liquid disappears and finally the completely solid mass cools down.

As a very simple case we
may take the diagram in fig. 4.
A, B and C represent the
three pure substances. AB,
BC and AC represent mix-
tures of two components.
Ear, Ebc and & represent the
three binary eutectic mix-
tures. The ternary eutectic
is represented by Eat*, con-
taining about equal quantities
of C and B and a smaller
amount of A. If a represent
the composition of a certain
liquid which is allowed to cool
and crystallize, composition
will change along the line A &.
At a certain point the A
component will crystallize out and the liquid will become poorer in A
(richer in B and C), and the composition will change from a towards
b (away from point A). After a time the liquid becomes satura-
ted for b which will start to crystallize, and now the liquid -changes
composition along the line bE a kc as the temperature continues to
fall; finally C also begins to crystallize, and the ternary eutectic
point is reached at which the three components crystallize simul-
taneously in definite proportions (represented by the position of
Eotc) until it is completely solidified.

It is probable that nothing quite so simple as this occurs in
ordinary rock-forming minerals, at least the silicates, but some
metallic alloys show this type. In considering silicates the following
considerations must be kept in mind : (a) The liability to form com-
pounds, which behave as new substances with their own fusion-
points and eutectics. (b) The occurrence of isomorphous compounds
is almost universal and these form mixed crystals unstable in
the changing magma, and liable to resorption (this may upset the
formation of a ternary eutectic altogether), (c) Compounds may
appear at an early stage which subsequently become unstable and
are replaced by different minerals (incongruent). (d) Many silicates
refuse to crystallize in ordinary crucible experiments (except in
presence of solvents which do not appear in the final product).

We must also keep in mind that in the crystallization of rocks
certain conditions prevail which may modify the process to an un-
known extent. Thus: (a) All magmas contain gases of various
kinds which may have a very powerful influence in determining
what minerals will form, (b) Intrusive magmas are under great
pressure and the pressure diminishes as they rise to the surface;
the pressure may act directly or by increasing the concentration of
the gases dissolved in the magma, (c) Cooling in deep-seated mag-
mas is extremely slow. This will tend to prevent supersaturation
by undercooling and lessen the chance of the abnormality in the




sequence of crystallization which may appear in rapidly cooled
melts. It will also favour the complete transformation of early un-
stable minerals into stable permanent forms. Many varieties of
minerals have already been obtained experimentally which are not
known to occur in rocks. They are stable only at high temperatures
(and possibly under low pressures).



As an example of the effect of isomorphous minerals on the se-
quence of crystallization we may take a mixture consisting of 50 %
diopside and 50% plagioclase (containing equal proportions of
albite and anorthite). The composition diagram (fig. 5) is a triangle
with each mineral at one of the corners and the mixture is repre-
sented by a point (F). Crystallization begins with a separation of
diopside (supposed to be a simple mineral and not an isomorphous
mixture, as it would usually be in rocks) at about 1275. At 1245
the excess of diopside (G) has separated out, and felspar begins to
crystallize. It has about 75% anorthite (H). Thereafter diopside
and felspar both crystallize, but as the temperature travels along the
line EGD from G to K the composition of the felspar changes from
H to L (if we suppose that all the early felspar which is unduly rich
in anorthite is stage by stage absorbed). The resulting rock has the
mineral composition above stated; but if resorption of felspar is
incomplete the last-formed felspar is richer in albite and has a
composition T. The felspar crystals in that case are zonal with basic
centres. If at any time crystallization is suddenly brought to an end,
a glassy ground-mass will be formed, which is richer in soda and
silica than the original magma and contains zoned felspar crystals.
This is exceedingly like what takes place in many basaltic lavas.
Again, if the original mixture had been richer in felspar, so that the
composition point lay below the line DE, felspar would have crys-
tallized out first. This seems to be in keeping with the structure of
many dolerites, which contain felspar partly enclosed in augite




FIG. 6.

crystals of later formation (ophitic structure), while others show that
the augite appears in porphyritic crystals and began crystallizing
before felspar. Another interesting feature of this diagram is that
there is no tertiary eutectic point, and the liquid residue continually
changes in composition up to its final disappearance.

The phenomena of these component systems are extraordinarily
varied. One of the best known is the system AUOj-CaO-SiOj which
has been very fully tested at the Geophysical Laboratory in Wash-
ington by Shepherd and Rankin. A copy of their diagram is given
here (fig. 6). It is divided into fields, of which six are occupied by
substances known to occur as minerals, cristobalite, tridymite,
wollastonite, anorthite, sillimanite and corundum. In each of these
fields the mineral named will crystallize if the temperature of the
melt falls. The fields are separated by lines which show under what
circumstances the two minerals whose fields adjoin will crystallize.
Where three fields meet, the conditions exist at which three minerals
will exist simultaneously (or, to express it otherwise, are in equi-
librium with a liquid of the composition indicated). In no case do four
fields meet in one point.

This system is also of much interest to technologists desiring to
understand the chemistry of the manufacture of Portland cement.
This is a mixture of lime, alumina and silica, with a fairly definite
composition, and the compounds which form on fusing or sintering
the mixture are indicated by the diagram. Similarly, the CaO corner
of the figure shows what is the result of heating lime containing a
little alumina and silica (rmpure limestone) to a very high tempera-
ture. Silica is also a refractory mineral and is used in silica-bricks
and ganisters for lining furnaces. A little lime and alumina are
mixed with it (either naturally or expressly to obtain certain results),
and the behaviour of such mixtures is indicated by the appropriate
corner of the ternary scheme. These investigations accordingly are
of the greatest value in many industries such as pottery, steel-
making, glass-melting, brick-making, cement manufacture, lime-
burning and the quartz-glass industry. During the war the Carnegie
Geophysical Institute at Washington, which has earned great fame



86



PFLANZER-BALTIN PHARMACOLOGY



for these researches, was able to direct the manufacture of chemical
and optical glasses in the United States in a most successful manner,
and performed very valuable services to American industry.

Theory of Ternary Mixtures. The theory of ternary mixtures has
been very fully worked out mathematically by Willard Gibbs,
Backhuis Roozeboom, Schreinemakers, Smits, Kuenen, Tammann
and others, and may be said to be well understood in its main ap-
plications. Experimental investigation has also made great progress.
It is a laborious matter, requiring great skill and very elaborate
appliances. The diagram we have given showing the tertiary system
CaO, AU Oj, Si O 2 , required over 7,000 experiments, in some of which
the heating had to be continued for many hours and even for days;
and the thermal results had usually to be checked by microscopic
examination of the product. Other systems equally important have
received very careful study. These are not so simple as the instance
quoted, because mineral transformations, either during or after
crystallization of the melts, often give rise to many complications.
Thus, for example, CaSiOj crystallizes as pseudo-wollastonite at
high temperatures, which may change to wollastonite at low tem-
peratures. MgSiO 3 has four forms kupferite, magnesia amphibole,
enstatite and clinoenstatite. Where both these substances separate
from the melt, none of the above-named minerals appears, but a
diopside clinoenstatite solid solution or isomorphous mixture, which
belongs to the common group of minerals known as the pyroxenes.

These facts are of the greatest interest to both mineralogists and
petrologists. They have introduced many new minerals (artificial)
to our knowledge, and taught us their relationships at atmospheric
pressures in certain dry meTts. They have also enabled us to under-
stand many of the peculiarities of the minerals that occur in rocks,
and the method of their origin.

As another instance we may quote the relations of fprsterite
(Mg 2 SiO 4 ) and rustalite (MgSiOj). Forsterite may crystallize from
melts of suitable composition and after a time it may become
unstable in the residual magma; then it is dissolved up or "cor-
roded " and clinoenstatite replaces it. Again, if an enstatite
(MgSiOj) mixture be fused and allowed to cool, forsterite begins to
separate out ; it will tend to be reabsorbed and converted at a lower
temperature to clinoenstatite, but if this be prevented the mixture
solidifies as forsterite, clinoenstatite and quartz. To the petrologist
this is of great interest, because forsterite is one of the constituents
of olivine, a very common mineral of the basic igneous rocks. Now
olivine generally occurs along with some member of the pyroxene
group, and the olivine crystals show rounded outlines, which have
been taken to indicate corrosion or resorption by the magma after
crystallization with concurrent formation of pyroxene. In some
rocks there is clear evidence that olivine crystallized early and sub-
sequently was entirely dissolved. In other rocks olivine is found
enveloped in clusters of enstatite crystals which have evidently
formed at its expense; and it is a very frequent characteristic of the
olivines of gabbro and norite that they are surrounded by " reac-
tion rims " or " corrosion borders " consisting of enstatite, tremolite
and other magnesian silicates that have a higher percentage of
silica than olivine itself. The meaning of these phenomena was
fairly well apprehended by petrologists, and now their conclusions
have been confirmed by experimental evidence. Another feature
of some interest is that, in the ternary system under consideration,
it has been shown that forsterite may crystallize early, then dis-
appear by corrosion, and a second generation of forsterite may sub-
sequently crystallize. Whether this is a common phenomenon is
not yet known, and its exact relation to the frequent appearance of
minerals in two generations in rocks remains to be demonstrated.

The number of ternary systems that have as yet been fully in-
vestigated is small, though the results are of the highest importance.
Those which contain the alkalis potash and soda present certain
special difficulties, such as the volatility of part of the mixtures and
the difficulty of crystallizing some of the minerals. Rapid progress is
being made and it is unlikely that experimental difficulties will retard
the advance of knowledge. A special case, of the greatest possible
interest to the petrologist, arises where one or more of the com-
ponents are volatile. Natural magmas are probably always richly
charged with gases. The theory of such systems has been explored
by Schreinemakers, Smits and others. Experiments with mixtures
enclosed in steel bombs which can withstand great pressures at high
temperatures have been very successful in certain cases, but as yet
only the borders of this field have been explored. A good deal of
work has been done on the dissociation pressure of sulphides of the
metals, a subject of great importance as regards the paragenesis of
natural sulphides and the conditions under which mineral veins
have been formed. The effect of steam in the formation of silicates
is under investigation and during the next few years will probably
be the subject of much research.

Quaternary Mixtures. We have seen that systems of three com-
ponents are much more complicated than systems of two com-
ponents; and the addition of a fourth component greatly increases
the difficulties. The theory of such systems is not as yet fully ex-
plored; in fact, it is quite probable that many of the problems will
not be solvable by mathematics. No four-component system has yet
been completely studied, though parts of such systems have re-
ceived investigation. As a diagram a solid figure bounded by three
equilateral triangles may be used, and projections similar to those



employed to represent the faces of crystals have been tried. Systems
more complicated than the quaternary systems are at present be-
yond mathematical and experimental investigation.

' Constitution of Rocks. In rocks the least number of components
that can be regarded as essential is seven (SiO 2 , Al 2 Os, Fe 2 O 3 ,
CaO, MgO, K 2 O and Na 2 O). In rock analyses as a rule from 12 to
20 components are ascertained, but most of these are in small amount
and may be regarded as unessential. To the seven main coinponents
we must add the volcanic gases (such as H 2 O, F, Cl, HC1, .SO 2 ,
B 2 O 3 ), most of which appear only in very small quantity in the
crystallized rock, but are believed to exert a powerful influence in
determining the crystalline phases that appear. High pressures
must also be employed, and in some cases it is certain that the pres-
sures were by no means constant. For these and other reasons it is
clear that the genesis of such a rock as granite or basalt presents
problems of the highest order of difficulty.

In the preliminary stages it may be possible to simplify the prob-
lem by considering rock magmas, not as a mixture of the seven
oxides above named, but as mixtures of minerals. If three minerals
be taken a ternary system is the result. For example, a granite
might be regarded as consisting of orthoclase, quartz and albite; a
nepheline syenite as consisting of nepheline, albite and aegirine;
a basalt as composed of olivine, diopside, anorthite. Such systems,
of course, are a mere approximation and it is already known that
it may not be safe to treat them as simply ternary. In the system
diopside-forsterite-silica, for example, it is proved that under certain
conditions spinel crystallizes, and the reactions can only be regarded
as those of a four-component mixture. Another difficulty that is
bound to prove important is the occurrence of isomorphous minerals.
In petrology this is practically universal. Except quartz, all the
common rock-forming minerals are members of complicated iso-
morphous groups (felspars, nepheline, sodalite, micas, pyroxenes,
amphiboles, olivines) ; and even in simple ternary systems, if two of
the three minerals are isomorphous, there may be, strictly speaking,
no eutectic mixture as the last stage of crystallization. It is not too
much to say that the crystallization of rocks is very largely a problem
of the formation of isomorphous crystals, and it is unsafe to apply
to rocks the results derived from mixtures of minerals that do not
show similar relations.

BIBLIOGRAPHY. For the recent advances in physico-chemical and
experimental petrology no English textbook is available. Marker's
Natural History of Igneous Rocks (1909) gives a sketch of the subject
from the standpoint of its time, but is now out of date. A more
adequate work is Boeke's Physikalische-Chemische Petrographie
('9'5)i which gives full references and is the best general account.
Vogt's Silikat Schmeldosungen (1904) is interesting but very specula-
tive. His Sulphid Silikatschmelzuneen (in course of publication)
deals with some special aspects of the problem. The fundamental
works on the theory of equilibrium are Roozeboom's Helerogene
Gleichgewichte and its continuation (3rd vol.) by Schreinemakers.
See also Bancroft, The Phase Rule, and Findlay, The Phase Rule;
Tammann, Krystalliziren und Schmelzen. For English and American
students the best authorities are the papers published by the workers
of the Geophysical Institution in Washington. See also Niggli,
Lehrbuch der Mineralogie (1920), Die Leichtfluchtigen Bestandtheile
im Magma (1920); Daly, Igneous Rocks and their Origin (1914);

Iddings, Igneous Rocks (1913); Holmes, Nomenclature of Petrol-
ogy (1920) ; Stark, "Petrographische Provinzen" (in Fortschritte der
Mineralogie, 1914). (J. S. F.)

PFLANZER-BALTIN, KARL, FREIHERR VON (1855- ),
Austro-Hungarian general, was born at Pecs in Hungary in 1855.
He served in the cavalry and on the general staff, but in 1914
found himself, on account of precarious health, unattached, and
it was only in the autumn of that year, when Rumania appeared
to be turning against the Central Powers, that he was charged
with the defence of Transylvania. But when the Russians at
this period crossed the Carpathians, and there was immediate
danger of their eruption into the plains of Hungary, Pflanzer-
Baltin, with a division improvised by his brilliant talent for
organization out of next to nothing, threw himself on this enemy,
and conducted the defensive in the form of a series of daring
offensive movements. After fighting with varying success in the
southern part of Eastern Galicia and in the Bukovina the VII.
Army under his command was driven back by Brussilov's offen-
sive in June 1916, whereupon he was relieved of his command.
In the summer of 1918 the Austro-Hungarian front in ; Albania
yielded before the attack of the Entente army. Pflanzer-Baltin,
entrusted with the command in this theatre of operations, won
back, after a brief and powerful attack, the old positions south-
wards of Fjeri and Berat the last considerable success which fell
to the Austro-Hungarian army in the field. (A.-K.)

PHARMACOLOGY (see 21.347). The science of experimental
pharmacology is a product chiefly of the last half-century, and



PHARMACOLOGY



the subject has more recently made rapid advances, due largely
to the creation of new laboratories and the institution of new
chairs devoted to pharmacological research. The chief impor-
tance of the work lies in the application of the knowledge gained
of the physiological action of drugs to the treatment of disease in
man and animals; and, though there have been periods when this
branch of therapy in spite of its antiquity and persistence
has been suspect, recent research leading to new, more accurate,
and more scientific use of drugs has placed the subject in a posi-
tion so indubitable that the time is not in sight when the practice
of medicine or surgery will be able to dispense with its services.

The main directions of recent advances in knowledge may be
indicated. The action of familiar drugs becomes daily more ac-
curately known, leading to a juster estimate of their value and
greater precision in the use of them in disease. New remedies are
being introduced and older remedies superseded. The enormous
development of synthetic chemistry has furnished many potential
remedies, all of which are now subjected to pharmacological in-
vestigation before they are used on man. One relatively recent
development which has proved fruitful in results of great practi-
cal importance in the treatment of disease is that of experi-
mental therapeutics, where the cure of disease artificially pro-
duced in experimental animals is investigated. So far this has
been most successful in the case of experimental trypanosomi-
asis, largely owing to the ease with which a disease of this nature
can be induced in laboratory animals and the constancy and
certainty of its duration.

Here only such developments of pharmacology need be men-
tioned as have already passed from the by-way of mere academic
interest into the highroad of practical application.

Of the simpler saline compounds the familiar Epsom salts mag-
nesium sulphate-^has been found to have more interesting actions
than that for which it is generally used. When given as a purgative
very little of it is absorbed into the blood, owing to the difficulty
which both magnesium and sulphate ions experience in passing
through membranes like the lining of the gut. But if injected
hypodermically or intravenously in sufficient quantity it has a
powerful action on the nervous system, causing a kind of motor
paralysis and anaesthesia. This effect of magnesium for the
sulphate ion takes no part in it has been utilized in the treatment
of tetanus, in which condition magnesium salts have been injected
intraspinally, with benefit in many cases in so far as the relief of
symptoms is concerned. This depressant action of magnesium on
the nervous system is antagonized in a dramatic way by calcium
salts; an animal paralysed by magnesium being restored, in suit-
able cases, to a normal condition in a few seconds by intravenous
injection of a soluble calcium salt.

Of the heavy metals arsenic and antimony have in recent years
claimed most attention. Both arsenic and antimony have been used
empirically in the treatment of syphilis for over a century but with-
out having any great vogue. When it was discovered that organisms
of the trypanosome type are the cause of syphilis and of many tropi-
cal diseases, and that arsenic is a powerful poison for such organisms,
an experimental justification for the employment of this substance
in the treatment of syphilis was furnished. The drawback to its use
was that it is so poisonous to higher animals that it is difficult to get
into the blood a concentration of arsenic sufficient to kill the para-
sitic organisms there present without injuring the host. It was
found, however, that certain organic compounds of arsenic could be
made which were very much less poisonous for mammals though
their toxicity for trypanosomes was retained or enhanced. Pursuing
this line of investigation of a large number of arsenical compounds
Ehrlich eventually discovered and recommended, as a result of
animal experiments, salvarsan as a remedy for syphilis. The value
of salvarsan and of nearly related compounds in the treatment of
syphilis is now common knowledge. One interesting point in regard
to this is that those unicellular organisms of that type which causes
syphilis readily become immune to the action of arsenic. It is there-
fore possible that, with the almost universal use of salvarsan now-
adays, strains of syphilitic infection may be developed which are
immune to arsenic ; and for people infected with syphilis from these
sources arsenical compounds like salvarsan would no longer have
any remedial value. The risk of this unfortunate sequel is small be-
cause usually salvarsan treatment renders the patient no longer
liable to infect other people and only in this way could an " arsenic-
fast " infecting organism be produced, but the risk would seem to be
not negligible. Fortunately no such immunity to mercury occurs.

The fact that antimony belongs to the same chemical group as
arsenic suggested the possibility that it, too, might be valuable in
these diseases and pharmacological investigation showed that
antimony has for trypanosomes a toxicity superior even to that of
arsenic. Though no organic compound of antimony has been dis-



covered comparable in advantageous properties with the salvarsan
compound of arsenic, the familiar tartar emetic (potassio-tartrate of
antimony) has been found, when administered intravenously,
adequate for the treatment of two important diseases, Kala-Agar
and Bilharzia diseases due to organisms different from trypano-
somes and for which no other effective remedy is known. These dis-
coveries have led to a revival of the use of antimony in medicine;
in the I7th and i8th centuries especially, antimony was regarded
almost as a panacea, but later it lost a prestige which it is now
regaining.

One of the established pharmacological actions of lead is to stimu-
late involuntary muscle of every kind, as exemplified in cases of
industrial poisoning by the occurrence of colic caused by irregular
and spasmodic contraction of the muscle of the bowel. While lead-
poisoning tends to become less common, owing to trade precautions
and earlier recognition of it, stress has been laid on the frequency
with which lead is used, especially in industrial districts in the N. of