HEAT 



2750 



HEATH 



when the weather is cool, must not be put 

 exactly end to end. A space has to be left 

 between the ends so that in the summer, when 

 they are heated, there will be room for them to 

 expand. Wagon tires are made just a little 

 smaller than the rim of the wooden wheel and 

 are heated until they expand to the proper 

 size to fit on the wheel. When they after- 

 wards cool they contract and draw the whole 

 wheel tightly together. (See EXPANSION.) 



(2) Changes Solids to Liquids. If ice is 

 brought near a flame, instead of getting hotter 

 it melts, or changes to water. This requires 

 a greater amount of heat in some cases than 

 it does in others. Ice is only thirty-two degrees 

 "cold," and immediately begins to melt if sur- 

 rounded by warmth. Metals also become 

 liquid if they are heated to a sufficient tempera- 

 ture. Lead does not have a very high melting 

 temperature, and can be changed to a liquid 

 over a hot gas flame. The melting, or fusing, 

 point of lead is only 585 degrees, but that of 

 most metals is very high. Platinum has such a 

 high fusing point that it can only be melted 

 in an electric furnace. 



(3) Changes Liquids and Solids to Vapor. 

 When liquids are heated to the boiling point 

 they pass into a gaseous condition. There are 

 some substances which, when they are heated, 

 will pass directly from a solid to a gaseous 

 state, camphor and zinc and snow among them. 

 But while melting cannot begin until the tem- 

 perature of the solid is raised to a definite 

 degree, the process of evaporation is going on 

 all the time from the surface of a liquid, no 

 matter what its temperature. Clothes hung 

 out to dry on a cold day will "freeze" dry. A 

 vessel of water in the open air will be emptied 

 by evaporation without ever reaching the boil- 

 ing point. 



(4) Produces Light. When certain substances 

 are raised to a very high temperature, they 

 give off light as well as heat. The example 

 with which most people are familiar is that of 

 some iron object which becomes red-hot, or 

 even white-hot, sueh as a glowing coal or a 

 flame. This property of matter has been util- 

 ized in the Welsbach gas burner, where, in- 

 stead of getting light from the gas flame, the 

 light comes from a cone of metal which is 

 heated white-hot by the flame. 



Related Subjects. The following articles in 

 these volumes bear more or less closely on the 

 general subject of heat : 

 Combustion Energy 



Electric Heating Evaporation 



Electricity Expansion 



Fire Radiometer 



Freezing Sun 



Heating and Ventilation Temperature 

 Molecule Thermometer 



HEATH, heeth, or HEATHER, heth' er, the 

 name of various modest evergreen shrubs com- 

 mon in Europe and Africa. The term also ap- 

 plies to large waste places on which such shrubs 

 grow. In this latter connection the term is 

 seldom used in America, where shrubs of 

 heather are rare. In recent years, however, 

 the hardy Scotch heather has become a popular 

 plant and cut flower in American flower shops, 

 it having been introduced in a few places in 

 Eastern United States. It has low, grayish, 

 hairy stalks, broomlike branches, needlelike 

 leaves and spikes of tiny, purple-rose, bell- 

 shaped blossoms. A similar species is common 

 in moors and on large tracts in Great Britain 

 and in continental Europe, and is called ling. 

 Heather flowers are rich in honey, and Mary 

 Howitt, in Autumn, says: 



Oh ! beautiful those wastes of heath 

 Stretching for miles to lure the bee. 



The flowers of either the cross-leaved or the 

 fine-leaved heath of the British Isles are the 

 heather-bells of Scotch songs and stories, and 

 they inspired Scott to write in the Lady oj the 

 Lake : 



For heath-bell, with her purple bloom, 

 Supplied the bonnet and the plume. 



Practical Uses. Most of nearly 400 known 

 species of heather are native to Africa, where 

 many are remarkable for the size and beauty 

 of their blossoms. In European countries the 

 uses of heather are numerous. It is used in 

 making brooms and brushes, and trailing shoots 

 are woven into baskets. The underground 

 rootstocks of a species common in France yield 

 the briarwood used for pipes. Heather seeds 

 are eaten by many birds. Poor people in Scot- 

 land use heather for thatching their houses. 

 In some places a liquid made from heath is 

 used in tanning leather. Young heather shoots 

 are used for forage, and no sweeter, softer out- 

 door bed could be desired by the shepherd 

 than one of heather branches. Heather con- 

 tributes greatly to the formation of peat bogs, 

 and in that way it is of economic value as 

 well as a thing of beauty in those desolate 

 places. See PEAT. 



Although true heaths are not common in 

 America, many familiar plants represent the 

 heath family in that country; among these 

 are the cranberry, huckleberry, rhododendron, 

 azalea and trailing arbutus. All are described 

 elsewhere in these volumes. M.S. 



