132 Progress of Foreign Science. 



was a witness at Vesuvius of frequent explosions which projected 

 the melted lava more than 200 metres high, he never perceived 

 any inflammation of hydrogen. Each explosion was succeeded by 

 volumes of a thick and black smoke, which would not have failed 

 to take fire, had they been formed of hydrogen, as they were 

 traversed by red matters more highly heated than would have been 

 necessary for their accension. This smoke, the evident cause of 

 the explosions, contained therefore other fluids than hydrogen ; 

 but what was its true nature*? 



Admitting, says he, that it is water which furnishes the oxygen 

 to the volcanoes, it must, since its hydrogen is not disengaged in 

 a free state, at least most usually, become engaged in some new 

 combination. This cannot be into any compound inflammable 

 on contact of air, by means of heat ; but it might happen to form 

 muriatic acid with chlorine. We have in fact several observations 

 at the present day, on the presence of this acid in the vapours of 

 Vesuvius ; and according to that excellent observer M. Breislack, 

 it should be at least as abundant in them, as sulphurous acid. 

 M. Menard de la Groye, and M. Monticelli regard the presence 

 of muriatic acid in the vapours of Vesuvius, as- incontestable. 

 M. Gay Lussac suggests that this position should be further ve- 

 rified by putting water containing a little potash, in open vessels, 

 at several places of this volcano. This water would gradually 

 become charged with acid vapours, and at the end of some time, it 

 would be easy to determine their nature. 



If the combustible metals (silicium and aluminum) be not in 

 the state of chlorides, the muriatic acid must then be a secondary 

 result. It proceeds from the action of water on some chloride 

 (probably that of sodium,) an action which is promoted by the 

 mutual affinity of the oxides. The production of muriatic acid 

 by the concurrence of water, and some oxide, on a chloride, ought 

 to be very frequent in volcanoes. The lavas contain chlorides, 

 for they exhale them abundantly on contact of the air. MM. Mon- 

 ticelli and Covelli have extracted by simple washings with boil- 

 ing water, more than 9 per cent, of sea salt from the lava of 

 Vesuvius of 1822. It exhales from the mouth of volcanoes ; very 

 fine crystals of it being seen in the scorire that cover the incan- 

 descent lava. 



It is known that the lava, especially those which are spongy, 

 contain much specular iron. It forms occasionally a kind of 

 veins ; and coats with beautiful micaceous crystals the walls of 

 galleries still too hot for remaining long in them. Now, the 

 peroxide of iron being very fixed at much higher temperatures 



* We are surprised at the above inference. Surely M. Cay Lussac cannot 

 have forgotten Sir H. Davy's experiments on the non-combustibility of hy- 

 drogen, when mixed with muriatic acid gas, &c. — Editor. 



