408 RECENT PROGRESS IN PHYSICS. 



placed opposite to it. But it is not necessary that tlie negative pole- 

 should end in a plate. With a simple platinum wire the same salts 

 furnish nomo-chromatic tints, which successively change, so that the ex- 

 periment may he interrupted with any color desired. Only chloride of 

 manganese gave colored rings like those obtained with acetate of lead. 

 Bottger used solutions of 1 part of the salt in 12 to 16 parts of water, 

 and employed a battery of 4 elements. He gives the following as the 

 best mode of performing the experiment : a short platinum wire is to 

 be soldered to the centre of a circular platinum plate, a glass dish is' 

 perforated in the middle, and the plate placed in it, so that the wire 

 passes through a cork in the hole, and projects a little from the bot- 

 tom of the dish. The glass dish is then placed upon a board in which 

 a mercury cup is inserted, and into this dips the wire from the dish, 

 while another wire passing through the board connects the mercury 

 with the positive pole. 



Eisner (Gewerbeblatt fiir Sachsen, 1842, No. 29 ; Dingler's Jour- 

 nal, vol. 85) applied Fechner's simple process to produce Nobili's 

 rings upon steel plates. He poured acid acetate of copper (solution 

 of verdigris in vinegar) over the plates, touched them in different 

 places with a zinc rod, dried them and heate 1 them over a spirit lamp, 

 when different colors are successively developed, and the operation 

 may be interrupted as soon as the desired tint is obtained. The theo- 

 retical reflections appended to the memoir do not appear to be based 

 upon quite clear ideas, and are therefore better omitted in this place. 



Becquerel (Comptes Kendus, February, 1844, No. 6; Dingler's- 

 Journal, vol. 91) repeated the experiments of Nobili in various ways, 

 and obtained particularly beautiful colors upon different metals when 

 used as positive poles in a solution of litharge in caustic potassa, while- 

 the negative pole was a platinum wire or plate. Lead is precipitated 

 on the platinum, and on the positive pole peroxide of lead, by which 

 these splendid colors are produced. Becquerel boiled finely powdered 

 litharge for a long time in a solution of caustic potassa of 20° to 22"^ 

 Beaume, and used six Daniell's elements for his battery. But the' 

 colors are readily developed with much weaker solutions and with 

 fewer elements when small platinum plates are employed. It is only 

 with very fine platinum wires, covered with glass except at the points,, 

 that more elements are necessary, but the rings thus obtained are 

 more perfect in form. 



Becquerel is said to have produced uniform shades by employing- 

 many wires projecting from the glass tube and radiating toward the 

 positive metallic plate. These colors resist very well v/hen rubbed with 

 the finer polishing powders, such as English rouge, but are changed 

 by being exposed to the action of acid or aramoniacal vapors. As a pro- 

 tection against this action, Becquerel recommends the application of two 

 coatings of a varnish, made as follows : ^ litre linseed oil, 4 to 8 gram- 

 mes finely powdered litharge^ and 2 grammes sulphate of zinc, are mod- 

 erately heated for several hours and then filtered. But Becquerel hini- 

 self admits that some of the colors are injured by this treatment. This 

 is also the case with shellac varnish. Becquerel has experimented with 

 gold, copper, silver_, (which gave no fine colors,) platinum, German 

 silver, and steel ; even bell-metal gave good results, but tin required 



