CLAY WORKING INDUSTRIES. 225 



The accumulation of clay in stock, however, is a necessity with most 

 works, whose winter supply has to be dug and hauled to market in the 

 favorable seasons of the year. 



The washing of the charge of hard clays is a practice resorted to at 

 the best works; it is much scoffed at by those who do not use it as being 

 an utterly useless expense. Its utility depends altogether on the condi- 

 tions under which hard clay is obtained; if from a mine under ground, it 

 is not likely to be in need of washing; if from open cut benchings, it is 

 sure to have more or less mud in it which ought to be removed. 



Even drenching with a hose pipe over a sink is beneficial, but the 

 use of a mechanical device is necessary to do the work thoroughly. 



The log washer, or a crude form of pug mill, used in washing iron 

 ores from adhesive clay would answer this purpose satisfactorily. 



The processes of grinding the clay and tempering it ready for use is 

 accomplished in three principal methods: 



1st. The wet pan. 



2d. The dry pan and pug mill. 



3d. The dry pan and wet pan. 



The wet pan is the characteristic implement of the fire brick makers 

 of the state; it is in all respects comparable to the machinery already 

 described under the preparation of brick clays, except that the wheels 

 are usually very broad and of much smaller diameter. The common 

 dimensions are twelve to fourteen inch face by twenty-four to thirty 

 inches diameter; the wheels weigh from three to six thousand pounds 

 each. 



The charge of clay is dumped in altogether and wet down as often 

 as necessary; the soft clay speedily becomes very plastic, especially as 

 the amount of water used is often considerable and as the wheels reduce 

 the hard clay and calcine finer and finer, the plastic clays are distributed 

 in a thinner and thinner enveloping layer over each particle. The grind- 

 ing usually occupies from ten to fifteen minutes, occasionally much more 

 time is' allowed. 



Such treatment as this will develop the very best plasticity that any 

 c'ay is capable of; the only thing which can be urged against its efficiency 

 is the fact that there' is no absolute means of regulating the sizes of the 

 particles of hard clay, which may survive the grinding without being 



crushed. 



The use of a dry pan proves itself of great value to the makers of 

 high grade refractories. It permits the accurate sizing of the flint and 

 calcined clays and it permits their reduction to a size with far greater 

 economy of power and time than can be attained in the wet pan. The 

 further tempering after grinding by dry pan may be accomplished by pug 



mill or wet pan. 



The use of a wet pan is by all means to be recommended. It is of 

 more.importance in making refractory material than sewer pipe and pav- 



15 * G. O. 



