188 GEOLOGY OF OHIO. 



yard right is not apparent and it is now chiefly confined to those who are 

 entering the business for the first time and are not familiar with the 

 results of modern practice. 



The statistics of the kilns actually in use in the state will prove of 

 interest in this connection. 

 A — Paving Material. 



1. Round down drafts— 



,: Common unpatented 252 



New discovery 20 



Eudaly 4 



276 



2. Rectangular down drafts — 



Unpatented 20 



Eudaly 41 



Yates 3 



Hallwood 3 



3. Updraft clamps used in burning paving material — ■ 72 



Updraft 16 



Total kilns 364 



B. — In the sewer pipe business the kilns employed are : 



1. Round down draft 369 



2. Rectangular Akron downdraft 79 



448 



The total number of kilns in the two industries is 812 — of which 

 621 or 76.4 per cent, are round and 191 or 23.6 per cent, are all other 

 kinds together. 



Of these round kilns, those used in the manufacture of brick have 

 an average diameter of twenty-five and one-tenth feet, and an average 

 capacity when set 25 courses high, of 30,000 bricks. 



If set full, the capacity would be about 40,000. The maximum dia 

 meter is thirty feet and the minimum seventeen feet. Of the sewerpipe 

 round kilns, the average diameter is twenty-seven and three tenths feet 

 with maximum and minimum diameters of thirty-three and twei^-two 

 feet. 



The production of paving material has now been as lully discussed 

 as the space will allow. The clays, their preparation, their manufacture, 

 their drying, and their burning have been treated. Much remains to be 

 said about the methods of handling the output, arrangement of plants 

 and similar questions which would be useful and interesting to those 

 engaged in this line of work, but their remains available space for the 

 discussion of only one more topic in this connection, which is the testing 

 of paving materials and the results of the Ohio materials which have 

 been subjected to official test. 



The Testing of Paving Material. The testing of paving material 

 has been subjected to more inquiry and discussion perhaps than any part 

 of its production. 



What constitutes the best means ot testing? As previously described, 



