Annual report of the Regents . ted brick when augermachines are used. The effect of these laminations will be seen inthe tests given below. As paving brick, unless made of fire clay, should be burned to thepoint of vitrification, it is essential that in clays used for this pur-pose the points of viscosity and incipient fusion should lie wellapart, not less than 250° F. and preferably 400° F^ The color of a paving brick is no indication of its quality. The clay should not show any disposition to blister as the pointof vitrification is approached, but this is likely to occur if an excessof iron
Annual report of the Regents . ted brick when augermachines are used. The effect of these laminations will be seen inthe tests given below. As paving brick, unless made of fire clay, should be burned to thepoint of vitrification, it is essential that in clays used for this pur-pose the points of viscosity and incipient fusion should lie wellapart, not less than 250° F. and preferably 400° F^ The color of a paving brick is no indication of its quality. The clay should not show any disposition to blister as the pointof vitrification is approached, but this is likely to occur if an excessof iron is present. In order to demonstrate somewhat definitely what are the char-acters of a good paving brick shale, the tests of a sample utilizedin Illinois for the manufacture of paving blocks is given herewith. The shale is rather fine-grained, and breaks up quite easily ingrinding. It was ground to pass through a 30 mesh sieve. 28,*^ of OlchewRky in Post. chem. tech. anolyf<e. 18^0; VVheelfr in Vitrifiedpaving trick. I obo Qi dO I—I
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