NITROGEN. 195 



teresting character ; some of the most powerful fulminating com- 

 pounds contain it.* 



THE ATMOSPHERE. 



PHYSICAL PROPERTIES. 



(a.) Transparent, colorless, inodorous, only slightly absorbed by 

 water; a bad conductor of heat and of electricity ; the latter when ac- 

 cumulated, passes through the air in a spark, but is diffused through 

 a vacuum in the form of a luminous cloud. 



(b.) The azure color and other hues in the atmosphere, are pro- 

 duced by reflected light. 



(c.) As we ascend, the sky grows darker, and at a great height, 

 the stars with the lustre of silver, are contrasted with a basis of black. 



(d.) Specific weight, 1.; it is unity for all other aeriform fluids ; 

 100 cubic inches, at the medium temperature and pressure, weigh 

 30.50 grains. f Compared with water, it is ji^ of the weight of 

 that fluid. Gallileo ascertained in 1640, that it has weight, and Tor- 

 ricelli introduced the barometer tube in 1643. 



(e.) Absolute weight ; at the ocean level, about fifteen pounds on 

 the square inch, equal to thirty four feet of water, and thirty inches of 

 mercury. Henry. 



(f.) Jls we ascend, the heights being in an arithmetical ratio, the 

 weight decreases in a geometrical ratio ; at three miles elevation, it 

 sustains 15 inches of mercury; at six miles, 7.5 inches; at nine 

 miles, 3f inches ; at fifteen miles, about 1 inch. Id. 



Air is compressed in direct proportion to the force applied. Dou- 

 ble the force will reduce it to half the volume ; double the force 

 again, and its volume will be again reduced one half, that is, to one 

 quarter of its first volume, and so on. A force has been applied to 

 it, equal to 110 atmospheres, and the law stated above, was found 

 still to hold good.J 



* In the Eng. Jour, of Science, Vol. XIX. 17, Mr. Faraday has given an ac- 

 count of an ingenious method of detecting minute portions of nitrogen, by the for- 

 mation of ammonia. D is a glass tube, four or five inches long, and one 

 fourth of an inch in the bore. At a, there is some zinc foil ; at b, a 

 piece of potash ; at c, a piece of turmeric paper moistened with pure wa- 

 ter, at the lower end, which is two inches above the potash ; heat the 

 ft lower end of the tube only in the spirit lamp so a? to melt the potash, and 

 almost instantly, the moistened paper will be reddened, indicating an al- 

 kali, and it is evident that it is ammonia, because the color is discharged 

 when the paper is withdrawn, and the colored part laid on the warm tube. 



Sea sand handled after ignition, yields ammonia, which is discovered by this treat- 

 ment. Ib. 



t Shuckburgh 30.199. Brande, 

 t Ed. Jour. Science, No. VIII, 224, 



