SEC. 1.]

Nitrate of Potassa.

dirt,” the other the “ black dirt.” The earth, however, con-tains calcareous nitre, and for that reason an alkaline i-vium is employed. In short, the process employed there isthe same as at the other saltpetre caves which we have des-cribed. One bushel of the clay dirt yields from three tofive pounds of nitre, and the black dirt from seven to tenpounds. It seems also, that the same dirt, if carried back tothe cave, will become impregnated with nitre.

Mr. Cornelius remarks, that these caves have been usedby the natives as burial places; in one of which he counted ahundred human skulls in the space of twenty feet square; andinfers, that, by the decomposition of animal matter, the acidof nitric salts arises, and therefore that this may have oc-casioned the formation of the nitrates of potassa and lime.

At Corydon, in Indiana , there is a cave, which, accord-ing to Stilson’s account, contains both nitrate of lime, andnitrate of magnesia. It is not worked.

Kain, in his remarks on the Geology and Mineralogy ofEast Tennessee, ( Silliman’s Journal , vol. i, p. 65 ,) observes,that the numerous caves which have been found in the Cum-berland mountains, and other parts of Tennessee have beenvery productive of nitrate of potassa; and in confirmation ofthe remarks before made, he adds, in investigating the causesthat have given rise to these salts, that wild animals bur-row in these caves; that, when pursued by the hunter, theymake them the places of their retreat, and probably diethere; that the aborigines have made them a place of burial;and that the streams of water, which flow through them, inwet weather, carry with them not only great quantities ofleaves, but many other vegetable productions.

Without offering any theory, by which we may accountfor the formation of nitre, in nitre caves, or in situationswhich cannot be influenced by the putrefactive process, wemay merely remark, that as nitric acid is composed of oxy-gen and azote, there must be some operation unknown to us,by which the union of these elements takes place. Nascentazote must unite with the base of oxygen gas; but whence,in saltpetre caves, proceeds the azote and the oxygen? Itappears that calcareous bodies facilitate the formation ofnitre, as they do in artificial nitre beds. The greater partof the nitrous earth is lime; and it also appears, that thesame earth, after the extraction of the saltpetre, will again fur-nish it. We know that lime is a compound of a base call-ed calcium united with oxygen; but in what manner it pro-motes the union of azote and oxygen, or furnishes either one