Water-boiling container with switch-on-dry and steam sensitive thermally responsive control units

A thermally-responsive electrical control for an electric heater of a water boiling container includes a switch-on-dry protector switch unit electrically connected with the cold leads of the heater and having a thermally sensitive switch means effective, in use, to interrupt the electrical supply to the heater should the element overheat through being switched-on when the container is dry. A removable steam-sensitive unit is mounted on the protector switch unit and includes an overcenter spring mechanism and a thermally-responsive actuator for the mechanism. The actuator of the said steam sensitive unit is arranged to impinged by vapor or steam issuing from the outlet of a passage leading to the interior of the container, and the electrical parts of the control are shielded from such vapor or steam. A mechanical link is provided between the overcenter spring mechanism and the switch means of the protector switch unit so that tripping of the overcenter spring mechanism by the actuator serves to operate the switch means of the protector switch unit. The steam-sensitive unit is optional and may be deleted to allow the switch-on-dry unit alone to control the heater.

BACKGROUND OF THE INVENTION 
This invention relates to thermally-sensitive electrical controls for 
electric heaters of water boiling containers such as electric kettles, 
jugs, urns, pans, coffee perculators, laboratory equipment and the like 
(hereinafter termed containers of the kind referred to) wherein the 
electric heaters are either immersion heaters or similarly constructed 
heaters mounted externally of the container in good thermal contact with a 
container wall thereof e.g. as by being brazed to the underside of the 
bottom of the container. The heating elements of such electric heaters as 
aforesaid terminate in so-called cold ends by means of which electrical 
connections are made to the heater. 
Electric immersion heaters (hereinafter termed electric immersion heaters 
of the first kind described) conventionally comprise a heating element 
carried by a head which is adapted to be secured in a water-tight manner 
in or adjacent an opening in the container wall. In use said head mounts 
externally of said container a thermally-sensitive electrical control 
(hereinafter termed a thermally-sensitive electrical control of the first 
kind described) in the form of a switch-on-dry protector switch unit which 
makes electrical connection with said cold ends and includes 
thermally-sensitive switch means effective to interrupt the electrical 
supply to the heater should the element overheat through being switched on 
dry. Switch-on-dry protector switch units per se are well known and are 
described in, for example, British patent specification Nos. 1,401,954 and 
1,064,643. 
Electric immersion heaters (hereinafter termed electric immersion heaters 
of the second kind described) of the first kind described are also known 
which additionally carry a tube for egress of vapour or steam from the 
interior of the container via the head of the heater, the tube being 
arranged, in use, so as to extend above the water level in the container. 
In this case the head mounts a thermally-sensitive electrical control 
(hereinafter termed a thermally-sensitive electrical control of the second 
kind described) of the first kind described which is additionally 
effective to interrupt the electrical supply to the heater in response to 
vapour or steam issuing from said tube upon the water in the container 
boiling. Such a thermally-sensitive electrical control of the second kind 
described together with an electric immersion heater of the second kind 
described is disclosed in British patent specification No. 1,316,436. 
In the preferred embodiment of the invention described in specification No. 
1,316,436 there is connected to the head firstly a protector switch unit 
(shown in FIGS. 3 to 5) which incorporates a thermally-sensitive switch 
for cutting off the power supply to the heating element if the kettle is 
switched on dry, and also a vapour or steam sensitive switch unit (shown 
in FIGS. 6 to 8) which incorporates a further thermally-sensitive switch 
for cutting off the power supply when vapour or steam issues through said 
tube. 
The steam-sensitive switch unit mounts on the protector switch unit and 
cooperates therewith to provide a line terminal connection to the heater 
element via the protector switch and the steam-sensitive switch connected 
in series. The provision of two separate thermally-sensitive switches and 
their connection in series results in a control which although effective 
is complicated and hence expensive. Moreover although switch-on-dry 
protector switch units per se are well known for use in non-automatic 
kettles (see British patent specification Nos. 1,401,954 and 1,064,643) 
the construction described in specification No. 1,316,436 necessarily 
involves substantial modification of a standard protector switch unit thus 
increasing costs. 
More generally it is known from British patent specification No. 1,274,552 
to provide a steam or vapour tube or passage either within or along an 
outer surface of a water boiling container for the flow of vapour or steam 
from within the container to an outlet in or adjacent the container floor 
for the purpose of controlling a thermally-sensitive electrical control 
associated with an electric heater which heater may or may not be integral 
with the container. 
Specifically described in specification No. 1,274,552 is an immersion 
heater of the first kind described in association with a 
thermally-sensitive electrical control which as with that described in 
specification No. 1,316,436 comprises two switch units namely a 
switch-on-dry protector unit and a steam or vapour sensitive unit mounted 
one on the other with the attendant disadvantages mentioned above in 
relation to the control of specification No. 1,316,436. 
It is an object of the present invention to provide an improved and 
simplified thermally-sensitive switch-on-dry and water boiling control. 
DETAILED DESCRIPTION OF THE INVENTION 
Thus according to the present invention there is provided a 
thermally-responsive electrical control for an electric heater of a water 
boiling container of the kind referred to, said control including a 
switch-on-dry protector switch unit adapted to make electrical connection 
with the cold leads of the heating element and including thermally 
sensitive switch means effective, in use, to interrupt the electrical 
supply to the heater should the element overheat through being switched on 
when the container is dry, said control further including a steam 
sensitive unit adapted to be mounted on said protector switch unit, said 
steam-sensitive unit including an over-centre spring mechanism and a 
thermally-responsive actuator for said mechanism, the control being 
adapted for the impingement on said actuator of said steam-sensitive unit 
of vapour or steam issuing from the outlet of a tube or passage leading to 
the interior of said container, electrical parts of said control being 
shielded from such vapour or steam, a mechanical link being provided 
between said over-centre spring mechanism and the switch means of said 
protector switch unit so that on said over-centre spring mechanism being 
tripped by said actuator, said link serves mechanically to operate said 
switch means of the protector switch unit. 
It will thus be seen that with a control according to the present invention 
there is only one electrical switch means namely that of the switch-on-dry 
protector switch unit which, as is conventional, may incorporate terminal 
pins whereby connection to a mains supply via a female socket connector 
may be made. Consequently no electrical connections have to be made 
between the protector switch unit and the steam-sensitive unit from which 
it follows that the protector switch unit can be made to be used alone as 
a switch-on-dry protector and yet in such a form as to be compatible for 
use with a simple non-electrical steam-sensitive unit when a control is 
required for automatic kettles or other water-boiling containers of the 
kind described. Thus not only is a great simplification achieved as 
compared with the control as described in specification Nos. 1,274,552 and 
1,316,436 but the protector switch unit may serve two functions, one by 
itself as a dry-switch-on protector and another as part of the composite 
switch-on-dry and boiling control according to the present invention. 
The manner of adaptation of the control for the impingement of steam or 
vapour on said actuator can take various forms. Thus for use with 
immersion heaters of the second kind described, the switch-on-dry 
protector switch unit will be adapted to engage said tube for steam or 
vapour so that steam or vapour passes through the protector unit to reach 
said steam sensitive unit. Alternatively provision may be made for steam 
or vapour to be fed directly to the steam sensitive unit e.g. laterally 
and from above as viewed when the control is fitted to the side and 
adjacent the base of a water-boiling container of the kind referred to. 
In order to provide a versatile control provision may be made both for the 
tube of an immersion heater of the second kind described and for steam or 
vapour to be fed directly to the steam sensitive unit. The control may be 
provided in a form in which for use with an immersion heater of the second 
kind described there is provided frangible means defining an opening to 
receive said steam or vapour carrying tube. Alternatively, whilst the 
control may be adapted to receive said tube, the path for steam or vapour 
to said steam sensitive unit may be made readily blocked off by the user 
as, depending on the design of the control, might be necessary to prevent 
steam or vapour fed directly to the steam sensitive unit passing via said 
path into the electrics of the protector switch unit. 
A control according to the invention adapted for the direct introduction of 
steam or vapour to the steam-sensitive unit from above as mentioned 
previously can conveniently receive steam or vapour via a tube or passage 
running down the outside of the container and communicating with a steam 
or vapour aperture in the upper wall of the container. Such a tube can be 
concealed or formed within a handle structure of the container. Likewise a 
steam or vapour passage can readily be defined between the container wall 
and a handle structure. With such arrangements an electric immersion 
heater of the first kind described, which is simpler to manufacture and 
install than one of the second kind described, is all that is required. 
The control according to the present invention is not however restricted to 
immersion heaters but is applicable to containers with external heaters. 
In such case, there being conventionally no head associated with the 
heater element, it will be necessary to provide a mounting plate for said 
protector switch unit and to arrange the cold ends of said heater element 
in relation to said plate so that in mounting said protector switch unit 
on said plate, electrical connections can be made with the cold ends. The 
plate will also need to be mounted so that, as with the head of an 
immersion heater, its temperature will rise with that of the heater 
element should a switch-on-dry condition arise. Thus the mounting plate 
may conveniently be in the form of a bracket mounted on the heater element 
or on the base of the container adjacent the heater element. In this way 
the switch-on-dry control function can readily be exercised particularly 
as the temperature rise of an element in good thermal contact with the 
container wall is much less rapid than with an immersion heater since the 
container acts as a heat sink. 
Steam or vapour may be led to the control via a steam tube exiting from 
said container, which tube may engage the protector switch unit in like 
manner as with controls for use with electric immersion heaters of the 
second kind described. Alternatively the arrangement may be as described 
above with the tube or passage running down the outside of the container 
directly to communicate with the steam sensitive unit. 
Preferably, the over-centre mechanism comprises a lever pivotably mounted 
on a body member of the steam-sensitive unit so as to be movable between 
first and second positions through an unstable dead-centre position. The 
pivotal mounting is preferably by means of at least one knife edge resting 
in a notch or bearing, the knife edge being retained in the notch by means 
of at least one C-spring extending between the lever and the body member. 
In such an arrangement, the dead-centre position occurs when the two ends 
of the C-spring lie in a common plane with the fulcrum of the lever. 
The mechanical link preferably comprises a movable member which is acted on 
directly or indirectly by a lever of the over-centre mechanism and by a 
thermally responsive actuator of the switch unit. The movable member is 
preferably an elongate member movable in the direction of its axis, the 
lever comprising a portion extending through an aperture in the elongate 
member so as to engage therewith to operate said switch means. 
There is further provided the combination of a thermally-sensitive 
electrical control according to the invention and an electric immersion 
heater of the second kind described, wherein a hot return of the heating 
element is in thermal contact with the head in a position which, in use, 
is below the cold leads of the heating element, a thermally-sensitive 
actuator of the thermally-sensitive switch means being in thermal contact 
with the head in the vicinity of said position. 
A preferred form of thermally-sensitive electrical control according to the 
invention for an electric heater of the second kind described will now be 
described with reference to FIGS. 1 to 7 of the accompanying drawings. 
There will further be described with reference to FIGS. 8 to 14 of the 
accompanying drawings a slightly modified version of the first described 
control whereby steam or vapour may also be fed directly to the steam 
sensitive unit and the application of this modified control to a heater 
mounted externally of the container as well as to a kettle having an 
immersion heater of the first kind described i.e. without a steam tube.

DETAILED DESCRIPTION OF THE DRAWINGS 
As shown in FIGS. 1 to 5 of the drawings, a thermally-sensitive electrical 
control is mounted on the head 10 of an electrical immersion heater. The 
head is secured in a water-tight manner in an opening in the wall of a 
kettle 6. The head 10 carries a steam tube 5 for conducting steam from the 
interior of the kettle to the thermally-sensitive control. The tube 5 is 
arranged so as to extend in use above the water level in the kettle. The 
immersion heater comprises two cold ends 3 and a hot return 11 which 
passes underneath the cold ends 3 and is brazed to the head 10 so as to be 
in thermal contact therewith. By virtue of the proximity of the hot return 
to the base of the kettle, the kettle is capable of boiling a small 
quantity of water if desired. 
The thermally-sensitive electrical control comprises a switch-on-dry 
protector switch unit 2 mounted on the head 10 and a steam-sensitive unit 
1 which is in turn mounted on the switch unit 2. The switch unit 2 is 
provided with three pins 4, including a line pin, a neutral pin and an 
earth pin, for connection to a female socket to supply mains electrical 
power to the heating element. The line pin is connected to one of the cold 
ends 3 via a pair of electrical contacts including a movable contact 7 
mounted on a resilient conductive strip 27 and a stationary contact 8 
(FIG. 3). When the contacts are separated, the supply of electrical 
current to the heating element is cut off. A bimetallic actuator 9 of the 
type disclosed in Offenlegungsschrift No. 2,556,062 is provided in the 
protector switch unit, the tongue of the actuator being riveted to a 
pillar of the unit, and the main body of the actuator being in thermal 
contact with the head 10 in the "cold" position of the actuator. A 
mechanical link in the form of an elongate member 12 is mounted in the 
protector switch unit 2 so as to be slidable in its axial direction, the 
member 12 including an upwardly extending stop 29 adapted to engage the 
lower end of the resilient strip 27. Thus, when the kettle is switched on 
dry, that is without the heating element being covered by water, so that 
the temperature of the element rises above its normal working temperature 
to, say 120.degree. C., the actuator 9 reverses its curvature with a snap 
action, moving the member 12 leftwardly as shown in FIG. 3, thereby moving 
the movable contact 7 away from the fixed contact 8. 
The steam-sensitive unit 1 comprises a body member 13 which seats over the 
switch unit 2. The body member 13 has apertures therethrough for the pins 
4 and includes a shroud 14 which surrounds the pins and guides the female 
socket in use. An aperture 15 through the body member 13 receives the end 
of the steam tube 5 and is sealed thereto by an O-ring seal 37. A lever 
member 16 is pivotably mounted on the body member 13 by means of two knife 
edges 17 formed integrally with the member 16 resting in notches 18 formed 
integrally with the member 13. Two over-centre C-springs 19 extend between 
notches formed in the lever member and body member respectively and bias 
the knife edges into engagement with the notches. The lever member 16 is 
pivotable between a first position in which two stops 25 provided on the 
lever member 16 are in contact with the face of the body member 13 and a 
second position (as shown in the drawings) in which two portions 20 of the 
member 16 came into contact with two pillars 21 formed on the shroud 14. 
In passing from one to the other position, the lever passes through an 
unstable dead centre position in which the two ends of each of the 
C-springs and the knife edge pivots are all in a common plane. 
A bimetallic actuator 22 similar to the actuator 9 is mounted by means of 
the rim of its domed area on the lever member 16. In a preferred 
embodiment, the thermally-responsive actuator of the steam-sensitive unit 
comprises a bimetallic element 22. The bimetallic element 22 preferably 
comprises a member of sheet bimetal having an aperture 52 with an outer 
perimeter 53 and an inner perimeter 54 defining a tongue 55 free at one 
end intermediate two lobe portions of said aperture, said inner perimeter 
54 and arcuate portions of said outer perimeter 53 smoothly merging at 
rounded ends of the aperture adjacent the tongue root 56, the tongue 
being, at least in part, generally centrally disposed with respect to the 
member, the member having been deformed in a die pressing operation to 
conform in shape to a die of domed configuration, said domed area being 
such as to reverse its curvature with a snap action with change in 
temperature, the width of the domed area being greatest in the region of 
the tongue root 56. Such an actuator is described in German 
Offenlegungsschrift No. 2,556,062 and British Patent Specification No. 
1,542,252. The actuator is orientated so that its tongue 23 bears against 
a pillar 24 formed on the body member 13 in its "hot" position. When the 
kettle boils, steam issues from the steam tube 5 and impinges on the 
actuator 22. The actuator then reverses its curvature with a snap action, 
so that its tongue 23 bears against the pillar 24, thus moving the lever 
member 16 from its first to its second position. A portion 26 of the lever 
extends through an aperture in the elongate member 12. Thus, when the 
lever moves from its first to its second position, the portion 26 of the 
lever engages the member 12 and slides it leftwardly as shown in FIG. 3, 
thereby separating the contacts 7,8 as described above. The effect is that 
when the kettle boils, the lever 16 is tripped by the actuator 22 from its 
first to its second position, thus interrupting the supply of electricity 
to the heating element. When the actuator 9 of the protector switch unit 
separates the contacts 7, 8, the movement of the member 12 trips the lever 
16 so that it moves from its first to its second position thus retaining 
the contacts in their separated position. 
A knob 28 is mounted on the lever member 16 and extends through an aperture 
30 in a housing 31 surrounding the thermally-sensitive control, for 
manually resetting the control. When the knob 28 is pressed downwardly, 
the lever member 16 is returned to its first position, thus allowing the 
resilient strip 27 to move the movable contact 7 into electrical contact 
with the fixed contact 8. The supply of current to the heating element can 
then be resumed. At the same time, the resilient strip 27 shifts the 
member 12 in the rightward direction as shown in FIG. 3. 
Thus, the parts of the control which carry electricity in use are all 
carried by the dry-switch-on protector unit 2 and are shielded from the 
steam issuing from the steam tube 5 by the body of the steam-sensitive 
unit 1, a mechanical link being provided between the over-centre mechanism 
and the switch means of the protector switch unit. 
Referring now to FIGS. 6 and 7 of the drawings there is shown the 
switch-on-dry protector switch unit of FIGS. 1 to 5, but used without the 
steam-sensitive switch. The element on which this unit is mounted will 
thus be protected if the kettle is switched on dry or allowed to boil dry, 
but will not be switched off automatically when the kettle boils. The unit 
2 is mounted on the head 10 without modification and is enclosed by a 
housing 32 which includes a portion 33 forming a shroud for the pins 4. 
The housing 32 is secured to the head 10 by means of an internally 
threaded ring 34 and the switch unit is secured to the housing by two 
screws 35 which enter two pillars 36 formed on the switch unit 2, as is 
the housing of the control of FIGS. 1 to 5. 
It will thus be seen that the mechanical steam-sensitive switch unit of the 
present invention enables the use of a protector switch unit which can be 
used in either an automatic or non-automatic kettle without modification. 
The unit costs of the switch unit can thus be reduced. 
As shown in FIG. 8 of the drawings, the thermally-sensitive electrical 
control 1, 2 is fitted to a jug 38 having an electrical heater 39 brazed 
to the underside of the bottom 40 of the jug. The control 1,2 is mounted 
on a bracket 41 brazed to a heated portion of the heater element, the 
bracket being provided in like manner as the head of an immersion heater 
with a mounting stud whereby the control is mounted thereto. A detachable 
base 42 of the jug encloses the heater 39, an opening in the side of the 
base 42 being provided to receive the control 1,2. A lid (not shown) is 
provided for the jug 38 and a steam or vapour venting aperture 43 is 
provided at the top of the side wall. This aperture 43 communicates with a 
passage 44 defined between a handle structure 45 and the jug wall. The 
passage 44 leads directly to the control 1,2 so that when water boils in 
the jug and the lid is in place steam or water vapour is directed to the 
control 1,2. 
Referring additionally to FIGS. 9 to 13 the thermally-sensitive electrical 
control comprises a switch-on-dry protector switch unit 2 mounted on the 
bracket 41 and a steam-sensitive unit 1 which is in turn mounted on the 
switch unit 2. The switch unit 2 is provided with three pins 4, including 
a line pin, a neutral pin and an earth pin, for connection to a female 
socket to supply mains electrical power to the heating element. The line 
pin is connected to one of the cold leads 3, which extend through the 
bracket 41, via a pair of electrical contacts including a movable contact 
7 mounted on a resilient conductive strip 27 and a stationary contact 8 
(FIGS. 9 and 10). When the contacts are separated, the supply of 
electrical current to the heating element is cut off. A bimetallic 
actuator 9 of the type disclosed in Specification No. 1,542,252 is 
provided in the protector switch unit, the tongue of the actuator being 
riveted to a pillar of the unit, and the main body of the actuator being 
in thermal contact with the bracket 41 in the "cold" position of the 
actuator. A mechanical link in the form of an elongate member 12 is 
mounted in the protector switch unit 2 so as to be slidable in its axial 
direction, the member 12 including an upwardly extending stop 29 adapted 
to engage the lower end of the resilient strip 27. Thus, when the jug is 
switched on dry, that is without any water in the jug, so that the 
temperature of the element rises above its normal working temperature, the 
actuator 9 is heated above its operating temperature by conduction of heat 
through bracket 41 and actuator 9 reverses its curvature with a snap 
action, moving the member 12 rightwardly as shown in FIGS. 9 and 10, 
thereby moving the movable contact 7 away from the fixed contact 8. 
The steam-sensitive unit 1 includes a body member 13 which seats over the 
switch unit 2. The body member 13 has apertures therethrough for the pins 
4 and includes a shroud 14 which surrounds the pins and guides a female 
socket in use. An aperture 15 is provided through the body member 13 
capable of receiving a steam tube leading from the interior of the jug but 
in this case is blocked off by a plug 46. A lever member 16 of unit 1 is 
pivotably mounted on the body member 13 by mean of two knife edges 17 
formed integrally with the member 16 resting in notches 18 formed 
integrally with the member 13. Two over-centre C-springs 19 extend between 
notches formed in the lever member and body member respectively and bias 
the knife edges 17 into engagement with the notches 18. The lever member 
16 is pivotable between a first position in which two stops 25 provided on 
the lever member 16 are in contact with the face of the body member 13 and 
a second position (as shown in the drawings) in which two portions 20 of 
the member 16 come into contact with two pillars 21 formed on the shroud 
14. The stops 25 are provided on the lever member in the proximity of the 
notches on the lever member for the two C-springs 19. Thus, a certain 
degree of warping or inaccurate formation of the lever member 16 does not 
affect the operation of the over-centre mechanism in view of the fact that 
any change in the distance between the knife edges 17 and the stops 25 
owing to warping of the lever member is taken up by a similar change in 
the distance between the notch for the C-spring and the knife edge 
fulcrum. In passing from one to the other position, the lever passes 
through an unstable dead centre position in which the two ends of each of 
the C-springs and the knife edge pivots are all in a common plane. 
A bimetallic actuator 22 similar to the actuator 9 is mounted by means of 
the rim of its domed area on the lever member 16. The actuator is 
orientated so that its tongue 23 bears against a pillar 24 formed on the 
body member 13 in its "hot" position. When the water in the jug boils, 
steam or vapour issues from the aperture 43 passes along passage 44 and 
impinges on the actuator 22 as described hereinafter. The actuator then 
reverses its curvature with a snap action, so that its tongue 23 bears 
against the pillar 24, thus moving the lever member 16 from its first 
(FIG. 9) to its second position (FIG. 10). A portion 26 of the lever 16 
extends through an aperture in the elongate member 12. Thus, when the 
lever moves from its first to its second position, the portion 26 of the 
lever engages the member 12 and slides it rightwardly as shown in FIGS. 9 
and 10, thereby separating the contacts 7,8 as described above. The effect 
is that when the water boils, the lever 16 is tripped by the actuator 22 
from its first to its second position, thus interrupting the supply of 
electricity to the heating element. When the actuator 9 of the protector 
switch unit separates the contacts 7,8, the movement of the member 12 also 
trips the lever 16 so that it moves from its first to its second position 
thus retaining the contacts in their separated position (see FIG. 10). 
A knob 28 is mounted on the lever member 16 and extends through an aperture 
30 in a housing 31 surrounding the thermally-sensitive control, for 
manually resetting the control. When the knob 28 is pressed downwardly, 
the lever member 16 is returned to its first position, thus allowing the 
resilient strip 27 to move the movable contact 7 into electrical contact 
with the fixed contact 8. The supply of current to the heating element can 
then be resumed. At the same time, the resilient strip 27 shifts the 
member 12 in the leftward direction as shown in FIGS. 10 and 11. 
As shown in FIGS. 10 to 13 the upper part of the body member 13 is adapted 
to provide a steam or vapour channel 47 open upwardly to communicate with 
passage 44 and laterally to direct steam or vapour toward actuator 22. 
Plug 46 prevents passage of steam or vapour into the switch-on-dry 
protector unit 2 and pins 4 are shielded from the steam issuing from the 
channel 47 by the shroud of the steam-sensitive unit 1, a mechanical link 
being provided between the over-centre mechanism and the switch means of 
the protector switch unit. 
Housing 31 is secured to the unit 2 by screws 35 which engage internally 
threaded pillars 48 on the unit 2 (FIG. 11a), these pillars extending 
through apertures in body member 13, thus securing steam-sensitive unit 1 
on unit 2. FIG. 11a also shows clearly the integral protective guides 50 
for the link member 12. 
Referring to FIG. 14 there is shown the control of FIGS. 8 to 13 fitted to 
an electric kettle having an immersion heater 49, the control being 
mounted in conventional manner on the heater head 10, the head likewise 
being secured in conventional manner in a water-tight fashion in an 
opening in the wall of the kettle. An aperture 43 is provided in the 
kettle wall and a passage 44 is defined between the handle structure 45 
and the kettle wall whereby steam or vapour issuing from aperture 43 is 
led to the steam unit 7 in like manner as with the water boiling jug.