Chemical Science, 201 



by M. Marianini on this subject is terminated by the following 

 conclusions, which give the result of his investigations. 1. The 

 electro-motive power in Ritter's secondary piles is not ])roduced by 

 the difficulty which they oppose to the passage of the electricity ; 

 since they acquire a polarity contrary to that of the voltaic piles 

 with which they have been put in communication ; because the more 

 rapid is the current the more readily do they arrive at a given state 

 of tension, and also because in varying the nature of the plates the 

 piles also acquire more or less readily a certain electro-motive 

 power. 2. The developement of piles of the second kind in Ritter's 

 columns have little or no influence on their activity, for on turning 

 and changing the humid layers which would make them, the polarity 

 of the whole is not changed. 3. The polarity of these secondary 

 piles arises solely from the alterations produced by the electric cur- 

 rent on the metallic surfaces in contact with the humid conductors ; 

 for the plates being washed and dried still preserve their power of 

 putting electricity in circulation if moistened pieces of cloth be put 

 between them. The fact otfers a ready explanation of all the phe- 

 nomena produced by these piles. — Aim. de Chimie, xxxviii. 40. 



5. Comparison of the Tourmaline and had electro- conductors. — 

 M. Becquerel has been engaged in examining the effect of heat upon 

 bad conductors of electricity, and comparing them with the effects 

 of heat upon the tourmaline, for the purpose of elucidating the 

 electric states of the latter body, and of bodies in general. Heat 

 which diminishes the conducting power of metals, increases that of 

 glass, gum-lac, and bad conductors of electricity. The eflects which 

 are produced when the temperature of glass is diminished, were 

 those first examined. A small glass tube, .04 of an inch in dia- 

 meter and between three and four inches in length was suspended to 

 a fibre of silk and hung in a glass cylinder, the bottom of which was 

 closed by a metallic plate : by heating the plate the temperature of 

 the tube could be varied, and the effects observed. When the tube 

 is dry and at common temperatures, it is powerfully attracted by an 

 excited stick of gum-lac held near it ; but leaving the tube exposed 

 to air, it soon becomes damp, and the attraction ceases. If again 

 heated to 68° or 77° Fahr. nothing happens ; for the heat is not suffi- 

 cient to dissipate the moisture on the surface ; but then, on remov- 

 ing the lamp and allowing the temperature to fall, peculiar effects 

 are noticed ; for the tube is immediately attracted, and continues to 

 be so as long as the cooling proceeds. Again, raising the tempe- 

 rature to 77°, the tube is not only attracted, but acquires two poles, 

 which disappear on the removal of the electrified gum-lac; whilst 

 on the contrary, when they are produced immediately on the re- 

 moval of the lamp, they continue during the whole time of cooling. 

 "When the temperature is raised to 212°, polarity is not occasioned 

 in the glass tube under the influence of the excited electric until 

 the moment when the thermometer begins to fall. When raised to 



