Geography of Ohio 157 



condition. Of the various cements made in this country this is 

 the oldest. It was used for structural purposes early in the last 

 century. Few plants are operating now in Ohio. The best, so 

 far as I am able to ascertain, is that at Defiance. 



Pozzuolane ceme^it. This is a very old kind of cement. It 

 was used by the Romans, as the name indicates. At first it was 

 manufactured by combining slaked lime and volcanic tufa. The 

 volcanic matter carried a high amount of silicic acid, which com- 

 bined readily with the hydrated lime. In this country furnace 

 slag which was cooled quickly is substituted for the tufa. This 

 slag is a by-product of blast furnaces, and is usually discarded. 

 A few furnaces, however, are now producing pozzuolane cement. 



Portland cement. This is an artificial mixture of clay and cal- 

 careous matter. Any raw material which furnishes silica, alumina, 

 calcium oxide, and some iron oxide, may be used. After these 

 ingredients have been thoroughly mixed, they are burned to a 

 clinker, and then ground fine. 



Quite a variety of raw materials contain the required ingredi- 

 ents: clay and marl; clay, or shale, and limestone; pure limestone 

 and argillaceous limestone. 



The largest Portland cement plant in Ohio is at Castalia. Here 

 they use travertine, a calcareous deposit of the springs that issue 

 from the limestone in that vicinity, and soft clay. A plant at 

 Middle Branch, in Stark County, uses a limestone and an associ- 

 ated shale. One in Logan County uses marl and glacial clay. 

 At Wellston, Jackson County, is a plant built at some distance 

 from the source of its raw material; the question of shipping 

 facilities for the finished product decided this location. 



ABRASIVES 



Natural. For many years this state has led all others in the 

 production of grindstones and pulpstones. The Berea formation 

 furnishes most of this material. For use as a grindstone the rock 

 must be homogeneous in texture, and its components must be 

 sufficiently cemented to endure, but not so completely cemented 

 that the stone will wear smooth. 



Pulpstones are sometimes very large, weighing from two to 

 four thousand pounds and even more, and measuring four to five 

 feet or more in diameter. These stones must stand much heat, 



