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As carbon is invariably present in organic substances, organic
compounds are sometimes called carbon compounds. Beside
carbon, they usually contain oxygen and hydrogen, and very often
nitrogen. Owing to the marked traits of these four non-metals,
they are especially fitted for study as types illustrating the prin-
ciples of chemical philosophy. Hence they are often termed
Typic Elements. They are of the greatest importance to the
physiologist in his study of nutrition and animal heat. On these
accounts in the following pages extended treatment is given to
the compounds of these elements.

The body of a living animal contains about 60 per cent, water
and 40 per cent, solids. They exist as more or less complex com-
pounds of elements, which are abundant in the following order of
percentage: Oxygen, 66.0; carbon, 17.5; hydrogen, 10.2; nitrogen,
2.4; calcium, 1.6; phosphorus, 0.9; sodium, 0.3; chlorin, 0.3; sul-
phur, 0.2; magnesium, 0.05; iron, 0.004; and traces of iodin,
fluorin, silicon, copper, manganese, and lithium.


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Notation. — The symbols H, O, etc., stand not only for the
element, but for a chemical unit of the element. When more
than one unit is expressed a large numeral is written before, mul-
tiplying all the symbols that follow it, as 2H, or a small numeral
is placed to the right and below the symbol, as Hj, for 2 units of
hydrogen. To express admixture of elements the plus sign is
used, thus Hj -h O means that 2 units of hydrogen are mixed with
I of oxygen. To express union or combination the symbols are
put as close together as the type will go; thus 2H2O means two
parts of the compound formed when hydrogen, two units, and
oxygen, one unit, unite by chemical attraction.


Classification. — It is assumed that the medical student is
a beginner in chemistry, and as yet is unfitted to appreciate the
reasons for arranging the elements according to the natural or
scientific classification (see page 116). The considerations which
make the most logical system desirable will be understood only
after the principles of chemical philosophy have been studied.
These principles will be elucidated in the course of studying the
Typic Elements — oxygen, hydrogen, nitrogen, and carbon, and
their compounds. These will be first considered in the order
best suited for the intellectual needs of the student, though ref-
erence will be made to the more systematic grouping given below:

Group T. Hydrogen, unique (Monovalent).

Group II. Halogens or the chlorin family : chlorin, broroin, iodin, and fluorin

Group III. The oxygen family : oxygen, sulphur, selenium, and tellurium (Di-

Group IV. The nitrogen family : nitrogen, phosphorus, arsenic, and antimony

Group V. The argon family : argon, helium, neon, cryptoti, xenon.

Group VI. The carbon family : carbon, silicon, (Quadrivalent).


Symbol, O. Atomic weight, 16.

History. — The discovery of oxygen was an incident in the
study of the composition of the atmosphere. The early Greek
philosophers regarded the air as an element, as they did the earth,
fire, and water.

Its complex nature was suspected when, early in the seventeenth
century, the observation was made that by combustion in a


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confined portion of air, the air lost weight, and that the remainder
would support neither life nor fire. Priestley showed that by
heating mercury in enclosed air for several days at a temperature
near its boiling-point, the mercury was changed to a red powder,
now called mercuric oxid, while the life-sustaining part of the
air disappeared. In 1774 he found that by heating mercuric
oxid a gas was liberated which, when mixed with the burnt-out
air, would restore to it the properties of supporting respiration
and combustion.

This operation is performed in a hard glass reduction tube
or retort, and the gas collected over water in a pneumatic trough,
the mercury being condensed on the cooler part of the glass tube.
The result may be written as follows:

Mercuric oxid yields mercury and oxygen.

Or, by short hand,

HgO = Hg +0.

In 1775 Scheele discovered oxygen by heating manganese
dioxid with strong sulphuric acid.

2Mn02 -h 2HjS0^ = aMnSO^ -h 2H2O -f O,

Manganese Add Manganese Water. Oxygen,

dioxid. sulphuric sulixiate.

F^eparation. — Many higher oxids, as manganese dioxid^
MnOj; lead dioxid, PbOj; and barium dioxid BaOj, yield a part
of their oxygen when heated. Barium dioxid above 400° C.
(752® F.) gives off half of its oxygen.

BaOj = BaO -h O.

Barium dioxid. Barium monoxid.

This lower oxid, BaO, heated at a lower temperature in a cur-
rent of air, takes up the oxygen it had lost. By alternating these
processes oxygen is now manufactured on a commercial scale at
a low cost.

In the laboratory potassium chlorate is the source. When
this compound is heated, it parts with its oxygen, leaving potassium
chlorid in the retort.

KCIO3 = KCl -h 3O.

Potassium chlorate. Potassium chlorid.

It is customary to employ a mixture of coarsely powdered
manganese dioxid i part and potassium chlorate 2 parts. This


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causes the KCIO3 to yield oxygen at a comparatively low tem-
perature, 200® C. (372® F.). The manganese dioxid is not de-
composed, though its presence causes the easy transmission of
oxygen from the chlorate.

Precaution. — The materials should be dry and free from
organic dirt. Serious explosions have happened from the action
of oxygen on the carbon of coal-dust or other impurities in com-
mercial manganese dioxid. To guard against such accidents

Fio. 33. — CoUecdoQ of gas disengaged by heat

a small sample should be tested by heating with some potassium
chlorate in an open test-tube.

In preparing oxygen for inhalation it is advisable to free it
from all traces of chlorin by passing the gas through potassium
hydroxid in a wash bottle before collecting it in the gas bags or
gasometer. Before removing the lamp withdraw the delivery
tube from the water, if collected in a pneumatic trough, or the
regurgitation of the water will cause an explosion. In making
a quantity of the gas it is customary to use a copper retort for the
potassium chlorate. In practice 250 gm. (8 oz., Troy) of the
chlorate yields about 68 L. (18 gal.) of oxygen gas.

Occurrence. — Oxygen is the most abundant element. It is
found widely distributed in nature, forming one-fifth part of the
volume of the air and eight-ninths, by weight, of all water. As an
ingredient in most minerals it makes up nearly one-half of the


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weight of the earth's crust, and it is present in almost all animal
and vegetable compounds.

Physical Properties.~Oxygen is a little heavier than air,
its specific gravity being 1. 10563 (air=i). It is an invisible gas,
colorless, tasteless, and odorless. It is slightly soluble in water,
0.04 volume dissolving in i volume of water at o® C. (32® F.).
In the proportion of about 3 per cent, by volume it is dissolved in
natural water at ordinary temperatures, and furnishes to the gills
of fishes the amount needed for the aeration of their blood. It
has been liquefied at —118*^ €.( — 244.4^ F.) under a pressure of
50 atmospheres. These are called its critical values.

Chemical Properties. — It has affinities of great power and
wide range, combining with every element except fluorin and the
argon group. As the air is practically one-fifth part oxygen
diluted, all its chemical reactions are those of this gas. There
is this difference only: the pure oxygen causes far more intense
displays of energy. By attaching various combustibles to copper
wire, first igniting them in the air and afterward plunging them
into jars of pure oxygen, the contrast will show how much the
diluent of the air mitigates the violent action of this gas. Sulphur
will burn in the air with a pale blue flame of little luminous power;
in oxygen, however, its flame is violet colored, emitting great light.

S + O2 = SO,

Sulphur. , Sulphur dioxid.

A piece of charcoal with a feeble spark and without flame, when
immersed in oxygen, become^ a white, glowing mass and is in-
stantly consumed in flames. A glowing chip of wood is a reagent
in testing for oxygen and the reaction is its bursting into flame.

C -h O2 = CO,

Carbon. Carbon dioxid.

If a piece of dry phosphorus the size of a pea be warmed in
a deflagrating spoon and then burned in oxygen, its light is of
insupportable brilliancy.

1^2 + 05 = T,0,

Phosphorus. Phosphorus pentoxid.

Fine iron piano wire or watch springs tipped with burning sulphur
and set on fire in oxygen will burn with dazzling corruscations.

3Fe + 40 = FesO,

Inn. Iron tetnudd.


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The non-metals burning in oxygen yield oxids, which in the
cases of sulphur, carbon, and phosphorus are gases that will dis-
solve in the water in the jar, giving to it a sour taste and an acid
reaction. Iron forms a solid compound without acid qualities,
which leaves a rusty stain on the jar. Other metals form oxids,
which are usually bases.

The presence of free oxygen is revealed by adding to the sus-
pected sample the colorless gas nitrogen dioxid, which unites with
more oxygen to form red fumes of the higher oxids. Free oxygen
is removed from mixtures of gases by means of its slow union with
phosphorus or by making use of the absorption powers of a solu-
tion of potassium pyrogallate.

Physiologic Effect. — Oxyhemoglobin of the blood-corpuscles
under the air-pump yields about two volumes of oxygen, which
is so loosely associated as to be separable without destruction of
the compound. This load is readily transferable to oxidizable
substances. The muscles and, indeed, protoplasm in general,
have the power of absorbing and storing up oxygen to be utilized
in the transforming of chemical into other forms of energy. If
an animal be enclosed in an atmosphere containing no oxygen
it shortly dies. It is the only pure gas that will sustain respir-
ation. At ordinary pressures no detriment follows its inhalation.
When disease interferes with normal oxygenation of the blood
benefit is obtained by enriching the air respired with about 60 per
cent, of this gas. The livid appearance disappears under its
judicious employment.

Uses. — The gas is made portable by condensing 40 gallons in
a small cylinder. By a rubber tube it is transmitted to a funnel
held near the face of the patient. It is used in this way in the
treatment of the later stages of pneumonia and consumption and
in resuscitation from coal-gas poisoning.

Law of Chemical Combination.— When Priestley, on the dis-
covery of oxygen, resorted to the balance, he was able to prove
that mercuric oxid contains an unvarying amount of oxygen joined
to an unvarying proportion of mercury. When the two elements
in these fixed proportions were caused to combine they produced
the compound. Any excess of either would not enter into the
union. ^

Potassium chlorate, when analyzed and its constituents weighed,
is found to be composed of 39 parts of potassium, 35.5 parts of
chlorin, and 48 parts of oxygen. All specimens of potassium
chlorate have exactly this composition.

When the composition of a salt is once ascertained, the knowl-
edge thus obtained applies to all samples of that salt. Common


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salt is, always and everywhere, sodium 23 parts and chlorin
355 parts.

When it is desired to make note of a chemical operation in
shorthand, symbols are used to express both the nature of the
elements and the relative weights engaged. Thus the equation,

KC103=KCl + 30,

written out in full, would read: potassium chlorate 122.5 (potas-
sium 39 parts, chlorin 35.5, and oxygen 48) yields potassium
chlorid 74.5 (potassium 39, chlorin 35.5) and oxygen 48 parts.

If these figures on each side of the equation are added, they
will be found to be equal, though the = mark is not used in an
algebraic sense; it means gives or yields.

Reactions* — We have learned that mercury, heated in air,
takes up oxygen, forming mercuric oxid, Hg+0 = HgO. This
is an illustration of the first kind of reaction, called combination.
The second kind is called decomposition^ as in the case of KCIO3,
given above, which reverses combination. The third kind is
double decomposition, when two or more compounds break up
and form two or more others, thus:

KCl + AgNOa = AgCl + KNO3.

This is read, potassium chlorid added to silver nitrate gives silver
chlorid and potassium nitrate.

When the composition of many compounds is studied it is
found that the most satisfactory unit for expressing the numeric
ratios of the combining weights is that of hydrogen, the lightest
element. The different symbols stand, then, not only for the name,
but also for certain relative weights or proportions (H being i)
in which the elements unite, or those in which they displace one
another in compounds.

H stands for i part of hydrogen, O for 16 parts of oxygen, O3
for 3 times 16 or 48 parts of oxygen, K for 39 parts of potassium,
S for 32 parts of sulphur, C for 12 parts of carbon.

A convenient statement of the facts just referred to is called
the law of definite or constant proportions or combination:

**A definite chemical compound always contains the same
elements united in the same proportions."

This law, first stated by Dalton in the eighteenth century, by
numerous experiments became more and more assured, and the
great generalization gradually took shape — that matter is inde-
structible. So far as our observation goes, it is not created, nor is


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it destroyed. It may change its form a thousand times, but does
not change its ultimate nature, neither gaining nor losing.

When a piece of charcoal is burned in oxygen it disappears
from view, but if the product contained in the vessel be weighed
it will be found to equal exactly the weight of the original
materials. The carbon has been taken into an invisible gaseous
compound, carbon dioxid. From this state it can be recovered
in the original amount as fine black dust by burning sodium in
the gas. The sodium liberates the carbon, taking the oxygen
away from it.

When KCIO3 has yielded its oxygen there is left in the retort
KCl, potassium chlorid, composed of potassium 39 parts and
chlorin 35.5 parts. There is a familiar salt used in medicine,
potassium iodid, which is composed of potassium 39 parts
and iodin 127. Now when chlorin and iodin unite to form
iodin chlorid, they do so in the same relative weight, 35.5 to
127. Dependent upon facts of the same character is the corol-
lary to the first law, which is called the law of equivalent pro-

" The proportions in which any two elements unite with a third
are the same in which they unite with each other."

Hence it is said that chlorin 35.5, iodin 127, oxygen 16, sodium
23, potassium 39, are equivalent to each other, taking hydrogen
as unity. Every element has an assigned equivalent weight,
which rules the proportions of its combinations with other

Chemical Arithmetic. — The constancy of the proportions in
chemical compounds definitely distinguishes them from mechan-
ical mixtures. When active chemicals are mixed in any other than
the exact proportion, the excess is inert. Chemistry is based so
surely uix)n numeric laws that calculations can be made for chem-
ical operations as for those of other exact sciences.

Suppose the problem to be: how much of the gas would be
obtained by heating a weight of, say 250 gm. (8 oz., Troy), of
potassium chlorate. The equation, already given, is as follows:

KCIO3 = KCl + 3O.

From the numeric values given for this equation (p. 70) we
calculate that 122.5 parts of KCIO3 will, when heated, give up 48
parts of oxygen. By a sum in rule-of-three (ratio and proportion)
we easily find how many would be given by 250 gm. of KCIO3:

122.5 : 250 :: 48 : ^
^=97-95 gn^- o^ oxygen.

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If it be desired to know the number of liters represented by the
weight of 97.95 gm. an additional calculation is required. Experi-
ments show that 22.4 L. of any normal gas weigh a number of
grams equal to twice the combining weight. Then one-half, or
1 1.2, would equal the combining weight, which, with oxygen, is
16. Therefore,


3 : 97.95 :: 11. 2 : x

= 68.56 L. of oxygen evolved from 250 gm.

of potassium chlorate.

Relations of Other Forces to Chemical Energy. — ^Melting
solids by heat, or at higher temperatures vaporizing them, favors
chemical change. Furthermore, all changes of decomposition or
of combination are set in action by the physical agencies, radiant
energy, heat, light, electricity, magnetism, and mechanical force.
These are convertible into one another and are but forms of the
one energy in the universe.

When potassium chlorate is heated to a high degree its par-
ticles are freed from their cohesion and chemical action causes
the potassium and chlorin to form a different compound, setting
the oxygen free.

At ordinary temperatures carbon remains in oxygen for a long
time without visible change, though if coal be finely divided and
packed so as to confine the heat that is produced by its gradual
oxidation, it ignites spontaneously. Whenever carbon is heated
to ignition there is immediate union with the oxygen. Moreover,
the union is itself attended by the evolution of still more heat. In
the oxygen experiments the degree of heat is so great that a brilliant
light is emitted. Burning in air is the same as burning in oxygen,
though the visible heat is less because the diluent nitrogen in air
takes up the heat without helping on the process, while in pure
oxygen the chemical energy of that active gas is increased by its
being heated. The term combustion is applied to this evolution
of heat and light by chemical action. Combustion is due to the
conversion of intrinsic or chemical energy into heat energy. The
substances that burn are called combustible. The process con-
verts them into incombustible products, such as carbon dioxid and
sulphur dioxid. All chemical actions are attended by changes
of temperature, but in writing equations it is customary to omit
mention of the energy of heat consumed or evolved.

The amount of heat evolved or absorbed in the chemical change
of a substance is definite and is always the same from given weights
of the reagents. If rapid union be induced, as in combustion,
then a higher temperature is noted, but no more heat in quantity
is given off than when union is gradual. The number of heat


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units or calories (p. 34) obtained is the same whether combustible
bodies are oxidized by degrees or whether the same substances are
burnt up. When coal is burned in a grate we have an example of
heat production by quick oxidation. When carbon compounds
are consumed in our bodies by their union with the oxygen of the
blood obtained from respired air, we have an instance of heat
production by slow oxidation. A given weight of the combustible
will yield the same number of heat units in both cases. One gram
of a carbohydrate, such as starch, burned with oxygen in a calor-
imeter, liberates 4100 calories. In the animal body the same
weight of starch is oxidized to the same products (carbon dioxid
and water), liberating the same number of calories. Combustion
means that the heat is given off in a short period, evincing great
intensity. The process has high velocity. Oxidation in the animal
body is distributed through greater periods and regulated so that
the escape of heat is compatible with life; indeed, is necessary to it.
It is dissipated as fast as it is produced. The velocity is so low
that the heat never reaches sufl5cient intensity to ignite the elements

To use a homely illustration: if a bucket slowly leaks, a gallon
of water can be poured into it at the same rate (slow oxidation)
and no water accumulates, but if poured quickly (combustion)
the water level rises, stands high in the bucket, and may even
overflow. Two-thirds of the amount of heat generated in the
body is converted to other forms of energy and escapes by radiation^
the remaining one-third finds outlets in the hot urine and feces,
which contain much more heat than the cool water drunk; in the
latent heat of vaporizing the water of perspiration and respira-
tion; and in warming the air inhaled, which has high specific
heat (p. 34).

The Heat of Decomposition.— The heat consumed in
slowly oxidizing mercury to form mercuric oxid is the same in
amount as that required to decompose it into its elements. To
form HgO it takes 30,660 calories, and to separate its elements
Hg and O the same number of heat units must be used.

Work-energy of Oxidation.— Heat is a source of mechan-
ical motion, as in the steam engine, and, on the other hand, the
arrest of motion causes heat. They are reciprocally convertible
in definite amounts, a certain amount of work-energy producing
a corresponding amount of heat-energy and vice versa. This
numeric relationship is expressed thus: one calorie equals 0.426
kilogram-meters, which is to say, that the amount of heat required
to warm one gram of water one degree Centigrade of temperature
will, when converted to work-energy, lift i kilogram weight through
0.426 meters.

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In order to have but one unit for all the different forms of energy,
that of Joule has been chosen. Thus i calorie (cal.) equals 4.18
joules (j.), or, reversing the statement, i joule = 0.239 cal.

Large amounts of energy are expressed by kilojoules (kj.) or
1000 joules. By experiment it is found that the heat of combustion
of a combining weight of carbon equals that which produces
406 kj. of work-energy. The equation C + 02=C02+4o6 kj.
reads thus: the sum of the intrinsic energy of 12 gm. of carbon
and 32 gm. of oxygen equals the energy of 44 gm. of carbon dioxid
plus 406 kj. This 406 kj. may be utilized in engines suited for
converting heat to motion, or in animals for maintaining the work-
energy and animal heat. The energy of CO2, an incombustible
product, is less than that of the combustible C and O by 406 kj.
Hence to restore CO2 to the original state of free C and free O this
energy must be supplied. In nature the source of this energy is the
sun, which, acting upon the leaves of plants as its instruments,
breaks up the CO2 of the air, storing C in the plant and giving
O back to the air.


Symbol, O5. Molecular weight, 48.

When the sparks of an electric machine are passed through
dry air or oxygen a peculiar odor is developed. This odor has
been observed after thunder-storms or when flint and steel are
Struck. The odoriferous substance is named ozone (Greek,
ozeittf to smell).

Occurrence. — Owing to its odor, ozone can be recognized in
the air when present in the proportion of only one part to a hun-
dred thousand. Delicate tests detect it in sea air, at the seashore,
where water evaporates from sand and where the waves are broken
into spray; in the country, and especially in the air of pine forests.
On the windward side of cities it can be found, but all trace dis-
appears on the leeward side. The organic impurities emanating
from cities destroy the ozone.

Preparation. — Ozone can be produced by slowly oxidizing
phosphorus in moist air. A stick of phosphorus, freshly scraped,
is put in a wide-mouthed bottle of air or oxygen and half covered
with water. The bottle is closed for an hour or two, when, at the
end of that time, the ozone is present.

Another method is by adding 2 part? of potassium perman-
ganate to 3 parts of sulphuric acid.

Siemen^s induction tube generates ozone by discharging elec-
tricity silently through an atmosphere of dry oxygen. A tube of
glass covered with tinfoil, like the outer coat of a Ley den jar, encloses


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the space to be filled with oxygen. In the axis of this tube is
another, smaller and lined inside with tinfoil like the inner coat
of a Leyden jar. The dry oxygen slowly traverses the space
between the tubes, while the electric
discharge from either a friction ma-
chine or an induction coil passes
invisibly from the tinfoil on one tube,
through the glass and oxygen, to the
tinfoil on the other tube. In its
transit a portion of the odorless oxy-
gen acquires the odor of ozone and

Online LibraryA.M James W. HollandA TEXT-BOOK OF MEDICAL CHEMISTRY AND TOXICOLOGY → online text (page 6 of 67)