Scientific American Supplement, No. 799, April 25, 1891 by Various

V >> Various >> Scientific American Supplement, No. 799, April 25, 1891

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The blades in the smaller size wheels should be 1/4 of the radius in
width, and for the larger sizes up to 20 feet, 1/5 to 1/6 of the radius
in width and spaced equal to from 1/4 to 1/3 of the radius.

They should be completely submerged at the lowest point.

For obtaining the horse power of a current wheel, the formula is

Area of 1 blade x velocity of the current in ft. per sec.
----------------------------------------------------------
400

x by the square of difference of velocities of current and wheel
periphery = the horse power; or

A x V 2
------ x (V - v) = h. p.
400

[TEX: \frac{A \times V}{400} \times (V - v)^2 = h. p.]

in which A equals the area of blade in square feet, V and v velocities
of current and wheel periphery respectively, in feet per second. Thus,
for example, a wheel 10 feet in diameter with blades 6 feet long and 1
foot in width, running in a stream of 5 feet per second--assuming the
wheel to be giving as much power as will reduce its velocity to one half
that of the stream--the figures will be

6' x 5' 2
------- x 2.5 = 0.468
400

[TEX: \frac{6' \times 5'}{400} \times 2.5^2 = 0.468]

horse power of the wheel.

The total power of the stream due to the area of the blade equals the

Square of the velocity of the stream
------------------------------------ x
Twice gravity (64.33)

volume of water in cubic feet per second x 62.5 (weight of 1 C') = the
value or gross effect in pounds falling 1 foot per second. This sum
divided by 550 = horse power. Thus, as per last example,

2
5
------ x 30 x 62.5
64.33
---------------------- = 1.32 the horse power of the current
550

[TEX: \frac{\frac{5^2}{64.33} \times 30 \times 62.5}{550} = 1.32 \text{
the horse power of the current}]

due to the area of the blades of the water wheel.

For the efficiency of this class of wheel, with slightly curved and thin
blades, divide the horse power of the wheel by the horse power of the
current area, equals the percentage of efficiency.

As in the last case,

0.468 / 1.32 = 0.351/2

per cent. efficiency of the water wheel.

With higher velocities of stream and wheel the efficiency will be from 2
to 3 per cent. less, although the horse power will increase nearly with
the increase in velocity of the current.

For details of application of various forms of current wheels for power
purposes see illustrated description Yagn's and Roman's floating motors
in SCIENTIFIC AMERICAN SUPPLEMENT, No. 463.

A very good example of a floating motor of the propeller class is
Nossian's fluviatile motor, illustrated and described in SCIENTIFIC
AMERICAN SUPPLEMENT, No. 656.

[Illustration: Fig. 24.]

Fig. 24 represents a very complete floating motor, in which the floats
are wedge shaped at the stem, for the purpose of increasing the current
between them, the wheel being an ordinary current wheel, as shown in
Fig. 23, with a curved shield or gate in front, which can be moved
around the periphery of the wheel for the purpose of regulating its
speed or stopping its motion by cutting off the stream from the buckets.

The float, rising and falling with the stream, is held in position by a
braced frame swinging on anchorages within the mill on shore, and
parallel with a swiveled shaft.

Tide wheels and tidal current wheels have been in use for more than 800
years, and were largely in use in Europe and the United States during
the first half of the present century. No less than three were running
in the immediate vicinity of New York, in 1840, for milling purposes.

Their day seems to be past, except in some special localities. We will
also pass them, and illustrate some of the

SELF-ACTING WATER-RAISING DEVICES.

The tympanum derives its name from its similarity to a drum as made by
the Romans, but its origin was Egyptian. It is a current wheel with
frame like Fig. 23, to the outside of which a set of chambers or tubes
are fixed, radiating spirally, so as to lead the water to the shaft as
the wheel revolves, as shown in Fig. 25. It has a lift of a little less
than half its diameter, and answers an excellent purpose for the
irrigation of rice and cranberry fields, or on streams running through
low lands in arid districts. It is still one of the Nile irrigating
wheels.

[Illustration: Fig. 25]

The building of these wheels is within the scope of the carpenter and
the tinsmith. A short wooden shaft made square or octagonal, as
convenient, with gudgeons in the ends and arms of wood bolted across
each of the sides of the shaft, or as shown in the cut, will form a
frame work upon which a rim may be fastened, to which the blades and
tubular buckets can be attached.

The directions in regard to the current wheel, Fig. 23, may be followed
as to number and form of blades, which must be made in length and width
proportional to the velocity of the stream and the quantity of water to
be lifted by each tubular arm. The tubes may be made of galvanized sheet
iron and attached to the outside of the wheel, as shown in Fig. 25.

THE NORIA OR BUCKET WHEEL.

This is a simple current wheel with pot buckets, rigid or swinging,
arranged on the rim of the wheel, to carry up and discharge the water
nearly at the top of the wheel, and through the long ages that it has
been in use for irrigation, village water supply, and even for private
establishments, has assumed a variety of forms in detail of construction
ranging from the bamboo wheels of the Chinese to the light iron wheels
of modern construction.

We illustrate the most simple of these forms in Figs. 26 and 27, in
which the first is a series of boxes or chambers in the rim of the wheel
with side openings in the forward part of the box as the wheel revolves,
and a lip extending from the inner edge of the opening to direct the
outflow into the trough.

[Illustration: Fig. 26.]

Another form, Fig. 27, is arranged with swing buckets or pots, pivoted
just above their centers, and with the catch trough so fixed as to tip
the buckets at the highest point, thus giving this wheel the greatest
possible advantage as to height of discharge for a given diameter.

[Illustration: Fig. 27.]

The power value of these wheels for raising water is a matter of
computation as nearly reliable as for other devices for the same
purpose, when the velocity of the current is known at the point of
contact with the blades.

The horse power of the wheel may be computed as for the current wheel,
Fig. 23, and, as the horse power is equal to 33,000 pounds raised one
foot high per minute, we may assume a construction of wheel that will
allow of discharging at 8 feet above the stream; then 33,000 / 8 = 4,125
pounds of water discharged at 8 feet elevation per horse power per
minute. As the net power of the wheel in the last example, for Fig. 23,
was 0.468 of a horse power, then 4,125 x 0.468 = 1,930 pounds of water
raised 8 ft. per minute by the size of bucket and velocity of current in
that case. From this a deduction of 20 per cent. should be made for loss
by spill and imperfect construction, so that 1,500 pounds or 176 gallons
per minute would be the probable output--over 253,000 gallons per day;
or, for irrigating purposes, equal to a rainfall of over 11/4 inches in
depth on 50 acres in one week.

The proportion of capacity of the lifting buckets for such a wheel
becomes of as great importance as its efficiency.

If the buckets are too large, the wheel will stall, and if too small,
the wheel will not give its full duty.

For obtaining the approximate capacity of the lifting buckets, assuming
the example as above computed, a 10 foot wheel with the velocity at
periphery of 21/2 feet per second is 150 feet per minute, or five
revolutions per minute, nearly. Then 1,930 lb. per m. / 5 revolutions =
386 pounds water capacity for all of the buckets on the wheel.

If such a wheel is constructed with 16 blades and 16 buckets, one
between each blade, then 386 / 16 = 24 pounds for each bucket, or 38 /
100 of a cubic foot.

The spill from this capacity of bucket being sufficient to compensate
for the friction of the shaft journals.

The lifting buckets of the noria class, Figs. 26 and 27, can be made of
positive dimensions to suit the computations as above; but those of the
tympanum class, Fig. 25, should be made of dimensions to conform with
the required capacity at the moment of leaving the water, as the water
at this point flows into the arm.

(_To be continued_.)

* * * * *

To remove paint and varnishes, which resist the action of strong lye,
Dr. Stockmeier recommends a mixture of water of ammonia, two parts, and
turpentine, one part; this applied to the surface to be cleaned will,
after a few minutes' action, enable the paint to be removed by use of
cotton waste or similar material.--(_Bayr. Gen. Ztg_.), Rundschau.

* * * * *

ON GAS MOTORS.

M. Witz, says the _Gas World_, has been conducting a series of
experiments on the Delamare-Deboutteville and Malindin gas engine,
driven by Dowson gas, and in which the gas generator takes the place of
the ordinary steam boiler. The engine was a one-cylinder motor in the
establishment of Messrs. Matter & Co., Rouen. Its power was 100 horse
indicated; the cylinder was 23 inches in diameter, the stroke 38 inches,
and the normal speed 100 revolutions. The engine is of the Simplex type;
the kindling is electric; the cycle of operations is fourfold, with
powerful compression. The Dowson generator is 30 inches inside diameter
and 76 inches in height from the bars to the top. Air is blown in by
steam driven in under the hearth. There is a siphon, a coke scrubber 110
inches high, a sawdust purifier, and a gasholder of 750 cubic feet
capacity, and a pipe to the engine 5.2 inches in diameter. The total
area occupied by this apparatus is 140 square yards, of which two-thirds
are built on. The anthracite employed was from Swansea, containing 5.4
per cent. of ash. The observations made with a string friction brake
were continued for 68 hours, everything used being carefully weighed and
measured. One day the machine was worked for 151/4 hours on end; the other
days it was worked with an interval of half an hour every 12 hours to
clear the hearth, poke the fire and lubricate the machine; and it was
clearly established that with a big enough generator it would be quite
possible to work continuously for several days.

The following were the data for a day of 24 hours, with an interval of
half an hour: 8:55 P.M. one day to 8:55 P.M. the next, interval 8:30 to
9 A.M. Anthracite used, 18.4 cwt.; coke used, 3.42 cwt.; water used for
steam injection, 217.3 gallons; water used in scrubber, 4,106 gallons;
water used in cooling the cylinder, 20,000 gallons; oil used in
cylinder, 14.84 pounds; grease, 1.8 pounds; revolutions of machine,
142,157, or 100.8 per minute; effective work, 75.86 French horse power,
or 77.4 British; gas used, 6,742 cubic feet per hour, at 772 mm.
pressure and 70.7 deg. F., or 83.7 cubic feet per effective horse power;
efficiency, 69 per cent.

Now, with regard to the comparison between the large gas motors and
steam engines of the same size, M. Witz goes on to remark that the gas
engine is by no means, as was formerly thought on high authority,
necessarily restricted to the domain of smaller work and sizes. Even in
early times it was seen that the gas engine belonged to a type in which
there were possibilities of improvement greater than those available in
the steam engine, because the difference of temperature between the
working substance in its hotter and its cooler condition was greater
than in the steam engine; and consumptions of 5,250 cubic feet per horse
power per hour soon descended step by step as far as 2,060, while the
power went up, past 4, 8 and 12, to 25 or 50 horse power; and in the
exhibition of 1889 there were gas engines seen in which the explosion
chamber had a diameter of as much as 23 inches.

But the price of coal gas seemed to be too high for use in these large
engines, in which sizes steam is comparatively cheap; and so poorer gas,
which, though possessing only about 28 per cent. of the heating power,
is still cheaper in proportion than coal gas, when it is made on the
spot, was introduced to tide over the difficulty. Difficulties have been
successively overcome, with the result which we have just seen, namely,
1.37 pounds of anthracite per effective horse power, or about half the
carbon which a steam engine of the same power of excellent design, and
well kept up, would consume. A 50 horse simplex at Marseilles, in
Barataud's flour mill, is said to have run for the last 2 years on 1.12
pounds of English anthracite per effective horse power; and thus M. Witz
says his predictions of 10 years ago, that the gas producer would some
day replace the boiler, are being verified in such a way as to surprise
even himself.

But the objection is stated, and it is a serious one: the weight of fuel
is not the only thing to be considered. The steam engine uses coal, the
producer requires English anthracite, which is dearer; the gas motor
uses a great deal of water and a great deal of oil, which cost money;
and gas motors are dear, while gas producers and their adjuncts cost a
tidy bit of money, and wear out pretty fast. Is not steam, after all,
more economical in the long run? Besides, producers are bulky and take
up a great deal of space; the weight of fuel is only one element in a
complicated problem.

In order to study the grounds of this objection, M. Witz has instituted
a comparison between the actual cost of large steam engines and that of
gas motors of similar size.

Take a good Galloway or multitubular boiler; for 75 horse power
effective the heating surface must be at least 74 square feet. Using
good Cardiff coal, with 4 per cent. of ash, and a heating power of
15,660 Fahr. units; the steam raised will be 8 to 9 pounds per pound of
coal, so that 9,400 to 10,577 Fahr. units are utilized in raising steam,
or 68 to 76 per cent., which is an excellent result. Take an engine of
16 inch cylinder diameter, 40 inch stroke, and 66 revolutions, etc.; it
will use 22.4 pounds of steam per horse power effective, which
represents 2.47 to 2.8 pounds of coal under the boiler. These 10 pounds
of steam carry 11,752 Fahr. units of heat, and produce work equal to 75
horse, or 1,143 Fahr. units of heat; which corresponds to an efficiency
of 9.7 per cent. In a gas motor, on the other hand, we find the
materials employed, as per the above data, to contain 8,958 Fahr. units
of heat, and to make gaseous fuel in which 6,343 units are available; a
return of 70.6 per cent, in the producer. The motor receives these
6,343, and converts 1,143 of them into work; an efficiency of 18 per
cent. In order to be equivalent from the heat point of view, a steam
engine ought to produce a horse power effective per 9.72 pounds of steam
at 5 atmospheres; but no such steam engine exists.

M. Witz goes on with comparative estimates. For a Corliss engine and
boiler, with chimney, etc., complete, and putting these up, he allows
L1,280; for a Simplex gas motor and Dowson producer complete, including
putting up, he allows L1,290, which he explains to be average actual
prices; but these prices do not cover cost of transport, and M. Witz
does not go into cost of masonry for buildings, apart from foundations,
etc., for the apparatus and machinery.

As to water, the gas motor takes 215 cubic feet per horse power
effective. A condensing steam engine uses five times as much.

The lubricating oil used at Rouen was a mixture of Russian oil at 430
fr. per ton, and Ferry and Heduit F.H. oil at 900 fr.; the average was
650 fr. per ton, or 2.8d. per pound. Wanner grease, at 6.4d. per pound,
was used for the moving parts. A steam engine requires less oil for the
cylinder, but the same quantity for the moving parts.

The attendance on the gas motor is too much for one man, not enough to
occupy two; reckon it at 4s. 91/2d. a day.

These elements enable us to calculate the daily cost of the gas motor,
of 75 actual horse power, in comparison with a steam engine of the same
size.

_Steam Engine_.

s. d.
Upkeep, interest and sinking fund at 15 per
cent, on L1,292 = L193.8 = per day. 12 11
Cardiff coal, 2.643 pounds per actual horse
power per hour; 2.643 x 10 x 75 = in 10
hours 1,982 pounds coal at 22s. a ton. 19 51/2
Oil, 3.36 pounds per day at 2.8d. per pound. 0 91/2
Grease, 0.67 pound at 6.4d. 0 41/2
Wages. 4 91/2
---------
L1 18 4

_Gas Engine_.

s. d.
Upkeep, interest and sinking fund at 15 per
cent. on L1,292 is, per day. 12 11
Anthracite, 1.156 pound per actual horse
power per hour = for 750 horse-hours, at
25s. 6d. 9 10
Coke, 0.215 pound x 10 x 75 = 1611/4 pounds
at 28s. 2 0
Oil, 0.0084 pound per actual horse power per
hour, or 0.0084 x 10 x 75 = 6.28 pounds at
2.8d. 1 51/2
Grease, 0.754 pound per day at 6.4d. 0 5
Electric kindling, on cost. 0 31/2
Wages. 4 91/2
---------
L1 11 8

The big gas engine making its own poor gas, and running 10 hours a day,
has thus the best of it in the comparison with the steam engine of equal
power.

* * * * *

A PROJECTING APPARATUS FOR BALANCES OF PRECISION.

The luminous projection apparatus illustrated herewith, when adapted to
a balance of precision, permits of effecting weighings very rapidly. For
the same approximation, the velocity of oscillation becomes five or six
times greater, and, by the method employed, the last centigrammes and
the milligrammes and their fractions are estimated directly, with
immediate verification. As the apparatus is independent of the parts of
the balance, it can be placed on all the existing laboratory balances of
precision.

[Illustration: PROJECTING APPARATUS FOR BALANCES OF PRECISION.]

The modification introduced into the balance consists in the displacing
of the center of gravity of the beam in such a way as to diminish the
sensitiveness, and consequently to obtain a much greater velocity, and
then, by optical means, to considerably increase the amplitude of the
oscillations.

Instead of the oscillations being observed through the microscope, they
are projected upon a divided screen forming a dial, the division of
which is seen by transmitted light.

The apparatus consists of a small achromatic objective placed at the
extremity of the tube of a microscope, in which there is a divided
screen that receives the enlarged image of the reticule fixed upon the
needle. Upon this reticule are projected the rays (condensed by a
powerful lens) that come from a luminous source placed behind the
balance. The focusing is done by means of a rack and pinion.

The luminous source employed is a gas burner with reflector. This is
placed in a walnut box in order to prevent any projection of heat upon
the balance. This burner, thus isolated, is lighted for but one or two
minutes at a maximum, at the end of each weighing. So, on fixing a
thermometer in the cage, we find that no variation, ever so slight,
occurs in the temperature. In order to effect a weighing, the gas being
turned down to a taper, we proceed as with an ordinary balance until the
extremity of the needle no longer emerges from the lower dial. Then we
count the difference of the number of the divisions made by the needle
to the right and left of zero. This difference, multiplied by the
approximate value, in milligrammes, of each division of this dial (value
given by the instrument) immediately gives the number of centigrammes
and milligrammes that must be added to the weights already placed upon
the pan of the balance in order to obtain an equilibrium, to about a
half division of the lower dial.

The value of each division of this dial varies from 3 to 10 milligrammes
according as the balance shows 0.1 or 0.5 milligramme. As the dial has
10 divisions on each side of the central mark, we thus estimate, without
tentatives, the three last centigrammes or the last decigramme,
according to the sensitiveness.

At this moment the doors of the cage are closed, in order to prevent
draughts of air, the gas is turned on by means of a regulating cock, and
the balance is manipulated by first lowering the beam and then bringing
the pans to a standstill. We then read the difference of the divisions
traversed to the left and right upon the luminous dial through the image
of the reticule. The images are reversed upon the dial, but practice
soon causes this petty difficulty to disappear. This number of divisions
indicates the number of milligrammes and fractions of a milligramme by
which it is necessary to shift the counterpoise on its arm in order to
obtain a perfect equilibrium, which latter is verified by a simple
reading. Every half division of the dial corresponds, as to weight, to
the sensitiveness indicated for the instrument.

With a little practice a weighing effected as above described takes but
a quarter or a fifth of the time that it does with an ordinary
balance.--_Revue Industrielle._

* * * * *

STARCHES FOR THE FINISHING OF COTTON FABRICS.

The starches have been classified by Dr. Muter, according to the
appearance they give under the microscope, into five groups:

_Class I_.--Hilum and concentric rings visible. All the granules, oval
or ovate. Tous-le-mois, potato, arrowroot, etc.

_Class II_.--The concentric rings are all but invisible, the hilum is
stellate. Maize, pea, bean, etc.

_Class III_.--The concentric rings are all but invisible, also the hilum
in the majority of granules. Wheat, barley, rye, chestnut, etc.

_Class IV_.--All the granules truncated at one end. Sago, tapioca, etc.

_Class V_.--All the granules angular in form. Rice, tacca, arrowroot,
oats, etc.

The principal starches used for finishing cotton fabrics are potato
(farina), wheat, Indian corn (maize), rice, tapioca, arrowroot, sago;
the last three not so often as those previously named.

[Illustration: POTATO STARCH.]

[Illustration: ARROWROOT STARCH.]

[Illustration: WHEAT STARCH]

[Illustration: RICE STARCH]

[Illustration: SAGO STARCH]

[Illustration: INDIAN CORN STARCH]

[Illustration: TAPIOCA STARCH]

* * * * *

MARBLE AND MOSAIC.

[Footnote: A paper recently read before the Architectural Association,
London.--_From the Architect_.]

By T.R. SPENCE.

I do not propose to enter into any historical details as to the first
and subsequent application of mosaics. In a general sense we understand
mosaic as a combination of various more or less imperishable
materials--fixed together by cement or other adhesive substances--and
laid over walls, floors, etc., with a view to permanent decorative
effect. The substance of the tesserae is of many kinds, namely, glass,
cheap and precious marbles, hard stone, and burnt clay, these mentioned
being mainly in use for architectural purposes. For decorative schemes
we collect as many gradations of color as are obtainable in such durable
materials in their natural or manufactured state, and thus form a color
palette which we regard in the same sense as a painter would his
pigments.

Of course, the first proceeding is to prepare a design on a small scale,
which shall embrace your notions of color only. Then follows a
full-sized cartoon, which I need hardly add shall embrace your best
efforts in drawing. A tracing is made of the latter and transferred to
sheets of cardboard. This cardboard is cut to the size of certain
sections of your design, and, for convenience, should not be more than,
say, 20 in. square. Of course, it will not always be square, but will
bear the same relation to your complete cartoon as a map of the counties
would to that of all England. Now, working from the small design (of
color), the tesserae are cut to the forms required, laid face downward,
and glued on to the cardboard sections containing your enlarged cartoon.
When the design is all worked out on these sections they are ready for
fixing on walls or floor by laying them home on a float of cement. When
the cement sets, the cardboard sticking to the face is washed off, and
the joints of tesserae flushed over with cement and cleaned off, leaving
all joints filled up level.

There are other processes used for the same end. The technical processes
need not occupy our attention at present. There is one process that may
appeal to you, and that is executing the work _in situ_ by floating on a
limited expanse of cement, and sticking on the tesserae at once. It has
the advantage of enabling the artist or architect to see the effect of
his efforts under the fixed conditions of light and height.

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