Improvements in Dental Chairs.
Year: 1889

page_text: Date of Application, 7th Nov., 1889-Accepted, 5th July, 1890
COMPLETE SPECIFICATION.
Improvements in Dental Chairs.
communication from FRANK RITTER and DEWELL STUCK, of Rochester. in the
County of Monroe, and State of New York, United States of America.
I, ALFRED JULIUS BOULT of 323 High Holborn in the County of Middlesex,
I.I.M.E., do hereby declare the nature of this invention and in what manner
he same is to be performed, to be particularly described and ascertained in and by
he following statement:
This invention relates to certain improvements in dental chairs, which improve-
ents are fully described and illustrated in the following specification and
ccompanying drawings.

page_text: The spring 6 is attached at one end to the lever, and at the other end to the seat-frame,
so that it operates to keep the front end of the bolt engaged with some one of
the teeth of the rack M, except when the bolt is withdrawn from such engagement by
the pressure of the operator's foot on the lever O. The rack M is attached to the
inwardly projecting flange of the seat-frame by the screws e e, Fig. 5, passing into
Ings on the rack. At its upper end of rack is provided with a projection, f, Fig. 2,
which, by coming in contact with the end of the extension a, prevents the chair from
being inclined too far forwards, and at its lower end it is provided with a stop, gr
Fig. 2, which may be a rubber bumper, which limits the backward inclination of the
seat. The ends of the arm L are pivoted in suitable eyes or sockets secured to the
seat-frame.
The back-standard E is attached to the soat-frame, by means of the arms P P¹,
which are pivoted at i, to the arms QQ, which also support the detachable
arm-rests R. The standard is provided with a suitable groove in which the slide F
can be adjusted up and down, being arranged to be secured in any desired position by
the clamp-screw and hand-wheel S. The slide carries the head-rest G, and the
back D, which is pivoted to the slide at j, and attached theroto so that its lower end
may be varied in its inclination therewith by means of the pivoted adjusting-bar k,
which engages with a series of teeth on the slide. The bar is pivoted to the back
at m, Fig. 1, and provided with projecting arms n, by which its inner end is swung
up and down, so as to engage it with any one of the teeth 1, for the purpose of
varying the inclination of the back relatively to the slide, as indicated by the full and
dotted lines in Fig. 2. It will be observed that the teeth are arranged in a
curved or inclined line relatively to the slide, to secure the requisite adjustment of
the back.
The head-rest G is adjusted to and secured in any desired position by means of a
single clamp-screw T, in the following manner; the cylindrical stem U is fitted to
slide lengthways and turn axially in the slide E, and is provided with an angularly
arranged arm V, which carries the clamp X, from which the head-rest is sustained by
the rod Y.
The rod Y is provided on the end where it engages with the clamp X with a ball o,
which permits the adjustment of the head-rost into any position relatively to
the clamp, which is itself movable lengthways, carrying the head-rest with it, on the
arm V. The stem U is movable lengthways in the slide, as indicated by the full and
dotted lines in Fig. 2, and it will thus be observed that provision is made for placing
the head-rest in any desired position relatively to the back, while the arrangement is
such that it can he secured in any such position by a single movement of the
clamp-screw T, which clamps all the joints at the same time, clamping the ball o
in the clamp X, the clamp X on the rod V and the stem U in the slide E. This
result is effected in the following manner; the clamp X consists of a suitable
socket p, fitted to slide freely on the arm V, provided at its upper end with a
screw-cap which fits over the ball o, and clamps it in place when the screw T is set
up, a suitable recessed friction-piece being interposed between the ball and the
arm V. The hall is thus prevented from turning in the clamp, and the clamp
is secured on the arm V. In order to cause the pressure of the clamp-screw T
to bind the stem U in the slide E, I fit into a longitudinal slot in the armn V, a bar Z,
which is caused to move lengthways by the force exerted by the screw, and this
motion is transmitted by a pivoted angle piece, s, Fig. 2, which moves the bar A',
located in a slot in the stom, lengthways and outwards, thus clamping the stem in
the opening in the slide. The bar Z is provided on its inner edge with a series
of inclined recesses, t, Fig. 2, which fit against a corresponding series of inclined
teeth u, projecting from the bottom of the slot in the arm V,-the arrangement being
such that, when the bar Z is forced inward by the clamp-screw, the inclined surfaces
cause it also to shift lengthways, the bar moving towards the stem U. At the corner
between the arm V and the stem U, is pivoted the swinging angle-piece s, which is
caused to turn on its pivot w by the movement of the bar Z-thus shifting
the bar A' in the slot in the stem U lengthways. The bottom of the slot in the

page_text: stem U is provided with a series of inclined teeth or projections, ¹ which fit
into corresponding recesses in the bar A, so that when the latter is moved
lengthways, it is also forced outwards, binding the stem U in the hole in the slide E
in which it is fitted. A spring a', Fig. 2, serves to return the bars A' Z to their
normal positions, when the pressure of the clamp-screw T is released.
The standard E is arranged so as to be set at various angles with the seat by means
of the pivoted bar B', which is provided with a series of openings or notches 6' with
which the catch engages, so that the inclination of the standard can be varied, as
represented in the full and dotted lines in Fig. 1. The bir B¹ is pivoted to the seat-
frame at w, and extends rearward through a slotted opening in the extension C₁
on the lower end of the standard. The catch is caused to engage with any one of
the openings in the bar B' by the spring x, located in a suitable recess in the
extension. The catch is provided with a suitable handle by which it is mani-
pulated, such for instance as the sliding hand-piece y, located at or near the top of
the standard, and connected with the catch by a cord,, Fig. 2. The bar B' is made
of sufficient length to enable the operator to adjust the standard, which swings on the
pivots i, so as to bring the back into any desired position, from vertical or nearly so,
to the horizontal or even lower, as is required when the chair is adapted to some
purposes other than used by dentists.
The adjustment of the foot-rest H relatively to the seat, is secured by causing its
inner portion D', Fig. 2, to slide in suitable guides in the side-pieces E' projecting
downward on each side from the seat-frame, and by providing the curved lever F
by which it is elevated. The side-pieces E E' are attached to the seat frame in any
convenient way, and project forward and downward a suitable distance. They are
provided on their inner faces with grooves, represented by the dotted lines cc",
Fig. 1, in which lugs or pins inserted in the inner portion of the foot-rest slide.
The pins may be provided with friction rollers or friction-slides pivoted theroon. It
will be observed that the upper set of guides cl, are inclined backward at a some-
what greater angle than the lower set, so that as the foot-rest H rises, its outer
extremity has a somewhat greater travel than the inner end. A cross-bar d¹ extends
between the lower ends of the side-pieces E E below the foot-rest. The lever F' is
pivoted to the foot-rest at e', and rests upon the cross-bar d', on which it also slidos
when pressure is applied to its upper end to raise the foot-rest. The operation of
the lever in raising the foot-rest is represented by the full and dotted lines in Fig. 2.
When the operator puts his foot on the end of the lever F, the other end of the
lever rises, elevating the foot-rest while the lever itself slides along the cross-bar d¹,
the pivoted catch engaging with one of its teeth on the bar, so as to hold the
foot-rest to the clevated position to which it may have been raised. The catch
pivoted to the side of the lever F¹ at k¹, Fig. 2, and extends downward along the side
of the lever, being given a corresponding curve and provided with a series of teeth
or hooks, which engage by the greater weight of the lower end of the catch,
with the cross-bar d'. At its upper end, the catch terminates in a foot-piece m¹,
arranged on the inside of and slightly above the end h¹, of the lever F', so that, when
it is dosired to lower the foot-rest, the tooth which has been engaged with the
cross-bar, is disengaged therefrom by the pressure of the foot on the upper end of
the pivoted catch, the descent of the foot-rest being controlled by the foot-lever F¹.
Rubber cushions may
be provided to prevent jar, such cushions being conveniently
applied as collars, n, Fig. 1, placed on the cross-bar d' inside the side pieces.
The foot-rest may be provided with the additional swinging foot-support, H',
Fig. 1.
is
Proceeding now to a description of the mechanism by which the seat is elevated,
lowered and secured in any desired position, it consists ossentially of the lifting-
clutch G, the holding clutch 1, the clamp, J', all of which operate on the cylin-
drical plunger B. and of the fluid column lowering mechanism M located within the
plunger. The base or standard A consists of two parts, the lower one K¹, of which
is provided with suitable projecting feet or a flange forming a pedestal which supports
the whole structure, and to which the upper cylindrical part L is fitted, so it can

page_text: turn in the horizontal plane, so that the body of the chair can be swung horizontally,
as indicated by the arrows g¹ in Fig. 5. The pedestal K', is provided with a sleeve ƒ³,
projecting upward inside the lower part of the cylinder L', which is fitted to turn
thereon, the lower part of the cylinder resting on a projecting rim or flange on the
pedestal at 1, Fig. 6. The lifting lever I, the lowering lever J, and the clamp-
lever Zare all attached to the cylindrical part L' of the base and swing with it.
The construction and operation of the lifting clutch G¹ will be understood from an
inspection of Figs. 6, 7, and 8. The plunger B which supports the seat, is hollow and
extends down within the base a suitable distance, according to the range of move-
ment it is designed to give to the chair. Its exterior is turned truly cylindrical, and
it is provided with a longitudinal slot or groove, s', into which is fitted a key or
pin, , Fig. 11, attached to the clamp, J', which causes the chair and cylinder L'
to swing together in the horizontal plane. The lifting clutch G₁ is raised by depressing
the outer end of the lifting-lever 1, and carries the plunger B and the chair-body
upwards a certain distance at each movement of the levor. The clutch G' is drawn
downward by the spring, ', Fig. 6,-its movements being indicated by the full and
dotted lines in that figure. The lifting lever I is pivoted at 2¹ between projecting
lugs on the cylindrical shell L', its inner end projecting inward and being pivoted
to a connection y which is pivoted to the wedge, which causes the clutch G¹
to grasp the plunger during its upward movement. The clutch G₁ consists of a
ring v, fitted to slide freely on the plunger B, and provided with a recess on one
side within which are located the friction-piece o", the wedge z¹, and the friction
rollers. The ring is widened on one side, to permit space for the recess
containing these parts, as represented at ". One of the sets of friction rollers, 711
is placed between the wedge and the side of the recess, and the other set 1 is
placed between the inner face of the wedge and the outer surface of the friction-
piece o¹¹. The inner surface of the friction-piece is cylindrical, fitted to the plunger B.
When the wedge is forced upward by the depression of the outer end of the lifting
lever, it acts through the friction rollers and forces the friction piece against the
plunger, and at the same time draws the opposite side of the ring against the
plunger, so that the latter is firmly gripped by the clutch, and the continued upward
movement of the inner end of the lever causes the plunger to rise a certain distance.
The inner end of the lever is then drawn downward by the spring ql, which movement
releases the friction of the clutch on the plunger, so that the clutch can descend
ready for another lifting operation. At its upper end, the friction piece is provided
with lugs, projecting over the recess, to hold it in place. At its lower end, the
friction-piece has a projecting ledge, k", extending toward the wedge, which prevents
the friction-rollers from falling out. At its upper end the wedge is widened or
provided with lugs projecting in each direction, as represented at ", Fig. 6, to
prevent the friction rollers from slipping out of placo, and to transmit the force of the
spring g' to the clutch. At the lower outer edge of the recess is secured the plate i",
Fig. 6, which holds the friction-rollers 711 up. The plunger serves as a guide for
the clutch during its movements.
The holding-clutch 1' is similar in construction and operation to the lifting-clutch,
being provided with a wedge and friction-rollers, and a friction piece which bears
against the plunger, but the wedge is attached to the standard by a suitable connec-
tion. Provision is also made for disconnecting the clutch from the plunger, by raising
it up slightly by means of the lowering lever J, Figs. 1 and 9. The holding clutch
is placed in the upper part of the standard. It consists of a ring, a", Figs. 6, 9
and 13, having an enlargement on one side in which is a recess which receives the
wedge, the friction-piece, d, and the friction rollers "g". The wedge is
supported by a connection or link, m, which is pivoted to the upper end of the
wedge and is attached to a pin inserted in the standard, so as to swing freely thereon.
The thickest part of the wedge is below, so that when the plunger tends to descend,
the weight langs on the wedge, and the friction caused by the wedge acting through
the friction-rollers, forces the friction-piece against the plunger, thus preventing it
from moving downward. The holding clutch is however drawn downward constantly

page_text: by the spring p, Fig. 6. Being attached to the upper part of the standard L, the
clutch turns with the plunger, whenever the chair is swung on the vertical axis.
Suitable plates or projections are used to prevent the friction rollers from slipping
out of the recess in the ring a"-one of these plates being represented at k
Fig. 13. The rollers are simple cylindrical rods, entirely free to adjust themselves in
the space between the wedge and the side of the recess on one side, and the friction-
piece d" on the other.
In order to rise the holding clutch, so as to permit the plunger and chair to descend,
by releasing the grip of the friction, 1 provide the inner end of the stem o of the
lowering lever J, Fig. 9, with a crank or eccentric, which raises the segmental
collar Vi as the stem turns, and this movement is transmitted to the holding clutch by
the rods "u". The shape of the segmental collar is shown in Figs. 14 and 15,-
it being cut away on one side, to permit the movement of the inner end of the lifting-
lever, and provided with a boss, 1, in which is formed a slot w", Fig. 15, which
receives the crank " on the inner end of the stem o111. It will thus be seen that
depressing the outer en of the lever J, raises the lifting clutch so as to allow the
plunger to descend, its movement being controlled by the fluid column mechanism M'.
The rods are secured in the collar o' by the set screws y", Figs. 14 and 15,
which facilitate the adjustment of the collar at the proper distance from the clutch.
The rods are firmly inserted in the ring a" of the clutch. At their lower ends
the rods enter and slide freely in holes in the flange-plate X', Figs. 6, 9 and 16,
which is caused to turn about the vertical axis of the standard by the rods, whenever
the chair is swung, horizontally. The springs 7 and p are attached at their lower
ends to the flange-plate X, so that their tension is not varied by the swinging of the
chair. The flange-plate is provided with a central opening, the edges of which pass
under the lower end of the tube constituting the fluid column, by which means the
plate is held down against the pull of the springs. On the upper side of the plate is
placed a washer, of rubber or other suitable material, against which the lower end
of the plunger strikes at the end of its descending movement, so as to avoid a blow
or jar at this time.
A clamp Jis provided by which the plunger can be firmly secured at any desired
point, and the swinging movement of the chair in the horizontal direction prevented.
This clamp is located at the top of the standard, and it is arranged to be operated by
the lever Y, Fig. 9, and the lever Z. The lever Y' is provided witha screw-stem t¹¹
threaded through a suitable opening in the standard L', which screw when the
outer end of the lever is depressed, forces the lever inward, its upper end closing up
the clamp J' on the plunger, and its lower end hearing at 21, Fig. 9, on the uppor
edge of the sleeve f¹ on the base or pedestal K', and producing friction at this point
so as to prevent the horizontal movement of the chair. The lever is represented in
Fig. 10 in side elevation, it being curved horizontally so as to fit in between the inner
surface of the standard L' and the clutches. The lever is made wide so as to secure
the requisite strength. The clamp consists of a divided ring, one portion of which is
forced against the plunger by the lever, while the other portion is supported against
the standard. A spring or springs is used to separate the portions of the divided
ring, when the clamp screw is released. The inner surface of the divided ring is
covered with felt or other suitable material adapted to produce a smooth and even
friction on the polished surface of the plunger. The clamp is shown in plan view in
Fig. 11, in which ", " represent the different parts of tbe divided clamp-ring and
mn the lines of division between the two parts. On each side of the line of
division n, the ring is shown for a short distance in horizontal section, in order to
represent the springs, p by which the portions of the ring are separated when the
clamp is not in use. These springs are simply stiff spirals inserted in suitable recesses
in one portion of the divided ring and bearing against the end of the other portion.
The ring itself is shown in section in Fig. 12. On one side of the clamp, the
segment is provided with the projecting lug 9", against which the upper end of
the clamp-lever Z bears, and on the other side the segment is provided with a
suitable projecting lug which is seated within a suitable recess in the upper part

page_text: of the standard. The clamp is provided with the key or pin (" which fits the
longitudinal groove in the plunger, and compels the plunger and the upper part of
the standard to travel together when the chair is swung horizontally. The inner
surface of the clamp-ring is faced with felt or other suitable fabric, as indicated
at *, Figs. 11 and 12. This material may be fastened to the ring in any suitable
manner, as for instance by the thread or cord 11 which is passed through the edges
of the fabric and draws them down tight against the surface of the ring, the edges
being notched if necessary to effect this purpose. The clamp-ring is located in a
suitable recess in the upper part of the standard, a suitably shaped cup, N", being
placed over it and secured to the top of the standard.
The mechanism constituting the fluid column, by which the chair is gradually
lowered, consists of a tube, O¹, located within the plunger B, and within which a
piston R', slides up and down, being connected to the plunger by the rod or tube ".
The piston K is fitted to the tube O₁ so that as the chair is lowered, the oil or other
suitable liquid in the tube passos slowly around the piston, thus securing a steady
descent without jerk or jar, and the piston is provided with a valve T, which opens
when the piston moves upwards, permitting the oil above the piston to pass below it.
The tube which holds the liquid column is closed at its lower end, so that no liquid
can escape from it, being secured in place on the cross-bar U', so that it does not
turn on its axis, but the piston turns within it and the plunger outside of it, when
the chair is swung around about its vertical axis. The cross-bar U₁ is secured to
lugs on tho podestal K¹ by the screws pl. The lower end of the tube O¹ is closed
by the plug S¹, which is fastened to the cross-har U by the scrow m",-one or more
pins, Fig. 6, inserted in the plug and the cross-bar, being asod to prevent the tube
from turning on its axis. The tube is provided near its upper end with a circular
rocess, within which is placed a leather washer, 11, Fig. 9, which slides within the
plunger B. At the lower ond of the plunger, it is provided with a recess in which is
fitted another leather washer, ', which slides on the tube. The plunger is thus
guided in its up and down movements. The piston R¹ is provided with a number of
circumferential grooves, d, Fig. 17, which serve to delay the oil in its passago from
below to above the piston as the plunger descends. The lower part of the piston e",
is made of a diameter to fit the interior of the tube O¹ closely, and the projecting
ridges, ff, between the grooves d¹¹, are made successively smaller from below
upwards, so as to permit the passage of the oil around the piston in a steady and
uniform manner. Thus the ridge is slightly smaller than the diameter of the
lower part of the piston, the next higher ridge f is slightly smaller than f", and
the ridge is smaller in diameter than This arrangement is somewhat
oxaggerated in the drawings. The piston R is provided with a series of holes,
which permit the oil to pass through the piston when the plunger rises, the valve T,
which is normally held closed by the spring on the rod y, opening at this
time to permit the movement of the oil, as represented by the full and dotted lines in
Fig. 17. The tube n" is perforated with a number of holes, al, which permit the oil
or air to pass freely into or out of it. The upper end of the tube is secured to
the plunger B in any suitable manner, as for instance by the head U" threaded into
the interior of the upper end of the plunger. The head is provided with
openings, which permit air to pass into or out of the tubes 1 and 2, as
indicated in Fig. 9. The opening into the tube n is partially closed by a
boss at the center of a cap k Figs. 9 and 18,-which boss is provided with
grooves pFig. 18, communicating with channels on the lower surface of the
cap, by which the air is caused to enter the tubo in a noiseless manner when the
plunger descends.
The lifting lever is provided with a joint represented in Fig. 6, by which it can
be folded inward toward the standard, so as to get it out of the operator's way. The
outer part of the lever swings on the pivot W, as represented by the full and dotted
lines in Figs. 1 and 6, a spring catch P" being employed to lock the joint in the
lever when desired. The catch is located in a recess in the inner part of the lever,
being provided with a spring by which it is constantly forced outward so that its

page_text: outer end engages with a notch in the outer part of the lever. A pin is inserted
in the catch and extends outwards forming a projecting stud n', Fig. 1, by pressure
on which the catch is forced inward, compressing the spring and disengaging the
outer end of the catch from the notch so that the outer end of the lever can fall by
its own weight out of the way of the operator's feet. The rubber bumper serves
to deadon the shock of the falling lever.
The segmental collar V1 is provided on its upper side with a series of rubber
bumpers, wo, against which the downward movement of the lifting clutch is arrested
without jur or shock.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, as communicated to me by
my foreign correspondents, I declare that what I claim is :-
1. The combination with the swinging back-standard of a dental chair, of the
notched bar B', pivoted to the seat-frame, and the spring-catch u, adapted to engage
in any of the notches of the notched bar, and to secure the standard in any desired
position, substantially as described.
2. The combination with the swinging back-standard of a dental chair, of the
notched bar B1, pivoted to the seat-frame, the spring-catch v, adapted to engage in
any of the notches of the bar, the handle y, located near the upper end of the
standard, and attached to the catch by a suitable connection z, substantially as
described.
3. The combination with the swinging back-standard of a dental chair, provided
with the extention C', of the notched bar B¹, pivoted to the seat-frame and passing
through a suitable opening in the extention, of the spring catch v, adapted to engage
in any of the notches of the bar, substantially as described.
4. The combination with the swinging back-standard of a dental chair of the
movable back D', pivoted at its upper end and supported by the pivoted adjusting
bar k, adapted to engage with the notches 1, to vary the inclination of the back,
substantially as described.
5. The combination with the swinging back-standard of a dental chair, of the
adjustable slide F, a suitable clamp, and the movable back D, pivoted at its upper end
to the slide and supported by the adjusting bar k, adapted to engage with a sorios of
notches fixed to the slide, substantially as described.
6. The combination with the swinging back-standard of a dental chair, provided
with notched bar B1 and spring-catch u, whereby the inclination of the standard may
be varied, of the adjustable slide F mounted on the standard and carrying the back D,
substantially as described.
7. The combination with the swinging back-standard of a dental chair, provided
with notched bar B' and spring-catch, whereby the inclination of the standard may
be varied, of the adjustable slide F mounted on the standard, and provided with
notches, the movable back D, pivoted to the slide, and the adjusting-bar k, sub-
stantially as described.
8. The combination with the back-standard of a dental chair, of the head-rest G
supported thereon by the bent arm UV, and rod Y, and adapted to be secured in
any desired position by three clamp-joints arranged to be secured by a single clamp-
screw, substantially as described.
9. The combination with the back-standard of a dental chair, provided with an
adjustable back, of the head-rest G, supported on the standard by the bent-arm UV,
and rod Y, and adapted to be secured in any desired position by three clamp-joints
arranged to be secured by a single clamp-screw, substantially as described.
10. The combination with the back-standard of a dental chair, of the projecting
arm V, arranged to support the head-rest G by rod Y, bali o, clamp X and clamp-
screw T, substantially as described.
11. The combination with the arm V, of the head-rest G, rod Y, ball o, socket p,
screw-cap q, friction piece r and clamp-screw T, substantially as described.
12. The combination with the head-rest G, of the bent arm UV, the longitudinally

page_text: movable bars ZA¹, pivoted corner pieces, and a suitable clamp by which the head-rest
is secured to the arm, substantially as described.
13. The combination with the head-rest G, of the bent arm UV, the longitudinally
movable bars ZA¹, pivoted corner-piece s, and clamp ✗, provided with ball o
supporting the head-rest on a rod v, substantially as described.
14. The combination with a suitable supporting arm, of the movable head-rest G,
adjustably supported on the arm by the clamp X, comprising the socket p, cap q,
ballo and friction-piece r, substantially as described.
15. The combination with the back-standard E, of the rod U, provided with a
longitudinal slot having inclined teeth o' projecting from its bottom, the longitudinally
movable bar A located within the slot and provided with inclined recesses fitting
teeth o', and a suitable clamping mechanism adapted to fasten the rod in the standard
by moving the bar lengthways in the slot, substantially as described.
16. The combination with the back-standard E, of the rod U, provided with a
longitudinal slot having inclined teeth o projecting from its bottom, the longitudinally
movable bar A located within the slot and provided with inclined recossos fitting
teeth o¹, the bent arm V provided with a longitudinal slot having inclined teeth, the
longitudinally movable bar Z located in the slot, the corner-piece s, and a clamp
provided with a clamp-screw T, substantially as and for the purpos's sot forth.
17. The combination with the seat frame of a dental chair, provided with exten-
sions E' E', of the foot-rest, II arranged to be adjusted on the extensions, the curved
lifting lever F, pivotal to the foot-rest at e¹ and resting on the cross-bar d' connecting
the lower ends of the oxtensions, and the toothed lover j¹, pivoted to the lifting lever
and adapted to hold the foot-rest in the desired position by the engagement of one of
its teeth with the bar d, substantially as described.
18. The combination with the plunger B of the lifting clutch G₁, consisting of the
recessed ring v¹, wedge ¹, friction-piece o", and friction-rollers, substantially
as described.
19. The combination with the plunger B of the lifting clutch G, wedge 21, friction
rollers, pivoted connection y¹, and the lifting lever I, substantially as described.
20. The combination with the plunger and lifting-clutch of the jointed lifting
lever I, provided with spring-catch P" and stud n*, substantially as described.
21. The combination with the plunger B of the lifting clutch G¹, provided with a
wedge operated by the lifting lever to cause the clutch to grip the plunger, and the
holding clutch f¹ provided with an operating wedge secured to the standard,
substantially as described.
22. The combination with the plunger B of the holding clutch 1', provided with an
operating wedge secured to the standard by a pivoted link or connection, substantially
as described.
23. The combination with the plunger B of the holding clutch I', provided with an
operating wedge secured to the standard, and a suitable lever and connecting
mochanism for elevating the clutch substantially as described.
24. The combination with the plunger B of the holding clutch I', provided with an
operating wedge secured to the standard, the rods, collar V₁, and lowering
lever J, provided with crank ", substantially as described.
25. The combination with the plunger B, of the lifting clutch G, provided with an
operating wedge actuated by the lifting levor the revolving standard L', spring g¹, and
revolving plate X', substantially as described.
26. The combination with the plunger B, of the holding clutch I', provided with an
operating wedge attached to the revolving standard L', the rods, collar V¹,
spring and revolving plate X', substantially as described.
27. The combination with the plunger B, of the holding clutch I', provided with
an operating wedge attached to the revolving standard L, the rods u , collar VI,
spring ", revolving plate X', and the lowering lever J, provided with crank a",
substantially as described.
28. The combination with the plunger B, of the standard-base K' having the
revolving standard L', supported thereon, the tube 0¹ secured to the standard base,

page_text: and the piston R' connected with the plunger and constructed to permit the liquid
in the tube O¹ to pass slowly around it, substantially as described.
29. The combination with the raisable seat of a dental chair of mechanism for
controlling the descent of the seat, consisting of the tube O¹ filled with "liquid and
the piston T, provided with a series of two or more circumferential grooves d'",
having the ridges between them of smaller diameter than the body of the piston,
substantially as described.
stationary
30. The combination with the plunger B, of the divided clamp-ring J',
base K, revolving standard L, clamp-lover Z' and the clamping screw ",
substantially as described.
111
31. The combination with the plunger B, of the lifting clutch G³, holding clutch I',
rods, and collar V, provided with bumpers w against which the downward
movement of the lifting clutch is arrested, substantially as described.
Dated this 1st day of November 1889.
W. P. THOMPSON & BOULT,
Agents for the Applicant.