176 DESCRIPTIVE MINERALOGY. 



the water several feet into the air ; but the gas soon diminished in quantity, and can now be 

 observed rising only in small bubbles through the bed of the stream (see page 137). 



The carbonic acid which is given out by various mineral waters is sometimes in a free 

 state, as is the case at Ballston and Saratoga, where large bubbles rise through the water at 

 regular and short intervals ; or it holds in solution various bases in the form of bicarbonates, 

 which, as soon as a portion of the acid is evolved, are deposited as simple carbonates. Such 

 phenomena are observed at the brine springs in Onondaga county and elsewhere, and at those 

 which are called ■petrifying springs, of which there are many in Western New- York. 



As I have already noticed this subject at length under the head of mineral springs, it will 

 be unnecessary to add further particulars (see page 134). 



ATMOSPHERIC AIR. 



Atmospheric Air. Shepard and Dana. — Reines Atmosphar-Ga*. Mohs, 



Description. Gaseous, transparent, tasteless and inodorous ; sparingly absorbed by water. 

 When in large masses, it reflects a blue colour. Its specific gravity is taken as the standard 

 for all gases and vapours, and is therefore 1000. It is about 780 times lighter than water at 

 40.5 Fahr., when water is at its greatest density, and is then also 10,600 times lighter than 

 quicksilver. Kane. 



Composition. The constituents of atmospheric air, are nearly as follows, viz : Nitrogen 

 gas 75.88, oxygen gas 23.04, watery vapour 1.03, carbonic acid 0.05. These ingredients, 

 however, are thought to be rather in the form of mixture than of true chemical combination. 

 Their proportions are moreover liable to slight variations from general and local causes. 



Atmospheric ciir is sometimes given out through tlie clefts of rocks, and is associated with 

 the other gaseous minerals which are peculiar to certain springs. Thus Dr. Daubeny states 

 that the gaseous matter evolved by the water of the Lebanon spring consists of about fifty 

 parts of atmospheric air and fifty parts of nitrogen, in the hundred. Small quantities of air 

 have also been detected in several of the Saratoga springs. In this case its origin is probably 

 the same as that of the other gaseous contents. The air which is uniformly found in the 

 water of firesh water springs may also, I think, be referred to some deep seated and general 

 agency. 



That atmospheric air does find its way into the interior of the earth, through the cracks and 

 fissures with which its crust is every where intersected, the large cavities it so frequently 

 envelopes, and perhaps through its porous and permeable structure, is an idea which seems to 

 be sufficiently well sustained. If such is really the fact, it will not be difficult to account for 

 the occurrence of atmospheric air, and occasionally of pure nitrogen, in the waters of certain 

 springs. To account for the latter, we have only to suppose that certain processes, occa- 

 sioning the abstraction of oxygen from common air, are going on in the interior of the earth.* 



* See Dr. Daubeny's Report on Mineral and Thermal Waters. Reports of the British Association for the Advancement of 

 Science f 1636. 



