550 Intelligence and Miscellaneous Articles. 



mercury, mercury-amalgam, tin, bismuth, antimony, copper, zinc, 

 cadmium, iron, lead, aluminium, and magnesium. 



Although, from causes hitherto unexplained, individual exceptions 

 occur, the author thinks himself entitled to lay down the general 

 rule that the so-called electronegative metals, platinum, gold, palla- 

 dium, silver, &c, render the above insulators positive by friction ; 

 while the electropositive metals, zinc, cadmium, iron, &c, put them 

 in the negative condition. An almost never failing example is ebo- 

 nite ; rubbed, or rather gently stroked, with platinum it becomes 

 positive, while with zinc or iron it is negative. 



The action of amalgam is especially remarkable. So far as the au- 

 thor's observations extend, it makes all insulators, without exception, 

 positive. Even guu-paper and collodion, two of the most negative 

 substances known, present no exception ; and though it is sometimes 

 difficult to make gun-cotton positive, it is soon found that this arises 

 more from the fibrous structure than from the nature of the substance. 

 At all events it can be made positive. 



At first the author used Kienmayer's amalgam rubbed in upon 

 greased leather. It is in'this case difficult to avoid points of amal- 

 gam being rubbed off and placed on the insulator. Yet this rub- 

 bing off, to which the action might be ascribed, principally occurs 

 at first ; the more the amalgam is dried in upon the leather, the less 

 it rubs off; in eight to fourteen days it entirely ceases to do so, pro- 

 vided the insulator has a smooth surface and is gently rubbed. This 

 rubbing off is quite avoided if the coating of mirrors be used instead 

 of solid amalgam ; the insulator is then to be gently rubbed between 

 the coated faces of two pieces of mirror. 



A certain indicator of positive electricity can thus be easily con- 

 structed from pyroxyline paper. Among other methods, this is at- 

 tained by gently pressing a strip of paper for a time between two 

 plates of ebonite which have been rubbed with fur. The strip then 

 becomes positive by induction. Instead of the paper a thin strip of 

 ribbon may be advantageously used. 



Ebonite, which rubbed with fur becomes so strongly negative, 

 when rubbed with amalgam attains a degree of positive electrification 

 which is little or not at all inferior to that of glass. Hence electrical 

 machines with disks of ebonite may be used. The author constructed 

 such a machine, and at first the action was equal to that of glass ; 

 but it rapidly diminished, which he is inclined to ascribe to the cir- 

 cumstance that the amalgam, owing to the sulphur in the ebonite, 

 appears to undergo a gradual decomposition. It was also found 

 that flaps of oiled silk could not be used ; for they made the ebonite 

 negative, and thus weakened and even inverted the action of the rubber, 

 while they increase it in the case of glass. Hence, to avoid this evil, 

 flaps of gun-paper would have to be used, which, indeed, serve very 

 well in the case of glass disks. — Berliner Monatsbericht , March 1867. 



