No. IV. — On the Solfatara of Pozzuoli. 1,S7 



of this salt * were annually procured. By an adaptation of 

 a number of tubes of baked earth united in one large reci- 

 pient, he succeeded in obtaining it in larger quantity. By 

 inspecting the account of this salt in his " Essais Mmeralo- 

 giques snr la Solfatara^'' we may form an idea of the extreme 

 uncertainty of chemical science at a period not very distant, 

 when that work was written. 



Sulphate of Lime or Gypsum in an earthy state is an ex- 

 tremely abundant production of this crater, particularly on the 

 exterior side next the lake Agnano, where the Monte Secco, from 

 which the water of La Pisciarella flows, is chiefly composed 

 of it. It seems difficult to account for the abundance of this 

 mineral ; for it would be hard to believe that the vast beds 

 ■which now appear on the surface should have been solely pro- 

 duced by the filtration of spring waters bringing from the deep- 

 seated limestone strata particles of the rock from which the 

 carbonic acid has been expelled by the superior affinity of the 

 sulphuric. It has been suggested that the origin of these 

 gypseous depositions is owing to the calcareous masses ejected 

 by the volcano when in a state of activity. This certainly is 

 rather hypothetical, nor, judging from the example of Vesuvius, 

 can we suppose it very adequate to the effect. T should think 

 it would be more plausible to suppose that a bed of Apennine 

 limestone had once cropped out from beneath the volcanic for- 

 mations, which, as this is one of the most active foci in the 

 neighbourhood, is rendered more probable from the theory of 

 the parallel lines of eruptive energy. The sulphate of lime, 

 which can be derived from the decomposition of the lavas of 

 the Solfatara (in which only 1 per cent, of lime occurs) is 

 quite insufficient to account for the effect ; they only produce 

 some small radiated specimens, which are occasionally met with. 



The Sulphates of Magnesia and of Soda each occur but in 

 a single part of the Solfatara, and the rarity of the former as a 

 volcanic mineral is rather to be wondered at, since it forms 

 about /j of the mass of the surrounding rocks. The origin 

 of the latter salt has excited some debate ; but if we admit 

 that sea- water is an agent in the production of volcanic phases, 



• Lalande. 



