256 Transactwns of the American Institute. 



pose it in the light until the water is again charged with air. There 

 is, therefore, some probability that the decomposition of carbonic 

 acid by plants is not a direct, but an indirect action, accomplished 

 through the agency of ozone. Whether this is true or not, it at 

 least aifords a highly interesting and instructive field of inquiry that 

 promises a rich reward to those who elect to reap therein. 



Nitric acid is only found after storms that have been attended by 

 vivid flashes of lightning. It is of little interest. 



The ammonia in the air is one of the products of pntrefiiction and 

 decay. It occurs in largest quantity whenever these changes are tak- 

 ing place. A minute trace is always discoverable ; but small as it is, 

 it bears an important relation to the vegetable kingdom, since it is 

 the natural stimulant of the growth of plants. One of the charac- 

 teristic properties of this substance is its exceeding solubility in 

 water, as is shown by the experiment known as the ammonia foun- 

 tain. Owing to this solubility the rain that descends after a pro- 

 tracted drought seizes upon the accumulated ammonia in the air, 

 and, conveying it to plants, produces the increased richness of verd- 

 ure that follows these storms. 



Of the variable ingredients of the air, the vapor of water is liable 

 to the greatest mutations. These are more or less familiar to us in 

 the fogs and clouds that appear and disappear without visible cause 

 or reason. In addition to the fog-like state, the vapor of water also 

 possesses a colorless, transparent condition, as in the experiment we 

 havetarranged in which water is boiling in a flask. The interior of 

 the vessel is, of course, filled with steam or vapor of water, but it is 

 as invisible as the atmospheric air. It is only when it issues from the 

 jet that it presents the fog-like condition. If we place a thermometer 

 in this issuing cloud the temperature is below the boiling point of 

 water, and if we let the steam fall on a sli]> of glass and place it under 

 the microscope we discover that the glass is covered with minute 

 vesicles or bladders of water. We therefore conclude that the fxDg- 

 like appearance is not steam, but condensed water ; true steam being 

 colorless and invisible, as we have just demonstrated. In its physio- 

 logical relations the vapor of water in the air presents facts of inte- 

 rest. It is a well established law that the rate of vaporization is 

 dependent upon the amount of vapor already existing in a given 

 space. When, therefore, the air is already saturated, as we might 

 say, with aqueous vapor, the escape of the insensible perspiration or 

 vapor from the lungs and skin is interfered with, and the slightest 



