The hydrometer intended for densities less than that of water, or the hydrometer for spirits, is constructed on a similar principle. The instrument is so arranged that it floats in pure water with most of the stem above the surface. A solution containing 10% of pure salt is used to indicate the zero of the scale, and the point at which the instrument floats when immersed in distilled water at 10° R. (54½° F.) is numbered 10. Equal divisions are then marked off upwards along the stem as far as the 50th degree.
The densities corresponding to the several degrees of Baumé’s hydrometer are given by Nicholson (Journal of Philosophy, i. 89) as follows:—
Baumé’s Hydrometer for Spirits. Temperature 10° R.
| Degrees. | Density. | Degrees. | Density. | Degrees. | Density. |
| 10 | 1.000 | 21 | .922 | 31 | .861 |
| 11 | .990 | 22 | .915 | 32 | .856 |
| 12 | .985 | 23 | .909 | 33 | .852 |
| 13 | .977 | 24 | .903 | 34 | .847 |
| 14 | .970 | 25 | .897 | 35 | .842 |
| 15 | .963 | 26 | .892 | 36 | .837 |
| 16 | .955 | 27 | .886 | 37 | .832 |
| 17 | .949 | 28 | .880 | 38 | .827 |
| 18 | .943 | 29 | .874 | 39 | .822 |
| 19 | .935 | 30 | .867 | 40 | .817 |
| 20 | .928 |
Baume’s Hydrometer for Salts.
| Degrees. | Density. | Degrees. | Density. | Degrees. | Density. |
| 0 | 1.000 | 27 | 1.230 | 51 | 1.547 |
| 3 | 1.020 | 30 | 1.261 | 54 | 1.594 |
| 6 | 1.040 | 33 | 1.295 | 57 | 1.659 |
| 9 | 1.064 | 36 | 1.333 | 60 | 1.717 |
| 12 | 1.089 | 39 | 1.373 | 63 | 1.779 |
| 15 | 1.114 | 42 | 1.414 | 66 | 1.848 |
| 18 | 1.140 | 45 | 1.455 | 69 | 1.920 |
| 21 | 1.170 | 48 | 1.500 | 72 | 2.000 |
| 24 | 1.200 |
| Fig. 5.—Jones’s Hydrometer. |
Carrier’s hydrometer was very similar to that of Baumé, Cartier having been employed by the latter to construct his instruments for the French revenue. The point at which the instrument floated in distilled water was marked 10° by Cartier, and 30° on Carrier’s scale corresponded to 32° on Baumé’s.
Perhaps the main object for which hydrometers have been constructed is the determination of the value of spirituous liquors, chiefly for revenue purposes. To this end an immense variety of hydrometers have been devised, differing mainly in the character of their scales.
In Speer’s hydrometer the stem has the form of an octagonal prism, and upon each of the eight faces a scale is engraved, indicating the percentage strength of the spirit corresponding to the several divisions of the scale, the eight scales being adapted respectively to the temperature 35°, 40°, 45°, 50°, 55°, 60°, 65° and 70° F. Four small pins, which can be inserted into the counterpoise of the instrument, serve to adapt the instrument to the temperatures intermediate between those for which the scales are constructed. William Speer was supervisor and chief assayer of spirits in the port of Dublin. For a more complete account of this instrument see Tilloch’s Phil. Mag., xiv. 151.