CHEMISTRY. 



ways, of which the most simple is to burn out 

 ^^ ' the oxygen from a confined portion of air, in a 



bell-glass inverted over a dish of water, by 

 means of a piece of phosphorus ; the phosphorus 

 is converted into phosphoric acid, and the re- 

 maining gas is tolerably pure nitrogen. A purer 

 gas may be obtained by passing atmospheric air 

 over copper heated to redness ; or by passing 

 chlorine through a solution of ammonia, (nitro- 

 gen and hydrogen ;) in this last case there is a 

 risk of the formation of the chloride of nitrogen, 

 a very explosive compound. 



Projp. — Distinguished for its negative proper- 

 ties ; destitute of colour, taste, or smell ; a non-supporter of combus- 

 tion and life ; has no noxious properties ; is not inflammable ; sp. gr. 

 •972 ; Eq. = 14-15 ; Symb. N. 



Nitrogen forms five compounds with oxygen, and one mixture, 

 viz. : the atmosphere. 



The atmosphere is composed of about ^ths of nitrogen, ith of 

 oxygen, and some carbonic acid and watery vapour. The air may 

 be analyzed either by burning a piece of phosphorus in a known 

 portion of it, or by passing it over finely divided copper, heated to 

 redness, or by mixing it with hydrogen in definite proportions, and 

 exploding the mixture by the electric spark ; the last method is best 

 accomplished by means of a eudiometer — a stout glass tube, so ar- 

 ranged that known bulks of gas can be measured. Suppose 100 

 measures of atmospheric air be mixed with 50 of hydrogen, and the 

 mixture exploded ; the volume, after explosion, will be found reduced 

 to 87 measures ; hence there has been a diminution of 63 measures, 

 of which one-third, or 21 measures is oxygen; the remaining two- 

 thirds is hydrogen. 



P/o/?. — Colourless and invisible; when pure, has no taste or 

 smell ; sp. gr. 1 ; it is 800 times lighter than water at 60°. At the 

 level of the sea, it exerts a pressure of 15 pounds on every square 

 inch, and is capable of supporting a column of water 34 feet high, 

 and one of mercury 30 inches ; that is, a column of mercury one 

 inch square and 30 inches long, has the same weight (nearly 15 

 pounds) as a column of water 34 feet long, and as a column of air • 

 of equal base reaching to the extreme limit of the atmosphere. 



The density of the atmosphere varies with the altitude ; diminish- 

 ing as the height increases. Height of the atmosphere not absolutely 

 known ; — believed to be about 45 miles. From this fact arises the 

 value of the barometer as an instrument for measuring heights, since 

 as the elevation increases in arithmetical progression, the density 

 dimiiiishes (or the barometer falls) in geometrical progression. 



The barometer is a glass tube closed at one extremity, a little 

 over 30 inches in length ; it is filled with mercury, and then inverted. 



