US 1518211

I'll run the requested searches for this specific patent number.

Search notes and caveats (read first)

The number 1518211 is a low-numbered US patent from the 1924-era series. My searches returned several unrelated documents sharing the digit string; per your instruction, I am not treating any of them as the patent:

• GB 1518211 — British patent (US 4,078,916 family), a polyester-recovery process — different document.
• GB 1518211.6 — a 2015 UK patent application number cited in US 11,183,842 / US 11,309,710 (British Gas) — not this patent.
• FR 1518211 — French glass-sheet drawing process (1967).
• EP 1518211 — image processing system (2001).
• ARE 1518211 — a Brazilian Supreme Court case; 1518211 also appears in an Indian exam-results PDF and a French trademark record.

None of these are US 1518211. I also could not retrieve a USPTO PatentCenter/Assignment record or a CAFC 2026 docket entry bearing this number via search — see the legal-status note below. My authoritative source is the Google Patents full text of US1518211A, corroborated by FreePatentsOnline.

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Bibliographic summary — US 1518211

Note on "assignee": the patent is a sole-inventor grant with no assignee named on its face; Google Patents lists the current and original assignee as "Individual." I have no authoritative record of any later assignment, and any chain-of-title would have to be confirmed through USPTO Assignment records, which I could not retrieve.

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Abstract

The original 1924 document contains no separately labeled "Abstract" — that practice postdates this grant. The "Definitions" passage on Google Patents is a machine-generated précis. Faithful gist of the specification's stated object:

To furnish electrical mechanism for measuring or testing the conductivity (resistance/acidity) of the electrolyte in the stomach, giving results readable directly in ohms, without removing the electrolyte from the stomach; broadly, the combination with a stomach tube or pump of electrical means arranged in the member introduced into the stomach, which member fills with the electrolyte so that its resistance can be accurately measured.

The stated advance over the art is that prior practice involved withdrawing stomach fluid and chemically testing it, detaching it from its natural surroundings; Maue instead measures resistance in situ in a fluid-holding nozzle at the gastric end of the tube.

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Structure of the device (for context on the claims)

• Perforated nozzle/bulb 1 (preferably hard rubber, oval/egg-shaped, two-part: slotted bulb screw-threaded to cup member 3) with lateral openings/windows 2 admitting stomach contents.
• Central passage 9 through cup member and spindle 6 connecting nozzle interior to flexible tube 8; tube 8 stretches over peripheral bead 7.
• Syringe 16 (plunger handle 17, tubular end 18) at the outer end of tube 8 to create suction — expressly only one example; any vacuum/suction device works.
• Two platinum plates 10, 10 (anode and cathode) inside the nozzle, supported on cup 3 by platinum wires 11 running through neck 12 and joined (soldered/fused) to copper conductors 15 in insulating tubes 14; wires run between inner tube 8 and an outer telescoping tube 13.
• Meter 18 (shown only in conventional outline): ohmmeter, Wheatstone bridge, or equivalent, with battery circuits, readable in ohms.

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The claims (all six; plain language)

Importantly, every claim in this patent is drafted as an independent "combination" claim — there are no formally dependent claims (the dependent-claim format was not standard in 1924). Claim 2 is essentially claim 1 plus the syringe; claim 5 is essentially claim 4 plus the measuring/reading means.

• Claim 1 — Electrolyte-holder + suction tube + electrodes + current means. In a device of this class: (a) an electrolyte holder insertable into a bodily organ; (b) a tube attached to it so suction can be created in the holder to draw in the electrolyte; (c) metallic members located in the holder; (d) means for passing electric current through those members to measure the resistance of the electrolyte once drawn into the holder.
• Claim 2 — Claim 1 + syringe. Same combination as claim 1, but limited such that the suction is produced by a syringe.
• Claim 3 — Stomach tube + perforated nozzle + circuit. The combination, with a stomach tube, of a perforated nozzle on its end, insertable into the stomach and receiving the stomach contents; an electric circuit including separated members inside the nozzle and conductors leading to them, so current can be passed through the stomach contents to measure resistance.
• Claim 4 — Apertured nozzle + suction tube + plates + two coaxial tubes + conductors between them. The combination of an apertured nozzle; a flexible tube attached for suction so stomach contents enter the nozzle when inserted; separated electrical plates in the nozzle; a second flexible tube telescoped over the first and attached to the nozzle; and electrical conductors connecting the plates and extending between the two tubes.
• Claim 5 — Claim 4 + conducting/reading means. The same combination as claim 4, together with means for determining and reading the conductivity of the stomach contents as measured by passage of the current through them. (The printed text here is OCR-garbled; the substance is clear from context.)
• Claim 6 — Stomach tube + perforated bulb + circuit with separated poles in the bulb. The combination, with a stomach tube, of a perforated bulb carried thereby and insertable into the stomach contents, and an electric circuit arranged with separated poles in said bulb, so current may be passed through the stomach contents inside the bulb to measure their conductivity.

Common inventive core across all six claims: (i) an apertured/perforated fluid-holding chamber introduced into the stomach, (ii) suction means (tube, optionally a syringe) to fill it, and (iii) spaced electrode poles inside that chamber energizable to measure conductivity/resistance of the gastric electrolyte in situ — with claims 4–5 adding the concentric double-tube conductor-routing structure and claims 5–6 adding the measuring/reading capability.

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Legal status and CAFC 2026 check

• Google Patents records "Anticipated expiration 1941-12-09" and status "Expired – Lifetime." This is consistent with the pre-1995 rule of a term ending 17 years from issuance (Dec. 9, 1924 + 17 years = Dec. 9, 1941).
• I found no CAFC 2026 docket entry, appeal, or litigation involving US 1518211. My searches did not return the CAFC docket, and I could not directly query the court's docket system. Given that the patent expired ~85 years ago, any 2026 appellate activity concerning this patent itself is highly improbable; a modern CAFC appeal matching the digits "1518211" would almost certainly concern one of the unrelated identifiers listed above (e.g., a 2015 UK priority application or a 1518211-series docket number), not this grant.

Confidence and uncertainty

• High confidence: title, inventor, filing date (1923-02-23), issue date (1924-12-09), application/serial number, claim text and structure, classification, and expiry — all drawn from the full patent text.
• Explicitly uncertain: (1) there is no assignee of record shown — I will not assert a company owner; (2) any chain of title would require USPTO Assignment records I could not retrieve; (3) the "Abstract" is my paraphrase, as the original has none; (4) claims 5 and 6 contain OCR-corrupted text, so my plain-language renderings of those two are reconstructions consistent with the surrounding specification, not verbatim quotations; (5) I could not verify CAFC/USPTO docket status directly, so the "no 2026 CAFC activity" statement reflects absence of search evidence, not a confirmed negative.

I'll search litigation-focused sources for this specific patent number.

Let me try a few more targeted litigation-database searches to be thorough.

Result: No litigation found involving U.S. Patent 151,8211

I searched litigation-focused sources (Google Patents' litigation/status data, CourtListener/recap, Unified Patents materials, Federal Circuit and district court documents referencing the number) for the literal identifier 1518211 / US1518211 / US 1,518,211. No lawsuit, PTAB proceeding, ITC investigation, or other contested proceeding involving U.S. Patent 151,8211 was found. I will not manufacture entries.

Why this negative result is credible (not just a search gap)

The patent record itself is decisive:

Because the patent expired on 1941-12-09 (a 17-year term from the 1924 grant), it has been in the public domain for roughly 85 years. The Google Patents "Cited By" list shows only forward citations (e.g., US 2,540,425; US 2,888,640; US 3,296,020) — it does not show any "Litigation" or "Cases" entries, which is where Google Patents would ordinarily list district court/ITC/PTAB matters. No CourtListener/recap docket or Unified Patents case-list entry ties to this number.

Similar numbers that appeared in search results — explicitly NOT this patent

To comply with the instruction to interpret identifiers literally and avoid returning near-matches, these were excluded:

• Appeal No. 2008-1511 — Therasense, Inc. (Abbott Diabetes Care) v. Becton, Dickinson & Co., Nova Biomedical Corp., and Bayer HealthCare LLC (Fed. Cir.; N.D. Cal. Nos. 04-cv-2123, 04-cv-3327, 04-cv-3732, 05-cv-3117). This is a Federal Circuit docket/appeal number, not U.S. Patent 151,8211. The patents at issue there were the '551, '745, '382, '164, and '890 patents — all modern patents.
• EP 1518211 A2 — "Image processing system" (European patent, WO 02/052508 family). Unrelated jurisdiction and technology.
• GB 1518211.6 — a UK priority application (British Gas Trading Ltd., filed 2015-10-14), cited in US 11,118,842 and US 11,309,710. Unrelated.
• FR 1518211 — a French trademark registration ("LA LETTRE DE BIEN-ETRE ET DE SANTE…"), INPI. Unrelated.
• CAS 1518211-59-0 — a chemical registry number (2,2-dimethyl-3-(pyridin-3-yl)cyclobutan-1-one). Unrelated.
• US 6,881,211 / '211 patent — Arrow International v. Medical Components (multilumen catheter). A different, later patent.

Summary table

Caveats and confidence level

• High confidence that no litigation is currently or recently pending, given the 1941 expiry and absence of any litigation entry in Google Patents and in my searches.
• Lower, though still reasonable, confidence that no suit was ever filed during the patent's 1924–1941 enforceability window. Pre-1941 federal court records are not comprehensively digitized in the databases searched (PACER coverage begins in the late 1980s–1990s; CourtListener/recap, Unified Patents, and Google Patents all skew modern). A definitive historical negative would require manual review of the pre-1941 Federal Reporter / Federal Supplement digests and federal court dockets for the S.D.N.Y. and other districts, plus USPTO assignment records (which show no corporate assignee — a further indication that commercial enforcement was unlikely).
• If you need a formal clearance-style negative, I would recommend a paid search of pre-1941 federal case digests and the USPTO Patent Assignment Search for reel/frame records on US 1,518,211.

Bottom line: Based on the sources available, there is no known litigation involving U.S. Patent 151,8211.

I'll verify the structured "no proceedings" default against live sources before drafting.

Two searches came back clean — but I got false-positive hits on a different patent (US 8,439,821, the "'821 patent") that I want to rule out explicitly, plus other jurisdictions' 1518211-series documents.

Proceedings overview

Total AIA trial proceedings on US 1518211: 0. The USPTO Open Data Portal structured record supplied in the prompt lists no AIA trial proceedings, and no IPR, PGR, or CBM proceeding appears in the record for this patent — so the breakdown is 0 active / 0 claims invalidated / 0 claims sustained / 0 settled / 0 institution denials. For a defendant, the bottom line is unusual and much stronger than "the patent has survived IPRs and is hardened": US 1518211 cannot be asserted against anyone at all. It was granted on 1924-12-09, expired on 1941-12-09 under the then-applicable 17-years-from-grant term, and the ODP record carries the legal status "Expired - Lifetime." Zero PTAB proceedings exist not because the claims were validated, but because there has been nothing left to challenge since before the AIA was enacted in 2011 or the PTAB existed. If a demand letter cites "1518211," you are most likely looking at a wrong patent number (see False positives below).

No proceedings to report

There is no IPR/PGR/CBM docket number to list, no petitioner, no panel, no FWD, no appeal. I am not going to manufacture one. The structural reasons are decisive:

• Term ended 1941-12-09. The ODP record shows the "Anticipated expiration" event on 1941-12-09, consistent with a 17-year-from-issue term measured from the 1924-12-09 grant. The last possible date for recoverable infringement damages (6-year lookback) therefore fell in the mid-1940s.
• AIA trials postdate the patent's death by ~70 years. IPR became available 2012-09-16 under the Leahy-Smith America Invents Act; PGR is limited to first-inventor-to-file patents; CBM was limited to financial-services claims and sunset on 2020-09-16. None can reach a 1923-filing-date medical device patent.
• No § 315(b) trigger. The one-year IPR bar requires service of a complaint alleging infringement. There is no such complaint on record for this patent, and none could now be filed with any damages exposure.
• No appellee/appellant activity. No Federal Circuit or CourtListener docket exists for this patent, and I found none on search.

False positives I ruled out (important if you are working from a demand letter)

Multiple unrelated documents share the digits "1518211." None is US 1518211.

If a letter or claim chart asserts "1518211" in a medical-device or diagnostic context, treat it as a probable citation error and confirm the intended patent before responding.

Strategic summary

Claim status: 1-6 are all expired, none canceled, none sustained — the distinction is academic. Claims 1-6 (as printed in the 1924 grant: claim 1, the electrolyte-holder/suction combination; claim 2, adding the syringe; claim 3, the perforated stomach-tube nozzle with separated members and conductors; claim 4, the telescoping dual-tube conductor routing; claim 5, the conductivity-reading means; claim 6, the perforated bulb with separated poles) were never adjudicated by the PTAB, never reexamined, and never litigated to my knowledge. Every one of them lapsed with the 1941-12-09 expiration. There is no narrowing amendment and no surviving-claim list to report, because expiration — unlike IPR — extinguishes all claims simultaneously and completely.

Estoppel landscape is not the operative doctrine here; § 286 is. Section 315(e)(2) estoppel has no work to do with zero IPR petitioners. The controlling constraint for anyone contemplating assertion is the damages bar: recovery is limited to infringement occurring within six years before suit, and no infringing act could have occurred after 1941. There is no live theory. Practically, the only remaining legal value of US 1518211 is as prior art — the ODP record shows 20-21 later US patents citing it, which is expected given a 1923 priority date. A 1923-filed, 1924-issued US patent is § 102(a)/§ 102(b) prior art against a very large swath of later work in intraluminal electrolyte sensing, suction-sampling probes, and in-vivo conductivity measurement. That is a sword against other people's patents, not a threat to you.

Pattern signals: none, structurally. No repeat petitioner (no petitioner at all), no patent-owner appellate aggression, no defensive aggregator involvement (Unified Patents did not exist until 2012, and would have no reason to file against a 1941-expired patent). The absence here is not the ordinary "well-asserted patents eventually attract IPRs" signal — it is the harder signal that this patent is not assertable, full stop.

Recommended next steps

• Do not budget for an IPR. There is nothing to invalidate. Filing one would be a waste of fees and would risk a § 325(d)/standing discussion with no possible benefit; the patent's rights expired on 1941-12-09 per the ODP record (Google Patents; FreePatentsOnline).
• Verify the patent number in the demand letter. Ask the sender to identify the patent by grant date and title. If they answer 1924-12-09 / "Electrical device for measuring the conductivity of the stomach contents," the demand is meritless on its face and can be rebutted with a two-line letter citing expiration. If they answer anything else, you are likely facing US 8,439,821 (Karl Storz) or another similarly numbered patent, and the analysis must be redone from scratch.
• Confirm the negative yourself before relying on it. I searched the open web (four queries) and found no IPR/PGR/CBM for this patent, and no litigation or appeal. The authoritative negative is the structured ODP block plus a direct check of PTAB E2E / PTAB Center and the USPTO PTAB Decisions search, plus CourtListener for any CAFC appeal. I did not independently query E2E's full-text docket in this session; the ODP block is the canonical source here, and no web source contradicted it.
• Redeploy the patent defensively. If you are defending against a modern patent covering in-vivo conductivity/suction sampling, pull US 1518211 as a § 102(b) reference. Its 1923-02-23 filing date predates essentially the entire field, and its citation trail through later patents is a ready-made roadmap.
• One caveat I cannot verify from the record provided: I found no ODP entry indicating an ex parte reexamination or a certificate of correction, and none for an early-20th-century maintenance-fee lapse (maintenance fees did not apply to patents granted before 1980-12-12). I am stating the term-expiration basis because the ODP record's "Anticipated expiration 1941-12-09" entry supports it directly; treat any contrary claim about later-term survivorship as unverified until you see the underlying file.

I'll search the assignment-focused sources for this patent before writing up the ownership chain.

Let me do two more targeted checks — one for any recorded post-issuance transfer, one for the inventor's commercial context.

Assignment & Ownership Reconstruction — US 1,518,211 A

Patent: US 1,518,211 A — "Electrical device for measuring the conductivity of the stomach contents"
App. No.: US 620,717 · Filed/Executed basis: 1923‑02‑23 · Granted/Published: 1924‑12‑09 · Anticipated expiration: 1941‑12‑09
Primary sources checked: USPTO Patent Assignment Center / assignment.uspto.gov (patent‑number search), Google Patents legal events, FreePatentsOnline bibliographic record, printed patent front page.

Headline finding: the USPTO assignment record for this patent is empty. No reel/frame entries exist in the searchable Assignment Center record for US 1,518,211 — there is nothing to reconstruct. Details and the important coverage caveat below.

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Inventors

Notes / unusual-pattern check:

• Single inventor, sole owner, no corporate employer named. This is a classic physician‑inventor filing rather than a corporate-assigned filing, and it is the single most important fact for the ownership analysis: there was never an operating company in this chain to fire-sale the asset from.
• The "all inventors departed the original assignee within 12 months" fire-sale precursor does not apply — there is no original corporate assignee and no co-inventor group.
• No attorney of record is legible on the printed patent as OCR'd (the front page shows no "Attorney" line; the spec closes with "In testimony whereof I hereunto affix my signature"). If that reading is correct, Maue prosecuted pro se, which is consistent with individual ownership and with the absence of any recorded conveyance. Caveat: this is an OCR-based observation of a 1924 printed page; I could not independently verify the attorney line from a clean image.
• Maue is deceased (obituary indexed in 1973, Columbia P&S). Any unrecorded succession, if it exists, would run through his estate, not a company — and an estate transfer 50+ years after expiration has no legal effect on an expired patent.

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Original assignee

Assignee of record: none. US 1,518,211 issued to Henry Peter Maue as an individual ("Individual" per Google Patents; the FreePatentsOnline bibliographic "Assignee:" field is blank).

• Product embodying the claims: No evidence of any. No manufacturer, distributor, or brand is named in the patent; the spec describes the ohmmeter/Wheatstone bridge readout at reference 18 only "in conventional outline," i.e., as an off-the-shelf instrument the physician would supply. There is no commercial-product trail.
• Primary line of business: Not applicable — the named owner was a practicing physician, not a business entity.
• Current status: Individual, long deceased (obituary indexed P&S 18, Winter 1973). The patent itself has been expired since 1941‑12‑09 and has been in the public domain for roughly 85 years.
• No corporate predecessor, successor, merger party, or bankruptcy estate is identifiable from the record. There is no SEC registrant in this chain.

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Assignment timeline

The USPTO Patent Assignment Center contains no records for US 1,518,211 (or for application 620,717). There are no reel/frame numbers, no conveyance types, no assignors, no assignees, and therefore no correspondent-of-record entries to report. Per the task instruction, I stop the timeline after this section.

Google Patents' legal-events panel likewise shows only: Application filed 1923‑02‑23 (Individual) → Priority to US620717A → Application granted 1924‑12‑09 → Publication of US1518211A 1924‑12‑09 → Anticipated expiration 1941‑12‑09. No "Assignment," "Change of Name," "Security Agreement," or "Litigation" entries appear.

Critical coverage caveat — read this before treating "no records" as "never assigned"

The statute-driven structure of the USPTO Assignment Center matters here:

• The searchable Assignment database contains recorded patent assignment information back only to August 1980 (USPTO Assignment Database documentation, https://www.uspto.gov/sites/default/files/documents/Assignment%20Database%20Webinar_20150120.pdf). This is explicitly stated in the USPTO's own description of the system.
• US 1,518,211's entire enforceable life ran 1924‑12‑09 → 1941‑12‑09 — roughly 39 years before the start of the digitized window.
• Therefore the online "no records" result is expected and non-probative for the 1924–1941 period. Any assignment Maue executed in that window (or any later-recorded paper trail) would live in the pre‑1980 paper/microfilm Assignment Records at the USPTO, retrievable only via a manual Patent Assignment Abstract of Title request or a physical visit to the Public Search Facility — not via assignment.uspto.gov.
• What is probative, and cuts the other way: the issued patent names no assignee, no corporate entity appears in any bibliographic source, and the inventor was an individual physician with no known commercial backer. That is affirmative evidence of individual ownership, not merely a search gap.

Recommended verification step if a formal negative is needed: request a Patent Assignment Abstract of Title for US 1,518,211 / App. 620,717 from the USPTO to confirm the pre‑1980 paper records show no conveyances.

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Timeline diagram

timeline
    title Ownership of US 1518211
    1920 : Maue graduates Columbia P and S
    1923 : Application filed by Henry Peter Maue
    1924 : Patent granted to Maue as individual
    1941 : Patent expired by its own term
    1980 : USPTO online assignment records begin
    2026 : No assignments found in online record

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NPE / troll-pattern signals

Note on the inverse signal: the closest thing to a "signal" here is unusually clean and points away from NPE activity — a sole-inventor, pro-se-looking 1923 filing by a physician, granted to the inventor personally, never assigned, and expired in 1941. That profile is the historical opposite of a patent-troll asset.

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Verdict

Insufficient data — meaning here that there are no recorded assignments to analyze, only the original individual ownership.

Justification: The Assignment Center returns no reel/frame entries for US 1,518,211; Google Patents shows the original and current assignee as "Individual" with legal events limited to filing, grant, and 1941‑12‑09 anticipated expiration; and the printed patent names Henry Peter Maue alone with no assignee and no visible attorney of record. Because no corporate assignee ever appears and the enforceable term ended in 1941 (39 years before the USPTO's online assignment records begin in August 1980), this is a non‑asserting, expired, individual‑inventor patent rather than an NPE vehicle — but the online record is not competent to prove a negative for the 1924–1941 window, so the formal verdict is "insufficient data" pending an Abstract of Title request.

Verification links:

• USPTO Assignment Center: https://assignmentcenter.uspto.gov/ (search patent number 1518211)
• USPTO legacy Assignment Search: https://assignment.uspto.gov/patent/index.html
• Google Patents legal events: https://patents.google.com/patent/US1518211A/en

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Contradictions / caveats flagged

1. Corporate-assignee fields are blank, not "unknown." FreePatentsOnline's "Assignee:" line is empty; Google Patents renders it as "Individual." Both are consistent with no corporate assignment, but both are modern aggregator renderings of a 1924 grant — they are not primary assignment records.
2. The online negative is not a historical negative. As stated above, the Assignment database's coverage begins August 1980 while this patent expired in December 1941. Do not represent "no assignments found" as "never assigned" in any downstream work product.
3. No contradiction with the earlier Litigation section. That section found no litigation and hinged on the same 1941‑12‑09 expiry and the absence of any corporate assignee; the assignment findings are fully consistent with it and reinforce it.

I'll run targeted searches for the literal identifier 1518211 in USPTO and patent-citation sources, then examine the patent's own citation record.

Key finding so far: the Google Patents record for US1518211A shows a "Cited By" list but no "Patent Citations" (backward) section — consistent with the 1924 facsimile, which lists no references. Let me verify that and probe the pre-1923 art landscape.

Prior-Art Analysis — US Patent 1,518,211

Status note on dates: The task header says "April 26, 2026," while the session context says 2026-09-26. Minor, but flagging it since it affects nothing materially here. Source: USPTO-hosted facsimile and full text, mirrored at Google Patents (https://patents.google.com/patent/US1518211A/en) and FreePatentsOnline (https://www.freepatentsonline.com/1518211.html). I could not run a live PatentCenter query; the facsimile PDF at patentimages.storage.googleapis.com/3f/cf/39/b328f239db9314/US1518211.pdf is the authoritative document of record.

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1. The headline finding: US 1,518,211 cites no prior art

The record for US 1,518,211 contains zero backward ("Patent Citations") references. The Google Patents entry for US1518211A has a "Cited By" section but no "Patent Citations" section at all, and the 1924 facsimile front page carries no "References Cited" block. This is what the record literally shows; per the operating rules I am not filling the gap with near-numbered documents.

This is historically expected, not anomalous: pre-1930s US grants were not required to list references of record, and examiners' "references cited" were not routinely printed on the face of the patent. The absence of cited art is therefore not evidence of novelty and provides no §102 analysis to perform on the patent's own citation record.

Consequence for your request: I cannot supply "full citation / dates / description / anticipating claim" for cited references, because there are none. Inventing them would violate your standing instruction. What the record does contain is:

• a forward-citation list ("Cited By") — later patents citing 1,518,211 as their prior art; and
• one express examiner-style citation of 1,518,211 inside a later patent's "References Cited in the file of this patent."

I report both below, then give a clearly-labeled reconstructed pre-1923 landscape.

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2. Forward citations of US 1,518,211 (it is prior art TO these — not the reverse)

All 21 entries post-date the 1923-02-23 filing/priority by 25–95 years, so none can anticipate any claim of 1,518,211 under §102. Their correct role is as §102(b)/§103 art against the later patents themselves. Count varied between fetches (19/20/21) — a live-page inconsistency worth noting.

The single most probative citation of 1,518,211 in the record: US 2,886,771 A (Rubissow, "Fluid-testing device," filed 1955-06-14, granted 1959-05-12) lists in its printed "References Cited in the file of this patent":

UNITED STATES PATENTS — 1,518,211 Maue Dec. 9, 1924; 2,260,840 Rowe Oct. 28, 1941; 2,540,425 Byrum Feb. 6, 1951; 2,674,719 Williams Apr. 6, 1954. FOREIGN PATENTS — 1,070,566 France Feb. 24, 1954; 725,586 Great Britain Mar. 9, 1955.

This confirms the patent was used as prior art by a later examiner in a fluid-conductivity cell context — the opposite direction from your request.

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3. Reconstructed pre-1923 landscape (NOT cited references — my own analysis)

Because the patent's citation record is empty, the only honest "most relevant prior art" answer requires going outside the record. The following are explicitly labeled by evidentiary status. None is a citation of record against 1,518,211.

Net §102 conclusion: On the record available, no single reference — cited or reconstructed — anticipates any of claims 1–6. Every element-complete in-body conductivity device I located (Funck 1929, Shugar 1936) post-dates 1,518,211. The pre-1923 art supplies the individual elements (stomach tube + suction; spaced electrodes in an electrolyte; bridge/ohmmeter measurement) but I found no single pre-1923 reference combining "apertured in-body fluid-holding chamber + suction fill + spaced poles energized to measure gastric-electrolyte resistance in situ" — which is the common core of all six claims.

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4. Where to search for a definitive answer (recommendation)

The absence of cited art is a record property, not a search result. For an authoritative anticipation search on US 1,518,211, run pre-1923 art in the retro-assigned classes (these classifications are modern, not 1924 originals): G01N27/07 (primary), 324/439, 604/114, 604/275 — plus US classes 128 (surgery) and 204 (electrolysis) as they existed pre-1923, and pre-1923 Medical Record, JAMA, Arch. Intern. Med., and the Rehfuss/Ewald/Boas gastric-analysis literature.

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5. Caveats and confidence

• High confidence: the patent has no backward/parent citations of record; the forward-citation table and dates (from the patent record); the Rubissow/US 2,886,771 express citation of 1,518,211; and that all forward citations post-date the priority date and therefore cannot anticipate.
• Explicitly uncertain: (1) I could not query USPTO PatentCenter/Assignment directly, so "no citations" reflects the Google Patents mirror plus the facsimile front page; (2) the pre-1923 landscape items are my reconstruction, not citations of record — the Rehfuss/Kohlrausch/1884-electrization items are non-patent literature I have not paginated here; (3) US 1,474,151's filing date is unverified and is the one item that could flip into §102 art if it predates 1923-02-23; (4) the "Cited By" count fluctuated (19/20/21) across fetches, so treat the list as approximate; (5) pre-1923 US grants and pre-1941 case/assignment records are not comprehensively digitized, so a formal negative requires manual review.
• Excluded as similar-but-different numbers (per instruction): GB 1518211 / GB 1518211.6, EP 1518211 A2 (image processing), FR 1518211, CAS 1518211-59-0, and US 2003/151821 A1 (Favalora, cited in WO 2008/015283) — none is US 1,518,211.

Bottom line: US 1,518,211 has an empty prior-art citation record; its only citation data are 21 forward references (all post-1923, all §102-ineligible as art against it), the most significant being US 2,886,771's express citation of Maue's patent in its "References Cited" list. No reference in the record, and no pre-1923 reference I could identify, anticipates any of claims 1–6.

I'll ground this analysis in the actual reference lists on the US1518211A page and then verify the dates/eligibility of candidate references before combining them.

Key hits so far: US 1,474,151 (electrode for ion concentration), US 1,346,057 (ohmic resistance of liquids, 1920), and the Einhorn/Gross duodenal tube art. Let me pin down dates and find more pre-1923 electrode/gastric-suction art.

Obviousness Analysis — U.S. Patent 1,518,211 (Maue)

35 U.S.C. § 103, with the Graham/KSR framework

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1. Scope note on the "Prior Art section" — read first

The full text of US1518211A supplied for this analysis does not contain a prior-art section proper. What the page actually contains are two reference lists, and I am interpreting them literally rather than inventing an examiner's citation list:

Consequence: a defensible § 103 opinion for this patent must be built from pre-1923-02-23 art located independently, using the page's lists only as leads. The core references I rely on below (Reardon, Rice, Einhorn/Gross, Rehfuss, Kussmaul) are all pre-1923 and were located outside the page's own lists. I state this openly rather than presenting them as page-sourced citations.

Threshold legal note: the application was filed 1923-02-23, so the governing statute is the pre-1952 law; the dispositive question at grant was the "invention" requirement of Hotchkiss v. Greenwood. The § 103 analysis you asked for is structurally identical (Graham v. John Deere: scope/content of art → differences → PHOSITA level → objective indicia), and I apply it below. § 102 (anticipation) is a separate question and is not decided here.

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2. The person having ordinary skill in the art (PHOSITA)

A physician-instrument-maker of ordinary skill circa 1922: familiar with (a) the Kussmaul/Wyman/Leube–Ewald stomach tube and gastric lavage practice; (b) the Einhorn/Gross perforated-tip duodenal tube and syringe aspiration (1909); (c) Rehfuss fractional gastric sampling (1914); and (d) the then-mature electrolytic conductometry art — platinum electrode cells, cell constants, and Wheatstone-bridge/ohmmeter readout — as set out in Kohlrausch's and Washburn's cell-design literature and in applied journals such as the Journal of Industrial and Engineering Chemistry. This is emphatically not a case requiring a new science: by 1920 both constituent technologies were mature and the physical relation (electrolyte concentration ↔ conductivity) was textbook.

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3. The prior art references relied upon

Deliberately excluded (not prior art): all of the page's "Cited By" items (1948+); US 1,498,960 (1924); US 2,204,295 (1940); Jeffress (1928); Langman (1949); and a Soviet author's certificate for a gastric-acidity electrode probe ("Способ и приспособление для определения кислотности желудка," author Шугар, 1936-07-31) that surfaced during searching. The last is notable only as evidence that the same in-situ gastric-conductivity concept was later and independently reduced to practice — it post-dates the patent by twelve years and cannot be used as § 103 art.

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4. Claim-by-claim obviousness

Claim 1 — electrolyte holder + suction tube + metallic members + current-passing means

Differences over the art: none of R1–R6 alone shows all four elements together. But the only unmet element in R3 is (c)+(d): R3's perforated capsule is a fluid-holding, suction-filled receptacle introduced into a bodily organ (elements (a),(b)) but contains no electrode pair. Conversely R1/R2 supply (c)+(d) for a liquid vessel but not a bodily-organ holder.

Combination: R3 (+R4) in view of R1 and/or R2.

Motivation, articulation:

• The patent's own specification concedes the pre-existing diagnostic practice: "Heretofore it has been customary… to remove a portion of the fluid contents through a stomach tube or other medical appliance and subject the same to chemical tests to ascertain the acidity." That admission establishes both the problem and the known starting structure.
• The object — measuring resistance of gastric electrolyte "without removing the electrolyte from the stomach" — is a pure elimination of a handling/transport step. Placing the sensing elements in the receptacle that already receives and holds the sample is the most direct, and arguably the only sensible, engineering response to that objective. There is no redesign of the fluid path required: R3's capsule is the sample chamber.
• R2 supplies a teach-away-free, express design incentive: it frames conductivity measurement as something that should be made operable by a non-physicist and to comparative accuracy, i.e., it pushes toward putting a simple, robust cell where the sample is.
• KSR factor: a finite, identified, predictable set of solutions (put a known two-electrode conductivity cell inside the known suction-filled receiving capsule) with a predictable result — the resistance of the drawn-in electrolyte. The result is precisely the physical quantity the electrode pair is designed to measure; there is no new principle of operation.

Conclusion: Claim 1 would have been obvious.

Claim 2 — Claim 1 + syringe for causing the suction

Differences: adds only the syringe.

R3 states, in terms, that "aspiration of fluid was to be done with a syringe" and that the Einhorn capsule is swallowed and the contents aspirated. The syringe limitation is therefore expressly met by the very reference supplying the holder. The specification itself treats the syringe as a mere example ("any other vacuum or suction device may be used").

Conclusion: Claim 2 would have been obvious — and, on R3 alone for the syringe element, near-anticipated in substance.

Claim 3 — stomach tube + perforated nozzle + circuit with separated members in the nozzle + conductors

Differences: a stomach tube (as opposed to duodenal) with a perforated nozzle forming part of an electric circuit with separated members inside the nozzle and conductors leading to them.

Combination: R3 (+R4) + R1/R2, optionally R5.

Motivation: once the electrodes are inside a tube-borne tip, the conductors must reach them through or along the tube. Routing a conductor to a distal tip of a flexible catheter is a routine mechanical expedient, and the tube itself is the obvious protected pathway. R2 teaches exactly this packaging — platinum electrodes with glass-insulated lead wires within a tube closed by rubber stoppers; R1 teaches electrode leads to an external resistance-measuring instrument. The choice of a stomach rather than duodenal tube is a mere change of the intended body lumen — R4 shows both were standard and interchangeable for gastric diagnostic sampling (Rehfuss used a gastric tube for exactly this diagnostic purpose).

Conclusion: Claim 3 would have been obvious.

Claim 4 — apertured nozzle + suction tube + plates + second flexible tube telescoped over the first + conductors between the two tubes

Differences: the concentric/coaxial double-tube conductor-routing architecture.

Combination: R3/R4 + R1/R2, in view of the known double- and multi-channel stomach-tube art.

Motivation:

• Multi-lumen and nested-tube construction was already old in this field: the Paine history records Auerbach and Ploss's "double recurrent stomach tubes" (1870) and Marcy's 1883 rule that in double tubes the efferent channel must be larger; Turck's gyromele (1894) was a flexible cable encased within a rubber tube; and multi-channel gastro-duodenal tubing (gastric + duodenal limbs joined at a Y-piece) was routine by the 1920s.
• Placing insulated conductors in the annular space between an inner suction tube and an outer protective tube achieves an entirely predictable set of results: (i) the wires do not obstruct the suction lumen (preserving flow capacity, the very concern Marcy articulated in 1883); (ii) the wires are shielded from gastric fluid, preventing short-circuiting/bypassing the cell; (iii) the outer tube protects the insulation during swallowing and withdrawal.
• KSR ("known technique to improve similar devices in the same way"): using a second telescoped tube to carry and shield conductors is the natural application of a known tube-in-tube construction to a new but closely analogous conductor-routing problem. The specification itself offers no unexpected result — it says only that the outer tube is "connected to the nozzle by being stretched over the peripheral bead… said tube protecting the wires."

Conclusion: Claim 4 would have been obvious.

Claim 5 — Claim 4 + means for determining and reading conductivity

Differences: adds the read-out instrument.

Combination: claim 4 combination + R2 (and R6).

Motivation: a conductivity/resistance measurement is meaningless without read-out, and the read-out art was fully developed: R2 used a Wheatstone bridge run off ordinary shop equipment; the specification names the same alternatives — "an ohmmeter, a Wheatstone bridge, or other equivalent instrument, having a scale to read in ohms." Supplying a standard bridge/ohmmeter to a completed electrode pair is the routine completion of the circuit, not an inventive contribution. Under § 112 ¶ 6 (or the 1924 equivalent construction), "means for passing an electric current… to measure the resistance" reads on the battery-and-bridge circuit the specification itself concedes is conventional.

Conclusion: Claim 5 would have been obvious.

Claim 6 — stomach tube + perforated bulb insertable into the stomach contents + circuit with separated poles in the bulb

Differences: restates claims 1/3 in bulb language, with the poles located in the perforated bulb.

Combination: R3 (perforated metal olive/capsule carried on the tube) + R1/R2 (electrode pair).

Motivation: R3's Einhorn tip is a perforated metal capsule that fills with the fluid to be examined — the claim's "perforated bulb… insertable into the contents of the stomach… that are inside the bulb." Mounting the two spaced poles inside that already-existing fluid-filled bulb adds no structure beyond the electrode pair and is the same solution reached under claim 1. R2 confirms that a tube-terminated electrode chamber with insulated leads was a known construct.

Conclusion: Claim 6 would have been obvious.

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5. Consolidated combination rationale (KSR "rational underpinnings")

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6. What a patent owner could argue — and why it likely fails

1. "Combination" / "new result" argument. That the combination of in-situ suction sampling with conductometry was new. Novelty is not the test. Under § 103 (and under Hotchkiss's "invention" standard in force in 1924), the combination of known elements each performing its known function with an expected result is not inventive. Every element here performs its known function.
2. "The prior suction devices were therapeutic, not analytical." Rebutted: R3/R4's Einhorn-Gross and Rehfuss tubes were expressly diagnostic, and R3 used a syringe to aspirate sample from a perforated capsule. The diagnostic purpose is squarely in the art.
3. "Conductivity ≠ acidity." Even if the response is non-selective, every claim measures conductivity/resistance, not acidity per se; and the specification's own claim to "test for acidity or other purposes" concedes the correlation is the operator's concern, not a structural limitation.
4. Teaching away. I found no reference disparaging placement of electrodes within a stomach-borne sampling receptacle, nor any express preference for remote/withdrawn measurement on grounds that would defeat the combination. The "no withdrawal" objective is motivation, not a teaching away.
5. Objective indicia. There is no evidence of record of commercial success, long-felt-but-unmet need, failure of others, licensing, or copying. The Google Patents record shows no assignee and no litigation; the "Cited By" trail of Leeds & Northrup conductivity-cell patents (US 2,888,640; US 3,025,459) shows the cell art advancing independently, not that anyone copied this device. Any secondary-considerations rebuttal is presently unsupported. (See the earlier section's note that pre-1941 records are not comprehensively digitised — a formal negative would require manual digests/USPTO assignment search.)

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7. Bottom line

On the record assembled, claims 1–6 of US 1,518,211 are each invalid as obvious under § 103 over the following combinations:

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8. Confidence and explicit uncertainty

High confidence: all reference dates used for the combination (US 1,346,057 filed 1918-11-08/pub. 1920-07-06; Rice 1920; Einhorn/Gross 1909; Rehfuss 1914; Kussmaul 1869); that every item in the patent page's "Cited By" list is post-1923 and therefore not § 103 art; that the Einhorn tube expressly used perforated capsule + syringe aspiration; and that the patent's own specification contains the prior-practice admission.

Explicitly uncertain / not asserted:

1. No examiner-cited prior-art list exists on the supplied page. My analysis uses pre-1923 references located independently. I did not reproduce them as if they were page citations.
2. US 1,474,151's filing date is unverified (publication 1923-11-13 post-dates the 1923-02-23 filing). Its availability under pre-AIA § 102(e) cannot be confirmed, so I did not rely on it. Its only confirmed appearances are on this patent's "Similar Documents" list and as a "Domestic Patent Reference" cited in US 2,733,201.
3. US 1,346,057's full specification text was not retrieved; I relied on its bibliographic record (title, dates, class G01N27/06) and title-level disclosure. Full-text verification of its electrode/read-out disclosure is recommended before relying on it as primary art.
4. No full text of the Einhorn 1909 or Gross 1909 primary papers was retrieved; I relied on the detailed secondary history in Paine's Annals of Internal Medicine article (which is itself pre-dating? no — 20th-century, and I have not verified its exact publication year). If Einhorn's own 1909/1910 publication is needed as the § 102(b) reference, its date should be confirmed directly.
5. Pre-1941 litigation, prosecution history, and USPTO assignment records were not retrievable, so the absence of objective indicia reflects absence of evidence in my sources, not a verified negative.
6. § 102 anticipation was not decided. Several claims (notably claim 2's syringe limitation, and claim 6's perforated-bulb + poles) sit close to the line, and a formal anticipation analysis with full reference texts could change the theory of invalidity from § 103 to § 102 as to individual claims.

Recommended verification steps before filing or relying on this opinion: pull the printed specifications of US 1,346,057 and US 1,474,151 (and US 1,474,151's filing date); obtain Einhorn's and Gross's original 1909 disclosures; and run a Kellogg/chemical-arts style search of the 1880–1923 conductometry and gastro-intubation literature.