hydrometer
Enable an AI agent to recognise a hydrometer, assess its fitness for a particular liquid-density measurement, interpret its indication and decide whether it may be used, cleaned, checked or withdrawn.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
Researched by: Codex + Grok
Purpose and description
Enable an AI agent to recognise a hydrometer, assess its fitness for a particular liquid-density measurement, interpret its indication and decide whether it may be used, cleaned, checked or withdrawn.
A hydrometer is a sealed, typically glass, weighted float that measures the relative density (specific gravity) of a liquid by the depth to which it sinks under gravity, reading that immersion against a calibrated stem scale.
It can be Select the hydrometer for a sample using its scale, range, compatibility and measurement requirements.; Inspect and prepare the instrument, then establish an appropriate free-floating measurement setup.; Record an indication together with sample temperature, reading convention and observed interference.; Apply only documented corrections or conversions supported for the instrument and liquid.; Check performance against suitable reference evidence and decide whether continued use is justified.; Clean, store, quarantine or withdraw the hydrometer according to its materials, condition and instructions..
Distinguishing features
A conventional hydrometer floats in a liquid and indicates density through its equilibrium immersion; a hygrometer indicates humidity.
A float hydrometer is read from immersion or an associated float indication; a refractometer uses an optical response and requires a different interpretation model.
Its density indication does not require liquid flow through a meter; a flow meter measures movement of liquid rather than its density.
A hydrometer may carry a density, relative-density or application-specific scale; a floating thermometer instead indicates temperature, although one instrument may combine both functions.
A device sold as a digital hydrometer requires an operating-principle check because its indication may come from float orientation or another sensing method rather than a graduated stem.
Scope
+ Identification of the instrument, its operating principle and its intended liquid or application
+ Float, ballast, stem and scale features that determine whether it can produce a usable indication
+ Density or derived scales, measurement range, resolution and reference conditions
+ Calibration evidence, corrections and suitability for a stated measurement task
+ Liquid compatibility, free-floating conditions, reading procedure and instrument condition
- The liquid batch's composition, production history and overall quality
- The sample cylinder's own design, condition and lifecycle, except its suitability for this hydrometer
- Independent models of thermometers, refractometers, hygrometers and flow meters
- The production process being monitored, such as fermentation or battery maintenance
- Laboratory-wide quality systems and waste-management procedures beyond requirements affecting this instrument
Characteristics
- Operating principle
- Graduated buoyant float; electronic buoyant float; other documented principle; unresolved Determines whether conventional immersion, meniscus and clearance requirements apply.
- Instrument identity
- Manufacturer, model and individual identifier where available Connects the physical instrument to the correct instructions and calibration evidence.
- Indicated quantity and scale
- Density with stated units; relative density with stated convention; named application-specific scale Prevents treating a derived scale as a direct measurement of composition in an unsuitable liquid.
- Usable indication range
- Lower and upper limits in the instrument's stated scale Establishes whether the expected sample value can be read within the instrument's supported range.
- Scale interval or display resolution
- Smallest marked interval or displayed increment in the stated scale Constrains reading precision without implying an equivalent measurement accuracy.
- Reference conditions
- Declared reference temperature in °C and any relative-density reference convention Allows the indication to be compared or corrected on the intended basis.
- Calibration support
- Applicable certificate, verification record, correction data and stated uncertainty Supports a task-specific decision about measurement reliability.
- Wetted materials and compatibility
- Documented wetted materials, permitted liquids, exclusions and temperature limits Determines whether immersion or cleaning could damage the instrument or contaminate the sample.
- Physical and reading condition
- Observed integrity, cleanliness, scale legibility, ballast stability and any unresolved defects Identifies conditions that can make a plausible-looking reading unreliable.
- Measurement setup
- Associated sample, vessel, temperature observation and reading procedure Makes it possible to distinguish instrument defects from unsuitable measurement conditions.
- Fitness for intended use
- Suitable; suitable under stated conditions; unsuitable; not yet established Expresses an actionable judgment against the required range, uncertainty and compatibility.
Also called
Where this came from
wikidata · CC0 1.0
Also registered as vr.tr.hydrometer
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 18 findings · 28 questions.
Instrument identity and principle Establishes what kind of hydrometer is present and how it produces an indication.
The registry name alone does not establish whether a graduated-float procedure or a different measurement procedure is appropriate.
Density sensing principle
Identifies the physical mechanism behind the indication.
Documented hydrometer mechanism
Record whether density is indicated by stem immersion, electronic float behaviour or another documented mechanism.
- What physical response does this instrument use to indicate liquid density? definition
- Does that mechanism place it within this hydrometer model, or does it require a neighbouring density-instrument model? boundary
Instrument and application identity
Connects the instrument to its documentation and intended application.
Identity and intended liquid
Record identifying markings and the liquid classes or applications for which its scale is documented.
- Which markings or records identify the manufacturer, model and individual instrument? provenance
- For which liquids or applications does the manufacturer support this instrument and its scale? boundary
Scale and interpretation Captures what the indication means and the limits within which it can be interpreted.
Hydrometers can carry different scales whose numbers are not interchangeable and may depend on liquid-specific assumptions.
Quantity, range and resolution
Establishes the readable quantity and its supported interval.
Scale meaning and limits
Record each scale's quantity, units or convention, endpoints and graduation or display increment.
- Does each scale indicate density, relative density or a derived property, and what units or conventions define it? definition
- What are the scale endpoints and smallest readable increments, and does the expected sample value lie within them? measurement
Reference and conversion basis
Makes temperature and liquid-specific interpretation assumptions explicit.
Supported reading interpretation
Record reference conditions and the evidence supporting any temperature correction or conversion to a derived property.
- What reference temperature and, where applicable, sample and reference-liquid temperature convention define this scale? definition
- Which documented correction or conversion applies to this sample, and what composition or temperature limits constrain its use? boundary
Sample and reading conditions Records whether the sample and setup allow a representative, interpretable indication.
Vessel contact, bubbles, temperature and reading convention can compromise an otherwise intact hydrometer.
Free-floating sample setup
Establishes suitable immersion, clearance and sample conditions.
Unobstructed float equilibrium
Record whether the hydrometer floats freely and whether bubbles, foam, suspended matter or sample variation interfere with the observation.
- Can the hydrometer reach a stable floating position without touching the vessel walls or bottom? measurement
- What sample preparation or repositioning is permitted if bubbles, foam, solids or an unrepresentative sample prevent a usable reading? action
Temperature and reading method
Captures the conditions and convention used at the moment of observation.
Interpretable observation
Record the raw indication, sample temperature, stability and applicable meniscus or electronic reading procedure.
- What raw indication and sample temperature were observed, and had the instrument and sample stabilised as required? measurement
- Which documented meniscus or electronic reading convention applies, including any accommodation for an opaque liquid? provenance
Calibration and use fitness Connects instrument performance evidence to the demands of a specific measurement.
Readable graduations and an intact float do not establish that the instrument meets a task's accuracy requirements.
Calibration evidence and corrections
Identifies applicable checks, calibration results and correction limits.
Applicable performance evidence
Record calibration or verification evidence tied to this instrument, including tested conditions, deviations and stated uncertainty.
- What calibration or verification record applies to this instrument, and which scale points and conditions were checked? provenance
- What deviations, corrections and uncertainty were established, and over what interval are they supported? measurement
Task-specific acceptance
Determines whether the instrument and procedure support the intended decision.
Fitness decision and recheck
Record the required measurement performance, the resulting use decision and events that require renewed checking.
- Do the supported range, uncertainty and use conditions meet the measurement requirement for this sample? boundary
- What failed check, damage event, unexplained reading or applicable review interval requires rechecking or withdrawal? action
Integrity, compatibility and care Captures physical defects and material constraints that govern immersion, cleaning and continued use.
Changes to a float's mass, surface or scale position can undermine its indication, while unsuitable liquids or cleaning methods can damage it.
Float and scale integrity
Assesses the parts whose condition supports buoyancy and readable indication.
Condition affecting indication
Record observable cracks, leakage, deposits, displaced components, illegible markings or other defects relevant to the instrument's construction.
- Is there evidence of cracking, liquid ingress, retained deposits, loose ballast or movement of an internal scale? measurement
- Which observed defects require quarantine, verification or replacement under the applicable instructions? action
Liquid contact and care
Establishes permitted sample contact, cleaning and storage for the actual construction.
Compatible immersion and cleaning
Record wetted materials, supported exposure limits and care procedures that preserve the float and prevent sample carryover.
- Are the sample and proposed cleaning agents compatible with the documented wetted materials and exposure limits? boundary
- What cleaning, drying and storage procedure preserves the instrument and limits contamination of its next sample? action
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Kinds and varieties
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Constant-mass hydrometer (ordinary glass hydrometer with a weighted bulb and graduated stem; the usual laboratory, brewing, and petroleum instrument)
- Constant-volume hydrometer (Nicholson hydrometer: a float of fixed volume loaded until it just submerges, density inferred from added mass)
- Twaddell hydrometer (Tw° scale used for industrial liquids denser than water, especially in the UK and Commonwealth)
- Baumé hydrometer (Bé°; separate scales for liquids heavier and lighter than water, historically used in chemistry, sugar, and acid trades)
- Brix / saccharometer hydrometer (degrees Brix or Balling, calibrated for sucrose solutions in brewing, winemaking, and sugar refining)
- API hydrometer (American Petroleum Institute gravity scale for crude oil and petroleum products)
- Lactometer / milk hydrometer (calibrated for milk specific gravity, used in dairy adulteration checks)
- Alcoholometer / proof hydrometer (Tralles, Gay-Lussac, or Sikes scales for ethanol-water mixtures)
- Which of these kinds and varieties hold for the sense of hydrometer this model covers, and on what evidence? provenance
Identifiers and schemes
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Wikidata - Q73780 - item 'hydrometer' (measuring instrument)
- ISO 80000-4 / quantity - relative density / specific gravity (dimensionless); mass density ρ in kg·m⁻³ - the measurand, not a product code for the instrument
- ASTM hydrometer designation - ASTM hydrometer numbers (e.g. 1H-10H API, 82H-90H specific gravity) per ASTM E100 - type number encodes scale, range and length
- UNSPSC - 41112306 (hydrometers) under laboratory and scientific equipment - procurement commodity code; confirm against current UNSPSC release
- Which of these identifiers and schemes hold for the sense of hydrometer this model covers, and on what evidence? provenance
Standards and regulation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- ASTM E100 - Standard Specification for ASTM Hydrometers (ASTM International)
- ASTM D287 - Standard Test Method for API Gravity of Crude Petroleum and Petroleum Products (Hydrometer Method) (ASTM International)
- ASTM D1298 - Density, Relative Density, or API Gravity of Crude Petroleum and Liquid Petroleum Products by Hydrometer Method (ASTM International)
- ISO 3675 - Crude petroleum and liquid petroleum products - Laboratory determination of density - Hydrometer method (ISO)
- OIML R 22 - International Alcoholometric Tables (International Organization of Legal Metrology)
- NIST Handbook 133 / NIST OWM hydrometer checking procedures - field inspection of commercial hydrometers in US weights and measures (NIST Office of Weights and Measures)
- EU Measuring Instruments Directive 2014/32/EU (MID) - alcoholmeters and hydrometers for spirit strength where used for legal metrology / excise (European Union; national transposition)
- Which of these standards and regulation hold for the sense of hydrometer this model covers, and on what evidence? provenance
Real-world use
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Brewing and winemaking: wort or must specific gravity before and after fermentation (original/final gravity) with a brewing hydrometer or saccharometer in a trial jar.
- Petroleum terminals and refineries: API gravity or density of crude and products by glass hydrometer in a cylinder, often with a hydrometer-method temperature correction to 15 °C or 60 °F (ASTM D1298 / ISO 3675).
- Dairy inspection: lactometer reading of milk to screen for watering or skimming.
- Battery maintenance: lead-acid electrolyte specific gravity with a battery hydrometer (often a small float in a syringe barrel).
- Sugar refining and food processing: Brix or Baumé of syrups, brines and acid solutions.
- Customs and excise: alcoholometers for spirit strength (Sikes, Tralles, Gay-Lussac) against legal tables.
- Aquaria and marine work: salinity/specific gravity of seawater with a swing-arm or glass hydrometer.
- Soil and geotechnical labs: soil-particle hydrometer analysis (ASTM D7928 / ISO 17892-4) using a specialized hydrometer in a sedimentation cylinder.
- Which of these real-world use hold for the sense of hydrometer this model covers, and on what evidence? provenance
Typical measurements
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- relative density (specific gravity) of the liquid - 0.60-2.00 for ordinary glass sets (petroleum light fractions ~0.65; water 1.000; battery acid ~1.22-1.28; concentrated acids/brines up to ~1.8-2.0) - 1 (dimensionless, usually vs water at a stated temperature)
- API gravity - roughly −10° to +70° API across crude and products (light condensates higher) - degree API
- Brix (sucrose mass fraction equivalent) - 0-30 °Bx typical for wort/must; up to ~80 °Bx for concentrated syrups - degree Brix
- Baumé - separate light and heavy scales; heavy liquids commonly 0-70 °Bé - degree Baumé
- Twaddell - 0-200 °Tw for liquids denser than water (0 °Tw = SG 1.000; 200 °Tw = SG 2.000) - degree Twaddell
- reference / observation temperature - typically 15 °C, 20 °C or 60 °F calibration; readings corrected from the actual sample temperature - °C or °F
- stem scale resolution - 0.0005-0.002 in specific gravity; 0.1-0.5 °API or °Bx depending on length class - scale division
- Which of these typical measurements hold for the sense of hydrometer this model covers, and on what evidence? provenance
Failure modes and hazards
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Broken glass stem or bulb: mercury or lead-shot ballast and glass shards; mercury-ballasted antiques are a toxic-spill hazard.
- Temperature error: liquid and hydrometer not at the calibration temperature, or no temperature correction applied - the dominant routine error.
- Meniscus / reading error: reading the wrong edge of the meniscus, or a dirty/wet stem changing displacement.
- Surface contamination or bubbles clinging to the bulb, making the instrument ride high (apparent density too low).
- Calibration drift or an off-spec ballast/scale (especially cheap plastic aquarium hydrometers).
- Using the wrong scale (Baumé heavy vs light; Brix vs SG; API vs SG) and converting with the wrong formula.
- Lead-acid battery hydrometers: acid splash and hydrogen around charging batteries.
- Soil hydrometers: mis-timed sedimentation readings, wrong dispersing agent, or temperature not controlled - biased particle-size distribution, not a physical failure of the float.
- Which of these failure modes and hazards hold for the sense of hydrometer this model covers, and on what evidence? provenance
Regional variation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- United States petroleum practice: API gravity at 60 °F, ASTM hydrometer numbers, ASTM D287/D1298.
- ISO / much of Europe and international oil trade: density in kg·m⁻³ at 15 °C (ISO 3675), not API, though API is still quoted for crude.
- United Kingdom and historic Commonwealth industry: Twaddell degrees for acids, bleaches and other liquids heavier than water; Sikes hydrometer for spirits (UK excise, now largely superseded by density meters but still referenced).
- France and much of continental Europe: Gay-Lussac alcoholometry (% vol at 20 °C); Baumé still seen in some chemical and food trades.
- Germany / Central Europe: Balling and later Plato scales in brewing rather than Brix/SG alone.
- Soil particle-size hydrometer methods (Bouyoucos / ASTM D7928 vs ISO 17892-4) differ in cylinder, hydrometer type (151H vs 152H), and temperature corrections by jurisdiction.
- Which of these regional variation hold for the sense of hydrometer this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- pycnometer (specific-gravity bottle) - A pycnometer measures density by mass of a known volume; a hydrometer infers density from buoyancy/immersion. Pycnometers are gravimetric and usually more accurate; hydrometers are faster field/lab floats.
- digital density meter (oscillating U-tube) - U-tube meters measure resonant frequency of a filled tube (e.g. ASTM D4052 / ISO 12185). No floating stem; typically higher precision and smaller sample, used as the modern replacement in many legal-metrology and petroleum labs.
- refractometer - A refractometer measures refractive index (often reported as Brix). It does not measure density; Brix-from-RI and Brix-from-hydrometer agree only for pure sucrose solutions and diverge with alcohol or salts.
- hygrometer - A hygrometer measures humidity of air or gas. The names are routinely confused; a hydrometer is for liquid density.
- lactometer vs general hydrometer - A lactometer is a hydrometer with a short milk-SG scale (often ~1.025-1.035) and sometimes a cream-volume neck; a general SG hydrometer covering 1.000-1.060 can substitute only if the scale resolution is adequate.
- salinometer / conductivity salinity meter - Electronic salinometers infer salinity from conductivity; a seawater hydrometer infers it from density. They disagree when composition departs from standard seawater (e.g. aquarium additives).
- Which of these neighbouring kinds and how to tell them apart hold for the sense of hydrometer this model covers, and on what evidence? provenance
Sources
- Hydrometer - Definition as a specific-gravity float instrument; constant-mass vs constant-volume types; Twaddell, Baumé, Brix/Balling, API, lactometer and alcoholometer scales; brewing, winemaking, dairy, battery-acid and petroleum uses; temperature correction and meniscus reading practice.
- NIST Handbook 105-3: Specifications and Tolerances for Reference Standards and Field Standard Weights and Measures - Specifications and Tolerances for Graduated Neck-Type Volumetric Field Standards - US weights-and-measures context in which hydrometers appear as field/reference density instruments alongside volumetric standards (consulted via NIST OWM handbook index; handbook numbering should be confirmed against the current OWM list before citing a clause).
- ASTM E100 - Standard Specification for ASTM Hydrometers - US specification for glass hydrometers used with ASTM density/gravity methods (petroleum, industrial liquids): construction, scale types (specific gravity, API, Baumé), dimensions and tolerances.
- OIML R 22 - International Alcoholometric Tables (and related OIML alcoholometry recommendations) - International legal-metrology alcoholometry: hydrometer/alcoholometer scales, reference temperatures and ethanol-water tables used in customs and excise.
What the second pass must settle
- Does the registry intend hydrometer to include electronic floating instruments and non-floating devices marketed under that name, or only conventional buoyant instruments?
- Which existing Vercy world model, if any, already owns this concept and should be linked instead of creating a separate publication?
- Which authoritative sources establish the required reading conventions, reference conditions and correction methods for each hydrometer subtype retained in scope?
- Which application-specific scales require additional liquid-composition assumptions or neighbouring models before their readings can support a decision?
- Which construction-specific defects, compatibility limits and calibration acceptance criteria can be supported by manufacturer documentation and applicable measurement procedures?