104 



DISCOVERY 



of coal or coke, with adequate transport facilities for send- 

 ing away the finished product from the works. 



The usual method is to burn chalk containing the 

 necessary calcium carbonate with the clay in cylindrical 

 kilns, upwards of 200 ft. long, which slowly revolve. The 

 kilns are inclined, enabling the mixture of chalk and clay, 

 which is well pulverised and made into a liquid paste 

 called " slurry," to travel slowly do\\Ti the kiln. At the 

 lower end, a blast of coal-dust is blown in, which 

 immediately catches fire and burns the on-coming slurrj^ 

 to hard grey nodules of varying sizes up to a man's fist. 

 The nodules, if suitably burned, are ground and reground 



value is believed to be tri-calcium siUcate ; therefore, if 

 the percentage of calcium carbonate gets too low, too much 

 bi-calcium silicate is formed ; whereas if it gets too higli, 

 there is too much free or loosely combined lime present 

 and the cement will be unsound. The general rule is that 

 the higher the percentage of lime, the higher the strength 

 of the cement ; but such factors as the fineness to which 

 the raw materials are ground and the correct temperature 

 of the kilns are most important. In a kiln one attempts 

 to arrive at what is called incipient fusion. 



Modern methods of cement manufacture therefore 

 ensure a cement of uniform quality from a particular 



Fig. I.— hessi,e qu.-vrry. 

 Output of chalk, with two diggers operated by five men iu all, totals 5,000 to 6,000 tons per week. 



to a powder so fine that, in order to qualify- for the 

 British Standard specification, 86 per cent, of it must pass 

 a sieve with 32,400 meshes to the square inch. In this 

 state it is the finished Portland cement. At Barton the 

 cement is ground so that approximately 97 per cent- 

 passes this sieve. The whole process is, at the present day, 

 carried out in the most scientific manner ; several chemists 

 are employed in a large establishment. This ensures the 

 product being not only good, but invariably good. In the 

 old days, when the manufacture was carried out by rule 

 of thumb, the resulting cement was very unreliable. 



The silica and alumina in the clay combine with the lime 

 in the chalk. The compound of the greatest cementitious 



establishment and have enormously increased the use 

 of all kinds of work in reinforced concrete, such as bridges, 

 retaining-weUs, reservoirs, factories, warehouses, floors, 

 and such things as seats, sign-posts, signal-posts, which it 

 is now becoming very common to make of this material. 

 The Humber-side possesses all the natural advantages 

 for manufacturing a first-rate Portland cement. The 

 calcium carbonate is there on both sides of the river, 

 in cliffs, some 200 to 300 ft. high, which constitute the 

 high ground laiown as the Lincolnsliire and Yorkshire 

 Wolds. They contain some of the largest chalk-quarries 

 in the country. The necessary clay lies at the foot of 

 these cliffs in the form of river-mud, probably deposited 



