VITRIFIED TILE SILOS. 99 



Vitrified Tile Silos. 



Vitrified clay blocks have during the past few years com- 

 manded considerable attention for building purposes. The dura- 

 bility of this material is indicated in a quotation from Sir Charles 

 Lyell's Antiquity of Man. 



"Granite disintegrates and crumbles into particles of mica, 

 quartz, and feldspar; marble soon moulders into dust or car- 

 bonate of lime, but hard, well burnt clay endures forever in the 

 ancient landmarks of mankind." 



It is not surprising therefore that vitrified tile or blocks 

 are being used extensively for silo building. They have a hard, 

 glass-like crockery surface, impervious alike to gas, moisture, 

 acid or air; they withstand temperature fluctuations without 

 contraction or expansion; they give the advantages of a double 

 or triple wall with dead-air spaces; they are easily handled; 

 and when properly reinforced against the bursting pressure 

 of the silage they have no superior on the market. 



Iowa Bulletin No. 141 states that "in clay blocks there are 

 many grades of quality ranging from almost worthlessness to 

 one of the highest quality of building material known. These 

 variations in quality are due mainly to three causes, quality 

 of raw material, method of burning, and defects in forming. 



"Brick clays are made up principally of two classes of ma- 

 terial, one that melts at temperatures usually secured in the 

 hottest portions of the brick kilns, and one that remains firm 

 at these same temperatures. Proper portions of each of these 

 classes of material are essential. The former, called the fluxing 

 material melts and binds together particles of the latter, while 

 the latter preserves the desired form of the brick or block 

 throughout the burning process. It will be readily seen that as 

 the fluxing material fuses it will fill all of the space between 

 the *)ther particles, and upon extreme heating it flows out over 

 the surface giving i't a glassy appearance. This process is known 

 as vitrification. 



"In all kilns the blocks nearest the fire become burned harder 

 than the other blocks and in any kiln only a portion of the 

 blocks will be fit for silo construction. For this reason silo 

 builders should not expect to secure such blocks at less than 

 standard prices plus a reasonable price for sorting." 



A variety of patented clay blocks and different methods of 

 reinforcement are now in use. Many of these have special 

 merits in the details. In general, the same methods of wire or 

 steel bands are used as with cement block silos. A study 

 of some of the patented blocks illustrated in Fig. 43 will bring 



