172 DESCRIPTIVE MINERALOGY. 



Uses. Hydrogen gas may be procured in large quantities by various processes. It was at 

 one time used for filling balloons ; but recently coal gas has been substituted for it, on account 

 of its being cheaper and more convenient. The latter gas, however, being much heavier 

 than pure hydrogen, the balloon must be very large. 



LOCALITIES. 



Hydrogen gas is evolved from various kinds of rocks, as limestone, the coal series, etc. ; 

 also from stagnant waters of various kinds. It is said in some cases to be found pure, but it 

 is most generally mixed with carbon or sulphur. I am not aware of its occurrence in any 

 quantity in a pure form in New- York ; but it is not improbable that, among the abundant loca- 

 lities of carburetted and sulphuretted hydrogen, it may hereafter be found to exist. According 

 to Beudant it is always mixed with the carburetted or sulphuretted hydrogen disengaged from 

 salzes or from fissures in the earth, in their immediate vicinity. 



CARBURETTED HYDROGEN. 



Carburetted Hydrogen Gas. Ckaveland. — Carburetted Hydrogen. Shepard. — Empyreumatisches Hydrogen- 

 Gas. Molis. — Grizou. Beudant. 



Description. Gaseous, colourless and transparent ; soluble in very minute proportions in 

 water. It has an empyreumatic odour. Its specific gravity is from 559 to 570, compared 

 wiih atmospheric air as 1000. 



This gas burns with a flame which is yellowish white or white, apparently according to the 

 relative proportions of its ingredients. It extinguishes burning bodies, is fatal to respiration, 

 and when mixed with atmospheric air or hydrogen gas and ignited, explodes violently. 



Composition. The real composition of this gas, which is known in chemical works under 

 the names of Light Carburetted Hydrogen or Marsh Gas, is carbon 74.87, and hydrogen 

 25.13 ; but its real atomic weight seems still to be a matter of uncertainty. It has usually 

 been thought to be a compound of one atom of carbon and two atoms of hydrogen ; but Kane 

 thinks there is reason to suppose it to be two atoms of carbon and four of hydrogen. As it 

 occurs in nature and under various circumstances, it is probably not constant in its composi- 

 tion. It may sometimes be mixed with variable proportions of these substances in their 

 separate form. Its formula is either CH,, or C.Hj. 



Uses. This gas, in the form in which it is sometimes evolved, may be employed for the 

 purpose of illumination. 



LOCALITIES. 



In the preceding part of this work I have given a full account of the localities of this gas, 

 under the head of Gas or Carburetted Hydrogen Springs (page 128). I will only add here 

 that it issues from clefts in rocks of various kinds, and principally abounds in the western 



