HYDRAULICS 



2887 



HYDROCARBONS 



the cistern, that is, twenty-five feet. But on ac- 

 count of the resistance of the air and the 

 friction of the liquid against the sides of the 

 pipe, the water never rises quite as high. 



Flow of Water in Rivers. Water flows in a 

 current, as in rivers, on account of the inclina- 

 tion of the channel. An inclination of three 

 inches per mile is sufficient to give motion to 

 water and to produce a velocity of three miles 

 an hour. But the flow is also affected by the 

 form of the channel as well as by the friction 

 along its banks and the bottom. Thus the 

 current in a river moves more swiftly at the 

 center, where there is less friction, than near 

 the shores or the bottom. 



Water Supply of Cities. The necessity of 

 providing a pure and plentiful supply of water 

 to cities is one of the many instances in which 

 the science of hydraulic engineering has- to 

 solve various difficult problems. The water- 

 works of some of the big cities are marvelous 

 feats of engineering, which compel admiration 

 for the knowledge, skill and ingenuity of the 

 engineers who planned and constructed these 

 works. The chief problem which has to be 

 solved in any of these undertakings is how to 

 convey the water from the source to the place 

 where it is to be used. Sometimes the water 

 has to be carried over great distances and this 

 necessitates the construction of large aque- 

 ducts, reservoirs and other similar works. 

 Then comes the problem of distributing the 

 water in the city over a wide area by means 

 of a great number of pipes of various sizes, 

 which bring it into the homes of the people. 

 These pipes must be arranged in such a way 

 that they shall always contain a constant flow 

 of water under the proper pressure. Another 

 problem which has to be solved is to furnish 

 enough pressure in order to force the water to 

 the top of tall buildings. In cities like Denver 

 and Los Angeles, which are situated near the 

 mountains, the water is conducted to the city 

 in large pipes from reservoirs built on the 

 mountains. As water tends to rise to the level 

 of its source, it will rise in the buildings to 

 the height of the reservoir. This is known as 

 the gravity system of waterworks. But in most 

 cities, such as New York, Boston, Philadelphia 

 and Chicago, a special system of pumping has 

 to be employed in order to attain a result 

 achieved thus easily in mountainous country. 



Various machines for using the force of fall- 

 ing water have been constructed and most of 

 them are described under their proper headings 

 in these volumes. C.R.M. 



Related Subjects. The reader will be assist- 

 ed to broader knowledge of hydraulics by refer- 

 ence to the following articles in these volumes : 

 Hydraulic Ram Turbine Wheel 



Hydrostatics Water Wheel 



HYDROAEROPLANE, hi dro aer' o plane, or 

 HYDROPLANE, a flying boat, or in other 

 words, any aeroplane designed to rise from and 

 alight on the surface of the water, or be pro- 

 pelled upon the water. It was evolved in the 

 simplest and most natural way from the earlier 

 forms of aeroplanes, and had its origin in the 

 mere adding, to the regular form of flying 

 machine, of floats which should prevent the 

 sinking of the machine if it happened to come 

 down into the water. This called attention 

 to other possibilities, and distinct forms were 

 developed, some having floats instead of skids, 

 some with regular boat bodies. This latter 

 form bids fair to be the more popular. By no 

 means have all the problems been solved, for 

 while it is comparatively easy to make a 

 machine which may be anchored upon or raised 

 from smooth water, a turbulent water surface 

 complicates matters. For a fuller discussion 

 of hydroaeroplane, with its relation to other 

 phases of aeronautics, see FLYING MACHINE. 



HYDROCARBONS, hi dro kar' bahnz, are 

 compounds of carbon and hydrogen. Some 

 of them occur in nature as natural gas, petro- 

 leum, turpentine, asphalt, etc. Others are made 

 artificially. The commercial products of petro- 

 leum, such as benzine, gasoline, kerosene, lubri- 

 cating oils and paraffin wax, are mixtures of 

 hydrocarbons. Coal gas contains hydrocar- 

 bons and so also the by-products in the manu- 

 facture of gas from coal. Acetylene, also used 

 as an illuminating gas, is a hydrocarbon. The 

 dangerous "fire-damp," which is the cause of 

 many dreadful explosions in mines, is the hy- 

 drocarbon methane, which is also the principal 

 constituent of natural gas and an important 

 one in coal gas. 



In chemistry the hydrocarbons are of great 

 theoretical interest. It is the common prac- 

 tice to regard all the compounds of carbon 

 as "derived" from the hydrocarbons. This 

 does not mean that all such compounds are 

 actually made from hydrocarbons, but only 

 that it is convenient to classify them according 

 to their theoretical relationship to the hydro- 

 carbons. For this reason organic chemistry, 

 the 'branch of the science which treats of the 

 compounds of carbon, is often defined as "the 

 chemistry of the hydrocarbons and their de- 

 rivatives." Hydrocarbons are divided into two 



