d = density of water at temperature t.
γ = 0.000025, the cubical expansion coefficient of glass.
From this volume the weight of the water may be readily obtained by referring to tables 13, 14 and 15a in Landolt and Börnstein’s book.
52. Example Showing Determination of Specific Gravity of a Fat.—The flask is emptied of its water, rinsed with alcohol and ether, and dried again for a few minutes at 100°. It is then filled with the dry, hot, fresh-filtered fat, which should be entirely free from air bubbles.
The stoppered flask is then replaced in the water-bath, kept for thirty minutes at the temperature of boiling water, removed, and treated as above. The weight of fat having been determined, the specific gravity is obtained by dividing it by the weight of water previously found.
| Example. | |
| Grams. | |
| Weight of flask, dry | 10.0197 |
| Weight of flask, plus water | 37.3412 |
| Weight of water | 27.3215 |
| Weight of flask, plus fat | 34.6111 |
| Weight of fat | 24.5914 |
| Specific gravity = 24.5914 ÷ 27.3215 = | 0.90008. |
The weight of the flask dry and empty and the weight of water at 99° to 100° contained therein may be used constantly if great care be taken in handling and cleaning the apparatus.
| Example. | |
| Grams. | |
| Weight of flask, dry and empty | 10.0028 |
| Weight of flask after three weeks’ use | 10.0030 |
Figure 29. Aereometers, Pyknometers, and Hydrostatic Balance.