A flask having a threaded neck and a cap adapted for threaded engagement on the neck are used. A laminated disc between the cap and the neck forms a gas tight seal and the cap has a central opening that exposes a medial region of the disc. Piercing the disc through the opening are two electrodes, the inner ends of which contact the sample within the flask and the outer ends of which can be connected to test equipment. Cylindric glass tubes are fitted over the external portion of the electrodes to provide physical support and silicone rubber or a similar material serves to retain the glass cylinders in place and form a gas tight seal between the cylinders and the electrodes. Shrinkable tubing is shrunk over the glass tubes to afford further mechanical support and sealing. A final relatively large diameter shrinkable tube is shrunk over both electrodes and their associated glass cylinders. The support and sealing means for the electrodes is confined to a limited portion of the medial region of the disc so that the remainder of such region can be punctured by a hollow needle to introduce a test sample within the flask

Adamson, M. J.

Fassbender, A. G.

Gilbreath, W. P.

English

NASA Technical Reports Server

United States Patent [ I  I I 3,938,035 
Fletcher et al. 1451 Feb. 18, 1976 
[541 ELECTRICAL CONDUCTIVITY CELL AND 
METHOD FOR FABRICATING THE SAME 
[ 76) Inventors: James C. Fletcher, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of William P. Gilbreath, 
San Jose, Calif.; Michael J. 
Adamson, San Jose, Calif.; 
Alexander G. Fassbender, San Jose, 
Calif. 
[22] Filed: July 16, 1974 
[ 2 1 ] Appl. No.: 489,009 
[52] U.S. CI. ............ 324/30 B; 204/195 R; 215/247 
[58] Field of Search ......... 204/195 R, 279; 73/61 R, 
73/6 I .  1 R; 324130 B; 2 151247-249 
[ 5 1 1 Int. CI.' .......................................... GOlN 27/07 
[561 References Cited 
UNITED STATES PATENTS 
2,135,386 I 1/1938 Crebbe ............................... 215/247 
3,760,969 9/1973 Shimamoto et a1 ................. 215/247 
3,784,453 1/1974 Dworkin et al ..................... 204/286 
Primary Examiner-Alfred E. Smith 
Assistant Exuminer-Wm. H. Punter 
Attorney, Agent, or Firm-Darrell G. Brekke; Armand 
G. Morin, Sr.; John R. Manning 
[571 ABSTRACT 
A flask having a threaded neck and a cap adapted for 
threaded engagement on the neck. A laminated disc 
between the cap and the neck forms a gas tight seal 
and the cap has a central opening that exposes a me- 
dial region of the disc. Piercing the disc through the 
opening .are two electrodes, the inner ends of which 
contact the sample within the flask and the outer ends 
of which afford connection of test equipment thereto. 
Cylindric glass tubes are fitted over the external por- 
tion of the electrodes to provide physical support 
therefor; silicone rubber or the like serves to retain 
the glass cylinders in place and form a gas tight seal 
between the cylinders and the electrodes. Shrinkable 
tubing is shrunk over the glass tubes to afford further 
mechanical support and sealing. A final relatively 
large diameter shrinkable tube is shrunk over both 
electrodes and their associated glass cylinders. The 
support and sealing means for the elctrodes is con- 
fined to a limited portion of the medial region of the 
disc so that the remainder of such region can be punc- 
tured by a hollow needle to introduce a test sample 
within the flask. 
5 Claims, 4 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19760012251 2020-03-20T02:12:15+00:00Z
U.S. Patent Feb. io, 1976 3,938,035 
INTRODUCE 
CURE RUBBER 64 
CONNECTORS AND 
SHRINK PVC 
TUBING 1 
SHRINK OUTER 
PVC TUBING 
3,93 8,035 
1 
ELECTRICAL CONDUCTIVITY CELL AND 
METHOD FOR FABRICATING THE SAME 
The invention described herein was made in the per- 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act of 1958, Public Law 
BACKGROUND OF THE INVENTION 
85-568 (72 Stat. 435; 42 U.S.C. 2457). 
1. Field of the Invention 
This invention relates to a test cell for testing electri- 
cal characteristics such as conductivity of a sample and 
to a method for fabricating such test cell. 
2. Description of the Prior Art 
Exemplary of the known prior art is Rosenthal, et al. 
U.S. Pat. No. 2,555,937 which discloses a stopper 
through which two electrodes extend so that when the 
stopper is placed in the neck of the test tube the elec- 
trodes are immersed in liquid in the test tube. No pro- 
cedure for introducing fluids into the test tube other 
than by removing the stopper is disclosed. 
US. Pat. No. 2,939,070 to Rosenthal discloses indi- 
vidual electrode support structures which are perma- 
nently mounted in the wall of an open top container so 
that when the container is filled with a sample liquid 
the electrical characteristics thereof can be measured. 
Meyer U.S. Pat. No. 3,201,685 discloses a probe that 
can be immersed in liquid to measure the electrical 
characteristics thereof. 
U.S. Pat. Nos. 2,964,941 (Marsh, et a].); 3,263,224 
(Berman, et al.); and 3,286,167 (Gwyn) disclose fit- 
tings for supporting two electrodes in a conduit or like 
path of fluid flow for measuring the characteristics of 
such fluid. 
SUMMARY OF THE INVENTION 
The preferred embodiment of the invention that is 
disclosed in specific detail hereinafter includes a flask 
and a screw cap for engagement with the neck of the 
flask. A laminated disc interposed between the cap and 
the flask neck affords a gas tight seal and the cap is 
apertured to expose a medial region of the disc. Trans- 
piercing the medial region of the disc are two elongate 
thin electrodes. At the point where the electrodes 
pierce the disc a gas tight seal is formed according to 
the invention. The gas tight seal occupies a limited 
surface area of the medial region of the disc so that a 
portion of the disc acts as a septum that can be punc- 
tured by a thin needle for introducing sample material 
into the flask without opening the same. The disc has a 
lamina of self-sealing material such as silicone rubber 
so that upon removal of the hollow needle the sample 
within the flask cannot escape and contaminates can- 
not enter the flask from the exterior thereof. 
The object of the present invention is to provide a 
test cell that permits introduction of samples into and 
removal of samples from the test cell without opening 
the test cell. This object is achieved because of the 
provision of the above mentioned laminated disc and 
confinement of the electrodes and their supporting 
structure to a limited portion of the exposed area of the 
disc. 
Another object of the invention is to provide a test 
cell of the character to which reference has been made 
above that is simple and inexpensive to fabricate. This 
object is achieved because fabrication of the electrode 
5 
0 
15 
!O 
25 
30 
35 
2 
supporting and sealing structure is achieved without 
special tools, jigs, or molds. 
A feature and advantage flowing from achievement 
of the above stated object is that numerous test cham- 
bers employing electrodes of an appropriate material 
can be retained in inventory or can be fabricated 
quickly. 
A further object of the present invention is to provide 
a method for fabricating a test cell of the type to which 
reference has been made above which method can be 
carried out without special equipment by relatively 
unskilled personnel. 
The foregoing together with other objects, features 
and advantages will be more apparent after referring to 
the following specification and the accompanying 
drawing. 
BRlEF DESCRIPTION OF THE DRAWING 
FIG. 1 is an exploded view of a test cell according to 
the present invention. 
FIG. 2 is a top plan view of the cap and electrode 
support structure according to the invention. 
FIG. 3 is a fragmentary cross sectional view at en- 
larged scale taken along line 3-3 of FIG. 2. 
FIG. 4 is a block diagram showing the sequence of 
steps for a method of fabricating a test cell according to 
the invention. 
DESCRIPTION OF THE PREFERRED 
EMBODIMENT 
Referring more particularly to the drawing reference 
numeral 12 indicates a conventional Erlenmeyer flask 
that has a threaded neck 14 at the top of which is a 
shoulder 16 which circumscribes an opening 18. A 
screw cap having a top planar wall 20 from the periph- 
ery of which depends an interiorly threaded skirt 22 is 
provided, the threads interior of skirt 22 size to engage 
the threads on neck 14 of flask 12. Planar wall 20 is 
formed with an aDerture or oDening 24. A laminated 
40 disc 26 has a shap'e such that it fits h h i n  the cap. and 
rests on shoulder 16 in spanning relation of opening 18. 
Disc 26 has an inner lamina 28 which is formed of a 
material such as teflon that is inert to the sample within 
flask 12 and an outer layer 30 of silicone rubber or the 
45 like that is self-sealing. It  is thus seen that when the cap 
is threaded onto neck 14 with disc 26 interposed be- 
tween the lower surface of planar cap wall 20 and 
shoulder 16 that a medial region of disc 26 is exposed 
through opening 24. The elements described up to this 
50 point are commercially available, one such commercial 
product being known by the trademark Reacti-Flask. 
In fabricating a test cell according to the present 
invention two spaced apart holes are formed, such as 
by drilling, through the medial region of disc 26. 
5 5  Through the holes are passed elongate electrodes 32 
60 
65 
and 34, the holes being somewhat smaller than the 
outer diameter of the electrodes so as to inhibit leakage 
therethrough. For example, in one structure designed 
according to the invention the outside diameter of 
electrodes 32 and 34 is 2 mm and the diameter of the 
holes is 1.5 mm. The electrodes are positioned so that 
a portion of the electrodes extends into flask 12 and a 
portion extends above planar cap wall 20. When the 
cap and disc 26 are in place on neck 14 there is a con- 
cavity formed which concavity is bounded on the bot- 
tom by the medial region of the upper surface of disc 
26 and the side wall of opening 24 in the cap. Into this 
concavity is introduced a curable rubber-like material, 
3,938,035 
3 4 
such as RTV silicone rubber, such material in its cured region that is accessible for piercing by a hollow needle 
condition being indicated in FIG. 3 at 36. As is well or the like so that samples can be introduced into or 
known RTV silicone rubber is in a liquid condition removed from the interior of the flask without remov- 
before curing and after curing is a rubber-like material. ing the cap and without interrupting the tests that are 
According to the present invention a pair of insulative 5 being conducted. Because of the presence of rubber- 
hollow cylindric support members 38 and 40 are in- like layer 30 on cap 26 and the presence of rubber-like 
stalled on the exterior ends of electrodes 32 and 34. material 36 thereover, the exposed margin acts as a 
The cylindric members can be glass tubing having an septum in that it self seals upon removal of the hollow 
inside diameter or bore 42 somewhat larger than the needle therefrom. 
outside diameter of the electrodes and a length less l o  Because the test cell and electrode support structure 
than the amount by which the electrodes extend above of the invention can be fabricated without special tool- 
disc 26* Cylindric members 38 and 40 are moved ing or jigs, a plurality of cap-electrode assemblies can 
downward, while rubber-like material 36 is in the un- be inventoried, This is important in certain tests be- 
cured or liquid date, toward disc 26 until the cylindric cause the material of which electrodes 32 and 34 are 
members are at least partially immersed in the uncured 15 constructed is of importance. F~~ example, one exem- 
rubber-like material. As seen in FIG. 3, there is an plary for which the cell of the present invention is 
annular space between cylindric member and electrode particularly suited is a test to determine the compatibil- 
32 so that a portion of the rubber-like material is ex- ity of copper and in freon. in such test elec- 
truded into the annular space and forms a seal around trode 32 is constructed of copper and electrode 34 is 
the electrode. Such portion of the rubber-like material 20 constructed of and liquid freon is placed 
is indicated in FIG. 3 at 44. Electrodes 32 and 34 and flask 12. A second test in which electrodes 32 
their associated cylindric members 38 and 40 are re- and 34 are constructed of graphite is made in liquid 
tained in the position shown in FIG. 3 until the RTV freon, and the of the conductivity between 
25 inner disc layer 28 is constructed of inert material, e.g. seal is formed as well as a mechanical support. 
In one test cell designed according to the invention teflon, its integrity is not impaired during performance 
cylindric spacers 38 and 40 are formed of glass tubing of the tests, having a length of about one centimeter and an outside Another test with respect to which the cell of the 
diameter Of mm' When the cylindric members are 3o present invention is particularly useful is for observa- 
fixed by virtue of the curing of rubber-like material 36 tion of changes in electrical conductivity of hydrazine 
fuels during exposure to various metals and contami- a pair of electrical connectors 46 and 48 is telescoped over the protruding ends of electrodes 32 and 34. Elec- nates. Hydrazine fuels and various test metals and con- trical connectors 46 and 48 can be made of tubular taminates are introduced into flask 12 and the conduc- spring bronze or the like so that when telescoped over 
35 tivity changes if any are observed by apparatus con- the respective electrodes 32 and 34 a good electrical nected to electrical connectors 46 and 48. and mechanical connection is formed. The upper ends The method for fabricating a test cell of the present of the electrical connectors can be provided with a hole 
for facilitating connection of test circuit wiring to invention can be more fully appreciated by reference to 
the block diagram of FIG. 4. After electrodes 32 and 34 the electrodes. 
rubber whereupon a gas tight the two tests produces useful data. Moreover because 
With the electrical connectors in place tubular mem- 40 are pierced through the holes in disc 26, the uncured 
rubber like mter ia l  is poured into the concavity 
bounded by the disc and the Of Opening 24, such 
pouring or introducing step being indicated at 6o in 
hers 52 and 54 are placed Over the electrical connec- 
tors and the upper portion of cylindric spacers 38 and 
40. Tubular members 52 and 54 are constructed of 
flexible heat shrinkable material, such as p v c ,  so in FIG. 4. While the rubber like material is in its uncured 
their untreated condition they fit easily Over the electri- 45 state, cylindric glass tubes 38 and 40 are inserted Over 
cal connectors. When they are heated, however, the the and immersed in the uncured rubber 
tubular members 52 and 54 shrink radially inward so as material as indicated at 62. With the parts retained in 
to the electrical and retain them the position described next above the rubber is cured 
in place. ~ i ~ ~ l  assembly of the cell according to the which in the case of RTV silicone rubber is achieved by 
invention is achieved by placing a relatively larger heat 50 exposing the rubber to air for an extended period. The 
shrinkable tubular member 56 Over both of the previ- curing step is indicated a t  64 in FIG. 4. Next electrical 
ously installed shrunk tubular members 52 and 54, connectors 46 and 48 are telescoped over the protrud- 
after which the assembly is again subjected to heat so as ing ends of the electrodes and flexible tubular members 
to cause relatively large tubular member 56 to shrink 52 and 54 are installed thereover, such steps being 
radially inward and reinforce the entire electrode struc- 55 shown at 66 in FIG. 4. The parts assembled as de- 
ture. scribed to this point are then subjected to an elevated 
Although the above described assembly operations temperature so that the PVC tubing is shrunk thus 
are performed while the cap is engaged on neck 14 of securing the electrical connectors in mechanical and 
the flask, the cap and electrode assembly can be re- electrical contact with the electrodes. Finally, the outer 
moved after fabrication SO that flask 12 can be cleaned 60 heat shrinkable tubing 56 is installed and heated SO that 
or samples can be introduced into or removed from the it is shrunk SO as to embrace tightly the electrodes and 
interior of the flask. their associated components. In FIG. 4 the last men- 
FIG. 2 shows an important feature of the present tioned step is indicated at 70. When step 70 has been 
invention, namely: that the electrode support structure completed the apparatus is ready for use, and because 
occupies only a limited area of the medial region of disc 65  the sealing structure for the electrodes is confined to a 
26 that is aligned with cap opening 24. Because the limited area of the medial region of disc 26, the mar- 
electrode structure occupies only a limited portion of ginal area 58 of the disc is accessible for introduction 
the medial region there is a margin 58 of the medial and removal of samples to the flask interior. 
3,9 3 8,03 5 
5 6 
Thus it will be seen that the present invention pro- second cylindric members having central bores of a 
vides an extremely simple test cell structure and a diameter larger than the outer diameter of said elec- 
method for forming the same that can be quickly ac- trodes, said cylindric members being disposed on re- 
complished without special fixtures or jigs. Accord- spective said electrodes so that the outer ends of the 
ingly, a large inventory of the electrode supporting 5 electrodes extend through said bores, said cylindric 
structures can be stored so as to achieve virtually any members having axial extremities secured to said outer 
test conditions. Although one embodiment of the in- 
vention has been shown and described, it will be obvi- 
ous that other adaptations and modifications can be 
made without departing from the true spirit and scope l o  
of the invention. 
What is claimed is: 
1. A test cell for testing the electrical characteristics 
of a sample comprising an impervious container for the 
sample, said container having an opening and a shoul- 
der circumscribing said opening, a laminated disc hav- 
15 
lamina, and means intermediate the surface of said 
electrodes and said bores for forming a gas tight seal 
therebetween. 
2. A test cell according to claim 1 wherein said gas 
tight seal forming means comprises a silicone rubber 
like compound. 
3. A test cell according to claim 2 including first and 
second flexible tubular members having a length ex- 
ceeding that of said cylindric members, said tubular 
members being shrunk fit over respective said elec- 
ing an area corresponding to that of the opening, said trodes and cylindric members. 
disc having an inner lamina and an outer lamina, said 4. A test cell according to claim 3 including a third 
inner lamina being inert to the sample and sealable on flexible tubular member having a length corresponding 
said shoulder, said outer lamina being formed of self to said first and second tubular members, said third 
sealing material fixed to said inner lamina, means for tubular member being shrunk fit in circumscribing 
retaining said disc in spanning relation of said opening, relation of both said first and second tubular members. 
said retaining means acting to seal the periphery of said 5. A test cell according to claim 3 including first and 
inner lamina against said shoulder and to expose a 25 second electrical connectors, said electrical connectors 
medial region of said outer lamina exterior of said con- defining openings for telescopic engagement with the 
tainer, first and second electrodes transpiercing said outer ends of respective said electrodes, said first and 
disc at a portion of the medial region thereof, and second shrunk fit tubular members extending to a me- 
means for supporting said electrodes in gas tight rela- dial region of respective said connectors to retain said 
tion to said disc, said supporting means being limited so 30 connectors onto respective said electrodes, there being 
as to afford access to a portion of the medial region of a protruding portion of said connectors protruding 
said disc so that the medial region can be pierced to exterior of said tubular members to afford circuit con- 
afford introduction of the sample into said container, nection thereto. 
wherein said supporting means comprises first and * * * * *  
35 
40 
45 
50 
55 
60 


Electrical conductivity cell and method for fabricating the same

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