**AREOMETERS** (Greek araios rare, leaky + metreö to measure, define) — devices for gravity test of liquids.

Theoretically fluid density can be measured And., if to accept to constants either the weight, or volume of a floating body; according to it exist And. two types: Ampere-second constant weight and in Ampere-second constant volume. In practice the greatest application was found by Ampere-second the constant weight for which the volume of an underbody And. (equal to the volume of liquid which is forced out by it) it is inversely proportional fluid densities. Change of depth of immersion And. forms a basis to an areometry. And. are produced from glass (more rare from brass) in the form of the soldered hollow cylindrical tube.

In the lower, wide part of the tube called by a body And., the load (fraction, mercury) serving for increase in mass of the device and shift of the center of gravity is placed. Thanks to a load placed in liquid A. is established in situation, perpendicular to a fluid level.

The majority of areometers are supplied with thermometers for registration of temperature of the studied liquid. In upper, narrow part A. — to a neck — the scale for determination of depth of immersion of the device in liquid (fig.) is located.

Massú A. is selected such that at his submersion a part of a neck remained over its surface. Counting of density is made on the scale graduation noted on bottom edge of a meniscus of liquid. U A., intended for opaque liquids (neftedensimetra), counting of indications is made on the upper edge of a meniscus (it is provided at creation of a scale and it is specified on the device). Since density of the studied liquid depends on temperature, And. graduate on a certain temperature, edges it is specified on its scale.

If temperature of liquid does not correspond specified on the device, true density is calculated according to special tables or on a formula: D_{ ist } = D_{ -ism } [1 — β (t ° — t°0)], where D_{ ist } and D_{ -ism } — respectively the true and measured density; β — the coefficient equal for glass And. 0,0000244; t ° — t°0 — temperature difference.

Devices usually graduate for measurement of density of liquids at a temperature of 15; 17,5 or 20 ° in relation to density of water at 4 °. In these cases density is designated respectively: D_{ 15/4 } , D_{ 17,5/4 } and D_{ 20/4 } or D_{ 15 } , D_{ 17,5 } AND D_{ 20 } .

The most widespread And. show directly density of liquids with an accuracy of 0,001 — 0,005 g/cm^{ 3 } . V A. a special purpose (alcoholometers, sakharometra, etc.) scales are graduated in percentage of the corresponding solutes.

Are widespread in laboratory and clinical practice And. for an urinometry — an urometra. Sanitary and food laboratories use galactometers — And. for gravity test of milk, the sakharometra showing weight percents of sugar to the weight of solution, and an alkogolemetra.

Indicators of density often use for definition of concentration of the studied solutions according to special tables.

**Bibliography:** Kivilis S. S. Technology of measurement of density of liquids and solids, page 32, M., 1959.

*B. V. Kulibakin.*