hydrometer

American  

[hahy-drom-i-ter] / haɪˈdrɒm ɪ tər /

noun

1. an instrument for determining the specific gravity of a liquid, commonly consisting of a graduated tube weighted to float upright in the liquid whose specific gravity is being measured.

---

hydrometer British  

/ ˌhaɪdrəʊˈmɛtrɪk, haɪˈdrɒmɪtə /

noun

1. an instrument for measuring the relative density of a liquid, usually consisting of a sealed graduated tube with a weighted bulb on one end, the relative density being indicated by the length of the unsubmerged stem

---

hydrometer Scientific  

/ hī-drŏm′ĭ-tər /

1. An instrument used to measure the density of a liquid as compared to that of water. Hydrometers consist of a calibrated glass tube ending in a weighted glass sphere that makes the tube stand upright when placed in a liquid. The lower the density of the liquid, the deeper the tube sinks.

---

Other Word Forms

• hydrometric adjective
• hydrometrical adjective
• hydrometrically adverb
• hydrometry noun

Etymology

Origin of hydrometer

First recorded in 1665–75; hydro- ¹ + -meter

Explanation

You may have used a hydrometer in the science lab to measure the specific gravity of a liquid. Specific gravity is the density of a substance as compared to the density of water. A hydrometer looks like a thin, transparent, closed tube, marked with a numbered scale and having a wider part at one end containing a small weight made of lead or steel. You put it into a container of the liquid whose specific gravity you're measuring, and when the surface of the liquid in the container lines up with an amount on the scale, that amount is the liquid’s specific gravity. Hydrometers are commonly used in industries that make beverages, test car batteries, and measure the salt content in aquariums. Hydrometer uses the Greek combining forms hydro-, "water," and -meter, "measure."

Example Sentences

He walks ahead of her with a hydrometer to measure the relative humidity of any space she’s about to enter.

From Los Angeles Times • Mar. 2, 2024

This is done by measuring the fraction of a floating object that is submerged—for example, with a hydrometer.

From Textbooks • Aug. 12, 2015

Figure 11.26 This hydrometer is floating in a fluid of specific gravity 0.87.

From Textbooks • Aug. 12, 2015

The glass hydrometer is filled with air and weighted with lead at the bottom.

From Textbooks • Aug. 12, 2015

He handed me a white enamel graduate and what looked like a battery hydrometer.

From "Invisible Man" by Ralph Ellison