The weight of the flask filled with the liquid whose sp. g. has to be determined is ascertained in a similar way. Of course the temperature must be the same. If the liquid does not mix with water, the bottle should be dried before filling, but otherwise the flask need only be rinsed out two or three times with the liquid.
Having obtained the three weighings, deduct the weight of the bottle from each of the others to get the weights of the water and liquid respectively. Divide the latter by the former, the result shows the sp. g. As an example, take the following, in which a rather large sp. g. bottle was used:—
| 1. Weight of bottle | 39.299 | gram |
| 2. Weight of bottle and water | 81.884 | " |
| 3. Weight of bottle and paraffin | 73.146 | " |
By subtracting 1 from 2 and 3 the result is as follows:—
| 81.884 | grams | 73.146 | grams |
| 39.299 | " | 39.299 | " |
| —————— | —————— | ||
| 42.585 | of water. | 33.847 | of paraffin. |
Divide the weight of the paraffin by that of the water—
42.585)33.8470(0.7948
29.8095
——————
.......
The sp. g. of the paraffin is 0.7948.
The sp. g. of a fusible solid may be obtained in the same way at a temperature some degrees above its fusing point.
The sp. g. of a solid in powder or gravel sufficiently fine to pass through the neck of the bottle is easily determined. If the bottle filled with water weighs 50 grams, and there is placed on the pan alongside of it 20 grams of a sand, the weight of the two together will of course be 70 grams. But if the sand is put in the bottle, it evidently displaces its own bulk of water; and if, on again weighing, the weight is found to be 62 instead of 70 grams, it is because the 20 grams of sand has displaced 8 grams of water. Bulk for bulk, the sand is 2-1/2 times as heavy.