THE MAGIC DUST OF TODAY

Evening Post, Volume CXXVI, Issue 98, 22 October 1938, Page 26

THE MAGIC DUST OF TODAY

The archaeologists of the future digging out the ruins of twentieth century civilisation, will undoubtedly call the present period the Concrete Age, for although cement was Known to the ancient Romans, it is only during comparatively recent years that it has become dominant as a building material, says a writer in the "Adelaide Chronicle." Today, apart from ordinary buildings, a hundred things from garden paths to whole ships are made of concrete, yet it is safe to say that not ;bne person-in a hundred knows how the magic dust, which with water and sand gives such a strong material, is obtained.

The Romans used the dust cast up by -Vesuvius lor making their cement. The. modern manufacturer has to bake his own material and does not. rely, iugon; a volcano to turn it into, dust. |Mahy forms of. lime, silica, and alumina are used as the raw material of 'cement, and the great rocks obtained by blasting and digging are "chewed" up by powerful machines into smaller pieces before being reduced to dust. jl'he powdering machine consists of a ibylirider inside which are a number of iteel balls. Each ball is less than six

inches in diameter, but the total weight is considerable—perhaps forty tons, and the effect of the cylinder being turned is to< convert the small pieces of rock into dust.

This dust is then passed to the manmade volcano, and it is literally a volcano, the temperature of the flames over which the powder is roasted being very high. It is interesting to note that to make a ton of cement requires nearly half a ton of coal. The "cinders" resulting are again pulverised, this time so fine that the resulting dust will pass through a mesh with 40,000 holes to the square inch. Incidentally, water will not pass through a mesh of this fineness.

To the outsider the most striking thing about a cement factory might seem to be the dust. Actually it is the skill with which the conversion of 'rocks into powder that is the most important substance in modern building is supervised. There is no "rule of thumb" in modern.cement-making, and what the Romans aided by a volcano, did by guesswork, modern science carries out with such precision that although many'different rocks are used, the quality of the finished product is always of a certain standard.