which accompany theBoracic Acid in the Lagoons of Tuscany. 287 



soffioni which are made use of there commence at less than 1 

 kilometre above the old village of Monte Cerboli, and follow 

 nearly the direction of the valley upon the right of the torrent 

 of the Possera. Monte Cerboli is built upon the abrupt point 

 of a mass of serpentine^ which extends, towards the north-west, 

 to the foot of the hill of San Michele. In its vicinity the calca- 

 reous strata of the alberese are converted into gypsum ; and the 

 traces of these ancient metamorphic influences may be followed 

 up to the present emanations, which are their last representatives 

 and continue their work. 



Our investigations upon the gases of the emanations of Lar- 

 derello were more complete than those made anywhere else. 

 There we examined separately the gases evolved from the highest 

 and lowest of the soffioni which are made use of, — the emana- 

 tions which break forth in the bed of the Possera itself, those 

 which arise from the artesian borings, and lastly those which, in 

 the upper part of the valley, are distinguished by a strong odour 

 of petroleum. 



The following are the numbers furnished by analysis* : — 



Lowest soffione. Highest soffione. 

 Temperature Temperature Mixture of the three un- 



=209°'4 F. =207°'6 F. absorbable residues. 



Hvdrosulphuric acid .... 41 37\nr.i Nitrogen 43"35 



Carbonic acid , 91-6 907 J Hydrogen .... 2856 



Oxygen O'O O'O 27 Protocarbonated "1 qq.qq 



(or traces) hydrogen .... J " 



Nitrogen -f- combustible g as 4'3 5'6 12'2 lOO'OO 



100-00 100-00 100-0 H : C^H^ : 1 : 098 



In order to determine accurately the composition of the com- 

 bustible part, which only exists in a very small proportion (2 to 

 3 per cent.) in the material of the emanations, we collected the 

 gas after having successively passed it through a solution of potash 

 and through concentrated sulphuric acid. Tm'o analyses of the 

 unabsorbed residue gave, — 



I. II. Average. 



Nitrogen 43-68 44-64 44-161 



Hydrogen 25-52 2540 25-46 \ll:C' IV : : 1 : 1-19 



Protocarbonated hydrogen . 30-80 29-96 30-38 J 

 100-00 100-00 100-00 



These analyses are very concordant, and show that, in the 

 soffioni turned to account at Larderello, the relation of the hydro- 

 gen to the protocarbonated hydrogen differs but little from unity. 



The proportion of hydrogen seems to be rather less in the 

 emanations of the ravine of the Possera. The following are the 



* The small quantities of oxygen presented by certain analyses must be 

 attributed either to the imi)erfectiou of the vacuum in the tubes, or, more 

 rarely, to an accidental introduction of air at the moment of collecting the 

 gas. 



