AMERICAN SALTPETRE CAVES IN TIME OF WAR.

Otago Witness, Issue 2263, 15 July 1897, Page 54

AMERICAN SALT PETRE CAVES IN TIME OF WAR.

Saltpetre, literally rock salt, chemically potassium, nitrate, also known as nitre, is remarkable for storing oxygen in a solid form. One volume of it has 3000 times as much oxygen as a like volume of atmospheric air. At a certain degree of heat thiß immense quantity of oxygen combines violently with carbon, th.ua forming carbonic acid gag, and also setting free a quantity of nitrogen. Gunpowder contains abonfc 75 partß of nitre to 15 of charcoal and 10 of sulphur. If ignited in vacua, the powder quietly resolves itßelf into" gas. But in the chamber of a gun, behind a ball, it explodes with energy and hurls the missile with deadly effeot. For this reason saltpetre is essential to any nation engaged in warfare. Edward Kawson was the first to attempt the manufacture of gunpowder in the New .England colonies. In 1839 the General Court of Massachusetts granted him 500 acres at Pequod, "so he go on with the business of powder, if the saltpetre come." By act of June 14, 1642, all towns and families were ordered to promote the manufacture of saltpetre. But nothing was accomplished, and in 1648 the General Coart voted to indemnify Kawson for his losses in the experiments made. I am indebted to Mr R. N. Toppan for this authentic information, not found in local histories. Kawson was deputy from Newbury, and seoretary of the colony.- At the opening of the revolutionary war the military stores of New England were mainly kept at Quarry Hill, near Medford, Mass., where they had 250 barrels of powder, which was seized by the British on September 1, 1774. The act set the country aflame, and stirred the indignation of Bnrke, Pitt, and Fox. After the news from Lexington and Concord, in 1775, the colonies were scoured for powder, and lees than 68 barrels were found. New York had but 1001b. Lord Dunmore had seiza^tbe entire supply in Virginia, and when Patrick Henry demanded its restoration at the head of troops, he only got its money value and not the powder. When Washington took command of the troops raised by the colonies he " made the alarming discovery that there was not more powder than sufficient to furnish each man with nine cartridges. By great address this dangerous deficiency was concealed from the f nemy " (" Holmes's Annals," vol. ii, p. 240). It is remarkable that no American history, BO far as I know, tells us whence the robbed ; and impoverished colonies got their powder j wherewith to wage the war of the revolution, \ A. similar gap exists concerning the war of 1 1812, when an embargo out us off from [ foreign supplies. We are told about almost everything eke, bub not where we found our saltpetre. That question is now answered. Among those who resisted the tyranny of Lord Dunmore in stealing the ammunition of Virginia were two young men named I Thomas Jefferson and James Madison. They vrere not only patriots and stateamen, bnt were also cave hunters. Among the caves j found by Jefferson was one that he j named for his friend "Madison's Cave," located in the Grottoes Ridge, in which also occur Weyer's Cave and the Cave ,of Fountains. Major Jed Hotchkiss, ■the veteran map maker and geologist, is my authority for saying that Madison's .Gave was mined for saltpetre during the three great wars of the Revolution of 1812 ' and of the rebellion — probably the only cave on the continent of which that can be said. But Jefferson found many other and richer saltpetre caves, which he describes in his •• Notes on Virginia " (p. 44). He says that one of the largest was on Rich Creek, a branch of the Kanawha, from which more than 11,0001b of nitre were obtained. Others were on the Cumberland River, and at least 50 were in the Greenbriar Valley, in one of which Jefferson found the typical megalonyx made famous by Cuvier. His account is all the more valuable because written while the war "of the Revolution was going on, and thus showing us whence the patriots obtained their mearis to carry it forward. To a limited extent gunpowder was seized from the enemy, and a few pounds of saltpetre were made from excavations under old stables, and by artificial „ prooesses, but the bulk of it undoubtedly came from the caves j of Virginia. Kentucky was originally set off from Augusta County, Virginia, as Kentucky j County in 1776, and was made a State in 1792. Among its early settlers were strolling chemists who knew of the caves in the Greenbriar Valley and elsewhere, and hunted | lor Bimilar ones in the newly-organised State. ■ They were richly rewarded. Under ledges, in " rock houses " and " rock castles," they found solid masses of nitre weighing from 1001b to 16001b. Previous to 1800 there had been found 28 saltpetre caves in Kentucky, from which more than 100,0001b of saltpetre had been obtained. These facts led Dr Samuel Brown, of Lexington, Ky., to make a journey of 1000 miles on horseback, in 1806, in order to lay them before the American Philosophical Society' at Philadelphia. He closed his able paper, probably the first of its kind, with these words : " A concern for the glory and defence of our country should prompt such of our chemists as have talents and leisure to investigate this interesting subject. I suspect that we have much to learn with regard to this salt — so valuable in time of peace, so indispensable in time of war." The time of war was nearer at hand than he may have thought, for it burst upon us in 1812, and we were cut off from foreign supplies. Dr Brown had estimated that what he called the Great Cave contained 1,000,0001b of saltpetre ; Scott's Cave, 200,0001b ; Davis's Cave, 50,0001b ; three others not named, 30,0001b. Since then the Mammoth Cave has been discovered, and the Wyandot Cave lind others in Indiana, and the nitre fever almost rivalled the subsequent gold fever of 1849. We have the authority of Flint's Geography for the statement that, during the war of 1812-15, the annual yield of manufactured saltpetre from Kentucky alone was 400,0001b, besides what was made in Indiana, Tennessee, and elsewhere. Part of this was used at home ; but most of it was carried by ox carts, or on pack mules, across the Alleghanies to the seaboard to be used in making gunpowder. The term " saltpetre caves " is a misnomer only justified by the general usage. That

which is found in these caves, and which is colloquially oalled "peter dirt," is soil impregnated with the nitrate of lime, whereas true saltpetre is the nitrate of potash. Professor W. B. Rogers holds that the " peter dirt " is derived directly from tha overhanging rocks, which agrees with Dr Simuel Brown's observation that the water trickling from rooky creviceß has the same properties as the liquor got by lixiviating the cave clay. Dr Brown says : •• The nitric acid is formed within the caves and is condensed j upon the rocks, the lime of which it disi solves." The fact seems to have been generally overlooked that the strata of sandstone overlying the oavernous limestone is rich in nitre. It was from this source that the first supplies of Kentuoky saltpetre came. The process was to blast the sandrock and break it into small fragments for the boilers, thus getting nitre directly without the aid of lye. ' | The reason it was given up was that the beet : sandrock was extremely hard because of the ! presence of iron, and it was practically easier and cheaper to treat the nitrous earth i found in the caverns. In order to give some idea of what was once a vital industry of our country, though now wholly abandoned, I shall briefly describe the work done at the Mammoth Cave, ! which may be taken as typical of the rest. This includes what was done at the Salts Cave and Dlxon'o Cave, belonging to the same estate. Dixon's Cave was, at some prehistoric time, a part of the Mammoth Cave. As measured by me it is 1500 ft long, from 60ft to 80ft wide, and about 100 ft high. The j : floor of this enormous hall is ridged by 18 transverse rocky piles some 40fb high and as many thick, cut by passageways for conreni- ; ence. And every block and fragment of those j massive ridges were laid there by the old saltpetre miners. By this means they got at the peter dirt to be carried outside for j further treatment.

The main works, however, were at the entrance to the Mammoth Cave. Cart roads were made through the more accessible avenues, and from the more distant places, even from rooms three miles underground, the negro miners brought the dirt in sacks. Hardly a yard of the cave as then known was left undisturbed. Audubon Avenue was particularly rich in nitrous earth. So wae Bat Avenue, near the end of which is the Crevice Pit, the ugliest black hole mortal ever looked into, and at whose bottom the men thought there must be a nitrous mine. The story has been often told of the miner's lamp dropped into that black chasm, and the sprightly negro let down as an animated plummet, who brought back, not the missing lamp, but a marvellous story whose truth was confirmed 30 years later by the discovery of the socalled Egyptian Temple. The Gothic Avenue was also diligently worked. The shovel and pick were plied from room to room of the I main cave, and out; through the windings of the Blue Spring avenue. Abundant aboriginal relics were found. / The nitrous earth thus collected was put in hoppers with each a capacity of 50 bushels, and which are still to be seen in the rotunda and vicinity, a few hundred feet within the cave, where may also be seen the pumps and double set of wooden pipes, one set to bring water from the cascade at the mouth of the cave, and the other to convey to the surface the liquor obtained by solution from the hoppers. The floors of the latter were peculiarly grooved to allow the saturated water to run into the basins, whence it was pumped out to the great iron boilers. When the lixiviated earth had been exhausted, it was cast aside and a new charge put into the hoppers. These piles of indurated earth extend for a long distance like miniature mountain chains. The liquor, after sufficient boiling, was poured into another set of hoppers containing wood ashes, whence, by filtration, a clear solution of the nitrate of potash was obtained. This was again boiled down to the right condition for crystallisation in troughs, whence, after twenty-four hours, the crystals were taken and packed for transportation.

The proportion of ashes to be used to the nitrified liquor was a source of much perplexity. Too much would "kill" the saltpetre, and too littlo would leave if; "iv the grease"; and in either case the salts would have to be run through the hopper agaiD. Ashes from oak aie three times as rich in potash aa those from pine, and only half as rich as those from elm or maple. Best of all were the ashes made by burning the dry wood in hollow trees, two bushels of which, according to Dr Brown, were equal in strength to 18 of oak ashes. It is stated that " the conj tract for the supply of the fixed alkali alone for Mammoth Gave, for the year 1814, was 20,000dol." That, if correct, gives us an idea of the extent to which saltpetre was manufactured here in the days when Gratz and Wilkina carried on the business exclusively for the Philadelphia market. Many curious facts might be added as to the antiseptic and sanitary value of the atmosphere in Mammoth Cave, which is both chemically and optically pure, except as tainted by torches. None of the deep pits contain foul air. Indeed the interior air is purer than that which is exterior, showing that ita purity is not due to ventilation, but probably to the disengaging of fiee oxygen in the formation of the nitrate I of lime, a theory advanced by Professor i Silliman. I In time of peace it is cheaper to import saltpetre from Ohili, India, and elsewhere than to make it at borne. But when the Southern Confederacy was cut off by the blockade of all its ports, it resorted to the caves of Virginia, Tennessee, and Alabama, particularly to the great Nicojack Cave, near Chattanooga, for the neans of making gunpowder, the process being substantially like what has already been described. It is strange that these interesting materials of American history seem to have completely escaped the attention of our best historians. It is certainly of historic moment that

when the fate of the nation trembled in the balances the mineral contents of our numeioub caverns enabled a waning force to gather new strength, and to prolong war far beyond what would otherwise have been possible. We doubt if victory could have been won in the war of the Revolution, or in the war of 1812, without the aid of the saltpetre caves of Virginia and Kentucky — Horace C. Hovby, in the Scientific American.