Wilfrid Richmond.

The Americana: a universal reference library, comprising the arts ..., Volume 10 online

. (page 125 of 185)
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rigidity, retraction and deformity of the valves,
and also frequently to adhesion of the cups along
the edges of closure.

These changes affect the function of the
valve, causing on the one hand narrowing of the
orifice so that the passage of the blood is ob-
structed, hence the technical use of the term
^obstruction,* or ^stenosis* ; on the other hand
the segments of valves may be so shortened and
puckered that they do not meet each other, and
so leakage results. To this condition the term
•insufficiency* or ^regurgitation* is applied.
Either obstruction of a valve orifice or leakage
through a valve calls upon the muscle of the
heart for more work. In the former case the
blood is forced under a greater resistance; in the
latter more blood must be forced to make up for
the leakage. The muscular wall thickens and
the cavity of the heart behind the leaky valve
enlarges to ^compensate,* as the expression is
for the. valvular defect. This compensation
may remain effective for years, the patient hav-
ing but little inconvenience from the disease.



Sooner or later the heart muscle feels the
effect of the prolonged overwork, it weakens,
becomes stretched, the cavity enclosed by
it enlarges, and the condition known as
^broken compensation* follows. The heart
can no longer supply a sufficient amount of
blood for the needs of the body, the circulation
is slowed, stagnation results with the associated
symptoms of distress in breathing and fre-
quently dropsy. There is marked impairment
in the functions of the organs of the body due
to imperfect blood supply. Valvular disease
is very common and may occur at any age, but
it usually involves the valves of the left heart,
mitral and aortic.

With care on the part of the patient life
may often be prolonged with comfort for many
years. Apart from the benefit derived from
rest, the drug digitalis by prolonging diastole
and stimulating the heart muscle to better con-
traction gives the best results. When properly
used it is a great boon to the patient.

The muscle of the heart undergoes a degen-
erative change in acute infective diseases asso-
ciated with fever, like typhoid fever, pneumonia,
and diphtheria, by which its contractile power
is lessened. It may reach such a degree as to
lead to death from paralysis of the heart wall.
If the patient recovers from the disease the
heart muscle in time recovers its normal tone.

An important disease of the heart muscle
is one occurring usually in males after middle
life, frequently associated with the symptom
known as angina pectoris. It is a degeneration
of the heart wall due to partial occlusion, by
thickening of the walls, of the two coronary
arteries which supply the heart muscle with
blood, thus disturbing the nutrition of the
muscle and the nerve ganglia. Angina pectoris
is characterized by the sensation of great con-
striction and pressure and often of a violent
tearing of the heart, with intense anxiety and a
feeling of impending death. The suffering is
often very great, and while the attack may be
of short duration the prostration following one
is marked.

Fatty degeneration of the heart muscle
occurs, but it cannot be diagnosticated with
exactness during life. Although the term is
often heard its use should be reserved as an
anatomical and not as a clinical diagnosis. That
is, one can be sure of it only when one sees the
exposed heart. On the other hand, collection of
fat between the muscle-fibres and around the
heart such as occurs in fat people may seriously
embarrass the heart by not allowing enough
space for it to move freely.



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HEART OF MIDLOTHIAN — HEAT



coffee, to tobacco, belong in this category. If
not used to excess the effect of the above may
be merely temporary, the heart resuming its
usual frequency and quiet action when the effect
of the stimulation has ceased. Prolonged abuse
of such substances or long continued nerve
worry or excitement may lead to a more per-
manent disturbance of the heart functions, indi-
cated by palpitation, either permanent or after
a trivial cause, or by irregularity in the rhythm.
The "tobacco heart* of the milder form is an
irritable one, with increased frequency of the
beat; in the severer grade marked irregularity
is characteristic. In the nervously tired person
palpitation is common, while the uncomfortable
sensations about the heart due to disturbed
digestion with fermentation in the stomach often
lead the individual to consult a physician feeling
that heart disease exists.

A nervous disorder of the heart of consider-
able interest is one associated with greatly in-
creased frequency of its beat, but with a regular
rhythm, combined with a marked prominence of
the eyeballs, enlarged neck (goitre) and tremor
of the hands. This complex has received the
name of exophthalmic goitre, a neuropathic
disturbance associated with irritation of the
sympathetic nerve leading to the rapid heart
action.

Still more uncommon and as yet unexplained
is the condition called Tachycardia (rapid
heart) characterized by paroxysmal attacks of
very rapid beating of the heart, lasting but a
short time and followed by normal frequency.
During an attack it may be impossible to count
the heart or pulse beats, owing to the rapidity.

Wm. Whitworth Gannett, M.D.,
Visiting Physician to the Massachusetts General
Hospital, Boston, Mass.

Heart of Midlothian, The, a romance by
Sir Walter Scott, published anonymously in 1818.
It takes its name from the Tolbooth or old jail
of Edinburgh (pulled down in 1815), where
Scott imagined Effie Deans, his heroine, to have
been imprisoned. The book is notable for hav-
ing fewer characters than any others of Scott's
novels. It has also, a smaller variety of inci-
dents, and less description of scenery.

Heart-urchin. One of a group of sea-
nrchins (see Echinoidea) of elongated form
and cordate outline from a lateral point of view.
The group is best represented by the genus
Spatangus, common in Europe, but heart-
urchins occur elsewhere, and are known as
fossils.

Hearts-ease, a violet (q.v.), especially the
common yellow violet of Europe, or a pansy.

Heat. Until the early part of the 19th cen-
tury, it was generally believed that heat is
a substance devoid of weight (imponderable),
and diffused through the mass of bodies. This
hypothetical substance was called caloric. Many
phenomena seemed to be explained by the as-
sumption of the existence of caloric, but finally,
through the experiments of Davy and Rumford,
in which heat was actually created from me-
chanical energy, the old caloric theory was aban-
doned. In its place we now have the molecular
motion theory. According to this theory heat
is nothing but a violent agitation of the mole-
cules of matter. These molecules are extremely
minute, but have a definite size and weight for



each definite substance. It has been estimated
that a molecule of water has a diameter of about
one fifty-millionth of an inch. Though mole-
cules are small in size, their velocity, even at
ordinary temperatures, is very great. In air, in
which the molecules dart about in straight lines
until they encounter other molecules, they at-
tain a speed of 1470 feet a second at the freezing
temperature. The average length of their path
between two encounters — the mean free path
— is about 1-277,000 inch, and the number of
molecules in a cubic inch of air is about 10
raised to the 21st power. Each molecule expe-
riences about 5,000,000,000 collisions a second.

Expansion of Solids, Liquids, and Gasw.—
The molecules of any substance attract one
another with a force called cohesion. It is co-
hesion that prevents a wire from breaking when
it supports a heavy weight. The pressure of
the atmosphere also helps to hold the molecules
of a body together. Opposed to both of these
forces is heat. The effect of the agitation of the
molecules is to make them jostle one another
apart. Thus it is that in general an increase of
temperature results in expansion, in solids, in
which the cohesion is enormous, the expansion
for a given increase of temperature is very
slight, especially when the test is made at low
temperatures. At higher temperatures, when
the molecules have somewhat weakened their
mutual hold through having moved further
apart, an increase of temperature equal to the
previous increase generally results in a some-
what greater expansion. To express such ideas
technically we employ the expression coefficient
of linear expansion, which means the fraction
of its length that a bar expands when heated
one degree centigrade. As the length varies
with the temperature, the length at the freezing
point, o° C, is taken as the standard length.
Using then this expression, we may say that the
coefficient of expansion of a solid generally in-
creases with the temperature. The coefficient
of linear expansion of a number of substances
will be found in the following table:

COEFFICIENTS OF LINEAR
Aluminium . . . .0.0000233

Gold 0.0000144

Iron 0.00001-2 1

Lead 0.0000293

Platinum 0.0000090

Copper 0.0000168

Zinc 0.0000292

Silver 0.0000193

Steel 0.0000123

G u i 1 1 a u m e's

nickel steel

(36 per cent

nickel) 0.00000087

Two notable cases may be remarked. It is
seen from the table that the coefficient for glass
is very close to that for platinum. This fact is
taken advantage of in the construction of incan-
descent electric lamps, and of those scientific
instruments where it is necessary to have a
wire pass through glass and leave an air-tight
joint. In making the joint, the glass around
the hole is softened by heat until it gathers
closely around the hot platinum wire. In cool-
ing, if the coefficient for platinum were higher
than that for glass, the platinum would contract
more rapidly than the glass and leave a leaky
joint. The second case to be noted is that of
Guillaume's nickel steel. The coefficient of ex-
pansion of this metal is so extremely small that



EXPANSION OF SOLIDS.
Wood (soft).... 0.000003
Wood (hard) . . .0.000006

Vulcanite 0.000067

Paraffin 0.00034

Quartz 0.0000013

Rock salt 0.00003

Ice 0.00005

Glass 0.0000083

Granite 0.0000087

Porcelain 0.000002s



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it is eminently suited to the construction of
clock pendulum rods, of surveying instruments,
and of standard # scales of length, and to many
other purposes in which much expansion now
proves an annoyance. Unfortunately the high
cost of nickel will preclude the employment of
this wonderful alloy in some cases.

The influence of expansion is seen in rail-
road tracks. On a cold day 6o-foot rails may
contract so as to draw apart one half of an inch.
The cables of the Brooklyn Bridge support the
slightly arched roadway. When they sag down
in hot weather through expansion, they tend to
make the roadway buckle. This tendency is
increased by the expansion of the roadway
itself. However, both tendencies were over-
come through the foresight of the engineers,
who provided a telescoping joint in the road-
way at the middle of the span. The parts of
this joint play in and out about a foot. On
hot days clock pendulums grow longer, and so
the clocks lose time. Glass when suddenly and
hence unevenly heated, expands more at one
point than at another, thus introducing internal
strains that cause fracture, but vessels made
of vitrified quartz, on account of their ex-
tremely low expansibility, resist this tendency
to crack; they will endure without injury the
sudden application of a blowpipe flame.

In liquids the molecules are so far freed
from cohesion that they are able to roll around
one another and to wander from one position to
another. ""The small remaining cohesion is as-
sisted by the pressure of the atmosphere or by
any other pressure to which the liquid may be
subjected and so the molecules in the body of
the liquid are prevented from flying directly
apart. It is on account of this small re-
sistance to expansion that we find liquids
very much more expansible than solids.
The term coefficient of cubical expansion is
employed to express the degree of expansibility
of a liquid. It means the fraction of its volume
that a liquid expands when its temperature is
raised one degree centigrade. The cubical
coefficient of a substance is three times as great
as its linear coefficient, because we measure the
effect of expansion in length, breadth, and thick-
ness, instead of merely noting the expansion in
length. Of course a liquid confined in a tube
of unchanging dimension could only expand in
length, but the effect in this one direction would
be three times as much as it would be if the
liquid were allowed to expand proportionally
in all three dimensions.

COEFFICIENTS OF CUBICAL EXPANSION, LIQUIDS.
Ethyl alcohol. ..o.oo t 06 Petroleum

Methyl alcohol. .0.00114 (heavy) 0.00090

Acetone ...... .0.00135 Mercury ..,,...0.00018x53

Ether 0.00148 Aniline 0.001x8

Olive oil 0.00080

The expansibility of water is strikingly ir-
regular. Starting at the freezing point, water
contracts as the temperature rises until at about
4° C. it has assumed its maximum density. A
further increase of temperature now causes the
water to expand, which it does at an increasing
rate until it begins to boil at 100 C.

Gases surpass even liquids in their expan-
sibility. Because in gases the molecules are rela-
tively very far apart, cohesion counts for nearly
nothing, leaving external pressure as almost the
sole force restraining expansion. It appears
that the coefficient of expansion of a gas is near-



ly independent of the external pressure, for
though a greater pressure tends to restrain ex-
pansion more, the greater crowding of the mole-
cules resulting from this pressure causes more
frequent blows among the molecules, and makes
the expansive force increase in nearly the same
proportion as the external pressure. This law
is not perfectly complied with because the mole-
cules in a gas are not quite free from cohesion,
especially when much compressed, and because
the diameter of the molecule is an appreciable
fraction of the distance between two molecules.
Another law, fulfilled only approximately for
the same reasons, is that all gases have the same
coefficient of expansion, as will be seen in the
following table, which gives the cubical coef-
ficient referred as a standard to the volume the
gas has at o° C.

COEFFICIENTS OF CUKCAL EXPANSION, GASES AT A
PRESSURE OF FROM 300 TO 5O0 MM.

Air 0.003667 Carbon dioxide. . . .0.003710

Hydrogen 0.003661 Nitrous oxide.. . . .0.0037x9

Nitrogen 0.003661 Cyanogen 0.003877

Carbon monoxide. 0.003667 Sulphur dioxide.. .0.003903

The Convection of Heat. — When the air in
contact with a hot stove becomes warmed, it ex-
pands and grows lighter than the other air.
Owing to unbalanced forces the hot air rises to
the ceiling and then spreads out to the walls. It
there becomes cooled, and therefore contracts
and becomes dense. As a result it descends at the
walls and finally returns to the stove only to
start again on the journey. During this proc-
ess, called convection, heat is carried by the air
from the stove to the most distant parts of the
room. Winds consist of convection currents in
the atmosphere. Some parts of the earth's sur-
face become more highly heated by the sun than
others. The air over the hot areas expands
and becomes specifically lighter than the sur-
rounding air. The general result is that the hot
air is forced to rise giving place to the surround-
ing cooler air which blows toward the hot area
as a surface wind. The hot air risen aloft
spreads away toward the cool regions as an
upper wind. Corresponding to the ascent
of air over the hot areas is a descent of air over
the cool areas. Much heat is brought from the
tropical regions to temperate regions by regular
winds.

Convection phenomena also occur in liquids.
A lar^e vessel of water supplied with heat at
one side of the bottom becomes through the
action of convection currents uniformly heated
throughout. Much heat is conveyed from the
equator toward the poles by means of the Gulf
Stream and other ocean currents. It is prob-
able, however, that with ocean currents differ-
ences of temperature have little to do with the
motion of the water, but that the motion is
caused chiefly by the action of winds that blow
with great steadiness in a westerly direction
across the equatorial portions of the great
oceans. Difference in salinity of the ocean at
different latitudes may possibly be a partial
cause of the phenomenon.

Thermometry. — Before proceeding further in
the discussion of heat phenomena, it will be
necessary to describe some of the methods em-
ployed for measuring temperature or the de-
gree of hotness of a Body. Most commonly the
methods depend upon the property of expansion.
In ordinary thermometers the expanding
body is either mercury or colored alcohol. The



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liquid, say mercury, is held in a glass tube hay-
ing a fine bore and at one end a spher-
ical or cylindrical bulb, the other end being
simply closed. Above the mercury, which fills
the bulb and part of the stem, is a space that
is free from air and contains only a small
amount of mercury vapor. When the ther-
mometer is warmed, the mercury rises in the
tube because the cubical expansion of mercury
is greater than the cubical expansion of glass.
The glass tube is provided with a scale, some-
times engraved directly on the tube, and some-
times engraved on some other material and
mounted at the back of the tube. For a Fahren-
heit scale, division number 32 is placed opposite
the mercury level when the thermometer is placed
in pure crushed melting ice, and division number
212 is placed opposite the mercury level when the
thermometer is placed in saturated steam over
boiling water. As the temperature of the boil-
ing point depends upon the atmospheric pres-
sure, which is ever varying, the standard boiling
point is taken to correspond to the average at-
mospheric pressure, which is measured by a
barometric column of 760 millimetres. The
space between these marks, the freezing and
boiling points, is divided into 180 equal divi-
sions, and then divisions equal to these are
extended above the boiling point and below the
freezing point. For the centigrade scale, which
is generally employed in scientific work, the
freezing point on the thermometer is marked
o° and the boiling point ioo°. For the Reau-
mur scale, much used for household purposes
in Germany, these points are marked o° and 8o°
respectively, and finally for the De Lisle scale,
which is used in Russia, the direction of the
graduation is reversed, the boiling point being
marked o° and the freezing point + 150 . With
this last thermometer, the greater the intensity
of the cold the higher the number representing
the temperature. Mercury thermometers permit
of the measurement of rather high temperatures,
mercury not boiling until the temperature of
about 357° C. (674.3 F.) is reached. Still
higher temperatures with mercury thermome-
ters may be reached by checking the vaporiza-
tion of the mercury through the introduction into
the upper part of the tube of a compressed gas
such as nitrogen. With such a thermometer
the only limitation is the softening of the glass
at high heats, and even this trouble is largely
lessened by the use of vitrified quartz for the
material of the bulb. On the other hand, mer-
cury freezes at about — 39 C. ( — 38.2 F.)
and so becomes useless for indicating tempera-
tures lower than this. For these lower tem-
peratures alcohol may be employed as the ther-
mometric substance because it resists freezing
until temperatures far below any met with in na-
ture are encountered. In addition to this ad-
vantage alcohol expands much more rapidly than
mercury, thus permitting a much larger bore
for the same length of degree. However, for
very high temperatures alcohol is not available,
as it boils at the moderate temperature of
78-3° C. (173° F.).

In practical work thermometry fairly bristles
with errors. For several months after a ther-
mometer is made the bulb gradually shrinks,
probably owing to some molecular instability in
the glass caused by the excessive heating em-
ployed in the process of blowing the bull). This
causes the thermometer to read too high. After



each time a thermometer is used for a very high
temperature the bulb on cooling fails to con-
tract promptly to the volume proper to the new
temperature, and so now the thermometer for
a while reads too low ; however, prolonged heat-
ing at the temperature of boiling mercury tends
to put the glass into a more stable state. Also
such troubles are much reduced by the use of
hard glass instead of soft glass for the bulbs.
Errors also arise from the following causes:
non-uniformity of the bore; variations of atmo-
spheric pressure, which cause a yielding of the
bulb; failure to have the stem of the thermom-
eter at the same temperature as the bulb; the
hydrostatic pressure on the bulb due to the
liquid being tested, especially when the ther-
mometer is sunk to great depths; a variation
in the internal pressure of the mercury itself
on the bulb when the thermometer is inclined
from the vertical position to the horizontal; a
peculiar jerking motion of the mercury when it
ascends a very fine bore; the fact that equal
volumes of the bore marked off on the tube do
not represent equal expansions of the mercury,
since at high temperatures the volume of the
boTe indicating a degree has increased (this is
quite distinct from the matter of the relative
expansion of glass and mercury) ; irregularities
in the expansion of the glass of the thermom-
eter; and lastly irregularities in the expansion
of the fluid itself, be it mercury, alcohol, air, or
any other substance. This last source of error
is worth much consideration because two ther-
mometers otherwise perfect but containing dif-
ferent liquids, as alcohol and mercury, fail to
agree in their indications. Further, we have no
right arbitrarily to select any particular fluid
as a standard and yet feel that our temperature
scale has anything more than an empirical value.
It will, however, be explained in the last sec-
tion how a theoretical definition for tempera-
ture measurement can be formulated (the ther-
modynamic scale), agreeing fairly with ordinary
thermometers, very closely with the hydrogen
or nitrogen thermometer, and perfectly free from
ambiguity.

In the hydrogen thermometer advantage is
taken of the increase of pressure of a gas at-
tending an increase of temperature, the volume
of the gas being kept constant. The hydrogen
is confined in a glass bulb about two inches in
diameter which is connected by a thick-walled
capillary tube with the top of one side of a
U-shaped apparatus consisting of two vertical
glass tubes connected by a rubber hose at their
lower ends and partly filled with mercury.
When the hydrogen in the bulb is warmed it
tends to expand and push the mercury down
its side of the U and to cause it to rise on the
other side, which is open to the atmosphere.
This effect is counteracted by raising the glass
tube on the open side,, the rubber tubing allow-
ing this to be done. The extra back pressure
of the mercury forces the hydrogen back to its
former volume. In measuring the pressure to
which the hydrogen at any time is subjected,
the difference in level of the mercury columns
must have added to it the length of the baro-
metric column measured at the time. For each
degree centigrade added to the temperature,
the hydrogen is found to increase in pressure
about 1/273 of its pressure measured at o° C
Similarly for each degree subtracted, the pres-
sure decreases 1/273 of the pressure at o* C



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If this law held to the limit, we would conclude
that at — 273 C the hydrogen would lose all
its pressure, thus indicating the cessation of all
molecular motion — a veritable absolute zero of
temperature. However, at extremely low tem-
peratures the perfect working of this law is
interfered with through the dominance of cohe-
sion which reduces unduly the pressure of the
hydrogen, and may cause it to assume the liquid
or even the solid state. Nevertheless, this limit-
ing temperature as predicted by the hydrogen
thermometer agrees almost exactly with the true
absolute zero of the thermodynamic scale
referred to above. On this absolute scale the
temperature of freezing water is approximately



Online LibraryWilfrid RichmondThe Americana: a universal reference library, comprising the arts ..., Volume 10 → online text (page 125 of 185)