TEMPERATURE. 311 



expands and contracts more than iron, when the compound 

 bar is heated it will curve with the brass on the convex 

 side ; when it is cooled, it will curve with the brass on the 

 concave side. 



(a.) Glass and platinum expand nearly alike. In fact, the rates 

 of expansion are so nearly alike that platinum, wires may be fused 

 into glass tubes, as is done in electrolysis apparatus and eudiometers. 

 If we attempt thus to fuse copper wire into glass, the glase will be 

 broken during the unequal contraction from cooling. 



486. Practical Applications of Expansion. The 



energy of expansion and contraction of solids, when heating and 

 cooling, is remarkable. This expansion of metals by heat is 

 utilized by coopers in setting hoops, by wheelwrights in setting 

 tires, and by builders in straightening bulging walls. When the 

 iron rails of our railways are laid, a small space is left between the 

 ends of each two adjoining rails to provide for their inevitable 

 expansion by the summer heat. The iron tubular bridge over the 

 Menai Straits is about 1800 feet long. Its linear expansion is abort 

 one foot, and is provided for by placing the ends of the huge tube 

 upon rollers. 



487. Expansion of Liquids. The expansion of 

 liquids may be illustrated as follows : Nearly fill a Florence 

 flask with water, and place it on a retort stand or other 

 convenient support. A long straw is supported by a thread 

 tied near one end. From the short end of this straw lever 

 is suspended a weight nearly balanced by the long arm of 

 the lever. This weight hangs in the neck of the flask, 

 and rests lightly upon the surface of the water ( 238). 

 By placing a spirit-lamp below the flask the water may be 

 heated. As it expands, it rises in the neck of the flask, 

 raises the weight, and lowers the end of the long arm of 

 the lever, which may be seen to move. 



488. Anomalous Expansion of Water. 



Water presents a remarkable exception to the general rule. 

 // water at 0C. be heated, it will contract until it 



