234 



PRINCIPLES OF CHEMISTRY 



Air always contains more or less moisture 2G and carbonic anhydride,. 

 proceeding from the respiration of animals and the combustion of 

 carbon and carboniferous compounds. The latter shows the properties. 



J?IU. 39. Apparatus for the absorption and 

 washing of gases, known as Liebig's 

 bulbs. The gas enters m, presses on the 

 absorptive liquid, aud passes from m into 

 6, c, d, and e consecutively, and escapes 

 through/. 



FIG. 49. Geisler's potash bulbs. The gas enters- 

 at a, and passes through a solution of potash 

 in the lower bulbs, where the earl ionic anhy- 

 dride is absorbed, arid the gas escapes from 1>. 

 The lower bulbs are arranged in a triangle, 

 SD that the apparatus can stand without 

 support. 



of an acid anhydride. In order to determine the amount of carbonic 

 .anhydride in air, substances are employed which absorb it namely, 

 alkalies either in solution or solid. A solution of caustic potash, KHO, 



is poured into light glass vessels, through 

 which the air is passed, and the amount 

 of carbonic anhydride is determined by the 

 increase in weight of the vessel. But it is 

 best to take a solid porous alkaline mass, 

 such as soda-lime. 27 With a feeble current 

 of air a layer of soda-lime 20 c.m. in length 

 is sufficient to completely deprive the 

 air of the carbonic anhydride it con- 

 FIG. 4i. Tube for the absorption of tains. A series of tubes containing calcium 



carbonic acid. A wad of cotton 



wool is placed in the bulb to prevent 



the powder of soda-lime being which occurs in the heavenly space. If, for instance^ 



carried off by the gas. The tube the amount of oxygen were diminished, then it would 



aSE"*!* 11 * 1 * 1 Chl ride f be replenished at the expense of the oxygen pervad. 



ing the space of the heavens. 



* The amount of moisture contained in the air is considered in greater detail by 

 physics and meteorology, and the subject has been mentioned above, in Chapter I. note 1, 

 where the methods of absorbing moisture from gases were pointed out. 



27 Soda-lime is prepared in the following manner : Unslaked lime must be reduced to a 

 fine powder and mixed with a slightly wanned and very strong solution of caustic soda. The 

 mixing should be done in an iron dish, and they should be well stirred together until the lime 

 begins to slack. When the mass becomes hot, it boils, swells up, and solidifies, forming a 

 porous mass very rich in alkali and capable of absorbing carbonic anhydride. A lump of 

 caustic soda or potash presents a much smaller surface for absorption, and therefore 

 acts much less rapidly. It is necessary to place an apparatus for absorbing water after 

 the apparatus for absorbing the carbonic anhydride, because the alkali in absorbing the 

 latter evolves water. 



