=116.= The problem of obtaining a sufficient and wholesome water-supply for a besieging army is usually one difficult of solution. The precautions which are necessary in ordinary camps (Art. of War, 352 and 358) become of still greater importance in this case, owing to the choice of the source of supply being limited to those which are not controlled by the besieged, and to the constantly increasing danger of pollution of all ground waters by the bodies of the dead men and animals and the refuse and filth of the camps. The evils arising from these sources may be largely or entirely removed by boiling the drinking-water, and the disagreeable tastes and smells may be removed by filtering through good filters. It is very difficult, however, to compel the men to boil the water, or to drink it after it is boiled, unless it is properly aerated and filtered. All available measures should, therefore, be adopted to supply them with wholesome water. The results of the most recent researches show that properly conducted _intermittent filtration_ with sand-filters will render a polluted water almost if not entirely safe. (See reports of Massachusetts State Board of Health on Purification of Sewage and Water, 1890.) And the analysis of water sterilized by a steam-jet at the Columbian Exposition in Chicago, 1893, gives reason to believe that this process may be very effective in removing disease germs. (See report of Allen Hazen, Chemist, Department of Water-supply, published in _Engineering News_, March 29, 1894.) In camps of some permanence one or both of these processes may be well worth applying. Small filters for limited amounts of water may be bought in the market, or may be improvised and set up for officers or company messes. Figs. 108-110, Pl. X, are given as suggestions; they serve as strainers in any case. If used intermittently they _may_ have a high sanitary value, and if made up partly of either animal or wood charcoal they remove more or less completely any offensive taste or odor which water may have. Security, however, requires doubtful water to be boiled. In all cases arrangements should be made to protect the water from surface pollution, for convenient access for the men, and for watering horses. (See the following books, treating on Military Hygiene in Camp and Garrison: Parker’s Practical Hygiene; Traité d’Hygiène Militaire, Morache; Manuel d’Hygiène militaire, Viry; Military Hygiene, Woodhull; the Soldier’s Pocket-book, Wolseley; etc., etc.) PART II. _MILITARY MINING, BLASTING, AND DEMOLITION._ CHAPTER I. NOMENCLATURE AND THEORY. =1.= =Military Mining= includes all the operations necessary for placing charges of explosive underground and exploding them at the time desired, for the purpose of destroying the men, materials, or works in their vicinity, or for breaking up the surface of the ground either to advance or retard the operations of a siege.