DETECTION OF NITRATES IN THE SOIL. 251 



bodies are formed which are capable of combining immediately : 

 nitric acid, on one hand, and on the other water, without which this 

 acid could not exist. The phenomenon, however, only takes place 

 in this instance at a considerably elevated temperature. At ordi- 

 nary temperatures, combustion of the elements of ammonia has not, 

 as far as 1 know, yet been observed ; and in a series of experiments 

 which I undertook, proceeding all the while upon ideas completely 

 in conformity with those advanced by Liebig, I did not succeed in 

 forming any nitrates by enclosing mixtures of chalk, potash, «&c., in 

 an atmosphere composed of oxygen and ammoniacal vapor. 



In a communication made to the Academy of Sciences, M. Kuhl- 

 man announces that he had ascertained the presence of nitrate of 

 ammonia in the products of the putrefaction of animal matter. If 

 this announcement be confirmed, if nitric acid be in reality one of 

 the numerous products of the putrid fermentation, the nitrification of 

 soils in contact w-ith organic matters would be readily explicable. 

 I must say, however, that I have sought in vain for nitrate of ammo- 

 nia in the product of the putrid fermentation of caseum. And after 

 all, we should still be at a loss to account for the formation of nitre 

 in many places, where it appears to be produced in the absence of 

 organic matter, as in the saltpetre soils of India, South America, 

 and Spain. Dr. John Davy, who visited the nitre districts of Cey- 

 lon, and Proust, who long inhabited the Peninsula, have given it as 

 their opinion that the nitre appears in soils which contain no vestiges 

 of organic matter. The assertion of Proust, however, is open to 

 suspicion, inasmuch as in his memoir he affirms that the lands close 

 to those that produce the nitre are extremely fertile, so that they 

 yield abundant crops without ever receiving manure. But at the 

 present day, it is a law that every fertile soil must contain or receive 

 dead organic matter. In Ceylon, according to Davy, the caverns, 

 the walls of which become covered with an efflorescence of salt- 

 petre with such rapidity, have a fertile and thickly wooded soil lying 

 over them, the percolations from which may readily penetrate their 

 interior. The observations which I had an opporti' lity of making 

 upon the nitre soils near Latacunga, were not perhaps of sufficient 

 precision ; but I think I can affirm that the soil was not without hu- 

 mus : patches were perceived here and there that were covered with 

 turf It must still be admitted, however, that in the localities which 

 have been particularly indicated there must exist some peculiar and 

 permanent cause of nitrification ; inasmuch as in other and fertile 

 soils, saltpetre only appears as it were accidentally, and never in 

 extraordinary quantity. 



Whatever the value of the ingenious but still very imperfect theo- 

 ries of nitrification, it is still of importance to ascertain the exist- 

 ence or absence of nitrates in the soil. Wollaston recommended 

 a process which enables us to do this very readily. It is founded 

 on the property possessed by the aqua regia — a mixture of the nitric 

 and hydrochloric acids — to dissolve pure gold, which, as^is familiarly 

 knuwn, resists the action of either of these acids applied separately. 

 The soil in which the presence of a nitrate is suspected ie treated 



