TRUE VOLCANOES. 441 



influence exerted, according to the admirable investigations 

 of Percival, Saussure, Boussingault and Liebig, by three 01 

 four ten-thousandth parts of carbonic acid in our atmo- 

 sphere on the existence of the vegetable organism. From 

 Bunsen's excellent work on the different kinds of volcanic 

 gas, it appears that among the fumaroles of different stages 

 of activity and local diversity, some (as for example at Hecla) 

 yield from 0.81 to 0.83 of nitrogen, and in the lava-streams 

 of the mountain 0.78, with mere traces (0.01 to 0.02) of 

 carbonic acid, while others in Iceland, as for instance near 

 Krisuvik, on the contrary, yield from 0.86 to 0.87 of car- 

 bonic acid, with scarcely 0.01 of nitrogen. 62 We find like- 

 wise in the important work on the emanations of gas in 

 Southern Italy and Sicily by Charles Sainte-Claire Deville 

 and Bornemann, that there is an immense proportion of 

 nitrogen gas (0.98) in the exhalations of a fissure situated 

 low down in the crater of Vulcano, while the sulphuric 

 acid vapours show a mixture of 74.7 nitrogen gas and 18.5 

 oxygen, a proportion which approaches pretty nearly to the 

 composition of the atmospheric air. On the other hand the 

 gas which rises from the spring of Acqua Santa 53 in Catania 

 is pure nitrogen gas, as was also the gas of the Yolcancifcos 

 de Turbaco at the time of my American journey. 64 



Are we to conclude that the great quantity of nitrogen 

 dispersed through the medium of volcanic action consists of 

 that alone which is imparted to the volcanoes by meteoric 

 water ? or are there internal and deeply-seated sources of 

 nitrogen ? It must also be borne in mind that the air dis- 

 solved in rain-water does not contain, like the atmosphere, 

 0.79 of nitrogen, but according to my own experiments, only 



withstanding the immense extent of the ocean and the trifling 

 amount of surface presented to it by the ships which traverse it, 

 yet the trace of silver in the sea-water has in recent times become 

 observable on the copper-sheeting of ships. 



62 Bunsen, Ueber die chemischen Prozesse der rullcanischen Gesteins- 

 bildungen in Poggend. Annalen, Bd. Ixxxiii, s. 242 and 246. 



53 Comptes rendus de FAcad. des Sciences, t. xliii, 1856, pp. 366 

 and 689. The first correct analysis of the gas which rushes with noise 

 from the great solfatara of Pozzuoli, and which was collected with 

 great difficulty by M. Ch. St.-Claire Deville, gave the following results : 

 sulphurous acid (acide sulfureux) 24.5, oxygen 14.5, and nitrogen 

 61.4. 



* See above, pp. 211- 218. 



