Intelligence and Miscellaneous Articles. 415 



Pyrophoric iron obtained by reducing at a low temperature either 

 the sesquioxide alone or a combination of oxide of iron and alumina 

 (precipitated from their chlorides by ammonia), gives up, like py- 

 rophoric nickel and cobalt, all its hydrogen in vacuo, and, like them, 

 retains the property of ignition at a low temperature in air. As to 

 the quantity of hydrogen which can be fixed by pyrophoric iron, its 

 determination presents special difficulties. The cold metal loses in 

 vacuo a portion of the gas which it absorbed. Boiling water, by the 

 use of which we succeeded in obtaining the hydrogen dissolved in 

 pyrophoric nickel or cobalt, gave with iron entirely different results. 

 In. fact, the pyrophoric iron which comes from the reduction of the 

 combined oxides of iron and aluminium, put with air-exhausted 

 water into a small balloon furnished with a discharge-tube, gave a 

 continuous disengagement of hydrogen when heated : thus 1 grm. 

 of iron liberated 10 cubic centims. of gas per hour ; and the libera- 

 tion went on until the iron was almost completely oxidated. The 

 water was therefore decomposed at about 99° by the minutely di- 

 vided iron. Pyrophoric iron from the reduction at a low tempera- 

 ture of the hydrate of the sesquioxide alone, decomposes water with 

 a rapidity nearly equal to that of the metal combined with alumina. 



With respect to the pulverulent iron less minutely divided 

 which is obtained on reducing by hydrogen the sesquioxide result- 

 ing from the calcination of the nitrate, it also decomposes water at 

 about 99°, but the decomposition is much slower. The reduced 

 iron of commerce and the spongy iron obtained by the galvanic pile 

 behave in the same manner*. 



Not being able to determine by immersion in boiling water the 

 volume of the gas condensed in pyrophoric iron, we essayed to de- 

 termine it by keeping the iron in cold water ; but here again we 

 had to recognize the decomposition, though slower, of the water : 

 1 gramme of pyrophoric iron, kept in water deprived of air and at 

 15°, liberated hydrogen regularly during two months. 



In brief, iron, nickel, and cobalt directly absorb hydrogen ; but 

 we cannot affirm that combination takes place : this is what we 

 have already proved for lithium and thallium. Pyrophoric iron, 

 nickel, and cobalt condense a greater quantity of gas than the com- 

 pact metals ; but the whole of the gas is liberated below a red heat, 

 and the metals deprived of hydrogen continue to be pyrophoric : this 

 property therefore does not depend on the presence of condensed 

 hydrogen. Finally, iron in a state of minute division exhibits a 

 property which is not found in either nickel or cobalt ; it decom- 

 poses water slowly at ordinary temperatures, and rapidly at about 

 100° : in this respect it approaches manganese, of which we shall 

 shortly make known some new properties. — Gortvptes Hendus de 

 VAcad. des Sciences, vol. lxxx. pp. 788-791. 



* The vapour of water, under the tensions comprised between 5 and 25 

 millims. is likewise decomposed by iron at the temperature of 100°, as 

 results from experiments by H. Sainte-Claire Deville. 



