Volcanos and Earthquakes, 33 



he mentions that chloride of iron, in contact with water, becomes 

 so exceedingly hot, that it is capable, in large quantities, of 

 raising itself to a white heat, and that the chlorides of silicium 

 and aluminium must be able to produce a much more extra- 

 ordinary degree of heat. 



It cannot be denied that there is some justness in these con- 

 clusions. But it must be remembered, on the other hand, that 

 the premises are only taken from appearances at Vesuvius,'^ 

 and that the occurrence of common salt and muriatic acid in 

 the products and exhalations of volcanos, seems by no means 

 to be general. We have already quoted Boussingault's obser- 

 vation, that muriatic acid is not evolved from the volcanos 

 under the equator in the New World. The hot springs in those 

 regions contain but little common salt.i* In my frequent ex- 

 cursions in the vicinity of the Laacher See and in the Ejfel, I 

 have never found any efflorescence of salt either on the undis- 

 turbed or fresh broken lavas, and other products of the extinct 

 craters in those districts. On the uncovered walls of trass, in 

 the Brohl valley, efflorescences are, indeed, to be found, but 

 they contain chlorides only as very subordinate ingredients.^ 

 The lixiviation of trass, basalt, and other volcanic rocks, also 

 gives but a trace of common salt.|| That muriatic acid must 

 have played a very insignificant part in the eruptions of these 

 ancient volcanos, seems to be proved by the mineral springs 

 which rise in their vicinity ; for common salt is one of their 

 least considerable components, indeed they frequently contain 

 mere traces of it. This is the result of more than forty analyses 

 of mineral springs in those regions, which I have undertaken 

 during these last few years. But these waters would extract 



Hodorborg, &c. Bonn, 1835, p. 22. It is worthy of notice, and speaks in 

 favour of the probability of the above-mentioned production of iron-glancc', 

 that in the places last mentioned, the appearance of combinations of cliloriiio 

 is very limited. 



* The observations of Von Humboldt, Gay-Lussac, Von Buch, and Mon* 

 ticelli, made at different times, shew also that the exhalations of mu- 

 riatic acid are very variable. They are sometimes so frequent as to sur- 

 pass the exhalations of sulphurous acid, sometimes only a few trac^^fe of it 

 are found. 



t Loco cit. p. 181. X Die vulkanischen Mineralquelleu, &c. p. 243. 



II Idem, p. 246 and 277. 



VOL. XXVI. NO. LI. JANUARY 18S9. C 



