| B = | 209·335 | m = | 63·5 | ||
| b = | 197·64 | 32 | |||
| 11·695 | 31·5 | ||||
| f = | 540 | ·002036 | |||
| 6315·3 | 0·0641340 | ||||
| 1·064 | 1 | ||||
| H′ = | 6719·5 | feet. | 1·064 | ||
Method by Tables supplied with boiling-point apparatus made by Messrs. Negretti and Zambra:—
| 209·335 | gives | 1464 | in Table I. |
| 197·64 | " | 7736 | " |
| 6272 | |||
| 63·5 | " | 1·07 | in Table II. |
| Height | 6711 | ||
96. Thermometers for Engineers.—1st. Salinometer.—Under the circumstances at which fresh water boils at 212°, sea water boils at 213°·2. The boiling temperature is raised by the chemical solution of any substance in the water, and the more with the increase of matter dissolved.
From a knowledge of this principle, marine engineers make use of the thermometer to determine the amount of salts held in solution by the water in the boilers of sea-going steamers. Common sea-water contains 1⁄33 of its volume of salt and other earthy matters. As evaporation proceeds, the solution becomes proportionally stronger, and more heat is required to produce steam. The following table from the work of Messrs. Main and Brown, on the Marine Steam-Engine, shows the relation between the boiling-point under the mean pressure of the atmosphere, or 80 inches of mercury, and the proportion of matter dissolved in the water:—
| Proportion of Salt in 100 parts of water | 0 | Boiling-point | 212° |
| "" | 1⁄33 | " | 213·2 |
| "" | 2⁄33 | " | 214·4 |
| "" | 3⁄33 | " | 215·5 |
| "" | 4⁄33 | " | 216·6 |
| "" | 5⁄33 | " | 217·9 |
| "" | 6⁄33 | " | 219·0 |
| "" | 7⁄33 | " | 220·2 |
| "" | 8⁄33 | " | 221·4 |
| "" | 9⁄33 | " | 222·5 |
| "" | 10⁄33 | " | 223·7 |
| "" | 11⁄33 | " | 224·9 |
| "" | 12⁄33 | " | 226·0 |
Fig. 74.
When the salts in solution amount to 12⁄33, the water is saturated. It has also been ascertained that, when a solution of 4⁄33 is attained, incrustation of the substances commences on the boiler. Hence, it is a rule with engineers to expel some of the boiling water, when the thermometer indicates a temperature of 216°, and introduce some more cold water, in order to prevent incrustation, which not only injures the boiler, but opposes the passage of heat to the water. The thermometer used for this purpose should be very accurately graduated, and the scale must be considerably higher than, though it need not read much below 212°.