136 Mr Forbes's Physical Notices of the Bay of Naples. 



was put under the direction of the Abbe Breislak, it appears to 

 have been stopped. * At present, however, it is carried on, 

 and apparently in the very same method as formerly, which 

 we find described bv Fougaroux de Bondaroy in the Mevwirs 

 of the Academy of Sciences, -f* The following was the apparatus 

 employed when I visited the spot. Figures 7 and 8 of Plate II. 

 represent the horizontal section and the elevation endways of 

 the furnaces ; the impure sulphur is deposited in the earthen 

 jars B, which are filled from the top e, and the mouths then 

 luted. When fire is placed in the receptacle at A, the sul- 

 phur is sublimed through the tubes a a into the receivers c, 

 also of earthenware, and kept cool by an opening / to the 

 open air. By this simple operation the sulphur is extracted 

 in a commercial state from the earth of the plain lying nearest 

 to the " fumerole."' 



The next production of the Solfatara which we shall notice 

 is the Sulphate of Alumina, the presence of which is easily ac- 

 counted for by the union of the sulphuric acid, of which the 

 origin has been already noticed, with the base of aluminous 

 earth, so abundant in felspathose lavas ; its external charac- 

 ter is generally filamentous or fascicular, and it is extracted 

 in considerable quantities by lixiviating the soil of that part of 

 the plain where it abounds. 37 cwt. used to be annually 

 prepared. J 



The Muriate of Ammonia is one of the most important com- 

 mercial products of the crater. Its occurrence is thus ac- 

 counted for. When muriatic acid combines with a hydrosul- 

 phuret, a portion of hydrogen is disengaged after the deposi- 

 tion of a sulphureous oily matter ; uniting with the compounds 

 of the atmosphere it forms water and ammonia, and the latter 

 combining with part of the muriatic acid is sublimed from the 

 " fumerole'' in the form of sal-ammoniac. Previous to the su- 

 perintendence of the Abbe Breislak, only two hundred weights 



• Spallanzani's Travels^ i. 83. 



t For 1765, 12rao edit. p. 418. 



X Sorae curious particulars of the alum of the Solfatara and a compari- 

 son with that of La Tolfa, near Rome, will be found in the Annales des 

 Mines. 



