WISCONSIN ACADEMY SCIENCES, ARTS, AND LETTERS. 



Kaolin is used to a considerable extent also for other dense wares 

 than true jDorcelain. In the manufacture of the so called English 

 or "tender" porcelain are used kaolin, plastic clay, " Cornish stone," 

 burnt bones, and steatite. The ''Cornish stone " is the partially 

 weathered granite, which by its complete kaolinization affords the 

 famous kaolin of Cornwall. 



Preparation of IxwUnfor jwrcelahi making. — The crude kaolin is 

 always first washed to free it from quartz and felspar fragments. 

 This is eifected by simply breaking up the clay, stirring in water, 

 and decanting the suspended matter. The coarse residue from 

 this washing is frequently of value, since it contains two essential 

 ingredients of the porcelain, viz, felspar and quartz. 



Use of kaolin as a refractory material. — As a fire clay or for 

 making fire-clay articles, I cannot find that kaolinized rock has 

 been much used. The chief difiiculties in the way of such use ap^ 

 pear to lie in the lack of uniformity so characteristic of this kind 

 of deposit, and in the fact that where of fine quality the material 

 is too valuable for other purposes. The use of kaolinized roclc from 

 near Trenton, New Jersey, as an ingredient of fire-bricks, has al- 

 ready been alluded to. The only other instance I find recorded is 

 that of the so-called " Lee Moor Porcelain Brick," made in Devon- 

 shire, England, by inixing a small quantity of inferior kaolin with 

 an excess of the coarse residue obtained from washing the same 

 kaolin. This residue consists chiefly of angular fragments of 



