76 SOURCE AND ASSIMILATION 



Experiments, made in this laboratory (Giessen) 

 with the greatest care and exactness, have placed 

 the presence of ammonia in rain-water beyond all 

 doubt. It has hitherto escaped observation, be- 

 cause no person thought of searching for it. All 

 the rain-water employed in this inquiry was col- 

 lected 600 paces south-west of Giessen, whilst the 

 wind was blowing in the direction of the town. 

 When several hundred pounds of it were distilled 

 in a copper still, and the first two or three pounds 

 evaporated with the addition of a little muriatic 

 acid, a very distinct crystallisation of sal-ammoniac 

 was obtained : the crystals had always a brown or 

 yellow colour. 



Ammonia may likewise be always detected in 

 snow-water. Crystals of sal-ammoniac were ob- 

 tained by evaporating in a vessel with muriatic 

 acid several pounds of snow, which were gathered 

 from the surface of the ground in March, when the 

 snow had a depth of 10 inches. Ammonia was set 

 free from these crystals by the addition of hydrate 

 of lime. The inferior layers of snow, which rested 

 upon the ground, contained a quantity decidedly 

 greater than those which formed the surface. 



It is worthy of observation, that the ammonia 

 contained in rain and snow water, possessed an 

 offensive smell of perspiration and animal excre- 

 ments, a fact which leaves no doubt respecting 

 its origin. 



Hilnefeld has proved, that all the springs in 



