Miscellanies. 405 



Whilst in the liquid state, its elastic force is under such energetic 

 restraint, that a gramme of this substance produces an explosion as 

 great as the same weight of powder : this spring, in the solid state, 

 is completely broken : the new body disappears insensibly by slow 

 evaporation. 



A fact not less curious than the solidification of this gas, is, that it 

 is effected by the sudden passage from the liquid to the gaseous 

 state, and that the approach and coherence of the molecules which 

 constitutes the solid state, is caused by the expansion of a liquid 

 which instantly occupies a space 400 times greater than its primitive 

 volume. 



A fragment of solid carbonic acid, slightly touched by the finger, 

 glides rapidly over a polished surface, as if sustained by the gaseous 

 atmosphere with which it is constantly surrounded until it is entirely 

 dissipated. 



If we introduce a few decigrammes of this substance into a little 

 flask, and stop it hermetically, the interior is filled with a thick va- 

 por, and the stopper is soon driven out with violence. 



The vaporization of solid carbonic acid is complete. It leaves 

 but rar&l-y a slight humidity, which may be attributed to the action 

 of the air on a cold body, whose temperature is much below that of 

 freezing mercury. 



The influence of cooling upon liquid carbonic acid, whose expan- 

 sive force is thus found to be annihilated at about the hundredth de- 

 gree (Cent.) below melting ice, begins to be manifest at a much 

 higher temperature : this expansive force, which at zero is equal to 

 36 atmospheres, is no more than 26 atmospheres at 20° below zero. 



It seems proper to add, that the term one hundred degrees below 

 zero, which I assign to the solidification of the liquid acid," is not hy- 

 pothetical. In the experiment which I made before the members 

 of the committee, the alcoholic thermometer sunk to — 87° ; and 

 by adding to these 6 degrees, which the fluid would have contracted 

 if the whole thermoraetric column could have been subjected to the 

 frigorific action, we shall have the actual temperature of 93° Cent, 

 below 0^, and this number cannot have been the maximum of the 

 effect of the blowpipe fed by liquid carbonic acid. — Idem. 



6. Exchanges of objects in JVatnral History. (Extract of a let- 

 ter from Dr. H. G. Bronn, to Prof. Silliraan, dated Heidelberg, 

 Germany, 13th June, 1836.) — The museum of Natural History con- 



