14 Prof > Wartmann on the Conductihility of Minerals 



in the conductihility that no satisfactory result could be obtained*. 

 The author tried to moisten the surfaces of the platinum with a 

 conducting liquid, and in some cases the readings were by this 

 treatment rendered more constant. But in most cases he only 

 succeeded in polarizing the forceps, or in developing electro- 

 chemical phfenomena which masked the result sought after. 



These obstacles became still more numerous in examining the 

 variations of conductihility in the same mineral. The conducting 

 substances which belong to other systems than the regular are 

 not numerous. The crystals to be obtained are nearly always 

 very small, and their texture rarely homogeneous. The natural 

 faces are in some cases covered by an insulating crust, although 

 of a fine polish. M. Wartmann has found some crystals perfect 

 conductors, and others of the same appearance which arrested 

 the most energetic currents, until by the continued friction of a 

 very hard body the surface was abraded. Some very beautiful 

 crystals of oxide of tin have proved themselves conductors along 

 their edges, and here and there on their faces, but everywhere 

 else they were insulators. Finally, the variable adherence of the 

 Burfaces of cleavage sometimes modifies the conductihility in 

 the most capricious manner. These difficulties have obliged 

 MM. Wiedemann and Senarmont to have recourse to the super- 

 ficial distribution of machine electricity, and to determine in a 

 manner less direct the sense of greater or less conduction. 



The experiments which M. Wartmann made in connexion with 

 this point were executed by passing a current simultaneously 

 round two galvanometers of Kuhmkorfi^. The crystal was clasped 

 in one direction between the jaws of a forceps, which latter was 

 connected with one of the galvanometers ; in the perpendicular 

 direction it was clasped between a second pair of forceps which 

 were connected with the other galvanometer. Multiplied experi- 

 ments have shown that manganite {acerdese) conducts much better 

 parallel to the axis than in the perpendicular direction. Plates of 

 sulphuret of molybdenum from Vallais exhibited the opposite de- 

 portmentj which appears to the author to be sufficiently pro- 

 nounced in certain crystals of arseniate of iron also. 



The results of M. Wartmann's investigation, similar in many 

 respects to those of MM. Hausmann and Henrici, are as follows: — 



1. The conducting minerals belong to five primitive ci-ystalline 

 types. None are found among the twelve species of the system 

 represented by the oblique unsymmetrical prism. 



2. Minerals present all intermediate degrees between perfect 

 conductihility and perfect insulating power. 



3. Native metals and their alloys are conductors. 



* Might not the difficulty be combated by enclosing the crystal between 

 two columns of mercury which should press uniformly against its surfaces, 

 and fipom which wireg might proceed to the galvanometer?— Ed. 



