lOOÜ 



dissolves somewhat in llio metal or becomes denser on the surface 

 and exercises a cataljtic intluence. 



It has, however, appeared that p^rophoric iron may be obtained 

 when different iron compounds are heated for a short time in a 

 hydrogen current at =b 350°. This succeeds with ferro oxalate, ferro 

 tartrate, ferro chloi'ide, and with the oxides of iron, from which 

 follows (hat no common admixture except liydrogen can be pointed 

 out here, to which the pyropiioric property could be ascribed. Now 

 it appeared, iiowevei-, that also pyropiioric iron can l)e obtained 

 when ferro oxalate is heated irithout contact with hydrogen, which 

 |)ioves that the hydrogen certaiidy does not cause the pyrophoric 

 plienomenon. ') 



To test the supposition expressed l>y one of us, it was examined 

 in the first place what the influence is of the temperature on the 

 pyropiioric phenonienon. Sealed to glass tubes with pyrophoric iron 

 were placed in a thermostat, which was i-egulated at different tem- 

 [)eratures between 250° and 340°. After a certain time the tubes 

 were taken from tlie bath and opened to find out if the iron was 

 still pyi'ophoric. The result is given in the following table : 



Duration of the 

 tieating 



Temperature 



Result 



The j)yroph()ric properly of iron, therefore, vanishes with heating 

 to higher tempei'ature. The rapidity with which this happens, 

 increases greatly with tlie temperature. 310° is about the temperature 

 at which the conversion has taken place almost completely in 48 

 hours. 



That at this temperatui-e a massing together of the powder should 

 have taken place, and that in consequence of this the pyrophoric 

 phenomenon would have disappeared, is pretty well out of the 

 question, and it was therefore of importance to make an attempt to 

 examine whether the transition pyropiioric iron -» noii-pyrophoric 



1) Thiebault [Bull. Soc. Ch. de Paris (8) 31, 135] found that when Bi-mellate 

 is heated in vacuo, pyrophoric Bi is formed ; in the same way we obtained 

 pyrophoric Bi from the citrate. 



