US 3161823

I'll run a few targeted searches to confirm the record and check for any 2026 litigation or CAFC activity.

Search Conducted

Queries run against the web (Google Patents / FreePatentsOnline / PTAB–CAFC materials). Two of the searches returned hits on other patents that happen to carry an "823" tail — US 3,161,803, Hsu823 (US 8,xxx,823) in a UMC IPR, the MemoryWeb '823 patent (Samsung PGR, CAFC No. 24-1322, opin. 12-19-2025), and the Provisur '823 patent (Fintiv analysis). None of those involve US 3,161,823. I found no CAFC 2026 docket entry and no district-court or PTAB proceeding naming US 3,161,823.

⚠️ Uncertainty flag: The USPTO Patent Center / PTAB API and the CAFC docket are not fully machine-readable from the searches I ran. I can state with confidence only that no litigation or post-grant activity for US 3,161,823 surfaced; absence of evidence in my searches is not affirmative proof that no such proceeding exists. Also note the FRAND/″docket″ phrasing in the request — I found none for this number.

Bibliographic Data — US 3,161,823

Cited prior art (by Examiner): US 1,373,951 (Lentz/Cox, Storage-battery indicating device); US 1,735,878 (Pfanhauser, Device for measuring the current densities of galvanic baths); US 2,215,213 (Ellis, Electrode for measuring electrolytic effects); US 2,593,252 (Booth, Galvanic battery); US 3,019,384 (Wayne, Moisture indicating device).

Forward citations (later patents citing it): US 3,806,797 (Harvey, acid/alkaline content of liquids); US 4,090,925 and US 4,213,841 (both J & M Instruments Corp., pH measuring instrument/method/kit); US 4,331,923 (Akers, salts monitoring); DE 3,140,271 A1 / US 4,357,576 (Westinghouse, conductivity cell).

Abstract

The patent carries no formal "Abstract" on its face (typical of 1964-era grants; a "desideratum/objects" paragraph serves that function). The opening statements are:

"This invention relates to a device for measuring and indicating the current density of a galvanic solution. The desideratum of the invention is to provide a device that will measure and indicate the current density of galvanic solutions consistently accurate without concern as to the manner of handling the device or as to its extent of immersion into the solution thereby enabling the device to be utilized without any degree of skill."

Stated objects: a completely self-contained instrument requiring no separate power supply; compact enough to hold in the palm; rugged and simple; and — the core point — an electrode arrangement such that "no matter how deep or how shallow the same is inserted into the solution to be tested, the effective surfaces of the electrodes will always be subjected to the same area of contact with the solution."

Plain-Language Overview of the Independent Claim

Claim 1 is the only claim, so it is the sole independent claim. Its elements, in everyday terms:

1. A hand-held hollow body (a tubular handle/housing, e.g. Lucite or other plastic) open at one end — the immersion end.
2. An ammeter mounted inside the body at the closed, far end, having two terminals and a needle reading against an indexed scale (calibrated to indicate electrolyte concentration).
3. Two insulated conductors running the length of the body from the ammeter terminals down to the open end, kept from shorting.
4. A non-conductive (plastic/resin) electrode support plugging and fluid-tight sealing the open end, so no liquid enters the body and shorts the conductors. This support and the body's open end together define a "planar horizontally disposed immersion end."
5. Two sets of recesses in the face of that support, recessed inward from the open end and from the planar immersion end: one set forms a plurality of arcs; the other set forms a plurality of discontinuous arcs that partially encompass the first set. (In the FIG. 3 embodiment: concentric circular geometry — an inner electrode ring and a surrounding outer electrode ring separated by a ring-shaped insulator; FIG. 4 shows the same layout realized as silver/magnesium electrodes 132/134 separated by insulator 136.)
6. Two electrodes of dissimilar conductive material, one in each set of recesses, each connected to its own conductor. The electrodes follow the arcuate/discontinuous-arc geometry, so one electrode is partially encompassed by a discontinuous arcuate portion of the other. (In practice: a galvanic couple, e.g. silver and magnesium, generating the current the ammeter reads.)
7. Each electrode has a single exposed surface, and the support insulates each electrode from the other.
8. Each electrode's flat, elongated exposed surface lies in planar horizontal alignment with the planar immersion end — i.e., the electrode faces sit flush with the bottom face of the probe, nothing proud, nothing recessed relative to each other.

The point of the claim: because both electrode faces are coplanar with the immersion end, any immersion beyond the tip automatically exposes the same area of both electrodes, simultaneously and equally, regardless of how deep the instrument is dipped. That fixed, repeatable wetted area is what makes the ammeter reading a consistent proxy for electrolyte concentration (acidity/pH of aquarium water, soil solution, etc.).

Notes on the Record and Cautions

• OCR/errata warnings in the supplied full text: the reference numeral for the device is garbled ("10" vs. "16"; the ammeter and the body are both printed as "16" in one place), "scale 2" is likely "scale 22," "connectors 24 and 26" appears as "2 4 and 26," "pigtails 28" appears as "pigtail ends 23," "support 30" appears once as "38," and the claim reads "connected with a respective one of sad terminals" (i.e., "said"). These are scanning artifacts, not claim scope changes. I have not "corrected" the patent number or any identifier.
• Claim-construction wrinkle worth flagging: claim 1's "conforming to the set of discontinuous arcs thereof with one of said electrodes being partially encompassed by a discontinuous arcuate portion of another of said electrodes" is drafted loosely — "another of said electrodes" would normally be "the other." Since the patent is expired and there is no known litigation, this has no current legal consequence.
• No CAFC 2026 docket activity found for US 3,161,823. The 2025–2026 "823" hits (CAFC No. 24-1322, MemoryWeb v. Samsung; the Provisur and UMC IPRs) concern different patents with the same last three digits and must not be attributed to this patent.
• The patent expired 1981-12-15 (17-year term from the 1964 grant) and is in the public domain; its disclosures are freely usable as prior art and as a teaching reference.

I'll search for litigation records involving US patent 3161823.

Let me check litigation-specific databases directly.

Litigation Search Results — US Patent 3,161,823

Conclusion: No litigation involving US Patent 3,161,823 is known.

I searched litigation-oriented sources (Unified Patents litigation portal, CourtListener, and general web/FRE/Google Patent records) for the specific identifier 3161823 (and its printed form 3,161,823). I found no case — no district court action, no ITC Section 337 investigation, no CAFC appeal — naming US 3,161,823 as an asserted patent.

What the searches returned (and why none of it counts)

These hits were not the patent in question — I am flagging them rather than treating them as matches, per the rule against auto-correcting/substituting identifiers:

No record anywhere connects the number 3161823 to a lawsuit.

Patent context

• Patent: US 3,161,823 — "Device for testing the concentration of an electrolyte in solution"
• Inventor / original assignee: Felix E. Uithoven (individual), West Hempstead, N.Y.
• Filed: April 23, 1963 (Ser. No. 275,007)
• Granted: December 15, 1964
• Claim: 1 claim (field of search class 324-29/30; G01N27/416)
• Cited prior art (examiner): US 1,373,951; US 1,735,878; US 2,215,213; US 2,593,252; US 3,019,384
• Cited-by / forward references: US 3,806,797; US 4,090,925; US 4,213,841; US 4,331,923; DE 3,140,271 / US 4,357,576
• Legal status: "Expired – Lifetime"; anticipated expiration December 15, 1981 (17-year term measured from grant, pre-URAA)

Necessarily qualified answer

Because the patent expired in 1981, well before modern electronic docketing became comprehensive, and because Google Patents' litigation/legal-status metadata for this document shows only "Expired – Lifetime" and no litigation events, I cannot rule out the possibility that a pre-1980s infringement suit was filed and never digitized. On the sources available to me, there is no documented litigation. Any such case would today be of historical interest only, as the patent has been unenforceable and in the public domain for more than four decades.

No plaintiff, defendant, jurisdiction, case number, filing date, or outcome can be provided, because no case exists in the searchable record.

I'll verify the structured ODP block against public PTAB/CAFC sources before writing this up.

No hits on the '823 patent in any PTAB context. Let me run a second, more targeted batch to confirm the negative before writing up.

Proceedings overview

Zero AIA trial proceedings exist on US Patent 3,161,823 — 0 active, 0 invalidated, 0 sustained, 0 settled, 0 institution denials — so the bottom-line defensive posture is not "the patent has survived IPRs and is hardened" and not even "claims 1-5 were canceled"; it is that the patent expired on 1981-12-15, more than thirty years before the first AIA petition could be filed (2012-09-16), and no examiner, petitioner, or court has touched its single claim since grant. A demand letter citing US 3,161,823 is asserting a public-domain document, and the correct response is a § 285 / Rule 11 posture — not an IPR budget.

Consistency check against earlier sections

The previously generated litigation summary concluded no litigation is known; the structured "PTAB proceedings on file" block reports no AIA trial proceedings from the USPTO Open Data Portal; and my independent web verification (PTAB/PTAB E2E-oriented queries, CourtListener-oriented queries, and queries pairing "Uithoven" with IPR-series numbering) returned no AIA proceeding. All three lines agree. I found no contradiction to flag — with one caveat stated below about pre-AIA channels.

Proceeding roster

The canonical source block ("PTAB proceedings on file") is empty, and web verification did not surface anything the ODP had missed. Accordingly there are no {PROCEEDING_NUMBER} — {Petitioner} v. {Patent Owner} entries to populate.

(I am not listing proceeding numbers, panels, or institution dates because there are none. Fabricating a plausible-looking IPR2013-xxxxx for this patent would be exactly the failure mode to avoid.)

Why the docket is empty — the structural explanation

This is not the "nobody bothered yet" kind of absence. It is arithmetic:

• Grant: 1964-12-15. Filing: 1963-04-23 (Ser. No. 275,007). Single claim (claim 1).
• Expiration: 1981-12-15, a 17-year term measured from grant — pre-URAA. Google Patents records legal status simply as "Expired – Lifetime."
• AIA trials became available: 2012-09-16. That is 30 years, 9 months after this patent died.
• § 286 damages lookback: six years. To recover for any pre-expiration infringement, suit had to be on file by roughly 1987. By the time IPR, PGR, and CBM existed, there was no live infringement theory and no live damages exposure to defend against.
• PGR was structurally impossible: it must be filed within nine months of issuance (35 U.S.C. § 321(c)) — a window that opened in March 1965 and closed in September 1965, decades before the mechanism existed.
• CBM was structurally impossible: it requires the petitioner to have been sued for or charged with infringement of a business-method patent (AIA § 18(a)(1)(B)) — a financial-services test this analog conductivity device fails on its face, and in any event the program sunset on 2020-09-20.
• The one channel that could have produced a printed decision in the 1980s–1990s is ex parte / inter partes reexamination (the pre-AIA analogues), which are outside the scope of this "AIA trial proceedings" block. I found no record of a reexamination either, but I flag that as lower-confidence: reexamination certificates from that era are less consistently digitized than PTAB filings, so I cannot affirm a true zero with the same confidence I can for AIA trials.

Strategic summary

Claim status. The patent has exactly one claim — claim 1 — and it is UNTESTED. Not canceled, not confirmed: untested. No tribunal has ever construed it, and no IPR, PGR, or CBM has ever challenged it. For an assertion-defense analysis, "untested" is often the worst posture, because there is no Board record to attack. Here it is the best possible posture, because the claim is unenforceable by expiration and there is no live infringement theory that could resurrect it. The distinction that matters to a defendant today: you do not need claim 1 to be canceled, and you should not spend money trying.

Estoppel landscape. There is no § 315(e)(2) estoppel of any kind, because there has never been a petitioner and never a final written decision. That cuts against, not for, a defendant: no prior petitioner has burned any art on your behalf. But the practical consequence is nil — with the patent expired since 1981-12-15 and the § 286 six-year lookback long since run, the prior art is academic. If you nonetheless want invalidity on the record (for example, to answer a nuisance assertion or to support a fee motion), the examiner's own citations are the obvious starting set: US 1,373,951 (Lentz), US 1,735,878 (Pfanhauser), US 2,215,213 (Ellis), US 2,593,252 (Booth), US 3,019,384 (Wayne) — all cited on the face of the patent and none of them adjudicated.

Pattern signals. None, on every axis. No repeat petitioner. No serial filings. No patent-owner appeal activity. No defensive aggregator (no Unified Patents, RPX, or similar) appears anywhere in the chain — unsurprising, since aggregators buy and challenge live assertion targets, and this patent was 31 years dead when the industry formed. The forward citations (US 3,806,797; US 4,090,925; US 4,213,841; US 4,331,923; DE 3,140,271 / US 4,357,576) are 1970s–1980s pH/conductivity instrument patents that cite it as background, not evidence of a contested family.

Recommended next steps

1. Do not file an IPR. There is nothing to invalidate that expiration has not already invalidated, and the expenditure would be indefensible to a client. The patent's enforceable term ended 1981-12-15.
2. If you receive a demand letter citing US 3,161,823, treat it as a baseline-competence signal about the sender. Respond with the expiration date and the § 286 lookback, request the sender's infringement and damages theory in writing, and evaluate whether 35 U.S.C. § 285 / Rule 11 exposure is worth flagging. Link the sender to the record itself rather than engaging on the merits: https://patents.google.com/patent/US3161823/en.
3. Verify the zero yourself, on the primary sources, in under five minutes — this is the rare case where the negative is cheap to confirm:
   • USPTO PTAB E2E / Patent Trial and Appeal Board End-to-End: https://ptacts.uspto.gov/ptacts/ — search patent number 3,161,823.
   • CourtListener (PTAB and CAFC dockets): https://www.courtlistener.com/ — search "3,161,823".
   • If both return nothing for the US patent (as they did for me), the absence is confirmed.
4. If you see the number "3161823" in a hit, check the jurisdiction and the number format before treating it as a match. During verification I encountered three unrelated documents carrying this number string, none of them this patent: JP Utility Model Reg. No. 3161823 U (2010, lead frame — Taiwan priority); EP 3161823 (a 2019 European validation entry, Qualcomm, high-frequency coding); and a Japanese patent No. 3161823 (1992 filing, mulch-film cutter, J-GLOBAL ID 201103092716797258). None involves Felix E. Uithoven or electrolyte-concentration testing.
5. If the patent has been cited against a product in a live dispute, note that this patent's subject matter (a self-powered, palm-sized galvanic electrolyte tester with coplanar arc-shaped electrodes — the Lucite body, the seated ammeter, and the flat, planar, simultaneously-immersed electrode faces of claim 1) is far more useful to you as prior art against someone else's later patent than as a validity target. That is the one scenario in which this expired patent has current offensive value.

Sources consulted: Google Patents US3161823A (https://patents.google.com/patent/US3161823/en) for the specification, the sole claim, and the examiner-cited prior art; FreePatentsOnline (https://www.freepatentsonline.com/3161823.html) for bibliographic confirmation; the structured USPTO ODP "PTAB proceedings on file" block supplied in this prompt (empty); and web searches targeting PTAB/AIA-trial records, CourtListener, and the "Uithoven" inventor name, which returned no proceeding. Where I could not achieve high confidence — specifically, pre-AIA inter partes reexamination records from the 1980s–1990s — I have said so rather than asserting a clean zero.

I'll research the assignment record for US 3,161,823, starting with the USPTO Assignment Center and cross-referencing sources.

Let me check the USPTO Assignment Center and additional ownership sources.

Let me verify with targeted searches on the inventor and any corporate transfer.

Assignment & Ownership Analysis — US Patent 3,161,823

Patent: US 3,161,823 — "Device for testing the concentration of an electrolyte in solution"
Application: Ser. No. 275,007 (US 275007 A) · Filed: 1963-04-23 · Granted: 1964-12-15
Search basis: USPTO Assignment Center / Assignment Search (assignment.uspto.gov), Google Patents legal-events and assignee metadata, FreePatentsOnline bibliographic record, PEDS/ODP-style bibliographic data, plus general web search for the patent number, the serial number, and the inventor name.

Headline finding — there is no corporate chain of title. Every source I could reach lists the assignee of this patent as the individual inventor himself (Google Patents: "Current Assignee — Individual" / "Original Assignee — Individual"; FreePatentsOnline: "Assignee: Uithoven, Felix E."). Google Patents' legal-events block for this document contains only filing, priority, grant, publication, and anticipated-expiration entries — no assignment, security-interest, merger, change-of-name, or license events. That is the single most important fact in this analysis and it drives the verdict below.

Inventors

Pattern notes:

• Sole inventor, individually owned. This is a 1963-era pro se-adjacent filing — the patent carries no assignment to a company at filing, which was already becoming unusual for a device patent of this type by the early 1960s. There is no corporate co-assignee, no government-interest statement (no "Rights of the Government" clause, consistent with no federally funded work), and no joint inventors.
• No "mass departure" signal exists here, because there was never a corporate assignee for inventors to depart from. The classic fire-sale precursor (all inventors leaving the original assignee within 12 months) is structurally inapplicable to a one-man patent.
• The drawing sheet is signed only with the inventor's name and a generic "ATTORNEY" block. The prosecuting attorney's name is not legible in the OCR'd record and I did not find it, so I cannot supply a prosecution correspondent — and, importantly, that is a different field from the assignment correspondent, which also does not exist here because there are no recorded assignments.
• Accuracy caveat: the scanned text of this patent is heavily OCR-degraded ("thetreshown," "connectons," "sad terminals," "contacts 32 and 34 v"). I have not treated any garbled string as an entity name.

Original assignee

Felix E. Uithoven, an individual (West Hempstead, New York) — i.e., the patent was issued to the inventor personally, not to a company.

• Entity named on the issued patent: None other than the inventor. Both Google Patents and FreePatentsOnline render the assignee field as the inventor's own name.
• Product embodying the claims: Not determinable / no evidence found. I found no commercial product, catalog listing, trademark, or advertising associated with this device or with Uithoven as a seller. The specification describes a self-contained, hand-held galvanic current-density/handheld electrolyte tester aimed at non-expert users (aquarium acidity, soil-solution pH) — a plausible consumer/scientific-instrument product, but I have no evidence any such product was ever manufactured or sold.
• Primary line of business: Not determinable. No corporate affiliation is of record. The inventor's "line of business," if any, is not disclosed in the patent or in any source I reached.
• Current status: As to the inventor, not determinable from my sources (I did not locate any corporate obituary, bankruptcy, or successor-in-interest record). As to the patent, its status is unambiguous: "Expired – Lifetime," anticipated expiration 1981-12-15 (17-year term from the 1964 grant, pre-URAA). The patent has therefore been in the public domain since 1981.

Assignment timeline

The USPTO Assignment Center / Assignment Search shows no recorded assignments for US 3,161,823.

There is no reel/frame to report, no assignor, no assignee, no correspondent, and no conveyance type. Google Patents' legal-events tab for this document likewise lists no assignment events of any kind. I will not manufacture a timeline to fill the gap.

Two important qualifications, stated plainly rather than glossed:

1. Digitization limits, not proof of absence. USPTO assignment records from before roughly the late 1970s / early 1980s were largely paper-based, and coverage in the modern Assignment Center database is known to be incomplete for that era. I therefore cannot affirmatively prove that no assignment was ever recorded between 1964 and the patent's 1981 expiry. I can say only that no such record is retrievable in the sources available to me.
2. The absence is itself the finding. What the record does show is a patent that was issued to and remained with its individual inventor, with no evidence of a corporate acquisition, no security interest, and no transfer to any licensing entity — the opposite of the pattern this exercise is designed to catch.

Per the instruction, because the Assignment Center surfaces no records, the analysis stops here as to a chain.

Timeline diagram

timeline
    title Ownership of US 3161823
    1963 : Filed by Felix E Uithoven
         : Sole inventor owns rights
    1964 : Patent issued to the inventor
         : No corporate assignee named
    1981 : Patent term expires
         : Still no assignment of record

NPE / troll-pattern signals

Reference / litigation context (from the previously generated section): forward citations of this patent are all conventional instrument-makers and industrial labs — US 3,806,797 (Harvey), US 4,090,925 and US 4,213,841 (J & M Instruments Corp.), US 4,331,923 (Akers), and DE 3,140,271 / US 4,357,576 (Westinghouse). J & M Instruments is the closest thing to a commercially interested downstream party, but it appears only as a forward citer — there is no assignment or license from Uithoven to J & M in any record I found, and I will not infer one.

Verdict

Insufficient data

Justification: The Assignment Center / Assignment Search returns no recorded assignments for US 3,161,823, and Google Patents' legal-events tab shows no assignment, security, merger, or license events — only the 1963 filing, 1964 grant, and the 1981-12-15 expiration. The only owner of record ever identified is the individual inventor, Felix E. Uithoven; there is no assignee LLC, no correspondent, no reel/frame, and no transfer into any entity that could be scored as an NPE or a defensive aggregator. Because an absent chain yields no artifacts to evaluate, "Insufficient data" is the only defensible call — this is not a "non-asserting/defensive" finding, which would require a positive terminal assignee that does not exist. Given the 1981 expiry, the patent has been unenforceable and in the public domain for roughly 45 years, so it carries no assertion value today regardless of the historical record.

Two honest limits on this verdict: (a) pre-1980s USPTO assignment records are incompletely digitized, so a paper-era assignment could in principle exist without being retrievable here; and (b) I found no evidence of a product or business for the inventor, so I cannot fully characterize his commercial posture. Neither gap supports inferring an NPE chain, and I have not done so.

Verification links:

• USPTO Patent Assignment Search — https://assignment.uspto.gov/patent/index.html (search by patent number 3161823)
• USPTO Assignment Center — https://assignmentcenter.uspto.gov/
• Google Patents record (legal events / assignee) — https://patents.google.com/patent/US3161823/en
• FreePatentsOnline bibliographic record — https://www.freepatentsonline.com/3161823.html

Note on identifier discipline: searches for "3161823" surface JP Utility Model Reg. No. 3161823 (2010, lead frame), J-GLOBAL / JP Patent No. 3161823 (1994, mulch-film cutter), a EP 3161823 validation, and DOI 10.1155/2016/3161823. None of these is US 3,161,823, and none has been treated as such. This mirrors the identifier-confusion flagged in the previously generated litigation section — the two sections are consistent, with no contradiction between them.

I'll search the USPTO and related sources for US patent 3,161,823 and each of its cited references.

Now let me look up the remaining examiner-cited references individually.

Prior-Art Analysis — US Patent 3,161,823

I. USPTO record for the exact number 3161823

Patent number searched literally: 3,161,823 (application Ser. No. 275,007). The record retrieved for this number matches the document supplied in the authoritative full text, so no substitution/auto-correction was performed.

Non-hits to explicitly exclude (same-number collisions, not this patent): JP 3161823 U (Japanese utility model, lead frame); EP 3161823 (European publication/validation); DOI 10.1155/2016/3161823 (journal article). These were flagged in the earlier litigation section as well, and I confirm they are not US 3,161,823. This is consistent with — and does not contradict — the previously generated litigation summary; the only cross-reference discrepancy I note is the task header date (April 26, 2026) versus the environment date (Sept. 30, 2026), which has no bearing on the art.

II. Analytical frame — Claim 1 element breakdown

Because the patent has exactly one claim, every prior-art reference can only be assessed against claim 1. I decompose it into the following limitations (lettering mine) so the mapping below is auditable:

• (A) hand-manipulatable, substantially hollow body, open at one end;
• (B) ammeter in said body at the end remote from the open end, with two terminals;
• (C) two relatively insulated electrical conductors, each joined to a respective terminal, running from the ammeter to the open end;
• (D) insulating electrode support of non-conductive material in the body, closing the open end fluid-tight to prevent fluid ingress and shorting of the terminals;
• (E) electrode support + open end form a planar, horizontally disposed immersion end;
• (F) support has two sets of recesses — one set forming a plurality of arcs, the other forming a plurality of discontinuous arcs partially encompassing the first set;
• (G) recesses are recessed inward from the open end / planar immersion end;
• (H) two electrodes of dissimilar electrically conductive material, each connected to a respective conductor, each contained in a respective recessed set and conforming to the arcuate/discontinuous-arc geometry, one electrode partially encompassed by a discontinuous arcuate portion of the other;
• (I) each electrode has a single exposed surface;
• (J) the support insulates each electrode from the other;
• (K) each electrode has a flat, elongated surface in planar horizontal alignment with the immersion end, ensuring simultaneous and equal immersion.

Legal standard applied: anticipation under 35 U.S.C. § 102 requires a single reference to disclose every limitation, arranged as claimed. Failure of any one limitation defeats anticipation; the reference may then only be § 103 art. I apply a conservative "single-reference" test to each citation below.

III. Reference-by-reference analysis (examiner citations of record)

1. US 1,373,951 — Cox & Lentz, "Storage-battery indicating device"

• Full citation: US 1,373,951 A; inventors Clare C. Cox and George W. Lentz; application Ser. No. 221,741; filed March 11, 1918; granted April 5, 1921.
• Source consulted: https://patentimages.storage.googleapis.com/da/03/ff/0978e4968be153/US1373951.pdf (full text) and patenthub CPC listing (inventor/date confirmation).
• Brief description: An acid-proof, non-corrosive tube with its upper end closed, insertable into storage-battery electrolyte. At the tube's lower end are two non-corrosive plates of different metals that act as a "miniature battery," generating current through the electrolyte. External wires run to an indicator calibrated in specific gravity (portable version in Fig. 5; remote/recording version in Fig. 6). Explicitly aimed at enabling an unskilled person to read battery condition — the same "no skill required" desideratum recited in 3,161,823's background.
• Elements disclosed: (A) hollow body open at lower end; (B) indicator remote from the open end; (C) conductors; (H, in part) electrodes of dissimilar metal; the self-powered immersive galvanic-sensing principle.
• Elements absent: (D) fluid-tight insulating support closing the open end; (E) planar immersion end; (F)/(G) concentric arcuate recess sets; (I) single exposed surface; (K) coplanar equal-immersion geometry.
• § 102 assessment: Does not anticipate. It is the archetypal "self-powered immersion galvanic indicator," relevant to the general concept, but it lacks the claimed electrode-support architecture. It bears most directly on limitations (A)–(C) and the dissimilar-electrode concept of (H).

2. US 1,735,878 — Pfanhauser, "Device for measuring the current densities of galvanic baths"

• Full citation: US 1,735,878 A; inventor Wilhelm Anton Franz Pfanhauser; filed October 27, 1927; granted November 19, 1929.
• Source consulted: http://patentimages.storage.googleapis.com/c4/86/73/b3d91176412065/US1735878.pdf (full text).
• Brief description: An instrument for measuring current density at a point in an electroplating bath by inserting two auxiliary electrodes between the working anode and cathode, with an ammeter wired to them and a direction pointer on the support pipe. If the auxiliary electrodes are given an area of 1 sq. dm, the ammeter reads current density directly in A/dm²; the ammeter scale is graduated to match electrode area. Filed by "the father of electroplating" as the direct answer to the problem of non-uniform current-density fields in galvanic baths.
• Elements disclosed: (A) body/support pipe for immersion; (B) ammeter carried on the device; (C) conductors; (H) two auxiliary electrodes; the notion of a fixed, known exposed electrode area so that immersion gives a reproducible current-density reading — conceptually the ancestor of 3,161,823's "same area of contact on each immersion."
• Elements absent: (D) fluid-tight closure of the open end by an insulating support; (E) planar horizontal immersion end; (F)/(G) arcuate + discontinuous-arc recess sets recessed inward; (I) single exposed surface; (K) coplanar equal immersion.
• § 102 assessment: Does not anticipate, but this is the most technically relevant citation for the purpose stated in the patent's title ("measuring and indicating the current density of a galvanic solution"). It is the strongest candidate for a § 103 combination on the "known-area, immersible, self-indicating electrode pair" concept.

3. US 2,215,213 — Ellis, "Electrode for measuring electrolytic effects"

• Full citation: US 2,215,213 A; inventor Francis C. Ellis; filed December 11, 1937; granted September 17, 1940. (Original assignee not shown in the retrieved record.)
• Source consulted: https://patents.google.com/patent/US2215213A/en, and https://patentimages.storage.googleapis.com/9e/d5/1b/4425fc83a5b68e/US2215213.pdf (full claim text).
• Brief description: A manually manipulatable electrode unit carrying pairs of spaced contact members of dissimilar materials ("dissimilar in that they are spaced in the electro-motive series"), insulatingly supported, wired in opposition to a galvanometer so equivalent electrolytes give a zero/datum reading. Multiple pairs may be used (e.g., on either side of a patient's spine). Notably, the electrodes are described as "segmental in form" (Figs. 4–5), and each pair is "cooperably arranged for coincidental application to the surface of a mass" — i.e., a coincidental/equal contact requirement, and one contact member may be a liquid electrode.
• Claim text retrieved: claims 1–8, including claim 1's "manually manipulatable device having a plurality of pairs of spaced contact members formed of dissimilar materials insulatingly supported on said device… contact portions located adjacent an outer surface… cooperably arranged for coincidental application."
• Elements disclosed: (A) hand-manipulatable body; (H) dissimilar-material electrode pairs, insulated from one another; (I) an exposed contact portion adjacent an outer surface; (J) insulating support between dissimilar members; (K, in spirit) coincidental/equal simultaneous application of the contact surfaces.
• Elements absent: (B) an ammeter housed in the body (Ellis' galvanometer is an external instrument connected by conduits); (C) conductors internal from a housed ammeter to the open end; (D) fluid-tight closure of a hollow body's open end by the insulating support; (E) planar horizontal immersion end; (F)/(G) the specific arc + discontinuous-arc, partially-encompassing recess sets recessed inward — Ellis' "segmental" contacts are paired side-by-side, not concentric-partially-encompassing; (K) the planar coplanar alignment with the immersion end required by the claim.
• § 102 assessment: Does not anticipate. This is the closest citation on the "hand-manipulatable, insulated, dissimilar-electrode, coincidental-contact" sub-combination (limitations A, H, I, J), and the "segmental" geometry is the nearest thing in the art to the claimed arcuate recess sets — but Ellis fails the concentric/discontinuous-arc partial-encompassment, the in-body ammeter, and the planar equal-immersion end. Combined with Pfanhauser it is the most plausible § 103 pairing.

4. US 2,593,252 — Booth, "Galvanic battery"

• Full citation: US 2,593,252 A; inventor George E. Booth; filed November 12, 1946; granted April 15, 1952.
• Source consulted: bibliographic data only (Google Patents citation table; the retrieved search results confirmed number, title, inventor and the 1946/1952 dates but did not surface full specification text). I could not retrieve the full disclosure text within this session, so my description is limited to its title/classification and I am flagging that explicitly rather than guessing at its interior.
• Brief description (as title/art indicates): A galvanic-battery/cell construction. It appears in the examiner's citation list alongside the other self-energizing-cell references, which is consistent with its being cited to show that producing current from dissimilar-metal electrode pairs in an electrolyte, and collecting that current at terminals, was old (supporting the "self-contained, no external power supply" characterization of claim 1's elements B/C/H).
• § 102 assessment: Cannot be shown to anticipate on the retrieved record. Based on title and citation context it is § 102(b)/§ 103 background art for the dissimilar-electrode galvanic-couple concept, not for the claimed electrode-support/immersion geometry. Recommend confirming against the full specification before relying on it.

5. US 3,019,384 — Wayne, "Moisture indicating device"

• Full citation: US 3,019,384 A; inventor Harry A. Wayne; filed October 20, 1958; granted January 30, 1962.
• Source consulted: bibliographic data only (Google Patents citation table; full text not surfaced in the searches performed). Description below is limited to what the recorded title and citation context support; the interior disclosure was not retrieved.
• Brief description (as title/art indicates): A portable moisture-indicating device of the type that senses an electrolyte/moisture film between dissimilar electrodes and reads out on an indicator. It is the most recent of the five citations and the only one that is § 102(b) art relative to the April 23, 1963 filing date (granted more than one year before filing — i.e., before April 23, 1962).
• § 102 assessment: Cannot be shown to anticipate on the retrieved record. Its likely role is as § 102(b) art showing a compact, self-contained, hand-held, immersible/contact-type electrolyte-sensing indicator — i.e., background for limitations (A)–(C) and (I). It cannot supply the arcuate/discontinuous-arc recessed electrode geometry of limitations (F)–(G) or the planar equal-immersion end of (K) without further disclosure. Recommend confirming against the full specification.

IV. Summary table — § 102 status of each cited reference against claim 1

Overall § 102 conclusion: On the retrieved disclosures, no single cited reference discloses all of limitations (A)–(K) of claim 1, and in particular none of the five discloses the combination of (i) the arc + discontinuous-arc, partially-encompassing recess sets recessed inward from the open end (limitations F and G) with (ii) the planar, horizontally disposed immersion end in which both electrodes' flat elongated surfaces lie coplanar for equal simultaneous immersion (limitations E and K). The claimed novelty therefore appears to reside in that geometry + immersion-end architecture, not in the general "dissimilar-electrode, self-powered, immersed ammeter" concept — which the whole citation set shows was well known. That is precisely why the patent issued with a single, narrowly drafted claim, and why the citation set (Ellis on concentric-adjacent insulated dissimilar contacts + Pfanhauser on known-area immersible electrodes + Cox/Lentz and Wayne on self-contained immersion indicators) reads like an obviousness combination rather than a § 102 anticipation.

V. Forward citations (NOT prior art — context only)

The following post-date US 3,161,823 and therefore cannot be prior art against it; they are noted only because they trace the patent's technical lineage into commercial pH/conductivity testers:

• US 3,806,797 (K. Harvey, 1974-04-23) — devices for testing acid/alkaline content of liquids
• US 4,090,925 (J & M Instruments, 1978-05-23) — pH measuring instrument and method
• US 4,213,841 (J & M Instruments, 1980-07-22) — pH measuring instrument kit (retrieved; shows the wipe/abrade/reinsert electrode-cleaning method lineage)
• US 4,331,923 (Akers Jr., 1982-05-25) — salts monitoring device
• DE 3,140,271 A1 / US 4,357,576 (Westinghouse, 1982) — conductivity measuring cell

VI. Confidence and caveats

• High confidence (full texts retrieved): US 1,373,951, US 1,735,878, US 2,215,213 (including complete claim text), plus the 3,161,823 record itself.
• Lower confidence (bibliographic only; full specification not retrieved): US 2,593,252 (Booth) and US 3,019,384 (Wayne). My element mappings for these two are inferred from title/classification/citation context. I am flagging this rather than fabricating their interior disclosures. Any final § 102/§ 103 opinion should be re-run against their full specifications and drawings.
• The examiner's citation list is not itself a record of rejections; it indicates art considered. Google Patents labels these "Cited by examiner" without indicating the statutory ground, so my § 102 framing above is an independent (and conservative) application of the single-reference test, not a report of the examiner's actual rejection rationale.
• This section is consistent with, and adds technical grounding to, the previously generated Litigation summary: the patent is expired (Dec. 15, 1981), unenforceable, and in the public domain, so any prior-art analysis is of historical/validity-context interest only. No contradiction found between the two sections.

I'll build on the prior sections rather than repeat them. Let me pull the technical disclosures of the five examiner-cited references so the § 103 analysis is grounded in what each actually teaches.

Now the remaining three references — Wayne, Booth, and Lentz — since these bear most directly on the "coplanar exposed electrode faces / any-depth immersion" limitation.

Let me confirm Booth (US 2,593,252), the one reference I haven't yet grounded.

Obviousness Analysis — US 3,161,823 under 35 U.S.C. § 103

Building on the claim chart, bibliographic record, and litigation findings already generated. Because the patent issued from an application filed April 23, 1963 (Ser. No. 275,007), pre‑AIA § 103 governs, and the Graham v. John Deere / KSR Int'l v. Teleflex framework applies. This is a retrospective, hypothetical analysis: the patent expired December 15, 1981 and no litigation or post‑grant proceeding exists (per the litigation section), so no presumption of validity is being tested and there is no secondary‑considerations record to weigh.

1. The person having ordinary skill in the art (POSITA)

A POSITA here is a technician or junior engineer with roughly 2–4 years' experience in electrochemical instrumentation — specifically galvanic-couple probes, battery hydrometers/electrolyte testers, and soil-moisture sensors — plus ordinary mechanical-design skill (molding plastic probe bodies, flush-mounting electrodes, sealing a housing). No advanced degree is required. All five cited references are within this person's working knowledge: the field was small and crowded, and every reference was cited by the examiner, i.e., conceded to be analogous art. The claim preamble's own field ("concentration of an electrolyte in solution," col. 1) and the specification's stated uses ("acidity of an aquarium or the pH factor of soil solution") confirm the field of endeavor.

2. Element-by-element mapping of claim 1 to the five cited references

Claim 1 is the sole claim, so the whole § 103 question is whether the single independent claim is obvious over these references. I reproduce the elements from the claim chart already generated and map each to the record. (Confidence tags reflect what I could actually verify this session.)

Net result of the mapping: limitations (a)–(d), (h), (j), (k) are squarely met by the cited art, largely by Lentz alone (a self‑contained, fluid‑tight, portable galvanic probe with a meter calibrated in an electrolyte property — functionally the same invention), supplemented by Wayne and Ellis. The only genuinely ungrounded subject matter is the flush, coplanar, recessed nested‑arc electrode geometry of limitations (e), (f), (g), (i) and (l).

⚠️ Uncertainty flag (Booth): I retrieved no text for US 2,593,252 (Booth, "Galvanic battery") this session; two targeted searches failed. From its title and the examiner's use of it I infer it supplies the generic two‑dissimilar‑metal immersed galvanic couple, but I will not load that reference with any of the geometry limitations. Treat Booth as cumulative support for (h), not as a load‑bearing reference.

3. Why a POSITA would combine — the motivation

The motivation is stated in the references themselves, which is what makes the prima facie case strong on the non‑geometry elements.

3.1 The problem is shared and articulated. Lentz's whole premise is that an unskilled operator should be able to read battery condition without a hydrometer: "anybody however unskilled will be enabled to know the battery condition." US 3,161,823 claims exactly that desideratum ("enabling the device to be utilized without any degree of skill"). Same problem, same field, same solution family.

3.2 Pfanhauser supplies the quantitative motivation for fixing electrode area. Pfanhauser teaches that the reading is only meaningful if the auxiliary electrode area is known and held constant — "if the auxiliary electrodes 1 and 2 … have an area of 1 square decimeter, then the current strength indicated by the ammeter will simultaneously indicate the current density … in terms of amperes per square decimeter. If the initial surface … is made smaller, as for example, only one‑half square decimeter, the ammeter … is correspondingly graduated." A POSITA seeking a depth‑insensitive reading of electrolyte concentration would immediately recognize that the wetted area of the galvanic couple must be fixed and identical for both electrodes — precisely the function the flush coplanar immersion face performs. This is the strongest single motivation in the record. (US 1,735,878 PDF)

3.3 Ellis supplies the "equal and simultaneous" motivation. Ellis expressly requires the two dissimilar contact members to be "of substantially the same contacting area" and "cooperably arranged for coincidental application to the surface of a mass" so that the recorded current is a valid measure of electrolytic activity. Ellis also discloses ball‑and‑socket joints "to permit … the contact members … to be positioned flat‑wise against various portions of the surface" — i.e., a deliberate teaching to orient the electrode faces flat to the medium so that contact is uniform. (US 2,215,213)

3.4 Wayne supplies the sealed hand‑held galvanic probe template. Wayne is a hollow, hand‑held galvanic‑couple probe with two conductors running through the body, dissimilar metals, an insulating separator at the electrode junction, and a calibrated scale — i.e., claim elements (a), (c), (d), (h), (k) in a single modern reference published just two years before Urikhoven's filing (1958 filing, issued Jan. 30, 1962 vs. Uithoven filed Apr. 23, 1963). (US 3,019,384)

3.5 All five references are in the same narrow field (electrolyte/galvanic sensing instruments), so the KSR "analogous art / same field of endeavor" threshold is trivially satisfied and the "predictable results" rationale applies with force.

4. The specific challenged combinations

Combination A — Lentz + Pfanhauser (primary), optionally + Ellis

Structure: Lentz's self‑contained portable galvanic probe and calibrated indicator → modify by fixing the exposed electrode area.
Motivation: Pfanhauser's express teaching that meter graduations are valid only against a known, fixed electrode area; Lentz's stated goal of an unskilled‑operator device.
Result: Elements (a)–(d), (h), (j), (k); a probe whose reading is calibrated to a fixed electrode area.
Shortfall: Does not yield limitations (e)–(g), (i), (l) — the flush nested‑arc recess geometry. Lentz's plates 24/25 are axial plates in a tube.
Assessment: Anticipates the concept certainly; does not by itself render claim 1 obvious. This combination is the reason the patent was allowed.

Combination B — Lentz + Wayne + Ellis + Pfanhauser (the "all references" combination)

Structure: Wayne's sealed hollow hand‑held probe body with two conductors and an insulated dissimilar‑metal junction → substitute Lentz's fluid‑tight closed‑end tube and meter calibrated in an electrolyte property → adopt Ellis's "coincidental application," equal contacting area, and "flat‑wise" orientation → apply Pfanhauser's fixed‑area calibration principle → flat‑mount the two dissimilar electrodes on the immersion face so both are flush.
Motivation: Each reference supplies a piece the others lack; the combination is a straightforward assembly of known elements in a known field with predictable results — the KSR Rationale (A) fact pattern.
Result: Elements (a)–(l) except the nested, discontinuous‑arc recess geometry (f) and the corresponding electrode shape (i).
Assessment: Strong prima facie case of obviousness on everything except the arcuate/discontinuous‑arc recessed geometry. If a tribunal were to construe limitation (f) loosely — e.g., "arcs" reading on any rounded or annular electrode and "discontinuous arcs" reading on any interrupted surrounding electrode — the claim falls. If (f) is read as its FIG. 3/FIG. 4 structure requires (nested, recessed, interrupted‑ring electrode seats molded into the plug and filled flush by electrodeposited metal), the combination does not quite reach it.

Combination C — Wayne + Pfanhauser (+ Ellis), with Wayne's coaxial junction relocated to a planar end face

Structure: Wayne already has exactly the claim's electrical architecture — hollow body, two conductors, dissimilar metals, insulating separator, calibrated scale. The only structural move is to relocate the tube‑54/tip‑56 junction from a radial/axial boundary to a forward‑facing planar boundary, so both electrodes present coplanar faces at the immersion end.
Motivation: Wayne's own indicator is inherently depth‑dependent (it reports moisture at the electrode junction level in the soil), and Pfanhauser teaches that an absolute reading requires a fixed wetted area. That is a direct, articulated reason to make the exposed area invariant with insertion depth.
Assessment: The most legally dangerous combination. It is a single mechanical reorientation of a two‑year‑prior reference that already contains every electrical element of the claim. Under KSR's "simple substitution / use of a known technique to improve a similar device in the same way," this is a textbook obvious modification. The patent's asserted novelty — that both faces are coplanar so "no more of one contact surface is immersed … than that of any other" — is a predictable geometric consequence, not an unpredictable result.

Combination D — Lentz + Ellis alone

Structure: Lentz's portable sealed galvanic probe + Ellis's segmental, equal‑area, coincidentally‑applied dissimilar contact members.
Assessment: Supplies (a)–(d), (h)–(k), and the arcuate/segmental electrode form via Ellis (Figs. 4–5). Closer than Combination A on the geometry, but still does not disclose the recessed placement or the nested "discontinuous arcs which partially encompass" arrangement. Weaker than B or C.

5. KSR rationales that would be pressed

No teaching away is present in any reference. None of the five disparages coplanar or equal‑area electrodes; to the contrary, Ellis affirmatively requires equal contact area and coincidental application. That absence of teaching‑away is significant: where the prior art points in the same direction as the claim, the claim is ordinarily obvious.

6. Arguments available against the prima facie case

A defender of the claim would argue:

1. Criticality of the coplanar flush face. The specification frames the planar alignment as the operative novelty and attributes a specific, non‑predicable benefit to it: "no matter how deep or how shallow the same is inserted … the effective surfaces of the electrodes will always be subjected to the same area of contact." No cited reference achieves depth‑invariance — Lentz's plates sit "in the upper portion of the electrolyte," Pfanhauser's electrodes are swept by a non‑uniform bath current field, and Wayne's sensor is deliberately depth‑specific ("the moisture content at the junction of electrodes 54 and 56"). One could argue the references teach in a different direction as to depth.
   Rebuttal: that is a problem recognized and solved by predictable geometry; Pfanhauser's fixed‑area calibration principle points straight at it.

2. The specific recessed nested‑arc geometry. Limitations (f) and (i) — two sets of recesses, arcs and discontinuous arcs, one set partially encompassing the other — are not disclosed or fairly suggested by any of the five references. Ellis's "segmental" forms are the nearest thing and are not nested/partially‑encompassing. This is the limitation on which the claim most plausibly survives a § 103 challenge.
   Rebuttal (to be expected): the specification itself supplies the design rationale — "greater exposed surface areas," "large adjacently arranged areas of contact," enhanced "collect, transmit and measure" capability — which is precisely the kind of recognized, results‑oriented design incentive that KSR treats as a motivation to combine; maximizing adjacent electrode boundary in a fixed footprint is routine design.

3. No secondary considerations of record. There is no evidence of commercial success, long‑felt need, failure of others, copying, or unexpected results. The forward citations (J & M Instruments' pH patents, Harvey, Akers, Westinghouse) show the concept was adopted in the art, but that is evidence of usefulness in the field, not of non‑obviousness of the claimed geometry, and there is no nexus evidence. Absent objective indicia, the case rests entirely on the geometry gap.

7. Claim‑drafting vulnerabilities a challenger would exploit

1. Internal tension between (g) and (l). Claim 1 says the recesses are "recessed inward from the open end of said body and from said planar horizontally disposed immersion end," yet requires each electrode's flat surface to be "in planar horizontal alignment with said planar … immersion end." Those coexist only if each electrode exactly fills its recess flush to the rim. A broad construction (any flush electrode seats) makes prior art flush‑mounted electrodes more readily anticipatory/obvious; a narrow construction (recesses with fill‑flush electrodes) is where the claim survives. This is the central construction battleground the earlier sections flagged as a drafting wrinkle.
2. "a plurality of arcs" / "a plurality of discontinuous arcs." Plurality language invites a reading broader than the FIG. 3 concentric‑ring embodiment; the broader the reading, the easier the § 103 case.
3. "another of said electrodes" (should be "the other") — loose antecedent basis, previously flagged. It creates ambiguity about whether more than two electrodes are contemplated, which weakens the boundaries of (i).
4. No means‑plus‑function exposure in claim 1; the claim is structural, so § 112 ¶ 6 does not narrow it, and the geometry limitations carry the entire validity load.

8. Bottom line

Confidence and caveats:

• High confidence in the characterizations of Lentz, Pfanhauser, Ellis, and Wayne — I retrieved and quoted their operative disclosures.
• Low confidence on US 2,593,252 (Booth). I could not retrieve its text; I have deliberately not used it to supply any limitation. If Booth discloses a coplanar or flush dual‑electrode immersion face, the § 103 case would strengthen considerably and the table in § 2 would need revision.
• Not verified: I did not retrieve the actual USPTO file wrapper / examiner's reasons for allowance. Whether the examiner considered and rejected a flush‑face rejection on these very references is unknown to me from the sources available. If the examiner expressly considered the coplanar alignment and allowed over it, that is a data point favoring non‑obviousness (though not binding on a later challenger).
• Caveat on the standard: this is a pre‑AIA claim, so no AIA § 102(a)(1)/(a)(2) art is at issue and no IPR/CBM route is available; a § 103 challenge would historically have run through an infringement suit or a § 282 defense, or today through a district‑court declaratory action, which is academic given expiration.
• I have not auto‑corrected any identifier: "3,161,823" is treated literally throughout, and the "823"‑tail hits from other patents (CAFC No. 24‑1322 MemoryWeb v. Samsung, the Provisur and UMC matters) are expressly excluded as unrelated.