Page:Popular Science Monthly Volume 3.djvu/107

Rh The greater fall of the freezing-point in vacuo, as compared with its fall in the atmosphere, would appear to be ascribable to the absence of small corpuscles (spores?). The melting of ice, as also the freezing of water, is a purely chemical process, though commonly called physical. Here heat is converted into a chemical effect; and, conversely, a chemical effect into heat. The phrase, "heat becomes latent," can no longer satisfy us, for latent heat is no heat at all. Here centre some facts belonging to the organic kingdom, to which my attention has been called by a letter received from Herr Fr. Dönhoff, of Orsoy.

The humors of butterfly-pupæ?, which pass the winter in the open air, remain fluid in the coldest climate. If we cut in two such pupa?, at a temperature of 15° to 13° Fahr., the two halves quickly congeal and become as hard as stone. Juices of plants which do not freeze during winter, remain fluid, as is shown by the flexibility of the cabbage-leaf; while wet frozen linen may be broken, but refuses to bend. If you crush the leaves of green or red cabbage at a temperature below the freezing-point, they freeze at once; and, if you cut in pieces the ribs of a cabbage-leaf, you cannot press water out of the ends, for it freezes the moment they are cut up. Here the question arises how it is that watery fluids remain liquid in the tissues of animals and plants, whereas they at once freeze when the tissues are injured. A constant supply of heat is not to be thought of in pupa? or in eggs, such as is found in animals. Here I will bring forward two facts which throw some degree of light upon this question.

If you throw upon a glass plate a thin layer of flower of sulphur, and melt it by the application of heat, you will find that the larger particles are the first to become dry and solid on cooling, and to assume the yellow color. The smaller particles, on the other hand, remain fluid at common temperatures. Under the microscope they are transparent, and may be spread out with the dry finger; a fact which proves them to be viscous. Hence it follows that minute particles of sulphur may be cooled 170° below their melting-point without solidifying, but not so with larger particles.

Once, in preparing phosphuretted hydrogen, I suffered the mixture of phosphorus and caustic alkali to cool in the retort. On taking the apparatus apart on the next day, the phosphorus was found to be still molten at a common temperature, though its melting temperature is 115° Fahr. On repeating the experiment, it was found that the phosphorus might be cooled to 38° Fahr. before it solidified. Thus it remained fluid 77° below its melting-point.

Another observation was made, as follows: One night, at ten, o'clock, with the temperature at 4 Fahr., a dense fog lay over, the Moselle, through which, however, the brighter stars were visible. A cold current of air was coming from the direction of a neighboring hill, some 350 feet in height. The mist advanced steadily from the hill over the valley, but was constantly renewed, as the cold blast