which accompany the Boracic Acidin the Lagoons of Timcamj. 291 



The fissure which unites the two centres of emanations of 

 Monte Rotondo and Sasso is extremely interesting to study in 

 regard to the modifications which these emanations undergo 

 from the bottom of the valley up to the summit of the ridge. 

 A little above Monte Rotondo vapours are met with issuing from 

 the soil at 209°*3 F. : although they are not put to any use, and 

 under the intluence of the air they become acidified and alumi- 

 nize the schists, they have a composition absolutely similar to 

 those of the lower soffioni, and are, like the latter, free from 

 oxygen. 



In proportion as we ascend, following the fissure, the action 

 of the air which penetrates into the interstices of the rock oxi- 

 dizes the sulphuretted gases, and produces true solfataras with 

 their accompaniments of alum, sulphate of lime, sulphur, &c. 

 These phtenomcna go on constantly diminishing in intensity up 

 to the little ridge, where we still meet with emanations at a tem- 

 perature of 194° F., consisting principally of aqueous vapour, 

 but carrying with them also traces of hydrosulphuric acid, and 

 small quantities of carbonic acid, and even depositing traces of 

 sulphm". Lastly, some hot acidulous or aluminiferous springs 

 occur on the slope of Sasso, as on that which faces INIonte 

 Rotondo. 



From the totality of these phenomena it is impossible not to 

 recognize relations of analogy between the causes which produce 

 boracic acid in Tuscany, and those which give rise to the trans- 

 portation and deposition of silica in the solfataras, and especially 

 in the geysers of Iceland. 



To recapitulate, this first portion of our memoir leads us to 

 the following conclusions : — 



1. The temperature of the gases, both in the soffioni and in the 

 artesian wells, sometimes attains, but never exceeds, 212° F. at 

 the surface, although the rapidity of the evolution seems to indi- 

 cate an internal pressure. 



2. All the emanations contain the same gases, the proportions 

 of which even are but slightly variable. As had been ascertained 

 by M. Payen, carbonic acid is the predominant gas. The pro- 

 portion of hydrosulphuric acid to carbonic acid was, at the maxi- 

 _ urn, 6-4* to 93-6. Oxygen appears to be entirely wanting. 

 Nitrogen, on the contrary, always exists in them in the propox'- 

 tion of 2 or 3 per cent. 



3. Lastly, a fact which has never yet been pointed out is the 

 following, — all the gases without exception contain a mixture of 

 free hydrogen and protocarbonatcd hydrogen (C^ H'*), of which 

 the sum attains on the average that of the nitrogen. Upon the 

 fissure which joins Larderello and Castelnuovo, the proportion 

 of the two combustible gases is nearly unity, the carbonated 



U2 



