The constituent parts of pure water, in volumes, are two parts of hydrogen and one of oxygen, and by weight one part hydrogen and eight parts oxygen. When pure it is transparent, tasteless, inodorous, and colorless, except when seen in considerable depths. But having such high solvent powers and affinity for almost every substance in nature, one can account for suspicions that science places on all waters, for it is never free from impurities. And well it may not, if doctors are to be believed, for they tell us, that chemically pure water is not best for man; that good potable waters have from one to eight grains weight in each gallon of certain impurities diffused through them. Impurities are arranged under the following general heads: Rain Water--Atmospheric influences. Spring and Well Water--Mineral properties. Rivers, Lakes--Vegetable and animal organisms. But what can we consider good drinking water? Dr. Frankland, of England, has given the following as a minimum limit of mechanical and chemical impurities held in suspension or solution, to be considered bad or polluted liquid: _A._ Every liquid which has not been submitted to precipitation, produced by a perfect repose in reservoirs of sufficient dimensions, during a period of at least six hours; or which, having been submitted to precipitation, contains in suspension more than one part by weight of dry organic matter in 100,000 parts of liquid; or which, not having been submitted to precipitation, contains in suspension more than three parts by weight of dry mineral matter, or one part by weight of dry organic matter in 100,000 parts of liquid. _B._ Every liquid containing in solution more than two parts by weight of organic carbon, or three parts of organic nitrogen, in 100,000 parts of liquid. _C._ Every liquid which, when placed in a white porcelain vessel to the depth of one inch, exhibits under daylight distinct color. _D._ Every liquid which contains in solution, in every 100,000 parts by weight, more than two parts of any metal, except calcium, magnesium, potassium and sodium. _E._ Every liquid which in every 100,000 parts by weight contains in solution, suspension, chemical combination or otherwise, more than 0.5 metallic arsenic. _F._ Every liquid which, after the addition of sulphuric acid, contains in every 100,000 parts by weight more than one part of free chlorine. _G._ Every liquid which in every 100,000 parts by weight contains more than one part of sulphur, in the state of sulphuretted hydrogen or of a soluble sulphuret. _H._ Every liquid having an acidity superior to that produced by adding two parts by weight of hydrochloric acid to 1000 parts of distilled water. _I._ Every liquid having an alkalinity greater than that produced by adding one part by weight of caustic soda to 1000 parts of distilled water.