HYDRIODIC ETHER (more correctly known as ethyliodide), a heavy, colorless liquid with a sharp, pungent taste and a pene trating ethereal odor, obtained by acting upon pure ethyl alcohol (C2H..0H) by iodine, in presence of red phosphorus. The proportion is 1 part of red phosphorus (or equal parts of red and yellow phosphorus), 5 parts of alcohol and 10 parts of iodine added slowly. After 24 hours the hydriodic ether is distilled off, and washed with a solution of sodium hydrate and water, and dried over calcium chloride. In large quantities it is prepared by adding sulphuric ether slowly to a warm, con centrated aqueous solution of potassium iodide, or by the action of hydriodic acid upon sul phuric ether. Hydriodic ether has the formula C21.151, boils at 162° F. (under ordinary atmo spheric pressure), and has a specific gravity of about 1.946. When not quite pure it becomes brownish upon exposure to light, from the liberation of iodine. In chemistry, hydriodic ether (or ethyl iodide) is largely used as a fundamental substance in the preparation of the various other compounds of ethyl.
The science that investigates the conditions and laws affect ing the occurrence and use of water as a material means of satisfying human needs and desires, and that takes into consideration also the proper balance between cost and benefits to be derived in each particular case from the practical application of these laws. Water for drinking purposes next to air is the most important substance necessary for the support of life. It must be had at short intervals in suitable quantities and qualities for the daily needs of mankind and for all animals and plants; thus to the extent to which these are used as a food, it is vital also in food production. The regulation of its supply for watering live stock and for irrigation in producing crops is an essential for the welfare and the increase of population. As a correla tive, the reduction of excess of water by drain age is equally important. Related to these is the conveyance away from human habitations and centres of population of waste products through sewage systems and the economic dis posal of manufacturing effluents or waste in running water, where this can be properly done.
The data for the study of hydro-economics necessarily fall into several groups of subjects, primarily those relating to the properties physical and chemical — of water as a sub stance, next to its occurrence in nature, these facts being included within the science of me teorology. Following these the measure
ments of its volume included within hydrology and the mapping of large bodies of waters, rivers, lakes and oceans, known as hydrography. All of these data are needed in the considera tion of the largest development and use of water for human needs, first, as above stated in the direct support of life involving ques tions of domestic and municipal supply; second, in the production of food directly through water needed for domestic animals and for the irrigation of crops or the relief of the excess from the tilled fields by means of drain age; third, in relative importance come ques tions of .conveyance of waste from towns and factories; fourth, the employment of water in the industries in the production of power directly by water wheels, included in the sci ence of hydraulics, or in steam production, this being within the range of thermodynamics. The fifth use of water is that of transportation of persons and goods, included under the head of navigation. This latter use, under modern conditions and due largely to the rapid de velopment of railroads, has declined in relative importance. From the standpoint of Federal law, however, navigation has priority over other uses, the Constitution of the United States pro viding, in Section 8, that Congress shall have the power ato regulate commerce with foreign nations, and among the several States, and with the Indian tribes." Under a very broad interpretation of this provisioh, Congress has undertaken the regu lation not only of the interstate but of many intrastate streams and has authorized the build ing of extensive levees and related works for the protection of agricultural lands from over flow. It has also made appropriations for the purchase and protection of forests at the head waters of streams whose lower reaches may be navigated — the tendency being to enter upon the development and use of the water resources of the country under Federal auspices as far as practicable under a liberal interpreta tion of Federal power conferred by this clause of the Constitution.