Specific gravity and density are related but distinct properties used to characterize liquids. Here's how they differ, particularly at a specified temperature of 23°C as highlighted in the reference:
Understanding Specific Gravity
Specific gravity is a dimensionless ratio. It compares the weight of a certain volume of a liquid at a specific temperature to the weight of an equal volume of water, also at that same temperature.
- Definition: As per the reference, specific gravity is the ratio of the weight of a given volume of material at 73°F (23°C) to that of an equal volume of water at the same temperature.
- Expression: It's properly expressed as “specific gravity, 23/23°C”. This notation emphasizes the temperature at which the measurement was taken for both the material and water.
- Dimensionless: Since it's a ratio, specific gravity does not have units. It’s just a number that indicates how much denser or less dense a liquid is compared to water.
Understanding Density
Density, on the other hand, is a measure of mass per unit volume and thus has units.
- Definition: The provided reference defines density as the weight per unit volume of material at 23°C and is expressed as D 23°C in g/cm³.
- Units: Density is typically expressed in grams per cubic centimeter (g/cm³), or kilograms per cubic meter (kg/m³) and indicates how much “stuff” is packed into a given space.
- Temperature Dependent: Density is temperature-dependent. Hence it must be noted with the correct temperature at which it was measured. For instance, the reference specifically notes D 23°C in g/cm3.
Key Differences Summarized
Here's a table summarizing the key differences:
| Feature | Specific Gravity | Density |
|---|---|---|
| Definition | Ratio of material weight to water weight at the same temp. | Weight per unit volume |
| Units | Dimensionless | g/cm³, kg/m³ or other units of mass per volume |
| Temperature | Indicated as 23/23°C | Indicated as D 23°C |
| Nature | Ratio | Physical quantity |
Example & Practical insights:
- If a liquid has a specific gravity of 1.2 at 23/23°C, it is 1.2 times as dense as water at 23°C.
- A liquid with a density of 0.8 g/cm³ at 23°C means every cubic centimeter of that liquid weighs 0.8 grams.
- Specific gravity helps in comparing the relative densities of different liquids easily.
In summary, while both specific gravity and density relate to the amount of "stuff" in a liquid, specific gravity compares it to water, while density provides the actual mass per unit volume with specific units. They are both measured at 23°C based on the provided reference.
