Asymmetric permeable member

A member for causing the circulation of a gas therethrough. The asymmetric member has numerous shaped pores through it such that the absolute effusional resistance to gas flow is anisotropic. The member is useful in causing the circulation of gases.

BACKGROUND OF THE DISCLOSURE 
The circulation of fluids through open and closed systems has many 
applications in the arts, sciences and technology. Mechanical 
reciprocating pumps, centrifugal pumps, undulating tubes, thermal 
gradients and fans are all commonly used to move fluids. One particular 
application where the above listed circulating systems are often 
impractical is in bacteriological research where a sterile flask has a 
plug of cotton or other porous substance in the neck thereof and ambient 
air or other gas is allowed to pass through the cotton. For many reactions 
such as fermentation reactions the rate at which the air passes through 
the cotton is an important factor which determines the rate at which the 
reaction takes place. 
A major shortcoming of the use of a cotton plug in the sterile shake flask 
is the very slow rate of gas exchange through the cotton plug. 
Consequently, the gas exchange through the cotton plug is rate limiting 
rather than the biological process in the bacteriological medium. 
Elaborate sterile gas pumping systems have been developed and used to 
increase the rate of air throughput. However, such systems are quite 
expensive, difficult to operate and maintain and provide a source of 
possible contamination. Some bacteriological processes are carried out 
under reduced pressure or elevated pressure and reactions are also carried 
out in the presence of a particular gas. 
More particularly, the forced flow of gases has typically utilized 
mechanical compressors or other devices which can give rise to impurities 
caused by the necessary presence of lubricants. The need for moving gases 
in highly purified conditions has made most mechanical systems 
impractical. Furthermore, many gases are not compatible with the common 
materials of construction and thus can not be pumped by conventional 
devices. Still further, some processes require elevated temperatures or 
reduced temperatures. Systems for circulating air or other gases is made 
more difficult by the presence of such conditions. 
SUMMARY OF THE INVENTION 
It is thus an object of the present invention to provide a gas circulating 
system which is simple to use, inexpensive to maintain and yet effective 
to increase the flow of gas through a chamber. 
It is another important object of the present invention to provide a gas 
circulating system useful for depolluting industrial smoke stack gases. 
It is a still further object of the present invention to provide a gas 
circulating system which consumes no energy. 
The circulating system of the present invention comprises at least one 
hollow member, which has at least one end open, fabricated from a 
relatively gas impermeable material. The hollow member is sealed, gas 
tight, across a chamber which has two sets of conduit ports, an inlet set 
of conduit ports and an outlet set of conduit ports, such that the two 
sets of conduit ports are separated by the wall of the hollow member, and 
the only flow of gas through the chamber must take place through the wall 
of the hollow member. The afore described assemblage will be called an 
activating unit. The wall of the hollow member has a thickness of less 
than about 3 millimeters and greater than about 0.001 micron. The wall of 
the hollow member contains a plurality of tapered holes passing between 
the surfaces of the wall. The smaller openings of the holes through the 
wall are substantially all either in unison on the outside surface of the 
wall of the hollow member or in unison on the inside surface of the wall 
of the hollow member, with the smaller openings on the inside surface the 
generally preferred embodiment. These tapered holes may be uniform in size 
and shape or they may be irregular. The tapered holes also may be highly 
branched and interconnected. The tapered holes may also be flared at the 
larger openings. The distance across the smaller openings of the tapered 
holes is less than three times the mean free path of the gas molecules 
which is to be employed in this gas circulating system under the operating 
conditions of pressure and temperature. The hollow member, the chamber and 
the conduit ports are all both chemically and physically stable to the gas 
and of a relatively nonvolatile nature under the operating conditions of 
temperature and pressure which are to be used. The mean absolute 
effusional resistance coefficient, .xi., of the wall of the hollow member 
is greater than 10.sup.-4 and less than 2.0 under the operating conditions 
in the said chamber. When the said activating unit is filled with a gas to 
the operating pressure and at the operating temperature, the operating gas 
is urged through the wall of the hollow member, through the chamber and 
through the inlet and outlet conduit parts. The operating activating unit 
described above will be referred to as an aerator. 
Some characteristics of the asymmetric gas-pervious hollow member may be 
set forth by a series of equations set forth below wherein: 
R.sub.i = the absolute effusional resistance of the wall of the hollow 
member to the gas in the first direction, from said "i" of the wall of the 
hollow member to side "ii" of the wall of the hollow member (see FIG. 7 of 
the drawing discussed below). 
T = the absolute temperature, .degree.K, of the gas adjacent to the hollow 
member. 
P.sub.i = the pressure of the gas on side "i" of the wall of the hollow 
member. 
d = thickness of the wall of the hollow member. 
A = the wall area of the hollow member. 
Q = the net gas flow rate through the wall of the hollow member. 
R.sub.ii = the absolute effusional resistance of the wall of the hollow 
member to the gas in the second direction, from side "ii" of the wall of 
the hollow member to side "i" of the wall of the hollow member. 
P.sub.ii = the pressure of the gas on the side "ii" of the wall of the 
hollow member. 
When the gas pressure is set so that P.sub.i is the operating pressure on 
side "i" at T .degree.K, and at the same time P.sub.ii is held near zero 
Torr so that P.sub.i is much greater than P.sub.ii, R.sub.i is defined by 
Equation (1) 
EQU R.sub.i = AP.sub.i /Qd Eq. (1) 
and correspondingly when the gas pressure is set so that P.sub.ii is the 
operating pressure on side "ii" at T .degree.K, and at the same time 
P.sub.i is held near zero Torr so that P.sub.ii is much greater than 
P.sub.i, R.sub.ii is defined by Equation (2). 
EQU R.sub.ii = AP.sub.ii /Qd Eq. (2) 
When for a particular hollow member with a given gas and at a temperature, 
T .degree.K, if R.sub.1 and R.sub.ii, the absolute effusional resistance 
of the given hollow member in the two opposite directions, as calculated 
from Equations (1) and (2) respectively are not equal under conditions 
where P.sub.i and P.sub.ii in Equations (1) and (2) respectively are 
equal, then the hollow member's absolute effusional resistance is 
anisotropic for those specific operating conditions. 
The hollow member's mean absolute effusional resistance coefficient, .xi., 
is defined by Eq. (3) 
##EQU1## 
and .xi. is a measure of the hollow member's anistropy. For a given single 
asymmetric gas-pervious hollow member and a given gas under specified 
temperature and pressure, the mean absolute effusional resistance 
coefficient .xi. must be greater than 10.sup.-4 and less than 2.0, and may 
have intermediate values such as 0.01. 
The tapered holes through the wall of the hollow member are of such a size 
that the diameter of the openings of the holes at the smaller end are less 
than about three (3) times the means free path of the molecules of the gas 
under the conditions employed and greater than the mean diameter of the 
molecules of the gas, with approximately one tenth to one fiftieth of the 
mean free path of the gas molecules a typical useful range and where the 
gas molecules pass through the smaller end of the tapered holes by 
effusion. 
As referred to herein the term "aerator" will be used to denote a gas 
circulating device which causes the flow of air or other gas through it.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The aerator 110 of FIG. 1 is particularly adaptable for use in the neck of 
a flask. Although numerous other uses of the aerator are possible, this 
application will serve to describe the aerator and is not to be considered 
a limitation on its possible use. Aerator 110 has cylindrical wall 111 
which may be made from a glass tube or other hollow member. A screen 112 
may be positioned over the upper end of wall 111 and screen 113 is 
positioned over the lower end to protect the gas circulating members. 
Within the outside wall 111, a perforated plate 114 is sealed gas tight to 
the outside wall 111 and through the perforations 115, and sealed gas 
tight thereto pass the asymmetric gas pervious hollow members 116, open at 
their upper ends 117 and sealed gas tight at their lower ends 118. 
As shown in FIG. 3, member 116 has a plurality of holes such as those 
indicated by reference character 121. Although the holes are depicted such 
that the smaller openings are all on the inside of the hollow member, the 
taper may be reversed as shown in FIG. 4 where all of the smaller openings 
of the holes, 124, are at the outside of the hollow member. Although the 
holes through the wall of the hollow member 116 and 123, FIGS. 3 and 4 are 
depicted as conical, the side walls of the holes may be concave or convex 
as viewed from the axis of the hole. Convex holes, 127 and 131 are 
depicted in FIGS. 5 and 6. A substantial majority of the tapered holes are 
aligned so that the larger openings of the holes are on one side of the 
wall of the hollow member and the smaller openings are on the opposite 
side of the wall of the hollow member. 
The size and shape of the holes form an important aspect of the present 
invention. When the end openings of the tapered holes are approximately 
circular, then the mean diameter of the smaller of the two openings must 
be less than three times as great as the mean free path of the molecules 
of the gas in which the aerator is to operate at the given temperature and 
pressure. When the opening of the holes is not circular, the important 
dimension is the shortest distance across the opening which passes through 
the center of the opening in the curved plane of the surface of the wall 
of the hollow member. This dimension will be referred to herein as "the 
distance across the smaller opening". The mean free path of the molecules 
depends upon the composition, pressure and temperature of the gas and may 
be calculated by methods known to those skilled in the art. The distance 
across the smaller opening also must be greater than the minimum diameter 
of the given gas molecules. For air at 239.degree. K. and 75 centimeters 
of mercury pressure, the mean free path of the molecules is about 0.09 
microns. The distance across the smaller opening must therefore be less 
than 0.27 microns and greater than 3 .times. 10.sup.-4 microns with 2 
.times. 10.sup.-3 microns being typical. 
For pure oxygen at 293.degree. K. at 7.5 centimeters of mercury pressure, 
the mean free path of oxygen molecules is about 1 micron. The distance 
across the small opening for an aerator for use under these conditions 
must be less than 3 microns and greater than 3 .times. 10.sup.-4 microns. 
A typical diameter would be 2 .times. 10.sup.-3 microns. For pure nitrogen 
at 278.degree. K. and 0.75 centimeters of mercury, the mean free path is 
about 9 microns and the distance across the smaller opening must be less 
than 27 microns and greater than 3 .times. 10.sup.-4 microns with about 2 
.times. 10.sup.-3 microns being preferred. For helium at 293.degree. K. 
and 7.5 centimeters of mercury pressure the mean free path is about 3 
microns. The distance across the smaller opening must be less than 9 
microns and greater than 2 .times. 10.sup.-4 microns with 2 .times. 
10.sup.-3 microns being preferred. For hydrogen at 203.degree. K. and 750 
centimeters of mercury pressure the mean free path is 0.03 microns. The 
distance across the smaller opening must be less that 0.09 microns and 
greater than 2 .times. 10.sup.-4 microns with 2 .times. 10.sup.-3 microns 
being preferred dimension. For carbon dioxide at 293.degree. K. at 750 
centimeters of mercury pressure the mean free path is 0.006 microns. The 
distance across the smaller opening must be less that 0.018 microns and 
greater than 3 .times. 10.sup.-4 microns with 4 .times. 10.sup.-3 microns 
being preferred. For air at 293.degree. K. and 7500 centimeters of 
mercury, the mean free path equals 9 .times. 10.sup.-4 microns. The 
distance across the smaller opening must be less than 2.7 .times. 
10.sup.-3 microns and greater than 3 .times. 10.sup.-4 microns with 6 
.times. 10.sup.-4 microns being preferred. In addition to the above 
mentioned gases the system is useful with a wide variety including but not 
limited to carbon dioxide, hydrogen, helium, argon sulphur dioxide, a 
perhalogenated hydrocarbon, monochlorotrifluoromethane, 
hexafluorocyclobutane, dichlorodifluormethane, tetrafluoromethane and 
water vapor or steam. 
The angular dimension between the opposite sides of the conical holes, 121 
and 124 indicated in FIGS. 3 and 4 respectively by reference characters 
"a" and "b" should be between 2.degree. and 150.degree. with about 
10.degree. being preferred. When the opening is conical and in addition 
the larger opening is flared as shown by 127 and 131 in FIGS. 5 and 6, the 
angle of the flare, indicated by reference characters "c" and "d" should 
be between 10.degree. and 180.degree. with 150.degree. being a preferred 
angular opening. While the exact angular dimension is not necessarily 
critical it is important that a substantial majority of the holes have 
their tapers in the same direction relative to the central axis of the 
hollow member. Substantially all the tapers in any given hollow member 
will be directed toward the central axis of the hollow member in unison, 
or the tapers will be directed away from the central axis in unison. The 
orientation of the tapers are depicted in FIGS. 3-6. With irregularly 
shaped holes it is difficult to quantify the size and shape and the hollow 
members containing irregularly shaped holes are best characterized by the 
hollow member's mean absolute effusional resistance coefficient, .xi., for 
a specified gas at a given pressure and temperature. 
The wall thickness, "e" of the hollow member, shown in FIG. 3, should be 
less than about 3 millimeters with about 0.02 millimeters being preferred. 
Hollow member wall thickness such as 0.005 millimeters, 0.05 microns, and 
as small as 0.001 microns are contemplated. 
The internal diameter of the hollow member, indicated by reference 
character "f", FIG. 3, should be less than about 10 centimeters with about 
0.5 centimeters being preferred. Hollow members with an internal diameter 
such as 1 millimeter and 0.1 millimeter are contemplated. The internal 
perimeter of the hollow member perpendicular to the axis of the hollow 
hollow member, should be less than about 32 centimeters. 
For use in the neck of a flask, the aerator is placed in the neck of flask 
150 as shown in FIG. 2. The reaction medium 151 is held in the flask and 
the air or other gas 152 is above the reaction medium 151. Aerator 110 is 
held in neck 153 of flask 150 by a wad of cotton 154. The direction of air 
flow is indicated by arrows 155. As shown by arrows 155 the gas passes 
downwardly through aerator 110 and upwardly through cotton wad 154 where 
the orientation of the tapers through the wall of the hollow member 
corresponds to that shown in FIG. 4. When used in this specific 
application, surrounded by a wad of cotton or similar material as in FIG. 
2, screens 112 and 113 of FIG. 1 may be used to protect the hollow 
members. 
The number of hollow members utilized within the aerator, FIG. 1, may be 
varied considerably with one hollow member having some effect and a larger 
number of hollow members increasing the effectiveness of gas flow. 
Generally, the effect of number of members is additive. For example, the 
aerator could have 1, 5, 87, 2340 hollow members depending upon the 
desired effect. The aerator of the present invention will operate either 
quiescently or in a flask which is secured to a shaker table. 
The number of holes in any one hollow member may be widely diverse 
depending upon the surroundings in which the hollow member is to operate. 
A hollow member having a single, tapered hole could be useful but 
generally a plurality of the holes is more useful. The number of holes 
should not, however, be such that adjacent holes intersect so that the 
geometry of the hole is destroyed. In other words, the number of holes 
should be such that there are actual separate holes although some limited 
overlapping is possible. 
Referring to Equation (3) above, the mean absolute effusional resistance 
coefficient, .xi., should be greater than 1 .times. 10.sup.-4 and 
preferably greater than 1 .times. 10.sup.-2 and less than 2.0. A 
coefficient of about 0.1 is preferred for many practical applications. 
There are three different classes of openings which hollow members of the 
present invention may utilize: First, idealized holes through a wall of a 
hollow member, which is otherwise substantially impervious to the gas, 
where holes are identical in size and orientation. Such holes may be 
truncated pyramids where the cross section may be circular, eliptical, 
triangular, square, or polygonal. Secondly, the openings may be referred 
to as real holes where the holes are tapered and of distorted shape 
passing through a wall of a hollow member which is otherwise substantially 
impervious to the gas. Thirdly, the wall of the hollow member may be 
porous wherein the asymmetric holes through the wall of the hollow member 
are both highly branched and forked with the generally smaller openings on 
the first surface of the wall and the generally larger openings on the 
second surface of the wall. The orientation of the holes through the wall 
of the hollow member is such that a substantial majority of the smaller 
openings are all on the inside surface of the hollow member, or a 
substantial majority of the smaller openings are on the outside surface of 
the hollow member thereby maintaining the orientation of the tapers 
through the wall of the hollow member essentially all pointed outward from 
the center or inward toward the center of the hollow member. The wall of 
the hollow members may, of course, contain openings of any or all of the 
three above described types. 
For many porous materials it is very difficult to measure the size of the 
openings on each side of the wall of the hollow member since the openings 
can vary in both size and shape. Further, the holes through the wall of 
the hollow member are not necessarily of simple and uniform dimensions. 
FIG. 7 depicts such a wall section having holes 136 and 137 passing 
through the wall. This porous hollow member as well as other gas pervious 
asymmetric hollow members can be characterized most readily by the 
above-described absolute effusional resistances, R.sub.i and R.sub.ii 
along with .xi., the hollow member's mean absolute effusional resistance 
coefficient. An isotropic, gas-pervious hollow member is one where .xi. = 
0 and the degree of anisotropy may be judged by the magnitude of the 
coefficient, .xi.. 
Generallly speaking, asymmetric pervious hollow members which show 
anisotropic effusional gas resistance properties, that is .xi. is 
different from zero, may be prepared in either of two ways or a 
combination of these two ways: 
(a) asymmetry is incorporated during the formation of the hollow member 
itself as during the casting; 
(b) the asymmetry is produced by modifying a symmetrical pervious hollow 
member. 
The later modification (b), may be carried out by one of two processes (c) 
or (d) or a combination of them: 
(c) the symmetrical holes through the wall of the hollow member are 
preferentially partially closed or filled on one side of the wall in 
preference to the opposite side by electroplating, acylation, 
esterification, etherification, vapor deposition, sputtering, heat 
treating, bending, stretching, radiation treatment or other process; 
(d) the symmetrical holes through the wall of the hollow member are 
preferentially enlarged on one side of the wall in preference to those on 
the opposite side by such processes as etching, leching, hydrolysis, 
electromachining, stretching, bending, heat treatment, radiation 
treatment, machining, punching, or by other processes. 
Hollow members may be made from sintered powders. When a compressed, 
finely-powdered solid is heated to a temperature somewhat below its 
melting point, the individual solid grains fuse together at their point of 
physical contact. This sintering, at the early stages, leaves large, 
interconnected voids and the mass is quite porous. As the temperature is 
increased, or the time of heating is increased, or both, the degree of 
sintering increases. The volume of the mass, upon increased sintering, 
decreases and the cross section of the void holes decreases in size. 
Asymmetric sintered hollow members may be prepared by different degrees of 
sintering on the two sides of the wall of the hollow member such as would 
occur when the two sides were exposed to different sintering temperatures. 
If the starting powder was made up of particles of different sizes and the 
powder was classified by particle size across the wall of the hollow 
member and then sintered, the side having the larger particles would have 
larger holes, the side with the smaller particles would have smaller 
holes, and inside the wall of the hollow member holes would be of an 
intermediate size. Thus, generally tapered pores would be produced by such 
a classification of the particles prior to sintering. Such pores or 
openings may be highly interconnected and branched but the average mean 
diameter of the openings of the openings on the first surface are smaller 
than the average mean diameter on the second surface and the average mean 
diameter of the holes inside the member are of an intermediary average 
mean diameter. The material of the wall of the hollow members is a gas 
impervious continuous phase. 
A wide variety of materials can be used for fabrication of hollow members. 
The material must be quite impermeable to gases and must be chemically and 
physically stable to the gas with which it is to be employed. Plastics 
such as nylon and polyethylene; metals such as aluminum and iron, ceramics 
such as glass and other silicates and the like are useful with 
consideration of corrosion resistance, temperature limitations and the 
like being adjusted to the environment in which the hollow members are to 
operate. The hollow member should be nonvolatile in the gaseous 
environment and the gas should be relatively insoluble in the hollow 
member. By "relatively insoluble" it is intended to mean that the gas will 
not dissolve in the hollow member to an extent sufficient to cause it to 
swell to an extent to weaken the hollow member or to change the size or 
shape of the openings to an extent to impair their function. 
Equations 1 and 2 may be further understood by reference to FIG. 7 where 
the wall of the hollow member 156 has a first side referred to as side "i" 
in the drawing and a second side referred to as side "ii". The absolute 
effusional resistance from side "i" to side "ii" is referred to both in 
Equation (1) and in the drawings by R.sub.i and the absolute effusional 
resistance in the reverse direction is referred to as R.sub.ii. From 
R.sub.i and R.sub.ii the mean absolute effusional resistance coefficient, 
.xi., may be calculated as shown in Equation (3) above. 
Since the wall of the hollow member may be very thin, it is appropriate in 
many instances that it be supported by an inert base. The base must permit 
the relatively free flow of the gas. As shown in FIG. 8, a coarse 
gas-porous base 158 is affixed to wall of the hollow member 157. The 
support may be any inert, porous substance such as sintered glass. The 
wall of the hollow member may be double supported as shown in FIG. 9 where 
the wall of the hollow member 160 is supported by bases 161 and 162. 
These asymmetric hollow members, 120, 123, 126, and 130 of FIGS. 3, 4, 5 
and 6 respectively, 156 of FIG. 7, 157 of FIG. 8, and 160 of FIG. 9 in 
which the mean absolute effusional resistance coefficient, .xi., is 
greater than 10.sup.-4 and less than 2.0 under certain specified 
conditions of gas composition, pressure and temperature, may be used to 
fabricate activating units for use as aerators. 
While the use of the activating unit of the present invention as an aerator 
has been discussed as being particularly useful in the neck of a flask, 
the invention has far greater applications. The activating unit or 
activating units, may be used in any conduit which has gas impermeable 
walls. Such an aerator is shown as 172 in FIG. 10 where it is sealed, gas 
tight, into conduit 173 connecting tanks 170 and 171. The conduit 174 
provides for the return circulation. The hollow member in the aerator, 172 
in FIG. 10 forms a gas-tight barrier across conduit 173 and thereby 
prevents the unrestricted free flow of gas through the conduit 173. The 
anisotropy of the effusional resistance of the hollow member to the gas 
urges the gas therethrough and through the conduit 173. 
Illustrative configurations of the aerator 172 of FIG. 10 are depicted in 
FIGS. 11-13. In FIG. 11 a plurality of members, 176, sealed gas tight at 
the lower end, are sealed gas tight through a perforated plate 177 into 
the gas distributor 178. The perforated plate, 177, forms a gas-tight seal 
with the body of the aerator 175. The gas which passes between A and B 
must pass through the walls of the hollow members 176. The direction of 
the net gas flow by effusion through the walls of the hollow members 176 
is indicated by the arrows 179 at the members 176 of FIG. 11. Such 
direction of flow results when the holes have their smaller openings on 
the outside of the member such as those shown in FIGS. 4 and 6 of the 
drawings. When the tapers of the holes through the hollow members 176 are 
substantially all in the reverse direction so that the smaller openings of 
the holes are on the inside. of the members 176, then the gas will be 
urged to flow from the outside toward the inside of the hollow member, and 
the net gas flow will be from B to A in FIG. 11. 
In FIG. 12 a plurality of members, 181, are sealed gas-tight through a 
perforated otherwise gas impervious partition 182 which is sealed 
gas-tight to the chamber 180. The gas distributor 183, connects all of the 
ends of the hollow members 181. When the holes through the hollow members 
181 have a substantial majority of their smaller openings at the outside 
of the hollow members, the net flow of the gas will be in the direction of 
the arrows 184 in FIG. 12. When the holes through the hollow members have 
a substantial majority of their openings at the inside of the hollow 
members, the net flow of the gas will be in the direction opposite to that 
indicated by the arrows in FIG. 12. 
In FIG. 13 a plurality of members, 189 are sealed gas-tight through two 
perforated, otherwise gas-impervious partitions, 186 and 187, which are in 
turn sealed gas tight to the body of the chamber 188. The only passage for 
the flow of gas between the points A and B of FIG. 13 is through the walls 
of the hollow members 189. The gas distributors 190 and 191 are connected 
to the common conduit at A. 
A number of aerator units such as those depicted in FIGS. 11-13 may be 
connected together in series, or in parallel, or in a combination of the 
two. Generally, multiple units will increase the gas flow. 
The number of hollow members used in a given aerator unit may be only one 
but usually will be numerous are even quite large such as 5, 80, 400 or 
12,000. The number of aerator units used together may be only one but 
usually, depending upon the requirements, many will be used together such 
as 40, 800 or even 30,000. 
FIG. 14 illustrates how this device may be used as a circulator to induce 
the circulation of air or other gas. An aerator, 194, of the type depicted 
in FIG. 13 is placed at the bottom of a room or a tank, 196, and a conduit 
is extended from the aerator unit 194 to the top of the enclosure. The gas 
is drawn in at A, effuses through the hollow members 195, as shown by the 
arrows and is discharged at B. The mean absolute effusional resistance 
coefficient, .xi., of the walls of the hollow members, 195, is greater 
10.sup.-4 and less than 2.0 at the temperature and pressure of the gas 
being circulated. 
The present embodiments of this invention are thus to be considered in all 
respects as illustrative and not restrictive, the scope of the invention 
being indicated by the foregoing description. All changes which come 
within the meaning and range of equivalency of the claims therefore are 
intended to be embraced therein.