112 GEOLOGY OF OHIO. 



Taking the measurements made under the most satisfactory condi- 

 tions, Nos. 3, 4, 6, 7 the results 1,922, 1,980, 1,987, 1,982, average, 1,970,. 

 show a closer agreement than was expected. These results are them- 

 selves the averages obtained in readings in different parts of the kilns. 

 The maximum temperatures on these four results show 2,010, 2,010, 

 2,045, 2,045, average 2,027, and the minimum temperatures show more 

 variations naturally. 



The other potteries tested were either distinctly past the maximum 

 temperature of the process or distinctly below it, and therefore were not 

 considered in the averages. 



Surprise may be felt that the heats assigned are so low. Conversa- 

 tions with clay workers has generaly shown a very erroneous view of the 

 heats they employ. A table in the appendix will show the relative heats 

 of the clay working and iron and steel working processes as measured 

 by the same instrument and the same observer. 



The kilns are naturally the most important, the most discussed and 

 the most interesting appliance of the stoneware pottery. 



An examination of the types of kilns in use in the potteries of the state 

 and a comparison of these types with those used by other clay working 

 industries, indicates that there is much in common in their construction 

 and principles. However, there is much less variation among the kilns 

 used for burning stoneware than in kilns of the same type used for pipe 

 or brick. 



Examining the kilns in use in Ohio stoneware potteries the following 

 facts have been classified: 



Name of kiln. 



Akron Dist 



Akron Squuare Downdraft. 

 " Round Downdrdft..., 



Mufflle Updraft 



Plain Updraft (old style).. .. 



Totals 



29 



18 



2 







49 



Zanesville 

 Dist. 



00 



2 



17 



10 



29 



State. 



29 

 20 

 19 

 10 



78 



Factories represented in this list, 32. 



It is thus seen that the Akron district, including all northeastern 

 Ohio, uses nearly all downdraft kilns and the standard square Akron kiln 

 is the most popular; It is to be noted, however, that the newest works, 

 almost all of them, are building the round kilns, and the new kilns 

 being built in all works are mostly all round. 



The Zanesville district, on the other hand, goes on record as using 

 almost entirely the updraft kilns, the only two downdraft being in com- 

 paratively new plants. 



It is impossible in the space assigned to give any adequate descrip- 

 tion of the technical points, pro and con, in these different kilns. But a 



