WATER 



6214 



WATER BUG 



Physical Properties. Although \vaur is com- 

 monly spoken of as a liquid, it exists also in 

 solid and gaseous forms. Water vapor is a nor- 

 mal component of the atmosphere, and when 

 as much water has evaporated into the air as 

 it is possible for it to hold the atmosphere is 

 xi id to be saturated. Under ordinary atmos- 

 pheric pressure water becomes a vapor at 212 

 F. (100 C.), and solidifies at 32 F. (0 C.). 

 On mountain tops, where there is little air pres- 

 sure, water boils at lower temperatures, and may 

 reach a much lower temperature than 32 F. 

 without freezing. See THERMOMETER; see, also, 

 HEAT, page 2750. 



The specific heat of water, or the amount of 

 heat required to raise one gram of the liquid 

 one degree, is greater than for any other sub- 

 stance except hydrogen; it is taken as 1, and is 

 the unit of measurement of the specific heat of 

 all other substances. 



Another feature of water, important in physi- 

 ography, is its exception to the general law of 

 expansion by heat. It is at its greatest density 

 at 39.2 F. (4 C.), when one cubic centimeter 

 weighs one gram. When heated from the 

 freezing point, it contracts until it reaches 

 39.2 F., after which it expands. Conversely, 

 when cooled from 212 F., it contracts until it 

 reaches 39.2 F., when it again begins to ex- 

 pand. This expansion with freezing is of great 

 importance, for it keeps the ice on top of the 

 heavier masses of water and thus prevents the 

 solid freezing of lakes and ponds, which would 

 cause the death of the animal life in their 

 waters. On the other hand, it causes the burst- 

 ing of water pipes and containers in freezing 

 weather. The water formed when the ice is 

 melting is of the same temperature as the ice 

 itself, and the temperature of boiling water is 

 not lower than that of the steam which it 

 forms. E.B.P. 



Consult Coles-Finch's Water: Its Origin and 

 Uses; Fuertes' Water and Public Health. 



Related Subjects. In connection with this ar- 

 ticle on water the reader may consult the follow- 

 ing topics in these volumes : 



Boiling Point 



Chemistry 



Cloud 



Dew 



Distillation 



Erosion 



Evaporation 



Freezing 



Frost 



Hail 



Humidity 



Hydrogen 



Ice 



Lake 



Mineral Waters 



Ocean 



Oxygen 



Rain 



River 



Snow 



Spring 



Steam 



Vapor 



WATER BEETLE, a name which includes 

 several distinct families of beetles which in- 

 habit the water. Some live permanent aquatic 

 lives, and others live in or near the water only 

 while, in the larval (young) state. Typical ex- 

 amples of water beetles are the whirligigs, the 

 diving beetles and the common water btTtlcx 

 of the ponds. Whirligigs damv and whirl on 

 llu 1 water; they have short antennae, long, 

 clawed front legs, paddle-shaped hind legs, and 

 compound eyes, adjusted for vision above and 

 below the water. Diving beetles are distin- 

 guished by their long, threadlike antennae and 

 flattened, fringed hind legs, fitted for swim- 

 ming. The common water beetles have short, 

 club-shaped antennae and resemble the diving 

 beetles in their habit of feeding on small fish 

 and larvae; in common with the whirligigs, 

 they have a receptacle for carrying air when 

 diving into the water. Water beetles are well 

 suited to aquarium life, and their habits afford 

 interesting study. 



WATER BUG, the general name applied to 

 those families of bugs which have a perma- 

 nent or temporary existence in the water. The 

 most familiar are the water boatmen, the back 

 swimmers, the giant water bugs and the water 

 skaters. The 

 complete life his- 

 tory of none of 

 these species is 

 known. Both 

 water boatmen 

 and back swim- 

 mers have long, 

 flattened, fringed 

 hind legs, which 

 serve as oars ; 

 these insects feed 

 on smaller water WATER BUG 



creatures and come to the surface for air; they 

 lie dormant in the mud at the bottom of the 

 water in winter. The eggs of the water boat- 

 men are attached to the stems of vegetation; 

 those of the back swimmers are deposited 

 within the stems. The latter have the peculiar 

 habit of swimming with the back downward. 

 The giant bug seen whirling around elec- 

 tric lights in hot weather, casting great shad- 

 ows on the ground, is a water bug that leaves 

 its home in the water for short flying periods 

 to find a mate or a new pool. Water skaters 

 have long, spiderlike legs, and run nervously 

 on the surface of the water. The beaks of all 

 water bugs are to be avoided, as the sting is 

 painful. 



