the molten . slag into large cisterns of water. This 

 partly disintegrates it and corrects the sulphur and 

 other chemicals. It can then be handled by a bucket, 

 and is conveyed to the crusher. Crushed to any size, 

 and used either screened or as "run of crusher" it 

 makes an excellent concrete aggregate. With practically 

 the same compressive strength, it is 15 to 20 per cent 

 lighter than a rock concrete. 



Cinders. Cinders are liable to contain sulphur and 

 other steel-corroding chemicals, also unburt coal, soot, 

 ashes and dirt. If you use cinders, watch the quality. 

 Screening to remove what impurities you can is only a 

 fair precaution. Cinder concrete does not possess as 

 much compressive strength as other concrete, but 

 weighs considerably less, and consequently is suitable 

 for roofs, fill between floor sleepers and so forth. 



STEEL. 



The reinforcing steel used is made by either the 

 Open 'Hearth or the Bessemer process, which are terms 

 used in the steel trade to designate the two methods 

 by which steel is produced. In the Open Hearth pro- 

 cess the correct proportions of iron, carbon, scrap, etc., 

 are melted and refined in large furnaces. In the Bes- 

 semer process, pig iron is reduced to steel in a con- 

 verter, using highly heated gases and air under pres- 

 sure. 



Open Hearth steel is usually on the market as a 

 medium steel, with an ultimate .tensile strength of 60,- 

 ooo to 70,000 Ib. per square inch. The elastic limit 

 is between 35,000 and 40,000 Ib. 



The Bessemer steel usually has a higher ultimate 

 strength, between 80,000 and 90,000 Ib. 



Reinforcing steel can be classed as plain or deformed. 

 Plain steel refers to bars rolled in round or square 

 sections. Deformed steel refers to the above steel 

 rolled to a special pattern in order to secure a me- 

 chanical bond with the surrounding concrete. These 



