KLEIN: CONSTITUTION OF PORCELAIN 659 



These were burned at various known temperatures. The com- 

 mercial bodies investigated represented the practices of the fol- 

 lowing countries: United States, England, Germany, France, 

 Austria, Denmark, and Japan. The end in view was to obtain 

 data concerning the changes involved by burning porcelain at 

 various temperatures; for bodies whose composition lay within 

 the limits of whiteware and hard fired porcelains it was found 

 possible to correlate to a certain degree the constitution and 

 microstructure with the burning temperature. 



The result of this investigation leads to the following conclu- 

 sions : Kaolin appears homogeneous microscopically when heated 

 up to 1200°. At about this temperature a trace of dissociation 

 occurs. As the temperature is raised above 1200° the dissocia- 

 tion increases very slowly at first, then at an increasing rate until 

 at 1400° it seems to be complete. The products of dissociation 

 are silica and aluminium silicate. The latter compound has 

 been identified as an amorphous phase of sillimanite from the 

 following facts: it shows no crystalline form, has an index of re- 

 fraction above 1.60, and by heating at a higher temperature 

 (about 1450°) it inverts to minute needle crystallites corre- 

 sponding to sillimanite in all determinable optical properties. 



Up to 1340°, in mixtures of quartz and feldspar, the quartz 

 dissolves to only a small extent in the feldspar glass. At 1460° 

 the quartz is practically completely dissolved in specimens 

 having as high a quartz content as 50 per cent quartz to 50 per 

 cent feldspar. 



In specimens containing kaolin and feldspar the kaolin dis- 

 sociates entirely at 1340°. The amount of crystallized and 

 amorphous sillimanite increases with an increased content of 

 kaolin, at least to a concentration of 50 per cent kaolin to 50 

 per cent feldspar. 



At 1460°, apparently 10 per cent kaolin is entirely soluble in 

 the feldspar glass. With higher concentrations of kaolin the 

 amount of crystallized sillimanite increases. The needle crys- 

 tals are well developed and comparatively large. 



At 1310°, in quartz-clay-feldspar bodies, the feldspar is present 

 as a glass; the clay shows almost complete dissociation with the 



