between Metals and Heated Salts. 103 



poles), on the other by the contact of bodies in 4ifferent states of 

 aggregation. 



After solidification, in those cases where the salt still continues 

 to conduct, there is, generally speaking, an ascending current 

 which is due to the difference of temperature. It is probable 

 that the anomalous appearance of a feeble ascending current at 

 the termination of the cooling of nitrate of potash was a conse- 

 quence of the difference of temperatures of the platinum of the 

 crucible and of the wire. 



A mixture of equivalent quantities of carbonate of soda and 

 carbonate of potash forms at first, on cooling, a greyish opal 

 mass, which after some time is changed into a white crystalline 

 salt. This change from one condition into the other appears 

 also to be accompanied by a peculiar development of electricity, 

 the current passing in an ascending direction. In the same 

 manner, on applying heat, the inverse transformation gives rise 

 to a current in the opposite direction, that is, a descending one. 



In the cases of carbonate and of phosphate of soda, quite at 

 the end of the cooling, after a descending current has been 

 observed for a long time, a weak ascending current makes its 

 appearance, the formation of which is probably due to a polar- 

 ization caused by the previous passage of the descending current. 

 I have satisfied myself, by special experiments, of the possibility 

 of such a polarization. 



When salts, such for instance as borate of soda, solidify after 

 fusion, and after solidification separate of themselves from the 

 sides of the crucible at a time when the salt still enjoys the 

 power of electrical conduction, a descending current is brought 

 about. If the separation be sudden this current is strong, but 

 of only momentary duration ; if the separation be gradual, the 

 current continues during the separation, but is of less strength. 



If borax which has separated from the crucible in the above- 

 described manner be immediately heated again, the re-establish- 

 ment of contact between the salt and the crucible is accom- 

 panied by the development of a current, which passes also in a 

 downward direction. The cause of this current is most probably 

 the sudden cooling which the strongly heated platinum under- 

 goes on coming in contact with the cooler salt, inasmuch as 

 similar currents occur when an air-bubble of some size, formed 

 on the side of the crucible, rises through the pasty mass of 

 melted borax, and bursts. 



