Module 3: Density and specific gravity

Density

is mass per unit volume of a substance. It is usually expressed as grams per cubic centimeter (g/cc).

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1 mL may be used as the equivalent of

1 cc

Density =

Mass/volume

Specific Gravity

is a ratio, expressed decimally

Does not have a unit

Specific gravity =

Weight of substance/weight of equal volume of water

Substances that have a specific gravity < 1

are lighter than water.

Substances that have a specific gravity >1

Are heavier than water

Specific gravity

has no dimension and is therefore a constant value for each substance.

A glass pycnometer, or

Specific gravity bottle

Pycnometer

Is a special glass bottle used to determine specific gravity of liquids

An aluminum pycnometer

is used to determine specific gravity of viscous liquids and semisolids that may obstruct the narrow opening in a glass pycnometer.

pycnometers consist of three parts:

• a cylindrical vessel,

• a closure with a small opening

• a threaded fitting ring

Pharmaceutical Applications of specific gravity

use of automated, computer-controlled pharmaceutical equipment, termed automated compounders, in the preparation of multicomponent mixtures for parenteral nutrition

Normal specific gravity of urine

1.020-1.028

A higher-than-normal specific gravity indicates that the urine is

concentrated (the person is dehydrated)

A low specific gravity indicates that the urine is

Dilute

Clinical Application of specific gravity

Urinalysis