304 SCIENCE IN SHORT CHAPTERS. 



is not exceeded, it regains its original size without becoming 

 sensibly weaker. Add to this its great tenacity, its non- 

 liability to be indented, or otherwise to vary in diameter, 

 and we have a far superior material. 



But this conclusion demands some qualification. There 

 is iron and iron, cast-iron and wrought-iron, and very vari- 

 able qualities of each of these. I need scarcely add that 

 common brittle cast-iron is quite out of the question for 

 such purposes, though there is a new kind of cast-iron or 

 semi-steel coming forward that may possibly supersede all 

 other kinds; but this opens too wide a subject for discus- 

 sion in the present paper, the main object of which has 

 been a popular exposition of the general physical laws which 

 must be obeyed by the builder, or engineer, who desires to 

 construct domestic or other buildings that will satisfy the 

 wants of intelligent people. 



The mischievous action of freezing water is not confined 

 to the pipes that are constructed to receive or convey it. 

 Wherever water may be, if that water freezes, it must ex- 

 pand in the degree and with the force already described. 

 If it penetrates stone or brick, or mortar or stucco, and 

 freezes therein, one of two things must occur either the 

 superfluous ice must exude at the surface or to neighbor- 

 ing cavities, or the saturated material must give way, and 

 split or crumble according to the manner and degree of 

 penetration. To understand this, the reader must remem- 

 ber what I stated about the little-understood viscosity of 

 ice, as well as its expansion at the moment of freezing. 



Bricks are punished, but not so severely as might be 

 anticipated, seeing how porous are some of the common 

 qualities, especially those used in London. They are so 

 amply porous that the water not only finds its way in to 

 them, but the pores are big enough and many enough for 

 the ice to demonstrate its viscosity by squeezing out and 

 displaying its crystalline structure in the form of snow- 

 like efflorescence on the surface. This may have been ob- 

 served by some of my readers during a severe frost. It is 

 commonly confounded with the hoar-frost tliat whitens the 

 roofs of houses, but which is very rarely deposited on per- 

 pendicular wall faces. 



