234 ON THE BORACIC ACID OF CENTRAL ITALY. 



actually decompose sulphates formed by the action of sulphuric acid on 

 borates. Before water is introduced into the fissures they are mere 

 soffioni ; borates of several bases are most probably abundant at great 

 depth, and are uninjured by the constant passage of sulphurous 

 vapours, and even sulphuric acid, on their way to the surface, whence 

 the latter escape, but boracic acid is not to be detected. "Water being 

 now introduced lowers the temperature, and the balance of affinities is 

 altered, the powerfully corroding influence of the sulphuric acid on the 

 borates is set in operation, whence the boracic acid is liberated, and 

 ascends in solution with the ejected water and steam. 



The following is the analysis of the dry gases issuing from a soffione 

 examined by Payen : — 



Carbonic acid 57*30 



Nitrogen 34-81 



Oxygen 6-57 



Sulphuretted hydrogen .... 1*32 



100-00 



Respecting the temperature of the fissures, none have satisfactorily 

 treated the question, though it has excited much attention from Pilla, 

 Murchison, Lardarel, &c. I think that some light is thrown on the sub- 

 ject by the presence of an instructive mineral round the lagoons, — viz., 

 Anhydrite (Ca 0. SO s ), evidently fonned at a temperature at which 

 water could not combine with the sulphate of lime to produce ordinary 

 gypsum. When gypsum (CaO. SO 3 + 2 HO) is heated to 260° Fah., it 

 loses its water of crystallization, and becomes plaster of Paris ; but on 

 cooling it again absorbs the original quantity of water. When it is 

 heated to redness this does not take place, but the mass melts into 

 an enamel, which, according to Regnault, is identical with anhydrite. 

 The heat, on the other hand, could not be very much above redness, 

 provided my theory of the borates be correct. 



The first care of the manufacturer is the removal of a certain quantity 

 of clay, and the formation of a Lagone or condensing basin, of more or less 

 circular form, the sides of which have to be strengthened by rough stones 

 to prevent them from falling in, the tenacity of the clay sufficing for the 

 bottom. The usual depth of a lagone is from 4 to 6 feet, more rarely as 

 many yards ; the capacity and depth have to be regulated with the ut- 

 most care, according to the force of the vapour in that particular vent. 

 During the period that the workmen are employed in digging a lagone, 

 the steam is conveyed away into the atmosphere, far above their heads, 

 by means of a tall wooden chimney, which protects them from being 

 scalded. A stream of water has been brought to the uppermost lagoon 

 at Lardarello, from near the Bagno del Morbo, not a quarter of a mile 

 off ; this lagoon is about 15 or 20 yards in diameter, with a jet of steam 



