108 APPLIED SCIENCE 



COEFFICIENTS OF EXPANSION (1F.) 



110. Expansion of Substance. When a substance con- 

 sisting of two or more bodies which have different coefficients 

 of expansion undergoes any change of temperature, it is 

 subjected to stresses, since its various parts do not expand 

 in an equal degree. Thus, Portland cement, which has a 

 coefficient of expansion of .000011, cannot make a reliable 

 joint under varying temperatures with leading, the coefficient 

 of which is .000028. On the other hand, the coefficient for 

 steel fortunately approaches very closely to that of concrete, 

 so that these materials may be combined to advantage in 

 construction work. In the case of brittle substances fixed 

 together, this unequal expansion is a frequent source of 

 fracture. The cracking of glaze upon tiles and terra cotta 

 may be attributed to this cause. The plastering on walls 

 and the seams of cheap wall-paper sometimes open on 

 account of unequal expansion. 



Allowance for expansion in non-metallic bodies, such as 

 stone, brick, or concrete, is not usually of importance because 

 the coefficients of expansion of such bodies is as a rule smaller 



