui loy,

PHOSPHORUS.

s acid, H 3 P0 4 , and the hemi-hydrate 2H3PO4.HOO. 1 Accord-
ly 1 a solution having the composition H 3 PO 4 + 0-3H 2 O, when
i with a crystal of H 3 PO 4 , deposits the hemi-hydrate. The
quor then has the composition 2l-I 3 PO 4 .H 2 O and solidifies to
crystals when inoculated with this hydrate. Another method
ing the crystalline acid has been described in the following
1 Crystals "of anhydrous phosphoric acid were prepared by
ng the ordinary C.P.* acid in an open vessel at a temperature
95 C. until it reached a specific gravity of approximately
The solution was then cooled below 40 C., inoculated with
of orthophosphoric acid, allowed to stand until cry stall! sa-
complete and the mother liquor then separated from the
iy centrifuging in a porcelain-lined centrifuge. The crystals
"in this way were then melted at a temperature of about 50,
water was added to bring to a specific gravity of D 2 { 1-85, the
noculated as before and the process repeated thrice. The
ere finally dried by allowing them to stand for several months
sphorus pentoxide. Crystals of the semi-hydrate were pre-
adding the proper amount of water to a weighed portion of
ivdrous phosphoric acid, cooling below 29 and inoculating
-stal of the hydrate." 2

cal Properties of the Solid Hydrates of P 2 O 5 . The
Dints, as registered by different investigators, are in fair
:, thus :

38 -G 3 41-75

.1-2-35 C. 2

I-LO . 27-0 6 29-0 7 , 20-35 5 , 2D-32" C. 2

lermal diagram of H 3 P0 4 and I1 2 () is shown in fig. .{,- on

TC are two melting-points, m, that of H.jPO,, and m,, tliat

4 .H 2 0, and two eutcctics, c, that of II^PO., a.nd 2!! ;i P()~.lI 2 O

i at of 2l-I 3 PO 4 .II 2 and ice. The solubilities according to

:1 Meir/ics are marked in the table opposite by an asterisk.

estimators reported also a distinct solubility curve eorre-

to a hydrate lOlJUPC^.HoO, \vhich started from the euteetic

led with a transition point at 25-85 C.

loric acid crystallises in four- or six-sided prisms belonging I

mbic system. 6 |

^termination of the molecular weight by (!ej)rcssion of the j

Dint indicates some electrolytic dissociation." A value of

:cn found for the molecular weight. 1 The acid apparent.lv

o uipt. rend., ]88.">, 100, 441; ISSfi, 102, , >I(i.
Joniinercial pure.

id Jones, /. A-tn.f.r. Chan. Xoc., 11)2"), 47, "2 !()").

m, Jler., 1874, 7, 097. |

ot, Ann. Chim. Phy*., I87S, [">], 14, -HI. !

tnd Menzies, J. Ar/ier. C/icni. >SV;r., !!)()!), 31, 1 ls;j. |

ympL rend., foe. at.

"Jompf. re////., 1908, 146, 1270; idem, Ann. ( hint. / ////*., 1<M)S, |,S], 14, f>(>r>.

I, Boogc and Andrews, loc. at.; Jones, [\. C " II inlrnlrs in Solution"

.1907. !

d Myers, Trans. Ch^n. Xuc., 1911, 99, ;>S4 ; /W., 191:5, 103, ~tt 2.

PHOSPHORIC ACIDS.

159

4-50

+25

-100

100

PER CENT. H 3 P0 4
Fro. 4. Hydrates of Phosphoric Acid.

SOLUBILITIES, MELTING-POINTS AND EUTECTICS

OF THE SYSTEM H 3 PO 4 H,O.

Grams

r .. Grams

>mpera-
t ure,

! I .. P() , per t< i- i j>i
, f i f Solid Phase.
1 00 Grams

Tempera- ,., J)() ^

ture, !/ ;!/-. : . Solid L hase.
x, JOO Grams

Solution.

Solution.

- 85

625 Iee-2H,PO,H,0

28-28 92-72 | 2H.,P0. 1 .IU)

81-0-

63

27-3(> 93-33 ,,

- 57

67-5 2H 3 PO 1 .H,0

26-08 93-21- i

-43-0

70-0 i ,,

e j5 23-50 ; 94-75 2fl.,PO,.H,()

- 29-0

7 2 .5 , ,

-i-.M.jl

-17-5

75-0 ,,

25-^lP- 94-1 2H,P() ] .I-I. )

- 16-3*

76-7

25-88 ; 95-22 ll,PO. "

()()

78-75

26-23 :f: 95-90

-i- 0-5- :

78-7

27-30 !)5-56

18-92

84-07

28-38 95-86

23-41

85 93

29-90 96-18

25-2-1

87-05

31-96 96-80

27-0*

87-7

34-06 97-40

27-3

88-5 J

36-15 98-00

28-75

90-0

40-02 : 99-27

. 29-32

91-60

m 1? 42-30 i:: 100-0

, 29-35*

91-60

m lt 42-35 100-0

160 PHOSPHORUS.

forms double molecules in glacial acetic acid which dissociate in process
of time. 1

The molar heat of fusion of H 3 P0 4 is 2-52 Cals., 2 that of 2H 3 P0 4 .H 2 O
7-28 Cals. 3 The heat of solution was found to be positive, 4 2-69 Cals.
per mol of the crystalline acid dissolved 2 and 5-21 Cals. per mol of
the liquid acid.

The heat of dilution was found to be 5

Mols water per mol II 3 PO 4 ! 11-19 13-88 : 19-88 j 29-99

Heat of dilution. Cals. . 33-13 19-93 , 12-2G 8-23

The heat of formation from the elements includes that of water,
and was found to be 2

crystalline.

II 8 P0 4 HsPO, i 1I 3 P0 4

fused, dissolved.

302-56 Cals. 300-04 Cals. ! 305-29 Cals.

The following tables summarise the principal determinations of
the densities at certain definite temperatures. If the percentages of
II 3 PO 4 are divided by 1-38 the quotient gives percentages of P 2 O 5 .

DENSITIES OF AQUEOUS SOLUTIONS OF

PHOSPHORIC ACID.

At 15 C.

Per cent. II 3 PO 4 .! 5 ; 10 : 20 30 ! 40 50 , 00

Density . . J1-027C l -0567 : M 190 1 -1 SSI) ! 1 -2051 1 -3-l,SG I -.1395

At ir-r> r c. 7

Per cent. 1\() 5 5 1 ( > i - ; * - l() -"50 00 ; OS

Density . " . 1 -037 ! 1 -079 , 1 -1 09 ] -271 1 -3S3 I -52 1 1-077 I -SOD

!

1 Gira.ii, Ann. Ch nn. /V///.s-., 1008. [H], 14, f)(J;l.

2 "".riioniscn, " Thcri ti.< )C h("tnixch< ( lilcrtuchicmjcti S* t ransl. Traiilx*, Si ut t.-jai I , !!)()().

3 -foly, lor,, cit.

4 (Jiran, Ca-tn-pl. Trad., H)()l ) , 135, DO]; l!)0;j, 136, f>r>L>.
c j-xiimclin, Zcitxc.h. pJii/*i/cfiL (>h< t., 11)07, 58, -Mio.

SchiiT, Antiulcn, lS(i( ), 113, IS. i, 102.

" "

j-xiimclin, Zcitxc.h. pJii/*i/cfiL (>h< t., 11)07, 58, -M

SchiiT, Antiulcn, lS(i( ), 113, IS. i, 102.

ila.Li er, " Koinniciitni r.ur rh.dnn. </c>//i.," I>cilin

At 25 C. 1

Per cent.

H 3 P0 4 .

5

10

15

20

25 j

30

35

40

Density

; 1-027

1-055

1-085

1-116

1-149 |1

183

1-219

1-256

Per cent.

II 3 P0 4 .

! 45

50

55

60

65

70

75

80

Density

1-294

1-336

1-381

1-429

1-477 1

527

1-579

,1-633

Per cent.

H 3 P0 4

i 85

90

i 91

Density

1-690

1-753

1-766

The vapour pressures of solutions at C. are 2

\
\

Grams H 3 PO 4 in

100 grams H 2 O 1

945

22

32

124

9

; 390-2

Pi

2 o |

4

612

4

377

9

710

i 0-636

mm.

Vapour pressures of water at 100 C. were lowered in a high ratio by
phosphoric acid, as appears from the following data : 3

Grams H 3 PO 4 in 100 grams ILO . 20-75
Lowering of vapour pressure . 30-1

!

149-16 ; 330-52
290-9 ! 507-3 mm.

The crystalline acid has an appreciable specific conductivity oC
about 1 x 10~ 4 reciprocal ohms (mhos), while the fused acid at the
same temperature has a conductivity of 1 x 10~ 2 mhos. 4 Specific
conductivities of the more concentrated solutions show a maximum
at about 43 per cent., as appears from the following data : 5

CONDUCTIVITIES OF CONCENTRATED SOLUTIONS
OF PHOSPHORIC ACID.

H 3 PO 4 , per cent.
Specific conductivity. K

1-4

0-014

2-87
0-02533

5-28
0-04245

16-09
-08064

30-71
0-12816

!I 3 PO 4 , per cent.
Specific conductivity, K

43-26
0-14916

52-83
0-13750

71-29

0-07876

92-07
0-02203

100-0
0-01406

The molar conductivity (=lOOO/c/c) thus varies from 97-50 in the
1-4 per cent, solution to 20-28 in the 43-26 per cent, solution and 1-31

1 Knowlton and Mounce, -/- Jnd. Eng. Ckcm., 1921, 13, 11-18.

2 Dietcrici, W ted. AnnaUn, .181)1, 42., 513; 181)3, 50, 47; 1897, 62, 616.

3 Tammann, Mtm. Acad. Si Petersburg, 1888, [7], 35, 9.

4 Rabinovitch, Zeitsch. anorg. Chem., 1923, 129, 60.

5 Phillips, Trans. Chem. Soc., 1909, 95, 59.

VOL. vi. : ii. 11

162

PHOSPHORUS.

in the 92-07 per cent, solution. Degrees of ionisatioii are low in the
concentrated acids.

The conductivities of the more dilute solutions up to 0-1 molar
have been determined to 156 C.

EQUIVALENT CONDUCTIVITIES OF DILUTE
SOLUTIONS OF PHOSPHORIC ACID. 1

HoPO,, mols I

per litre . ! 0-0002 ! 0-002 0-010 j 0-0125 0-050 j 0-080 ; 0-100

A at 18 C . 338 330-8 ; 283-1 203 ! 191-2 122-7: 104 96-5

Aat 4 >5 c C 378 l 367-2 ! 311-9 ! 222 208-1 132-6 ; 112- ! 104-0

The temperature coefficient was positive as usual at ordinary tem
peratures and reached a maximum at temperatures which varied with
the ion concentration. Thus, in the case of the 0-0002 molar solutions,
the maximum had not been reached at 156 C. (A -804-7), while in
the 0-1 molar solution it occurred at about 75 C. Other results were
expressed by the formula 2

A^/V^ " 0822 ^ 1 -f- 0-014550

It is clear that the degree of dissociation is less at the higher tem
peratures ; thus for a 0-1 molar solution it is estimated as 38-5 per
cent, at 18 ( . and 11-5 per cent, at 150 C. J ^

The viscosities of concentrated solutions of phosphoric acid arc high ;
those of moderately concentrated solutions arc given below :

VISCOSITIES OF SOLUTIONS OF PHOSPHORIC ACID.

j Il-.PO.,, niols per litre . . 0-25 : 0-50

1 ,y relative at. IS C. (water 1 ) 1-0(51 ; l-l-ltf

: H-.POj, equivalents per lit. re . 0-125 0-25

7; relative at 25 ( .(water j) ! 1-(K>12 j 1 -005(5

The refractive index of a solution of the acid of density 1-180 was
at 7-5 C.

Spcet nil line
)t

II

H >!nhnnx," Wa.sJiin.Lrt on, 11)07;
(*h t in., HMO, 70, :>:*;">. Sec. also

PHOSPHORIC ACIDS. 163

The molar refraction was 23-6. 1 The equivalent refracting power of
the HJPO 4 ~ ion has been calculated as 21 -6. 2 Refractivities may con
veniently be used in determining the concentration of aqueous solutions
and also in testing for freedom from the meta- and pyro-acids. 3

Basicity and Neutralisation of the Phosphoric Acids. The
crystalline forms and other properties of the different phosphates of
sodium were described by Graham. 4 The ordinary phosphate of soda
" is a highly alkaline salt, although generally viewed as neutral in
composition. Mitscherlich found that a solution of this salt required
the addition of half as much acid as it already possesses to deprive it
of an alkaline reaction." 4 By heating, the salt was found to contain
25-2 molecules of water to 1 molecule of phosphoric oxide. One of
these molecules was retained to a higher temperature than the others.
" The phosphate of soda contains 3 atoms base ; namely. 2 atoms soda
and 1 atom water. When this last atom was lost the sodium salt
changed into that of a different acid, namely, a pyrophosphate." 5 In
modern symbols

Na HP0 4 .1.2HoO > Xa 2 HPO 4 ~ 12H,O

2Xa 2 HP0 4 >Xa 4 P 2 7 ~K 2 O "

Sodium biphosphatc was known as a dimorphous salt ct . . . of
the 4 atoms of water which the crystals contain, they lose, I find,
2 atoms at the temperature of 212 (F.), and not a particle more till
heated up to about 375." After heating to 212 t: it contains 3 atoms
base, namely, one atom soda and 2 atoms water united to a double
atom of phosphoric acid. The salt cannot sustain the loss of any
portion of this water without assuming a new train of properties."
Several other forms were obtained by heating to higher temperatures,
and at a low red heat a glass was obtained which was deliquescent,
not crystallise blc from solution, and which gave the reactions of Ci phos
phoric acid ignited per ,SY.V In modern symbols-

2XaHoPO 4 .2HoO >2XaIIoPO 4 -r2rL,O at 212 F.

^Xali.PO.!- >XaoIIoP.,6 7 -rHob at 100 F.
2XaIloPOj~--->2XaP6 3 V2H 2 O~n.t dull red heat

When at least half as much alkali as it already contained was
added to ordinary phosphate of soda and the solution was concentrated,
tufts of slender prismatic needles appeared. This salt was highly
alkaline in reaction. :: It is a fact of extraordinary interest that the
acid of this sub-phosphate is not convertible into pyrophosphorie acid
by the action of heat on the salt/ In modern terms Xa 3 PO 4 is un
changed on ignition.

The heat of neutralisation, Q 1!? of phosphoric, acid (1 mol) with
XaOIi (n mols) in. dilute solution has been determined with the
following results :-

n
ft,

7

5
3

1

14

8

2
27

1

3-0
34-0

6
35

3

mols
Cals.

Thus heat was evolved in a uniform manner as the alkali increased
from to 0-5 and 0-5 to 1-0 in the neutralisation of the first hydrogen.
It was also evolved in a uniform manner but at a lower rate between
1-0 and 2-0 alkali, showing that the affinity of dissociation of the
second hydrogen is lower than that of the first, and at a lower rate
still during the neutralisation of the third hydrogen, showing that
this has an even lower dissociation affinity (see Constants," p. 165). 1
Heats corresponding to the neutralisation of the first, second and
third hydrogens were 14-8, 12-3 and 6-9 Cals. Heats of neutralisation
by the "alkaline earths in very dilute solution were in the same order,
e.g. for JCa(OH) 2 , etc., 14-8, 9-7 and 5-3 Cals. respectively. 2

The heat of dissociation, fti, probably is positive, since dissociation
diminished with rise of temperature. This agrees with the fact that
the heat of neutralisation, Q n , of the first hydrogen ion, viz. 14-8 Cals.,
is somewhat greater than that of a completely dissociated strong mono
basic acid, viz. 13-5 Cals. The following calculation also shows a
quantitative agreement : 3

in which x is the electrical conductivity and Q d =1-530 Cals. at 21-5 C.
Therefore (1 -a)fti = 1-242, in which the value of the amount of
undissociated phosphoric acid, (1-a), has been introduced. Now
Q n = 13-520 + (1 - a) Q (l - Therefore Q n - ] 4-76 Cals. calculated.

The heat of dissociation of the first hydrogen as calculated from the
change of the constant with temperature was found to be 2-00 Cals. at
25 to 37-5 C., 4 which, when combined with the preceding value of
a, gives Q = 15-14 Cals.

The molar refractivities (hiring neutralisation, .U(/x - 1 )//J, when
plotted against the percentage of alkali added gave curves which
showed discontinuities at the points corresponding to primary and
secondary salt.

Most important confirmation of the discontinuities tit these points
was obtained by plotting the static acidities (II" 1 ) expressed as their
negative logs (pll.) against the alkali added. The discontinuities in
these graphs were clearly marked. Parts of these neutralisation
curves were obtained lirst by the physiological chemists on account of
the use of phosphates as mixtures of regulated acidity ( t: buffers ") for
comparison with the acidities and alkalinitics of physiological thuds. 5

Thomson, " Xhwrnockkniixtry, " translated by Burke 1 , (Longmans, MIUS); FUATO and

1909,

Trans.

urhenius, Mcdd. (jr. Vat. A!:ad. Xobdinxt., J01J, [27], 8; ZriMi. pkyxikal. Ch<-m.,
\, 96; 1892, 9, 339.

owet.t and ALilleU, ,/. Amw. Chun-, tioc., 1929, 51, 1004.

linger, Vertag. Phystol. Lab. te Utrecht, 1909, 10, J09; Sorensen, Hiuchcm. Zcitxch.,
21, 131; 1909, 22, 352; Salni, Zeitsch. ykysikal. Ghem., 1906, 57, 471; J rideaux,
Chem. Soc., 1911, 99, 1224.

PHOSPHORIC ACIDS. 165

Other series of results within the range which is suitable for " buffer "
mixtures have been determined. 1 The points of inflection were also
determined by the conductivity method. 2

The neutralisation curves have been expressed by three constants
corresponding to the first, second and third dissociations, viz. :

= [H-][H 2 P0 4 - 4 _

- - 3 ~

_
[H 3 POJ - [H 2 P0 4 -] 3 ~ [HP0 4 =]

The value of the first constant was determined as 1-1 x 10~ 2 by measure
ments of the conductivity of the free acid. 3 The second constant was
determined as 1-95 x 10~ 7 by conductivity measurements in solutions
of XaH 2 PO 4 . 3 This value was confirmed by calculations from the
neutralisation curve as determined by means of the hydrogen electrode. 4
The value of the third constant, viz. 3-6 x 10~ 13 , was first determined
by measurements of the conductivity of ammonium phosphates and also
by the distribution of the ammonia between water and chloroform. 3
It was shown that this result was incompatible with the observed values
of hydrion concentration during the later stages of neutralisation by a
strong alkali. A calculation based on these values gave K% =3-0 x 10~ 12
in decimolar solutions. 4

A review of all the data revealed a slight drift in the constants of
this acid (as of others) with changes in concentration, etc. The con
stants were corrected for alterations in the " activities " of the HP0 4 =
and other ions in the more dilute solutions for which ionic strengths
could be calculated. These corrections, applied to the results of
Michaelis and Garmendia, 5 and to new results, gave constants w r hich
were hardly affected by changes in concentration, 6 namely K 2 =5-9 x 10~ 8 ,
7v 3 =lxlO~~ 12 . The value of Jv 1; corrected for ionic strength, was
0-9 x 10~ 2 at c = 0-l and OSxlO~ 2 at limiting (low) concentration. 7
A redetcrmination, 8 with the aid of the quinhydrone electrode, in
solutions of c = 0-06 down to c= 0-005 molar gave /i x = 0-8 x 1()~ 2 ,
K 2 = T-4 x 10- 8 , K 3 = 0-8 x 10- 12 .

Other values of (uncorrccted) constants obtained in moderately
dilute solutions are : K l -0-94 x 10~ 2 , K 2 = 1-4 x 1<)- 7 , K 3 -2-7 x 10~ 12 ;" 9
A" 2 = 8xlO- 7 , #3=2-3 xlO- 12 ; 10 K z =5-0 x 10" 13 . 11

It is suggested that the following rounded constants will represent
|jII values in phosphate solutions of concentrations from 0-1 molar
downwards with sufficient accuracy for many purposes :

K = l-5 x 10~ 7 ; K = 2-Q x 10~ 12

1 Clark and Lubs, J. BaclwioL, 1917, [2], I, 109, 191; Clark, The Dtttruination
of Uydroytii Ions, 1 Baltimore, 1920, and later edition, .1928 ; Michaelis and Kruger,
Biochem. Zcitsdi., 1921, 119, 307.

2 JK.usi.or, G niters and Gcibel, Ztiisch,. coi-org. Cher/i., 1904-, 42, 225.
: < Abbott and .Bray, ,/. A-tntr. Chun,. &oc., 1909, 31, 729, 1J9.1.

4 J J rideaux, ioc. cit.

5 JMicluiclis and Garmendia, Biochtm. Zeitech., 1914, 67, 431.

Pridcaux and A. J. Ward, Traus. Ckem. Soc., 1924, 125, 423.

7 Sherrill and Hughes, J. Ain.tr. Chtin. Soc., 1926, 48, 1801.

8 Jowett and Millett, J. Armr. Cham. Soc., 1929, 51, 1004.

9 Eritton, Trans. Chew. Soc., 1927, p. 614.

10 Blanc, J. Chirti. pliys., 1920, 18, 28.

11 Kolthoff, Eec. Trav. chim., 1927, 46, 350.

166

PHOSPHORUS.

The complete titration tabulated was obtained by means of the
hydrogen electrode in a 0-01277 molar solution of phosphoric acid to
which was added 0-0919 normal sodium hydroxide at 20 C., the
titration to XaH 2 PO 4 requiring 13-9 c.c. of the alkali. 1

11-0

10 13-9 20 27830 4CT41-7 50

C.c. OF 0-0919 N NaOH TO 100 c .c. OF 0-01277 M ;-! 3 P0 4 AT 20C.

FIG. />.- Neutralisation. Curve of Orthophosphono Acid.

THE TITRATION OF PHOSPHORIC ACID.

c.r.. XaOil ; 15-0 1(5-0 : 17-5 20-0
p\\ ; f>-S(> I (Ml! (> !) (>-71

-(>(> | 27 i>7-r)
7 07 : sol s-;ji)

1 1-^(5 1 1-40 | I Mi) ; 11 ,">7 1 1 ( .(I 1 1-72 1 1-S1

The two point. s of indection on the neutralisation curve have lont
been recoo-nisecl by Llie effects upon indicators, which can be used for
titru.tino- the acid in two stages. The first, a.t XalLPO,, yjll - 1--5,
corresponds sufficiently well to the chani> - c-j)(>int, of methyl orange
(alkaline) or methyl red, while the second, at. XaJlPOj and ^11^9,
corresponds to tliat of |)hcnol})ht]ialcin. 2

PHOSPHORIC ACIDS. 167

The basicity of the acid has also been determined by conductivity
titrations. 1

Thc constitution of phosphoric acid is deduced from the basicity,
which shows three hydroxyl groups, and thus a saturated character,
with no hydrogen directly attached to phosphorus ; this explains the
lack of oxidising properties, which indicates the absence of O O
chains, and the direct formation of the acid from POC1 3 . The acid
chloride and the resulting acid probably have the same structure,
which is represented under the older theories as containing quinque-
valent phosphorus, O=P=C1 3 , or on the newer as being tercovalent
with a ^ mixed bond," O< .......... P = (OH) 3 or OP^P

Phosphoric acid is a co-ordinated compound with the co-ordination
number 4, and may accordingly be written H 3 IPO 4 ] (see section on
" Phosphorus in Combination "). Although the trivalent ion seldom is
actually present, except perhaps in solid Na 3 P0 4 , etc., it is written

\ " /
according to Lowry as _ \p/ _ Such a compound as Xa 2 HP0 4 is

O/ ^O

of course equally a co-ordination compound and may be written as

o

4 2Xa" on this scheme.

_ )Hi

Mono-, di- and tri-esters are known, e.g. ethyl phosphates, which
have not been prepared in tautomeric forms. The trimcthyl and
triethyl phosphates have vapour densities corresponding to simple
molecules OP(OC 2 H 5 ) 3 , etc. 3

Chemical Properties. The chemical reactions of phosphoric acid
can be classified mainly under salt and ester formation, hydration,
dehydration (see p. 170) and complex formation. Towards reducing
and oxidising agents the aqueous solution is comparatively inert.

It has already been shown that even the first dissociation of phos
phoric acid is much lower than the dissociation of the halogen acids
and sulphuric acid. Consequently its catalytic action (due mainly to
hydrion concentration) on various chemical reactions is much slighter;
e.g. the relative strength of phosphoric acid in the inversion of cane
sugar was 6-21 when that of HC1 was 100. 4 It is largely expelled from
its salts by the stronger mineral acids in ordinary aqueous solution,
although in the presence of only small quantities of water, or at higher
temperatures, these conditions are reversed owing to (a) the great
affinity for water, (/>) the low volatility, of phosphoric acid. Thus
while on the one hand phosphoric acid is produced as described on
p. 156 by the interaction of dilute sulphuric acid with calcium phos
phate at temperatures below the boiling-point, on the other hand
sulphuric acid is completely expelled by evaporation at 150 to 200 C.
with concentrated phosphoric acid.

The direct action of phosphoric acid on ethyl alcohol at about 200 C.
is one of dehydration, and the acid is therefore conveniently used in

1 BeriliL lot, I)., Ann. Ckr,. ./%*., 1891, [6], 23, 5; 1803, [6], 28, 5.

2 Prideaux, -/. Soc. Chc.ni. Ind., ]923, 42, (572 (Chcni. and hid.).

3 Vogclis, Annaltii, 1849, 69, 190; Carre, Ann. Chim. Phys., 1905, [7], 5, 3-45; Arbusov,
Her., 1905, 38, 1171; Young, Proc. Roy. Soc., 1909, 81, B, 528.

4 Ostwald, Zeitsch. pkysikal. Chem. t 1888, 2, 127.

168 PHOSPHORUS.

the preparation of ethylene, as it is not, like sulphuric acid, reduced
under these conditions. Glycerophosphoric acid, which probably is
mainly monoglycerylphosphoric acid, is made by heating glycerol with
concentrated phosphoric acid at 100 C., neutralising with baryta and
decomposing the barium salt with sulphuric acid. 1 Similar condensa
tions have been reported with sugars, e.g. mannitol, etc.

Phosphoric acid is not affected by the ordinary reducing agents in
solution, including nascent hydrogen (cp. phosphorous acid, p. 148).
The reduction of phosphorus pentoxide and phosphates by carbon at
high temperatures has been discussed on p. 157.

Ordinary oxidising agents have no effect, but with the meta- or pyro-
acid hydrogen peroxide gave perphosphoric acid (q.v. p. 184).

The formation of complexes with other acids is extremely character
istic of phosphoric acid and its anhydride. The phosphotungstates
and phosphomolybdates are well-crystallised compounds which are
used in analytical chemistry (see " Estimation," pp. 181-183). The
yellow precipitate (NH 4 ) 3 PO 4 .12]\IoO 3 is the ammonium salt of a phos-
phomolybdic acid, H 3 PO 4 .12MoO 3 , which is prepared by adding aqua
rcgia in small quantities to the ammonium salt. Phosphotungstic acid,
n 3 PO 4 .12WO 3 . ( ?:ILO, may be prepared as greenish crystals by evapora
tion of the mixed acids in the correct proportions and extraction with
other. 2 These acids, witli the borotungstic, silicotungstic acids, etc.,
are usually formulated as co-ordination compounds. The phosphorus
is represented as the central atom with a co-ordination number of G,
thus : 3

II 7 [P(W 2 7 U H 7 [P(Mo 2 7 ) 6 ]

Phosphoiodic acids, such as P 2 O 5 .m 2 O 5 .III 2 O, and their salts, 4
phosphotclluric acids and their salts, e.g. (NlI 4 ) 2 P 2 TeO 10 , have also
been prepared.

A complex acid is probably present when silica dissolves in phos
phoric acid, as it docs to the extent of about 5 per cent, at 2GO C.
C oiicoiil rat cd phosphoric acid at 100 to 200 C. etches the surface of
olass, and it has been found to attack quart/ at 300 C. 7 Phos
phoric acid at high temperatures also destroys the gla /e on porcelain.
Platinum is not affected unless a. reducing agent is present, which may
give phosphorus and a phosphide.

31 is no doubt on account of this formation of complexes that con
cent rated phosphoric acid is capable of dissolving such inert metals
as hm<>sfen and /.irconinm, as well as silicon and carborundum. 8 The
less noble metals are attacked by phosphoric acid, but iron tends to
become passive. 1J The basic oxides, ferric oxide 1 and alumina arc
dissohrd bv the concentrated acid. 6

1 i MV.-i .!,!<! Tulin, / /v;//.s-. Clitnt. Xnc., 1 ( . )().">, 87, 1>19.

\\ u, ,/ I ;,<>! < /," n, , I <:!<>, 43, I si).

:1 !;, rMiirnis .n,l I m-.UiT, /M/.sr//. <nti</. Chan., 1 1) 1 1 , 70, 715.

1 ri.i ti.-iu .!// < /,,, f/ti/,.., isus, j7], 15, ;i ( .)l.

[ i. i! ; ,- ( "/ , /;, / /iifitnt/i! tttf. d> i 7 f /////. ^(inrc nut luiltitm, I /ioxjj/iufc//, -nnd Arxnifitc/i,
I, {.. i , !! i)i

iJ.mJ- i -Mili-- .;n.l M;iriM)f!rt, < <>,,i[>t. n ml., ISSJ, ISSO, 1SS7; 1SSS, 106, l. Jo.

II. i.i u , /. / ; . niKj.tr. C/t<f/<., I .H)i\ 15, !)I7.
1 \\ in ; .l i an*! .f.tnin-rct , Cuin^t. //W., 11)11,152, 1770.
i ];, Vrr . ;t ,,,i I>.UTIH. ./. Ain-r. ( /u m. Mac., HUO, 32, 7f>O; ( Ihirkson and HciJicnngion,

f h, l,i. ,!/ . /. /.;/., I . -S, 32, Sll.

PHOSPHORIC ACIDS. 169

Physiological Action. The principal uses of combined phos
phorus have already been dealt with (see p. 13). The ions of phos
phoric acid, together with those of carbonic acid, play an important
part as regulators of acidity, or natural "buffer" mixtures (see p. 164),
in physiological fluids, especially in the blood. Salts which take part in
this regulation are XaH 2 PO 4 "arid Xa 2 HPO 4 , NaHCO, and Na 2 CO 3 .
The pH value of blood is 7-3 to 7-4 at blood temperature (37 to
38 C.) and about 7-5 at 18 C. : the ratio of monohydrogen phosphate,
i.e. Na 2 HPO 4 , to dihydrogen phosphate, i.e. XaH 2 PO 4 , at this point
is about 4 : 1 (see table of Neutralisation, p. 166"). Even the small
amount of phosphate present in the blood and cell protoplasm has a
considerable effect in regulating the pH to its " resting :: value
slightly on the alkaline side of neutrality. Any steady increase in
the content of acid is countered by the formation of more XaH 2 PO 4 ,
which, being more readily diffusible than Xa 2 HPO 4 , passes into the
kidneys. Acidity of the urine is thereby increased and the cell proto
plasm or blood loses some of its alkali reserve. The necessity of con
stant small amounts of phosphate for the body metabolism is evident. 1

Phosphoric acid is poisonous only at a high concentration, when it
shows the usual corrosive effects of acids. 2 The salts, and even the
acid in low concentration, favour the growth of moulds and fungi,
provided that the hydrogen-ion concentration also is favourable.

Phosphoric esters are also present in the blood, and their hydrolysis
by means of an enzyme, phosphatase, which has been found in the
bones, is probably one step in the process of ossification. The pro
perties of these esters have been largely determined by Robison and his
collaborators. 3

Uses.- Many pharmaceutical preparations contain phosphoric acid
or phosphates, or glycerophosphoric acid, which, as already stated, is
made by heating glycerine with the ortho- or meta-acid. Lecithin is
an ester of glycerophosphoric acid which contains choline, (CH 3 ) 3 =
X(OII)-CIIo-CI-IoblI, and two molecules of a fatty acid radical
(stearyl or oleyl).

Acid phosphates arc used in baking powders, " self-raising " flours
and for ct improving " flours. The acid is also an ingredient of some
non-alcoholic beverages.

Sugar phosphates, mainly the hexosc mono- and di-phosphates, play
an important part in alcoholic fermentation. The calcium salts of these
esters have been prepared.

The acid, or calcium superphosphate, is used ia the sugar-refining
industry as a defecator to coagulate gums and other organic impurities
and cause them to form a scum. 4

It has been employed instead of sulphuric acid in the hydrolysis
of cellulose to give sugars. As a dehydrating agent in organic prepara
tions, such as that of ethylcne from ethyl alcohol, it is sometimes
preferred to sulphuric acid.

1 .Henderson, Ann. J. Phyxtul., 100(5, 15, 257; .1008, 21, 427; J. Biol. Chun., 1900,
7, 20; .Henderson, Bock, Field and .Stoddard, J. Jj*,ol. Chun., 1024, 59, ,370; ^Lecture;*
0)i Certain A*p(-ct.K of .tiiochunixtry, Dale, Drummond, Henderson and tlill, London, 1!)2G.

2 ro-r^iale, J. Pharm. Chi-ni., 18f>0, [3!, 36, 241.

3 Full references to this work may be obtained from the Annual Reports of the, Chemical
Society, especially vol. xxvi, 235, 1020; also "The Sirj ti.ifica/icc of Phosphoric Esters in
Metabolism^ R. Robison, Oxford Univ. Press, 103.3.

4 Meekstroth, Chun. Met. E,KJ., 1022, 26, 223.

170 PHOSPHORUS.

Other miscellaneous uses are : In dental cements and filling pastes,
with kaolin, other silicates, chalk and magnesia. Solutions containing
the acid and ferrous phosphate will give a protective coating to iron and
steel. * Carbon is activated by being dipped in a solution of metallic
salts and phosphoric acid and then igniting. Solutions containing
ammonium phosphate with the sulphate and a soluble zinc salt may
be used for iireproofing materials. Phosphates are sometimes included
in photographic toning and fixing baths.

Dehydration of Orthophosphoric Acid and Production of the
Pyro- and Meta-acids. When heated in open vessels of gold or
platinum the acid loses water, being converted successively, and to
some extent concurrently, into the pyro- and mcta-acids, thus :

2H 3 P0 4 >H 4 P 7 +H 9

nH 3 P0 4 > (HP0 3 ) n 4-?iH 2 O

Salts of these acids are prepared by heating the orthophosphates
(see p. 155).

According to Graham 1 the pyro-acid was formed largely even at
100 C., while Watson found that conversion w r as complete between
255 and 260 C. 2 Exposure to a current of moist air raised the tem
perature of dehydration, while dry air lowered it. 3 Thus air saturated
with water vapour at 68 C. will leave 0-2 per cent, of water in the
ortho-acid kept at 181 C., and will dehydrate it and produce 0-02 per
cent, of H 4 PoO 7 at 191 C. When air which has been dried by passing
through 96 per cent, sulphuric acid at 12 C, is drawn through phos
phoric acid at 186 C. this acid is dehydrated to 80-8 per cent, of
H 4 P 2 O 7 . Other dehydrating agents have a similar effect. Phosphorus
oxy chloride reacts in the following manner :

5H 3 P0 4 +POC1 3 =3II 4 P 2 7

A mixture of the ortho- and meta-acids may be condensed together
to form the pvro-acid by heating on the water- bath, thus :

H 3 P0 4 -rIIPO 3 =H 4 P 2 O 7 5

Metaphosphoric acid is the final product obtained when phosphoric
acid is heated in the air and was produced in this way by Her/clius. 6
The minimum temperature required for dehydration is about that of
molten lead, 327 C. The mcta-acid begins to be formed at about
300 C. and dehydration can be completed at 316 C. 7 or by heating
until fumes are continuously evolved.

Aqueous vapour pressures in equilibrium with the mcta-acid are
much lower than those over the pyro-acid. The pressure over the
pyro-acid became appreciable at ]()() C. and readied 100 mm. some
what above 100 C,, while that over the mcta-acid became appreciable
at 190 C. and reached 100 mm. a little over 210 C. 3

Known as i- Pa rke rising " or "~ Cuslet Usinu."

Loc. cti.j p. J5f).

Watson, Chuti. AVu;*, 18<K>, 68, I!)!).

BalarcH , Zcitech. anonj. Chon., 11)10, 67, 2. M ; 68, 20<>; 69, LMf>.

Geuther, J.prakt. Chu/i., 187;$, [2j, 8, ;$">!).

Gouther, loc. at.; Joly, Coi/ipt. rend., J886, 102, 7(30.

Berzelius, Ann. Chim. Pkys., 1819, [2], 10, 278.

firpu-nrv Jnr ri t -n IM^- \I -.1 / M rr,l I //,/ /. , / ^ irr

PHOSPHORIC ACIDS. 171

Other methods of preparing pyro- and meta-phosphoric acids are
given later in this chapter.

Pyrophosphoric Acid, H 4 P 2 O 7 . The history and chief modes of
preparation of this aeid have already been given (p. 170). A purer
product was made by the double decomposition of a soluble lead salt
with sodium pyrophosphate, Na 4 P 2 O 7 , whereby lead pyrophosphate,
Pb 2 P 2 O 7 , was precipitated ; this was then decomposed by BUS. 1 The
silver salt, Ag 4 P 2 O 7 , yielded anhydrous H 4 P 2 O 7 when warmed in a
current of drv hvdroo-en chloride. 2

/ ^ o

Physical Properties. The concentrated aeid, prepared by dehydra
tion of orthophosphoric acid, is a highly viscous liquid and probably is
polymerised. By the depression of the freezing-point the molecules
in aqueous solution showed a complexity corresponding to (H 4 P 2 7 ) 4
and (H 4 P 2 O 7 ) 5 . 3 The molecular weight in glacial acetic acid corre
sponded to (H 4 P 2 O 7 ) 3 , but diminished with time. 2 The acid prepared
as above from Pb 2 P 2 O 7 appeared to dissolve in water as simple mole
cules. 3 The freezing-point curve of H 4 P 2 O 7 showed two eutectics one
at 23 C. with a solution containing H 4 P O 7 + 1-25EUO and the other at

-75 C. with IT 4 P 2 O 7 -f-6-87H 2 O. The maximum freezing-points are
(1) +61 C. or higher, the melting-point of the anhydrous acid; (2)

-f-26 C., the melting-point of the crystalline hydrate H 4 P 2 O 7 -i- - 2 -H 2 O. 2
The acid which crystallised from concentrated solution was, however,
found to contain anhydrous H 3 PO 4 . 3

The molar heat of fusion of the solid acid was about 2-3 Cals., there
fore very similar to that of H 3 PO 4 . The heat of solution of H 4 P O 7
(solid) was about 7-85 Cals., that of H 4 P 2 O 7 .I-5lI 2 O (solid) i-5 Cals.
The heats of transformation by means of liquid water were :

II^PoCL (solid) -i-HoO =2H 3 PO 4 (solid) ---6-97 Cals.
H 4 P 6 7 (liquid) -fBUO =2H,,PO< (liquid) -r 9-09 Cals.
H 4 P 2 O 7 aq. - 2H 3 PO 4 aq. - r 4-25 Cals.

From these other thermal equations can be derived in the usual manner.
The heats of formation from the elements were close to those of
2II. 3 P0 1 -IL0.

2P-r3-JO 2 +2H 2 =H 4 P 2 O 7 + Q

H 4 P,,O 7 solid
Q (Cals.) = 5:32-23, 535-69

H,P 2 7 liquid
529-94, 533-40

II 4 PoO 7

540 : 16 :

The electrical conductivities of aqueous solutions of pyrophos-
})horic acid are as follows : 4

: c, mols/litrc . . 0-00125 0-0025 0-005 0-0125 0-025 0-05

jit, molar conductivity . 602-0 . 556-7 503-3 438-6 ; 384-9 353-8

1 Braun, Z(-it*ck. anal. Chtin., 18(35, 3, 4(58.

2 Giran, Compi. rend., 1902, 134, 1499; 135, 961, 1333; 1903, 136, 550; 1908, 146,
1270, 1394.

3 Holt and Myers, Trans. Chem. Sac., 1911, 99, 394.
-1 Abbott and Bray, loc. at.

172

PHOSPHORUS.

The degree of primary ionisation calculated from these values is high,
being 96 per cent, at the lowest concentration. For dissociation
constants, etc., see below.

All the evidence shows that pyrophosphoric acid is tetrabasic and
that each hydrogen is that of a stronger acid, i.e. more dissociated at
the same dilution, than orthophosphoric acid.

With regard to heats of neutralisation, 1 mol of the acid, to which
n equivalents of strong alkali were added, gave the following successive
amounts of heat, the sum of which is the total heat of neutralisation at
each step :

n .

Q (Gals.)

. i 1
If 14-4
{ 15-3

2

14-2
15-65

3

3rd and 4
13-1

4 ;

th=24-l !

7-8* ;

1
6

i-s 1 ;

The constants of the successive dissociations were deduced from
the conductivities of the salts : 3

NaH 3 P 2 O 7

Xa 2 H 2 P 2 O 7
K,

Xa 3 HP 2 O 7

Na 4 P 2 7

0-14

0-011

0-0 29

0-0 8 36

or Jf 3 =7-6 xlO~ 7 , 7v 4 = 4xlO- 9 , 4 or # 4 =4-9 xl()~ 9 . 5

These constants determine the titration exponents pH and the best
indicators for the successive hydrions. The aeid can be titrated as
dibasic, using methyl yellow, methyl orange or brornophenol blue, and
as tetrabasic using phenol phthalein, thymolphthalein or thymol blue
in the presence of a moderate excess of soluble barium salt. The
values of p\\ in the partly neutralised acid were corrected for the salt
error, and the constants /v 3 and 7Q which prevail in solutions of low
concentration were thus deduced : G

The true constant 7v 4 found by introducing the correction for ionic
strength was 0-45 x 10~~ 10 at a concentration of 0-02 inol/ litre, and
increased with decreasing concentration to !<(> x 10 10 at c =0-00128.
The unconnected constant decreased from 4-Oxl()~ J at c=0-02 to
1-5 x 10- at c =0-001 25. 5

Hydration to Orthopliosplioric Acid.-- r T\\^ process of depolymerisa-
tion of concentrated solutions of pyrophosphoric acid which has already
been noted very likely consists in the hydration of the molecules of
condensed or poly-acid. The further hydration, with formation of
orthophosphoric acid, proceeds only slowly at low temperatures and in
dilute solutions. A dilute aqueous solution was kept for six months
without chano-c. 7 The velocity of the reaction lias been followed bv

Thomson, loc. cit.
Abbott and Bray, loc. cit.

Morton, Trans. Okcni. Soc., 1928, p. MOL
Kolr.hoif. AW Traw. rMtn.. 192K. A*I. fi 2fi.

2 Giran, loc.. cit.

Kolthofl , ltc.G. Trav. ckim., 1927, 46, 350.

PHOSPHORIC ACIDS. 173

taking the difference in the relative titres to methyl orange and phenol-
phthalein.

H 4 P 2 O 7 +H 2 0=2H 3 PO 4

A solution containing 15-6 grams of P 2 O 5 per litre was about half-
transformed in 121 days (H 4 P 2 O 7 /H 3 PO 4 initially =87/4; finally
43- 1/47-9 J. 1 The reaction was greatly accelerated by hydrogen ions,
which in practice are usually supplied by nitric acid (see ct Analysis, 53
p. 181). It was found to be unimolecular. 2

Constitution.- The formulae must, on account of the properties of
pyrophosphoric acid and its relation to orthophosphoric acid, show the
phosphorus atoms as saturated. This can be done either by the elec
tronic formulae or by those containing quinquevalent phosphorus,
since as already shown the two kinds of formulae are interchangeable.
The molecule may be (1) symmetrical or (2) unsymmetrical :

HO\ /0\ /OH HCk /0\ ,0

\p/ o Np T-TO NP/ \p^
/ \~ ~7 \ / \ / \

HO/ \O/ \OH HO/ X 0/ \OH

(1) (2)

The corresponding acid chloride is pyrophosphoryl chloride (q.v.).
When this is treated with water it gives orthophosphoric acid, but
when water vapour acts on a solution of the chloride in carbon disulphide
some pyrophosphoric acid is produced.

Pyrophosphatcs may split up in an unsymmetrical manner. Thus
by heating with PC1 5 in a sealed tube :

Xa 4 P 2 O 7 -i- 3PC1 5 - XaP0 3 -r 4POC1 3 + 3XaCl

and bv fusion :

XaA g3 P 2 7 = Ag 3 P0 4 -!- XaP0 3

The ethyl and methyl esters have been prepared by the usual
methods. Thus (C Z I1 5 )P Z O 7 by the action of C 2 II 5 I on Ag 4 P 2 O 7 at
100 C. The product was a liquid soluble both in water and in alcohol. 3
The elevation of the boiling-point of ben/ene by this ester corresponded
to simple molecules. 4 The decomposition of the ester on heating
supports the asymmetrical constitution :

(CoH 5 0). } = P =Oo =PO(OC II 5 ) > (C 2 H 5 O) 3 PO +O P(OC 2 H 5 )
O 2 P(OC 2 II 5 ) >OoPOH^C 2 H 4

the products being tiicthyl phosphate, mctaphosphoric acid and
ethyl en c.

In most reactions pyrophosphoric acid is transformed into ortho-
phosphoric acid. It was dehydrated by PC1 5 , thus

H 4 P 2 7 -r PC1 3 - 2HP0 3 -r POC1 3 -i- 2HC1 5
Thionyl chloride, SOC1 2 , and phosphorus trichloride also gave IIP() 3 .

1 Bcrthclot and Andre, Corn.pl. re.n.d., 1896, 123, 776.

2 Monlcmartim and Egidi, GazzeUa, 1902, 32, 381; l!J03, 33, 52; Pessel, Monatsli.,
1923, 43, 601.

3 de Clermont, Cornel, rend., 1854, 39, 338.

4 Cavalier, Cornet, rend., 1906, 142, 885; Rosenheim and Pritzc, Bar., 19U8, 41, 2708.

5 Ccuthcr, J. pra/d. Chew., 1873, [2], 8, 359.

174 PHOSPHORUS.

The acid gave compounds with albumin which, unlike those of
HPO 3 . were soluble. 1

The pyrophosphates are more stable than the free acid and show
some reactions which are described on p. 180. Among these may be
mentioned the white precipitate of Ag 2 H 2 P 2 O 7 which is insoluble in
acetic acid (see "History"). 2

Polyphosphoric Acids. The complex metaphosphates, (MPCK) r ,,
probably contain a complex anion. The di-, tri-, etc. phosphoric acids
however (pyrophosphoric acid and its series) are not polymers but
condensation products, belonging to the series wH,PO 4 - (m - 1)H 2 0.
and give tetra-, penta- and hexa-valent ions from H 4 P 2 O 7 . II 5 P 3 6 10
and H,.P 4 O 13 . 3 The salts were made by melting together (X^aP0 3 ),
and Xa 4 P 2 O 7 in various proportions. They were transformed into
orthophosphates in warm water. 4

Metaphosphoric Acid. The production of this lowest hydrate
of phosphoric anhydride by heating phosphoric acid (p. 170), or the
production of metaphosphates by heating di hydrogen phosphates
(p. 163), has already been outlined. In those methods of preparation,
XII 1 mav take the place of II ; thus JTP0 3 has been prepared by
heating "(NH 4 )JIPO 4 5 and NaPO 3 by heating Xa(XH 4 ) 2 PQ 4 or
inicrocosmic salt, XaXH 4 HPO 4 . 6 The free acid can also be produced
by the combined oxidation and dehydration of II 3 PO. 3 , as for example
bv bromine, thus

2II 3 P0 3 + 2Br 2 = 4lIBr -f 2HPO 3 7

The acid appears as a transparent, vitreous, tough mass, which
usually is deliquescent and dissolves in water with much heat. At a
red heat it volatilises without decomposition 8 giving a vapour with a
density corresponding to a molecular weight of 70-8 to 78-2, the
theoretical value for ( IIPO :J ) 2 being SO. 9

The properties of the vitreous acid varied considerably according
to the mode of preparation. The degree of hydra.tion never corre
sponded exactly to IiPO : ,, which requires 88-7 per cent, of P 2 0-, but
reached a constant value at about 78 per cent., and the acid then
volatilised unchanged. After a short heating the acid contained
S. 3-tSi) per cent, of HPO-, and "!(>! $ per cent, of water, and was readily
soluble in water. After he?! ting at. duli redness for "periods of several
hours the acid dissolved at first readily and then with diii icnity and
with a characteristic crackling sound. This sound was due to the
splitting of small particles with a glassv iraeture.
not yet pure IIS O.j, but contained water in the
. <S{)-2ii/H)-71 and 8<H)/ICH. After heating for 21- hours at a dull red
heat the acid dissolved very slowly (several days) without crackling. 10

io! moll, il>i l , 1|}(M), 32, lM!).
StatiLic, /,< -tt*< h. nnoitj. C/icnt.,
an- ninl ihtir >SV//.:r," 1 I>cilin,

PHOSPHORIC ACIDS. 175

The lowering of the freezing-point of aqueous solutions shows that
metaphosphoric acid is polymerised. 1 In a fresh solution containing
initially 0-852 mol of HPO 3 the molecular weight lay between (HPO 3 ) 2
and (HP0 3 ) 3 . 2 Pure metaphosphoric acid is best prepared from
Pb(PO 3 ) 2 (from Pb(XO 3 ) 2 and NaP0 3 aq.). The precipitate is sus
pended in water and decomposed by a current of H 2 S. The. lowering
of the freezing-point of the acid freshly prepared in this manner
indicated a molecular weight of 102, which, as the acid was ionised,
indicated the presence of some complex molecules. Evaporation of
this solution gave one in which the acid had a molar weight of
172. 2

The heat of formation of the solid acid from its elements is given as
224-0 to 226-6 Cals., and that of the acid in solution as 236-4 Cals. 3
On adding the heat of formation of I mol of water the sum of the
heats (for H 2 O and HPO 3 ) is found to be almost the same as that
evolved in the formation of orthophosphoric acid.

Esters of metaphosphoric acid arc known. Ethyl nictaphosphate,
C 2 H 5 PO 3 , was prepared by heating dry ethyl acetate with phosphoric
oxide and extracting the product with ether and warm alcohol, from
which the ester was precipitated by ether. 4

Aqueous Solutions of Metaphosphoric Acid. The physical properties
of the solutions are not well defined, as the acid is in process of de-
polymerisation and hydration (see below). The refractive index was
investigated by Gladstone. 5 Heats of neutralisation were those of a
monobasic acid ; when one equivalent of alkali was added the heat
evolved was 14-4 Cals.. 6 14-84 Cals. 7 The electrical conductivity of
the simple acid HPO 3 . calculated from that of the changing acid which
contained both (1IPO 3 ),, and H 3 PO ; i, was round to be of the same
order as that of a strong monobasic acid (e.g. I!IO tJ ). s

The Hydration of :\Ie.taph.oxp]i.oric Acid.- The change of metaphos
phoric into orthophosphoric acid was observed by Graham. 9 In
solutions of ordinary metaphosphoric acid two changes are proceeding,
the depolymerisation of (IIPO 3 ),, and hydralion with formation of
IT 3 PO 4 . The change of osmotic pressure on standing was shown by
the freezing-point method. The lowering in a normal solution of the
acid changed from 0-697 to 1-152 in 12 days, that in a double-normal
solution from 1-425 to . M5() in the same time. 2 The conductivity at
18 C. did not alter much for the first 20 hours ; it then fell steadily.
The first period lasted longer at 18 C. than at 25 (!., and presumably
at lower temperatures would be greatly extended. During this period
depolymerisation may be the main reaction. The subsequent decrease
in conductivity is due to the conversion of the highly dissociated
HP0 3 into the less dissociated ir 3 PO 4 . s The velocity of the change

1 Kaoult, Compt. i f-.nd., 188-1, 98, f>()9, J047; .188-1, 99., 91-i; Curnec, Ami. Cknir
Phyx., JiU.V[8|, 29, 490; [SJ, 30, 6:>.

2 Molt and Myers, loc.-. c/.l.

3 Giran, loc. at.

Lanohohl, Bcr., 1010, 43, 18f>7; ibid., 1911, 44, 2070.

3 Gladstone, ,/. Chan. oc., 1870, 23, 101.

r> Thomson, "TlH-nnochc.HtixcJu ( ntrwirhii./11/n.ii," Stuttgart, I90(>.

7 Giran, loc.. n/., and /iiV. Ac/rA?-.s *v/ Ic plto^.-pliurt tt l< .x acidt ^ pftoxphonquct,"* Paris,
.1903.

8 Prideaux, Trans. Faraday Xor., U)09, 5, 37.
9 Graham, loc. at.

17 6 PHOSPHORUS.

was such that a half-normal solution kept at C. was completely
converted in 150 days, at 31 C. in 5 days and at 95 C. in less than
an hour. 1 The change was accelerated by strong mineral acids.

There is general agreement that during the change the titre to
methyl orange remains constant. This will be the case whether pyro
phosphoric acid is formed as an intermediate product or not (see
p. 181). The titre to phenolphthalein increases, and this also agrees
equally well with both suppositions. The velocity constant was found
to correspond to a unimolecular reaction. 1 The change, however, con
sists of at least two, if not three parts, and several observers have
found that there is no simple constant thus, the velocity did not
agree with either a unimolecular or a bimolccular reaction ; 2 the
constant increased with time; 3 the velocity was not proportional at
each moment to the amount of unchanged substance. 4

It cannot be assumed that, because pyrophosphoric acid is produced
as an intermediate product in the dehydration of H 3 PO 4 that it will
also be produced during the hydration of HPO 3 . The amounts
observed may be present in the original HPO 3 or be produced by the
heat developed when this is placed in water. The pyro-acid has been
detected in the last fractional precipitates of silver phosphates, etc.
(see "Estimation"). 2 Since there is some evidence that metaphos-
phoric acid is hyd rated more rapidly than pyrophosphoric acid 5 the
latter may accumulate up to a certain maximum concentration.

The foregoing results have been elucidated by the observation that
hydration of the simple molecules HP0 3 leads to a preponderance of
orthophosphoric acid, while hydration of the hexapolymcr, (HPO 3 ) 6 ,
leads to a considerable proportion of each acid, ortho- and pyro- (see
p. 177).

Metaphosphates become hydrated in neutral and alkaline as well
as in acid solution, according to the equations

NaPO 3 +H Q =NaII PO 4
XaPQ 3 + XaOH =-- XaJIPO 4

At a temperature of 73 C. the velocity constant whether referred to a
unimolecular or a bimolccular reaction diminished with time ; after
an hour rather less than three-quarters of the original metaphosphate
remains. 6 The product is mainly orthophosphatc, as was proved by
titration with methyl orange and phenolphthalem, although small
quantities of pyrophosphate were formed by a side reaction. The
pyro-acid was determined by titration to bromophcnol blue in the
presence of zinc sulphate, which leads to a, complete precipitation of
pyrophosphate, the ortho-acid being unaffected, thus

XaJIJPA + 2ZnSO. 4 = Zn 2 P 2 O 7 -;- Xa 2 SO 4 + H 2 S0 4

The hydration of hexametaphosphate, (XaPO 3 ) 6 , also proceeded
as a unimolecular reaction. In neutral or alkaline solution ortho-

1 Sabatior, CumpL rend., 1888, 106, 63; 1881), 108, 738, 80-1.

2 Trlolt and Mvers, loc. cit.

3 Pessel, Monatsh., 1923, 43, 601.

1 Blake, Arner. Che-m. /., ]902, 27, 08; Giran, CompL rcvd., J908, 146, 1393.

5 Vogel, Neues Jahrb. Pharm., 1857, 8, 94.

6 Dragunov and Rossnovskaya, Zeitsch. aiiorg. G/icm., 1931, 200, 321.

PHOSPHORIC ACIDS. 177

phosphate is formed ; in acid solution ortho and pyro-acids in about
equal amounts.

The chemical properties of metaphosphoric acid, apart from those
which are due to the fact that dehydration has proceeded to a maximum,
do not differ essentially from those of the other hydrates of phosphorus
pentoxide. The acid dissolves freely in certain oxygenated organic
compounds aldehydes, kctones and anhydrides, e.g. benzaldehyde,
benzophenone and acetic anhydride. 1 It was chlorinated but not
dehydrated by phosphorus pent a chloride :

HP0 3 + 2PC1 5 - 3POC1 3 + IIC1 2

Complex Metaphosphoric Acids and their Salts. The poly
mers of met a phosphates are considerably more stable than those of
the acid itself and consequently a great variety of these salts has been
reported, having the general formula (MP0 3 ), ? , in which n varies from
1 to 6 or possibly up to 10. The heating of Xa 2 H 2 P 2 O 7 yielded a
soluble salt, cc Graham s salt," 3 and an insoluble salt, " Maddrell s
salt." 4 A sodium salt having the formula Xa 3 P r> Q 9 .6lI 2 Q may be
crystallised from the melt obtained by fusing Xa 2 IIPO 4 .12lI 2 O either
alone or with ammonium nitrate. 5 From the sodium salt there may
be prepared by double decomposition salts of many of the heavy
metals, e.g. Pb 3 P 3 O 9 .3H 2 O. These may be decomposed by H 2 S, etc.
giving the free acids, which slowly decompose, yielding the ortho-acid.
One structure which lias been assigned to the. complex acid 1I 3 P 3 O 9 is

I-ICK

\PO-O X

0< >PO OH

\PO_(X

HO/

Trimctaphosphatcs arc often moderately soluble, e.g. Ag ; >(PO 3 ) 3 .Ii 2 O
and J*a ;i (PO.j) 6 .GlloO. They often crystallise with molecules "of
water, e .g. Zn 3 (PO,j G .9lI 2 O, and also up to 15, e.g. Mg 3 (PO,) 6 .!5l-I 2 O.
The electrical conductivities of their solutions agree well with those
wliich should be shown by the salts of a. tri basic acid. 6

Monometaph.ospliates.- The insoluble salt obtained by heating
mieroeosmic salt, XaXH 4 lIPO 4 , was apparently polymerised meta-
phosphate, 7 while soluble salts obtained by neutralising mctaphosphoric
acid with sodium carbonate belonged to two series and quickly changed
into orthophosplmte when moist. 8

A salt which proved to have the simple molecular weight by the
free/ing-point method was prepared by the action of ethyl hexameta-
phosphate dissolved in alcohol on sodium cthoxide :

(CJ-i 5 PO,,) B -i-GCoII 5 OXa =6(C H 5 )oXaP0 4

> (C 2 II 5 ) 2 XaP0 4 = XaPO 3 + (CJl^Q

1 Heimann, ^ l>c.il.-ra(j(: z. Kc.nnhiixdf-.r O/ihn- -n-nd Mtfnphoxphorxaure, * JToicU lbcrLj;, 1902.

- CiHither, J. -pral L Chf-m., 1871), [2|, 8, 3-19: Jk-imann, he. at.

- Graham, Phil. T-Kin*., 1833, 123, 2,13. l Maddrcll, Phil. Md*!., 1847, [3], 30., 322.
5 Fk itmann and Hennoborii, A /male//, KS-J-8, 65, 304; v. Knorro, Zcit*ch.. (i/iorg.

Chun.., 1900, 24, 30!).

v. Knorrc, loc. ciL: \\ arscliauc:r, " BcMruyc. zur Ke.mtlnis der MelfipJio^pJuilc., Leipzig,
1903. Sec also Wiesler, * titdratjr,, cic..^ Berlin, 1.901; Mullor, Jlcitrayc, etc., Berlin,
1900; Tarnniann, Zc.dwh. j>ky*ibtf . Ch.c in., 1890, 6, 122; Lindboom, Bc.r ., 1875, 8, 122.

178 PHOSPHORUS.

The sodium salt was crystallised as a granular substance. It precipi
tated salts of barium, silver and lead (see " Trimetaphosphates "). 1

Dimetaphosphates of copper, manganese, cobalt and zinc are said
to be formed when an oxide or nitrate of these metals is heated with
an excess of phosphoric acid between 316 and 400 C. 2 The zinc salt
had the formula ZnP 2 O 6 .4H 2 O, and when treated with alkali sulphides
gave the alkali salts K 2 P 2 O 6 .2H 2 O, etc. 3 Other authorities, however,
have adduced reason for supposing that these salts are tri- or tetra-
metaphosphates. 4

Tetrametaphosphates. These salts are said to be formed when
orthophosphates of metals of high atomic weight silver, barium,
lead are heated with an excess of phosphoric acid at about 300 C. 5
The free acid, H 4 P 4 12 , prepared by decomposing the silver salt with
H 2 S, was rapidly hydrated to H 4 P 2 6 7 . 6

Pentametaphosphates. Alkali and ammonium salts of H 5 P 5 15
have been prepared the latter by heating (NH 4 ) 2 P 2 O 6 to 200 or
250 C. The melt was dissolved in water and the salt precipitated by
alcohol as an amorphous white mass. 7 K 4 NH 4 P 5 O 15 .6H 2 O was obtained
in the crystalline state. Calcium, strontium and barium salts, when
added to solutions of pentametaphosphates, gave gummy or flocculent
precipitates.

Hexametaphospliates were made by heating to a red heat XalI 2 P0 4
or NaNII 4 HP0 4 , i.e. in a platinum crucible at about 700 C., with rapid
cooling. 8 When the solution from this melt was added to silver nitrate,
one of the products was a crystalline salt, probably Ag fi P G O ]8 . 9

The conductivities of these salts and of the pentametaphosphates
showed that only some of the kations were dissociated, and that there
were probably complex anions, e.g. Na 4 [Na 2 (PO :} ) ]. 7 Complex fcrro-
and ferri-mctaphosphates arc also known, >f 4 [Fe(PO 3 ) (5 ], M 3 fFc(PO.j) ( .].

The ethyl ester has been prepared by boiling ethyl alcohol with
P 2 5 for some hours. A viscous liquid insoluble in ether but soluble in
chloroform was obtained, the molar weight of which in naphthalene
corresponded to (CJI 5 ) ( .P (; O ia . 10

The polymetaphosphates arc distinguished by giving gelatinous
precipitates with salts of most metals, and by decolorising red solutions
containing Fe(CNS) :J . 9

Still more complex nietaphosphates have been reported as resulting
from the fusio?i of salts of bivalent metals with Na,NlI. 1 IIP() 4 . 11

Sodium (".ctraphosphatc, Nu (i P 4 O 13 , arid deca.phosphate, Xa. r >P 1() 31 ,
were also said to be a mono- the. products obtained by fusing complex
metaphosphntes with pyrophosphates. 12 The acid JI (; P 4 O 13 was crystal.

1 Pascal, (-onipt. rend., 11)23, 177, 1298; 192-1, 178, 211; 192-1, 179, 9G(i; 1924,
180, <)()!.

2 Fleit rnann and Heimcboru;, lor. r/L; Maddro.ll, lor. cit.; v. Knorrr, lor. cit.

3 Glal.zcl, l t>b(-r liitnctaphosphorxdnrc -U/HJ f r< i l)<t-nict<iphoxph() ix(un c >SV//r:r," \Vurz-
burg, 1880.

4 Pn.scal, lor. n t.; Tamina.nn, lor. n t.

: I^lcit ma.nn, A titialcn, IS-19, 72, 228. So^ also (llai/.c^l, v. Knorrc, Fainnianii, War-

PHOSPHORIC ACIDS. 179

Used from a syrupy liquid obtained by adding more phosphorus pent-
oxide to a solution obtained by adding the pcntoxide to water (q.v.,
p. 133).i

The complex basic phosphates such as 5CaO.3P 2 O 5 , which was made
by passing the vapour of phosphorus pentoxide over anhydrous calcium
oxide, are supposed to be derived from more hydrated condensed acids
such as H JO P 6 Oo . 2

Properties and Reactions of Ortho-, Meta- and Pyro-phosphates.

Orthophosphates. Solubility. The tribasic phosphates of the
alkali metals and ammonia are soluble, while those of the alkaline
earth metals and the common metals are insoluble. They arc usually
prepared by double decomposition between disodium hydrogen phos
phate and a salt of the required metal, thus

+2CH 3 COoH

Na 2 HPO 4 4-~3AgX3 = Ag 3 P0 4 -f 2XaXO 3 + HXO 3

3

Formation of the yellow precipitate of Ag 3 PO 4 is a common test for
orthophosphates. On account of the acid which is liberated precipita
tion is not complete (see p. 181). Acid phosphates of the alkaline
earth metals, e.g. CaHPO 4 . are precipitated from solutions which are
nearly neutral. Moiioammonium phosphates, MXH 4 PO 4 , which are
so much used in quantitative analysis, are precipitated from neutral or
slightly acid solution then made ammoniacal (MgXH 4 PO 4 ), 3 or neutral
or slightly acid solution (ZnXl-^PO^ in presence of sodium acetate and
acetic acid, pH -=6-1 -6-0). 4

The effect of igniting orthophosphates is stated on p. 174. The
nature of the original salts may be deduced from the nature of the
residue. CaIIP0 4 may be distinguished from Ca 3 (PO 4 ) 2 by washing
with ammonia ; in the former case the washings will contain soluble
phosphate. Mg :J (PO 4 ) 2 uiay be detected in ignited Mg 2 P 2 O 7 by wetting
with AgXO-5 solution, which, if the former is present, imparts a yellow
colour due to Ag 3 PO 4 .

Precipitated phosphates of the zinc group and of the alkaline earth
metals and magnesium dissolve in acetic acid, whereas those of iron,
aluminium and chromium remain undissolved, a fact which is much
used in qualitative analysis. The hydrion concentrations, expressed
as pll, at which the various precipitates appear have been determined. 5
All phosphates dissolve in excess of dilute strong acids, in many cases
only that amount of acid being required which will convert the pre
cipitate into a primary or dihydrogen phosphate (cf. CaII 4 (P0 4 ) 2 , p. 222).

The precipitates obtained with magnesia mixture (magnesium
chloride in ammoniacal solution), or ferric chloride in an acid solution
to which sodium acetate has been added, arc often used as tests for
phosphate (sec p. 180), and in the latter case the phosphate is removed
from solution as ferric phosphate. Another common test is the formation
oC yellow ammonium phosphomolybdatc when a nitric acid solution of
ammonium molybdatc is added to phosphate solution (see pp. 180. 181).

1 Rakusin and Arseneefu Ctn-.m. Ze.if., 1923, 47, H).").

2 Kroll, Zfiitwk. anorrj. C/iem., 1012, 76, 387; 77, 1; 78, 5.

3 Epperson, J. Amcr. Chern. Soc., 1028, 50, 321.

4 Ball and Agruss, ,L Amer. Cham. Soc., 1930, 52, 120.

5 Briuon, Trans. Chwn. Soc., 1927, p. G14.

ISO

PHOSPHORUS.

It is also possible to eliminate phosphate as insoluble phosphomcta-
stannlc acid by adding tin to a nitric acid solution of phosphoric acid.
Pyro- and M eta -phosphates. The behaviour of the pyro- and
meta-phosphates towards the foregoing reagents and others which may
be used in distinguishing these salts are tabulated below:

COMMON AND DISTINCTIVE REACTIONS OF ORTHO-,
PYRO- AND META-PHOSPHATES.

Reagent.

Ortlio-.

Pyro-.

Silver nitrate, neu
tral or slightly
alkaline solution.

Yellow precipitate, White crystalline White gelatinous

dissolving in acetic precipitate, not precipitate, not

acid. dissolving in acetic dissolving in acetic

acid. acid.

Barium chloride,
neutral or alkaline.
Do. acid.

White precipitate. White precipitate. White precipitate.
Xo precipitate. Xo precipitate. White precipitate.

Albumin, acid solu
tion.

Xo reaction.

Xo reaction.

Coagulated.

Ammonium molyb-
date with nitric
acid.

Yellow crystalline Xo precipitate in Xo precipitate in
precipitate on cold or on gentle cold or on eentle
warming. warming. warming.

Zinc acetate to acid
solution.

Xo precipitate.

White precipitate, Xo precipitate,
soluble in excess of
pyrophosphatc.

Salts of chromium.

Precipitate, soluble Precipitate, insolu- Precipitate, insohi-
in cold acetic acid. blc in acetic acid. ble in acetic acid.

Special tests.

.Lead acetate gives Magnesium chloride i Magnesium salts
white Pb^PO.J,, gives white pre- ! give no precipitate,
almost insoluble cipitate, soluble in
in acetic acid. excess of MgCL or \

pyrophosphatc. |

Lutco cobaltic chlor- i .Bismuth salts in
idc, Co(XH 3 ) (5 Cl 3 , alkaline solution
gives a reddish- give a white pre-
yellow crystalline cipitate.
precipitate,

( o(XJI 3 ) ( .XaR,O 7 .
1 I. 1 , H,,().

Estimation of the Phosphoric Acids.

The titrations are based upon the degrees of dissociation o(! the
first, second, etc. hydrogen ion. The dissociation constants and
appropriate indicators arc; mentioned on pp. 10.5. 172, 170.

Orthophosphoric Acid may be titrated with sodium or potassium
hydroxide Free from carbonate. The equivalent point indicating
NaII 2 P0 4 occurs at ?;!!--= CY/. 4-2, which is within the transition range
of methyl yellow, methyl orange and bromophcnol blue. The end-
point tint should be matched against that of a comparison solution
containing about the same concentration of XaII P() 4 .

The acid may also be titrated as dibasic, using phenolphthalcin,
* Note. The results depend somewhat un the complexity of the metaphosphatcs (see
pp. 177 d acq.).

PHOSPHORIC ACIDS. 181

thymolphthalein or thymol blue, the end-point tint being matched
against a solution of Xa 2 HPO 4 .

The results are closer to the theoretical if the solutions are saturated
with sodium chloride. See also ic Neutralisation Curve," p. 166.

Pyrophosphoric Acid (p. 171) may be titrated as a dibasic acid to
pll = 4-0 using methyl yellow, etc. as before: also as a tetrabasic acid
using phenolphthalein, thymolphthalein or thymol blue in the presence
of barium salt. Electrometric titrations have also been performed. 1

Metaphosphoric Acid may be titrated with methyl orange, etc.
irrespective of its progressive hydration (p. 175). The phenolphthalein
titre, however, varies with time (see p. 176).

Special methods of analysing the pyro- and meta-acicls have been
indicated on pp. 172. 176. 180. These acids may easily be converted into
the ortlio- form by boiling alone or in the presence of some nitric acid,
and then determined by one of the methods described in the following.

Determination of Orthophosphates. (1) With Silver Nitrate.
This depends upon the precipitation of silver orthophosphate in solu
tions of low and controlled acidity. In the assay of commercial 85 per
cent, phosphoric acid of density 1-710 the syrup is diluted to a con
venient volume and an aliquot part is taken which contains about
0-1 gram of H 3 P0 4 . It is neutralised to phenolphthalein with approxi
mately dcci normal alkali (free from chloride). 50 c.c. of decinormal
silver nitrate are then added while the solution is kept neutral to litmus
by stirring in /inc. oxide or a suspension of the hydroxide. The whole
or a measured part of the filtered solution is acidified with nitric acid
and, after the addition of feme alum, the unused silver nitrate is
titrated with standard decinornuil ammonium thiocyanate in the usual
manner. Alkali phosphates may also be determined in this way.

Silver phosphate is also quantitatively precipitated in the presence
of sodium acetate and acetic acid, the phosphoric acid then being
titrated as a tri basic acid according to the equation

H 3 P0 4 -f 3AgXO 3 + :3CH 3 COONa = Ag 3 PO 4 + 3XaX0 3 -r 3CH 3 COOH

Tliis reaction is also used in the method of llolleman 2 as modified by
VVilkic. 3 A phosphate solution containing phcnolphthalein is reddened
by the addition of alkali, then just decolorised with nitric acid. An
excess of standard silver nitrate is then added and decinormal sodium
acetate and alkali to slight pink colour, followed by 2 c.c. of decinormal
II 2 S0 4 . The solution is diluted and filtered and the excess of silver
determined by titration with decinormal ammonium thiocyanate.

(2) With "Molt/bdatc. Precipitation of phosphate in nitric acid
solution by means of ammonium molybdatc serves not only as a quali
tative test, but also For the quantitative separation of phosphate in a
preliminary or even final manner. Insoluble phosphates are previously
dissolved in nitric acid, while the phosphoric acids arc nearly neutralised
with ammonia and then acidified with nitric acid. The nitric acid
solution of ammonium molybdatc (3 per cent.) is added hot, the mixture
boiled and the precipitate collected on a filter. The precipitate may
now be treated in various ways :

(a) The precipitate is rcdissolved in ammonia, reprecipitated with

1 Morton, Quart. J. Phann., 1930, 3, 438.

2 llolleman, J. Xoc. Chew.. In.d., 1894, 13, 763, 843.

3 AVilkie J. Soc. Chtm. Ind. t 1910, 29, 794, Kosm, J. Amcr. Che,n. Sac., 1911, 33, 1099.

182 PHOSPHORUS.

nitric acid and ammonium molybdate. washed with a solution of
ammonium nitrate and nitric acid, and dried for a long time at 160 to
180 C. preferably in a current of air. The precipitate is then
(NH 4 ) 3 PO 4 .12MoO 3 containing theoretically 3-782 per cent. P 2 0- and
1-65 per cent, phosphorus. Under the conditions given the practical
factor for conversion to per cent. P 2 O 5 is 3-753. * If the precipitate is
greenish it should be heated again with a small crystal of NH NO 3
and a little ammonium carbonate which gives the correct yellow.

(b) On gentle ignition the precipitate is converted into a blue-
black substance 24MoO 3 .P 2 O 5 which contains 3-947 per cent. P 2 CL.

(c) The precipitate is dissolved in 2-5 per cent, ammonia, thesolu-
tion nearly neutralised with hydrochloric acid and precipitated with a
solution of magnesium salts (see p. 183).

(d) The well- washed precipitate is dissolved in a known quantity
in excess of standard alkali, the excess alkali being titrated with
standard nitric acid using phenolphthalein :

2[(NH 4 ) 3 PO 4 + 12MoO 3 ] + IGXaOH -f- H 2 O =2(NH 4 ) 2 HPO 4

+ (NH 4 ) 2 Mo0 4 -r23Na 2 Mo0 4 +23H 2

1 c.c. decinormal NaOH corresponds to 0-000309 gram P 2 5 .

(tf) The molybdate method has been adapted to the determination
of small quantities of phosphorus colorimetrically. The solution in
nitric acid is evaporated to clryncss to render the silica insoluble, and
the residue taken up with nitric acid. After the addition of an excess
of ammonium molybdate the colour is matched against a standard of
nearly the same concentration in phosphate. The maximum colour is
developed after a few minutes, while that in the presence of silicic acid
requires some hours. Darker solutions precipitate in time while lighter
ones fade."

A eolorimetrio method has also been devised which is not inter
fered with by silicic-, acid. Iron, however, should be removed by means
of eupferron. The solution should contain 0-002 to 0-025 milligram of
P./) r> and 2 c.c. of nitric acid (density 1-12). To this is added 2 c.c. of
a quinine solution made by dissolving 1 gram of the sulphate in a slight
excess of nitric , acid and adding enough baryta to precipitate all the
sulphate. The colour developed after the addition of the molybdate is
compared with that of a standard/ 5

A nephclometrie method using a strychnine molybdate reagent has
also been devised. 4

A similar method is used for the determination of inorganic phos
phates in urine. r> 1 to 5 e.e. of the urine, containing about 0-5 milli
gram of phosphorus, are diluted and treated with a solution of ammonin.ni
molybdnte in 15 per cent, sulphuric acid (5 e.e.), 1 c.c. of 1 per cent.
hydroquinone solution and 1 c.c. of 20 per cent, sodium sulphite
solution. The bluet colour is compared in Xcsslcr glasses with that
developed by the same solutions when mixed with a standard phos
phate solution of which :"> c.c. contain 0-5 milligram of phosphorus.

1 TivjKhvclI-Mall, ^Analytical (J/tcMixtry, Vol. JJ, Qua /Uitahve," Chapman and Hall,

i <>;$<).

- Srhn-mcr, ./. At/icr. dhoti. /SVx;., .1903, 25, 1056; Schreiner and Brown, ibid., 1904,
26, i)7f>.

a (Jrrgoiro, Hull. Nor:, chini. Jlcly., 1920, 29, 253.
l .Julhisbcruor, liiwhc-ni. Zcitttch., 1926, 177, 140.

PHOSPHORIC ACIDS. 183

The standard phosphate is made by dissolving 4-38.8 grams of KH 2 PO 4
in 1 litre and diluting this stock 10 times before use.

(/) The amount of molybdenum in the precipitate may also be
determined by several methods. A quick volumetric method consists
in reduction to molybdenum sesquioxide and titration with perman
ganate. The precipitate, after washing with acid ammonium sulphate
solution, is dissolved in 10 per cent, ammonia, then treated with an
excess of dilute sulphuric acid and filtered through zinc. The reduced
solution and its washings are run directly into 50 c.c. of 20 per cent,
ferric alum. The MoO :} is reduced by the zinc to Mo 2 O 3 (or Mo 24 O 37 )
and this is again oxidised by the ferric sulphate, giving its equivalent
of ferrous sulphate, which is titrated with IOInO 4 . Since the pre
cipitate contains IP to 12MoO 3 and 3 atoms of oxygen oxidise Mo O 3 ,
it follows that 36FeslP. Therefore the iron value of the KMnO 4
multiplied by P/36Fe (i.e. 0-01540) gives the value of the KMnO 4 in
terms of phosphorus. The factor is 0-0158 if the reduction product
is Mo M 37 .

(3) Volumetrically , by Uranyl Solutions. Phosphates which are
soluble in water or acetic acid may be determined quickly with a
solution of uranyl acetate or nitrate which has been standardised
against pure sodium or potassium phosphate. The uranium solution
is run into that of the phosphate, containing ammonium acetate and
acetic acid. A greenish-yellow precipitate of uranyl ammonium
phosphate is deposited. The excess of uranium which appears at the
end-point is recognised by spotting on a white tile and mixing with
drops of a solution of potassium ferrocyani.de. The uranyl salt gives
a dark brown colour of uranyl ferrocyanidc.

KH 2 PO 4 -r UOo(CH 3 C0 ) 2 -r CH 3 COoXH 4 =UOoXH 4 P0 4

-!- CH 3 COoK + 2CH 3 C0 2 H

It is possible also to use cochineal as an inside indicator, the end-point
being shown by a change of colour from pink to green.

(4) Magnesium Phosphate Method. This is the most important and
most accurate final method for the determination, of phosphorus in all
its compounds. If the phosphate is present as a salt soluble in water
the solution is slightly acidified and magnesia mixture (containing
magnesium chloride and ammonium chloride) is added. The solution
is heated to boiling and a hot 2-5 per cent, solution of ammonia is added
drop by drop until phcnolphthalein is reddened and a crystalline pre
cipitate obtained, which is ready Cor filtration after standing about
10 minutes. The precipitate is washed with 2-5 per cent, ammonia,
filtered off on a Gooch crucible or on paper and ignited wet or dry to
MgoP 2 O 7 , which contains 27-86 per cent, of phosphorus, 63-79 per cent,
of P 2 6 5 and 85-342 per cent, of PO 4 .

An ammonium phosphomolybdatc precipitate is treated as de
scribed under (2c) (p. 182) for conversion into MgXH 4 PO 4 . The
washed precipitate of MgNH 4 P0 4 may be determined volumetrically
by solution in a known quantity in excess of standard hydrochloric
acid and back-titration with decinormal alkali using methyl orange, thus

MgXH 4 P0 4 + 2IIC1 = NH 4 H 2 P0 4 -r MgCl 2

The most important materials or products in which it is necessary
to determine phosphorus are phosphatic rocks of all sorts, soils,

184 PHOSPHORUS.

fertilisers (including basic slag), iron, steel and non-ferrous phosphor
alloys. The former classes are dealt with in the appropriate sections
of this Volume, so that it remains only to mention some special methods
which are used in the case of phosphorus alloys.

Phosphorus in Alloys. Many commercial varieties of iron con
tain phosphorus, probably in the form of a phosphide (q.v., p. 06),
The metal is dissolved in HXO 3 (1:1), the solution evaporated to
drvness, the residue taken up with hydrochloric acid and evaporated
again until the silica has all been rendered insoluble. The residue is
then taken up in hydrochloric acid, evaporated to drvness again, taken
up in nitric acid and treated with ammonium nitrate and ammonium
molybdate reagent. The precipitate is washed with dilute nitric acid
until free from iron salts, then with water if it is to be weighed as
under (2a) (p. 181) or with a solution of potassium nitrate if it is to
be titrated as under (2d) (p. 182). This method also applies to other
metals which contain phosphides. If tin is present, as in the phosphor
bronzes, all the phosphoric oxide is found with the insoluble mcta-
stannic acid after solution of the alloy in nitric acid. This precipitate,
after washing, drying and weighing, may be fused with three times its
weight of potassium cyanide. The residue is extracted with water,
the metallic tin filtered off, and the excess of cyanide destroyed with
HC1, any copper and tin remaining in solution being precipitated with
H 2 S. In the filtrate, after boiling, the phosphate is determined by
any of the methods already described.

Perphosphoric Acids. The methods which have been used
successfully in the preparation of pcrsulphuric acids and pcrsulphal.es
have also been applied toperphosphoric acid and the perphosphatcs, i.e.

(a) The addition of II 2 Oo at low temperatures.

(/;) Anodic oxidation.

(a) Hydrogen peroxide docs not combine with orthophosphonc
acid. .But when .metaphosphoric acid or phosphorus pentoxidc were
treated with 30 per cent, hydrogen peroxide at C., solutions were
obtained which had oxidising properties and which by analysis proved
to contain pm.o-nop}).oxph-oric. acid, II.jPO-. With pyrophosphoric acid
in excess, per(l-ij)Jw}>ph.oric acid, H d P 2 () 8 , was obtained. 1

Slightly acid or alkaline phosphate solutions of the alkali metals,
cU 1 .. combine with varying- proportions of n().> H1 < l loose manner.
Such solutions give the reactions of lloOo."

(/;) Electrolytic oxidation. The perphosphates of the alkali metals
a.nd of ammonium have been prepared in this way. As in the electro
lytic, production of persulphales 3 low temperatures are advantageous
and the presence of iluoridcs and ehroniat.es increases the yield,
probably by maintaining a high anodic over-voltage. A low anodic
current -density (e.g. about 0-015 amp. /em. 2 ) is favourable. The
electrolyte may consist of a. solution of KI! 2 ! > () 4 with (luoridc and
chroma te. On evaporation at 100 (\ after the electrolysis potassium
perphosphatc, K 4 P 2 () 8 , can be crystallised. 1

J Sehniidlm and Massini, />/-., J!)10, 43, 1 H>:>; d Ans and .Friedrich, Her., 19JO,
43, I8SO; d Ans, Zfil.^c/i.. Klt ktrucki .ni.., I1H1, 17, 8,10.

2 Uusain and Part.in^ton, Trtutfi. Faraday tioc., 19:28, 24, 23o.

;i Tliis Series, Volume VII, Tart JL.

4 Fichlcr and MulJer, Utlv. Chim. Ada, 1918, i, 297; Miro, ibid., 1919, 2, 3.

PHOSPHORIC ACIDS. 185

Perphosphates of ammonium may be prepared in good yields by
electrolysis, but auto-oxidation and -reduction may occur with the
production of ammonium phosphate and ammonium nitrate. 1

Perphosphates of rubidium and caesium are more easily prepared,
even in the absence of fluorides or chromates. The permonophosphates
of these metals however require in their preparation rather higher
current-densities. 2

If the perphosphoric acids are regarded as derivatives of hydrogen
peroxide their constitution with quinquevalent phosphorus will be

O O

y(OH) 2 : |;

O =P< (H0)o =P O P - (OH) 2

V) OH

Pennon ophosphoric Acid. Perdiphosphoric Acid.

Reactions and Z)efe6*^0n.- Permoiiophosphoric acid is a strong
oxidising agent. It liberates iodine at once from acidified potassium
iodide (cf. Caro s acid) and oxidises manganous salts in the cold to
permanganates. Hydrolysis in dilute solutions is represented by the
equation

H 3 PO 5 -r H 2 O - II 3 P0 4 + H 2 O 2

Perdi phosphoric acid liberates iodine only slowly from acidified
potassium iodide, and can be kept for- long periods in dilute solution.

Oxidation of manganous salts in acid solution to red manganic salts
is characteristic of true pcrphosphatcs. They should not give the
characteristic tests of hydrogen peroxide with chromic acid or titanic
acid. They oxidise acid aniline solutions to nitrosobenzenc and
gradually to nitrobenzene.

Potassium pcrphosphatc gives with silver nitrate a dark precipitate
which changes to white Ag 3 PO 5 , then to yellow Ag 3 PO 4 with evolution
of ozone and oxygen.

1 Gut/.wjJlur, lid*. Chim. AcMi, 1928, n, 32,3; Husairi and Partington, loc. cit. See
also Fiehtcr, J. Soc. Ckc.m. Jnd., 1029, 48, 347T.
- Ilusaiii and Partmgtcm, loc. cit.

CHAPTER XIII.
PHOSPHORUS AND SULPHUR OR SELENIUM.

PHOSPHORUS combines directly with sulphur in various proportions
to give sulphides, the formulae of some of which resemble those of the
oxides. It also gives oxysulphides, thiophosphites, thiophosphates
and the corresponding acids. The latter salts may be made by the
action of alkalies or alkali sulphides on phosphorus sulphides.

Historical. It was recognised early that phosphorus combines
violently with sulphur when the two are heated together to a sufficiently
high temperature (see p. 187 J, 1 and various products were examined,
sonic of which afterwards proved to be compounds and others mixtures. 2
Among the earliest products to be prepared and analysed were P 4 S 3
and P 4 S ;{ . 4 The: substance P 4 S was shown later to be merely a solid
solution of the two elements, while the latter, P 4 S 3 , is one of the best-
known compounds and is prepared in large quantities for use in the
nuil cli industry (q.v. and sec p. 10).

Physical Mixtures. -When sulphur and phosphorus are melted
together at. temperatures below 1.00 C. each lowers the melting-point
of the other but. there is no sign of combination. The eutectie mixture
solidified at. ( !)-8" (!. and contained 22-8 per cent, of sulphur. 5 The
mixed crystals deposited on the sulphur side of the eutectic were iso-
morphous with the octahedral form of sulphur up to a maximum of
about, 20 per cent, of phosphorus, while the crystals on the phosphorus
side \\ere isoinorphous with phosphorus up to a maximum of about
f> per cent, of sulphur. On distillation at low temperatures (under
reduced pressures) the products behaved as mixtures; all the phos
phorus distilled away and the sulphur was left. 6

The System Phosphorus -Sulphur and Compounds. -The two
elements mixed in various proportions were fused in scaled tubes at
about 2OO ( . The solids so formed were heated and the temperatures
determined at which complete liquefaction took place. These tem
peratures are the initial freey.iiig-points of liquid at that temperature
in equilibrium with the solid phases.

i>\ this method points on the temperature-composition curves were

1 M..P---I.II, Mt^tlfnn. rn>hn., 17KI, 6, f>4.

i .rryriiu; , Annul n, 1813, 47, 1 1?9, LMf); Furada.y, Quart. J. /Sr,/., 1818, 4, 361;
iVll.tirr. Ann. i h.in. / ////*., 1 7<M>, [ I ], 4, 1.

: L.-mniiK , C<,/Hi t. nml., lS(il, 58, 890; 188 1 , 93, 485); 1883,96,1630; 1884,98,45.

- Doult.uch, (\ni*l. nml., 1902, 135, 1 6f> ; 1904, 138, 364; 1900, 142, 1045.

I>ninlKTt, (\impt. raid., 1883, 96, 1-199, 16^8, 1771; 1885, 100, 3fx~>; 1886, 102,

PHOSPHORUS AXD SULPHUR,

187

obtained corresponding to the compounds P 4 S 3 , P S.>, PoS 5 and perhaps
pc p e pc i

* 3^6? 1 4^7? - 1 6-

FREEZING-POINTS AND COMPOSITIONS OF THE
SYSTEM PHOSPHORUS-SULPHUR. 2

| The melting-points of compounds and eutectics are printed in heavy
type, the corresponding compositions of the liquid phases in italics.
Solid phases of uncertain composition are enclosed in brackets.]

Per cent.
Sulphur.

Solid Phase.

Freezing-
point,
C.

Per cent.
Sulphur.

Solid Phase.

. Freezing-
point,
C.

o-o

P

+ 44

43-6

P 4 S 3

167

6-0

; 5

27

45-0

5 5

154

10-0

.,

20

60 -0

P 4 S 3 +P 2 S 3

46

12-0

.,

13

55-0

P 2 S 3

230

16-0

. ?

+ 3

60 -8

P 2 S 3

296

20-0

P+(P 2 S)

- 7

67-6

P,S 3 +P,S 3

^ o Z o

230

24-0

(P 2 S)

+ o

72-1

1 J 2 S 5

272

26-0

. ,

11

75-0

P 2 S 5 +(PS )

243

30-0

24

80-0

(PS)

300

34-0

;?

38

SG-1

(PS 8 )

314

36-0

(P 2 S)+P 4 S 3

44

90-0

,.

308

38-0

P 4 S 3

86

95-0

,.

260

40-0

122

100-0

s

115-2

41-0

146

Other compounds not included in this set of experiments have
been described, e.g. P. 4 S 7 (nvpt. 303 C.), P 3 S (j (m.pt. 298 C,), 3 and
P 4 S 8 (m.pt. 311 C.).

A metas table scries between phosphorus and P 4 S 3 has also been
reported, with a eutcctic at -40 C. and 33-5 per cent, sulphur, but the
latter point may be due to supercooling. 4

Tetraphosphorus Trisulphide or Phosphorus Tetritatrivulphide,
P 4 S 3 , may be })rc|)ared by heating- together the theoretical propor
tions of red phosphorus and sulphur in a sealed tube or in an atmo
sphere of carbon dioxide." It is recommended G to use an excess of red
phosphorus, mix intimately with powdered sulphur and heat to 100
C. in. a wide tube in a current of carbon dioxide. The reaction is

1 Giran, Conrpt. rrnrf., 1 !)((), 142, , }98; Boulouch, loc. <;//.; lIollY, Ztitxch. physlkal.
Cheni., JSJKJ, 12, 10(5: Mai and Sclietler, Her., 1003, 36, 780; Stock and Hofniann, ibid.,

1003, 36, 31-~); l-iudolpli, ~ Zuf Kc.nii.lii.is dar Phosphor snlfidc, inxbexuiidwi dc.fi Tetra-
<pko*pliortriiiljul<,,^ BorJin, 1010; Schonck and Schuril, tier., ]OOG, 39, i5i>2; ^Lock
and. {Rudolph, -ibid., 1000, 42, 2002; J010, 43, loO: Stock and Hci^covici, ibid., 19JO,
43, 415, 1223; Jlcr.scovici, ^ Zur KwnUns dtr Pkoxpliorjiilfuh,* 13erlm, 1010; JSlock and
v. J3cxold, Btr., 19()8, 41, (J57.

2 Giran, Loc. cit. 3 Stock and v. J3czold, loc. ell.

4 Boulouch, loc. cit.

5 Lomoinc, Loc. ciL; Isarnbcrt, loc. cit.; Rammo, Ber., 1879, 12, 94-1; Helil , loc. at.;
Mai and Schcfl er, loc. cit.; Stock and v. Bczold, loc. cit.; Rudolph, loc. cit.; Stock and
Rudolph, loc. at.

Stock and Rudolph, loc. cit.

188 PHOSPHORUS.

started by stronger heating in one spot. After the reaction has ceased,
the contents of the tube are heated until distillation begins, in order
to dissociate the higher sulphides of phosphorus. The product, after
cooling in an atmosphere of carbon dioxide, may be extracted with
carbon disulphicle, which dissolves the !\S 3 , or distilled, when P 4 S 3
passes over.

Details of the preparation according to Stock 1 are as follows : The
sulphur, phosphorus, carbon disulphide and benzene should be both
pure and dry. The red phosphorus (155 grams) is mixed with the
sulphur (95 grams). This mixture, in portions of 40 to 50 grams is
carefully warmed to 100 C. in a beaker standing 011 a sand-bath,
while a current of C0 2 is passed on to the surface. The part of the
beaker which is on a level with the upper edge of the mixture is then
heated with a small flame until the reaction starts and spreads rapidly
through the mass. The melted substance is then heated to the point
of distillation in a current of CO 2 , which is maintained until the product
is cold. It is then crushed and extracted with about twice its weight
of warm CS 2 . On evaporation of this, the sulphide, having a melting-
point of 130 to 150 C., remains. It is powdered, boiled with water
and steamed. The powder is again extracted with CS 2 , which is shaken
with P*O 5 , filtered and evaporated until crystals form. These are
dried over P<>0 5 in a water-pump vacuum. The product now melts at
160 to 171 C. but still contains CS 2 , which may be removed by extrac
tion in a Soxhlet apparatus with benzene. As this proceeds, fine
crystals are deposited from the benzene. These are sucked dry on a
filter and finally freed from solvent in a current of dry hydrogen.
Another crop of crystals may be obtained by evaporation of the mother-
liquors. The yellowish needles, of melting-point about 173 C., are
soluble in benzene and carbon disulphicle. Solutions are turbid on
exposure to air, but remain unaltered in an atmosphere of hydrogen.
They can be heated to 700 C, without alteration in the absence of
oxygen and moisture.

In the commercial process phosphorus and sulphur are heated
together in a current of carbon dioxide to 330 or 340 C., and the
compound sublimed. The commercial product may contain 83 to 98
per cent, of P 4 S 3 with free sulphur, water, volatile matter, phosphoric
acid and other impurities. 2 If it is to be used in the match industry
it should not contain free phosphorus.

The purified compound is a yellow crystalline substance which
has a constant composition and which does not alter on fractional
distillation or crystallisation. 3 The vapour density was found to agree
with the formula P 4 S 3 . 4 It has been confirmed that the molecular
weight of the vapour agrees with the theoretical (220) at about 700 C.,
but above this temperature dissociation takes place, a molecular weight
of 179 being found at 1000 C. 5 Molecular weights slightly above the
theoretical (228 to 264) were found for this compound when dissolved
in benzene at its boiling-point. 6

The density of the solid was 2-0. 7 The melting-point was found to

1 Stock, loc. cit. - Clayton, Proc. C/tem. Soc., 1902, 18, 129; 1903, 19, 231.

JLemoine, loc. cit.

4 Lemoinc, loc. cit.; Ramine, loc. cit.; Helfl, loc. cit.

5 Stock and v. Bezold, loc. cit.

6 Stock and Kudolph, Stock and v. Bezold, Helft , loc. cit.

1 Lemoine, loc. cit.; Isambert, loc. cit.; Stock and v. Bezold, loc. cit.

PHOSPHORUS AND SULPHUR, 189

be 165 to 167 C. by Isambert, Helff, Mai and Scheffer, 1 also by Rebs
and Giran, 2 but Stock and his collaborators give 171 to 172-5 C.
The boiling-point is above 400 C. ; it is given as 410 to 420 C., 3
408 to 418 , 4 407 to 408. 5 In a water-pump vacuum the sulphide
may be distilled at about 230 C.

The heat of formation was low, namely, 16-4 Cals. per mo I P 4 S 3
and of the same order as the heat of transformation of yellow into red
phosphorus. As already mentioned, the vapour is dissociated at higher
temperatures, and in an atmosphere of carbon dioxide this dissociation
appears to begin at about 380 C.

The compound ignites in air at about 100 C. 3 and shows a greenish
glow of slow combustion at about 80 C. 6 The conditions of this glow
resemble, but are not identical with, those required in the cases of
white phosphorus and phosphorous oxide. 4 It did not appear in pure
oxygen until, at 65 C., the pressure was reduced below 300 mm., and
was steady at 242 mm. in dry and 250-3 mm. in moist oxygen. At
higher temperatures the glow appeared and disappeared at higher
pressures. Inflammation occurred between 80 and 90 C. 6 The
products of combustion are phosphoric oxide and sulphur dioxide.
Chlorine converts the sulphide into phosphoric and sulphuric acids,
while aqua regia also dissolves it. 7

Cold water has no effect, but boiling water slowly decomposes the
sulphide into phosphoric acid and hydrogen sulphide. 3 With potassium
hydroxide solution the sulphide behaves like a mixture of sulphur and
phosphorus, giving phosphine, hydrogen, etc., and potassium sulphide. 8

Like its constituent elements, this sulphide of phosphorus dissolves
very freely in CS 2 (solubility 60 to 100 at ordinary temperatures). It
is also moderately soluble in solvents such as benzene and toluene.

Diphosphorus Trisulphide or Phosphorus Tctr it ahexa sulphide,
P 2 S 3 or P 4 S 6 . The preparation of a compound of this composition by
heating the constituent elements in the correct proportions was reported
by the earlier workers. 7 It was described as a yellowish-white sub
stance which could be obtained as a sublimate 9 and purified by sub
limation. 10 It gave a vapour the density of which corresponded to
P 4 S G . li When hydrogen sulphide is caused to react with phosphorus
trihalides the solid remaining has the composition P 2 S 3 . 12

The substance melted at 290 C., 3 296 C. 13 It" sublimed between
490 and 550 C. It did not fume or glow in the air, but in other
respects its chemical properties resembled those of P 4 S 3 .

Tetraphosphorus Heptasulpliide or Phosphorus Tctriiahepta-
sulphide, P 4 S 7 . This compound was first obtained during the distilla
tion of P 4 S 6 in a vacuum, 14 and was separated by heating under pressure

L Loc. cit. 2 Rcbs, Annalcv, 1883, 246, 365; Giran, Inc. cif.

3 Lemoine, Joe. dl, 1 Mai and Scheffer, loc. cit. 3 Stock and Rudolph, loc. at.

f> SeharfT, ^ Caber das Leucliten dc-s Phosphors -und eivigcr seiner Vvrbrndunycn" Mar
burg, 1007.

7 Lcmoine, Isambert, loc. cit.

s Lcmoine. Joe. c./L; Stock and Rudolph, loc. cit.
9 Ber/A-lius, Annah-n, 1843, 47, 120, 255.
10 Krafil, and Xcumann, Bf-.r., 1901, 34, 567. 1] Isambert, loc. cit.

12 Serullas, Ann. Chitn. Phy*., 1820, [2], 42, 33; Gladstone, Phil. Mag., 18-19, [3],
35, 345; Ouvrard, Ann. Chim. P hys., KS94, [7], 2, 221. For other methods, see also
Sprinirer, PJmrm. Zt.itu/tg, 1900, 43, 164; Besson, Com.pt. rend., 1896, 122, 467; 1896,
123, 884; 1807, 124, 151.

13 Giran. loc. cit., D. 187. 1; -Mai, loc. cit.

190 PHOSPHORUS.

with carbon disulphide in which, as distinguished from P 4 S ? , it was
only sparingly soluble. In the methods of preparation which have
been described l the phosphorus should be in slight excess over that
required for P 4 S 7 . The ingredients may be heated together in. a sealed
tube and the product recrystallised from carbon disulphide in pale
yellow crystals.

The melting-point was 310 C. and the boiling-point 523 C. 2 A
maximum melting-point corresponding to P 4 S 7 was found on the
thermal diagram of P 4 S 6 and P 4 S 10 . 3 The solubility in carbon di
sulphide was 0-0286 gram per 100 grams solvent at 17 C.

A compound having the empirical formula PS 2 was said to be
formed by heating together the elements in the proportions theoreti
cally required, 4 or by distillation 5 or heating with carbon disulphide
in a sealed tube at 210 C. 6 Other methods include the exposure to
sunlight of P 4 S 3 (1 part) with sulphur (2 parts) dissolved in carbon
disulphide, 7 or a solution of phosphorus and sulphur with a little iodine
in carbon disulphide. 8 Pale yellow transparent needles of the compound
are deposited.

The molecular weight deduced from the vapour density was P 4 S 8 5
or P 3 S 6 . The melting-point was 248 to 249 C. 10 or 290"to 298 C. 11
The boiling-point is given as 516 to 519 C. 12

The chemical properties are similar to those of the other sulphides
of phosphorus, but the compound is less stable, and easily decomposes,
giving P 4 S 3 with separation of sulphur.

Phosphorus Pentasulphide or Diphosphorus Pentasulphide or
Phosphorus Tetritadecasulphide, P 2 S 5 or P 4 S 10 . The methods which
have been already described in connection with the other sulphides
have been successfully used in the preparation of this compound from
the theoretical proportions of the elements :

(a) By fusion. This method is used in the preparation of the com
mercial product, which is not pure. 13 A slight excess of sulphur should
be used and the heating should take place in an atmosphere of C0 2 .
The compound may be purified by heating in a vacuous scaled tube
for several hours at 700 C., and then by crystallisation from carbon
disulphide. 14

(b) By heating phosphorus (20 grams) and sulphur (GO grams) in a
sealed tube with iodine (0-5 grain) and carbon disulphide (150 c.c.) at
211 C., followed by recrystallisation. 15

(c) By the action of H 2 S on POC1 3 . 16

(d) By passing the vapour of PSC1 3 through a red-hot tube. 17
Details of the preparation have been given by Stock. 18 Pure, dry,

1 Stock and v. Bczold, loc. cit.; Stock and Hcrscovici, loc. cit.

2 Stock and Hcrscovici, loc. cit.

3 Stock, B(-.r., 1906, 39, 1967; 1909, 42, 2002.

4 Ramme, loc. cit.; llelil, loc. cit. 5 Mai, Antutlc.n., 1891, 265, 192.

6 Scidel, " Uc.b(,r Schwcfelphosphorverbi.ndu /igeji, etc.," Gottingen, 1875.

7 Dervin, Co",n>pt. rend., 1904, 138, 366.

8 Bonlouch, loc. cit. 9 Ramme, TIelff, loc. cit. ll) Scidel, loc. cit.

1 Ramme, HeliT, Dervin, loc. cit.

2 Reckhnghausen, Bar., 1893, 26, 1517.

ckulu,*" Annaleu, 1854, 90, 399; Goldschmidt, Bc.r., 1882, 15, 303; V. and C.
Mever, tier., 1879, 12, 609; Eclli , loc. cit.; Robs, loc. cit.

Ramme, loc. cit. 15 Ramme, loc. cit.; Stock and Thiel, Bar., 1905, 38, 2720.

Besson, loc. cit.

Baudrimont, Ann. Ctu-ni. Phys., 1864, [4], 2, 5. is Stock, Ber., 1910, 43, 1223.

PHOSPHORUS AND SULPHUR. 191

red phosphorus (100 grams) is intimately mixed with sulphur (260
grams). Portions of 30 to -10 grams are heated until they combine, in
the manner described under P 4 S 3 . The product is ground up and heated
in an evacuated and sealed glass tube to about 700 C. The contents
are powdered and extracted with CS 2 . They are recrystallised twice
from the same solvent and dried at 100 C. in a current of hydrogen.
The yield should be about 60 per cent, of the theoretical.

Properties. The compound has been prepared in two forms :

(a) Pale yellow crystals obtained by repeated recrystallisation from
carbon disulphide, in which they are only sparingly soluble (1 in 1.95).
Density 2-03.

(b) A nearly white substance obtained by rapid condensation of the
vapour, followed by extraction with carbon disulphide. This form
was more soluble in this solvent (1 in 30), had a higher density (2-08)
and a lower indefinite melting-point (247 to 276 C.). 1

The melting-point of the commercial sulphide was 255 C. 2 and that
of the recrystallised product 275 to 276 C. 3 The melting-point was
raised to 284 to 291 C. by repeated recrystallisation from carbon
disulphide. 4 Boiling occurs with partial decomposition a.t 513 to
515 C. 4 Other values which have been found are 520 C., 5 523-6 C. 6
The sulphide distils in a water-pump vacuum at 332 to 340 C..
probably with considerable dissociation (sec Ci Vapour Density * ). 7

The vapour density at temperatures slightly above the boiling-
point corresponded to simple molecules P 2 S 5 . 8 Later investigators,
however, found that it was slightly below the theoretical, being 208 at
300 C., and decreased at higher temperatures, down to 133 at 1.000 C. 9
The molecular weight in boiling carbon disulphide was [82 to 401, cor
responding approximately to double molecules (P 4 S 10 requires 444 ). 10

The compound does not glow in air, but is highly inflammable,
giving a mixture of the oxides. It was attacked only slowly by cold
water, but rapidly by hot water, giving phosphoric acid and hydrogen
sulphide. 11 It did not form addition compounds with bromine or
iodine. 12 It was converted into PSC1 3 by phosphorus pentachloricle
and by several other acid chlorides : 13

PoS 5 +3PCl 5 =5PSCl 3
PoS 5 -f 5POC1 3 = 5PSC1 3 + PoO 5
2PoS 5 -r 6SOCU = 4PSC1 3 + 3SO o ~ OS
P S 3 + SbCU = PSC1 3 - SbPS 4

d o -Jfc

Ammonia, in the gaseous or liquid form, was readily absorbed by
the pcntasulphidc giving a phosphorus hexammonio-penta sulphide,

1 Stock and Thicl, loc. cit.; Thicl, Zur Kcnntnis dr.s PlioKpliorpmtnsuIfi<lt,% Berlin,
1905.

2 Stock and Scharfenbeni, Her., 1908, 41, 558.

3 Stock, Joe. oil.; V. and C. Meyer, loc. cit.; HclJT, loc. ciL

4 Stock and Hcrscovici, loc. cit,. 5 Isnmbert, loc. cit.
fi Rccklinghausen, loc. cit. Sec also Goldschmidt, J3cr., J8S2, 15, 303.

7 Mai, Loc. cit.

8 Isambert, loc. cit.; Meyer, loc. cit.; Helff, loc. cit.

9 Stock and v. Bezold, loc. cit.

10 Stock and Thicl, loc. cit.

11 Fvckule, loc. cit.; Stock and Hcrxcovici, loc. cit.
:2 Hunter, Chtm. News, 1925, 131, 38, 174.

13 Carius, Annalen, 1S58, 106, 331; 1S59, 112, 80; Weber, J. praU. Chcm., 1859,
[1], 77, 65; Glatzol, Zeitsch. anorg. Chvn., 1893, 4, 186; 1905, 44, 65.

192 PHOSPHORUS.

P 2 S 5 .6NH 3 , as well as lower ammoniates. This compound may be
ammonium diimidopentathiopyrophosphate, S{P(SNH 4 ) 2 (NH)} 2 . 1

The pentasulphide dissolved slowly in cold alkalies, quickly in hot,
and gave salts of thiophosphoric acid. 2 Sodium sulphide also gave a
thiophosphate. 3

Uses of the Sulphides of Phosphorus. The pentasulphide of
phosphorus is used to replace the oxygen of organic compounds by
sulphur : thus ethyl alcohol gives ethyl mcrcaptan, and acetic acid
thioacetic acid. 4 The reactions, however, are somewhat complex ;
thus with ethyl alcohol the first product has been shown to be clicthyl-
dithiophosphate, SP(SH)(OEt) 9 , the mercaptan being produced by a
secondary reaction. 5 Phosphorus pentasulphide, boiling under atmo
spheric or other definite pressure, has been, recommended for use in
constant temperature baths in place of sulphur. The compound P 4 S 3 ,
which is one of the most stable sulphides in dry air, but resembles
phosphorus in some respects, is used as a substitute for this element in
the manufacture of matches. 6

Phosphorus Oxy sulphides. The compound P 4 O 6 S 4 was prepared
by heating together P 4 O 6 and sulphur in an atmosphere of nitrogen
or carbon dioxide :

P 4 6 +4S=P 4 6 S 4

It appears as colourless rectangular prisms which melt at about 102 C.
and boil at 295 C. The vapour density is 11-8 to 12-5 (air =1), which
corresponds to the formula given. It is very easily soluble in CS 2 .
In moist air it decomposes as follows :-

P 4 O 8 S 4 + CH 2 O = -il-IPOg + 4H 2 S 7

Another oxysulphide, also a derivative of P 2 5 , was produced when
II 2 S dissolved in POC1 3 containing carbon disulphide was allowed to
react for some weeks at C. Small needle-shaped crystals having the
composition P 2 O 2 S 3 then separated. They incited at about 300 C ,. and
sublimed in a vacuum with decomposition. The compound was de
composed by moist air with production of H 2 S.

2POC1 3 -f 3II 2 S =P 2 2 S 3 -r GHCl 8

Thiophosphites, Thiohypophosphates and Thiophosphates.

Since the sulpliidcs, oxysulphidcs and halosulphidcs of ])hos])horus
are completely hydrolyscd by water with evolution of IL>S, it is evident
that the thioxyaeids of phosphorus are unstable. Various salts of
these acids may however be prepared by using alkalies or ammonia
instead of water and by other reactions, of which a general outline only
is given, here.

Thiophosphites. These salts may be regarded as derived from
mono-, HoPSOo, di-, II 3 PS 2 O, and tri-thiophosphorous acids, TI 3 PS 3 .
They were prepared, with other products, by heating metals with a
mixture of sulphur and phosphorus, e.g. Ag 3 PS 3 , or metallic sulphides

1 Stock, loc. cit. 2 Bcrzdiu.s, loc. clt.; Stock and Jierscovici, Joe. at.

3 Glutzel, lac. clt. - 1 Kekule, he,, at.

5 .Pischtschiminko, J. Russ. Phys. Chtm. 8oe.., 1925, 57, Jl.

6 Scvene and Cohen, British Patent, 16314, 1898.

7 Tlior-Qc and Tutton, Trans. Chcm. Soc.. 1891. ^o. 1010.

PHOSPHORUS AXD SULPHUR. 193

with phosphorus sulphides, e.g. Cu 3 PS 3 from Cu 2 S and PoSg. 1 When.
P 4 S 3 was dissolved in alkalies phosphiiie, hydrogen and phosphorus
were produced. By evaporation in vacuo crystals of Na 2 H(PSO 2 ).2H 2 O
were obtained. "With an excess of sodium hydroxide, after long
standing, the normal salt Na 3 PSO 2 was deposited. When the alkali
was replaced by Na 2 S the evaporation in vacuo gave Xa 2 Ii(PS 2 O).2 2 -H 2 0. 2
An ammonium salt, (XH 4 ) 2 II(PSO 2 ).IL->O, has been prepared similarly
from P 4 S 3 and solution of ammonia after long standing at C.
Solutions of these salts gave a characteristic yellow to red precipitate
when mixed with a solution of lead acetate. When the salts were
heated or their solutions were boiled, H S was evolved and phosphites
produced.

Thiohypophosphates, for example those of copper, silver and
nickel, Cu 2 P 2 S 6 , Ag d P S G , and Xi PoS G , respectively, have been prepared
by heating the metals with phosphorus and sulphur. The ease with
which they are decomposed by water depends on the eleetroailimty
of the metal. Thus the zinc salt is decomposed by boiling water, while
the nickel salt, which forms grey hexagonal crystals, is scarcely ai i ected
by water. 3

Thiophosphates. The general methods of preparation recall
those used in the preparation of phosphates, sulphides being used in
place of oxides, with protection of the product from oxidation or
hydrolysis :

(a) The heating of metallic sulphides with phosphorus penta-
sulphide gives the most highly thionised thiophosphates. The poly-
sulphides which arc formed at the same time may be removed by
alcohol. From the solutions dithiophosphates may be isolated.

3M 2 S-rP 2 S 5 =2M 3 PS 4

(b) The heating of metallic chlorides with phosphorus pcnta-
sulphides gives thiophosphates together with PSC1 3 .

(c) By the action of alkalies on thiohalides. PSC1 3 is the chloride
of monothiophosphoric acid, and with alkalies it gives monothio-
phosphatcs.

By fusing crystalline sodium sulphide with phosphorus penta-
sulphidc and dissolving the product in a little water, crystals of tri-
s odium tetrathio-orlhophosphate were obtained.

3(Xa 2 S.OH 2 O)+P 2 S 5 =2(Xa 3 PS 4 .8lI 2 O)-f llHoO 1

The crystals were needle-shaped or tabular, in the monoclinic system.
The corresponding potassium salt, K 3 PS 4 , was obtained as a yellow
crystalline mass by fusing KC1 with P 2 S 5 .

These thiophosphates arc hydrolysed in dilute solution with evolu
tion of IloS. They can be dissolved unchanged in alkalies. With
salts of the heavy metals they give precipitates which are decomposed
on warmino 1 , o-ivino- II S. TJicv arc casilv oxidised bv nitric acid,

& to t> ~ ./ _ ./ ^ 7

potassium dichromatc, etc. with deposition of sul])lmr. When treated

1 Fornmcl, Ann. Ch ,-,n. /Vry.v., 181)0, [7J, 17, 088.

2 Lotnoinc, Co-nipt, rr./i.d., 1881, 93, 48!).

:5 Fcrraiul, loc. c. iL, and CompL wad., 18!)G, 122, C> 2\.; Priodcl, ibid., 1894, 119, 260.
4 Glatzel, Zafsch. anory. Chun,., 1893, 4, 180; 190"), 44, 05.

194 PHOSPHORUS.

with solutions of sulphides, e.g. BaS, the trithiophosphates were pro
duced, as represented by the equation

2Xa 3 PS 4 +3BaS+2lI 2 O=Ba 3 (PS 3 O) 2 +3Xa 2 S+2H 2 S

Dithiophosphates, M 3 (PS 2 O 2 ), were also produced by this reaction. 1

Other tetrathiophosphates which have been prepared by the foregoing
methods are Cu 3 PS 4 (CuCl and P 2 S 5 ), 2 Ag 3 PS 4 (AgCl and P 2 S 5 ), 2
Hg 8 (PS 4 ) 2 (HgS and P 2 S 5 ), Pb 3 (PS 4 ) 2 (PbCl 2 and P 2 S 5 ), Fe 3 (PS 4 ) 2
(FeS and P 2 S 5 ), Ni 3 (PS 4 ) 2 (XiCl 2 and P 2 S 5 ). (For thiophosphates of
As, Sb, Bi see this Volume, Part IV. 3 )

The preparation of barium trithiophosphate has been described above.
The magnesium salt, Mg 3 (PS 3 O) 2 .20H 2 O, was prepared by the action
of the tetrathiosodium salt on magnesium hydrosulphide. 1 The
ammonium salt, (XH 4 ) 3 (PS 3 O).H 2 0, was prepared by the action of
water on ammonium imidothiophosphate (see "Ammomates of P 2 S 5 ").
From a solution of this compound by interaction with salts of various
metals, e.g. CuSO 4 , their trithiophosphates have been prepared. 4

Trisodium ditiiiophosphate, Xa 3 (PS 2 O 2 ).llH 2 O, has been prepared
from P 2 S 5 and a rather concentrated solution of sodium hydroxide.
The solution was heated to 50 to 55 C. until the trithio-salt was
decomposed. The salt was precipitated by alcohol, and when re-
crystallised from water appeared as colourless six-sided prisms. 5 The
ammonium, salt, (NH 4 ) 3 (PS 2 O 2 ).2H 2 0, was prepared similarly from
aqueous ammonia and P 2 S 5 . From these soluble thiophosphates those
of the heavy metals may be obtained by double decomposition. 5

Trisodium. monothiophosphate was obtained from the solution of
mixed thiophosphates by heating to 90 C. in order to decompose
dithiophosphate. On cooling, the crystalline salt Xa 3 (PSO 3 ).12H 2
separated in six-sided tables, melting at 60 C. 5 This salt was also
prepared from PSC1 3 as follows :

PSC1 3 + 6XaOH - Xa 3 (PS0 3 ) + 3XaCl + 3lI 2 O 6

Ammonium dihydromonothiophosphate was prepared by the hydrolysis
of imidotrithiophosphoric acid, thus

H S [P(XH)S 3 ] +8H 2 = (NH 4 )H 2 (PS0 3 ) +2H 2 S *

The salt was repeatedly precipitated by alcohol and dissolved in water.
A similar or identical salt having the constitution SP(OH) 2 (OXH 4 )
was prepared by the action of phosphorus pentasulphide on acetoxime
in carbon disulphide solution. The part insoluble in CS 2 was extracted
with alcohol, boiled and crystallised from cold water in monoclinic
prisms."

From the alkali monothiophosphates those of other bases have
been obtained by precipitation.

A scries of pyrothiophosphatcs, M 2 P 2 S 7 (in which M is a divalent
metal), has been prepared by the methods already described. 8 The
free acids decompose immediately on liberation, but a mixture of them

1 Ephraim and Majler, Bar., 1910, 43, 285. 2 Glatzel, loc. cit.

3 Sec also \Yallsoni, Chem. News, 1928, 136, 113.

4 Stock, tier., 1906, 39, 1967.

5 Kubierschky, J. prakt. Chcm., 1885, [2], 31, 93.

6 Wurtz, Conipt. rend., 1847, 24, 288.

7 Dodge, Annultn, 1891, 264, 185. s Fcrrand, Joe. cit.

PHOSPHORUS AND SELENIUM. 195

has been prepared as a yellow oil having the composition H 4 P 2 2 So
by the action, of liquid hydrogen chloride on ammonium trithio-
phosphate at low temperatures. 1

Esters of the thiophosphoric acids have been prepared, e.g. ethyl
tetrathiophosphate, (CoHg)^^ 2

The compounds containing nitrogen as well as sulphur are described
in Chapter XIV., pp. 202-204.

Thio phosphates. Detection. Many of the reactions already de
scribed, such as the production of H 2 S and phosphoric acid when these
salts are treated with acids, will serve to detect the thiophosphates.
The alkali and ammonium salts are soluble, the others mostly insoluble.
Calcium, barium and strontium monothiophosphates, barium and
strontium dithiophosphates and barium trithiophosphate arc insoluble,
the other alkaline earth salts soluble. Thiophosphate solutions mixed
with alkali sulphides give a green colour with ferric chloride. Mono
thiophosphates give a blue precipitate with cobalt sulphate soluble in
excess of the cobalt salt, dithiophosphates a green precipitate soluble
in excess of dithiophosphate, and trithiophosphates a brown solution.
Several other tests have been described. 3

PHOSPHORUS AND SELENIUM.

When red phosphorus is melted with selenium in a current of
carbon dioxide a, reaction is said to occur without notable loss of
weight. The products are sensitive to moist air, phosphine and
selcniuretted hydrogen being evolved. The action of concentrated
alkalies or alkali selcnicles gives sclcnophospha/tes (q.v.).*

The solution of selenium in yellow phosphorus is also extremely
sensitive to moisture, and quantities of phosphine and hydrogen
selcnide arc evolved during the preparation, unless the selenium is
dried at a temperature which is high enough to convert the red partly
into the black modification. The melting-point of the phosphorus is
greatly lowered ; the solution containing phosphorus 4-4 parts and
selenium 3-0 parts melts at -7 C. On distillation of such solutions,
approximating to P 4 Sc and P 2 Se, phosphorus passes over with only
traces of selenium. The residue, or other mixtures containing more
selenium, when distilled in a current of carbon dioxide at a higher
temperature gave a. distillate of oily drops which solidified to a red
mass which had a composition closely approximating to P 4 Se 3 . The
second residue, a black vitreous mass, distilled at a red heat and had
approximately the composition P 2 Sc 5 . ;j

A compound P 4 Se ;J lias also been prepared by wanning 5-6 grams of
powdered selenium with 2-8 grams of yellow phosphorus in 30 c.c. of
tctralin (tctrnhydronaphthalciic). After the reaction has begun the
mixture is boiled for a long time in an atmosphere of carbon dioxide.
The liquid is decanted and immediately deposits an orange substance,
sometimes in crystalline form (needles). Further quantities extracted
with boilino- tctralin and washed with alcohol increase the yield to

- Michaelis, Annalw, 1872, 164, 39.

, 1S6-1, [1], 93, -130; Muthmann

196 PHOSPHORUS.

3-5 grams. The substance may be purified by extraction with a 1 : 1
mixture of carbon disulphide and petroleum ether. A crystalline
deposit forms in the extraction flask. The substance melts at 242 C.
to a dark red liquid with the formation of a slight sublimate. It is
inflammable, and slightly decomposed by boiling water with evolution
of the hydrides of selenium and phosphorus. It is oxidised powerfully
by cold nitric acid. The resulting solution was used for analysis, which
gave results agreeing fairly well with the formula P 4 Se 3 and also with
the analysis of Meyer, 1 being about 1 per cent, high in -phosphorus and
1 per cent, low in selenium. 2

Selenophosphates. By treating melts of the composition P 2 Sc 5
and P 2 Se 3 with concentrated KOH greenish to colourless crystals of
an octahedral habit are obtained having a composition correspond
ing to K 2 HPSe 3 O -r 2-J-H 2 O. When a solution of K 2 S is substituted
for KOH a thioselenophosphitc is crystallised, 2.K 2 S.P 2 Se 3 +oH 2 0.
When XaOH is used instead of KOH long greenish prisms of NayPSe^O
+ 10H 2 are obtained.

Sulphoselenides. When the selenides of phosphorus are melted
Avith sulphur, products are obtained which have the composition
P 4 SSe 2 (m.pt. 225 to 230 C.) and P 4 S 2 Se (m.pt. 190 to 200 C.). 3 *

i Loc. oit. 2 Mai, Bcr., 1926, 59, [B], 1888. .Meyer, Inc. cit.

* Note. Compounds of phosphorus and tellurium are described in this Series,
Vol. VII., Part II.

CHAPTER XIV.

PHOSPHORUS AND NITROGEN.

A-MiDo-pnospiroKors and -phosphoric acids are prepared by the action
of dry ammonia on the anhydrous oxides or oxylialides such as phos-
phorylchlorid.es. The imido-derivatives, in which =NII replaces =O,
can often be obtained from the a mi do-derivatives by heating. Other
methods are the hydrolysis of amido-esters and of phosphorus chloro-
nitrides (q.i:.).

Ami do- derivatives of PJiosphorous and Ortho-phosphoric Acids.

Diamidophosphorous Acid, (XH 2 ) 2 POII, was made, together with
diammonium phosphite, by the action of ammonia on phosphorous
oxide dissolved in ether or benzene :

P 4 6 - 8XH, = 3(NH 2 ) 2 POH -f- (XH.O^POH *

It is a white solid, which can be melted and sublimed with sonic decom
position, and combines with water, evolving much heat. It was
hydrolysed by hydrochloric acid giving phosphorous acid, which was
decomposed into phosphine and phosphoric, acid.

Phosphorus Triamide, P(XH 2 ) :J , is said to be formed by the
action of dry ammonia, on phosphorus tribromide at -70 C. It was
a yellow solid which decomposed at C. giving a brown substance,
diphosphorus triinude. P.->(Xri) :5 , and was further decomposed on
further heating into phosphorus, nitrogen and ammonia. 2

Monamidophosphoric Acid, XII 2 PO(OH) 2 , has been obtained
by several reactions, among which are the hydrolysis of cliphenyl
amidopliosphate by means of alkali, thus

and the action of nitrous acid on diamidophosphorie acid. The sodium
salt (which results in the former method) may be converted into the
lead salt, which may then be decomposed by hydrogen sulphide at
C. The acid is precipitated from the filtrate by alcohol in the form
of tabular or cubic crystals. It is very soluble in water, has a sweetish
taste, and is hydrolysed after long standing at room temperature or
rapidly in hot solution, into ammonium dihydrogen phosphate, thus

XII 2 PO(OIi). 2 -rlloO =XH 4 OPO(OH) 2 3

1 Thorpo and Tut.ttm, 7V ,,,.,. (;/>cm. ,W., ISO I, 59, 1027.

2 .HuLiol, Co////;/, rend., 100"), 141, l-o-".

3 Sf-nW,; A !(> ft I, (,;> J \MM T !!)X: I!)4. ifi. 12S. 140: 1898.20.740.

198 PHOSPHORUS.

Ammonium and hydroxylamine salts of this acid furnish interesting
examples of isomerism. Thus, ammonium hydrogen amiclophosphate,
XH 2 PO(OH)OXH 4 (prepared by double decomposition between the
silver salt and ammonium sulphide, with subsequent precipitation
with alcohol as needle-shaped crystals), is isomeric with hydrazine
phosphite, X 2 H 4 .H 3 PO 3 , while hydroxylamine amiclophosphate,
XH,I 3 0(OH)(OXH 3 OH) 9 is isomeric with hydrazine phosphate,
XJI^HoPO^ 1

The mono- and di-sodium salts and the corresponding potassium
salts have also been prepared. The salt XH 2 PO(OH)(OK) was ob
tained by hydrolysing chphenylamidophosphate with a boiling solution
of KOH, acidifying the cold solution with acetic acid and washing the
precipitate with alcohol. It forms rhombohedral crystals which are
very soluble in water. The solution is neutral and is gradually hydro-
Ivsed on standing. Lithium, silver and lead amidophosphates were
precipitated by adding salts of these metals to alkali amidophosphates.

Diamidophosphoric Acid, (XH 2 ) 2 PO(OIT), is capable of giving
salts of a tribasic acid, such as (XH 2 ) 2 P(OK) 2 (OAg). Silver salts have
been prepared in which hydrogen of the amido-group is replaced by silver,
yielding ultimately the dark brown explosive (X"HAg) 2 P(OAg) 3 . 2

The free acid was prepared by hydrolysing the compound
(XH 9 )oPO(OC G H 5 ) obtained from C1 2 PO(OC G H 5 ) and aqueous ammonia,
thus

C1 2 PO(OC C H 5 ) 7 (XH,),PO(OC 6 H 5 ) -> (XH 2 ) 2 PO(OH) -HC 6 H 3 OII

^-N 1 I 3 1J f,U

Triamidophosphoric Acid or Phosphoryl Triamide, PO(XH 2 ) 3 ,
was prepared by passing dry ammonia into dry phosphoryl chloride.
After washing out the ammonium chloride, an insoluble white powder
was left, which was scarcely affected by dilute acids or alkalies, but
Avas decomposed by fusion with potash. 3

The preparation of this compound has not been confirmed by other
investigators. 1

The products of further heating of the amides are described
on p. 202.

Amido- and Iniido- derivatives of Metaphosphoric Acid.
In metaphosphoric acid, O(PO)OH, or its polymers such as dimcta-

phosphoric acid, HO(POK >(PO)OII, the hydvoxyl may be replaced

\0/

by XII 2 , and the = O by =XII, giving amidomctaphosphorie acids
and imido metaphosphoric or metaphosphiniic acids.

The action of ammonia on phosphorus pcntoxide at low tempera
tures yielded, a substance, or mixture, which was easily soluble in water
and in alcohol.

The composition of the product corresponded to the formula
XH(PO)OII, which may be regarded as derived from (XII 2 )a ) O(OII )
by loss of ammonia. It may also be represented as phosphoryl

PHOSPHORUS AND NITROGEN. 199

hydroxylamine, (PO)XHOH. 1 The soluble salts gave precipitates with
salts of the heavy metals. 2

When the products of the action of ammonia on phosphorus penta-
chloride (q.v.) were well washed, the residue was found to have the
empirical composition of a phosphor} ! imidoamide, XH(PO)NH 2 , of
which it is probably a polymer. 3 On heating this compound, or other
amides of phosphoric acid, ammonia is lost and phosphonitril, PNO,
is left, thus

XH(PO)XH 2 =PNO +NH 3 4

This is a white powder which fuses at a red heat giving a black glass.
It is not affected by aqueous acids and alkalies, nor even by hot nitric
acid, but may be hydrolysed by fusion with caustic alkalies. On
account of these properties it is represented as a polymer (PXO). n of
high molecular weight and probably cyclic structure (see below). 5

POOH

Dimetaphosphimic Acid, [HO(XH) = P = O] 2 or HX< XH,

POOH

was considered to be identical with the diamide of pyrophosphoric
acid, O = |"(PO)OH.XH 2 ] 2 , and both formulas have been assigned to the
product of the action of ammonium carbamate on POC1 3 . G

Trimetaphosphimic Acid, [XIT(POOH)| 3 , was obtained by the
action of water on a sodium acetate ethereal solution of P 3 X 3 C1 6 (q.v.,
p. 205). The acid was soluble in water, and was obtained as a colloidal
substance on evaporation. It gave a series of salts. The trisodium
salt, Xa 3 PI 3 P 3 X 3 O 6 .4lI 2 0, crystallised in rhombic prisms below 80 C.,
whilst above 80 C. a monohydrate was formed. The trisilver salt
was precipitated in plates when silver nitrate was added to a nitric
acid solution of the sodium salt. A hexasilver salt, Ag, ; P 3 N ; >0 G , was
thrown down as a white precipitate when an excess of ammoniacal
silver nitrate was added to a solution of the trisodium trimctaphos-
phimate. On heating or long standing in solution, especially in the
presence of strong acids, the metaphosphirnates arc hydrolysed into
ammonium salts and phosphoric acid. Several cyclic structures are
possible for the acids ; the rnctaphosphimic ring contains the
radicals Nil PO(OII) , the nitrilophosphoric ring the radicals
X = P (OH)o- . On the former hypothesis, di- and tri-meta-
phosphimic acids arc :

PO(OH)

0(OH) H / \ n

J>XH and ! , respectively.

b(OH) ( H0) \

XH

1 Gladstone and Holmes, Trans. Cham. Soc., 1SC4, 17, 225; 1SGO, 19, 1; 1SG8, 21,
64; Mente, A ttnalf-n, 1888, 248, 232.
~ SchilT, loc. c.it.

3 Gcrh;irdt, A;ni. Oh.-un. /^//,v., 1846, ["^1, 18, 188, 204; .1847, [3], 20, 25f>.
1 Gcrliardt, loc. clt.\ Gladstone, Trans. C htin. Soc., "I8-")0, 3, 121; SchilT, loc. cit.
5 Gladstone. Tran.x. Chc-tu. Soc.. 1850. ^?. 121: 186!), 22, 15; Gladstone and Holmes.

200 PHOSPHORUS.

Tetrametaphosphirnic Acid, which was prepared by the hydro
lysis of P 4 X 4 C1 S , may be regarded as constituted in a similar manner,
forming an eight-membered ring. It crystallised in needles containing
two molecules of water. P 4 X 4 H 8 8 .2H 2 O, and was only slightly soluble
in water, still less so in acids. The solubility in 10 per cent, acetic acid
was about 0-5 gram in 100 grams solvent.

This acid is more stable towards hydrolysing agents than the other
metaphosphimic acids, and even resists the action of hot nitric acid
and aqua regia. There are two series of salts derived from a di- and a
tetra-basic acid respectively. Thus the dipotassium salt, K 2 H B P 4 X 4 8 ,
which forms prismatic crystals, on treatment with excess of potassium
hydroxide gives the tetrapotassium salt, K 4 H 4 P 4 X 4 O 8? which forms
sparingly soluble tabular crystals. Ammonium and sodium salts have
also been prepared. The tetra-argentic salt, Ag 4 H 4 P 4 X 4 O 8 , was formed
as a white precipitate on mixing silver nitrate with the acid, and the
octo-salt, Ag 8 P 4 X 4 O 8 , as a yellow precipitate from ammoniacal silver
nitrate and ammonium tctraphosphimatc.

Pentametaphosphimic Acid and Hexametaphosphimic Acid
were similarly obtained by hydrolysis in ethereal solution of the corre
sponding nitrilo-chlorides. Like the lower polymers they gave crystal
line sodium salts containing water of crystallisation, and anhydrous
penta- and hexa-siiver salts by the use of ammoniacal silver nitrate.
The free acids can be regenerated by the action of H 2 S on the silver
salts. The acids are more stable towards hydrolysing agents than is
trimetaphosphirnic acid.

These acids may be regarded as the lactams of amidopolyimido-
phosphoric acids, and the first stage in the hydrolysis probably consists
in the formation of these open-chain acids, thus

[HX(PO)OH] n -rlloO =II 2 X{IIX(PO)OIIj n ,(PO)(OTI) 2

The hydrolysis of hcptaphosphorus ehloronitride appears to yield at
once the hvclratcd open-chain compound of the type shown on the
right-hand side of the above equation, in which -n is 7. Ileptasodmm
and heptasilvcr salts of this acid have been prepared. 1

A.-ttiidc8 and hiiidcs of Condensed Plioxplioric. Ac/ids,

These may be regarded as derivatives of di phosphoric, acid (pyro-

/ PO(OII) 2

phosphoric), Lri- and tetra-phosphoric acids, etc., i.e. ()<^ ,

MK)(OII) 2

etc., by the substitution of = XI1 for ---() or of -XH 2 for hydroxyl
in tlicse open-chain compounds. The possibilities of isomerism arc
evidently very numerous, since cither the amido- or the imido- replace
ment gives [he same empirical formula.. The general method of pre
paration consists (a) in the hydrolysis of the melaphosphimie acids
already described, or (h) in heating, or fractional! v precipitating with
alcohol, the products of the reactions between FOCI., and XII. } .

Monamidodiphosphoric Acid, (XlIo)P.>().,(()!I) ;] , was made by
several reactions, amon.<_>\st which were the hydrolysis of a, solution of
diamidoui phosphoric acid (^/.z .), or as barium salt by saturating a

] Stokes, A-mcr. Clitm. ,/., 3SH:>, 15, IDS; 1S!U, 16, J^. J, 1-10; 180"), 17, 27">; ]89fj,
18, 021); 180S, 20, 74:0; idem, Zcit*c/i. a/to/y, Chun., 1800, 19, 4^.

PHOSPHORUS AND NITROGEN. 201

solution of pyrophosphoric acid with ammonia and adding Ba(OH) 2 .
The trisilver sale was obtained as a white precipitate.

Diamidodipliosphoric Acid was prepared by the action, of
phosphoryl chloride at low temperatures on ammonia in the presence
of some water, thus

2XH 3 + 2POC1 3 +3H 2 O =6HC1 - (XH 2 ) 2 P 2 O 3 (OH) 2

It may also be obtained by several other reactions. The diammonium
salt has been prepared in the crystalline state and various other salts
as precipitates. 1

Triamidodiphosphoric Acid, (NH 2 ) 3 P 2 O 3 (OH) 5 was prepared
by similar reactions. It formed a scries of salts in which it was mono
basic. !3ut in addition to the white monosilver salt, (NH 2 ) ;J P 2 O 3 (OAg),
an orange-coloured trisilver salt was prepared from ammoniacal silver
nitrate, to which the constitution NH 2 (NHAg) 2 P 2 O ; >(QAg) was
assigned. 1

Amiclo- and imido- derivatives of condensed phosphoric acid of still
higher molecular weight have bccu prepared in great variety by
Gladstone, and by Stokes. For example, monoimidotetraiiiido-
tetraphosphoric acid, XH=P 4 O 7 (XH 2 ) 4 , has been obtained by
heating the product of general reaction (b) (p. 200) to about 200 C.. 2
while tetramidotetraphosphoric acid, (HO) 2 P 4 O 7 (XH 2 ) 4 , was ob
tained by hydrolysing ammonium diamidotctraphosphatc either with
acids or with alkalies, thus

(XH 2 ) 2 P 4 7 (OJI)(OXH 4 ) 3 + HC1 = (XH 2 ) 4 P 4 O 7 (OH) 2 -r NH 4 C1 + 2H 2 O 2

The structures assigned were

/PO(XII )o /PO(NIIo)o

o< ~ ~ o(

>P(\ >PO(OII)

0< >NII and 0<

>P(K >PO(OH)

\ \

\PO(XII 2 ) 2 NPO(X1I 2 ) ?

Many other derivatives have been obtained. 3 Their general properties
have already been indicated.

The imidodiphosphoric acids arc isomcric with aimdodiphosphoric
acids. Monimidodiphosphoric acid,

PO(OH)

PO(OII)

was prepared by heating trimctaphosphimic acid, 3 dissolving in aqueous
ammonia, and adding a salt of magnesium, which precipitated mag
nesium ortho- and pym-phosphates, leaving a soluble magnesium salt
which on treatment with ammoniacal silver nitrate o-a.ve a crystal
line precipitate of XII - P 2 O 2 (OAg) ;i OII. This, when treated with
sodium chloride, gave a soluble non-crystallisablc trisodium salt.
A tetrasilver salt has also been prepared in two modifications as a

1 Gladstone and Holmes, luc. oil. 2 Gladstone, loc. cit. 3 Stokes, loc. cit.

202 PHOSPHORUS.

voluminous white precipitate which on boiling passes into a yellow
form. These may have the imido and the amido-structures (see
p. 200) respectively. 1

A dibasic imidodiphosphoric acid, which can be regarded as
derived from the last-mentioned compound by the loss of the elements
of water, was prepared by warming to about 50 C. a solution of
4 grams ammonium carbamatc in 10 grains of phosphoryl chloride. 2
Thus

3NHoCOOXH 4 + 4POC1 3 =2XH(POC1 ) 9 +3C0 2 +4XH 4 C1

NII(POC1 2 ) 2 + 3H 2 O = NH(POOH) 2 ~ 4HC1

The barium or ferric salt may be precipitated, and from the former the
free acid may be regenerated. Other derivatives were prepared by
similar reactions. 2

Nitrilophosphoric Acids.

These compounds, in which trivalent nitrogen bridges phosphoryl
radicals, are obtained by heating amido-compounds, with loss of
ammonia. The polymerised [XPO] W , phosphonitril, has been referred
to already (p. 199).

The potassium salt of nitrilodiphosphoric acid,

PO

// \

o

PO(OH)

was obtained by heating potassium triamidodiphosphate, the ammonium
salt by heating triamidodi phosphoric acid, and the silver salt by inter
action between silver nitrate and a suspension of the sparingly soluble
potassium salt in water. 3

Nitrilotrimetaphosphoric acid is said to be formed by heating
crude imidodiphosphoric acid to 290- 300 C., washing "out am
monium chloride, dissolving the residue in ammonia, acidifying and
filtering off the white precipitate. The solution contained this acid,

POOIL

o

POOIK

which yielded a crystalline sodium salt. 2

Aviido-, Imido- and Nitrilo-thiopliospliorw Acids.

These compounds are made by the application of a few general
methods :

(1) By the action of ammonia on thiophosphoryl halidcs.

(2) By the action of ammonia on sulphides of phosphorus.

(3) By heating ammonium chloride with sulphides of phosphorus.

Monothioamidophosphoric Acids. These are derivatives of
SP(OH).j in which the hvdroxvl groups arc successively replaced by
-NH 2 . " ~

1 Stokes, loc. cit. 2 Mentc, loc. cit. * Gladstone and Holmes, loc. cit.

PHOSPHORUS AXD NITROGEX. 203

The monamide, SP(XH 2 )(OH) 2 , was prepared from aqueous
ammonia and PSC1 3 . The solution, which contained XH 4 C1, gave
precipitates with salts of cadmium and lead. The salts of the alkaline
earth metals were soluble. 1

The diamide, SP(XH 2 ) 2 OH, was obtained by the action of gaseous
ammonia on PSC^. 1 It was also prepared by the action of ammonia
on PSF 3 . 2 In both cases the product was digested with water.
Hydrolysis proceeded according to the equation

SP(XH 2 ) 2 F-rH 2 O=SP(NH 2 ) 2 OH+HF

The solution contained a new acid radical, which gave precipitates with
salts of mercury, copper, silver and lead. The product derived from
PSCly, but not that derived from PSF 3 , gave precipitates also with salts
of zinc and cadmium. Xo precipitates were obtained with salts of
barium and calcium.

The triamide, SP(XI-I 2 ) 3 , was prepared by saturating PSC1 3 with
ammonia. It was a white solid of density 1-7. When heated it
dissociated into ammonium sulphide and sulphur, leaving phosphorus
in the residue, probably as " phospham," and was decomposed by warm
water giving H 2 S and ammonium thiophosphate. 3 It was only slightly
soluble in alcohol or carbon disulphide.

Thiophosphoryl Nitride or Nitrilomonothiophosphoric Acid,
SPX, was obtained by gradually heating together, from 180 to 328 C.,
P 2 S 5 and XH 4 C1 in. the quantities required by the equation

P 2 S 5 -r 2XH 4 C1 - 2SPX + 2HC1 -f 3H 2 S

It resulted also on. heating amido- and imido-thiophosphates in a
vacuum. It was a white powder, fairly stable to aqueous reagents,
but hydrolysed by water at 140 C., thus

SPX -;- 4II 2 = H 3 P0 4 -:-H 2 S ~ XH 3

On strong heating it gave P 3 X 5 (q.v.). 4 "

Di- and Tri-iniido- and -amido -thiophosphates. A great
variety of these compounds, chiefly in the form of their ammonium
salts, was obtained by the action of ammonia, usually in the liquid
form, on phosphorus pcntasulphicle. 5 Some of the ammonia could be
driven off by heating under reduced pressure, leaving the acid salts.

Gaseous ammonia at ordinary temperatures reacted with phos
phorus pcntasulphide giving a hexammoniatc, P S 5 .CXH 3 , and perhaps a
heptammoniate, P 2 S 5 .7XH 3 . The former may rearrange itself so as to
give tctrammonium diimidopentathiodiphosphate :

XII XII

! ii

(XH 4 S) 2 =P S P = (SNH 4 ) 2

The addition of another molecule of ammonia, either by means of
liquid ammonia or by saturating with the gas, yields a substance having

1 Gladstone and Holmes, loc. at.

- Thorpe and Rodger, Trans. Cho/,,i. >S oc., 1889, 55, 320.

3 Schiil, A-ttnalcn, 1857, 101, 303; Chevricr, Co-mpL rend., 1868, 66, 74.8.

4 Stock and Hoi mann, .Ber., 11)03, 36, 314, 898; Stock, Hofmann, ]\Iullor, v. Sckonthan
and Kuchlcr, Jlcr., 1906, 39, 1967. Sec also GlatzeJ, Luc. cit.

5 Stock and co-workers, loc. cit.

204 PHOSPHORUS.

the empirical composition of the heptammoniate, which, however, may
consist of equal mols of (a) diammonium nitrilodithiophosphate,
N = P(SNPI, 1 )o, and (b) triammoniuni iinidotrithiophosphate,

HX = P(SNH 4 ). V On treatment with liquid ammonia the nitrilo-
compound dissolved and could be obtained by evaporating the solvent,
while the imido-compound, being sparingly soluble, crystallised. The
nitrilo-compoimd lost one or more molecules of ammonia when heated
in a vacuum. When treated with KOII or NaOH it gave hydrated
dipotassium or disodium compounds as oils, the latter of which could
be made to crystallise. Characteristic insoluble salts were those of
lead (yellow) and of barium (white). The imido - compound,
HX P(SXII 4 ) 3 , was a white crystalline substance which deliquesced
in moist air and gradually lost ammonia. It was insoluble in all
ordinary solvents. It was hyclrolyscd slowly by water and smelt of
H 2 S. It lost one molecule of XH : > when warmed to 50 ( . in a vacuum.
By heating at gradually increasing temperatures from 00 to 180 C.
n an atmosphere of II S it was transformed into the free acid.

Imidotrithiophosphoric Acid, IIX =P(S1I) 3 . prepared as above,
was a yellow liquid having a density of 1-78, and like its ammonium
salt, was insoluble in all the solvents which were tried. It was dis
sociated only at a high temperature, but was partly hydrolyscd by
water, thus

HN = P(SH) 3 -i-;il-I 2 O=O3 J (OII) 2 (SXII 4 )-h k ->II 2 S

With liquid hydrogen chloride this acid formed the addition product
HN=P(SII) 3 .i-ICl/

Plioxpfiorus Halonilridex or A

The action of ammonia on phosphorus haiides gives cither ammoniates
or, by elimination of all hydrogen as ammonium chloride, halonitrides.
The amides, which should be formed as intermediate products, seem
to be difficult to isolate from the true 1 haiides, tilt bough the oxyhalides
(p. 109) and thiohalides (p. VI tf) readily yield such compounds.
Exceptionally, phosphorus diamidotiifluoride, PF ; ,(XH .,)>,, was
prepared as a white mass by the following re-action :

Chloronitrides.- --It was sliown by Lie-big in is:$2 that when PC1 5
was treated with dry ammonia and ihe product h.ealcd, a, while stable
sublimate was obtained. The empirical formula. FXl h, was assigned
to this substance by Laurent, while Gladstone and Holmes on account
of its high vapour density represented ii as ( PXC1 .,),. -

Preparation. Equal mols of P(1 5 and XH^C l may be heated to
150 C. in a. scaled tube which is opened occasionally to permit the
?scape of hydrogen chloride formed according to the equation

Hie product was extracted with petroleum el her and the insoluble
>art distilled up to nearly a red heat. The distillates after washing

1 Poulenc, Cuitipt. rcfi.d., J^sMl, 113, 7").

2 Licbiir, A-/}iirilf-ii, ls:?4, II, I .Si); Laurcni, ( (itiipL rend., ISfiO, 31, , $,")(}; (Jhul.^Loue

PHOSPHORUS AND NITROGEN.

205

with hot water, was redistilled under reduced pressure, and yielded
the fractions described below. 1 Alternatively, 120 to 130 grams of
ammonium chloride may be added to 400 grams of phosphorus penta-
chloridc dissolved in a litre of ,9?/m-tetrachlorocthane, and the mixture
boiled under a reflux condenser guarded by a calcium chloride drying
tube until hydrogen chloride is no longer evolved. This requires about
20 hours. The ammonium chloride is filtered off and the solvent dis
tilled away in a water-pump vacuum. The residue, about 220 grams
of a pasty material, is freed from oil by suction and by washing
with benzene at C. This leaves about 100 grams of a crystalline
powder which is rccrystallised from benzene and fractionated at a low
pressure. The fractions may be recrystalliscd from benzene.

When the powder is heated above 255 C. it changes to a colourless
transparent solid, while at 350 C. there is produced a colourless elastic
mass which resembles rubber in appearance and in its property of
swelling when placed in benzene. 2

MELTING- AND BOILING-POINTS OF THE PHOSPHORUS
CHLORONITRIDES OR PHOSPHONITRILIG CHLORIDES.

Formula.

(PNC1 2 ) 3

(PNCL),

(PXC1 2 ) 5 (PXC1 2 ) 6 i

belting-point, c C.

114

123-5

41 ! 91 1

Boiling-point (13 mm.), C. .

127

188

224 202 ;

Boiling-point (760 mm.), G C. .

250-5

328-5

Polymerises Polymerises ;

Triphosphonitrilic Chloride, P 3 X 3 C1 6 , forms large rhombic
crystals of density 1-98. Its properties arc typical of those found in
the scries. It is easily soluble in the usual organic solvents, also in
glacial ace-tic acid and sulphuric acid, undergoing reaction with the latter.
It also reacts with many organic compounds containing hydroxyl
groups alcohols, phenols, etc. Aniline when added to the benzene
solution gave a dianilidc, X P(XII.C, ; LI 5 ) 2 . Ammonia when passed
into a. solution of P :J X.jC l in carbon tetrachloridc gave needles of a
chloroamicle, possibly P 3 X T .jCl 4 (NH 2 ) 2 , which was insoluble in organic
solvents. Liquid ammonia gave a white solid hexamide, P 3 X 3 (XHo) 6 . 3
Hydrolysis proceeds when an ether solution is shaken with water,
with production first of P,X 3 CI 4 (OIl)o, then of trinictaphosphimic
acid, |XH(POOI!)J : > and 1IC1, and finally ammonium phosphate.

Tetraphosphonitrilic Chloride, P 4 X 4 C1 S , forms colourless prisms,
density 2-18. The molar weight was determined by vapour density
and depression of the freezing-point of benzene. Solubility relations
are similar to those of the tripolymer. An ocloanilldc., {XP(XHC (5 II 5 ) 2 J- 4 ,
has been prepared. 4 Like the trinitrilic chloride it was scarcely
affected by water alone, but an ether solution gave first an hydroxy-
chloridc and then tctrametaphosphimic acid, [Xil(POOII)J. 1 .2lI 2 O.

1 Slokcs, Amcr. Ckf-.rn. J., 1895, 17, 275; 1897, 19, 782.
- SJchenek and Corner, Btr., 1924, 57, B, 1343.
3 Bcsson and Ilossct, Co nipt, rcvd., 1900, 143, 37.

206

PHOSPHORUS.

Pentaphcsphonitrilic Chloride, P 5 X 5 C1 10 , was also crystalline.
The formula was established by analysis, and by molar weight in
boiling benzene. The chloride was hydrolysed in ether solution giving
pentametaphosphimic acid.

Hexaphosphonitrilic Chloride, P 6 X 6 C1 12 , forms long prismatic
crystals. The formula was established by the methods used in the
case of P 5 N 5 C1 10 . Hydrolysis takes place rather more readily, since
hydrochloric acid is evolved when the chloride is kept in moist air.
Hydrolysis in ether solution gave hexametaphosphimic acid.

" Heptaphosphonitrilic Chloride, P 7 X 7 C1 14 , was a liquid which,
after solidifying, melted at-18 c C. ; otherwise its properties were
similar to those of the other chloronitrides.

When strongly heated these compounds leave an inert residue of
XPO (q.v., p. 199).

Bromonitrides or Nitrilic Bromides. These compounds have
formulae similar to those of the chloronitrides, i.e. (PNBr 2 ) riJ and were
prepared by analogous reactions, i.e. by the action of ammonia on
phosphorus pentabromide.

Triphosphonitrilic Bromide, (PXBr 2 ) 3 , formed rhombohcdral
crystals which melted at 188 to 190 C., were insoluble in water but
soluble in organic solvents. 1

Structure of Halonitrides. On account of their stability towards
heat and hydrolysing agents, as well as the requirements of valency,
cyclic formulae have been assigned to the halon it rides in which the
rings are composed either of >X PC1 2 or of >X and >PC1 2 alternately. 2
Thus the tri-compounds may be represented by

(a) CUP X X POL (b) PCI 2

/\

or X X

PC1 2 C1 P PClo

~ \/

It has been supposed that the angle of least strain of the rings or
polyhedra is 135, which is most closely realised in the t.etra-eompound,
which is also the most stable of the series. The structure assigned
will determine that of the corresponding nietaphosphimic acid which
is produced by hydrolysis. Dhnetaphosphhnic acid, if its existence is
admitted, could not be cyclic according- to formula (a). Formula (b)
is adopted in describing these compounds.

Phosphorus Nitride or Triphosphorus Pentanitride, P ; ,X 5 .

A compound which appears to have this composition has been obtained
by several methods :

(a) By passing the vapour of phosphorus penta chloride in a current
of nitrogen over heated magnesium nitride. 3

1 Bcsson, G (J7npl. re.n.d., 181)2, 114, 1204, 1-180.

2 Wichelhaus, tier., 1870, 3, 103; Stokes, /or,, n t.

PHOSPHOR-US AXD NITROGEN. 207

(b) The black substance produced by the reaction, between liquid

ammonia and phosphorus in a sealed tube gave an analysis
which agreed fairly well with the foregoing composition. l

(c) By saturating the pentasulphidc, P 2 S 5 , with pure dry ammonia

at ordinary temperatures, and heating the product in a current

of ammonia at 850 C. 2

The product is described as a powder, white to dark reel in colour
according to the time of heating at 250 C. The density was 2-5.
The nitride was tasteless, odourless, and chemically inactive at ordinary
temperatures. The heat of formation (from white phosphorus) is
given as -81-5 Cals. per mol. 3 The molar heat of combustion was
474-7 Cals. (at constant pressure). The nitride dissociated into its
elements in a vacuum at about 760 C. 4 It was reduced to phosphorus
and ammonia by hydrogen at a red heat, and burned when heated in
oxygen or chlorine. It was hydrolysed by boiling water, thus

P 3 X 5 -f 1 2H 2 = 3H 3 P0 4 -f 5XH 3

It acted as a reducing agent on metallic oxides and was decomposed
by many metals from 80 C. upwards, giving phosphides of the metals.

1 Stock and Johansen, Bar., 1908, 41, 1593.

2 Stock and Hofmann, Bcr., 1903, 36, 314; Stock and Griinebcrg, ibid., 1907, 40, 2573.

3 Stock and Wrede, Ber., J907, 40, 2925.

4 Stock and Gruneberg, loc. cit.

CHAPTER XV.
PHOSPHATIC FERTILISERS.

OCCUKRCNCE AND CIRCULATION OF PHOSPHORUS.

Mineral Phosphates. Practically all the phosphorus in the ten-
mile crust of the earth is present in the lithosphcre, of which it forms
0-157 per cent., 1 and is combined as phosphates of many bases. Com
pared with other acidic and basic oxides phosphoric anhydride is
eleventh in order of abundance, falling immediately below titania
(1-050 per cent.) and above carbonic anhydride ((HOI per cent.).
On (.he average igneous rocks contain 0-299 per cent, of phosphoric
n rili yd ride, which is greater than the percentage in sedimentary rocks
generally, and about three times the proportion found in average
limestones. The mineral apatite, which is widely diffused in the deep-
seated igneous rocks, is only slowly attacked by atmospheric weathering,
but in the course of ages it and other phosphatic igneous rocks gradually
dissolve as phosphates of calcium, iron and aluminium, 2 3 and become
changed into the carbonated or hyclrated secondary phosphate rocks.

Phospha.fes occur in rocks of all the geological epochs. Apatite is
associated with granites a.nd gneisses.

Pala-o/.oic phosphorites (eoprolites) have been found in England
and (Jcrmany. In the Mcscr/oie epoch phosphorites occur in the
Triassir, .Jurassic and (Yefa.ceous formations. The 1 tertiary phosphate
deposits in the United Slates of America and X. Africa, are the most
o\ie!isi\e and valuable in the world. Quaternary deposits include
fossil bones, I he guanos and phosphogiuvnos. The high-grade second
ary deposits which arc used as sources of fertilisers and of phosphorus
ocncrallv have no doubt been segregated by processes in which animal
life luis played a large part. Thus the skeletons of marine animals
and organisms collecting on the floor ol the ocean arc dissolved in areas
conianuno- a high concentration of carbon dioxide; their component
phosphates are ivprecipif at ed on shells, or by ammonia, derived from
(lie deeav of nitrogenous matter, and form concretions of tribasic
calcium pho.sphat e. K :>> (i The small quantities of phosphates which are
\\idelv present in limestones 7 and dolomites may under certain condi
tions "be concentrated by the leaching out of the calcium carbonate

( larl.r and U M.-.hiii . ion, / /<" . \<il. ArtifL ,SV/., I .X.A., \ l .) 2 2, 8, H)S. sjoc also Clarko,
"/){(( "I fit "< In int- *tnj, " V\ :i>hiriLii<Mi, 1 JL O.
:- Limi-n-n, />"// <!<l , !!):_:>, 1 8, 1 I!).

, . 1 nn r. -I. Xf/., I ( .H(i, [ 11, 42, ^S.~>.
r,t.

I^-nanl, " I ><-r /,-*< rt Dcpoxit.*" (London, |S!)J), p. . W7.
/. Kmj. l!h<-ii). y l!)l?i, 40, ;>!) r r.
ntnx. Antcr. //<*/. Miti. Kn<j., KSiKJ, 21, l. Ji).

PHOSPHATIC FERTILISERS. 209

in the form of bicarbonate. All sedimentary deposits which consist
of the remains of animals or plants must contain phosphate. The
breaking down of these deposits disseminates the phosphatic material
in the soil. These deposits are largely derived also from the gradual
solution and subsequent deposition of widely diffused particles of
apatite which are a constant constituent of igneous rocks. Granite
contains 0-6 per cent., basalt 1 per cent, and gneiss 0-25 per cent, of
phosphoric oxide on the average. Fertile soils contain 0-2 to 0-5 per
cent, of phosphoric oxide, poor soils about 0-1 per cent. Some phos
phate must be present in a soil which supports any flora. The plants
use these supplies mainly in their seeds, which are eaten by animals,
and the phosphorus subsequently segregated mainly in the nerves,
brain and bone. It is then partly returned to the soil as animal remains.
Phosphorus is not of course lost in the same way as combined nitrogen,
by decomposition, since phosphorus compounds which are likely to be
formed in nature are non-volatile. But considerable quantities of
dissolved phosphates find their way to the sea, and this occurs especially
under a system of water-borne sewage. The loss thus incurred is an
additional argument in favour of the treatment of sewage with recovery
of all fertiliser values.

Ordinary sea- water may contain from 0-06 to 0-07 milligram of
P 2 O 5 per litre, 1 the amount varying with the season. This supply is
drawn upon by diatoms and algrc, and returned when they decay. The
supply is also continually supplemented from rivers, etc. 2 - 3 The algae
are devoured by molluscs and crustaceans, which in their turn supply
food to animals higher in the scale, 4 until finally, as the bodies of fishes,
the phosphorus is assimilated by sea-birds, who return some of it to
the land in their excrement. This ultimately becomes guano, and the
phosphate may then be converted into phosphatie limestone. The
remainder of the phosphate from these and other sources accumulates
on the bottom of the sea as a mud which contains 3Ca, 3 (P0 4 ) 2 .CaF 2 , as
well as Ca 4 P 2 O 9 .4l.I 2 and Ca :J P 2 O 8 .H 2 O, derived from minerals and
animal remains. 5

Assimilation by Plants. It is probable that plants obtain all
their phosphorus from phosphates. Organic compounds containing
phosphorus, like the phosphoprotcins, are rapidly decomposed by soil
bacteria, and the phosphoric acid combines with the bases in the soil.
The assimilation of ph.osph.orus from phosphates which arc insoluble in
water is probably aided by acid secretions from the root-hairs, and also
perhaps by the carbon dioxide exhaled during the respiratory process.
Soluble phosphates are quickly assimilated. The absorption of H 2 P0 4 ~"
ion by a growing plant may be demonstrated by a fall of acidity. If
the plant absorbs the base as well (i.e. lime), the acidity or hydrogen-
ion concentration of the soil is maintained, and phosphate thus remains
in solution. This is, of course, only one of the numerous reactions by
which, the acidity is regulated. A difference in the lime requirements
may thus account for the difference in the availability of phosphatic
fertilisers for different plants. This theory will also account for the
greater availability of insoluble basic phosphates when applied to

1 Matthews, /. Marine, ttiol. A^oc., 1917, n, 122, 2oL

2 Gill, ibid., 1927, 14, ]0~>7. :! Atkins, ibid., 1920, 14, 447. ; Limlgren, /oc. at.
5 .Basset, Zcitsch. anorg. Chnri., 1908, 59, 51.

r> Annual Reports of the Chemical Kocitty, 192G, 23, 217, and 1927, 24, 237.
VOL. vr. : ii. 14

210 PHOSPHORUS.

soils which lack lime, and thus confer on the phosphate a potential
acidity which is due to the demands of vegetation for this base. The
demands are greatest in the case of legnminosse (beans, etc.), brassiere
(cabbages, etc.) and roots, and especially potatoes and beetroot.

The" general effect of phosphates is to favour the formation and
ripening of seeds, and in this respect it acts in the opposite direction to
combined nitrogen, which favours the growth of stalks or straw at the
expense of seed or fruit.

The concentration of phosphorus in vegetable matter is not high,
being rather less than 0-1 per cent, in dry fodder, but much higher
about I- per cent. in grains. The phosphates assimilated by plants
supply the loss of phosphorus eliminated in animal metabolism, and
which, in the case of human adults, amounts to 3 or 4 grams of phos
phoric anhydride a day. The reserve of calcium phosphate present in
the bones weighs about 2 kilograms. 1

From the earliest ages the natural circulation of phosphorus has
been altered and controlled by farmers. The systematic return of all
kinds of excreta to the soil is still the basis of the intensive cultivation
practised in densely populated areas of India and China, where the soil
bacteria arc so active at the favourable temperature prevailing that
the nitrogen and phosphorus become available almost at once for
another crop. The return of bones to the soil is a less ohvious form of
economy, partly because when in the massive form these disintegrate
very slowly.

After the demonstration of the chemical basis of agriculture by
Liebig in 1 8 !(), and others, bones were recognised as essential on
account of their high phosphorus content. Great quantities of bones
were imported into Kngla.nd for this purpose in the first quarter of the
nineteenth century. Later, they were largely superseded by the
highly concentrated Peruvian guano or by superphosphate, which arc
more readily available to the plants. Bones, however, when finely
ground, and after the extraction of fat and of gelatin by steaming, still
retain their place as a. slow fertiliser in schemes of manuring. A typical
analysis of raw bones shows

Moisture . . . . . .12 percent.

Organic matter . . . . .28 ,,

Fat 10

Calcium and magnesium phosphates . . 4-1- ,,

Calcium carbonate, sand, etc. . . 5 ,.

if a good deal of the organic protein (ossein) has been left in the bone,
as is the case when the fat. has been extracted by solvents, and not by
steaming, the resulting bone-meal quickly decomposes in the soil, the
phosphoric acid being made partly soluble by the decomposition pro-
duets of the proteins. Such a. bone-meal will contain (approximately)
If) per cent, of calcium phosphate, 1-5 per cent, of magnesium phos
phate and o\ er ;5() per cent, of organic matter.

The question of availability is largely one of solubility. It was
surest cd by Licbi" 1 that bone-dust should be rendered soluble 1 by
treatment witb sulphuric acid. Hut the action of the acid on the
protein matter makes t be product viscous and difficult to dry. Hone
superphosphate is more easily made from a de^-elat inised bone-dust

1 Si-e further, p. 4.

PHOSPHATIC FERTILISERS.

211

or from bone-ash. This latter product was formerly imported in. large
quantities from South America, and contained from 65 to over 80 per
cent, of calcium phosphate. The ash may be completely dissolved in
an excess of hydrochloric acid, and the calcium monohydrogen phos
phate then precipitated by careful addition of lime. This process is
also used to recover phosphate of lime from the acid liquid which is
obtained as a by-product in the manufacture of glue from bones. The
phosphate of lime so prepared is fairly free from impurities, and may
of course be made soluble again by the addition of more acid :

Ca 3 (P0 4 ) 2 + 4HCl=CaH 4 (P0 4 )o+2CaCU
CaH 4 (PO 4 ) 2 + Ca(OH) 2 =2CalIP0 4 +2H 2

The chemical exploitation of bones thus led by a gradual transition to
the artificial fertiliser or mineral phosphate industry which will now
be described.

Sources of Phosphates. The most available and most exploited
sources of phosphorus and its compounds at the present day are the
phosphatic rocks, or phosphorites, which consist of tribasie calcium
phosphate associated with calcium carbonate, alumina, magnesia, etc. 1
Phosphates of alumina are also useful. The production of these
secondary rocks from the older rocks has already been mentioned
(p. 208). Although the apatites themselves, as pure minerals, contain a
high proportion of phosphoric anhydride, they are difficult to decompose,
and are admixed with other minerals of a still more refractory nature.

There arc many other possible sources of phosphates in which the
acid is combined with the common bases. Thus there are nearly loO
minerals which contain 1 per cent, or more of phosphoric oxide. 2 In
the following table is given a small selection of those which are of
special interest :

MINERALS CONTAINING PHOSPHORUS.

TABLE I.

Xarnc, Occurrence, etc. Chemical Composition. Crystal System. Density.

Apatite. . . . 3Ca 3 (L ) O d ) 2 .Ca(Cl or F) 2 Hexagonal 3-16-3-23

Igneous rocks and mcta-
morphLc limestones.

Pyromorphitc . . ; 3Pb 3 (I > 0. 1 ) 2 .PbCl 2 Hexagonal 6-5-7-1

Upper levels of lead m i ncs.

Wavellito

Fissures in slate.

Vivian itc . . .

Some iron (copper and ,
tin) ores and as earthy -.
mineral.

2Al. i (OH) a (P0. 1 ) 2 .9.H 2 Rhombic

Fe 3 (PO,) 2 .8H,,0 Monoclmic

Struvite
Guanos.

.MgXHjPO.j.GH.O

Orlhorhombic

1-68

Turquoise . . . Alo(OH) v PO,.HoO or i Amorphous with , 2-72
Trachyte or breccia. 2Af(OH) 3 .4AlP0. 1 " .9H 2 . crystal granules I

1 See analyses, p. 213. 2 Phillips, Trans. Amer. Inst. Mm. Eng., 1893, 21, 188.

212

PHOSPHORUS.

The next table illustrates the great variation of basicity and
hydration shown by phosphoric acid in nature, and also of the bases
with which it may combine. Minor constituents are omitted for the
sake of brevity. When the crystalline system is not stated the
mineral is amorphous or massive.

MINERALS CONTAINING PHOSPHORUS.
TABLE II.

Stercorite

XaXII 4 HP0 4 .4H 2

Monoclinie

Bobierrite

M<r 3 (P0 4 )o.3HoO

Launayite

Mg 3 (NH 4 ) 2 H 4 (P0 4 ) 4 .8ir 2

Triclinic

Monet it e

CaIIPO 4

Monoclinie

Brushite

CaHPO 4 .2H,0

5;

Cellophane

Ca,(P0 4 ) .IIoO

Isoclase

Ca 2 (6lI)P0 4 .2H O

Monoclinie

Dihydrite

Cu(CuOH) 4 (P0 4 )

Triclinic

Libethinite

CuPO 4 (CuOII) "

Rhombic

Tag elite

CuP0 4 (CuOii).ir o

Monoclinic

II ope it e

Zn 3 (PO 4 )o.4lI 2 O

Rhombic

Variscite

AlPO 4 .2HoO

?;

Zepharovichitc

A1P0 4 .:3II 2

Callainite

A1P0 4 .2JI1

Callaite

Alo(OI-I) 3 P6 4 .()II 2 O

R/mmbic

Augelite

A1 2 (OIT) 3 PO 4

Monoclinie

Sphccrite

Al 5 (On) 9 (P0 4 ) 2 .12lU)

Evan site

AUtoii^.AiPOj.Girx)

Kraurite

Ft^on^pOt

Rhombic

Ludlamitc

Fc 7 (OH)o(P0 4 ) 4 .Sir o O

Monoclinie

Monazitc

CeP0 4

Triclinic

Xcnotime

YP0 4

Tetragonal

A ut unite

(UOo)oCa(PO 1 ) .8lL>O

Rhombic

Boriekite

CaFc^OIiyPO^.^llX) !

Cirrolite

Ca 3 Alo(OH),(Pb 4 ),"

Triphyllitc

(Mn,Li,Fc)PO 4

Rliombic

Amblygonite

Al(Li)PO 4 (F,OII) i

Triclinic

Chalcosidcrite

(Al, Fe)o(FeO) 4 .Cii(PO 1 ). 1 .SlL ) () :

Iron ores often contain phosphates which arc reduced during t.lui
smelting process, the ])hos])horus passing into the iron as phosphide
and being again eliminated as basic, calcium phosphate in basic sla<>-
(q.v., p. 216). 1

The phosphates of lime are the most valuable naiural fertilisers
and raw material of the fertiliser and phosphorus industry, which
uses also to a less extent phosphates of aluminium and the "apatites.
Over 80 per cent, of the easily decomposiblc phosphorit.es mined arc
used in the preparation of superphosphate or other fertilisers (H):$0).

The Composition of Phosphorites. Phosphoric anhydride,
in the form of tribasie calcium phosphate, forms about 65 to Vl) per

1 See also this Scries, Volume IX., Part, 1.1.

PHOSPHATIC FERTILISERS.

213

cent, of a rock suitable for use in the fertiliser industry. There is
present, in addition, an excess of calcium carbonate, also ferric oxide
and alumina, silica (2 to 8 per cent,), organic matter and moisture
(2 to 3 per cent.). The following analyses furnish a comparison
between the principal constituents of the raw materials. Complete
analyses are given in three typical cases of the most important classes.

ANALYSES OF PHOSPHATIC MATERIALS.

! Bone-ash . . ! 39-55 ; 52-46 . . . . j . . : . . \ . .

j Precipitated ! : :

: phosphate . 39-45 44-88 : . . . . . . : . .

i Canadian Ptock. 33-51; 46-14; .. ..>..!..

, Spanish Hock . ; 33-38 i 47-16 .. ..!....

; Flondan Rock . 33-61 48-08 5-54 1-20 1-38 229 7-15

, Algerian Rock . ! 30-38 49-53; 1-01 0-32 0-47
; Xauru Roek . 39-34 48- i3 .. .. ; ..

1-85

0-75 volatile on

ignition.
2 01 SO,.

ANALYSIS OF AMERICAN ROCK.

P.,0-. i CaO. MuO. AUV Fc,0 3 . ^ OS3 . 011

" " - " - j : - j Ignition.

SiO,. Other Constituents.

Anaconda Manul . :

44-2 0-47

1 20 0-53

7-20 5-()0 Xa.,0, 0-42; K.>0,
; : 14; S, 0-71; Cr,

005; V, 0-09; P,
1-10 ; H.,0, 1-0.

The Distribution of Phosphatic Rocks. Great Britain. The
deposits arc of historic interest only, in view of the abundant high-
grade rock which is imported. The nodular deposits of the Eastern
counties, known as coprolitcs, contain the remains of the teeth and
bones of fish and reptiles. The richer beds contain a satisfactory
percentage of phosphate, as is evident from the following analysis :

JLvine lie ins. Cambridge.

Calcium phosphate, per cent.
Calcium carbonate, per cent.

56-0
10-0

70-9
10-3

The fossil bone bed at Sutton (SulTolk) once contained 50 to 60 per
cent, of calcium phosphate, but the remaining deposits are of much
poorer quality.

The working of the English beds has long been discontinued, except

1 Laribun, hid. Eny. Chem., 1929, 21, 1172.

214 PHOSPHORUS.

that during the Great War some thousands of tons of coprolites were
mined at Trumpington, Cambridge, and in Suffolk.

Europe. Useful deposits are found in France, Germany, Czecho
slovakia. Poland, Belgium and Spain, the deposits of Estrcmadura in
the last-named country being inspected by Dr Daubeny as early as

1843.

France. Phosphatic limestones are found in the Pas de Calais,
Meuse and Somme regions, and the last-named deposits were among
the earliest to be worked. Specimens have been found which contain
up to 78 per cent, of calcium phosphate. Those from the Meuse and
the Ardennes contain about 40 per cent. A limestone with less than
30 per cent, of calcium phosphate is hardly considered worth using for
the manufacture of superphosphate. France also controls the output
of North Africa.

North Africa. The deposits of Algiers were discovered in 1873 and
were fully reported upon in 1886. They are of Eocene age and contain
58 to 68^ per cent, of calcium phosphate in a soft rock, together with
marl, considerable amounts of silica, calcium fluoride and chloride,
nodules of gypsum and almost pure limestone. The beds usually are
several feet thick and run continuously from Morocco to Egypt at a
distance of over 100 miles from the sea. Those at Constantino (Algiers)
are 120 miles from the port of Bona, and those at Gafsa (Tunis) 150
miles from the port of Sfax.

The potential resources in this region have not yet been fully
explored but are probably the greatest which have been discovered
up to the present. It has been estimated that there are 1000 million
tons available in Morocco. 1 This estimate has recently been increased
to 3000 million metric tons. 2

United States. The principal deposits are in South Carolina,
Florida, Tennessee, Arkansas, Utah and Wyoming. The South
Carolina deposits are of Miocene age and occur both as " land " and
" river " rock. They contain 25 to 28 per cent, of phosphoric oxide
and 35 to 42 per cent, of lime. They were the earliest to be exploited,
namely, from 1868 onwards, and in 1803 they furnished about one-fifth
of the world s supply. Since this date the production has declined,
while that of Florida has great!} increased. In 1913 Florida and
Tennessee together produced some 90 per cent, of the total output from
the United States of America. The hard-rock deposits of Florida are
of Tertiary age. and they run parallel to the coast for 141 miles.
After concentration by mechanical means they contain usually from
77 to 79 per cent, of calcium phosphate (more rarely up to 82 per cent.)
with 3 per cent, of oxides of iron and alumina, some calcium Jiuoride
and other constituents, and 3 per cent, of moisture. The best grades
of Tennessee rock were guaranteed to contain 72 per cent, of calcium
phosphate, and 65 per cent, is common. The soft rock is a phosphatic
clay. The river pebbles are dark grey to black and arc very cheaply
obtained by dredging.

Deposits are found also in. Canada, the Wext Indies , Mexico and
South America.

Oceanic Deposits and Guanos. Guano. This valuable natural
manure is produced from the excrement of sea-birds, and occa
sionally of other animals, which has been chemically altered by ex-
1 Pietvkowsky, Naturwiss., 1922, 10, 350. 2 Chemical Aye, 1931, p. 281.

PHOSPHATIC FERTILISERS. 215

posure. Peruvian guano has been mined for many centuries. That from
the Chincha Islands was used by the ancient Peruvians according to
von Humboldt, 1804.

Guano contains from 11 to 17 per cent, of phosphoric oxide, 11 to
19 per cent, of lime, up to 1 per cent, of magnesia, 3 to 35 per cent.
of nitrogen, about 2-5 per cent, of potash and 13 to 30 per cent, of
water. Hence it is almost a complete plant food.

Phospho- guanos. These deposits occur chiefly in oceanic islands,
situated in tropical latitudes, and have probably the same origin as
guano, but the changes have been more far-reaching, so that their
composition is transitional between the guanos and the phosphatic
rocks. By intense bacterial action the nitrogenous compounds have
been converted quickly into ammonia and nitric acid, and the soluble
nitrates and ammonium salts have been washed out by heavy rain,
or the breaking of high seas over low- lying atolls. The resulting
deposit contains usually less than 1 per cent, of nitrogen. The phos
phate of lime ranges from 60 to 77 per cent. When it is 50 per cent,
or less the deficit is usually composed of organic matter (loss on ignition)
or calcium carbonate, or both.

The Pacific Island deposits belong to this class and are found
chiefly on those islands which lie between Australia and Japan. The
Barker Island deposit, now exhausted, contained about 78 per cent,
of calcium phosphate and 6 per cent, of magnesium phosphate. Rich
deposits were also found on the Fanning Island and Makatea Islands in
the Paurnotu Group, Angaur Island in the Pclcw Group, etc.

The Australasian Dominions, Australia and Xew Zealand, largely
obtain their supplies from Nauru and Ocean Islands, the produce of
which was, after 1920, divided in definite ratios between the United
Kingdom, Australia and New Zealand. Nauru is a coral island over
200 feet high and covering an area of about 5,000 acres, a considerable
part of which consists of a deep deposit containing 80 to 87 (usually
86 to 87) per cent, of calcium phosphate, which probably has been
formed by the leaching of guano deposits into the coral limestone.
The phosphate is quarried out, leaving pinnacles of the harder limestone.
The reserves on the island are estimated at 80 to 100 million tons.
From 1013 onwards the island has yielded nearly 100,000 tons per
annum. The Ocean Island deposits arc of about the same quality,
and about 50 feet thick on the central table-land. The reserves are
estimated at 50 million tons, and the output for several years was
between 100,000 and 200,000 tons per annum.

Other well-known deposits are those of Christmas Island, also
llcdonda and Sombrero (West Indies).

The phosphates of the British Empire are described in an official
pamphlet. 1 Analyses of all the different types of phosphate minerals
have been collected by Fritsch. 2

The World s Production of Phosphate Rock. The amounts
of phosphate rock mined annually increased only slowly from the
beginnings of the industry in 1847 to 250,000 tons in 1869, then to
about one million tons in" 1887 and about seven million tons in 1913.

1 :; Phosphates, 1913-1919" Imperial Mineral Resources Bureau, H.A1. Stationery
Office, 1921.

2 JFntsch, "The Manufacture of Chemical Manures," Scott, Greenwood, 1920.

216

PHOSPHORUS.

After the great fluctuations during the Great War and post- War years,
the production had again reached four million tons in 1919 and seven
million tons in 1920, made up as follows (round numbers) :

Tons.
United States of America .... 3,000,000

North Africa 3,000,000

Oceanic Islands 500,000

Other Countries 500,000

Total

7,000,000 ]

The amounts, in round numbers, for the succeeding years (millions
of tons ) are :

1924
Less than 8

1925, 1926
Average 9

1

1927, 1928
Average 10 !

1929, 1930
Average 11

The greater part of the increase is due to the North African deposits. 2
The yearly production, from these sources is now greater than that
which is obtained from the North. American deposits.

It has been estimated that the available phosphate deposits would
last for a century, 3 but this estimate docs not fully take into account
the North African deposits (p. 214) or the proportion which will be
conserved and returned to the soil by future generations. The present
annual requirements of a great agricultural country like France or
Germany appear to be of the order of a million tons. 4

BASIC SLAG.

This is a by-product produced in the manufacture of steel from
pig iron which contains phosphorus (phosphide) (sec p. GO). 5 The
possibility of removing the phosphide dissolved in pig iron by carrying
out oxidation in a Bessemer converter lined with a basic instead of a
siliceous material was demonstrated by Snelus in 1872, by Thomas and
Gilchrist at Elacnavon in 1878 and at the Eston works in 3870. The

utilitv of the slag as a fertiliser was tested in the South and North of

"
England from 1881 by Wrightson, Somervillc, Middleton and GilehrisL

The converters, and afterwards the open hearths, in or on which
the pig iron containing phosphide * was oxidised, arc lined with lime
or magnesia. The ferrous phosphate produced by oxidation, instead
of being immediately reduced again by the excess of iron, is decomposed
by the lime according to the equation

Fc 3 (P0 4 ) 2 -r 4CaO = Cu 4 P.A, + ;3Fc

and the phosphate combines further with any calcium silicate or fluoride
which is present. The hard sJag is crushed, separated from inclusions
of iron, and then ground in a ball mill.

PHOSPHATIC FERTILISERS. 217

In the open-hearth process the slag may be removed by ladling or
tilting, when the phosphorus content of the iron has been reduced from
1 per cent, or over to about 0-2 per cent. This furnishes a high-
grade slag. A " new " slag by means of which the phosphorus content
is reduced to about 0-02 per cent, is of much poorer quality (see Table I.).

OPEN-HEARTH SLAG: HIGH-GRADE AND "NEW."

TABLE I.

Silica. ! Lime. Iron.

High-grade . 18-80 , 37-30 ; 7-80 18-54 ! 14-33 ; 77-39

New . . . I 9-40 : 51-30 14-00 ! 7-40 j 11-10 , 14-90 j

___ i i i I

In the ordinary process the slag is allowed to (low off continuously.
It then shows a diminution in phosphoric and silicic anhydrides and an
increase in lime and total iron as the carbon and phosphorus in the
metal diminish say from 1-77 and 1-30 per cent, respectively to 0-09
and 0-023 per cent, (sec Table II.).

OPEN-HEARTH SLAG : CONTINUOUS FLOW.
TABLE II.

Silica. : Lime. Iron.

Total Soluble : V , i
P ]> () * boluble

- 5 * -" P..O-.* i

At first . . 20-30 33-20 8-00 ! 17-08 15-30

89-92

After (U hours . 10-20 -1-7-80 14-70 10-85 1-GG 15-30 ,

The solubility of basic slag has been found to increase with increasing
calcium silicate. Some of the constituents other than phosphate have
value on certain soils which happen to be deficient in. these constituents.

Basic slag is a slow fertiliser ; the phosphate is not immediately
available as is that of calcium superphosphate. It is particularly
valuable for fruit trees, and for heavy grass-land, on which it develops
the growth of white clover and hence increases the amount of combined
nitrogen. It neutralises acid soils, and its beneficial effects extend

over manv years.

* iVote. Percentage of the total PO.-.

1 " c Jiiisic Slags: their Production and Utilisation in Agriculture," Trans. Faraday Sue.,
1921, 1 6 (ii), 2G3.

218 PHOSPHORUS.

SUMMARY OF PIIOSPHATIC FERTILISERS.

The chief varieties of naturally occurring or manufactured phos-
phatic fertilisers may be classified briefly as i ollows :-

(1) Natural nitrogenous phosphates such as guano, bone-dust.

(2) Finely ground phosphatic rock.

(3) Superphosphate of various grades with 16 to 20 per cent.

total phosphoric acid or with 8 to 10 per cent, of water-soluble
phosphoric acid.

(4) Double superphosphate with about 40 per cent, of soluble

phosphoric acid.

(5) Precipitated dicalcium phosphate.

(6) Basic slag or " Thomas phosphate."

(7) " Wolter phosphate," obtained by decomposing phosphate rocks

with calcium carbonate, sand, carbon and sodium sulphate in
a furnace. " Rhenania phosphate," obtained by decomposing
the rock with leucite or phenolite, potash or soda.

(8) Ammonium phosphates and superphosphates, which may con

tain also ammonium sulphates.

A scientific study of the various systems should determine the best
conditions for the various reactions between salts and acids. The
phosphates of calcium are the most important.

THE SYSTEM LIME AND PHOSPHORIC ACID.

Since the phosphorus compounds which arc used in the arts, as
well as phosphatic fertilisers, are derived from the decomposition of
phosphates of lime, and the interactions of these are also of importance
in biochemistry, a short account of the best investigated of these
compounds will be given here.*

The phosphates of lime which occur in nature or arc produced
during the course of manufacture of phosphorus compounds arc salts
of orthophosphoric acid. The hydrogen is replaced by calcium in
stages giving successively mono-, di- arid tri-caleium phosphate. Of
these the mono-calcium salt alone is freely soluble. The solids
deposited on evaporation, or obtained by double decomposition, arc
generally mixtures of the di-, tri- or more basic compounds, but pure
crystalline forms have been prepared, especially of the more acid
phosphates. The more basic phosphates are very sparingly soluble,
and the solubilities arc not definite. The solids arc not in equilibrium
with solutions of their own composition, but arc in process of trans
formation which is so slow that equilibrium is not attained in most
operations.

Tribasic calcium phosphate, Ca 3 P 2 O 8 , may be made by washing
precipitated calcium phosphate with ammonia, which dissolves any
excess of phosphoric acid above that required to form this compound.
It is a white earthy powder which retains water tenaciously, and also
adsorbs halides, bicarbonatcs and hydroxides. 1 It has also been
prepared from CaII 4 (PO 4 ) 2 by dissolving this in a large excess of water

* Note. In accordance with the general plan of this Series, full accounts of the
various phosphates will be found under the heading of the metal in the appropriate
Volume of this Series.

1 Bassett, Trans. Chem. Soc., 1917, in, 620.

PHOSPHATIC FERTILISERS. 219

and adding ammonia free from carbonate with constant stirring and
at such a rate that the solution is only faintly alkaline until the end of
the operation. The amorphous gelatinous precipitate is washed with
water by deeantation until the dissolved phosphate is reduced to a
minimum. Analysis of a dried sample gave a ratio P O 5 /CaO =0-835,
the theoretical ratio being 0-845. 1 Ca 3 (P0 4 ) 2 contains 54-2 per cent,
of CaO and 45-8 per cent, of P 2 O 5 . According to the analyses given
on p. 213, phosphate rock evidently is more basic than this, and often
contains much carbonate. It is considered probable that these rocks con
tain oxy-apatite, Ca0.3Ca 3 P 2 O 8 , hydroxy-apatite, Ca(OH) 2 .3Ca 3 P 2 O 8 ,
or carbonate-apatite, CaC0 3 .3Ca 3 P 2 8 , with usually a further excess of
lime or calcium carbonate. The composition of the solid phases formed
by long shaking of CaHPO 4 with Ca(OH) 2 passes the point correspond
ing to Ca 3 P O 8 , and becomes fixed only at a ratio which corresponds
nearly to Ca"(OH) 2 .Ca 3 P 2 Og. 2

Repeated extraction of Ca 3 P 2 O 8 with boiling water yields finally
Ca(OH) 2 .Ca 3 P 2 O 8 . 3 The preparation is more certain in the presence
of alkali. 1 The tribasic phosphate is suspended in a large excess of
water contained in a pyrex flask and boiled for long periods with alkali
free from carbonate, removing the supernatant liquid each day.
After several weeks the precipitate reaches a constant composition
which undergoes no further change, the ratio of P 2 5 /CaO (in grams)
being then 0-76. The hydrolysis is expressed by the equation

10Ca 3 (PO 4 ) 2 + GH 2 O-3[3Ca 3 (P0 4 ) 2 .Ca(OH) 2 ]-r2H 3 P0 4

Both the basic phosphate and Ca 3 (P0 4 ) 2 adsorb definite quantities of
Ca(OH) 2 . These quantities when plotted as functions of the concen
trations of Ca(OII) 2 have the usual form of adsorption isotherms and
therefore give no evidence of the formation of definite compounds,
1 gram of the basic calcium phosphate when in equilibrium with a
solution containing 1-099 grams of Ca(OH) 2 per litre adsorbs 0-0201
gram of the hydroxide. After 6 months of contact this amount is
increased to 0-0243 gram. 1

A hydrate Ca 3 P 2 O s .iI 2 O has been described as a hygroscopic
powder, but this also is not in equilibrium with a definite solution
but gives solutions containing greater proportions of phosphoric acid
and dissolves with hydrolysis, depositing lime. 4

Dicaicium phosphate, Ca 2 II 2 P 2 O 8 or CaHPO 4 , is the first substance
to be precipitated when calcium hydroxide is added to phosphoric acid.
It is formed by the interaction of mono- and tri-calcium phosphates,
and is then called " reverted phosphate." Thus

Ca 3 P 2 O 3 -r CaII 4 P 2 8 =2Ca 2 H 2 P 2 8

It is also deposited when any aqueous solution of calcium phosphate
is evaporated to dryness with hydrochloric acid. It occurs as an
anhydrous more soluble form and as a hydratcd less soluble crystalline
form (monoclinic needles). The solubility product [Ca^~][HPO 4 = ] is

Lorali, Tartar and Wood, J. Aitier. Chun. Xoc., 1929, 51, 1097.

2 J3a*sutt, Trim*. Cktut. Hoc., 1917, in, 620.

3 Wanngton, Trails. C/te-m. tioc., 1873, 26, 983.

220 PHOSPHORUS.

variously given 1 2 as 4 x 10~ 7 or 3-5 to 12 x 10~ G . This compound, like
the tribasic and indeed all the phosphates of lime, decomposes in con
tact with water giving a more acid solution and a more basic solid.
The original solid compound is in. equilibrium only with a solution
containing a higher ratio OL PO 4 /CaO. This is clearly shown in the
accompanying table.

THE COMPOSITION OF SOLUTIONS SATURATED
WITH CALCIUM HYDROGEN PHOSPHATES. 3

25 C.

40 C.

Solid Phases.

Concentration Grams per 100 Grams
Saturated Solution.

! CaO PA
. i 3-09 to 36-1 to

Ca.JI.PC3, .

! 0-83 2-39

CaHPO t -rCaHPO t .2.H.,0 . i 0-105 ! 0-417

CaHPOj.it-LO .

. : 0-070 to \ 0-166 to
0-040; U-093

CaO ; iU)-
1-77 to 42-4 to

CaO ! P,0.

0-636 to 58-08 to

36-8? 4-88; 33-2i

27-25 5-72- > 29-61 i

0-059,; i 0-153

Three quintuple points in this system have been determined by
Bassett 4 as follows : 5

EQUILIBRIA BETWEEN SOLID PHASES AND SOLUTIONS
AT THREE TEMPERATURES.

Solid phases as spt-ciiicd; solutions in .square brackets.

21 CaliPOj. 2 !!.,()-; (H 38Cat; ,(!*() ,),.( 1,() ^^ 1-07 !7Cai i i O,

; " " ; -j2-374!i,() : lOOOTP-.O., -i 0-0627CaOj

Changes during Neutralisation. - In tlic neutralisation of phos
phoric acid with lime there is only a. gradual increase 1 in the pll value
until more than one equivalent of iiine has been added ; that is until

PHOSPHATTC FERTILISERS. 22]

some 33 per cent, of the acid has been neutralised, corresponding to
the formation of CaH 4 P 2 O 8 . The pH value then begins to increase
more rapidly with further addition of lime and a precipitation of di-
calcium phosphate, Ca. 2 H 2 P 2 O 8 , may occur if suflicient time is allowed. 1
When 39 to -15 per cent, of the acid has been neutralised there is a sharp
drop in the ptl value, winch is due probably to the precipitation of
clicalcium phosphate from supersaturated solution. This not only
leaves the solution relatively poorer in hyclroxyl ions through the
removal of HPO 4 % since by hydrolysis

1IP(V ~- 1I-- -f OH" > H 2 PO 4 - ~ Oil-
but also diminishes the ratio CaO/P 2 O 5 in the solution, since a solid
corresponding to 67 per cent, neutralisation is being removed from a
liquid corresponding to 45 per cent. The precipitation may be delayed
tmtil about li equivalents of lime have been added and the pll value
has become 6-7. 2 Further addition of lime then produces a gradual
increase in alkalinity, absolute neutrality (j/H 7) being reached
after the addition of about 2 equivalents, i.e. at 67 per cent, neutralisa
tion. A slight further addition of lime then produces a sharp drop in
the alkalinity, which is not observed however when the .neutralisation
is carried out in the presence of dissolved sucrose. 2 This " kink " in
the curve is probably due to supcrsaturation. The process of deposition
with increase of acidity in the presence of precipitated solids would
probably continue much further if suflicient time were allowed, since
it has been calculated from the results of Jiassctt that the solution in
equilibrium with dicalcium phosphate or even with tricalcium phosphate
has a much greater acidity (])li approximately 5-5) than the solutions
in which these precipitates arc lirst produced. A continuation of the
titration with lime up to 3 equivalents (TOO per cent, neutralisation)
gives only a slight increase in alkalinity, which becomes somewhat
greater after the addition of 3 equivalents. In contradistinction then
to the alkalies and even baryta, and strontia, calcium hydroxide appar
ently does not give high alkalinitics when in the presence of precipitated
calcium phosphate. This is due not only to the sparing solubility
of Ca(OH) 2 , but also to its combination with Ca ;5 P 2 O s to give hydroxy-
apatite, 3Ca 3 P 2 O 8 .Ca(OII) 2 .

The practical significance of these observations is that phosphates
can only remain freely soluble in soils with a relatively high acidity
(pll less than 5-5) ; the solid present in contact with such solutions
is either Ca!I 4 P 2 () fi .II 2 O or CaoIIol o^a ni il finely divided and anhydrous
state. Neutral or even, faintly acid solutions (pll 5-5 to 7-0) will
contain but little dissolved phosphate, being in equilibrium with
CaHP0 4 .2lIoO, Ca,(PO 4 ) 2 or Ca(Ori) 2 .^a,P,O 8 , or a mixture of
these solids. The solubility of these solids is however sullicient for
the requirements of plants, since it is found that the amount of phos
phorus in the extract even of a rich soil is only of the order of 1 milli
gram per litre, while soils of average I ertilitv mav contain onlv 0-1

te> I " f" 1 / *j .

to 0-2 milligram per litre. The fact that this very low concentration
appears to be suflicient for the growth of plants makes it probable
that these are able to use insoluble phosphate, 3 as has also been pointed

1 Farnel!, J. ,SV;e. Chc.m. Ind., WiNi, 45, JUST.

2 Bntton, Trans. Chc /n. Soc., 11)27, p. 614.

3 Tidmorc, /. Amir. Soc. Ayron.., 1030, 22, 481.

222 PHOSPHORUS.

out by N. M. Comber and others. It is important that there should
be a sufficient reserve of phosphate in the soil which may gradually
become available. The removal of phosphoric acid by plants increases
the amount of basic phosphate and should be compensated by the
addition of an acid-producing fertiliser such as ammonium sulphate.
The value of phosphates in a really soluble form has long been
recognised.

The Acid Phosphates. On account of the relatively higher
degree of dissociation of sulphuric acid it is capable of liberating
phosphoric acid from phosphates, and the reaction is favoured by the
low solubility of calcium sulphate.

Ca 3 P 2 O 8 +3H 2 SO 4 =3CaSO 4 + 2H 3 PO 4

This probably is the first stage of the reaction by which superphosphates
are produced. It is succeeded by

Ca 3 P 2 8 -f 4H 3 PO 4 =3CaH 4 P 2 O 8

When two mols of sulphuric acid are added to one of the tribasic
phosphate more than 96 per cent, of the phosphate is rendered freely
soluble in water, superphosphate being formed as follows :

Ca :3 P 2 8 -f- 2H 2 S0 4 = 2CaS0 4 ~ CaII 4 P 2 8

In practice it is arranged that a little of the tribasic phosphate is left
undecomposcd, and this then reacts according to the equation

Ca 3 P 2 O s -r CaH 4 P 2 O 8 =4CaHPO 4

The amount of freely soluble phosphate is thus reduced. When the
superphosphate is brought into contact with water the insoluble part
is increased by the production of a solution containing from 12 to
5-J- times as much phosphoric acid as lime (see p. 220), or about 4 times
as much when CaHP0 4 is present as a solid. The presence of CaS0 4
in commercial phosphate does not much alter these ratios, as is shown
by the following solubilities : :

Solid Phases. I*2^f,> grams/litre. CaO grams/litre.

CaSO 4 .2HoO, CaHPO 4 .2lIoO, 317 77

CaII 4 P 2 8

CaSO 4 .2lIoO," C aS0 4 . , 545 38

CaII 4 P" 2 8 .H 2 O !

The ratio P 2 O 5 /CaO is 4-1 in the solutions which arc in contact with
solid "reverted" phosphate and sulphate of lime, and 14 in the
solutions which arc in contact with solid superphosphate and sulphate
of lime.

The Manufacture of Superphosphate.

The Finely ground rock is mixed with sulphuric acid in the pro
portions required by the equations

CaCO, + IIoS0 4 -i- I-LO = CaS0 4 .2H.,0 + CO

1 Cameron and Boll, J. Airier. Chc.m. Soc., 190(5, 28, 1220.

PHOSPHATIC FERTILISERS. 223

The evolution of carbon dioxide plays an important part in keeping the
mass porous ; if a sufficient proportion of carbonate is not present in
the rock it may be supplied by blending. The heat evolved by the
reaction is used to evaporate the surplus water. This heat depends
on the composition of the rocks those which contain much carbonate
evolve more heat and may be treated with cold acid, while those which
contain little may require hot acid. Chamber acid of density 1-53
to 1-61 is used ; this is also the chief source of the water required.
The hydrates retain their water when dried at 300 C., or even to a
great extent up to 150 C.* If artificial drying is used the temperature
should not rise over 150 C. or else an undue proportion becomes
insoluble. The loss in weight is 10 to 124 per cent. The product
hardens on cooling and is cut out and powdered by a mechanical
disintegrator (see p. 226). It contains, when freshly made, 30 to
45 per cent, of phosphate (calculated as Ca 3 P 2 O 8 ) soluble in water,
according to the composition of the rock used. A more concentrated
form (" double superphosphate ") is made by adding sulphuric acid
sufficient in amount to set free all the phosphoric acid, which, after
filtration, is concentrated to a syrup and used to decompose more
phosphate according to the equation

Ca 3 P 2 8 +-1H 3 P0 4 +3H 2 =3(CaH 4 P 2 8 -f-HoO)

The manufacture has been of great value as an outlet for surplus
sulphuric acid, of which 11 cwt. (69 per cent, acid) is required for
every ton of (ordinary) superphosphate.

"Retrogression. Superphosphate may require to be stored for
several months, and during this time insoluble CaHPO 4 is formed
according to the equation on p. 222 from the small amount of un-
deeomposed Ca ;i P 2 O 8 . Even a week after manufacture the soluble
phosphate may have diminished by about 2 to 4 per cent. This
1-6 retrogression " is particularly marked when the phosphatic material
contains more than 2 per cent, of iron plus alumina. The excess of
these bases reacts with the CaII 4 P 2 O 8 to give insoluble phosphates of
iron and aluminium according to the equation

CaH 4 P 2 O 8 .IIoO +Fc (S0 4 ) 3 -i 5II

= 2[FePO 4 .2H 2 0] + CaS0 4 .2H 2 O + 2H 2 SO d

The phosphates of iron and a hi minium form gelatinous precipitates
which arc insoluble in weak acids, or in hydrolysed acid phosphates
or sulphates. Ferric phosphate may he decomposed, using up more
sulphuric acid, as in the equation

3FcPO. l -f:3lI 1 ,SO. l ^^FcP0 4 .2H 3 P0 4 -f-Fc 2 (S0 4 ) 3

or it may easily lose its water, becoming insoluble, thus :
FcPO,.2H 2 -i- CaSO 4 = CaS0 4 .2H 2 +FeP0 4

If the original rock contains up to 2 per cent, of iron oxide the resulting
phosphate of iron is soluble, but with more than 4 per cent, of iron
oxide the phosphate is insoluble hence such a rock is considered
unsuitable for the. manufacture of superphosphate. The "regression"

224 PHOSPHORUS.

of the phosphate by the iron salt just described may be avoided if the
rock is dissolved in ammonium sulphate solution and then treated with
sulphur.dioxidc ; the iron, is then converted into (XH 4 ) 2 SO 4 .FeSO 4 .()H 2 O.

The Treatment of Special Ores. Alumina does not appear to induce
" retrogression." It may be removed by caustic alkalies or hot
alkali carbonate solutions. Redonda phosphate (A1PO 4 ) may be made
soluble by fusion with ammonium bisulphate, giving a dry powder
which is a mixture of ammonium alum, ammonium bisulphate and
biphosphate.

Hocks which contain calcium chloride or fluoride (apatites) are
decomposed according to the equations

CaCl 2 + HoS0 4 = 2HC1 -f CaSO 4
CaF 2 + H 2 SO 4 = 2HF + CaSO 4

The corrosive, gases which are liberated are absorbed in towers con
taining water and furnish solutions of hydrochloric or hydroduosilicic
acicl by reaction with the silica of the phosphate rock. Thus

4 + 2HF=H 2 SiF 6

By addition of common salt silicofluoride may be precipitated and the
filtrate may be worked up for hydrochloric acid. Thus

H 2 SiF 6 + 2XaCl = Xa 2 SiF 6 + 2HCI

Apatite may be treated by the following process (Palmer) : l
Perchloric, or chloric acid made by electrolysis of the sodium salts is
mixed with the coarsely ground rock. The. liquid, containing H :) PO 4 ,
is precipitated by the alkaline kathode liquors so as to give a slightly
acid precipitate of the composition CaTIPO 4 .2iI 2 O, which is soluble
to the extent of 95 per cent, in ammonium citrate see Phosphate
Analysis (p. 22.5). 2

Phosphoric Acid. By using three mols of sulphuric acid instead
of two, the whole of the lime is converted into sulphate and the whole
of the phosphoric, acid set free according to the equation

Ca 3 P 2 O s + 3H 2 S0 4 = 2H 3 P0 4 + 3CaSO 4

The raw material should contain at least 50 per cent, of Ca. l ] > 2 O 8 and
be as free as possible from sesquioxides. It may be ignited if high in
organic matter, reduced to a, fine powder, and fed continuously into
tanks lined with wood or hard lead alloy, where it meets on the counter
current principle hot sulphuric acid of about 5 per cent, concentration.
The reaction is quickly completed and the precipitated calcium sulphate
is allowed to settle and filtered off continuously through filter presses.
This sulphate is " phospliatic gypsum " and contains :3 to 4 per cent.
of phosphoric acid of which 1 per cent, is soluble in water. The
solution is evaporated in Drought-iron pans up to a concentration of
50 per cent, phosphoric acid, which may be further refined for use in
pharmaceutical products or foods.

PHOSPHATIC FERTILISERS. 225

The crude phosphoric acid is also used in the manufacture of " high
analysis " or " triple superphosphate." The solution containing about
45 per cent, of H 3 PO 4 is mixed with more of the ground rock and
evaporated. The product, distinguished from ordinary superphosphate
by freedom from gypsum, sets to a tough mass. It is broken up while
comparatively fresh and dried at about 200 C. It contains CaH 4 P 2 O s
mixed with sandy crystals, is non-hygroscopic and may have the
following composition :

Total ? 2 O 5 . . . ! 48-0-49-0

Water-soluble PoO* . . I 41-0-42-0

2

Citrate-soluble P O 5 . j 4-0- 5-0
Citrate-insoluble PoO* . i 2-0- 3-0

CaO 20-80

Fe.Oo-rAloOo 2-25

7 3

Xa 2 O+K 2 O 2-0
SiOp " 1-4

together with fluoride, sulphate, other bases (Cu, etc.) and about 2 per
cent, of water. 1

Electrolytic Methods. If apatite or other phosphatic material is
placed round the anode in a solution of sodium chloride which is being
electrolysed, a citrate-soluble calcium phosphate is precipitated. Or
perchloric acid may be made separately in the anode compartment and
mixed with the alkali produced at the kathode, giving a precipitate of
Ca 2 H 2 P 2 O 8 . 2

Alkali Treatment. Phosphate rock may also be made soluble by
heating the powdered material with soda ash, carbon and silica, thus :

Ca. 3 (PO 4 ) 2 + 3SiO 2 + 3Xa 2 CO 3 = 3CaSiO 3 4- 2Na 3 P0 4 + 3C0 2

The History and Technology of Superphosphate Manufacture.
Allusion has already been made to the suggestion of Liebig that
bones could be made more available for agriculture by line grinding
and treatment with acid. This treatment of bones and other phos-
phoritic materials was patented by J. B. Lawes in 1842, but the claim
was modified later to cover only minerals such as apatite, phosphorite,
etc. A paper published by the Ilev. Hcnslow called attention to the
use of crag coprolites from Suffolk, which with guano and bones were
used by Lawes in his factory at Deptford. From 1842 to 1854 the
manufacture was essentially a British industry and in the early period,
until about 1870, the plant was of the simplest description. The right
quantity of acid, determined by trial and error, was run on to a heap of
ground phosphatic material in a "den" made of tarred pitch pine or
tarred bricks secured by cast-iron plates, arid mixed by means of rakes
and shovels. The mass soon set and dried itself by the heat of the
reaction, and after storing for a month or so was broken up, screened and
bagged. The only machinery used consisted of stone mills for grinding
the rock. Rotary stirrers operated by hand were sometimes installed and
were in service into the twentieth century. The production of 1 ton of
superphosphate requires about 11 cwt. of chamber acid, 69 per cent.
H 2 SO 4 , and the weight of superphosphate from a good grade of rock,

1 Larison, 2nd. Emj. Che.ru., 1929, 21, 1172.

2 Palmaer, United States Patent, 748523 (1903); Wiborgh and Palmaer, ibid., 707886
(1902).

996 PHOSPHORUS.

containing about 32 per cent. P 2 O 5 , is rather less than twice the weight
of the rock. This industry helped to absorb some of the large excess
of sulphuric acid which became available after the decline of the
Leblanc process.

The necessity of mixing in a closed room by external power became
urgent with the introduction of rocks which evolved hydrochloric or
hydrofluoric acid when treated with sulphuric acid. Machinery suited
to these operations has now been devised. 1 The stone grinders were
replaced by ball mills and later by rotary crushers and roll-jaw crushers
which will reduce 90 per cent, of the material to a fine powder which
will pass through a sieve having 10,000 meshes to a square inch. Hand
labour was employed at first for the mixing. Charges of sulphuric acid
and phosphates were weighed into a closed ;t den :5 and, after the
reaction was completed, were dug out with the aid of gravity. These
reaction chambers were replaced by mechanically operated "dens,"
some of which could be rotated. Various types of mechanical exca
vators are used. In one the block of superphosphate is forced by a
ram against tearing and cutting wheels, and the broken material after
falling through a grid is elevated to the storage rooms. Or the fixed
chambers, each holding 150 to 200 tons, are emptied by grab-buckets
which are let down into the mass. The reaction in modern plant,
aided by fineness of grinding and good mixing, is complete in a few
minutes.

Mixed and Concentrated Phosphoric Fertilisers.

The manufacture of fertilisers containing potassium or ammonium
or both in addition to phosphoric acid has called for an accurate know
ledge of the interaction of the salts concerned and also for the greatest
refinements of chemical engineering in order to produce a material of
uniform, dry and yet not dusty character.

Potassium Phosphates. Basic or neutral phosphates (Rhenania
phosphates) may be made directly from rock phosphate by mixing it
with potassium chloride, some form of carbon and soda, and heating
to over 1000 C. in an electric furnace. 2 One of these products lias the
composition Ca 2 KNaP 2 O s , with some silica. Such products may
contain 23 to 31 per cent, of soluble phosphoric acid. Potassium
superphosphate has been made by mixing potassium sulphate and
calcium carbonate with concentrated phosphoric, acid in a lead-lined
vessel. 3 The CaSO 4 .2H 2 O is separated and the iilter-pressed solution
is evaporated to dryness by steam heat. The residue may be treated
with more phosphoric acid and again, evaporated. The reaction is
expressed by the equation

K 2 SO 4 + 2H 3 P0 4 + CaCO, = 2KH 2 PO 4 + CaSO 4 + CO 2 + 1I 2 O

Ammonium Phosphates, Ordinary superphosphate may be
treated with aqueous ammonia up to 3 per cent, without any marked
increase in the citrate-insoluble proportion. 4 The calcium salt is present

1 Parrisk and Ogilvie, L * Artificial Fertilisers,* vol. i., Benn, 1927.

2 Wedge, United States Patent, 1624195 (1027).

3 "Annual Reports of Applied Chemistry," 1922, p. 434.

PHOSPHATIC FERTILISERS. 227

as CalI 4 P 2 8 and CaHP0 4 up to 2 per cent, of ammonia, but is wholly
converted into Ca 3 P 2 O 8 at 6 per cent, ammonia. 1

The ground rock may be treated directly with 2 mols of sulphuric
acid and 1 mol of ammonium sulphate, which react according to the
equation

Ca 3 P 2 O 8 + (NH 4 ) 2 S0 4 4- L>H 2 SO 4 =3CaS0 4 -f 2(NH 4 )H 2 PO 4

The solution is filtered from calcium sulphate and more ammonia is
added until the phosphates of aluminium and iron settle. On concen
trating the filtrate phosphates and sulphates of ammonia may be
crystallised. 2

In another process crude calcium acid phosphate is mixed with
ammonium sulphate solution below 80 C., and the mixture concen
trated and filtered, when (XH 4 )H 2 PO 4 crystallises. (XH 4 ) 2 HP0 4 is made
from ammonia, fumes of phosphoric acid and water. 3 Or calcium phos
phate is just dissolved in sulphuric acid, the calcium sulphate filtered
oil and the acid solution treated with ammonia and carbon dioxide.
The ammonium sulphate and phosphate form a good mixed fertiliser. 4

Very soluble fertilisers are prepared by reactions between phosphoric
acid and ammonia or its salts. Thus, if ammoniacal gas liquor is mixed
with crude phosphoric acid, diammomum phosphate, (XH 4 ) HP0 4 ,
may be crystallised in the anhydrous state. 5 The composition of
such products may range from 45 per cent. P 2 O 5 and 14 per cent,
nitrogen to 18 per cent. 1 3 2 5 and 18 per cent, nitrogen. By varying
the proportions, inonoammoniuni phosphate, (XH 4 )H 2 PO 4 , may be
obtained as a white granular solid, which is non-hygroscopic and stable
under ordinary conditions. The product prepared by evaporation
down to 2-3 per cent, of water and grinding contains about 53 per
cent. P 2 O 5 (of which 48 per cent, is soluble in water), with 13-3 per
cent, of ammonia and up to 3 or 4 per cent, of a mixture of iron and
aluminium, magnesium and the alkali metals.

Various t4 sulphophosphates " arc made by mixing ammonium (also
alkali) sulphate solution with 55 per cent. H 3 PO 4 at 80 C., thus :

(XlI 4 )oS0 1 -r H,P() 4 = (NH 4 )HS0 4 -;- (NH 4 )HJP0 4
koSO! -i- H,P0 4 - K11S0 4 -r KH 2 P0 4

The products may be obtained in a dry form and are easily soluble in
water. On account of their high proportion of free acid they may
be mixed with basic slag or phosphatic chalk and still retain a large
proportion of soluble phosphate.

.By stiirting with a purer phosphoric acid, ammonium salts may be
obtained in a purer state. 11 ammonia gas is passed into 75 per cent,
phosphoric, acid a, reaction takes place with great heat evolution, and
on cooling acid ammonium phosphate, (XH 4 )iI 2 P0 4 , crystallises in the
anhydrous state. Further saturation with ammonia yields a mixture
of the mono- and di-ammonium salts, and on further addition of con
centrated ammonia solution, or by carrying out the whole reaction in

1 .Moss, Jnd. Eng. 67/ev/v., 1931, 23, Xo. 1, 19.

2 Gordon, tiutjhsh Patent, 310-128 (1928).

:i J eacock, United States Pdtt.nl, 995S9S (1911).

1 Liljemmli, English Patent, 2758-13 (1926); see also English Patent, 252953 (1925).

5 Chemical Age, 1929, 21, 002.

JLarison, loc. ci,L

228 PHOSPHORUS.

more dilute solution, the salt (XH 4 ) 2 HPO 4 may be obtained as white
non-hygroscopic crystals containing 53-8 per cent. P 2 O 5 and 25-8
per cent. NH 3 .

By suitable combinations of the methods just described, mixtures
of potassium and ammonium phosphates may be prepared. The
preparation of very concentrated fertilisers containing potassium and
ammonium phosphates has been described by Ross and Merz, 191 6, 1
Ross, Jones and Mehring, 1926. 2

Mixed fertilisers containing ammonium phosphate with other salts
have been made in the form of cylindrical granules like smokeless
powder. 3 The slower operations of solution, neutralisation, evapora
tion and crystallisation are avoided, the bases, acids and neutral com
ponents being combined, ground, mixed and kneaded in one operation.
Salts of potassium or other base are passed through valve-locked
mains into a mixing pan which contains scrapers and muller mechan
isms enclosed in a gas-tight hood. Liquid phosphoric acid and gaseous
ammonia are admitted simultaneously with the salts and combine
under pressure in about ten minutes to form diammonium hydrogen
phosphate. The sticky mass is removed by means of a vertical screw
and passes into an extruding machine which had to be designed specially
deal with non-plastic masses. The extruded sections are dried,
^ with cold air. then at a temperature below 70 C. They are then
: into pieces about Ij diameters or 1/8 inch long, screened and
polished. The product is uniform, non-hygroscopic and is easily
drilled into the land.

1 United Stales Patent, 1 191615 (1910).

2 United States Patent, 1598259 (1926).

3 Klugh; reported in Chemical Age, 1932, 26, 274.

XAME JXDEX.

ABBOTT, 165, 171, 172.

Abel, 62.

Ad air, 157.

Adie, 143.

Adlucary, 133.

Agruss,"l70.

Albert, 157.

Albirms, 5.

Allison, 42.

Amagat, 91.

Amat, 142, 145, 147.

Amato, 75.

Andre, 173.

Andrews, 157, 158.

d Ans, 184.

Antoine, 91.

Arbuzov, 55, 144, 140, 167.

Archibald, 73.

Arctowski, 30.

von Arcnd, 29, 125, 135, 130, 140.

Armstrong, 02.

Arnold, GO.

Arrhenins, 130, 1.62, 1(54.

Arsonecff, 170.

Aston, 23, 40.

Atkins, 200.

Auger, 147.

A wen, 42.

BAILEY, 134.

Bakei-, 110.
Baknmn, 07.

Balard, 7(5, 101, 103, 1-13, 144.
Balaroli , 170, 174.
Ball, 170.

Banthien, 123, 127.
Barnett. 131, 174.
BassetU 20:), 210, 220.
Baudmmmt, 02, 03, 00-08, 100.
Bauer, 12, 01, 02.
Bausa, 150, 153.
Baxter, 44, -15, 47, 48.
Beatty, 10J, 102.
Bcck,"41, 131.
Becker, 140.
Beekmann, 23.
Bell, 11, 210, 222.
Beriiegren, 41.
Berber, 133.
BerLhelot, 1)., 43, 52.

Berlbelot, M., 70, 86, 87, 03, 06, 98, 101,
158, 164, 107, 173.

Berzelius, 42, 155, 170, 186, 189, 192.
Besson, 63, 64. 76, 77, 89, 93, 98, 101, 12

174, 189, 190, 192, 205, 206.
Beyers, 168.

v. Bezold, 187, 190, 191.
Bhandakar, 74.
Billandot, 9.
de la Billardiere, 75, 78.
Blitz, 23, 96, 101.
Bineau, 77.
Bird, 28.

Blackwekler, 3, 208.
Blake, 176.
Blanc, 141, 165.
Bleckrode, 73.

Bloch, L. and E., 97, 121, 122.
Blondlot, 64, 65.
Blunt, 61.
Blyth, 71.
Bock, 169.
Boeseken, 16, 31.
Bokhorst, 21-23, 25, 35, 38, 40.
Booii c, 157, 158.
IBordel, 72.
Bose, 42.
Bossuet, 61.
Bottger, 11, 02, 72, 81.
Boulouch, ISO, 187, 190.
t iowen, 26.
Boyle, 5, 116, 155.
Boylston, 45.
Braun, 1.71.
Bray, 165. 171, 172.

1

renne? 1 , 71.

reunin.u:, 123.

ndirman, 1(5-18, 40, 41, 01.

riedieb, 206.

i-i.u^s, 1.82.

1 , 73, 77.

165, 166, 170, 220, 221.
rodie, 31.

e Broglie, 41 .
owii, 182.
uhl, 63.
Brukl, 28.
Bryant. I !.
Buck, SI.
Badriikorl, 89.
Bull, 90.
Bun sen, 61.
Burgess, 125.
Burke, 03, 96.

PHOSPHORUS.

CABELL, 127.

Cahoiirs, 94, 95.

CailJetet, 72.

Cain, 78.

Calvcrt, 80. 95.

Cameron, 219, 222.

Carins, 191.

Carpenter, 157.

Carrara, 93.

Carre, 167.

Casselmann, 95.

Cavalier, 150, 173.

Cavazzi, 62, 65, 67, 76, 143.

Caven, 56.

Centnerszwer, 21, 116, 124.

Chalk, 125.

Chancel, 10.

Chanton, 120.

Chapman, 33, 125.

Chappuis, 120.

le Chatelier, 66.

Chevrier, 113, 114, 203.

Chretien, 168.

Christomanos, 19, 20, 62, 63, 99-101, 122.

Clark, 3, 34, 42, 71, 155, 163, 165.

Clarke, 67, 208.

Clarkson, 168.

de Claubry, 89.

Clausius, 122.

Clayton, 188.

clc Clevmont, 173.

Clever, 195.

Cloez, 114.

Cohen, 15, 20, 32, 75, 119, 192.

Colson, 32.

Compton, 19.

Cooper, 162.

Co i i en winder, 103.

Corno, 150.

Corncc, 150, 153, 163, 175.

Cowper, L26.

Crafts, 84.

Cronander, 98.

Cronllebois, 80.

Curie, J8.

(Jushman, 60.

Out hbertson, 25, 55.

D.UJIILIKX, 53.

Da.le, 17, 92, 1(50.

Dal ton, 75, 76.

Da.mien, 17, 18, 51 .

Darrin, I OS.

Dai i vi I Her, 41 .

Davidson, 208.

Davy, I!., 60, 68, 75, 7(5, 86, 89, 5)3, <M,

"133, MO.
Davy, ,]., IK).
Defaeqz, 65.
Dejardins, 2(>.
Demole, 101.
Dennis, 66.
Dei-Yin, 92, 190.
"Desch, 61.
-Deschamps, 12! .
Dcvillc, 23, 94.

Dickinson, 78.

Dieckmann, 7, 66.

Dieterici, 161.

Dixon, 11, 29, 119.

Dobbie, 26.

Dodge, 194.

DouShty, 102.

Downey, 116, 120, 121, 123, 124, 128.

Dragunov, 176.

Drawe, 153.

Drechsel, 80.

Druminond, 76, 169.

Dufet, 145.

DutTendaek, 26.

Dulong, 70, 125, 135, 138, 140.

Dumas, 43, 61, 68-70, 75, 86, 1X>.

Duncan, 2.1 .

Dusart, 25.

Dushman, 75.

EASTMAX, 162.
Eder, 26.
Edwards, 61.
Efremort, 65, 66.
Ecidi, 173.
Elster, 122.
Emeleus, 121.
Emmerling, 62-64.
Engels, 78.
Ephraim, 194.
Epperson, 1 79.
fitard, 69.
Ewan, 118.
Ewing, 88.
Eydmann, 120.

FADAKOWSKY, 123.
Fair, 131, 134.
Fairweather, 157.
Faraday, 17, 18, 186.
Farncll^ 220, 221.
Favre, 93, 164.
Federlin, 143, 144.
Ferrand, 193, 194.
Fichter, 184, 185.
Field, 169.
Fineh, 131.
Finek, 143, UO.
Fireman, 103.
Firth, 139.

Fleitniann, 174, 177, 178.
Folio Uesjardins, 7.
Fonzes-J)iacoii, ()3.
Foote, 18, 19.
de Forerand, 23, 76, Hi*.
Fourcroy, 133, 145.
Fourmer, 81).
Foussereau, 17.
Fo\vler, 134.
Fox, 26, 71.
de Fra.nchis, 20.
Franek, ()3.
Francke, 82.
Frank, 7.
Fnmkenhemi, 39.
Fraser, 131.

XAME I3SDEX.

Freesc, 66.
Friedel, 193.
Fricdrich, 104.
Frumkin, 21.

GAIOIEXBIA, 165.

Garrison, 120, 123.

Gattermann, SO, 81.

Gautier, 61, 69, 82, 103.

Gay-Lussac, 60, 89, 102.

Gazarian, 70, 71.

Geibcl, 165.

Geitel, 122.

Gengernbre, 6S.

Gerliardt, 199.

Germann, 103.

Geuther, 26, 93, 97, 99, 129, 138, 141, 170,

173, 177, 206.
Gewecke, 64.
Gibson, 24, 54.
Gill, 209.
Giran, 20, 23, 132, 158, 160, 171, 172, 175,

176, 187, 189.
Gladstone, 17, 54, 76, 89, 92, 97, 98, 101,

114, 163, .175, 189, 198, 199, 201-204.
Glatzel, 178, 191-194, 203.
Gluhmann, .174.
Goldschmidt, 97, 190.
Gomolka, 33, 34, 64.
Gordon, 227.
Gore, 134.
Gorlacher, 121.
Graham, 68, 75, 125, 155, 163, 170, 172,

177.

de Gramom, 20.
Granger, 61. 62, 65, 66, 87.
Gregoire, 182.
Gregory, 155, 170.
Groshemtz, 41, 14 L.
v. Grot-Urns, (54.
Griincbercr, 207.
Guldbcrg/ 100.
Guntz, 86, 87.

Gustavson, 98, 133, 143, 1.74.
Gutzwjller, 185.
Guye, 73.

HAAGEN, 5-1.

Hackspill, 61, 82.

Hager, 160.

Halm, 166, 11)5.

Hambly, 133.

Mar kins, 3.

Harries, 126.

Hartley, 25, 124, 1.32.

Hat c hot l,, 66.

Hausknechf, 80, 81.

Hautefeuille, 32, 62, 90, 130, 132, 168.

Heimann, 177.

1-lelrr, 187, 188, 190, 191.

v. Heltnholtz, 34, 37, 122.

Hcmpel, 8.

Henderson, 109.

Hermeberg, 1.74, 177.

Hennin, 73.

Henry, 113.

Henstock, 128.

Heraeus, 168.

Hernctte, 131. 134.

Herscovici, 187, 190-192.

Hertz, 23.

Hess, 16, 17.

Hctherington, 168.

Heumann, 89, 97.

Heyn, 12, 61, 62.

Hicks, 26.

Hill, 169.

Hilperfc, 66.

Hinshelwood, 75.

Hiorns, 62.

Hittorf, 25, 29, 31-33, 39.

Hoeflake, 131.

van t Ho ft , 76, 77.

Hofmann, 69, 70, 75-78, 80, 82, 85, 11

140, 187, 203, 207.
Holborn. 162.
Holland, 96.
Holl eman, 181.

Holmes, 97, 114, 199, 201-204.
Holroyd, 58. 96.
Holt, 78, 158, 171, 174.
Honda, 18.
Hopkin, 132.
Houdremont, 7.
Huff, 151, 153.
Hughes, 165.
Hugot, 60, 70, 104, 197.
Hunter, 72, 191.
Huntingdon. 61, 62.
Hurtzig, 97/141.
Husain, 184, 185.
Huthstcmor, 26.
Hvoslcf, 66.

IKED A, 118.
Inouye, 20.
IpatiefT, 27, 68.
rsarnberi, 79, 186-189.
[tahener, 142.
Ivanov, 55.

JABOIX, 61.

Jackson, 15, 35, .132.

Jacob, 8, 157, 226.

Jacobsohn, 150, 152.

Jagcr, 91., 99, 100, 104.

Jakovlev, 26.

Janneret, 168.

Janoxvsky, 65, 93.

Jeep, 101.

Joannis, 60.

Johansen, 32, 207.

Johnson, 54, 77, 79, 80, 104.

Jokote, 71.

Johbois, 16, 21, 22, 32, 33, 63, 64.

.)oly, 150, 151, 158, 160.

Jones, 44, 76, 157, 158.

Jones, H. C., 158.

Joslin, 67.

Joubcrt, 117.

232

Jowett, 164, 165.
Juliusberger, 182.
lung, 18, 41, 149, 154.

KAHLENBERG, 133.
KanonikofT, 54.
Kastle, 101, 102.
"Catz, 62.

\ 224.

, 26.

, 99, 190-192

, 131.

1, 157, 158.

78.

133.

>^odowskv, 92.

>Ithoff, 137, 139, 141, 165 172

nstantinoff, 66, 67.

Oij, 74, 75.

PP, 15, 51.

walski, 121.

a-fft, 5, 93, 189

nit, 93.

^mers, 97.

>H, ]?4, 179.

iger, 165.

tierschky, 194, 195

;hler, 203.

isch, 28, 62, 63, 67

ikel, 4.

ter, 165.

LAAR, 37.

padius, 67.

Igrebc, C4, 65.

re, 89.

ft eld, 175.

;on, 213, 225.

ent, 204.

emann, 133.

isier, 155, 156.

c, 17, 73.

* , 15.

me, 40, 185, ISO, 189 193

ult, 76.

d, 123.

T, 72, 81, 82.

rier, 81, 82, 125.

sky, 344.

, 126.

>nstadt, 56.

ry, 125.

i, 99.

PHOSPHORUS.

Liebig, 204.
Liljenroth, 227.
Linck, 18, 41.
Lindboom, 177.
Lindgren, 3, 208, 209.
Linhart, 144.
Loessner, 138, 139.
Loew, 123.
Lomax, 157.
, Lombard, 95, 96.
| Lorah, 219.
i Lubs, 165.
de Lucchi, 23.
Ludert, 178.
Ludlam, 119
Luff, 56.

Luginin, 93, 96, 98, 101, 103 164
Lupke, 63, 70.
Luther, 142.

MclKTOSH, 73.

Maclvor, 65, 86, 114.

McLennan, 42.

Macleod, 53, 120.

MacRae, 21.

Maddrell, 177, 178.

Maggiacomo, 146.

Malm, 76, 93.

Mai, 187, 189 , 190, 196.

Major, 143, 144, 194.

Marckwald, 34, 37.

Marggraf, 155, 186.

Margottet, 168.
Marie, 135, 136.
Marmi, 151.
Maronneau, 67.
Martens, 92.
Martres, 156.

an Marum, 116.

lascart, 90.

lassini, 184.

lasson, 21, 52.

lathias, o2.

fatignon, 63, 70.

-attcuci, 122.

atthows, 209.

"attliiessen, 17.

awrow, 139

ay, 11.

cekstroth, 169.

ehring, 157.
-eiftsenheimcr, 56.

elcher, 162.
Mellman, 64.
Melville, 119, 121.
Mensching, 23.
Mente, 198, 199, 202.
Menzies, 158.
Messinger, 70, 78.
Metcalfe, 25, 55.

Meyer, 18, 23, 41, 190, 191 ]<n H<>
Michaelis, 29, 92, 93, 97, 98 114 HO

135, 136, 140, 146, 165 ]<),> "
Mihr, 125, 127, 129.
Miller, 120, 130.
Millett, 164, 165.

NAME INDEX.

Millikan, 26.

Miro, 184.

Mitchell, 93, 137, 139, 143, 144, 150.

Mohler, 19.

Moissan, 63, 70, 86, 134,

Montemartini, 173.

Moore, 45, 48, 162.

Moot, 92.

Morgan. 53.

Morton, 149, 172, 181.

Moser, 29.

Mounce, 161.

Muir, 11.

Muller, 29, 94, 97, 117, 177, 184, 203.

Mum ford, 53.

Murphy, 61.

Murray, 208.

Muthmann, 139, 195.

Myers, 78, 139, 158, 174, 176.

VA:N~ XAME, 153, 157.
Xeogi, 133.

Neumann, S3, 93, 95, 189.
Newman, 27.
Xikolaiefi, 27, 68.
Xorderskjold, 103.
North, 130, 144, 146.
Xoyes, 1G2.
Nursey, 64.

OULINO, 02.

Oder, 76-78, 81, 93, 102, 103.

Ocilne, 226.

Olic, .1.5, 32.

Olszcwsky, 73, 91.

Oppcnhcim, 90.

Osann, 12.

Ossendowsky, 19.

Ostersetzer/113.

Oslwald, 39, 120, 123, 136, 137, J41, 142,

]67.

Oudlet, 1J7.
Ouvrard, 103, 104, 115, 189.

PALAZZO, J46.

Palm, 153.

Palmaer, 225.

Palmer, 74.

PanormoiT, 174.

Paquelin, 140.

Parkinson, (5.1. .

Par rava.no, 151.

Parrish, 226.

Partinnton, 125, 184, 185.

Pascal, IS, 178.

Pauxcr, KK).

Pawlesosky, 91.

Peacock, 227.

Pearson, 70.

Pelletier, 6J, 68, 140, 186.

Percy, 62.

Perperot, 94.

P^yr-cnr A-> 1 Q/l

Pessel, 176.

Peters, 4.

Petit, 76.

Peto, 131.

Petrikaln, 124.

Petterson, 16.

Philip, 12.

Phillips, 53, 161, 211.

Pickcrine, 92.

Pierre, 90, 99.

Pietvkowsky, 214.

F^insker, 150, 151-154, 168.

Pisati, 16, 20.

Pischtsehiininko, 192.

Pitsch, 125.

v. der Plaats, 43.

Plotnikoff, 143.

Plucker, 25.

Posgialc, 169.

Poleck, 62.

Polk, 140.

Pope, 163.

Poulenc, 87, 204.

Poundorf, 138.

Power, 168.

Prause, 168.

Preuner, 21, 22, 24, 25.

Prideaux, 21, 5.1, 58, 94, 95, 101. 102,

165, 167, 175.
Prm vault, 92, 99.
Prinz, 113.
Priize, .151, 173.
Purcell, 124.

QrmjKi;, 18.

PtAJUKOVITCH, 161.

Railton, 146.

Rakusin, 179.

Ralston, 94, 97.

Rarnmc, 187, 188, 190.

Kammelsberg, 140, 144, 153.

Ramsay, 21, 23, 52-54, 91.

Kamstcd, 137, 139.

Rankine, 71.

Raoult, 175.

Ratclirre, 56.

Rathke, 113.

Raylcigh, 120.

Raymond, 68.

Readman, 7.

Rcbs, 188, 190.

Rccklinahausen, 190.

Peed, 53, 100.

Rcaencr, 123.

.Rcglm, 152, 153.

Rcgnault, 15, 33, 90, 91.

Remsen, 92.

Renard, 208.

Renault, 61, 63.

Reisers, 17.

Reylier, 162.

Rinde, 129.

Ringer, 164.

Ritchie, 50.

Robinson, 7.

Robison, J69.
Rodger, 203.
Rdmer, 205.
Rosanovskaya 176

PHOSPHORUS.

.

Rosin, 181.

Ross, 157, 158, 227

Rossel, 63.

Rosset, 205.

Ry, 75.

Rudolph, 125, 187-189
Rupp, 143, 149.
Russell, 119, 130.
Rutgers, 132.

SABANEEFF, 140, 145, 154 198

Sabatier, 63, 176.

Sacerdote, 73.

Sachs, 144.

le Sage, 125.

Sakalatwalla, 66.

Salm, 164.

Saltmarsh, 26.

Salzer, 150, 152, 153.

oaizmann, 199.
Sanfourche, 131, 134
Sanger, 150.
Schacht, 19.
Scharfenberg, 191
Scharff, 116, 122, 187 189
Scheele, 5, 155.

Scheffer, 77, 79, 131.
Schcmtschuschny, 65-67

Schepeleff, 67

o

Schmidlin, 184.

Schmidt, G. C., 123.

Schmidt, K., 123."

Schonbcin, l l6, 120 122
Schdnn, 61.

Schonthan, 203.
Schreinor, 182. "
Schroder, 30.

Schrottcr, 29, 31,33,62-64
Schuh, 153.

Schwarz, 174.

Seidell, 190, 219, 220

Semenoff, 117 ? 113"

Senderens, 62.

Julias, 70, 77, 78, 80, 114, 189

Sevene, 192.

Seyboth, 64.

Shenstono, 131.

Sherrill, 165.

Shields, 91.

f, 89.

Sidgwick, 58.

Sieverts, 138, 139, 143 144

Silbermann Q3 i (\A

o . 7 -lAJ-i, <^o, IDi.

Silva, 84.

Skinner, 73, 77

Slare, 116.

Smith, 71, 81, 95, 96, 132 158

^,15,21-23,33,3740,13^
Sommer, 140.

S0rensen, 164.
Springer, 189.
van de Stadt, 75 147
Stamm, 24, 25, 35, 40
otange, 174.
Stead, 64, 66
Steel, 208.

Stern, 92, 98, 99.
Stiefelhagen 92

Stoddard, 169.
Stokes, 197-202 995
Straub, 28.

Sugden, 52-54, 94, 100.
oveclberg, 30.

Tartar, 219.
Tassel, 88.
Tauchert, 28, 150.
Tausz, 121.
Terenin, 26.
Ter-Gazarian, 43

. 177, 17

Thomas, 157.
Thomlinson, 157

, .
Thomson, J. J. 122

, .

Thummel, 62.
Tidmore, ^21
Tilden, 174.
Timmermann 91
Tivoli, 65.
Topley, 75.
Trautmann, 133
Trautz, 74, 75.
Travers, 131.
Traxler, 103.
Treadwell, 182
Troost, 23, 32, 90, 103.
Tucker, 61.
Turley, 157.
Turner, 42.
Tutm, 168.

Tutton, 70, 97, 103, 126-129, 131
Twymann, 157

Tver, 121.

VAXIXO, 143.
Vauquelin, 145.
Veit, 66.
Vigier, 60.
Ville, 146.
Vitali, 62.
Vogcl, 63, 176.
v. Vo<rcl, 12 J .
Vogelfs, 167.
Voigt, 96.

WAGGAMAX, 157.

Wagner, 78.

Wahl, 37.

Waiden, 53, 91, 100, J39

Walker, 11, 28, 104.

Walls om, 194.

Walton, 120.

Ward, 165.

Warington, 219.
Warschauer, 177, 178.
Washington, 3, 208.
Weber, 4, 98, 113, 1*91.
Wedekind, 66.
Wedge, 226.
Weekhorst, 12.

IXDEX.

: V-. Weimarn, 29.
1 Weiser, 120, 123.
West, 130, 131
Weyl, 27.
I Wiborgh, 225.
: Wichelhaus, 92, 98, 99
; Wieland, 143.
I Wiesler, 177.
I Wigand, 33.

Wilkie, 181.
1 Wllkins, 53, 100.
! Wilkinson, 94, 97.

Williams, 132.

Wingler, 143.

Winter, 70.

Wohler, 65, 113 143

Wolf, 42.

Wologdine, 66.

Wolter, 115.
: Wood, 219.
1 Worms, 174.

Wrede/207.

Wroblewskv, 91

Wu, 168. "

Wulf, 149, 154.

Wunder, 168.

Wurtz, 94, 102, 139, 143-145, 194.

YOUNG, 167.

235

SUBJECT IXDEX.

ABSORPTION of radiation by gaseous and
combined phosphorus, 26.

Acids, Phosphorous, Phosphoric, etc., see,
under "Phosphorous, etc.

Alkali phosphides, 60.

Alkaline earth phosphides, 61.

Alky! hypophosphites, 146.

phosphates, 167.

phosphites, 146.

Allotropic forms of phosphorus, 31 et seq.
Allotropy, Theory of, 38, 39.
Aluminium phosphides, 63.
Amiclodiphosphoric acids, 200, 201.
Amidometaphosphoric acids, 198 et seq.
Amidophosphoric acids, 197, 198.
Animal body, Proportion of phosphorus,

4.

Antimony phosphides, 60.
Arsenic phosphides, 64, 65.
Atomic weight of phosphorus, 43-50.
Atomicity of gaseous phosphorus, 24, 25.

BARIUM phosphide. 61.

Basic slag, 216, 217.

Black phosphorus, Crystalline structure, 4.

, Preparation and properties, 40, 41.

Bone-ash, 5, 211, 213.
Bones, 4, 210.
Boron phosphide, 63.

CADMIUM phosphides, 63.
Caesium phosphides, 61.
Calcium phosphates. System lime-phos
phoric acid, 2.18.

phosphide, 61.

Chemical combinations of phosphorus, 27.
Chlorides of phosphorus, see "Phosphorus

chlorides."

Chromium phosphides, 65.
Cobalt phosphides, 66.
Combined phosphorus, Physical properties,

5.1 c.t xeq.

Condensation of phosphorus vapour, 40.
Copper phosphides, 61, 62.

salts. Reactions with phosphorus, 28.
Critical constants of phosphorus, 37.
Crystalline forms of phosphorus, 17.

DENSITIES of solid, liquid, and caseous
phosphorus, 16, 20, 24, 32, 33, 41,

42.

Detection of hypophosphites, etc., see
Hypophosphites/ etc.

phosphorus, 30.

Dipole moment of phosphine, 57.

ELECTRIC furnace method for the prepara
tion of phosphorus, 8.
Estimation of hypophosphites, 148 et *eq.

phosphates, 180.

phosphites, 148 et seq.

phosphorus, 30.

FERTILISERS, Phosphatic, ^Manufacture of,

225, 226.

, , Mixed, 227, 228.
Fireworks containing phosphorus, ]2.
Huophosphoric acid, 89, 106.
Fluorescence of phosphorus vapour, 2<j.
Fhiorobromide, Fluorochloride, etc., .see

"Phosphorus liuorobromicle," etc.

GLOW of phosphorus, 1 1.6 ct *eq.
Gold phosphides, 61, 62.
Guanos, 215.

HEAT of dissociation ol ^aseous phosphorus,
24.

fusion, Latent, of violet phosphorus,

37.

, , of white phosphorus, 15, 16.

sublimation, Latent, of phosphorus,

36, 37.

vaporisation, Latent, of liquid phos
phorus, 23.

, Latent, of hypophosphorous, phos
phorous and phosphoric acids, .136,
141, 160, 171.

, Specific, of white phosphorus, 15.

History of phosphorus, 2, 3.

compounds, xcc, under respective

compounds.

Hydrogen phosphides, 68 c.t My.; $ce also
under " : Phosphine/ etc.

Hydroxyphosphines, 82.

Hypophosphates, 153, 15-4.

Hypophosphites, 139, 140.

, Structure of, 145-147.

Hypophosphoric acid, 150-153.

Hypophosphorous acid, 135 et &eg.

, Detection, 148-150.

, Estimation, 148-150.

LULDO-DERIVATIVES of diphosphoric acid,
201, 202.

SUBJECT INDEX.

237

lonisation of air bv elowim y phosphorus,
122, 123.

potential of phosphorus, IS.
Iron phosphides, (56.

LATENT heats, see under ; " Heats/

Lead phosphides, 64.

Lime, Phosphates of, see under ;; Calcium/

MAXGAXESE phosphides, 65.
Mass spectrum of phosphorus, 49, 50.
Matches, Composition of, 11.
Melting-point of phosphorus compounds,

see under respective compounds.

red phosphorus, 33.

violet phosphorus, 35.

white phosphorus, 14, 15.

Mercury phosphides, 63.

Metallic salts, Reactions v. ith phosnliorus,

27, 28.
Metaphosphoric acid. see "Phosphoric

acid, Meta-/"

Metaphosphorous acid, 147.
Metaphosphoryl bromide, 112.

chloride, 1H).

Mineral phosphates, 1, 211-2.10.

Molar weights in liquid phosphorus, 16.

of gaseous phosphorus, 24.

of phosphorus compounds, we under

respective compounds.
Molybdenum phosphides, 65.

NICKEL phosphides, G7.
Xitrilodiphosphorie acids, 202.
Nitnlotrimetaphosphoric acid, 202.

OOEAXEC deposits, 208, 201).

Organic compounds of phosphorus, 06.

Oxidation of phosphorus, 27, 116-124, 126,

131.
Oxyu on, Rate of absorption by phosphorus,

118, 119.
Oxyhalides of phosphorus, 105-112; see

also ;- Phosphorus oxyfluoride," etc.
0/one, Production of, by oxidation of

phosphorus, 120.

PACKING effect for phosphorus atom, 40.
Parachors of phosphorus compounds, 53.
Pcrphosphoric acids, 184, 185.
Phosphate minerals, 208, 211-2J5.
Phosphates, Assimilation by plants, 209.
, Circulation of, 200-210."
, Distribution of, 214, 215.
, Met a, 176-17!).

of lime, 218-222.

, Ortho-, meta- and pyro-, 155.

. World s production, 215, 216.

Phosphatic fertilisers, 209-218, 225-223.

Phosphide, Hydrogen, Liquid, 80.

, , Solid, 81, 82.

Phosphides, Metallic, set under respective

metals.

Phosphinc, 68-76.
Phosphincs, Alkyl, 82-85.
Phosphites, Detection, 148-150.

Phosphites, Primary and secondary 144

145.

Phosphonium halides, 76-80.
Phosphoric acid, Meta-. 174, 17.1.
, Ortho-, Chemical properties, 166-

168.

- , Crystalline, 158.
, History, 155.

, Physical properties, 158-166.

, Preparation, 156-157.

, Physiological action, J69.

, Pyro-, 171-174.

, Uses, 169.

Phosphoric acids, Complex hetero-, 168.

, Dehydration, 170.

, Detection, 179-180.

, Estimation, 1SO-184.

, Poly-, 174.

Phosphorous acid, Chemical properties

142-144.
, Preparation and physical properties

140, 141.

Phosphorus, Alloys, 12.
, Assimilation by plants, 209.
, Atomic weight, 42-50.
-, Black, 40-42.

bromides, 99-102.

bromomtrides, 206.

, Chemical reactions, 27-30.

chlorides, 77 el $f-q.: see also "Phos

phorus trichloride, " etc.

chloronitrides, 204-206.
, Colloidal, 29.

compounds, Use in medicine, 13.
, Critical constants, 37.

, Detection, 30.

dichloride, 81).
, Discovery, 5.
, .Estimation, 30.

fluorides, 86 el seq.

fluoroaminomate, 88.

fiuorobromide, 88, 81).

nuorochloride, 88.

halides, 45, 48, 86 cl scq.

in animal body, 4.
bones, 4, 210.

iodides, 102-104.

nitride, 206.

oxides, 125-134.

oxy bromides, 111.

oxychlorides, 106-109.

oxyiluonde, 105, 106.

oxvhalides, 105-112: see also under

""Meta-," "Pyro-.""

oxyiodi.de, 112.

oxysulphid.es, 192.

pentabuornide, 101, 102.

pentachloridc, 96-98.

pentafluoride, 87, 88.

pent oxide, 131-134.

, Physiological action, 12, 13.
, Red, Preparation, 10, 31.
, , General properties, 28, 29.
, , Physical properties, 32, 33.
, Reducing action on metallic salts, 27,
28.

238

PHOSPHORUS.

Phosphorus, Reduction to, by carbon, 5, 6.
, Scarlet, 29.

selenicle, 195, 196.

sulphides, 186-192.

sulphoselenides, 196.

tetritadecasiilphide, 190-192.

tetritaheptasulphide, 189, 190.

tctritahexasulphide, 189.

tetritatrisulphide, 1ST, 188.

tetroxidc, 130.

thioamides, 203, 204.

thioamido-acids, 192, 193.

thioiodides, ] 15.

thiotriamide, 203.

thiotribromide, 114.

thiotrichloridc, 112, 113.
- thiotrifluoride, 112.

triamide, 197.

tribromide, 99-101.

trichloride, 89-93.

trifiuoride, 86, 87.

triiodide, 103.

trioxide, 125-130.
- vapour, 23-27.
, Violet, 33-40.
Phosphoryl chlorodibromide, 111.
dichlorobromide, 110.

monochloride, 110.

tribromide, etc., see "Phosphorus oxy-

brornide," etc.

See also under "Metaphosphoryl,"
"Pyrophosphoryl."

Plants, Phosphorus as constituent in, 4.

Platinum phosphides, 67.

Potassium phosphides, 60.

Pressure, Effect on melting-point of phos
phorus, 38.

, Effect on oxidation of phosphine, 74,
75.

, phosphorus, 123.

Pyrophosphoric acid, see Phosphoric
acid, Pyro-."

Pyrophosphorous acid, 147, 148.

Pyrophosphoryl chloride, 109, 110.

RED phosphorus, 28, 32; see also "Phos
phorus, Keel."

Refractivity, Atomic, of combined phos
phorus, 55.

of gaseous phosphorus, 25.

of liquid phosphorus, 17.

of solid phosphorus, 17.
Rubidium phosphide, 61.

SCARLET phosphorus, 42; sec also "Phos
phorus, Scarlet.
Selenidcs of phosphorus, 10f>.

Selenophosphates, 196.

Signal lights, 12.

Silver phosphides, 61, 62.

salts, Reactions with phosphorus, 28.
Sodium phosphides, 60.

Soils, Content of phosphorus, 4, 209.
Solubilities of phosphorus compounds, see
under respective compounds.

of white phosphorus, 19, 20.

Spectra of phosphorus and its compounds,

26.

_____ glow, 123, 124.
Stereochemistry of phosphorus compounds,

55, 56.

Strontium phosphides, 61.
Structure of phosphorus compounds, 52;

see also under the respective acids,

etc.

Superphosphates, 222 et scq.
Surface tension of liquid phosphorus, 23.

phosphorus compounds, see under

respective compounds.

TETRAPHOSPHORCsheptasulphide, 189, 190.

trisulphides, 187 et seq.
Thioamidophosphoric acids, 202, 203.
Thiohahdes of phosphorus, 112-115; see

also "Phosphorus thiofluoride," etc.
Thiohypophosphates, 193.
Thiophosphates, 193-195.
Thorium phosphide, 64.
Tin phosphides, 64.
Titanium phosphides, 63, 64.
Tungsten phosphides, 65.

USES of phosphorus, 4-13.

VALENCY of phosphorus, 58, 59.
Vapour density of phosphorus, 23, 24.

pressures of liquid phosphorus, 22.

red phosphorus, 32, 33.

violet phosphorus, 35.

Violet phosphorus, 33-35.

Volumes, Molar, of combined phosphorus,

51-53.
, Specific, of liquid phosphorus, 21.

WATER, Action on phosphorus, 27.
White phosphorus, see under " Phos
phor us. ;:

X-RAY absorption by phosphites, 1-47.

diffraction by black phosphorus, 41.

ZINC phosphides, 63.
Zirconium phosphides, 64.