220 Aiudi/ses of' Books. [Sept, 



most volcanos : the following is the manner in which he accounts 

 for the production of sal ammoniac which is so frequent an 

 ingredient. 



" The rock of this mountain is a sort of trachyte, which, 

 besides a little potass, consists essentially of silex and alumine, 

 with an occasional admixture of iron, lime, and magnesia. 



" The muriatic acid (exhaled from the volcano) acting upon 

 these ingredients, forms severally with them, a quantity of saline 

 matter, proportionate to that in which it is emitted, but the most 

 abundant salt of this class, is the muriate of ammonia, the form- 

 ation of which may, perhaps, be thus accounted for. 



** When muriatic acid is suffered to act upon an alkaline 

 hydrosulphuret, it combines with the base, and separates the 

 sulphuretted hydrogen ; very little, however, of the latter exhales 

 in a gaseous condition, but it is for the most part precipitated 

 in the shape of a heavy oil, which is found by analysis to con- 

 sist of one atom hydrogen, and two atoms sulphur. Now as 

 sulphuretted hydrogen consists of one atom of each ingredient, 

 it follows, that the formation of this body must be accompanied 

 by the disengagement of an equal volume of hydrogen gas. 

 But what becomes of this latter body, since it is not to be 

 detected afterwards in a separate state? It is probable that it 

 has united with the oxygen of the atmosphere, or with its 

 nitrogen, perhaps indeed with both; in the latter case, the 

 presence of the ammonia is explained ; in the former it is ren- 

 dered more comprehensible, since we have many examples in 

 which nitrogen, in its nascent state, is known to unite with 

 hydrogen, held in combination by weak affinities." P. 168. 



The crater of Volcano, one of the Lipari Islands, is in a state 

 somewhat similar to that of the Solfatara. Our author describes, 

 however, the process there going on as so far different, inasmuch 

 as the vapour given out in the crater of Volcano consists of 

 sulphurous acid ; whereas in that of the Solfatara, it was com- 

 posed of sulphuretted hydrogen. The operations, too, of the 

 former appear to be going on with much greater vigour than 

 those of the latter, and exhibit, says our author, perhaps the 

 nearest approximation to a state of activity, during which a 

 descent into the crater would have been practicable. 



" Nor (he continues) can I imagine a spectacle of more 

 solemn grandeur, than that presented in its interior, or conceive 

 a spot better calculated to excite, in a superstitious age, that 

 religious awe which caused the island to be considered sacred 

 to Vulcan, and the various caverns below as the peculiar resi- 

 dence of the god." 



Quam subter, specus, et Cyclopum exesa caminis 

 Antra Etnea tonant, validique incudibus ictus 

 Auditi referunt gemitum, striduntque cavemis 

 Stricturae Chalybum, et fomacibus ignis anhelat 

 Volcani domus, et Vulcank nomine tellus. 



