162 WRITINGS OF JOSEPH HENRY. [1855- 



vegetable life, and deserve the special attention of the agri- 

 cultural chemist. 



Analysis of the Air. — But before proceeding to give an 

 account of these, it may be well to pause here for a moment 

 to describe the simplest* method by which the constitution 

 of the air may be approximately analyzed. For this pur- 

 pose we introduce into a large glass vessel filled with ordi- 

 nary air a small quantity of limpid lime water, or better 

 still, baryta water, and having closed the vessel agitate the 

 liquid. All the soluble substances, including the carbonic 

 acid, will be absorbed. The latter will unite with the lime 

 or baryta water and form insoluble carbonates, which may 

 afterwards be separated from the water, dried and weighed, 

 and the amount of carbonic acid thus determined. To obtain 

 the amount of vapor in a given quantity of air the latter is 

 drawn through a tube containing chloride of lime, a sub- 

 stance which has a great aflBnity for moisture. The increase 

 of weight found after the process will indicate the amount 

 of water in the portion of air submitted to the experiment. 

 The volume of this air may be readily ascertained by attach- 

 ing the tube containing the chloride of lime to the upper 

 part of a vessel, say a cubic foot in capacity, filled with water, 

 from which the liquid is suffered to run out by an orifice 

 at the bottom ; an equal bulk of air will enter through the 

 tube containing the chloride, and when all the water has 

 run out, the vessel will be filled with air, or in other words, 

 one cubic foot of the moist atmosphere will have passed 

 through the drying tube. The quantity of aqueous vapor 

 is more variable than that of the carbonic acid. 



After having separated the water and carbonic acid, in 

 order to ascertain the amount of oxygen and nitrogen in a 

 cubic foot of air, we burn in the mixture a piece of phos- 

 phorous, which combines with every atom of the oxygen, 

 forming a soluble substance called phosphoric acid, which is 

 absorbed by the water, leaving the nitrogen in a separate 

 state. Other and more refined methods are frequently em- 

 ployed, but this will serve to indicate in a general way the 

 mode in which the results are obtained. In this manner, 



