34 SCIENCE IX SHORT CHAPTERS. 



Bricks arc punished, but not so severely as might be antici- 

 pated, 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 into them but the pores 

 are big enough and many enough for the ice to demonstrate its 

 viscosity by squeezing out and displaying its crystalline struct- 

 ure in the form of snow-like efflorescence on the surface. This 

 may have been observed by some of my readers during a 

 severe frost. It is commonly confounded with the hoar-frost 

 that whitens the roofs of houses, but which is very rarely de- 

 posited on perpendicular wall faces. 



The mortar most liable to suffer is that which is porous and 

 pulverulent within, but has been cleverly faced or pointed with 

 a crust of more compact material. This outer film prevents 

 the exuding of the expanding ice crystals, is thrust forth bodily, 

 and retained by ice-cement during the frost, but it falls in scales 

 when this temporary binding material thaws. Mortar that is 

 compact throughout does not suffer to any appreciable extent. 

 Tliis is proved by the condition of the remains of Roman brick- 

 work that still exist in Britain and other parts of Europe. 

 Some of the old shingle walls at Brighton and other parts of 

 the south coast, where the chalk for lime -burning was at the 

 builder's feet, and where his mortar is so thickly laid between 

 the irregular masses of flint, also show the possible duration of 

 good mortar. The jerry builder's mortar, made of the rid- 

 dlings of burnt clay ballast and dust-hole refuse just flavored 

 with lime, crumbles immediately, because these materials do 

 not combine with the lime as fine silicious sand gradually does, 

 to form an impermeable glassy silicate. 



Stucco is punished by two distinct modes of action. The 

 first is where the surface is porous, and the water permeates 

 accordingly and freezes. This, of course, produces superficial 

 crumbling, which should not occur at all upon good material 

 protected by suitable paint. The other case, very deplorable 

 in many instances, is where the water finds a space between the 

 inner surface of the stucco and the outer surface of the mate- 

 rial upon which it is laid. This water, when frozen, of course, 

 expands, and wedges away the stucco bodily, causing it to 

 come down in masses at the thaw. This, however, only occurs 

 after severe frosts, as the ordinary mild frosts of our favored 

 climate seldom endure long enough to penetrate to any notable 

 depth of so bad a conductor as stone or stucco. It is worthy of 

 note that water is a still worse conductor than stone. 



