Gunpowder was scarce throughout the war, and nitre or saltpetre, its principal ingredient, was not to be purchased from abroad. A powder mill was established at Cahaba,[360] but the ingredients were lacking. Charcoal for gunpowder was made from willow, dogwood, and similar woods. The nitre on hand was soon exhausted, and it was sought for in the caves of the limestone region of Alabama and Tennessee. In north Alabama there were many of these large caves. The earth in them was dug up and put in hoppers and water poured over it to leach out the nitre. The lye was caught (just as for making soft soap from lye ashes), boiled down, and then dried in the sunshine.[361] The earth in cellars and under old houses was scraped up and leached for the nitre in it. In 1862 a corps of officers under the title of the Nitre and Mining Bureau[362] was organized by the War Department to work the nitre caves of north Alabama which lay in the doubtful region between the Union and the Confederate lines, and which were often raided by the enemy. The men were subjected to military discipline and were under the absolute command of the superintendent, who often called them out to repulse Federal raiders. As much as possible in this department, as in the others, exempts and negroes were used for laborers. For clerical work those disabled for active service were appointed, and instructions were issued that employment should be given to needy refugee women.[363] These important nitre works were repeatedly destroyed by the Federals, who killed or captured many of the employees.[364] In the district of upper Alabama, under the command of Captain William Gabbitt, whose headquarters were at Blue Mountain (now Anniston), most of the work was done in the limestone caves of the mountain region.[365] Several hundred men--whites and negroes--were employed in extracting the nitre from the cave earth. To the end of September, 1864, this district had produced 222,665 pounds of nitre at a cost of $237,977.17, war prices.[366]