1826.] Scientific Notices-— Chemistry/. 465 



power possessed by these metals of condensing such quantity 

 of oxygen on their extended surface, as to occasion the con- 

 ditions necessary to the oxidation of the metal. 



The inflammability of Romberg's pyrophorus, prepared by 

 heating to redness a mixture of alum and flour, depends pro- 

 bably on the same cause ; for the inflammation does not take 

 place, except when the heat has been so moderated as to be in- 

 sufficient for the fusion of the sulphuret of potassium. 



These phenomena are analogous to those observed by M. Do- 

 bereiner, as belonging to platina, and with the faculty which 

 silicium and zirconium have of oxidating under certain circum- 

 stances, as M. Berzelius has shown. Perhaps, also, they may 

 assist in discovering the causes of the formation of nitric acid 

 in artificial nitre-beds.— (Annales des Mines, xii. 210.) 



With these effects should be ranged the remarkable one ob- 

 served by Dr. Gobel, as produced by the residue left upon 

 igniting the tartrate of lead in close vessels. See vol. xvi. 

 p. 385, of this Journal. — Ed. — (Institution Journal.) 



5. Precipitation oj a Metal from Solution by other Metals, 

 Professor Fischer, of Breslau, remarks that the reduction of 



a metallic oxide from its solution in an acid or alkali by a 



metal, depends upon the following causes : — 



1. Principally the relative affinity of the two metals for 

 oxygen. 



2. The affinity of the oxide of the reducing metal for the acid, 

 or alkali : — for this reason tin, bismuth, and iron only reduce a 

 small number of salts, whilst zinc reduces a great number. It 

 is for the same reason that there are but few alkaline solutions 

 reduced by metals : silver dissolved in ammonia is not reduced 

 by zinc ; copper dissolved in ammonia is not reduced by tin, 

 antimony, bismuth, or iron. 



3. The electric tension which may exist between the precipi- 

 tating and precipitated metal. 



4. The affinity of the metals for each other : — copper is pre- 

 cipitated by iron in a state of purity ; precipitated by zinc, a 

 kind of brass is formed. 



5. The state of saturation and concentration of the solution : 

 — the precipitation is more rapid as the fluid is more acid and 

 concentrated. If the metal is required in fine dendritical crys- 

 tals, the solution should be dilute. Many metalHc salts, redu* 

 cible by certain metals when dissolved in water, are not so when 

 dissolved in alcohol. 



6. The tendency of the precipitated metals to assume the gra- 

 nular or crystalline state : — lead, silver, and tin are precipitated 

 from their solutions more readily than gold or platina. 



7. The position of the reducing metal, relative to the. solu- 

 tion : — when the metal is in plates or wires offering, a large sur- 



Neit) Series ^ vol. xii. 2 h . 



