1 24- Mr Forbes's Physical Notices of the Bay of Naples. 



This result comes surprisingly near 6.5^ when we consider 

 the round-about method by which it is obtained, and amply 

 confirms that already obtained by direct analysis. 



6. To sum up the results contained in this paper, we have 

 found, 



First, That the salt analyzed is a 6i-cyanide. 



Second, That 100 grains of the salt give off by heat about 

 31 cubic inches of cyanogen. 



Third, That what is wanting to make up the whole two 

 atoms of cyanogen is converted into a black carbonaceous 

 substance, consisting of carbon and azote in the same propor- 

 tions. 



It is possible that the volume of cyanogen given off, though 

 nearly constant in the four experiments above stated, may at 

 times vary. According to these experiments, about one-sixth 

 of the whole is converted into the black solid compound, or 

 from every three atoms of the salt we obtain one atom in this 

 slate. 



This solid 6i-carburet of azote I have described in the pa- 

 per on the Carburets of Azote, above alluded to. 



PoRTOBELLo, ^Oth May 1829. 



Art. XX. — Physical Notices of the Bay of Naples. By 

 James D. Forbes, Esq. Communicated by the Author. 



No. IV. — On the Solfatara of Pozzuoli. 



" Neapolim inter 

 Et Cumas, locus est miiltis jam frigidus annis 

 Quamvis jetemum pinguescat ab ubere sulphur." 

 Corn. Severus. 



The next object which demands our attention in a survey of 

 the Phlegraean fields is the Solfatara of Pozzuoli, generally 

 considered after Vesuvius the most important feature of the 

 Bay of Naples. So much, however, has been written on the 

 subject, that, had not its importance required a separate ar- 

 ticle, I should willingly have passed it over more slightly ; for 

 it would be difficult, without a continued residence on the spot, 



