1 Miscellaneous Contributions by Dr. Hare. 



portion of the carbonate, the evolution of gas from it must 

 cease. 



3. Illustration of the cold consequent to Rarefaction : or 

 Relaxation of Pressure. 



Cold and cloudiness arising from rarefaction. 



Incipient rarefaction, in the air of a receiver, is usually in- 

 dicated by a cloud, which disappears when the exhaustion 

 has proceeded beyond a certain point. A delicate thermom- 

 eter placed in the receiver, shows that a decline of tempera- 

 ture accompanies this phenomenon. We may therefore in- 

 fer, that the cloud is the consequence of refrigeration. But, 

 in the present state of our knowledge, it is nearly as difficult 

 to account for the disappearance of heat, as for the appear- 

 ance of the cloud. This phenomenon, in common with 

 many others, must be referred to those unknown peculiarities 

 which determine the capacities of substances for caloric. By 

 rarefaction the capacity of air for caloric, becomes greater 

 than that of the aqueous vapor which it contains. This va- 

 por being consequently deprived of it, condenses into a fog. 

 The aqueous particles, receiving heat subsequently from the 

 surrounding medium through the receiver, and air pump 

 plate, are vaporized again; and of course, cease to be visible, 

 in the form of a cloud. 



Cold produced by the palm glass. 



Two bulbs are formed, 

 at each end of a tube, 

 one having a perforated 

 projecting beak. By 

 warming the bulbs, and 

 plunging the orifice of the beak into alcohol, a portion of this 

 fluid enters, as the air within contracts, by returning to its 

 previous temperature. The liquid, thus introduced, is to be 

 boiled in the bulb which has no beak, until the whole cavity 

 of the tube, and of both bulbs not occupied by liquid alco- 

 hol, is filled with its steam. 



While in this situation, the end of the beak is to be sealed, 

 by fusing it in a flame excited by a blowpipe. 



As soon as the instrument becomes cold, the steam which 

 had filled the space within it, vacant of alcohol in the liquid 

 form, condenses, and a vacuum is produced ; excepting a 



