The specific gravity of a sample can be determined with the accuracy required for mixer selection and loading as follows:
- Weigh any bottle empty in pounds or grams.
- 'Weigh the bottle filled with water and calculate the weight of water (B minus A = weight of water).
Weigh the bottle full of sample and calculate the weight of the sample (C minus A = weight of sample D). Specific gravity is C/B (weight of sample/weight of water).
Specific gravity of a substance is defined as the ratio of its density (specific weight) to the density of some standard substance. For liquids, the standard usually employed is either water at 4° Centigrade (39.2°F.) or water at 60° F. The mass in grams of 1 milliliter of water at 4° Centigrade is unity. Thus, for practical problems, the specific gravity of a liquid is frequently taken as numerically (not dimensionally) equal to the density in grams per milliliter.
Specific gravity of a liquid is determined by:
- By weighing a known volume or weighing an equal volume of water and liquid and comparing.
- By determining the loss of weight of a plummet or known volume weighed in air and in liquid, or by comparing the weight of a plummet of unknown volume in water (at 4°C) and in the liquid.
- By means of hydrometers, weighted glass floats that sink in the liquid to a depth that depends on the density of the fluid. The reading is taken at the liquid line on a calibrated stem that extends above the liquid. Hydrometers are calibrated:
- In terms of the specific gravity of the liquid at 60°F. compared with water at 60° (called 60/60° F.)
- In percentage of a substance in solution, mix, or
- In arbitrary divisions such as °Baume (Be); degrees A. P. I.
