mechanical work to be expended. In
any given machine the work may be ac-
counted for as follows:
Friction.
Heat rejected during compression.
Heat acquired by the refrigerating
agent in passing through the pump.
Work expended in discharging the
compressed vapor from the pump.
Against which must be set —
Work done by the vapor entering the
pump.
Assuming that vapor alone enters the
pump, the heat rejected in the condenser
is —
Heat of vaporization acquired in the
refrigerator, with the correction necessary
for difference in pressure.
Heat acquired in the pump, less the
amount due to the difference between
the temperature at whidi liquefaction
occurs and that at which the vapor en-
tered the pump.
Though circumstances vary so much
that no absolutely definite statement can
be made as to the working of ether ma-
chines in general, the following particu-
lars, taken from actual experiment in
this country, will serve to show what
may be expected under ordinary condi-
tions :
Production of ice, tons per 24
houTB 16 tons.
Production of ice, lb. per hour. 1,400 lbs.
Heat-units per hour abstracted in
ice-making 246,000 units
Indicated horse-power in steam
cylinder, excluding that re-
quired for circulating the cool-
ing water, and for working
crane, &c 88 I. H. P.
Indicated horse-power in ether
pump 46J I. H. P.
Thermal equivalent of work in
ether pump, units per hour. . . 119,261 units
Ratio of work in pump to work
in ice-making 1 to 2.06
Temperature of water entering
condenser 62® Fahr.
Assuming the coal consumption per
indicated horse-power to be 2 lbs. per
hour, and the price of coal 15s. a ton,
the total cost of producing transparent
block ice in this country on the ether
system, with such a machine as that just
referred to, may be taken at about 5s. per
ton, excluding allowance for repairs and
depreciation. The production of ice would
be about 8.3 tons per ton of coal. For
cooling water and other liquids another
machine is used ; but in this case the ice-
boxes are dispensed with, the liquid be-
ing passed direct through the refrigera-
tor without the employment of brine.
Methylic ether, a liquid with a latent
heat of vaporization of — , and which
boils under atmospheric pressure at 10 5"
below zero Fahr., has been employed by
Tellier in machinery of practically simi-
lar design to that used with ordinary
ether. Tellier's apparatus has never
come into use in this country, and need
not be further dwelt on, for beyond the
difference in size of pump, and the obvi-
ous alterations due to the higher work-
ing pressures, it presents no features of
importance. Some years ago Raoul Pic-
tet, of Geneva, successfully introduced
sulphur dioxide as a refrigerating agent,
and in France a large number of his ma-
chines hav6 been made and put to work.
In this country, also, they have been
used, but to a much smaller extent. It
is a liquid with a latent heat of vaporiza-
tion of 182°, and imder atmospheric
pressure boils at 14" Fahr. This ma-
chine is also of similar design to those
in which ether is employed ; but Pictet
combined the refrigerator with the ice-
making tanks, the brine being circulated
by means of a fan. In this way the space
occupied was reduced, and the efficiency
somewhat increased. The cost of produc-
ing ice by the Tellier and Pictet machines
may be taken at practically the same as
that by the other process. Some of the
more volatile derivatives of coal tar have
been used in compression machines, espe-
cially in the United States ; but it will be
unnecessary to refer to them in detail,
as their application has been exceedingly
limited.
Anhydrous ammonia, which may now
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VAN NOSTKAND'S ENGINEERING MAGAZINE.
be obtained as an article of commerce,
Las of late years been very largely intro-
duced as a refrigerating agent, more
especially in Germany and in the United
States. Under atmospheric pressure, an-
hydrous liquid ammonia boils at 37.30°
below zero Fahr., and under this condi-
tion its latent heat of vaporization is
900°. So far as the cycle of operation is
concerned, it is precisely the same as for
either ; the liquid is vaporised in the re-
frigerator by the action of the pump,
-which then compresses the vapor, and
delivers it into the condenser at such
pressure as to cause it to hquefy. In the
construction of ammonia machines, how-
ever, there are two essential points of
difference. For, in the first place, the
pressure of the ammonia vapor is much
higher than that of ether at the same
temperatures, its tension at 60° Fahr.
being 108 lbs. per square inch ; and, sec-
dndly, owing to the action of ammonia on
copper, no brass or gun metal can be
used in any part with which the gas or
hquid comes into contact. One of the
chief difficulties encountered in the com-
pression of ammonia is leakage at the
pump gland. The gas is extremely
searching, and even at the comparatively
low pressure of 30 lbs. per square inch
above the atmosj^here it will readily find
its way through an ordinary gland;
while at the pressiu-e existing in the con-
denser, which may be taken at from 150
to 180 lbs. per square inch, this tend-
ency is of course much aggravated. In
order to minimise the leakage and to
simplify the construction of the gland,
the pumps are frequently made single-
acting, as in this way the gland is ex-
posed only to the refrigerator pressure,
which is seldom above 30 lbs. It is also
usual for glycerine, or some lubricant
that does not saponify with ammonia, to
be injected into the pump, so as to form
a liquid seal for the gland, and in some
cases for the piston as well ; this is the
general practice in the United States.
In Germany, on the other hand, where
the compression machine has been very
largely appHed, the double-acting pump
is more usual. To lessen leakage, Linde
provides a chamber in the gland box,
into which glycerine or some suitable
lubricant is constantly forced at a slight-
ly greater pressure than that prevaUing
in the condenser, so that the tendency
is for the lubricant to leak inwards, in-
stead of ammonia outwards. Any lubri-
cant that does get into the pump passes
out with the ammonia, and is separated
from it in a suitable vessel. Up to the
present time, so few ammonia compres-
sion machines have been constructed in
England, that as yet no general practice
has been estabhshed; but, on the whole,
the feeling seems to be in favor of the
singfle-acting pump.
With regard to the other parts of the
apparatus, but little need be said.
Wrought-iron coils or zig-zags are used
for both the condenser and the refriger-
ator, their precise form depending on
the fancy of the designer. The refriger-
ator is generally combined with the ice-
tanks, the cooling pipes being placed
either below or at the side of the molds,
sometimes in a separate compartment
and sometimes in the same tank. With
the cell system an independent refriger-
ator is used, the cooled brine being cir-
culated by a pump in a similar manner
to that described for the ether system.
Owing to the low temperature which
may be attained by the use of ammonia,
care has been taken in the selection of a
brine that will not congeal with the de-
gree of cold to which it will be subjected.
A solution of calcium or magnesium
chloride in water is generally used. The
mechanical work expended in compress-
ing ammonia may be accounted for in a
precisely similar manner to that expended
in the compression of ether. Notwith-
standing that the degree of compression
is so much greater with ammonia than
with ether, the energy axpended in com-
pressing, heating, and delivering the gas
is less, owing to the much smaller
weight of ammonia required to produce
a given refrigerating effect, the weights
being in the inverse ratio of the heats of
vaporization, or as one to 5.45. For
this reason the cost of making ice is
much less with ammonia than with
ether, one ton of coal being capable of
producing as much as 12 tons of ice in
well-constructed ammonia apparatus hav-
ing a capacity of 15 tons per 24 hours.
With coal at 15s. a ton, the cost of mak-
ing ice by the ammonia compression sys-
tem may be taken at about 3s. 9d. per
ton for a production of 15 tons per 24
hours, exclusive of allowances for re-
pairs and depreciation. Through the
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REFRIGERATING AND ICE-MAKINa MACHINERY.
131
courtesy of the maDager of the Linde
British Ice Company, the author is en-
abled to give the following results of a
test made by a committee of Bavarian
engineers, with a machine erected in a
brewery in Germany. The test, he be-
lieves was carried out in an impartial
manner ; and though it is not put for-
ward by the Linde Company as showing
the results attained in the ordinary
working of their machines, it will never-
theless be of interest as indicating what
may be expected under the most favor
able conditions :
!NomiDal capacity of machine,
tons of ice per 21 hours 24 tons.
Actual production of ice, tons
per 24 hours 39.2 tons.
Actual production of ice, lbs. per
hour 8,669 lbs.
Heat -units abstracted per hour in
ice making 731,800 units
Indicated horse power in steam
cylinder, excluding that re-
quired for circulating the cool-
ing water and for working
cranes 53 I. H. P.
Indicated horse-power in ammo-
nia pump 38I.H.P.
Thermal equivalent of work in
ammonia pump, units per hour 97,460 units.
Ratio of work in pump to work
in ice-making 1 to 7.5
Total feed-water used in boiler,
lbs. per 24 hours 26,754 lbs.
Ratio of coal consumed to ice
made, taking an evaporation of
8 lbs. of water per lb. of coal.. 1 to 26.3
In this case the pumps were driven by
a Sulzer engine, which developed one in-
dicated horse-power with 21.8 lbs. of
steam per hour, including the amount
condensed in steam pipes. Ammonia
compression machines are manufactured
in this country by Messrs. Siebe, Gor-
man & Co., the Birmingham Refrigera-
tion Company, and Linde British Ice
Company.
St/stem C, — This is known as the ab-
sorption process, and was first applied
by Carre about 1850. The principle
employed is chemical or physical, rather
than mechanical, and depends on the
fact that many vapors of low boiling-
point are readily absorbed by water, but
can be separated again by the application
of heat to the mixed liquid. A consid-
erable number of machines in which
ammunia was used in combination with
water as an absorbent were made by
Carre in France ; but no very high de-
gree of perfection was arrived at, owing
to the impossibility of getting an anhy-
drous product of distillation ; the am-
monia distilled over contained about 26
per cent, of water, which caused a use-
less expenditure of heat during evapora-
tion and rendered the working of the ap-
paratus intermittent Taking advantage
of the fact that two vapors of differ ent
boiling points, when mixed, can be sep-
arated by means of fractional condensa-
tion, Rees Reece brought out, in 1867,
an absorption machine, in which the dis-
tillate was very nearly anhydrous. The
action of the machine was briefly as fol-
lows : Ordinary liquid ammonia of com-
merce, of 0.880 specific gravity, was
heated, and a mixed vapor of ammonia
and water was driven off. By means of
vessels termed the analyzer and the rec-
tifyer, the bulk of the water was con-
densed at a comparatively high tempera-
ture, and run back to the generator ;
while the ammonia passed into a con-
denser, and there assumed the liquid
form under the pressure produced by the
heat,and the cooling action of water cir-
culating outside. The nearly anhydrous
liquid was then utilized in a refrigerator
in the ordinary way, but instead of the
vapor being drawn off by a pump, it
was absorbed by cold water or weak
liquor in a vessel called an absorber,
which was in communication with the
refrigerator ; and the strong liquor thus
formed was pumped back, to the gener-
ator, and used over again. This appara-
tus was afterwards improved by Stanley,
who introduced steam coils for causing
the evaporation in the generator; and
then by Pontifex & Wood, who have suc-
ceed in bringing the absorption machine
to a considerable state of efficiency.
Their apparatus, as applied to the cool-
ing of liquids, consists of a generator,
containing the coils, to which steam is
supplied from an ordinary boiler ; an an-
alyzer, a rectifyer, and condenser ; a re-
frigerator or cooler, in which the nearly
anhydrous ammonia obtained in the con-
denser is allowed to evaporate; an ab-
sorber, through which weak liquor from
the generator continually flows and ab-
sorbs the anhydrous vapor produced in
the refrigerator ; an economizer or inter-
changer, by means of which the cold,
strong liquor from the absorber is heated
by the hot, weak liquor passing from the
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132
VAN NOSTBAND'S ENGINEERING MAGAZINE.
generator to the absorber; and pumps
for forcing the strong liquor produced in
the absorber back into the analyzer,
where, meeting with steam from the gen-
erator, the ammonia is again driven off,
the process being thus carried on con-
tinuously.
Assuming the action of the economizer
to be perfect — which, of course, is a con-
dition never met with in practice — all the
heat given out by the steam in the gen-
erator coils would be found in the water
issuing from the condenser, less that por-
tion directly lost by radiation and con-
duction. In this case the total heat ex-
pended would be that required to vapor-
ize the ammonia, and the water, which in
the form of steam unavoidably passes off
with the ammonia to the rectifyer and
condenser, plus the heat lost by radiation
and conduction. In the refrigerator,
the hquid ammonia in becoming vapor-
ized will take up the precise quantity of
heat that was given off during its cooling
and liquefaction in the condenser less the
amount due to difference in pressure, and
less, also, the small amount due to the
difference in temperature between the
vapor entering the condenser and that
leaving the refrigerator. Again, when
the vapor enters into solution with the
weak liquor in the absorber, the heat
taken up in the refrigerator is given to
the cooling water^ subject to slight cor-
rections for differences of pressure and
temperature. Supposing there were no
losses, therefore, the heat given up by
the steam in the generator, plus that
taken up by the ammonia in the refriger-
ator, would be precisely equal to the
amount taken off by the cooling water
from the condenser, plus that taken off
from the absorber. The sources of loss
are:
Inefl&ciency of the economizer.
Radiation and conduction from all ves-
sels and pipes that are above normal tem-
perature.
Useless evaporation of water which
passes into the rectifier and condenser.
Conduction of heat into all vessels
and pipes that are below normal tempera-
ture.
Water passing into the refrigerator
along with the liquid ammonia.
It will have been seen that the heat
demanded from the steam is very much
greater in the absorption system than in
the compression. This is chiefly due to
the fact that in the absorption system
the heat of vaporization acquired in the
refrigerator is reject-ed in the absorber,
so that the whole heat of vaporization re-
quired to produce the anunonia vapor
prior to condensation, has to be supplied
by the steam. In the compression sys-
tem the vapor passes direct from the re-
frigerator to the pump, and power has
to be expended merely in raising the
pressure and temperature to a sufficient
degree for enabling liquefaction to occur
at ordinary temperatures. On the other
hand, a great advantage is gained in the
absorption machine by using the direct
heat of the steam, without first convert-
ing it into mechanical work ; for in this
way its latent heat of vaporization can
be utilized by condensing the steam in
the coils and letting it escape in the
form of water. Each pound of steam
passed through can thus be made to give
up some 950 units of heat; while in a
steam-engine using 2 lbs. of coal per in-
dicated horse-power per hour, only about
160 units are utiUzed per lb. of steam
without allowance for mechanical ineffi-
ciency. In the absorption machine, also,
the cooling water has to take up about
twice as much heat as in the compression
system, owing to the ammonia being
twice liquified, namely, once in the con-
denser and once in the absorber. It is
usual to pass the cooling water first
through the condenser and then through
the absorber. The cost of producing
clear block ice in this country, with an
absorption machine of 15 tons capacity
per twenty-four hours, may be taken at
about 4s. per ton, with good coals at
15s. per ton, exclusive of allowance
for repairs and depreciation. About 10
tons of ice can be made per ton of coal
consumed, assuming an evaporative duty
of 8 lbs. of water per lb. of coal.
System D, — ^In this, which is known as
the binary absorption system, liquefac-
tion of the refrigerating sigent is brought
about partly by mechanical compression,
and partly by absorption ; or else the re-
frigerating agent itself is a compound
of two liquids, one of which liquefies at
a comparatively low pressure, and then
takes the other into solution by absorp-
tion. An apparatus of the first kind was
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COPPEK MINING.
133
brought out in 1869, in Sydney, by
Messrs. Mort & NicoUe, who used am-
monia, with water as an absorbent. The
machine consisted of an evaporator or a
refrigerator, a pump, and an absorber.
The evaporator was supplied with strong
ammonia liquor, which was vaporized by
means of the reduction of pressure in-
duced by the pump, and so abstracted
heat from the uquid to be cooled. The
weak Hquor passing, out at the bottom
of the evaporator was led by pipes to the
pump, where it met wth the ammonia
vapor, along with which it was forced
through cooling vessels under sufficient
pressure to cause the solution of the am-
monia, and the strong liquor thus formed
was again passed into the evaporator.
This machine was only used by the in-
ventors in Australia, so far as the author
is aware, and he has no particulars as to
fuel consumption or cost of working. It
was not likely, however, to be & very
economical apparatus, because the whole
of the water entering the evaporator
with the ammonia had to be reduced in
temperature, giving up it heat to the am-
monia vapor, and to that extent prevent-
ing the performance of useful cooling
work. But this disadvantage was in
some degree compensated for by reduc-
ing the temperature of the strong liquor
before it entered the evaporator by means
of an interchanger, through which the
very cold, weak liquor passed on its way
to the pump.
In machines of the second kind, in
which both liquids are evaporated at a
low temperature, the foregoing objection
does not exist, and though this mode of
working has not as yet been introduced
into this country, it has been successfully
employed in the United States for sev-
eral years by Messrs. De Motay & Bossi.
The liquid used is a mixture of ordinary
ether and sulphur dioxide, and has been
termed ethylo sulphurous dioxide: its
adoption was decided on after a series of
experiments with numerous other com
binations of ethers and alcohols with
acids. In these investigations it was
found that Uquid ether at ordinary tem-
peratures possessed an absorbing power
for sulphur dioxide amounting to some
300 times its own volume ; while at 60°
Fahr. the tension of the vapor given off
from the binary hquid was below that of
the atmosphere. In working, both Hquids
evaporate in the refrigerator, under the
influence of the pump, and in the con-
denser the pressure never exceeds that
necessary to liquefy the ether. The com-
pressing pump has less capacity than
would be required for ether alone, but
more than for pure sulphur dioxide. As
to the cost of making ice by this process,
the author has no particulars; but he
believes it to be somewhat less than with
ether. An interesting application of the
binary system has lately been made by
Baoul Pictet, who found that by com-
bining carbon dioxide and sulphur diox-
ide he could obtain a liquid whose vapor
tensions vere not only very much less
than those of carbon dioxide, but were
actually below those of pure sulphur di-
oxide at temperatures above 7° Fahr.
This is a most remarkable and unlooked-
for result, and may open up the way for
a much greater economy in ice produc-
tion than has yet been obtained. As to
the results that have been obtained with
this process, the author has no definite
particulars; but he understands it is
stated to give a production of 35 tons of
ice per ton of coal.
COPPER mining is largely carried on in New
South Wales, the most important amines
being the Great Cobar, situated 497 postal miles
west of Sydney, in the center of the vast plains
which lie between the Macquarie and the Bosan
rivers. The ore is so rich and abundant that
the industry has been a very profitable one un-
til a very recent period, notwithstanding the
great distance of the mine from the settled por-
tion of the colony. The produce of the mine
has to be hauled by wagons a distance of eighty
miles to Nyngan, the nearest railway station. The
industry has caused a large settlement to spring
up at Cobar, and it is estimated that witliin a
radius of three miles the population is within
3,000 and 4,000. The Great Cobar Mine gives
employment to about 900 persons. The com-
pany working the mine at present experiences
great diflBculty in getting the copper to market.
The amount of refined copper produced during
the year was 4,765 tons. During the year 1884
the Great Cobar Company raised 21,5ol tons of
ore, and smelted 23,899 tons, yielding 2,7C9
tons of fine copper. At the end of the year
the company had ready for smelting 1,000 tons
of 10 per cent, ore, 5,000 tons 8 per cent, and
2.233 tons 5 per cent. Up to the close of 1884
the company had smelted 122,795 tons of ore,
tbe average yield of which was 13.17 per cent,
of fine copper. The greatest depth of the main
shaft is 564 feet, and from that diamond drills
have been sunk 60 feet further. The lode at
this depth is said to show a thickness of 40 feet
of fair yellow sulphide ore.
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VAN NOSTRAND'S ENGINEERING MAGAZINE.
AMOUNT OF HORSE-POWER USED IN PROPELLING STREET
CARS.
By AUGUSTINE W. WRIGHT.
From Proceedings of the Assoolation of En.ineerfnf: Societies.
At the present time great interest is
manifested by street railway companies
regarding the question of the substitu-
tion of some motive power to propel their
cars other than horse-flesh. The various
systems, electrical, cable, compressed air,
Honigman, steam dummies, etc., etc., are
prominently before the public, and each
for itself claims, if not perfection, cer-
tainly that it is better than any other
^stem.
It appears to me that great ignorance
exists upon the part, of inventors and
street riulway companies themselves as to
the amount of power required to start a
street car and to maintain it in motion
under average conditions. The follow-
ing is an attempt toward a solution of
this problem. We will begin with horse-
power: Watt's experiments, made with
large horses of the London brewers, gave
33,000 pounds raised one foot high in
one minute as the power exerted by an
average horse, and this as you all know,
is the allowance in figuring engine power.
This is on the assumption that a horse
can exert a force of 150 pounds over 20
miles per diem at the rate of 220 feet per
minute, or 2^ miles per hour during 8
hours. But the horse's power is very
variable at diflferent speeds. Tredgold's
experiments gave 125 pounds ; Smeaton,
100 pounds ; Hatchette, 128 pounds ; all
20 miles per diem at 2^ miles per hour.
Gayffier fixed the power of a strong
draught horse at 143 pounds, 22 miles
per diem at 2f miles per hour, and an
ordinary horse, 121 pounds for 25 miles
per diem at 2^ miles per hour.
As the speed of a horse increases his
power of draught diminishes very rapidly,
until he can only move his own weight.
The following table shows the results
obtained by different authors ; those of
Tredffold being for six hours' daily labor,
and ULOse of Wood for ten hours :
Velocity.
Miles per hour.
Tests of dmught according to
8.
4.
5.
6.
7.
8.