400 RECENT PROGRESS IN PHYSICS. 



in contact witli zinc in sulphuric acid diluted to one-half until it was 

 perfectly clean, and then in an acidulated saturated solution of sul- 

 phate of copper in a brass vessel, with which the iron was brought in 

 contact. V. Ruolz used either cyanide of gold dissolved in cyanide 

 of potassium, or cyanide of gold in prussiate of potash, (yellow or 

 red,) or else sulphuret of gold in neutral sulphuret of potassium ; 

 and though the latter is reported as the best by the commission which 

 examined the subject, (Dingler's Journal^ vol. 83, Comptes Rendus, 

 November, 1841,) their experiments were all made with the cyanogen 

 compounds only. In one of these experiments one gramme of dry 

 chloride of gold was dissolved in 100 grammes of water with ten 

 grammes of yellow prussiate of potash, and the battery used con- 

 sisted of six Daniell's elements, each plate of which was two decimetres 

 square. The precipitate was found to be proportional to the time, 

 and amounted, on a brass plate of fifty square centimetres, to 0.063 

 grammes of gold per minute when the fluid was heated to 60° C, 

 0.0296 grammes when heated to 35°, and 0.0126 grammes with a 

 temperature of 15° ; while, according to the comparative experiments 

 of Dumas, with fire gilding upon a like surface, 0.1297 grammes were 

 deposited as a maximum, and 0.0214 grammes as a minimum, and by 

 the wet way only 0.0137- — 0.0211 grammes. 



Similar results were obtained by the commission with solutions of 

 one part of cyanide of silver in 100 of water and ten of yellow prus- 

 siate of potash. But with cyanide of platinum the coating was one 

 hundred times slower ; with the double chloride of platinum and 

 potassium dissolved in caustic potassa, the commission of the Academy 

 states that the results were equal to those obtained with gold. The 

 experiments in coating with copper, tin, cobalt, and nickel, are very 

 superficially reported ; of nickel, its easy precipitation upon iron is 

 only mentioned, and in coating iron with zinc its favorable electrical 

 action in protecting the iron is pointed out, while V. Ruolz after- 

 wards alleges (Dingler's Journal, vol. 86, Comptes Rendus, August, 

 1842, No. 6) that iron covered with zinc is more easily rusted at bare 

 spots than that coated with lead or tin ; which experience is also con- 

 firmed by Eisner, (Dingler's Journal, vol. 88.) 



The circumstances which were concerned in producing these con- 

 tradictory experiments are not to be ascertained from the respective 

 memoirs. But when the commission adds, " We are convinced that, 

 by this process, iron can be coated with brass ; it needs only that 

 copper and zinc should be precipitated upon it, and then the object, 

 surrounded by coal dust, is to be heated to redness, whereby brass 

 will be produced," it appears very much like a conviction obtained at 

 the desk, and may be considered as that additional part of the new 

 invention which every such commission thinks it a matter of duty to 

 contribute. 



The new process met with general favor, and it was soon found 

 that equally good results were obtained with a solution four to six 

 times more dilute, and that the use of one element only, or of the 

 simple battery in which the zinc was placed in a solution of table salt, 

 was more convenient. But with large quantities of the solution, and 



