216 IS NITRIC ACID FOOD FOR PLANTS ? 



ammonia), and conducted in this cavern, in order to see whether 

 nitric acid would be formed, would have completely decided the 

 question, if nitric acid had been found in the mixture after a cer- 

 tain time ; but this experiment was not made, neither was the 

 water which filtered through the roof of the cavern subjected to 

 examination. The conclusion that nitric acid is formed in these 

 cases, at the expense of the nitrogen of the air, is not in any way 

 confirmed — it is only certain that the cause of the formation 

 of nitre in these caves remains unknown to those who have ex- 

 amined them. 



It often happens that the well-water of towns contains a con- 

 siderable quantity of nitre which does not exist in the wells and 

 springs outside the towns. Berzelius detected nitrates in the well- 

 water of the city of Stockholm. Margraf also mentions its Ex- 

 istence ; and I, myself, have shown the presence of nitrates in 

 the waters of twelve wells in the town of Giessen,* although they 

 could not be detected in the waters of six wells separated 2300 

 paces from the town. Animal matter, in a state of decay and 

 putrefaction, existed abundantly in the soil in all the places where 

 nitrates were found, and its nitrogen was converted into ni- 

 tric acid wherever the conditions for this conversion were found 

 united. 



A large proportion of the nitre used in France, for the manu- 

 facture of gunpowder and for other purposes, is obtained at Paris. 

 The manufacturers of nitre use in its preparation the lower par's 

 of old broken-up houses, which have been in constant contact 

 with the liquids of the street. Nitre exists in large quantity in 

 the lower parts of houses, while the upper parts do not contain a 

 trace of it. 



It cannot be denied that plants grow more powerfully and 

 luxuriantly in a soil capable of forming nitre, than they do in a 

 soil unfit for its formation. 



The favorable influence of such a soil on vegetation is justly 

 ascribed to the animal matters contained in it, to the alkalies, and 

 to the phosphates existing in the animal matter. Out of the ani- 

 mal matter also, is formed the ammonia so necessary for the sup- 



* Annates de Chimie et de Physique, vol. xxxv., 232. 



