REPORT ON MINERAL AND THERMAL WATERS. 39 



feet in 24 hours, whereas the water in the same time emitted 

 was calculated at 259 cubic feet ; and Bischoff notices one 

 spring which gave out in the same time 4237 c. f., the water 

 being 1157 c. f. and containing 1909 cubic inches of this 

 gas, and another which evolved of gas 3063, and of water 

 3645 cubic feet, which contained of gas 871. 



Such statements are worth recording, as enabling our suc- 

 cessors to ascertain whether there be any secular variation in 

 the quantity of gas evolved; and it is therefore to be regretted, 

 that Bischoff has not mentioned the names of the springs which 

 he had examined with reference to this point. 



The uninterrupted manner in which the carbonic acid rises 

 up through the spring is explained by Bischoff, by supposing 

 it held in chemical solution by the water at a great depth, and 

 therefore under an enormous pressure. 



Such a supposition would enable us to understand the trifling 

 irregularities observed in the flow of gas, without imagining 

 that the state of the atmosphere above has any direct influence 

 upon the energy of the volcanic operations below, since the 

 barometric pressure, the relations to moisture, &c. of the air 

 surrounding the spring, might favour at one time more than at 

 another the escape of gas from the spring, or its diffusion 

 through space. Some have supposed*, that the water of the 

 spring is iPorced upwards by the elasticity of the confined gas, 

 but Bischoff justly remarks, that the flow of the former is too 

 equable for any such thing to happen. 



An explanation of this kind can only be resorted to in such 

 cases as those of the Sprudel at Carlsbad, and at the Geysers 

 in Iceland, where the spring appears, as it were, by fits and 

 starts. 



Yet in these cases the phsenomenon may, perhaps, be more 

 readily accounted for by the extrication of steam in cavities 

 connected with the fissure through which the spring rises, as 

 was first suggested by Sir G. Mackenzie f. Dutrochet, how- 

 ever, has described an intermitting -spring in the Jura, which he 

 ascribes with more reason to a periodical evolution of carbonic 

 acid gas ; though, even here an accumulation of gas taking 

 place in a cavity connected with the spring, may have been 

 competent to produce the phenomenon. 



That Nitrogen escapes occasionally from thermal springs, is Nitrogen. 

 by no means a new discovery, for it was remarked by Priestley 



* Berthier, Annales de Chimie, vol. xix. f Travels in Iceland, 



