86 M. Giiy-Lussac on I'ulcanos. 



cano, or at the surface of the earth by means of air, hydro- 

 chloric acid must necessarily be produced. Messrs. Monti- 

 celU and Covelli have in fact observed the production of 

 acid vapours in crevices nearly incandescent; but they took 

 them for sulphurous acid. I am, on the contrarj'^, convinced 

 that they were essentially composed of hydrochloric acid. It is 

 allowable to doubt the accuracy of their observation, since they 

 have expressed considerable uncertainty as to the natux'e of 

 these acid vapours, whether they were sulphurous or muriatic. 



It is well known that lava, especially when it is spongy, con- 

 tains a great deal of specular iron. In 1805, on inspecting, 

 with M. de Humboldt and M. de Buch, a gallery formed ou 

 Vesuvius by the lava of the preceding year, which after en- 

 crusting the surface had gradually sunk below it, I saw so 

 great a cjuantity of specular iron, that it formed what I may 

 be allowed to call a vein : its beautiful micaceous crystals co- 

 vered the walls of this gallery, in which the temperature was 

 still too high to permit us to stay long. Now the peroxide of 

 iron being in a high degree fixed at a temperature much higher 

 than that of lava, it is not probable that it was volatilized in 

 that state : it is very probable that it was primitively in the 

 state of chloride. 



If, indeed, we take protochloride of iron which has been 

 melted, and expose it to a dull red heat in a glass tube, and 

 then pass over its surface a current of steam, we shall obtain 

 a great quantity of hydi'ochloric acid and of hydrogen gas ; 

 and black deutoxide of iron will remain m the tube. Itj instead 

 of steam, we use dry oxygen, we shall obtain clilorine and 

 peroxide of iron. This experiment is easily made by mixing 

 chloride of iron with dry chlorate of potass ; at a very mode- 

 rate temperature chlorine disengages itself in abundance. If 

 we suffer a stream of moist air to pass over the chloride at 

 the temperature above mentioned, approaching to a red heat, 

 we obtain chlorine, hydrochloric acid, and peroxide of iron. 

 The effects observed with perchloride of iron are the same. 

 If it be exposed to moisture, hj'drochloric acid is immediately 

 obtained, or chlorine if it be exposed to oxygen; in either 

 case peroxide of iron is formed. 



I can imagine, therefore, that iron in the state of chloride 

 exists in the smoke exhaled by volcanos, or by their lava at its 

 contact with the air, and that by means of heat, of water, and 

 of the oxygen of the air, it is changed into peroxide, which 

 collects, and assumes a crj^stalline form during precipitation. If 

 we suffer a stream of chlorine at the temperature of about 

 -100° to pass over a steel h;u]isichord-wire, the wire imme- 

 diattly becomes incandescent, but not nearly so soon as with 



oxygen. 



