CHEMICAL SCIENCE. 235 



" I have constantly found in the atmosphere a volatile matter, of com- 

 plex composition, which, for some years, I supposed to be due to local 

 exhalations ; but multiplied observations, in different and distinct local- 

 ities, have established its general existence. More lately, this sub- 

 stance has been found by different observers in Europe and this country, 

 coloring and contaminating the salt obtained by the evaporation of 

 rain and snow. Liebig notes its presence in the samples of water he 

 operated upon ; but Zimmerrnann had earlier observed it, and after 

 partially separating it from other substances, called it pyrrhine. This 

 substance, so widely diffused, has characters which lead me to assign 

 to it important influences ; and, connected as it is with ammoniacal 

 products, I deem its study a subject of general interest. It is to this 

 body that \ve may trace the properties of rain, as distinguished from, 

 other waters. 



" When about 50 pounds of recently obtained rain-water are exposed, 

 at a low temperature, in a closed space, to the absorbing action of 150 

 pounds of dry caustic lime, all those substances, not very volatile in 

 an atmosphere formed in part of their own vapors, remain. Successive 

 portions of rain-water maybe thus concentrated, and the fixed parts 

 obtained nearly dry. Generally we find a residue of a gum-resinous 

 appearance, brown or yellow in color, and not wholly soluble in water. 

 In the mass are the remains of animalculse, spores of fungi, and atmos- 

 pheric dust. "\Vaterextracts other substances in mixture with pyrrhine, 

 mineral and ammoniacal salts, if they exist. Alcohol and ether extract 

 parts, but evidently alter the composition of the substance. Obtained 

 from carefully filtered solutions, pyrrhine appears as a brown-yellow, 

 adhesive substance, having a strong odor of perspired matter. Repeated 

 evaporations render it insoluble partly, and it evidently is a changing 

 body, having no fixed composition. In solution, its instability becomes 

 its most marked character, and, like water which has dissolved yeast, 

 the solution has the power of conferring motion and change of compo- 

 sition on other bodies. This character is displayed when it is mixed 

 in solution with vegetable juices, weak syrups, and gum-water. After 

 its solution has been freed from ammoniacal salts, the changes following 

 in its fermentation produce ammonia. It reduces the salts of silver and 

 gold, blackens in concentrated sulphuric acid, forming with this and 

 other strong acids, salts of ammonia. 



" When fertile soil is undergoing fermentation, the vapors by con- 

 densation afford a substance much like pyrrhine. Arable soil has also 

 in its mass a body closely connected with pyrrhine ; but the state of 

 admixture here renders it more compound than where it is obtained 

 from the atmosphere through the aid of falling rain. The constant 

 presence of this body in the atmosphere, the ease with which its con- 

 stituents unite to form ammonia under the presence of acids, leads to 

 the supposition that it has been one, if not the chief source, from which 

 experimenters have obtained ammonia salts. Dissolved in rain-water, 

 and falling on the surface of the earth, this substance can induce 

 changes under the vegetable covering which cannot result from any 

 solution of ammoniacal salts. It has that influence which alone can 

 impart motion, or cause fermentation, and without which neither ger- 



