EFFECT OF AMMONIA UPON VEGETATION. 89 



periment. The sap and dried leaves of this plant contain 

 nitrate of potash (saltpeter) and a small quantity of am- 

 monia. When the dried leaves are burned ammonia is 

 given off in sensible quantities with the smoke, and can be 

 detected by bringing a piece of reddened litmus paper into 

 contact with the smoke when the color will be changed to 

 a blue ; or by using a feather dipped into vinegar or any 

 weak acid, the white cloud of carbonate of ammonia will 

 appear. (Litmus paper is used for testing the presence of 

 acids and alkalies. It is absorbent paper steeped in a red or 

 blue vegetable coloring matter, as the juice of red cabbage, 

 of the red beet, or of the berries of the poke root. Litmus 

 is a red color obtained from some species of lichens, and is 

 changed to blue by ammonia. An alkaline liquid or vapor 

 will change the red to blue, and an acid will change the 

 blue to red again. This test can be used by farmers in a 

 variety of ways ; in detecting the escape of ammonia from 

 manure, or acidity in milk). 



In this case however the ammonia may be in part pro 

 duced by the combustion, which decomposes the water con- 

 tained in the tobacco to the extent of 14 per cent, in its 

 usual air dry condition and thus disengages hydrogen, 

 which can easily combine with the nitrogen disengaged in 

 the combustion of nitrate of potash present in the leaves, 

 and so form ammonia. 



But there are other circumstances which tend to favor 

 the belief, in a much stronger manner, that ammonia does 

 enter into the circulation of plants in many cases. 



Experience has shown that plants grow most rapidly and 

 luxuriantly when liberally supplied with manures con- 

 taining animal substances. Dried blood ; fish scrap ; guano ; 

 the dung of fowls ; decomposed urine and night soil; are all 

 rich in ammonia and are the most efficacious of manures. 

 The same is true of the salts of ammonia, These substances 

 are used when in a state of decomposition and when the 

 evolution of ammonia is in most active progress. Flowering 

 plants also grow with greater luxuriance when a small 

 quantity of ammonia is added to the water given to them. In 



