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Scientific American Supplement, No. 787, January 31, 1891 online

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SCIENTIFIC AMERICAN SUPPLEMENT NO. 787




NEW YORK, January 31, 1891

Scientific American Supplement. Vol. XXXI., No. 787.

Scientific American established 1845

Scientific American Supplement, $5 a year.

Scientific American and Supplement, $7 a year.

* * * * *




TABLE OF CONTENTS.


I. BIOGRAPHY. - CHARLES GOODYEAR. - The life and discoveries of
the inventor of vulcanized India rubber, with portrait. - 1
illustration

II. BIOLOGY. - Can we Separate Animals from Plants? - By ANDREW
WILSON. - A debated point well discussed. - The bases on which
distinctions must be drawn

III. ELECTRICITY. - A New Electric Ballistic Target. - A target
for investigations of the velocity of projectiles, now in use at
the United States Military Academy, West Point, N.Y. - 1
illustration.

Electric Erygmascope. - An electric lighting apparatus for
examining earth strata in bore holes for geologists' and
prospectors' use. - 1 illustration

The Electro-Magnet. - By Prof. SILVANUS THOMPSON. - Continuation
of this exhaustive treatise, giving further details on special
points of construction. - 1 illustrations

IV. ENTOMOLOGY. - Potash Salts. - The use of potash salts as
insecticides, with accounts of experiments

The Outlook for Applied Entomology. - By Dr. C.V. RILEY, U.S.
entomologist. - The conclusion of Prof. Riley's lecture, treating
of the branch of entomology with which his name is so honorably
associated

V. INSURANCE. - The Expense Margin in Life Insurance. - Elaborate
review of the necessary expenses of conducting the insurance of
lives, with tables and calculations

VI. MATHEMATICS. - The Trisection of Any Angle. - By FREDERIC R.
HONEY, Ph.B. - A very ingenious demonstration of this problem,
based on the properties of conjugate hyperbolas

VII. METEOROLOGY. - Note on the Mt. Blanc Meteorological Station

The Flood at Karlsbad. - Account of the recent flood and of its
destructive effects. - 1 illustration

VIII. MECHANICAL ENGINEERING. - Station for Testing Agricultural
Machines. - A proposed establishment for applying dynamometer
tests to agricultural machines. - 1 illustration

Steam Engine Valves. - By THOMAS HAWLEY. - A review of modern
slide valve practice, the lap, cut-off, and other points. - 6
illustrations

IX. MISCELLANEOUS. - Science in the Theater. - Curious examples of
stage effect in fictitious mesmerizing and hypnotizing. - 4
illustrations

Theatrical Water Plays. - Recent episodes in real water plays at
Hengler's Circus, London. - 2 illustrations

X. NAVAL ENGINEERING. - The French Ironclad War Ship Colbert. - An
armored wood and iron ship, with central battery. - 1
illustration

XI. PHYSIOLOGY AND HYGIENE. - Newer Physiology and Pathology. - By
Prof. SAMUEL BELL. M.D. - An excellent presentation of modern
practice in the light of bacteriology

Test Card Hints. - How to test the eyes for selecting eyeglasses
and spectacles

The Composition of Koch's Lymph. - What Prof. Koch says it is and
what it can do. - The cabled account of the disclosure so long
waited for

XII. TECHNOLOGY. - Firing Points of Various Explosives. - The
leading explosives, with the temperature of their exploding
points tabulated

The Recovery of Gold and Silver from Plating and Gilding
Solutions - A paper of interest to silver and gold platers, as
well as photographers

Water Softening and Purifying Apparatus. - An apparatus for
treatment of sewage, etc., chemically and by deposition. - 1
illustration

* * * * *




THE FRENCH IRONCLAD WAR SHIP COLBERT.


The central battery ironclad Colbert is one of the ten ships of the
French navy that constitute the group ranking next in importance to
the squadron of great turret ships, of which the Formidable is the
largest. The group consists of six types, as follows:

1. The Ocean type; three vessels; the Marengo, Ocean, and Suffren.
2. The Friedland type, of which no others are built.
3. The Richelieu type, of which no others are built.
4. The Colbert type, of which there are two; the Colbert and the
Trident.
5. The Redoubtable type, of which no others are built.
6. The Devastation type, of which no others are built.

[Illustration: THE FRENCH IRONCLAD WAR SHIP COLBERT.]

The Colbert was launched at Brest in 1875, and her sister ship, the
Trident, in 1876. Both are of iron and wood, and the following are the
principal dimensions of the Colbert, which apply very closely to the
Trident: She is 321 ft. 6 in. long, 59 ft. 6 in. beam, and 29 ft. 6
in. draught aft. Her displacement is 8,457 tons, her indicated horse
power is 4,652, and her speed 14.4 knots. She has coal carrying
capacity for 700 tons, and her crew numbers 706. The thickness of her
armor belt is 8.66 in., that protecting the central battery is 6.29
in. thick, which is also the thickness of the transverse armored
bulkheads, while the deck is 0.43 in. in thickness. The armament of
the Colbert consists of eight 10.63 in. guns, two 9.45 in., six 5.51
in., two quick firing guns, and fourteen revolving and machine
guns. - _Engineering._

* * * * *

A compound locomotive, built by the Rhode Island Locomotive Works, has
been tried on the Union Elevated Railroad, Brooklyn, N.Y. The engine
can be run either single or compound. The economy in fuel was 37.7 per
cent, and in water 23.8 per cent, over a simple engine which was
tested at the same time. The smoothness of running and the stillness
and comparative absence of cinders was fully demonstrated.

* * * * *




STEAM ENGINE VALVES.

[Footnote: Lecture delivered at Wells Memorial Institute, Boston, in
the Lowell Free Course for Engineers. From report in the _Boston
Journal of Commerce_.]

By THOMAS HAWLEY.

RIDING CUT-OFF VALVES - PECULIARITIES AND MERITS OF THE DIFFERENT
STYLES.


In considering the slide valve in its simple form with or without lap,
we find there are certain limitations to its use as a valve that would
give the best results. The limitation of most importance is that its
construction will not allow of the proper cut off to obtain all the
benefits of expansion without hindering the perfect action of the
valve in other particulars. At this economical cut off the opening of
the steam port is very little and very narrow, and although this is
attempted to be overcome by exceedingly wide ports, sixteen inches in
width in many cases in locomotive work, this great width adds largely
to the unbalanced area of the valve. The exhausting functions of the
valve are materially changed at the short cut off, and when much lap
is added to overcome this defect, there usually takes place a choking
of the exhaust port. You might inquire, why not make the port wider,
but this would increase the minimum amount of load on the valve, and
this must not be overlooked. Then the cut off is a fixed one, and we
can govern only by throttling the pressure we have raised in the
boiler or by using a cut off governor and the consequent wastes of an
enormous clearance space. You will observe, therefore, that the plain
slide valve engine gives the most general satisfaction at about
two-thirds cut off and a very low economic result. The best of such
engines will require forty-five to fifty pounds of steam per horse
power per hour, and to generate this, assuming an evaporation of nine
pounds of water to a pound of coal, would require between five and six
pounds of coal per horse power per hour. And the only feature that the
valve has specially to commend it is its extreme simplicity and the
very little mechanism required to operate it.

Yet this is of considerable importance, and in consideration of some
special features at its latest cut off, the attempt has been many
times made to take advantage of these features. For instance, at 90°
advance, the valve opens very rapidly indeed and fully satisfies our
requirements of a perfect valve. This is one good point, and in this
position also the exhaust and compression can be regulated very
closely and as desired without much lap, and as the opening of the
exhaust port comes with the eccentric at its most rapid movement the
release is very quick and as we would have it. This is only possible
at the most uneconomic position of the valve as regards cut off.

The aim of many engineers has been to take advantage of these matters
by using the valve with 90° angular advance of eccentric ahead of
crank, for the admission, release, and compression of the steam, and
provide another means of cutting off, besides the one already referred
to, viz., cutting off the supply of steam to the chest, and overcome
the objection in this one of large clearance spaces. This is done by
means of riding cut off valves, often called expansion valves, of
which, perhaps, the most widely known types in this vicinity are the
Kendall & Roberts engine and the Buckeye. The former is used in the
simplest form of riding cut off, while the Buckeye has many peculiar
features that engineers, I find, are too prone to overlook in a casual
examination of the engine. In these uses of the slide valve, too,
means are suggested and carried out of practically balancing the
valve.

The origin of the riding cut off is most generally attributed to
Gonzenbach. His arrangement had two steam chests, the lower one
provided with the ordinary slide valve of late cut off, and steam was
cut off from this steam chest by the expansion valve covering the
ports connecting with the upper steam chest. This had the old
disadvantage that all the steam in the lower chest expanded with that
in the cylinder, at a consequent considerable loss. This was further
improved by causing the riding cut off to be upon the top of the main
valve, instead of its chest, and resulted in a considerable reduction
of the clearance space.

This is the simplest form, and is shown in Fig. 1. The steam is
supplied by a passage through the main valve which operates exactly as
an ordinary slide valve would. That is, the inside edges of the steam
passage are the same as the ordinary valve, the additional piece on
each end, if I may so term it, being merely to provide a passage for
the steam which can be closed, instead of allowing the steam to pass
the edge. The eccentric of the main valve is fastened to the shaft to
give the proper amount of lead, and the desired release and
compression, and the expansion valve is operated by a separate
eccentric fastened in line with or 180° ahead of the crank. When the
piston, therefore, commences to move from the crank end to open the
port, D, the expansion valve is forced by its eccentric in the
opposite direction, and is closing the steam port and would have
closed it before the piston reached quarter stroke, thus allowing the
steam then in the cylinder to do work by expansion. The eccentric
operating this expansion valve may be set to close this steam port at
any point in the stroke that is desired, the closing occurring when
the expansion valve has covered the steam port. Continuing the
movements of the valves, the two would move together until one or the
other reached its dead center, when the movements would be in opposite
directions.

[Illustration: FIG. 1.]

There are three ways of effecting the cut off in such engines, the
main valve meanwhile being undisturbed, its eccentric fastened
securely so as not to disturb the points of lead, release, and
compression. All that is required is to cause the edge of the
expansion valve to cover the steam port earlier in the stroke, and
this can be done, first, by increasing the angular advance of the cut
off eccentric; second, by adding lap to the cut off valve; and third
by changing the throw of the eccentric. In all these instances the
riding valve is caused to reach the edge of the steam port earlier in
the stroke. We will take first, as the simplest, those methods by
which the lap of the cut off valve is increased.

It will be noted that there is but one edge of this valve that is
required to do any work, and that is to close the valve. The
eccentrics are so placed that the passage in the main valve is opened
long before the main valve itself is ready to admit steam to the
cylinder, so that only the outer edges are the ones to be considered,
and it will be readily seen that the two valves traveling in opposite
directions, any lap added to the working edge of the cut off valve
will cause it to reach the edge and therefore close the port earlier
than it would if there was less lap. And we might carry it to the
extreme that we could add lap enough that the steam passage would not
be opened at all.

In Fig. 2 is shown the method by which this is accomplished, in what
is called Meyer's valve, and such as is used in the Kendall & Roberts
engine. We have only one point to look after, the cut off, so we can
add all the lap we wish without disturbing anything else. In this
engine the lap is changed by hand by means of a little hand wheel on a
stem that extends out of the rear of the steam chest. The valve is in
two sections, and when it is desired to cut off earlier, the hand
wheel is turned in such a direction that the right and left hand
screws controlling the cut off valve move one valve portion back and
the other forward, which would, if they were one valve and they should
be so considered, have the effect of lengthening them, or adding lap
to them. The result would be that the riding valve would reach the
edge of the steam port earlier in the stroke, bringing about an
earlier cut off. If the cut off is desired to be later, the hand wheel
is so turned that the right and left hand screws will bring the valve
sections nearer together, thus practically taking off lap. Now this
may be done by hand or it may be done by the action of a governor.

[Illustration: FIG. 2.]

In the latter case the governor at each change of load turns the right
and left hand screws to add or take away lap, as the load demands an
earlier or later cut off; in other cases the governor moves a rack in
mesh with a gear by which the valve sections are brought closer
together or are separated. The difficulty with the case where the hand
wheel is turned by hand is that the cut off is fixed where you leave
it, and governing can only be at the throttle. For this reason
anywhere near full boiler pressure would not be obtained in the
cylinder of the engine. If the load was a constant one, and the cut
off could be fixed at about one-third, causing the throttle to open
its widest, very good results would be obtained, but there is no
margin left for governing.

If the load should increase at such a time the governor could not
control it under these conditions, and it would lead to a decrease in
speed unless the lap was again changed to give a later cut off. On
this account the general practice soon becomes to leave the cut off at
the later point and give range to the throttle, and we come back once
more to the plain slide valve cutting off at half stroke, and the only
gain there is, is in a quick port opening and quick cut off. But these
matters are more than offset by the wire drawing between the steam
pipe and chest, through the throttle, and the fact that there is added
to the friction of the engine the friction of this additional slide
valve and a considerable liability to have a leaky valve.

In the case where the governor changes the position of the cut off
valve a greater decree of economy would result. In this engine, of
which the Lambertville engine is a type, the main valve is a long D
slide, with multiple ports at the ends through which the steam enters
the cylinders. It is operated from an eccentric on the crank shaft in
the usual manner. The cut off valve is also operated from the motion
on an eccentric fixed upon the crank shaft. The rod or stem of the cut
off valve passes through the main valve rod and slide. Upon the outer
end of the cut off valve rod are tappets fastened to engage with
tappets on the eccentric valve rod. Connection between the cut off
eccentric, therefore, and the cut off valve is only by means of the
engagement of these tappets. The eccentric rod is fastened to a rocker
arm having motion swinging about a pin or bearing in the governor
slide, which may be raised or lowered by a cam operated by the
governor. The cut off slide is of cylindrical shape and incloses a
spring and dash pot with disks attached by means of which the valve is
closed. The motion for operating the valves is relatively in the same
direction, the cut off eccentric having the greatest throw and greater
angular advance to cause it to open earlier and quickly before the
main valve is ready to admit steam. The cut off eccentric rod swinging
the rocker arm, the tappets thereon engage with those upon the cut off
valve rod and open the passages to the main valve, and in their
movement compress the spring in the main valve. According as the speed
of the engine, the rock arm will be raised or lowered so that the
tappets upon the eccentric rod may keep in engagement a shorter or
longer time before they disengage, thus allowing the spring that has
been compressed by the movement of the cut off valve to close that
valve quickly and the supply of steam to the engine, the cut off valve
traveling with the main valve for the balance of the stroke. This
device will give a remarkably quick opening and a quick cut off, but
in view of the fact that the governor has so much to do, its delicacy
is impaired and a quick response to the demands of the load changing
not so likely to occur. The cut off cannot be as quick as in some
other engines, because the valves are moving in opposite directions,
and while this fact would help, so far as shortening the distance to
be traveled before cut off, the resistance of the valves to travel in
opposite directions, or rather the tendency of the valve to travel
with the main valve, hinders its rapid action.

[Illustration: FIG. 3.]

This is one great objection to the rack and gear operated by the
governor, that two flat valves riding upon each other and sliding in
opposite directions at times require a considerable amount of force to
move them, and as only a slight change in load is required by the
load, the governor cannot handle the work as delicately as it should.
It is too much for the governor to do well. To overcome this
difficulty the Ryder cut-off, shown in Fig. 3, was made by the
Delamater people, of New York. The main slide valve is hollowed in the
back and the ports cut diagonally across the valve to form almost a
letter V. The expansion valve is V-shaped, and circular to fit its
circular-seat. The valve rod of the expansion valve has a sector upon
it and operated by a gear upon the governor stem, which rotates the
valve rod, and the edge of the valve rod is brought farther over the
steam port, thus practically adding lap to the valve. Little movement
is found necessary to make the ordinary change in cut-off, and it is
found to be much easier to move the riding valve across the valve than
in a direction directly opposite. It would require considerable force
to move the upper valve by the governor faster than the lower, or in a
direction opposite to that in which it is moving, but very little
force applied sideways at the same time it is moving forward will give
it a sideways motion. In this device the governor has only to exert
this side pressure and therefore has less to do than if it were called
upon to move the upper valve directly against the movement of the
lower.

Something similar is the valve of the Woodbury engine, of Rochester,
N.Y. The cut-off valve is cylindrical, covering diagonal ports
directly opposite, and is caused to be rotated by the action of the
governor that operates a rack in mesh with a segment. Very little
movement will effect a considerable change in the lappage of the
valve, the valve turning about one-quarter a revolution for the
extremes of cut off. The cut off valve rod works through a bracket and
its end terminates in a ball in a socket on the end of the eccentric
rod. In this case the governor has not as much to do as in other
instances.

[Illustration: FIG. 4.]

Still another method of effecting this change in cut off, but hardly
by increasing the lap of the valve, is shown in the next drawing, Fig.
4. The cut off valve is held upon the main valve by the pressure of
steam upon its back and rides with it until it comes in contact with
the cut off wedge-shaped blocks, when its motion is arrested, and the
main valve continuing its movement the steam port is closed by the
main valve passing beneath the cut off valve. Thus the main valve
travels and carries the cut off valve upon its back again until the
cut off valve strikes the wedge on the other end and the cut off is
effected. The relative positions of the blocks are determined by the
governor, that will raise or lower them so that the cut off valve will
engage with them earlier or later as desired. This device was designed
specially as an inexpensive method of changing the common slide valve
into an automatic cut off. The cut off would not be as quick as in
other cases we have cited, depending here upon the movement of the
lower valve alone, and that, too, is in its slowest movement; whereas
in the other cases, the edges approaching each other, by the differing
movement of the valves the cut off is very rapid, provided the
distance to travel is not long. In this device considerable noise must
result by the cut off valve striking the cut off blocks, and a
considerable amount of leakage is likely to occur past this valve.

But there is one great objection in the valve gears thus far cited,
that the travel of the expansion valve upon the main valve is
variable. I have in mind the case of a Kendall & Roberts engine, which
had been run for a long time at no better economy than would be
obtained from a plain slide valve engine, and when it was attempted to
get an earlier cut off by separating the two cut off valves, they had
worn so much in their old place on the valve that shoulders were found
sufficient to cause a disagreeable noise and a leaky valve. This is
very apt to occur, not only where the valve is run for a long time on
one seat, but in cases of variation of the travel of the expansion
valve. The result is that a change will bring about a leaky valve,
something that every engineer abhors.

The construction of the Buckeye engine, which is also of this type, is
such that the travel of the valve on the back of the main valve is
always the same, no matter what the cut off may be. Then this engine
makes use of our second proposition as a means of effecting the cut
off, viz., by advancing the eccentric. You will readily observe that
anything that will cause the cut off valve to reach a certain point
earlier in the stroke will bring about an earlier cut off as it
hastens everything all around. This is the plan pursued in the
Buckeye, in which the governor, of the shaft type, turns the eccentric
forward or back according as the load demands. Then, in addition, the
valve is balanced partially, the attempt not being made to produce an
absolutely balanced valve, on the ground that there should be friction
enough to keep the surfaces bright and to prevent leakage. The most
perfect valve will, of course, be entirely balanced under all
conditions of pressure so as to move with perfect ease. With the
riding cut off valve in connection with the plain slide valve, this is
not accomplished, and it does not matter whether it is partially
unbalanced to prevent leakage or not, the fact that it is not entirely
balanced prevents it reaching the ideal valve.

[Illustration: Fig. 5]

This valve, Fig. 5, differs from the others also in this particular,
that the exhaust takes place at the end of the valve instead of under
the arch. Two eccentrics are used, the one for the main valve being
fastened to the shaft and the other riding loosely upon it and
connected to the fly wheel governor, by which it may be turned forward
or back as the load requires. The three points of lead, or admission
and exhaust and compression, are fixed and independent of the changes


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Online LibraryVariousScientific American Supplement, No. 787, January 31, 1891 → online text (page 1 of 11)