A specific gravity bottle, also known as a density bottle or relative density bottle, works by precisely measuring the volume of liquid it can hold and then comparing the mass of that volume of the liquid to the mass of an equal volume of water. This allows for the calculation of the liquid's specific gravity (relative density).
Here's a breakdown of the process:
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Calibration & Volume Determination: The specific gravity bottle has a known, precise volume. This volume is typically indicated on the bottle itself. It's crucial that the bottle is clean and dry before use. Some bottles come with a thermometer built-in to ensure the temperature of the liquid is known, as density is temperature-dependent.
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Empty Bottle Weighing: The empty, clean, and dry specific gravity bottle (along with its stopper) is weighed very accurately using a balance. This provides the mass of the empty bottle.
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Filling with Water: The bottle is then carefully filled with distilled or deionized water at a specific temperature (often 20°C or 25°C), ensuring no air bubbles are trapped. The stopper is inserted, displacing any excess water through a capillary hole in the stopper. The outside of the bottle is dried carefully.
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Weighing with Water: The bottle filled with water is weighed again. This provides the mass of the bottle plus water.
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Calculating Water Mass: The mass of the water is calculated by subtracting the mass of the empty bottle from the mass of the bottle plus water.
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Filling with the Liquid: The bottle is emptied, cleaned, and dried thoroughly. It's then filled with the liquid whose specific gravity you want to determine, using the same procedure as with the water (no air bubbles, specific temperature, drying the outside).
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Weighing with the Liquid: The bottle filled with the liquid is weighed again. This provides the mass of the bottle plus liquid.
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Calculating Liquid Mass: The mass of the liquid is calculated by subtracting the mass of the empty bottle from the mass of the bottle plus liquid.
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Calculating Specific Gravity: The specific gravity is calculated using the following formula:
Specific Gravity = (Mass of Liquid) / (Mass of Equal Volume of Water)
Since the specific gravity bottle ensures that the volume of liquid and water are the same, the ratio of their masses directly gives the specific gravity.
In summary, a specific gravity bottle works by precisely measuring the mass of a known volume of a liquid and comparing it to the mass of the same volume of water, thereby determining the liquid's specific gravity.
