As to the germicidal results obtained in chemical closets, few data are available. A disinfecting compound may not sterilize more than a thin surface layer of the solid matter deposited. Experiments by Dr. Alvah H. Doty with various agents recommended and widely used for the bedside sterilization of feces showed "that at the end of 20 hours of exposure to the disinfectant but one-eighth of an inch of the fecal mass was disinfected."[5] Plainly, then, to destroy all bacterial and parasitic life in chemical closets three things are necessary: (1) A very powerful agent; (2) permeation of the fecal mass by the agent; (3) retention of its strength and potency until permeation is complete. The compounds or mixtures commonly used in chemical closets are of two general kinds: First, those in which some coal-tar product or other oily disinfectant is used to destroy germs and deodorize, leaving the solids little changed in form; second, those of the caustic class that dissolve the solids, which, if of sufficient strength and permeating every portion, should destroy most if not all bacterial life. Not infrequently the chemical solution is intended to accomplish disinfection, deodorization, and reduction to a liquid or semiliquid state. [5] Annual Report, Mass. State Board of Health, 1914, p. 727. [Illustration: Fig. 15.--Chemical closet. _A_, Water-tight sheet-metal container; _B_, metal or wooden cabinet; _C_, wooden or composition seat ring; _D_, hinged cover; _E_, 3 or 4 inch ventilating flue extending 18 inches above roof or to a chimney; _F_, air inlets.] [Illustration: Fig. 16.--Chemical tank closet. _A_, Tank, 2 feet 3 inches by 4 feet 2 inches, 5/64-inch iron, seams welded, capacity 125 gallons; _B_, 14-inch covered opening for recharging and emptying tank; _C_, 12-inch galvanized sheet-metal tube; _D_, 4-inch sheet-metal ventilating pipe extending above ridge-pole or to a chimney; _E_, agitator or paddle.] A simple type of chemical closet is shown in figure 15, and the essential features are indicated in the notation. These closets with vent pipe and appurtenances, ready for setting up, retail for $20 and upward. A chemical tank closet, retailing for about $80 per seat, is shown in figure 16. The Department of Agriculture occasionally receives complaints from people who have installed chemical closets, usually on the score of odors or the cost of chemicals. LIQUEFYING CLOSET.