FREEZING OF PLANTS AND ANIMALS. 97 



The greater fall of the freezing-ppint 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 physi- 

 cal. 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. Donhoff, of Orsoy. 



The humors of butterfly-pupa?, 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 cab- 

 bage-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 be- 

 low 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 as- 

 sume the yellow color. The smaller particles, on the other hand, re- 

 main 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 solidify- 

 ing, 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 phos- 

 phorus might be cooled to 38 Fahr. before it solidified. Thus it re- 

 mained fluid 11 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.. 



TOL. III. 7 



