If the granulated compound metal is now mixed with 1617 parts by weight of quicksilver, it becomes suddenly liquefied and expanded: liquefaction is the reverse of solidification, and hence cold is produced from the natural heat of the compound metals being rendered latent by the change from the solid to the liquid state; so that a small quantity of water placed in a glass tube, and surrounded with the metals whilst liquefying in the mercury, becomes rapidly converted into ice, the fall of the temperature, as shown by a thermometer, being from 60° Fahr. to 14°, which is 18° degrees below the freezing point of water. In the former case, by hammering the iron the latent heat is made sensible; whilst in the latter case, by the liquefaction of the compound metal in mercury, the sensible heat is rendered latent. The heat rendered latent by melting different substances is not a constant quantity, but varies with every special body employed, and the Drs. Irvine have proved this fact by the following experiments:—
| Heat of fluidity. | Ditto, reduced to the specific heat of water. | |||
| Sulphur | 143.68° | Fahr. | 27.14 | |
| Spermaceti | 145 | " | — | |
| Lead | 163 | " | 5.6 | |
| Bees'-wax | 175 | " | — | |
| Zinc | 493 | " | 48.3. | |
| Tin | 500 | " | 33. | |
| Bismuth | 550 | " | 23.25 |
Every one of these substances requires more heat to bring them into the liquid condition than ice, for which 140° of heat are sufficient, or are rendered latent during its conversion into water.
In coining at the Mint, the cold blank pieces of gold, silver, or copper become hot directly they have sustained the violent and sudden pressure of the coining press, and they must be heated again, or annealed, to restore the equilibrium of the heat disturbed by the violent blow, or else they remain hard and unfit to sustain the finishing process of milling.
The condensation of water when it assumes a smaller bulk by union with sulphuric acid, is easily proved by measuring a pint of water and a pint of acid, and mixing them together, when a very great increase of temperature may be perceived; and by placing into the mixture a cold copper wire that previously could not ignite phosphorus, it becomes very hot, and when removed and wiped it will cause phosphorus to fire directly it touches that substance. When the mixture of sulphuric acid and water is measured after it has cooled, it has no longer a bulk of two pints, but is found to have lost bulk equal to one or more ounces by measure. The heat evolved by a mixture of four parts of strong sulphuric acid and one part water is shown by the thermometer to be 300° Fahr., and this mode of obtaining heat has been used by aeronauts for the purpose of obtaining artificial warmth without the danger of setting fire to the gas in the balloon.
Fig. 382.
Aeronauts in the car warming their hands by a bottle containing sulphuric acid and water.
When alcohol and water are mixed a change of density occurs, and heat is produced; and if equal measures of alcohol of a specific gravity of .825, and water, each at 50° Fahr., are mixed, a temperature of 70° Fahr. is obtained; if the mixture is made in a glass vessel, as shown in the annexed cut, the combination is very apparent. To perform the experiment properly, water is poured into the lower tube and bulb, and alcohol into the top one; when this is done, the stopper is inserted, and the whole thoroughly shaken and mixed together; the warmth which is thus obtained is apparent to the hand, whilst the contraction is shown after the mixture is cold, as it no longer fills the two bulbs of the instrument. (Fig. 383.)
