Wilfrid Richmond.

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

. (page 127 of 185)
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of an inch long, while the length of the long-
est heat waves is about 1/300 inch. The short-
est ultra-violet waves are about 1/250,000 inch
long. All ether waves have the same velocity
as Tight, namely, 186,300 miles a second. All
may be reflected, refracted, and polarized; and
may be absorbed by transmission to a degree
depending upon the substance used for trans-
mission and the particular wave-length of the
rays.

Thermodynamics. — The most cogent reason
for discarding the caloric theory of heat is that
heat may be generated from that which is not
in any sense substance — heat may be derived
from mechanical energy. Heat is generated when
a brass button is rubbed on the carpet, when a
bullet is struck with a hammer, and when two
pieces of ice are rubbed together, a process result-
ing in their melting. The relation between
mechanical energy and the heat energy generated
by its consumption was first carefully investi-
gated by J. P. Joule before 1850. One pound-
calorie of heat energy is obtained from 1,400 foot-
pounds of mechanical energy. That is to
say, the energy due to the fall of 1400 pounds
through the distance of a foot is sufficient if
transformed into heat to raise the temperature
of a pound of water through one degree centi-
grade. This number of foot-pounds is called the
mechanical equivalent of heat, for it has been
found that the process ts reversible. When by
means of an air-engine or a steam-engine one
pound-calorie of heat is consumed in generating
mechanical energy, 1400 foot-pounds of the latter
are obtained. The first taw of thermody-
namics states that when mechanical energy is
converted into heat, or when heat is converted
into mechanical energy, the quantity of mechan-
ical energy is equivalent to the quantity of heat
energy. The second law of thermodynamics
states that it is impossible for a machine with-
out the consumption of external energy to make
heat pass from a body at a low temperature to
one at a high temperature. When external
energy is supplied, the transfer of heat
becomes possible through the use of a re-
versible engine. A reversible engine is one
that, while it may, on the one hand, take heat
from a high temperature source and transfer
it to a low temperature escape with a conver-
sion of a definite portion of the heat into me-
chanical energy, may, on the other hand, when
its operation is reversed by the application of
external mechanical energy equal in amount
to that generated in the first operation, take
back the same heat from the low tempera-
ture escape and transfer it, together with an
amount of heat equal to that lost in the first
operation, to the high temperature source. The
fraction of the heat leaving the high temperature
source converted into mechanical energy, or,
when the engine is reversed, the fraction of
the heat entering the high temperature source
obtained from the mechanical energy applied has
been shown by Carnot to be the same for all
Vol. m — 31



reversible engines of whatever nature and work-
ing with any substance whatsoever, provided
they work between the same temperatures. This
fraction may be called the thermodynamic effi-
ciency of the engine. The thermodynamic effi-
ciency of good steam-engines occasionally ex-
ceeds 20 per cent. This means that 20 per cent
of the heat energy supplied to engine is trans-
formed into mechanical energy, the remaining
80 per cent escaping unused at the condenser or
exhaust.

Using the provisional absolute scale as indi-
cated by a hydrogen thermometer, experiment
shows that the efficiency, W/H, is roughly repre-
sented by the following equation in which W
stands for the mechanical energy realized, H for
the heat (measured in the equivalent foot-
pounds) leaving the high temperature source, T
for the temperature of the source, and T 1 for
the temperature of the cooler escape.
W T — T 1



H T

This suggests a new definition for a tempera-
ture scale, namely that numerical values of tem-
peratures be so adjusted as to fulfil exactly the
above formula. Since the formula only fixes a
ratio between the temperatures T and T* corre-
sponding to a given efficiency, an infinite number
of sets of numerical values for these tempera-
tures could be found to satisfy the formula^ But
if it be decided that a definite numerical range,
say one himdred degrees, be comprised between
the freezing and boiling points of water,
only one set of values becomes possible.
This decision makes the value of the freezing
point very nearly + 273 Abs., and the
value of the boiling point +370° Abs.
Lord Kelvin was the first to propose this
thermodynamic scale. Theory shows that
its indications would correspond exactly to
a thermometer containing a perfect gas. Hy-
drogen is not quite a perfect gas, for its mole-
cules attract each other slightly and they occupy
an appreciable fraction of the space holding the
gas. Hence there are small deviations of the hy-
drogen thermometer from the thermodynamic
scale, especially at low temperatures. In spite
of these difficulties much progress in the real-
ization of the thermodynamic scale has been
achieved through ingenious mathematical con-
siderations relating to two sets of experimental
observations: those made by Regnault on the
expansion and on the increase of pressure of
hydrogen and other gases when heated, and
those made by Joule and Kelvin on the temper-
ature changes suffered by gases in passing
through a porous plug. Nevertheless, the ther-
modynamic scale offers us a theoretical ideal
which is independent of the thermal properties
of any particular substance, but is only related
m a definite way to a fixed universal law.

When a small amount of heat is transferred
from or to a gram of a substance, the heat trans-
ferred (measured in calories), divided by the
average absolute temperature of the substance at
the time of the transference is called the change
of entropy of the substance. For convenience, the
zero of entropy is generally taken to correspond
to water at the freezing point and under the nor-
mal atmospheric pressure. It may be shown that
when two bodies at different temperatures are



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HEATH — HEATING AND VENTILATION



placed in contact and their temperatures become
equalized, the average entropy rises, for from
the above definition of entropy, the heat leaving
the hotter body must reduce its entropy less than
it increases the entropy of the cooler body into
which the heat enters. Consequently the aver-
age entropy of the universe is constantly rising
and tending toward a maximum. At the same
time the availability of the energy of the uni-
verse is tending toward zero.

Ernest R. von Nardroff, E. M. t D. So,
Principal Stuyvesant High School, New York
Ctty.

Heath, Daniel Collamore, American pub-
lisher : b. Salem, Maine, 26 Oct. 1843 ; d. 29 Jan.
1908. He was graduated from Amherst in 1868, -
became a iunior member of the firm of Ginn
and Heatfe, publishers of Boston, and in
1886 established in Boston the house of D. C.
Heath & Company, publishers of text-books for
schools and colleges, with branch offices in New
York, Chicago and London.

Heath, Francis George, English writer:
b. Totnes, Devon, 15 Jan. 1843. He entered the
civil service as a clerk of the higher division
in the customs department in 1862, and was
transferred as surveyor to the outdoor division
of that department in 1882. In 1896 he founded
and in 1897 became editor of the Imperial Press,
in connection with which he directed from
1896 the publication of the Imperial library.
He was for several years prominent in his ac-
tivity for the preservation and extension of open
spaces in and about London; and published:
<The «Romance» of Peasant Life* (1872) ; ( The
Fern World ) (1877; 10th ed. 1902); <Our
Woodland Trees* (1878); ( Where to Find
Ferns ) (1881), and other volumes.

Heath, Perry Sanford, American journal-
ist and politician : b. Muncie, Ind., 31 Aug. 1857.
He learned the printer's trade, in 1877 became
a newspaper reporter, in 1878-&0 was editor of
the Muncie Times, and in 1881 established the
Pioneer at Aberdeen, S. D. In 1881-03 he was
a correspondent at Washington, D. C, in 1894-6
president and general-manager of the Cincinnati
Commercial-Gaxctte (now the Commercial-Trib-
une), and in 1897-1900 was first assistant post-
master-general of the United States. In 1900
he was elected secretary of the Republican Na-
tional committee.

Heath, William, American soldier: b.
Roxbury, Mass., 7 March 1737; d. there 24 Jan.
1814. When the Massachusetts congress in 1774
voted to enroll 12,000 minute men, volunteers
from among the militia. Heath, then a farmer
in Roxbury, was commissioned as one of the
generals. In June 1775 he received the appoint-
ment of brigadier in the Continental army, and
in August 1776 was created major-general.
When the troops moved to New York Heath
was stationed in the highlands near King's
Bridge, with orders to throw up fortifications
for the defense of that important pass. In 1777
he was transferred to Boston, and the prisoners
of Saratoga were entrusted to him. In June
1779 he was again in New York, at the High-
lands, with four regiments, and was stationed
near the Hudson till the close of the war. He
was the last surviving major-general of the war.
Consult: ( Memoirs of Ma j .-Gen. Heath, con-



taining Anecdotes, Details of Skirmishes, Bat-
tles, etc., during the American War* (1798)-

Heathcock, Heath-hen. See Blackcock.

Heath'cote, Caleb, American merchant: b.
Chesterfield, Derbyshire, England, 6 March
1665 ; d. New York 28 Feb. 1721. He was suc-
cessful in a mercantile career in New York
from 1692, save for the years 1698-1701, was a
councillor of the province^ was a petitioner for
a license to build Old Trinity, was mayor of
New York in 1711-14, and held other posts,
among them those of judge of Westchester
County; commander-in-chief of the military of
the colony; surveyor-general; and receiver ^gen-
eral of customs for North America. His letters
and despatches afford interesting glimpses of
the history of his time.

Heaths, or Heather, a group (Ericoideee)
of the order Ericacea. The leaves of the heaths
are simple and entire; their flowers oval, cylin-
drical, or even swelled at the base; the anthers
of many with horn-like appendages. From 400
to 500 species are known, 12 or 15 of which in-
habit Europe, and have small flowers, while all
the remainder are natives of South Africa, many
of them bearing brilliantly colored flowers, and
forming one of the most characteristic genera
of that region of dry plains. The common heath
of Europe (Calluna vulgaris), a low shrub, often
covers exclusively extensive tracts of dry land,
and is used in domestic economy; mixed with
oak-bark it is employed in tanning; and also,
when tender, for fodder. This species forms
the "heather* of British moorlands; but in
Scotland are two other species, whose flowers
are the "heather-bells* of Scottish song and
story. Many South African species, remarkable
for the size and beauty of their flowers, are
much cultivated in greenhouses, and have been
so improved and hybridized that they exhibit a
wonderful richness of color.

Heating and Ventilation. Generally speak-
ing, tile methods of heating buildings may be
divided into two general classes — the direct
and the indirect system, or a combination of the
two. Heating by means of an open fire, by a
stove, and by radiators placed in the rooms to
be warmed are examples of the former method,
while furnace-heating and heating by means of
a current of air warmed by indirect steam or
hot-water coils are examples of the latter
method. When a direct radiator is fitted with
a connection to the outer air, it is said to be
arranged on the direct-indirect principle. Hot
water, steam, or electricity may be the vehicle
used for conveying heat to radiators. Ventila-
tion is only obtained by supplying air, and in
some systems of heating and ventilation the air
is made so hot that part of it is available for heat-
ing purposes. This is the case in furnace-heating.

It is well known that when two bodies of
different temperature exist, heat passes from
the warmer to the cooler body until their tem-
peratures are equal If a building be of a
temperature of 70 F. and the outer air of a
lower temperature, heat will be transmitted by
the walls, windows, and other exposed surfaces,
and the temperature of the air in the building
will be lowered. It is only by supplying to the
building an amount of heat equivalent to that
transmitted by the walls and windows that it
is possible to maintain the building at constant
temperature. If we supply more heat than is



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HEAXINO AMD VENTILATION



transmitted by the walls, the temperature of the
room rises.

Heat is measured in units which have as
exact a value as a ton of coal or a pound of
sugar. British physicists have selected as the
unit of heat that quantity which will raise the
temperature of one pound of water one degree
on the Fahrenheit scale when the water's tem-
perature is near 39 F. This unit is designated
as the British thermal unit It is known with
reasonable accuracy just how many heat-units
are transmitted by each square foot of wall,
window, and other exposed surfaces of the vari-
ous materials used in building construction, un-
der such extreme conditions as to building and
outside temperature as may exist With these
data and the plans of a building, calculation will
show the heat-loss from a building or a room*
and the heating-apparatus should be propor-
tioned to supply this amount of heat Allow*
ances are made for various conditions that may
exist, depending upon the judgment and ex-
perience of the designer. The heat required
can be supplied by radiation from an open fire
or from a stove, but this is an unsatisfactory
method. • Direct radiators supplied with steam
or hot water can be placed in a room to furnish
the heat necessary, or the heat may be sup-
plied by hot air from a furnace, or by air heated
by indirect radiators supplied with steam or
hot water.

Heating by hot air is a slightly more ex-
pensive method than heating by direct radia-
tion, for to be effective the air must be taken m
from outdoors, sometimes at very low temper-
ature, and heated above the temperature of the
room to be warmed. If cold an* at 40 ° F. is
heated to ioo° F., and is supplied to a room at
this temperature, it is evident that as soon as
this air is cooled from ioo° to 70 no more heat
can pass from the air to the room if the tem-
perature of the latter remains at 70 . Under
these conditions only one-half of the heat that
has been supplied to the air is available for heat-
ing the room. This will tend to show why
heating by hot air is more expensive, estimated
from the cost of fuel, than the direct system.
When the advantages of the air supply that
accompanies indirect heating are taken into ac-
count the increased fuel cost becomes insignifi-
cant.

Direct heating is usually obtained by steam
and hot-water radiators. Although manufac-
turers have greatly improved the appearance of
direct radiators, at best they are unsightly and
objectionable from an artistic point of view.
This objection may be overcome by concealing
the radiators in boxing beneath windows, when
the walls of the building are thick enough to
permit the boxing to be built in without project-
ing into the room. A screened opening is pro-
vided in the front of the boxing near the floor,
and one at the top over the radiator, to permit
a circulation of air, so that the radiators can be
effective.

In residence-heating it is frequently the cus-
tom to heat the first floor by the indirect method
and the upper stories by the direct. When an
owner will pay for it, the indirect method is
used throughout the building. Such a system
is much to be preferred to tne direct.

The simplest method of connecting steam-
radiators is by the gravity system, and it is usu-



ally employed unless steam exhausted by en-
gines is available for heating. This system
comprises distributing-mains connecting with
the top of the boiler, and with vertical riser-
pipes from which horizontal branches lead to
the radiators. Usually a return pipe is con-
nected to the opposite end of the radiators from
that at which steam is admitted, this return
connecting, through return risers and mains,
with the boiler at a point below the water-line.
As the steam in the radiators condenses, the
resulting condensation flows back by gravity
through the return pipes to the boiler. The
flow and return pipes are made sufficiently large
to insure a practically uniform pressure through-
out the system. The system is simplicity itself,
as the fire only needs attention. When the
boiler is once filled, no more water is required.

It is only recently that the steam exhausted
by engines and pumps has been used for
heating. Before this time steam direct from
the boilers was used in direct radiators for heatr
ing mills and factories. The radiators consisted
of coils of pipe suspended from the walls or
ceilings. Sometimes the condensation was re-
turned to the boilers by a pump or other device ;
sometimes it was allowed to go to waste. As
the steam exhausted by engines, pumps, etc,
contains a very large percentage of the heat
that it contained upon entering the engine, some-
one conceived the idea of utilizing this steam
for heating buildings, thereby saving the steam
direct from the boilers that would otherwise
have to be used. This practice is now almost
universal where exhaust-steam is available, and
the saving that it has occasioned is very great
By placing what is known as a back-pressure
valve in the exhaust-pipe, sufficient pressure is
maintained to cause the exhaust-steam to cir-
culate through the pipes and radiators of the
heating-system, the latter being connected to the
exhaust-pipe between the engine and the back-
pressure valve. The condensation that occurs
in the heating system can be collected and re-
turned to the boilers by various methods. Usu-
ally a pump or similarly acting device is em-
ployed.

A hot- water system arranged on the gravity-
principle has flow and return pipes similar to
the gravity-system of steam-heating described.
The entire system is filled with water. As the
water is warmed in the boilers it becomes lighter
in weight per cubic foot, making a difference in
pressure between the flow and return pipes and
causing a circulation to begin. The water rises
in the flow pipes to the radiators and is there
cooled. On its return to the boiler the water
is again heated, and so the circulation is main-
tained. As the difference in weight between the
water in the flow and return pipes is very
slight, the motive power producing the circula-
tion is very slight also. Hence the pipes have
to be relatively larger than for steam-heating
and very carefully connected to avoid excessive
friction, which would stop or retard the cir-
culation. As large pipes are costly, in some
large plants heated by hot water, a circulation is
brought about by pumps.

Direct steam-radiators emit about 250 Brit-
ish thermal units per square foot of radiating
surface per hour, and hot- water radiators about
180 heat-units per square foot. Consequently
about one third more radiating surface is neces-



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HEATING AND VENTILATION



sary with hot water than with steam. The pipes
also must be larger, hence the hot-water sys-
tem is the most expensive in first cost. Hot
water, however, is cheaper to operate, for water
will circulate with a very low fire and supply
the small amount of heat required to warm a
building in mild weather.

With direct steam-heat, operating on the
gravity-system, it is impossible to vary to any
appreciable extent the temperature of steam in
a radiator; hence with this system the alterna-
tive is, all the heat the radiator will supply or
none at all. This is the principal objection to
heating by means of direct steam. Air warmed
by the relatively cooler hot-water radiators is
thought by some to be more agreeable than air
heated by steam-radiators.

With indirect heating the lack of means of
regulating the steam-temperature is not of so
much moment, for the air-supply can be partly
shut off by partly closing a register in mild
weather; or else, if the full air-supply is re-
quired at all times, arrangements can be made
for passing part of the air-supply around the
indirect radiators, which is called ^y-passing*
them. Another method is to divide the indirect
radiator into independent sections and place
some of the sections under the control of a
regulator that automatically shuts off the sup-
ply of steam when the room becomes too warm.
The method of ^by-passing* the radiator, or
subdividing it, is used mainly with the fan-
system of supplying air.

The cost of indirect hot-water heating is
greater than that of indirect heating by steam,
as the radiators and pipes must be larger, the
same as in direct heating. Hot water is, how-
ever, cheaper to operate. The principal objec-
tion to its use in indirect heating is the possi-
bility of damage to the indirect radiators through
the freezing of the water in them in severe
weather, if the circulation should from any
cause be arrested.

The direct-indirect system consists of direct
radiators connected with the outer air by means
of an opening in the building-walls beneath the
window-sill, the radiator being set under the
window opposite the opening. With this sys-
tem there is always the possibility of getting too
much air when the wind blows strongly. Fur-
thermore, in situations where the air is smoke-
laden or dusty, it is not easy to keep the smoke
and dust from entering a building supplied
with air by this means.

As has been said, a supply of air may be
brought about by the gravity-method or by means
of fans. In the gravity-method the heated column
of air in the flue is lighter than the outdoor
air; hence it rises. As in the case of hot- water
heating, the motive power is very slight, and it
becomes less as the outdoor temperature in-
creases. For this reason the gravity system is
not a positive one, and it cannot be depended
upon to supply much air in mild weather. Its
use for schoolhouse ventilation is therefore to
be deprecated. An important advantage of this
system is its simplicity, as no machinery is re-
quired with it.

With the fan-system some type of fan is em-
ployed, to give a positive supply of air. The
air is blown over coils, usually steam, and de-
livered to the room at a temperature slightly
above that of the room, if the air-supply is in-



tended to ventilate only, or at a higher temper-
ature if the air-supply is to carry with it the
heat necessary to balance that transmitted by
the walls and windows. In the former event
the indirect coils act as tempering-coils, being
sufficient only to raise the air to about 70 F.
If the air-supply is to furnish heat for warming
the rooms, additional coils, known as supple-
mentary coils, are provided. These raise the
air-temperature from 70 to from ioo° to 120
F. Sometimes the supplementary coils are com-
bined with the tempering coils, the whole being
divided into several independently controlled
sections. In some instances the supplementary
coils are divided into a number of small coils,
one being placed at the base of each air-supply
flue, and so arranged that, by adjusting dampers
controlled by hand or automatically, the tem-
perature of the ait supplied to any room can be
regulated independently of that supplied to other
rooms. If all of the air is passed through one
group of coils, independent regulation of the
temperature of the air in the branch ducts and
flues is impossible. This independent regula-
tion can be obtained, however, by the douWe-
duct system. The coils are divided into two
groups, one for tempering and one for supplying .
additional heat. All of the air is passed through
the tempering coils, but only part of it through
the supplementary coils, the balance "by-passing*
the latter coils and flowing through a system
of ducts, usually located below the system con-
veying the air of higher temperature, to the
base of the flues. At the junction of the two
ducts a mixing-damper is provided, so arranged
as to open in one duct as it closes in the other.
By adjusting this damper the air can be mixed
to give the resultant temperature required.

In situations where direct radiators can be



Online LibraryWilfrid RichmondThe Americana: a universal reference library, comprising the arts ..., Volume 10 → online text (page 127 of 185)