Constant Temperature Hydrometer Bath (Hydrometer)

ASTM D1298


K26400 Constant Temperature Hydrometer Bath

A versatile constant temperature bath designed for density/gravity determinations of petroleum products at temperatures of up to 195°F (90°C), and also for Reid Vapor Pressure determinations using immersion bombs. Microprocessor PID control provides quick temperature stabilization without overshoot and the unit is protected by an overtemperature control circuit that interrupts power should bath temperature exceed a programmed cut-off point. Dual LED displays provide actual and setpoint temperature values in °C/°F. Communications software (RS232, etc.), ramp-to-set and other enhanced features are available as extra cost options.

Features and Benefits

Holds 12 hydrometer cylinders.

Can be used for Reid Vapor Pressure immersion type cylinders.

Conforms to ASTM D323, D1298, D6074, D6158 and related specifications.

Specific Gravity

Specific gravity is the ratio of the density of a substance to the density (mass of the same unit volume) of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for liquids or air for gases. Temperature and pressure must be specified for both the sample and the reference. Pressure is nearly always 1 atm equal to 101.325 kPa. Temperatures for both sample and reference vary from industry to industry. In British brewing practice the specific gravity as specified above is multiplied by 1000. Specific gravity is commonly used in industry as a simple means of obtaining information about the concentration of solutions of various materials such as brines, hydrocarbons, sugar solutions (syrups, juices, honeys, brewers wort, must etc.) and acids.

Specific gravity, as it is a ratio of densities, is a dimensionless quantity. Specific gravity varies with temperature and pressure; reference and sample must be compared at the same temperature and pressure, or corrected to a standard reference temperature and pressure. Substances with a specific gravity of 1 are neutrally buoyant in water, those with SG greater than one are denser than water, and so (ignoring surface tension effects) will sink in it, and those with an SG of less than one are less dense than water, and so will float. In scientific work the relationship of mass to volume is usually expressed directly in terms of the density (mass per unit volume) of the substance under study. It is in industry where specific gravity finds wide application, often for historical reasons.



A hydrometer is an instrument used to measure the specific gravity (or relative density) of liquids; that is, the ratio of the density of the liquid to the density of water. A hydrometer is usually made of glass and consists of a cylindrical stem and a bulb weighted with mercury or lead shot to make it float upright. The liquid to be tested is poured into a tall container, often a graduated cylinder, and the hydrometer is gently lowered into the liquid until it floats freely. The point at which the surface of the liquid touches the stem of the hydrometer is noted. Hydrometers usually contain a scale inside the stem, so that the specific gravity can be read directly. A variety of scales exist, and are used depending on the context. Hydrometers may be calibrated for different uses, such as a lactometer for measuring the density (creaminess) of milk, a saccharometer for measuring the density of sugar in a liquid, or an alcoholometer for measuring higher levels of alcohol in spirits.

Why we need to know?

  • The quality of the oil (Mass) the ratio of its volume. Common units – grams/ cubic centimeter, kg/ cubic meter or public Dun/ cubic meter and so on. As the volume changes with temperature. Therefore density can’t be divorced temperature exist independently. For ease of comparison, the Western countries use 15°C the provisions of the standard density as petroleum.
  • Specific gravity is important in that it can be converted to density. Specific gravity compares the mass of a given volume of material to the mass of the same volume of water. This produces a value that is equal to density at one temperature and close to the value of density at other temperatures. Density is one of the key characteristics of materials.
  • Specific gravity is a very important concept in the water/wastewater field.  The specific gravity of a substance will determine where a compound can be found in water in case of a spill.

Density or Specific Gravity for General Oil and Pentas Flora Recovered Oil:


General Oil

Density@15°C (kg/l)

Base Oil


Bunker Fuel

0.910 – 0.999



Heavy Oil

0.910 – 0.960

Light Fuel Oil 80 cSt

0.957 – 0.991

Medium Fuel Oil 180 cSt

0.982 – 0.991

Tyre Oil

0.900 – 0.950

Waste Engine Oil

0.860 – 0.890

Pentas Flora Recovered Oil

Density@15°C (kg/l)

Eco Light Fuel Oil

0.870 – 0.890

Super Light Fuel Oil

0.840 – 0.860

Green Light Fuel Oil

0.890 – 0.930

Base Light Fuel Oil

0.870 – 0.900