310 REPORT ON NITRIFICATION 



would accumulate on tlie surface by reason of the continued evapora- 

 tion going on there, a process which tends to draw up soluble matters 

 of all sorts from below, and to deposit them above; for the water, as 

 it evaporates, leaves behind it the non-volatile substances dissolved 

 in it, and, after evaporation, is replaced b}^ fresh fluid from the deeper 

 and moister parts of the ground, which brings with it fresh supplies 

 of soluble matter. Either of the modes mentioned will account for 

 the formation of the nitrates, supposing their origin to be from organic 

 matter, and will account for any case in which they accumulate on 

 the surface of the ground during dry and warm weather. 



In various other countries the soil, in certain localities, becomes 

 impregnated with considerable quantities of nitrates. This is the 

 case in Persia, in Egypt, in Hungary,* and in Spain. The product is 

 of less importance than that of Hindostan, and the explanation of it 

 probably depends upon the same principles. 



The production of nitre in the open air, in such quantities as to be 

 of value, only takes place under particular circumstances, but in caves 

 a considerable amount of nitrates is often protluced. The earth cov- 

 ering the floor of caverns containing ammonia-producing matters as 

 well as mineral salts, the oxidation of the ammonia into nitrates takes 

 place wherever the air is not entirely stagnant; and being protected 

 from the rain, the nitrates Avill accumulate, until, after a series of 

 years, the quantity becomes considerable. Longchamp remarks, 

 that the earth in caves nitrifies itself sufficiently for extraction in 

 eight or ten years. Whether we suppose the nitrates to be produced 

 entirely from ammonia or not, the conditions furnished by a cavern, 

 of protection from the weather, together with a moderate and uniform 

 degree of moisture, will be equally operative. 



In the western part of this country many caves exist, especially in 

 the geological formation known as the cavern limestone, which have 

 the earth on their floors impregnated Avith nitrates, t The most noted 

 of these is the Mammoth Cave of Kentucky. During the war of 1812 

 they were pretty industriously worked for nitre, and, it is said, in 

 large part exhausted. What the exact amount got from them was 

 I have no means of ascertaining; nor have I seen any systematic cal- 

 culation of what is probably obtainable from them now since they 

 have had time to re-nitrify themselves.:}: All approximative estimates 

 of those who are best informed put it down at but a fraction of the 

 present annual consumption ;§ but on this point I speak more from 



^ Nitre is found iu Hungary in large quantity, mostly in boggy places, and in those 

 subject to inundation: there is also much artificial production of it there. 



f The formation of nitrates iu these caves may in some part be due to a kind of nitrifi- 

 cation described further on, (page 312) which takes place on the surface of the rock itself 



J The nitrate produced in these caves is nitrate of lime, which has to be converted into 

 saltpetre by the action of a solution of carbonate of potash. Having to furnish the potash 

 adds greatly to tlie expense of obtaining nitre from such sources .Supposing that we used 

 commercial potash, 100 pounds of the best American ash would be required to form 133 

 pounds of nitrate of potash. The difirculty of supplying a sufliciency of potash became a 

 serious obstacle in the working of these caves. The wood wluch grew near the scene of 

 operations was burnt in large quantity, and the ley extracted from its ashes usc;d. Here, 

 however, this impediment arose, that the country being, for the most part, purely lime- 

 stone, the ashes of plants growing there are much less rich in potash than in lime. 



§1 have heard the amount estimated at 150,000 pounds. 



