PRODUCTS 0" PUTREFACTION. 43 



vals of time between the showers are in summer greater ; and 

 when several wet days occur, the rain of the first must contain 

 more of it than that of the second. The rain of a thunder-storm, 

 after a long- protracted drought, ought for this reason to contain 

 the greatest quantity conveyed to the earth at one time. 



But all the analyses of atmospheric air hitherto made have 

 failed to demonstrate the presence of ammonia, although, accord- 

 ing to our view, it can never be absent. Is it possible that it 

 could have escaped our most delicate and most exact apparatus ? 

 The quantity of nitrogen contained in a cubic foot of air, as am- 

 monia, is certainly extremely small, but, notwithstanding this, 

 the sum of the quantities of nitrogen from thousands and millions 

 of dead animals is more than sufficient to supply all those living 

 at one time with this element. 



From the tension of aqueous vapor at 15° C. (59° F.)=0,98 

 lines (Paris measure), and from its known specific gravity at 

 0° C. (32° F.), it follows that when the temperature of the air is 

 59° F. and the height of the barometer 28", 1 cubic metre, or 

 35-3 cubic feet of aqueous vapor are contained in 48-1 cubic 

 metres, or 1698 cubic feet of air ; 35-3 cubic feet of aqueous 

 vapor weigh about 1^ lb. Consequently, if we suppose that 

 the air saturated with moisture at 59° F. allows all the water 

 which it contains in the gaseous form to fall as rain, then 1 pound 

 of rain-water must be obtained from every 1132 cubic feet of 

 air. The whole quantity of ammonia contained in the same 

 number of cubic feet will also be returned to the earth in this 

 one pound of rain-water. But if the 1132 cubic feet of air con- 

 tain a single grain of ammonia, then the few cubic inches usually 

 employed in an analysis must contain only 0-0000048 of a 

 grain. This extremely small proportion is absolutely inappre- 

 ciable by the most delicate and best eudiometer ; it might be 

 classed among the errors of observation, even were its quantity 

 ten thousand times greater. But the detection of ammonia must 

 be much more easy when a pound of rain-water is examined, 

 for this contains all the gas that was diffused through 1132 cubic 

 feet of air. 



If a pound of rain-water contain only £th of a grain of am- 

 monia, then a field of 26,910 square feet must receive annually 



