AMMONIA OBTAINED FROM VEGETABLES. 71 



the flowers of the lime tree, yield distilled waters in which ammonia 

 can be detected (Schiibler), the seeds of plants thus distilled yield it in 

 abundance (Gay-Lussac), and traces of it may be found in most vege- 

 table extracts (Liebig). 



4°. Ammonia is also given off, among other products, when wood is 

 distilled in iron retorts for the manufacture of pyroligneous acid, and by 

 a similar treatment it may be obtained from many other vegetable sub- 

 stances. 



The above facts, however, are not to be considered as proofs that am- 

 monia enters directly into the circulation of plants either by their roots 

 or by their leaves. That which is associated with sugar in the beet, may 

 have been formed by the same converting power which, in the intei-ior 

 of the plant, has produced the sugar from carbonic acid and water. So, 

 that exhaled by the leaves of the goosefoot, which grows in waste places, 

 especially near the sea, may have been produced during the upward 

 flow of the sap or during its passage over the leaf. And we knoio that 

 the nitrogen does not exist in the state of ammonia in the seeds of plants, 

 or in wood, or in coal — though from all of them it may be obtained by 

 the processes above described. 



The production of ammonia, by the agency of a high temperature, 

 may be illustrated by a very familiar experiment often performed, 

 though for a very different purpose. The juice and dried leaf of tobac- 

 co contain nitre (nitrate of potash) and a little ammonia. But when 

 tobacco is burned, ammonia in sensible quantity is given off' along with 

 the smoke, chiefly in the state of carbonate of ammonia. This may be 

 shown by bringing a lighted cigar near to reddened litmus paper, when 

 the blue colour will be restored ; or to a red'rose, when the leaves will 

 become green ; or to a rod dipped in vinegar or in dilute muriatic acid, 

 when a white cloud will appear. — [Runge, Einleitung in die technische 

 Chemie, p. 375.] 



In this case a portion of the ammonia given off' by the tobacco has 

 most probably been formed during the combustion, at the expense of the 

 nitrogen cont'ained in the nitrate of potash which is present in the leaf. 



5°. But there are other circumstances which are strongly in favour of 

 the opinion, that ammonia not unfrequently does enter, as such, into the 

 circulation of plants. 



Thus it is proved, by long experiencB, that plants grow most rapidly 

 and most luxuriantly when suppHed with manure containing substances 

 of animal origin. These substances are usually applied to the roots or 

 leaves in a state of fermentation or decay, during which they always 

 evolve ammonia. Putrid urine and night-soil are rich in ammonia, 

 and they are among the most efficacious of manures. This ammonia 

 is supposed to enter into the circulation of plants along with the water 

 absorbed by their roots, and sometimes even by the pores of their leaves. 

 We can scarcely be said to have as yet obtained decisive proof that it 

 does so enter, but probabilities are strongly in favour of this supposition ; 

 and when we come hereafter to consider minutely the mode in which it 

 is likely to act, when within the plant, we shall find the probabilities 

 derived from practical experience to be strengthened by the deductions 

 of theory. 



But though the facts so long observed in reference to the action Ji an- 



