=Organic Matters in general.=—_Test_: Eight grains of chemically pure permanganate of potash in one ounce of distilled water. In half a pint of the suspected water in a tumbler, put one drop of the solution. If the red color disappears in one half hour, add more. For every drop that loses color in the half-pint there will be found one and a half to two grains of putrid organic matter in a gallon of the water. If the action is rapid, the matter is probably animal; if slow, vegetable. To =purify= such water, if it must be used, drop in the solution until a slight red tinge remains. The organic matter is then all oxidized and rendered harmless. It is better, however to boil such water before using it for drinking. _Precautions with regard to Drinking-Water._ Do not drink water that has been standing long in lead pipes, or lead cisterns or tanks. Filter it before drinking. See that the current of ground-water in the well from which you get your drinking-water is from the well toward any possible source of contamination (privy-vault, cesspool, etc.), and not _vice versa_. If the use of a suspected water is unavoidable, boil it first. It can be rendered palatable by an infusion of tea or coffee. APPENDIX A. ALPHABETICAL LIST OF THE COMMON DISINFECTANTS, WITH A BRIEF DESCRIPTION OF EACH, AND THE AVERAGE PRICE AT RETAIL. =Carbolic Acid.=—A product of the distillation of coal-tar. When pure and free from water, a transparent crystalline solid. Dissolves in twenty parts of cold water. Coagulates albuminous matters. A one-per-cent solution of it in water arrests putrefaction. For disinfection use at least a one-per-cent solution. The chief objection to its use is its odor. This may be modified to some extent by mixing the pure acid with camphor, forming a liquid, which may then be diluted. This acid is often used in combination with other disinfectants. A preparation much used by the New York City Board of Health for the disinfection of clothing contains eight ounces of sulphate of zinc and three ounces of carbolic acid to three gallons of water. Another for privies, water-closets, etc., is composed of ten pounds of copperas, one pint of carbolic acid, and five gallons of water. The strong acid injures iron pipe. Do not use in combination with the permanganate of potash or the chloride of zinc. “=Dead Oil=” (heavy oil of coal-tar) contains from 5 to 15 per cent of carbolic acid mingled with impurities. It is used for the disinfection of drains, streets, stables, etc. =Thymol= also occurs in coal-tar, but is usually obtained from oil of thyme. Its action is similar to that of carbolic acid. =Carbolic Powders= are made by mixing five parts of the pure acid, or ten parts of the crude, with one hundred parts of sawdust, clay, or lime. Squibb’s Carbolic Acid (No. 1), containing 77.90 per cent of pure acid, costs $1 a pint; (No. 2), with 37.46 per cent of pure acid, 75 cents a pint.