Scientific American Supplement No. 360, November 25, 1882
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Various >> Scientific American Supplement No. 360, November 25, 1882
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It has been found that for grain and other elevators, which are not run
constantly, gas engines, although costing more for the same power,
are cheaper than steam engines for elevating purposes where only
occasionally used.
For this reason it is impossible without considerable investigation to
say what is really the most economical engine to adopt in any particular
case; and as comparatively few users of steam power care to make this
investigation a vast amount of wasteful expenditure results. Although,
however, no absolute rule can be given, we may state that the number
of instances in which an engine which is wasteful of fuel can be used
profitably is exceedingly small. As a rule, in fact, it may generally be
assumed that an engine employed for driving a manufactory of any kind
cannot be of too high a class, the saving effected by the economical
working of such engines in the vast majority of cases enormously
outweighing the interest on their extra first cost. So few people appear
to have a clear idea of the vast importance of economy of fuel in mills
and factories that I perhaps cannot better conclude than by giving an
example showing the saving to be effected in a large establishment by an
economical engine.
I will take the case of a flouring mill in this city which employed two
engines that required forty pounds of water to be converted into steam
per hour per indicated horse-power. This, at the time, was considered a
moderate amount and the engines were considered "good."
These engines indicated seventy horse power each, and ran twenty-four
hours per day on an average of three hundred days each year, requiring
as per indicator diagrams forty million three hundred and twenty
thousand pounds (40 x 70 x 24 x 300 x 2 = 40,320,000) of feed water to
be evaporated per annum, which, in Philadelphia, costs three dollars
per horse-power per annum, amounting to (70 x 2 x 300 = $420.00) four
hundred and twenty dollars.
The coal consumed averaged five and one-half pounds per hour per
horse-power, which, at four dollars per ton, costs
((70 x 2 x 5.5 x 24 x 300) / 2,000) x 4.00= $11,088
Eleven thousand and eighty-eight dollars.
Cost of coal for 300 days. $11,088
Cost of water for 300 days. 420
-------
Total cost of coal and water. $11,503
These engines were replaced by one first-class automatic engine,
which developed one hundred and forty-two horse-power per hour with a
consumption of _three pounds_ of coal per hour per horse-power, and the
indicator diagrams showed a consumption of _thirty_ pounds of water per
hour per horse-power. Coal cost
((142 x 3 x 24 x 300) / 2,000) x 4.00 = $6,134
Six thousand one hundred and thirty-four dollars. Water cost (142 x
3.00= $426.00) four hundred and twenty-six dollars.
Cost of coal for 300 days. $6,134
Cost of water for 300 days. 426
------
Total cost of coal and water. $6,560
The water evaporated in the latter case to perform the same work was
(142 x 30 x 24 x 300 = 30,672,000) thirty million six hundred and
seventy-two thousand pounds of feed water against (40,320,000) forty
million three hundred and twenty thousand pounds in the former, a saving
of (9,648,000) nine million six hundred and forty-eight thousand pounds
per annum; or,
(40,320,000 - 30,672,000) / 9,648,000 = 31.4 per cent.
--_thirty-one and four-tenths per cent_.
And a saving in coal consumption of
(11,088 - 6,134) / 4,954 = 87.5 per cent.
--_eighty-seven and one-half per cent_., or a saving in dollars and
cents of four thousand nine hundred and fifty-four dollars ($4,954).
In this city, Philadelphia, no allowance for the consumption of water is
made in the case of first class engines, such engines being charged the
same rate per annum per horse-power as an inferior engine, while,
as shown by the above example, a saving in water of _thirty-one and
four-tenths per cent_. has been attained by the employment of a
first-class engine. The builders of such engines will always give a
guarantee of their consumption of water, so that the purchaser can be
able in advance to estimate this as accurately as he can the amount of
fuel he will use.
* * * * *
RIVER IMPROVEMENTS NEAR ST. LOUIS.
The improvement of the Mississippi River near St. Louis progresses
satisfactorily. The efficacy of the jetty system is illustrated in the
lines of mattresses which showed accumulations of sand deposits ranging
from the surface of the river to nearly sixteen feet in height. At Twin
Hollow, thirteen miles from St. Louis and six miles from Horse-Tail Bar,
there was found a sand bar extending over the widest portion of the
river on which the engineering forces were engaged. Hurdles are built
out from the shore to concentrate the stream on the obstruction, and
then to protect the river from widening willows are interwoven between
the piles. At Carroll's Island mattresses 125 feet wide have been
placed, and the banks revetted with stone from ordinary low water to a
16 foot stage. There is plenty of water over the bar, and at the most
shallow points the lead showed a depth of twelve feet. Beard's Island, a
short distance further, is also being improved, the largest force of men
at any one place being here engaged. Four thousand feet of mattresses
have been begun, and in placing them work will be vigorously prosecuted
until operations are suspended by floating ice. The different sections
are under the direction of W. F. Fries, resident engineer, and E. M.
Currie, superintending engineer. There are now employed about 1,200 men,
thirty barges and scows, two steam launches, and the stern-wheel steamer
A. A. Humphreys. The improvements have cost, in actual money expended,
about $200,000, and as the appropriation for the ensuing year
approximates $600,000, the prospect of a clear channel is gratifying to
those interested in the river.
* * * * *
BUNTE'S BURETTE FOR THE ANALYSIS OF FURNACE GASES.
For analyzing the gases of blast-furnaces the various apparatus of Orsat
have long been employed; but, by reason of its simplicity, the burette
devised by Dr. Buente, and shown in the accompanying figures, is much
easier to use. Besides, it permits of a much better and more rapid
absorption of the oxide of carbon; and yet, for the lost fractions of
the latter, it is necessary to replace a part of the absorbing liquid
three or four times. The absorbing liquid is prepared by making a
saturated solution of chloride of copper in hydrochloric acid, and
adding thereto a small quantity of dissolved chloride of tin. Afterward,
there are added to the decanted mixture a few spirals of red copper, and
the mixture is then carefully kept from contact with the air.
To fill the burette with gas, the three-way cock, _a_, is so placed that
the axial aperture shall be in communication with the graduated part, A,
of the burette. After this, water is poured into the funnel, t, and the
burette is put in communication with the gas reservoir by means of a
rubber tube. The lower point of the burette is put in communication with
a rubber pump, V (Fig. 2), on an aspirator (the cock, _b_, being left
open), and the gas is sucked in until all the air that was in the
apparatus has been expelled from it. The cocks, _a_ and _b_, are turned
90 degrees. The water in the funnel prevents the gases communicating
with the top. The point of the three-way cock is afterward closed with a
rubber tube and glass rod.
If the gas happens to be in the reservoir of an aspirator, it is made
to pass into the apparatus in the following manner: The burette is
completely filled with water, and the point of the three-way cock is
put in communication with a reservoir. If the gas is under pressure, a
portion of it is allowed to escape through the capillary tube into the
water in the funnel, by turning the cock, _a_, properly, and thus all
the water in the conduit is entirely expelled. Afterward _a_ is turned
180 deg., and the lower cock, _b_, is opened. While the water is flowing
through _b_, the burette becomes filled with gas.
_Mode of Measuring the Gases and Absorption_.--The tube that
communicates with the vessel, F, is put in communication, after the
latter has been completely filled with water, with the point of the
cock, _b_ (Fig. 2). Then the latter is opened, as is also the pinch cock
on the rubber tubing, and water is allowed to enter the burette through
the bottom until the level is at the zero of the graduation. There are
then 100 cubic centimeters in the burette. The superfluous gas has
escaped through the cock, _a_, and passed through the water in the
funnel. The cock, _a_, is afterward closed by turning it 90 deg.. To
cause the absorbing liquid to pass into the burette, the water in the
graduated cylinder is made to flow by connecting the rubber tube, s, of
the bottle, S, with the point of the burette. The cock is opened, and
suction is effected with the mouth of the tube, r. When the water has
flowed out to nearly the last drop, _b_ is closed and the suction bottle
is removed. The absorbing liquid (caustic potassa or pyrogallate of
potassa) is poured into a porcelain capsule, P, and the point of the
burette is dipped into the liquid. If the cock, _b_, be opened, the
absorbing liquid will be sucked into the burette. In order to hasten
the absorption, the cock, _b_, is closed, and the burette is shaken
horizontally, the aperture of the funnel being closed by the hand during
the operation.
If not enough absorbing liquid has entered, there may be sucked into the
burette, by the process described above, a new quantity of liquid. The
reaction finished, the graduated cylinder is put in communication with
the funnel by turning the cock, _a_. The water is allowed to run from
the funnel, and the latter is filled again with water up to the mark.
The gas is then again under the same pressure as at the beginning.
After the level has become constant, the quantity of gas remaining is
measured. The contraction that has taken place gives, in hundredths of
the total volume, the volume of the gas absorbed.
When it is desired to make an analysis of smoke due to combustion,
caustic potassa is first sucked into the burette. After complete
absorption, and after putting the gas at the same pressure, the
diminution gives the volume of carbonic acid.
To determine the oxygen in the remaining gas, a portion of the caustic
potash is allowed to flow out, and an aqueous solution of pyrogallic
acid and potash is allowed to enter. The presence of oxygen is revealed
by the color of the liquid, which becomes darker.
The gas is then agitated with the absorbing liquid until, upon opening
the cock, _a_, the liquid remains in the capillary tube, that is to say,
until no more water runs from the funnel into the burette. To make a
quantitative analysis of the carbon contained in gas, the pyrogallate of
potash must be entirely removed from the burette. To do this, the liquid
is sucked out by means of the flask, S, until there remain only a few
drops; then the cock, _a_, is opened and water is allowed to flow from
the funnel along the sides of the burette. Then _a_ is closed, and
the washing water is sucked in the same manner. By repeating this
manipulation several times, the absorbing liquid is completely removed.
The acid solution of chloride of copper is then allowed to enter.
As the absorbing liquids adhere to the glass, it is better, before
noting the level, to replace these liquids by water. The cocks, _a_ and
_b_, are opened, and water is allowed to enter from the funnel, the
absorbing liquid being made to flow at the same time through the cock,
_b_.
When an acid solution of chloride of copper is employed, dilute
hydrochloric acid is used instead of water.
Fig. 2 shows the arrangement of the apparatus for the quantitative
analysis of oxide of carbon and hydrogen by combustion. The gas in the
burette is first mixed with atmospheric air, by allowing the liquid to
flow through _b_, and causing air to enter through the axial aperture of
the three way cock, _a_, after cutting off communication at v. Then, as
shown in the figure, the burette is connected with the tube, B, which is
filled with water up to the narrow curved part, and the interior of the
burette is made to communicate with the combustion tube, v, by turning
the cock, a. The combustion tube is heated by means of a Bunsen burner
or alcohol lamp, L. It is necessary to proceed, so that all the water
shall be driven from the cock and the capillary tube, and that it shall
be sent into the burette. The combustion is effected by causing the
mixture of gas to pass from the burette into the tube, B, through the
tube, v, heated to redness, into which there passes a palladium wire.
Water is allowed to flow through the point of the tube, B, while from
the flask, F, it enters through the bottom into the burette, so as to
drive out the gas. The water is allowed to rise into the burette as far
as the cock, and the cocks, _b_ and _b_, are afterward closed.
[Illustration: DR. BUeNTE'S GAS BURETTE]
By a contrary operation, the gas is made to pass from B into the
burette. It is then allowed to cool, and, after the pressure has been
established again, the contraction is measured. If the gas burned is
hydrogen, the contraction multiplied by two-thirds gives the original
volume of the hydrogen gas burned. If the gas burned is oxide of carbon,
there forms an equal volume of carbonic acid, and the contraction is the
half of CO. Thus, to analyze CO, a portion of the liquid is removed from
the burette, then caustic potash is allowed to enter, and the process
goes on as explained above.
The total contraction resulting from combustion and absorption,
multiplied by two-thirds, gives the volume of the oxide of carbon.
The hydrogen and oxide carbon may thus be quantitatively analyzed
together or separately.--_Revue Industrielle_.
* * * * *
THE "UNIVERSAL" GAS ENGINE.
The accompanying engravings illustrate a new and very simple form of gas
engine, the invention of J. A. Ewins and H. Newman, and made by Mr. T.
B. Barker, of Scholefield-street, Bloomsbury, Birmingham. It is known as
the "Universal" engine, and is at present constructed in sizes varying
from one-eighth horse-power--one man power--to one horse-power, though
larger sizes are being made. The essentially new feature of the engine
is, says the _Engineer_, the simple rotary ignition valve consisting of
a ratchet plate or flat disk with a number of small radial slots which
successively pass a small slot in the end of the cylinder, and through
which the flame is drawn to ignite the charge. In our illustrations Fig.
1 is a side elevation; Fig. 2 an end view of same; Fig. 3 a plan; Fig. 4
is a sectional view of the chamber in which the gas and air are mixed,
with the valves appertaining thereto; Fig. 5 is a detail view of the
ratchet plate, with pawl and levers and valve gear shaft; Fig. 6 is
a sectional view of a pump employed in some cases to circulate water
through the jacket; Fig. 7 is a sectional view of arrangement for
lighting, and ratchet plate, j, with central spindle and igniting
apertures, and the spiral spring, k, and fly nut, showing the attachment
to the end of the working cylinder, f1; b5, b5, bevel wheels driving
the valve gear shaft; e, the valve gear driving shaft; e2, eccentric to
drive pump; e cubed, eccentric or cam to drive exhaust valve; e4, crank to
drive ratchet plate; e5, connecting rod to ratchet pawl; f, cylinder
jacket; f1, internal or working cylinder; f2, back cylinder cover; g,
igniting chamber; h, mixing chamber; h1, flap valve; h2, gas inlet
valve, the motion of which is regulated by a governor; h3, gas inlet
valve seat; h4, cover, also forming stop for gas inlet valve; h5, gas
inlet pipe; h6, an inlet valve; h8, cover, also forming stop for air
inlet valve; h9, inlet pipe for air with grating; i, exhaust chamber;
i2, exhaust valve spindle; i7, exhaust pipe; j6, lighting aperture
through cylinder end; l, igniting gas jet; m, regulating and stop valve
for gas.
[Illustration: IMPROVED GAS ENGINE]
The engine, it will be seen, is single-acting, and no compression of the
explosive charge is employed. An explosive mixture of combustible gas
and air is drawn through the valves, h2 and h6, and exploded behind
the piston once in a revolution; but by a duplication of the valve and
igniting apparatus, placed also at the front end of the cylinder, the
engine may be constructed double-acting. At the proper time, when the
piston has proceeded far enough to draw in through the mixing chamber,
h, into the igniting chamber, g, the requisite amount of gas and air,
the ratchet plate, j, is pushed into such a position by the pawl, j3,
that the flame from the igniting jet, l, passes through one of the slots
or holes, j1, and explodes the charge when opposite j6, which is the
only aperture in the end of the working cylinder (see Fig. 7 and Fig.
2), thus driving the piston on to the end of its forward stroke. The
exhaust valve, Fig. 9, though not exactly of the form shown, is kept
open during the whole of this return stroke by means of the eccentric,
e3, on the shaft working the ratchet, and thus allowing the products of
combustion to escape through the exhaust pipe, i7, in the direction of
the arrow. Between the ratchet disk and the igniting flame a small plate
not shown is affixed to the pipe, its edge being just above the burner
top. The flame is thus not blown out by the inrushing air when the slots
in ratchet plate and valve face are opposite. This ratchet plate or
ignition valve, the most important in any engine, has so very small a
range of motion per revolution of the engine that it cannot get out of
order, and it appears to require no lubrication or attention whatever.
The engines are working very successfully, and their simplicity enables
them to be made at low cost. They cost for gas from 1/2d. to 11/2d. per hour
for the sizes mentioned.
[Illustration: Fig.9.]
* * * * *
GAS FURNACE FOR BAKING REFRACTORY PRODUCTS.
In order that small establishments may put to profit the advantages
derived from the use of annular furnaces heated with gas, smaller
dimensions have been given the baking chambers of such furnaces. The
accompanying figure gives a section of a furnace of this kind, set into
the ground, and the height of whose baking chamber is only one and a
half meters. The chamber is not vaulted, but is covered by slabs of
refractory clay, D, that may be displaced by the aid of a small car
running on a movable track. This car is drawn over the compartment that
is to be emptied, and the slab or cover, D, is taken off and carried
over the newly filled compartment and deposited thereon.
The gas passes from the channel through the pipe, a, into the vertical
conduits, b, and is afterward disengaged through the tuyeres into the
chamber. In order that the gas may be equally applied for preliminary
heating or smoking, a small smoking furnace, S, has been added to
the apparatus. The upper part of this consists of a wide cylinder
of refractory clay, in the center of whose cover there is placed an
internal tube of refractory clay, which communicates with the channel,
G, through a pipe, d. This latter leads the gas into the tube, t, of the
smoking furnace, which is perforated with a large number of small holes.
The air requisite for combustion enters through the apertures, o, in the
cover of the furnace, and brings about in the latter a high temperature.
The very hot gases descend into the lower iron portion of this small
furnace and pass through a tube, e, into the smoking chamber by the aid
of vertical conduits, b', which serve at the same time as gas tuyeres
for the extremity of the furnace that is exposed to the fire.
[Illustration: GAS FURNACE FOR BAKING REFRACTORY PRODUCTS.]
In the lower part of the smoking furnace, which is made of boiler plate
and can be put in communication with the tube, e, there are large
apertures that may be wholly or partially closed by means of registers
so as to carry to the hot gas derived from combustion any quantity
whatever of cold and dry air, and thus cause a variation at will of the
temperature of the gases which are disengaged from the tube, e.
The use of these smoking apparatus heated by gas does away also with the
inconveniences of the ordinary system, in which the products are soiled
by cinders or dust, and which render the gradual heating of objects to
be baked difficult. At the beginning, there is allowed to enter the
lower part of the small furnace, S, through the apertures, a very
considerable quantity of cold air, so as to lower the temperature of the
smoke gas that escapes from the tube, e, to 30 or 50 degrees. Afterward,
these secondary air entrances are gradually closed so as to increase the
temperature of the gases at will.
* * * * *
THE EFFICIENCY OF FANS.
Air, like every other gas or combination of gases, possesses weight;
some persons who have been taught that the air exerts a pressure of 14.7
lb. per square inch, cannot, however, be got to realize the fact that a
cubit foot of air at the same pressure and at a temperature of 62 deg.
weighs the thirteenth part of a pound, or over one ounce; 13.141 cubic
feet of air weigh one pound. In round numbers 30,000 cubic feet of air
weigh one ton; this is a useful figure to remember, and it is easily
carried in the mind. A hall 61 feet long, 30 feet wide, and 17 feet high
will contain one ton of air.
[Illustration: FIG. 1]
The work to be done by a fan consists in putting a weight--that of the
air--in motion. The resistances incurred are due to the inertia of the
air and various frictional influences; the nature and amount of these
last vary with the construction of the fan. As the air enters at the
center of the fan and escapes at the circumference, it will be seen that
its motion is changed while in the fan through a right angle. It may
also be taken for granted that within certain limits the air has no
motion in a radial direction when it first comes in contact with a fan
blade. It is well understood that, unless power is to be wasted, motion
should be gradually imparted to any body to be moved. Consequently, the
shape of the blades ought to be such as will impart motion at first
slowly and afterward in a rapidly increasing ratio to the air. It is
also clear that the change of motion should be effected as gradually as
possible. Fig. 1 shows how a fan should not be constructed; Fig. 2 will
serve to give an idea of how it should be made.
[Illustration: FIG. 2]
In Fig. 1 it will be seen that the air, as indicated by the bent arrows,
is violently deflected on entering the fan. In Fig. 2 it will be seen
that it follows gentle curves, and so is put gradually in motion. The
curved form of the blades shown in Fig. 2 does not appear to add much to
the efficiency of a fan; but it adds something and keeps down noise. The
idea is that the fan blades when of this form push the air radially from
the center to the circumference. The fact is, however, that the air
flies outward under the influence of centrifugal force, and always tends
to move at a tangent to the fan blades, as in Fig. 3, where the circle
is the path of the tips of the fan blades, and the arrow is a tangent to
that path; and to impart this notion a radial blade, as at C, is perhaps
as good as any other, as far as efficiency is concerned. Concerning the
shape to be imparted to the blades, looked at back or front, opinions
widely differ; but it is certain that if a fan is to be silent the
blades must be narrower at the tips than at the center. Various forms
are adopted by different makers, the straight side and the curved sides,
as shown in Fig. 4, being most commonly used. The proportions as regards
length to breadth are also varied continually. In fact, no two makers of
fans use the same shapes.
[Illustration: FIG. 3]
As the work done by a fan consists in imparting motion at a stated
velocity to a given weight of air, it is very easy to calculate the
power which must be expended to do a certain amount of work. The
velocity at which the air leaves the fan cannot be greater than that of
the fan tips. In a good fan it may be about two-thirds of that speed.
The resistance to be overcome will be found by multiplying the area of
the fan blades by the pressure of the air and by the velocity of the
center of effort, which must be determined for every fan according to
the shape of its blades. The velocity imparted to the air by the fan
will be just the same as though the air fell in a mass from a given
height. This height can be found by the formula h = v squared / 64; that is to
say, if the velocity be multiplied by itself and divided by 64 we have
the height. Thus, let the velocity be 88 per second, then 88 x 88 =
7,744, and 7,744 / 64 = 121. A stone or other body falling from a height
of 121 feet would have a velocity of 88 per second at the earth. The
pressure against the fan blades will be equal to that of a column of air
of the height due to the velocity, or, in this case, 121 feet. We
have seen that in round numbers 13 cubic feet of air weigh one pound,
consequently a column of air one square foot in section and 121 feet
high, will weigh as many pounds as 13 will go times into 121. Now, 121
/ 13 = 9.3, and this will be the resistance in pounds per _square foot_
overcome by the fan. Let the aggregate area of all the blades be 2
square feet, and the velocity of the center of effort 90 feet per
second, then the power expended will bve (90 x 60 x 2 x 9.3) / 33,000
= 3.04 horse power. The quantity of air delivered ought to be equal in
volume to that of a column with a sectional area equal that of one fan
blade moving at 88 feet per second, or a mile a minute. The blade having
an area of 1 square foot, the delivery ought to be 5,280 feet per
minute, weighing 5,280 / 13 = 406.1 lb. In practice we need hardly say
that such an efficiency is never attained.
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